Correlation with the FOB price for iceberg lettuce is also provided

The ability to provide account-specific products and services represents a major change from the days of uniform product offerings. While these services can be costly, many shippers are finding that they enable them to become preferred suppliers to large buyers, potentially stabilizing demand and somewhat lowering market risk. Many California grower-shippers obtain products from other countries during the off-season, sometimes via joint ventures. This enables shippers to extend shipping seasons and sell products produced in several locations via one marketing organization, maintaining a year-round presence in the marketplace.For example, shippers based in Salinas, California, also commonly ship out of the San Joaquin Valley, Imperial Valley, southwestern Arizona, and Mexico. The rapid growth in multi-location firms has contributed to the integration of the Mexico-California-Arizona vegetable industries, in particular.Because most vegetable crops are not perennials, the location of production can shift readily, based on relative production and marketing costs and growing season. Increasingly,bato bucket buyers are contracting with grower-shippers for high-volume perishable items to stabilize prices, qualities, and volumes.

While contracts were relatively common in the food service sector, they are new to retail. The entrance of super centers to food retailing has led this change as these mass-merchandisers focus on driving costs out of the distribution system. The introduction of contracting is likely to have structural implications at the grower-shipper level, since shippers need to offer large, consistent, year-round volumes to meet buyers’ contracting requisites.The evolution of the California produce industry has enhanced its efficiency by cutting marketing costs and improved communication of consumer demand back to growers. However, the consolidation of purchasing within the hands of a few large buyers raises concerns about oligopsony exploitation of producers. Perishable crops, which must be harvested, sold, and marketed within a very short time frame, tend to give growers relatively little bargaining power in dealings with buyers. Sexton, Zhang, and Chalfant and Richards and Patterson analyzed this issue recently for several fresh fruits and vegetables. Although the results differed among the commodities studied, in general the authors concluded that retailers were often able to reduce prices to growers below competitive levels as a consequence of their market power. In addition to apparently exerting buyer market power for at least some commodities, the manner in which retailers set prices to consumers for those commodities can also have an important effect on producer welfare. To the extent retailers exercise oligopoly power to consumers by marking up the price of a commodity above full marginal costs, they reduce sales of the commodity, an outcome detrimental to producers. Further, evidence from scanner data shows that retailers set prices for produce commodities with little regard for the underlying trends in the farm commodity market. For example, among 20 retail chains studied by Sexton, Zhang, and Chalfant, nine maintained the same weekly price for iceberg lettuce over the two year period from 1999-2000, despite wide fluctuations in the FOB price received by producers.Table 3 illustrates the wide variability among four Los Angeles retail chains in setting prices for iceberg head lettuce and iceberg-based bagged salads.

The table contains the correlations in the weekly retail prices charged by the various chains for iceberg head lettuce and the various brands of iceberg-based bagged salads .Correlation coefficients fall in the range of –1.0 to 1.0 , with values near zero indicating very little correlation between the movements over time for the particular price pair. Each chain’s head lettuce price is positively correlated with the FOB price , but the correlations are much lower than if the retailers were merely adding a cost-based mark up to the FOB price. Correlation between retail and farm pricing essentially disappears for the bagged salads, however. In all cases, the correlations are nearly zero, and in some cases are negative, meaning the retail price moved on average in the opposite direction of the farm price. To understand retailer pricing for fresh produce commodities, one needs to appreciate that the modern retailer sets prices for 30,000 or more product codes.Pricing decisions are not made with an eye towards profitability of any single product, but, rather, are oriented toward the profitability of the entire store. The produce section is traditionally a source of high profits for retailers, and, because of the importance consumers attach to produce, retailers can use their produce aisle as a way to differentiate themselves and attract consumers to the store. Accordingly, stores’ pricing policies for produce vary widely. Some stores prefer to offer consumers stable prices week in and week out . Other stores regularly feature produce as a sale item, so prices vary dramatically from week to week . Neither pricing strategy is likely to be beneficial to producers. Sexton, Zhang, and Chalfant demonstrated that retailers who maintain stable prices over time despite fluctuations in sales and price at the farm level cause lower producer income on average because price must fluctuate even more in those sectors, such as food service, which do not artificially stabilize price, in order for the market to clear.Marketing arrangements are different for processed foods, including fruits and vegetables, nuts, grains, meats, and dairy.

Growers in these industries sell to processing firms rather than to food retailers. Like the food-retailing sector, the food processing sector has also become increasingly concentrated, and effects of high processor concentration can be especially severe in terms of their impacts on grower processor relations. Most raw farm products are generally bulky and perishable, making shipment costly and limiting growers’ access to only those processors located within a limited radius of the farm. For example, broilers are generally shipped 20 or fewer miles, and processing tomatoes are hauled 150 or fewer miles. Thus,dutch bucket hydroponic even if many processors operate in an industry nationally, typically only one or a few firms buy from a given geographic region California food processors are themselves a diverse lot. A key distinction is whether or not the processor has successfully developed its own brand identification. Processors with successful brands are able to capture a price premium in the market. Examples of California processors with leading brands include Blue Diamond , Sunsweet , Heinz , Del Monte , Sun Maid , Diamond , Lindsay , and Sunkist . Processors who lack dominant brands sell primarily to food service buyers and to the private label market. Private labels refer to retailers’ house brands. These brands generally sell at a discount compared to major brands, resulting in a lower return for the processor. Great variety also exists in the form of business arrangements among growers and processors. Grower-processor relationships can be thought of as comprising a continuum with pure “arm’s length” exchange or spot markets at one extreme, and grower-processor vertical integration at the other extreme.In between the extremes are various forms of contractual relationships between growers and processors. Pure arm’s length exchange or spot markets are increasingly rare. Two key factors have contributed to the decline. First, as the number of firms buying in a given geographic area has declined, the efficiency of price discovery in spot markets diminishes, and concerns over buyer market power escalate. Second, arm’s length transacting is a poor way to coordinate activity and transmit market information between buyers and sellers, and this type of coordination has become increasingly important in meeting consumers’ demands in the marketplace. The processing tomato industry illustrates some advantages of vertical coordination and problems of conducting transactions through spot markets. Unlike tomato sectors in many other countries, tomato production in California consists of two completely separate, dedicated industries rather than a single, dual-usage industry; tomatoes are grown either for processing or for fresh usage. Tomatoes are perishable and costly to transport. Thus, processors have an incentive to procure production near their processing facilities. Timing of production is also critical. Tomatoes must be harvested immediately upon ripening and then processed quickly to avoid spoilage. The efficient operation of processing facilities and the effective processing of the harvest require that a processor’s deliveries be spread uniformly over an extended harvest period of 20 or more weeks. Similarly, processors specialize in producing different types of tomato products.

Some plants produce only bulk tomato paste, which is then remanufactured at other locations into various processed tomato products, while others produce whole tomato products. The preferred type of tomato to grow depends upon the intended finished product. Delivery dates and product characteristics cannot be communicated effectively through spot markets. Nor will a central market work when processors are interested in procuring product only in the vicinity of their plants.Thus, the California processing tomato industry transacts essentially its entire production through grower-processor contracts. These contracts specify the specific acreage the product is to be grown on, variety of tomato to be grown, delivery dates, and premiums and discounts for various quality characteristics. Price terms in these contracts are set with the intervention of a producer bargaining cooperative.Cooperatives are firms that are owned by the producers who patronize them, although many cooperatives also do business with nonmembers. California is home to many large and important food-marketing cooperatives. Producers who are members of a marketing cooperative essentially have vertically integrated their operation downstream into the processing and marketing of their production. A number of incentives can account for producer cooperative integration, including avoidance of processor market power, margin reduction, and risk reduction . Cooperatives are the leading marketing firm in several California agricultural industries including almonds , walnuts , prunes , citrus and raisins . However, the recent years have represented difficult times for some California marketing cooperatives. Tri Valley Growers , a fruit and tomato processing cooperative, formerly the second largest cooperative in California, declared bankruptcy in the summer of 2000. Around this same time the Rice Growers Association, a large and long-lived rice milling operation closed its doors, as did Blue Anchor, a diversified fresh fruit marketer. Reverberations from the failure of these prominent California cooperatives were felt nationally and caused some to wonder whether the model of cooperative marketing was well suited for 21st century agriculture. Indeed cooperatives do face some important challenges competing in the market environment we have described here. As noted, retailers prefer suppliers who can both provide products across an entire category and provide them year around. Cooperatives are traditionally organized around a single or limited number of commodities and member production is likely to be seasonal. Cooperatives can attempt to surmount these difficulties by undertaking marketing joint ventures with, for example, other cooperatives, and sourcing product from nonmembers, including internationally. However, cooperatives may face impediments relative to investor-owned competitors in pursuing such strategies. For example, various laws affecting cooperatives specify that at least 50 percent of business volume must be conducted with members. Joint ventures with firms that are not cooperatives are not afforded legal protection under the Capper-Volstead Act.Doing business with nonmembers may also adversely affect a cooperative’s membership, if it is perceived that most of the benefits of the cooperative can be obtained without incurring the financial commitment associated with membership. This issue was important for TVG when it appeared that tomato producers selling to TVG under nonmember contracts received a better deal than member growers. Cooperatives may also face challenges in procuring the consistent high-quality production that the market place now demands. Cooperatives usually employ some form of pooling mechanism to determine payments to members. In essence, revenues from product sales and costs of processing and marketing flow into one or more “pools.” A producer’s payment is then determined by his/her share of the total production marketed through each pool. The problem with some pools is that high quality and low-quality products are commingled and producers receive a payment based upon the average quality of the pool. Such an arrangement represents a classic adverse selection problem, and its consequence is to drive producers of high-quality products out of a cooperative to the cooperative’s ultimate detriment. Cooperatives can obviate this pooling problem through operating multiple pools and/or by designing a system of premiums and discounts based upon quality, but the key point is that investor-owned competitors face no similar hurdles in paying directly for the qualities of products they desire.

Field crops are concentrated in the more recently developed areas of the region

The west side of the San Joaquin Valley was the region most affected by the 1987-93 drought and by reduced allocations from CVPIA and CALFED decisions. Consequently, this area is among the most innovative in implementing market transfer initiatives and adopting water-conserving irrigation technologies. Clearly the economic fate of this region, and the others, is closely tied to long run supplies of irrigation water and to current initiatives that seek to reallocate surface water supplies among competing agricultural, municipal and industrial, and non-consumptive environmental uses.With the majority of the state’s agricultural production located in “The Valley,” most kinds of production can be found somewhere within its confines. What is surprising is the diversity in types of farming enterprises, ranging from older, smaller, more intensively cultivated farms on the east side to the larger, more extensive farms on the west. Fruit and nut crops, including grapes and citrus, are important to the region, contributing 39 percent of the total value of production in 1995. While the majority of permanent plantings lies on the east side of the valley,u planting gutter recent plantings of nuts and some deciduous fruits have been made on the west side. Livestock and livestock products are located throughout the valley and contribute an additional 28 percent of the region’s agricultural production.

Cotton is the most important field crop. Recent introductions of pima varieties have augmented traditional upland cotton production but total cotton acreage has fallen due to poor profitability. The region is an important producer of most field crops . Irrigation and a long growing season have also led over time to increased vegetable production . Summer melon production is important, as is seasonal production for many of the major vegetables . Some seasonal production is timed to fill marketing niches as the fresh produce industry moves in the spring from desert to coastal areas and in the fall back toward the desert. Of the major categories, nursery products and cut flowers appear relatively insignificant in comparison with the total value of agricultural commodities .This region of the state is very similar to that of the North, being largely dominated by livestock and livestock-related economic activity an private and leased public lands. The Mountain region covers about 15 percent of the state’s land area, and land is mostly in public ownership; less than 10 percent of the total land area is in farms. Together, livestock , livestock products , and field crops—mainly range land and pastureland production —, amount to about three quarters of the value of the region’s agricultural activity in 1995. In truth, the dominance of these commodities in the region’s agricultural economy is larger because the geographic location of fruit and nut production , and nursery products recorded for the region, actually occur on the west slope, foothill “valley” portions of several mountain counties.This area is still a base for significant agricultural production despite progressive development with a large urban population.

Los Angeles County was once the most important agricultural county in the United States, measured by the value of its agricultural production. Los Angeles County was ranked as California’s number one agricultural county into the 1950s. Despite urbanization, 21 percent of the region’s land area remains in farms, with often intense and complex interactions between agriculture and urban constituencies. The average size of farms is the smallest among state agricultural production regions, while the average value of farm products sold per acre is the highest. With 69 percent of cropland irrigated, production is mostly high valued nursery products, fruits and vegetables. High-valued crops grown in the South Coast area are those suitable to its moderate climate and usually frost-free growing seasons. High values are needed to rationalize the application of some of the highest-cost irrigation water in California. Nursery products, foliage and flowers are the most important economically of all product categories, making up 35 percent of the regional value of 1995 production.San Diego County alone produced $585 million of nursery products, foliage and flowers in 1995. Avocados and citrus , strawberries, and wine grapes are the main fruit crops . Vegetable production, some of which is seasonal before and after the winter desert production season, includes broccoli, celery, lettuce, and bell peppers. Egg production and dairying are the two major intensive livestock product enterprises.Including the eastern areas of the Los Angeles area , this region also extends across the more remote desert valleys—the Coachella, Palo Verde, and Imperial Valleys—irrigated by early diversion rights to Colorado River water. Only 28 percent of the land area is in private ownership, and only 10 percent of the land area is in farms. Because of the severe climatic conditions, a high proportion of cropland is irrigated . The western San Bernardino and Riverside areas include remnants of the once-dominant citrus and dry lot dairying industries, which are gradually being displaced by urban expansion.

Livestock and livestock product activities contribute the greatest proportion of the value of production in the South Coast region by capitalizing on the region’s proximity to markets and a long tradition of cattle feeding in the Imperial Valley and other desert valley areas. Vegetable production , predominantly in the irrigated desert valleys, includes important winter and early season production of asparagus, carrots, lettuce, melons, and sweet corn. Highly productive desert lands with irrigation benefit from temperate winters and nearly frost-free growing seasons to produce a variety of high-valued fruit and vegetable crops that are in supply during the off- and early seasons of the major production regions. Fruit production is mainly in the western areas and in the Coachella Valley . Field crop production includes alfalfa hay production for the region’s livestock activities, cotton, sugar beets, and wheat, including durum.Risk is substantially greater in the production and marketing of perishable fruits and vegetables than in more stable commodities.15 Investments in permanent plantings are large and must be paid back over the period of economic production. Figure 2 shows the pronounced change in the distribution of field crop, tree fruit and nut, and vegetable acreages and value of production over the decade of the 1980s. In 1980, production of fruit, nuts, and vegetables contributed over half of the value of production , but only used 27.9 percent of the acreage in production. In 1990, these more intensive, higher-valued, higher-risk crops amounted to 73 percent of the value of production, while using 38.7 percent of acreage. The residual nature of field crops is evident as farmers and ranchers seek more intensive production enterprises. Shifts toward increased acreages of vegetables and permanent plantings continued through the decade of the 1990s, most noticeably with substantial increased acreages of nut crops , deciduous tree fruits , and wine grapes. The composition of California agricultural production is compared for the years 1955, 1975 and 1995 in Figure 3. Total value of agricultural production grew three-fold from 1955 to 1975, from $2.68 to $7.43 billion. Change in composition between 1955 and 1975 was not as dramatically different as that which has occurred over the last period, 1975-95, partly due to an overall increase in irrigated acreage through most of the first period.By 1995, high-valued fruit and nut, vegetable,planting gutter and nursery and greenhouse products contributed 60 percent of the aggregate value of production for the state, and total value of agriculture production amounted to almost $22 billion. Field crop and livestock/livestock product categories were reduced by about one-half and one-third, respectively, in terms of their relative contribution to the value of California agricultural production. In 2001, the value of nursery, greenhouse and floriculture exceeded the value of field crops, and the dairy sector alone accounted for 17 percent of the state’s value of agricultural production . As a consequence, the share produced by livestock, poultry, and products actually rose from 25 percent in 1995 to 28 percent in 2001.The shifting composition of agricultural production is also reflected in changes in the state’s “Top Twenty” agricultural commodities over time. Table 2 shows the “Top Twenty” commodities ranked by gross farm income for the 2001 crop year, with comparisons for 1981 and 1961. Comparison of the 1961 and 2001 lists shows that whereas there were a total of 12 livestock/livestock products, and field crops identified in 1961, only 5 were on the 2001 list. In sharp contrast, there are now 13 fruit, nut, and vegetable crops on the 2001 list, compared to only 8 on the 1961 list. Nursery products and foliage and cut flowers have been added since 1961, appearing on both the 1981 and 2001 lists.California is now the number one milk producer in the United States. California’s dairies and the dairy processing sector are part of a dynamic system that has progressively become more efficient, larger, and more specialized over its history. Herd sizes are, on the average, ten times larger than the national average, and cows are, on the average, significantly more productive.

Dairy processing capacity has more than doubled during the 1990s. The state’s dairy industry evolved from “local” dairies that originally provided fluid milk to nearby growing population centers in the San Francisco and the Los Angeles area milk sheds. The San Joaquin Valley milk shed was first a center for lower-valued manufacturing milk used mainly for butter and cheese production. With improved transportation systems and reduced land available for dairies in or near the main population centers, the San Joaquin Valley is now the major source of fluid milk serving both the Bay Area and the Los Angeles Basin. Processing continues to be concentrated there as well. Continuing urbanization and waste disposal challenges have caused more dairies to move into Central Valley and South desert areas, principally into the San Joaquin Valley. California’s dairies are highly specialized. As the number of dairies decreased, their size has become significantly larger, requiring more capital-intensive specialized production systems based on genetics, herd health, nutrition, and high levels of management. Urban expansion in the Los Angeles area led to the development of the dry lot, feedlot style dairy using concentrates and feed stuffs often grown in other areas. Modern dairies often milk 3,000 or more cows daily and use waste effluents and solids on silage and forage crops on adjacent cropland.Wine grape production occurs throughout the state. California’s premium wines come from grapes grown predominantly in cooler, coastal valleys, most notably in the Napa Valley, but also in other North Coast areas as well as in some Central Coast areas. Higher yielding vineyards in the San Joaquin Valley produce standard and mid-quality table wines often marketed in larger-sized bottles and containers. The California wine-grape vineyard and wine-production industries have grown sporadically over the last half century. Following World War II, about 80 percent of the wine produced was in the fortified appetizer or dessert wine category with production chiefly in the San Joaquin Valley. Americans did not then know much about quality wines, but gradually, as tastes changed, the industries also changed toward the production of both standard table and world-class premium quality wines. Bearing acreage increased from about 120,000 acres in the early 1960s to over 300,000 acres by the mid-1990s. Rapid expansion occurred in the 1970s and again in the 1990s. By 2001, there were 480,000 bearing acres of wine grapes with an additional 90,000 non-bearing acres. The specter of oversupply is real, affecting marginal plantings, particularly in the San Joaquin Valley, as new and potentially higher yielding vineyards incorporating disease-resistant root stocks and up-to-date trellising, irrigation, and management systems come into production. Marginal plantings are often removed out of economic necessity during periods of oversupply. Some grape varieties are better for fresh use because of certain combinations of characteristics: attractive appearance, large berries, good eating quality, and resistance to injury when handled, shipped, and stored. Fresh grapes are among the nation’s most popular fruits in terms of quantity consumed, and they are second, following bananas, in sales value. California table grapes are harvested from late May through late fall. Harvest begins in the desert regions, primarily in the Coachella Valley in Riverside County, and continues in the San Joaquin Valley, beginning first in Kern County and moving northward through the summer and fall. With careful treatment, California grapes may be enjoyed through March of the year following harvest.

The spread of irrigation broadly paralleled the intensification movement

Our second most abundant category was Braconidae which was dominated by Aphidiinae, parasitoids of aphids commonly found on crop plants at our research sites. This research supports the enemies hypothesis in UA and empowers urban farmers to adopt on-farm management practices that increase agroecosystem function and increase ecosystem services. However, we did find conflicting results, floral provisioning is an important predictor of increased abundance of natural enemies, including PH, and increased biological control services in many urban specific and rural farm diversification research. Our findings indicated that floral richness was a strong predictor, across many PH taxa, of reduced abundance. Two factors presented by Heimpel and Jervis in 2009 may be important factors in this observed reduction; 1. In areas of high floral occurrence, parasitoids may be seeking hosts away from concentrations of food sources as these areas may increase the opportunity for hyper-parasitism. Hyperparastioids, specifically the cynipds, were a large proportion of our collected wasps. Many of these cynipoids, specifically the subfamily Alloxystinae are known secondary parasitoids of baraconid aphid parasitoids. In both chapters 3&4, these PH were found in high abundance,plastic planters bulk indicating that there may be significant pressure from secondary parasitoids in areas of high floral nectar. Secondly, floral nectar may not be in great demand in urban areas.

Landscaping with flowering plants is common and may be introducing an important confounding variable. Given these findings, floral provisioning may not be promoting biological control services in urban farms. A second salient explanatory variable that had a positive impact on PH abundance across measured farms was on-farm non-crop areas. Many previous research efforts regarding ecosystem function in fragmented landscapes have focused on matrix and patch quality as explanatory variables for species occurrence or resulting ecosystem services in fragmented landscapes. While these factors continue to be compelling, recent meta-analysis call into question on-farm spatial composition as an important determinant of ecosystem function . These non-crop areas differed greatly during sampling, but were often distributed throughout the farm. Future research on agroecosystem function should pay closer attention to the composition and evenness of these often overlooked ruderal patches within urban farms. A note on other important natural enemy taxa: Our research explicitly looked at aphids and parasitic Hymenoptera in urban agroecosystems. Both PH and aphids have been shown to be resilient in the context of urbanization and fragmentation in agroecosystems. Less mobile taxa, such as ground beetles and spiders have shown significant declines with habitat fragmentation. Overall ecological function of cities should be an important topic in future discussions regarding urban planning and growth. Important ecosystem services, linked with declines in diversity of terrestrial invertebrates should not be overlooked in the context of this research.

Two competing legends dominate the telling of California’s agricultural history. According to the first legend, California farmers are progressive, highly educated, early adopters of modern machinery, and unusually well organized. Through irrigation, they made a “desert” bloom. Through cooperation, they prospered as their high-quality products captured markets around the globe. This farmers-do-no-wrong legend is the mainstay of the state’s powerful marketing cooperatives, government agencies, and agricultural research establishment. According to the opposing legend, the California agricultural system was founded by land-grabbers who continue to this day to exploit impoverished migrant workers and abuse the Golden State’s natural environment.Although the contest between these competing interpretations of the nature of California’s farm system has raged for the past one and-a-half centuries, neither account has engaged in a systematic accumulation and dispassionate analysis of the available data, and both have generally lacked the comparative perspective needed to assess why California agriculture developed as it did.This chapter analyzes major developments in California’s agricultural history to provide a better understanding of how and why the state’s current agricultural structure and institutions emerged. We will focus on major structural transformations: the growth and demise of the extensive wheat economy of the nineteenth century; the shift to intensive orchard, vine, and row crops; and the emergence of modern livestock operations. Intertwined with our discussion of sectional shifts will be an analysis of some of the special institutional and structural features of California’s agricultural development.

Here we offer a brief look at the subjects of farm power and mechanization, irrigation, the labor market, and farmer co-operatives. In all of these areas, California’s farmers responded aggressively to their particular economic and environmental constraints to create their own institutional settings. The results have been remarkable. In recent years, this one state alone has accounted for one-tenth of the value of the nation’s agricultural output. What distinguishes California from other regions more than the volume of output, however, is the wide diversity of crops, the capital intensity, the high yields, and the special nature of the state’s agricultural institutions.When disgruntled miners left the gold fields, they found an ideal environment for raising wheat: great expanses of fertile soil and flat terrain combined with a climate of rainy winters and hot, dry summers. By the mid-1850s, the state’s wheat output exceeded local consumption, and California’s grain operations began to evolve into a form of agriculture quite different from the family farms of the American North. The image of lore is of vast tracts of grain, nothing but grain, grown on huge bonanza ranches in a countryside virtually uninhabited except at harvest and plowing time. While this picture is clearly overdrawn, it contains many elements of truth. California grain operations were quite large by contemporary standards and extensively employed labor-saving, scale-intensive technologies. As examples, they pioneered the adoption of labor-saving gang plows, large headers, and combined harvesters.Most of the wheat and barley was shipped to European markets, setting a pattern of integration into world markets that has characterized California agriculture to the present. Large-scale operations, mechanization, and a reliance on hired labor would also become hallmarks of the state’s farm sector. Not only were California wheat farms typically larger and more reliant on laborsaving machinery and animal power than mid-western and eastern wheat farms, Californians grew fundamentally different varieties of wheat and employed different cultural techniques than their eastern brethren. These biological differences, although not generally appreciated, were critical to the success of the early California wheat industry. In fact, when eastern farmers migrated to California they had to relearn how to grow the crop. In the eastern U.S. , grain growers planted either winter-habit varieties in the fall to allow the seedlings to emerge before winter or spring-habit varieties in the spring shortly before the last freeze. The difference was that winter-habit wheat required prolonged exposure to cold temperatures and an accompanying period of dormancy to shift into its reproductive stage. Spring-habit wheat, by contrast,good drainage pots grew continuously without a period of vernalization, but generally could not survive extreme cold. With the mild winters of California, farmers learned it was advantageous to sow spring-habit wheat in the fall . California’s wheat experience exemplifies what happens in the absence of continual biological innovation. After learning to cultivate Sonora and Club wheats in the 1850s, 1860s, and 1870s, California grain growers focused most of their innovative efforts on mechanization, and purportedly did little to improve cultural practices, introduce new varieties, or even maintain the quality of their seed stock. According to contemporary accounts, decades of monocrop grain farming, involving little use of crop rotation, fallowing, fertilizer, or deep plowing, mined the soil of nutrients and promoted the growth of weeds. Complaints that the land no longer yielded paying wheat crops became common from the 1890s. The grain also deteriorated in quality, becoming starchy and less glutinous. It is interesting to note these unsustainable “soil mining” practices may well have been “economically rational” under the high interest rates prevailing in the state in the mid-nineteenth century.The result was such sharply declining yields in many areas that wheat, formerly the state’s leading staple, ceased to be a paying crop and was virtually abandoned .2Between 1890 and 1914, the California farm economy fundamentally and swiftly shifted from large-scale ranching and grain-growing operations to smaller-scale, intensive fruit cultivation. By 1910, the value of intensive crops equaled that of extensive crops, as California emerged as one of the world’s principal producers of grapes, citrus, and various deciduous fruits.

Tied to this dramatic transformation was the growth of allied industries, including canning, packing, food machinery, and transportation services. A vantage point on the state’s transformation is offered in Table 1, which provides key statistics on the evolution of California agriculture between 1859 and 1997.Almost every aspect of the state’s development after 1880 reflected the ongoing process of intensification. Between 1859 and 1929, the number of farms increased about 700 percent. The average size of farms fell from roughly 475 acres per farm in 1869 to about 220 acres in 1929, and improved land per farm dropped from 260 acres to about 84 acres over the same period. Movements in cropland harvested per worker also point to increased intensity of cultivation after the turn of the century. The land-to-labor ratio fell from about 43 acres harvested per worker in 1899 to 20 acres per worker in 1929.Between 1869 and 1889, the share of California farmland receiving water through artificial means increased from less than one percent to five percent. Growth was relatively slow in the 1890s, but expansion resumed over the 1900s and 1910s. By 1929, irrigated land accounted for nearly 16 percent of the farmland.Data on the value and composition of crop output put California’s agricultural transformation into sharper relief. Between 1859 and 1929, the real value of the state’s crop output increased over 25 times. Growth was especially rapid during the grain boom of the 1860s and 1870s, associated primarily with the expansion of the state’s agricultural land base. Subsequent growth in crop production was mainly due to increasing output per acre and was closely tied to a dramatic shift in the state’s crop mix. After falling in the 1860s and 1870s, the share of intensive crops in the value of total output climbed from less than 4 percent in 1879 to over 20 percent in 1889. By 1909, the intensive share reached nearly one-half, and by 1929, it was almost four fifths of the total.Figure 1 provides further documentation of the transformation of California’s crop mix over the late 19th and early 20th centuries. The Figure shows how cropland harvested in California was distributed across selected major crops over the 1879-1997 period. The acreage data reveal that in 1879, wheat and barley were grown on over 75 percent of the state’s cropland whereas the combined total for the intensive crops was around five percent. By 1929, the picture had changed dramatically. Wheat and barley then accounted for about 26 percent of the cropland harvested and the intensive crop share stood around 35 percent.In absolute terms, the acreage in the intensive crops expanded over ten times over this half century while that for wheat and barley fell by more than one-third.4Data on shipments of California fresh, dried, and canned fruits and nuts reveal the sector’s spectacular expansion over this period. During the 1870s and 1880s, growth rates exceeded 25 percent per year . Shipments continued to grow at robust rates of about eight percent per annum over the 1890s and 1900s. By 1919, California produced 57 percent of the oranges, 70 percent of the prunes and plums, over 80 percent of the grapes and figs, and virtually all of the apricots, almonds, walnuts, olives, and lemons grown in the United States. In addition, California produced significant quantities of apples, pears, cherries, peaches, and other lesser crops. The spectacular growth in California production of specialty crops had important international consequences as traditional Mediterranean exporters of many crops were first driven from the lucrative U.S. market and then faced stiff competition from the upstart Californians in their own backyard of northern Europe. California production significantly affected the markets and incomes of raisin growers in Málaga and Alicante, prune growers in Serbia and Bosnia, and citrus growers in Sicily.Explanations for the causes and timing of California’s structural transformation have long puzzled scholars. The traditional literature yields numerous causal factors, including: increases in demand for income-elastic fruit products in eastern urban markets; improvements in transportation, especially the completion of the transcontinental railroad; reductions in the profitability of wheat due to slumping world grain prices and falling local yields; the spread of irrigation and the accompanying breakup of large land holdings; the increased availability of “cheap” labor; and the accumulation of knowledge about California’s environment and suitable agricultural practices.

How To Grow Hydroponic Carrots In A Bucket

Growing hydroponic carrots in a bucket is possible, although it can be a bit challenging because carrots typically require deep soil for proper root development. However, you can try the following steps to grow hydroponic carrots in a grow bucket:

  1. Choose the right carrot variety: Select a carrot variety that is suitable for container gardening and has a shorter maturity period. Look for varieties specifically bred for small or round carrots, as they tend to perform better in confined spaces.
  2. Prepare the bucket: Take a large, sturdy bucket or container with drainage holes at the bottom to prevent waterlogging. Ensure it is clean and sterilized before use to minimize the risk of diseases.
  3. Create a hydroponic system: Set up a hydroponic system for the bucket. You can use a nutrient film technique (NFT) or a deep water culture (DWC) system. In NFT, a thin film of nutrient-rich water flows over the roots, while in DWC, the roots are submerged in a nutrient solution.
  4. Use a growing medium: Carrots need a loose and well-draining growing medium to allow their roots to develop properly. You can use a mixture of perlite, vermiculite, or coconut coir as the growing medium in the bucket.
  5. Planting the seeds: Sow the carrot seeds directly into the growing medium,dutch bucket for tomatoes following the recommended depth and spacing guidelines provided by the seed packet. Cover the seeds with a thin layer of growing medium.
  6. Maintain optimal growing conditions: Place the bucket in a location that receives adequate sunlight or use artificial grow lights to provide sufficient light for the plants. Maintain the temperature between 60°F and 70°F (15°C to 21°C). Regularly monitor and adjust the pH and nutrient levels of the hydroponic solution to ensure the plants receive the necessary nutrients.
  7. Watering and nutrient supply: In a hydroponic system, you will need to regularly supply the nutrient solution to the roots. Follow the instructions provided with your hydroponic system for nutrient mixing and feeding frequency. Avoid overwatering and ensure proper drainage.
  8. Thin and support the seedlings: Once the carrot seedlings emerge, thin them out to allow sufficient space for the remaining plants to grow. You may need to remove weaker or overcrowded seedlings. Consider using plant supports or trellises to prevent the carrot tops from falling over.
  9. Harvesting: Harvest the carrots when they have reached the desired size. Gently loosen the growing medium around the base of the carrot, grasp the foliage, and pull the carrot out.

Growing carrots hydroponically in a bucket may require some experimentation and adjustments to optimize growing conditions. It’s important to research specific techniques for the hydroponic system you plan to use and select appropriate carrot varieties to increase your chances of success.

One persistent issue encountered in urban farms is pest outbreaks and crop damage

In addition, agricultural workers often distrust water supplied by employers, and do not bring enough of their own water to adequately hydrate during the day.However, the lack of association of volume depletion to AKI was surprising, given the above findings. Volume depletion has been posited as a mechanism for AKI and potentially further damage.Recent research suggests that chronic volume depletion leads to sustained release of vasopressin and increased uric acid levels, which may precipitate long-term damage to the kidneys.Our findings suggest that heat strain, not volume depletion, may be a more concerning risk factor in this population. Surprisingly, we found an inverse dose–response relationship of body weight and AKI, where those classified as overweight had lower odds of developing AKI than those classified as normal weight. Obesity is generally accepted as a risk factor for the development of AKI;however, one study found that increased BMI is associated with decreased mortality from AKI in elderly surgical patients.The inverse relationship of obesity to AKI in our results is puzzling, though potentially explained by the fact that the addition of occupational characteristics attenuated the relationship of BMI to AKI. If AKI is a result of agricultural work,bato bucket it is conceivable that obese participants modified or reduced their workload, thus reducing their risk of AKI.

Limitations of our study include using a convenience sample by approaching employers to recruit participants at their work sites. Farms that were willing to allow a team of researchers to measure hydration and heat strain may be more likely to protect their workers, for example, stopping work earlier in the day under conditions of extreme heat, and adhering to state regulations for high heat protection. Recruitment of agricultural workers in California is difficult, due to their mobile lifestyle and concerns regarding documentation status, and recruiting a convenience, employer-based sample was the only way to gain access to workers during the course of their work day. A second limitation is the calculation of the PSI variable, used to estimate heat strain. Owing to limitations of our equipment, some of the measurements of heart rate and core body temperature were missing, which may have affected our estimates. We were able to account for this by working with a team of exercise physiologists, clinicians and statisticians to provide robust and accurate estimations. Finally, estimates of AKI based on KDIGO guidelines use a 24-hour measure of urine output, which is not feasible in the field setting. Additionally, elevations in serum creatinine in our sample are potentially related to muscle injury , which we were unable to assess in our study. Despite these limitations, we were able to estimate the incidence of AKI over the course of a work shift and test associations between traditional and occupational risk factors. Agricultural workers are a vulnerable population, often undocumented, living in poverty, culturally and linguistically isolated, with reduced worker protections.The development of AKI over the course of a work shift in this population may lead to further kidney damage, including chronic kidney disease, particularly because it is unlikely that workers know they are damaging their kidneys while working in the fields.

Further research is needed to evaluate the long-term consequences of repeated AKI among farm workers. While occupational regulations are in place to protect workers from heat-related illness, we have shown that workers who experience high levels of heat strain and who are paid by the piece are at increased risk. Fortunately, these risk factors are both modifiable, and incident AKI associated with heat strain and piece rate work may be prevented. Urbanized areas are the fastest-growing habitat worldwide. In the United States, over 80% of the population now lives in cities. It is expected that urban populations will continue to increase significantly in the coming decades. Matching urban population growth is an increase in urban food production; urban agriculture has grown 30% in the United States in the last three decades. Growing food in the city has become an increasingly common pathway to affordable, nutrient-rich, and culturally appropriate foods for people who live in high-cost cities. A myriad of issues complicates urban agricultural production. Once urban farmers gain access to land, they must address many abiotic factors unique to cities that disrupt the ecosystem services many agroecological practices rely on. Increased impervious surface and decreased canopy cover affect hydrological and bio-geochemical cycles and increase urban temperatures. Past land uses can affect soil quality and composition. These abiotic factors often exacerbate crop damage from herbivorous insects. Herbivorous pests in urban agriculture can become more persistent and increase in abundance in response to favorable environmental conditions in cities and cause damage to crops. In urban agriculture, management of pests is almost universally accomplished through cultural practices as pesticides are rejected for environmental and health reasons.

Many urban agriculturalists turn to agroecological pest management practices to increase on-farm beneficial insects and regulate pest populations. Agroecological practices proven on rural farms, such as crop diversification and floral resource provisioning, have been implemented to varying degree in the built environment, often with conflicting results. This research focuses on understanding urbanization impacts on agroecological pest management in urban agriculture. Specifically, how on-farm diversification schemes affect biological control services from parasitic Hymenoptera . Recognizing how these biological control services function in fragmented urban landscapes is vital to urban farmers. Understanding agroecological pest management practices and factors that may affect ecosystem function on urban farms necessitates understanding urban farm biophysical composition. Over three years, biophysical data were collected on twenty-nine urban farms in the San Francisco Bay Area. The physical composition of urban farms were measured, including overall size, areas of production, and percentage of land not in agricultural production. Indicators of specific management practices, such as type and percentage of mulch and ground cover, floral diversity, and crop and non-crop biodiversity, were recorded, and overall production was assessed. We found that practices associated with APM are widely adopted and are often practiced concurrently. Our research shows that urban farms are highly productive, and most crops grown feed local community members. Land use and spatial composition of urban farms varied, but the production area as a percentage of the total area is often low,hydroponic grow kit and areas set aside for pollination gardens or beneficial habitat are common. As agroecological pest management in urban agriculture is an understudied topic, a systematic review of research specific to UA and biological control services was conducted. Previous findings recorded significant impacts on both natural enemy and herbivorous pest populations in response to landscape and local effects, but findings remain inconsistent. Local management factors related to agroecological practices, including increased floral abundance, mulch and leaf litter, high plant species richness, and structural diversity, had significant beneficial effects on natural enemy abundance, richness, and biological control services. We conducted a two-year experiment testing the effects of local management practices and landscape effects on parasitic Hymenoptera, aphids, and crop damage on common Brassica crops. Two fundamental hypotheses in conservation biological control: the enemies and the floral nectar provisioning hypotheses, were tested in novel urban agroecosystems. Local and landscape factors were measured and assessed for their influence on PH populations on eleven San Francisco Bay Area urban farms. Farms were selected to represent a variety of sizes and surrounding imperviousness. Our research indicated that Local factors, including increased mulch coverage, crop richness, and percent of non-crop areas, were predictors of increased PH abundance and aphid parasitism rates. To test the effects of floral provisioning on PH we sampled thirteen common floral species across community partner sites to link common floral species in urban farms to PH families and subfamilies known to utilize aphids as hosts. We found that PH had no feeding preference, and floral species had little impact on PH abundance. To assess the second criterion of the nectar provision hypothesis, a demonstrable reduction in pests or crop damage, we looked at aphid abundance, rates of parasitism, and overall crop damage on brassicas.

Our results show that farms with increased floral richness have lower aphid counts per plant. Our findings indicate that on-farm habitat manipulations can increase ecosystem function, supporting the enemies hypothesis in fragmented urban agriculture sites. Growing food in the city is not uncommon, but it has rarely been straightforward or without controversy. Historically, the practice has been implemented, supported, and championed during periods of domestic turbulence and economic stress. Conversely, urban agriculture has often been left with little support when “crises” have subsided, or even actively suppressed . Post-WW2, urban agriculture has been especially prevalent in the context of social movements . As worker wages stagnated in the late 60s and 70s, and access to culturally relevant foods became more difficult for rent-burdened people, urban agriculture became a means to supplement diets, especially in BIPOC communities. When the Black Panther Party started community garden networks to support their Free for Children Breakfast Program in the late 60s, the Hoover administration said that the program was the “most influential activity going for the BPP and, as such, is potentially the greatest threat to efforts by authorities to neutralize the party.” Fifty years later, Billy X Jennings, the official archivist of the BPP said that the Breakfast Program was “one of the biggest and baddest things [the BPP] ever did” . Oakland, California, was the epicenter of urban agriculture in the 60s. Presently, in Oakland and many other San Francisco Bay Area cities, urban farmers continue to farm the city. However, urban farmers continue to face challenges. Despite the inclusion of urban agriculture and sustainable urban food production in many city plans, formal policy and financial support are often lacking . Often, urban agriculture is relegated to degraded vacant lots on the margins of high-value urban land. Even though urban agriculture is very productive, it fails to generate substantial profit at scale, therefore, falls outside the concept of “highest and best use”, creating an economic disincentive for support . A lack of secure tenure affects the implementation of long-term practices and investment in farming operations. Despite these difficulties, urban agriculture seemingly thrives – growing every decade and providing fresh and culturally appropriate foods to a wide range of diverse urban communities . While urban agriculture exists in the margins of urban land use cycles, it also persists in a nexus of social, economic, and ecological factors that co-create and shape this land use. These social-ecological and biophysical factors can often seem insurmountable when creating and maintaining urban agroecosystems. Compacted soils must be remediated, and entire ecosystems created out of vacant lots, old sports fields, and former parking lots. Many innovative cultural technologies and practices are implemented during the creation and maintenance of urban agriculture sites. Every urban farmer must draw on a multitude of cultural technologies and agroecological knowledge to overcome the technical barriers of creating thriving agroecosystems that feed their community .Urban farmers often choose to manage pest outbreaks through cultural and mechanical practices that rely on regulating ecosystem services provided by naturally occurring “enemy” arthropods that predate or parasitize crop pests. During initial stages of the research project outlined in Chapter 1 of this dissertation, urban farmers demonstrated a great interest on the ecological management of crop pests, and questioned whether on-farm management practices, such as floral provisioning and agroecosystem diversification, would be impacted by the conditions in the built environment and, if so, whether on-farm management practices could essentially offset these impacts. Concerns about urbanization effects and pest management are not unfounded. Several conditions exist in urban areas that can impact ecosystem function regarding pest management. Firstly, urbanization fragments the landscape and creates a selection pressure for disturbance tolerant species . Frequently these disturbance tolerant species are herbivorous insects who impact urban cropping systems. Herbivorous insects in urban areas have been documented to be more fecund, larger, and persist for longer . Secondly, natural enemies have been shown to suffer detrimental effects from urbanization, disallowing them to reduce or stabilize urban herbivore populations in urban agroecosystems . Because urban farmers typically employ agroecological management practices for pest control, these effects are especially compelling.

Previous research on the impact of bio-char on soil water retention is inconsistent in its outcomes

As discussed previously, a natural cone of depression occurred in the same area during the fall 2020 season, with low groundwater elevations in the same area occurring in the spring 2021 season, as shown by real-world groundwater monitoring data from the DWR . This finding is further supported by the parent model outputs of groundwater flux seen in Figure 14. The general trend of groundwater flow in the parent model is away from the model boundaries and towards the center of the model, where the cone of depression occurs; water always flows from areas of high hydraulic head to low hydraulic head. The cone of depression in our model is more exaggerated than the natural cone of depression that occurs in the same area. Therefore, we have identified it as a systematic error in this model. We want to emphasize that this underestimation in heads can create uncertainties for the fluxes in the child model; for the current state of the project, we were more interested in running the child model scenarios than prioritizing the calibration of the parent model. Flow magnitudes in Layer 1 are very high in the southwest corner of the parent model domain, indicating high magnitudes of flux away from the foothills of the Coast Ranges . The steep gradient and high-magnitude fluxes in that area could be a result of the topography of the ground surface, or a “pulling” of water towards the cone of depression due to high amounts of groundwater pumping in the central area of the parent model domain,blueberry cultivation where a lot of pumping for agriculture occurs.

Both are plausible explanations, and both may contribute to the presence of the cone of depression. Flow in Layer 6 illustrates the influence of pumping wells that extract groundwater from the shallow to middle layers of the model, with the cluster of concentrated head gradients displaying the “pull” of water from groundwater pumping wells. All layers indicate flow away from the Sacramento River near the child model domain area where the ag-MAR field sites are located. This is significant because in the area of interest, the Sacramento River is a losing stream, meaning it does not take water from the surrounding groundwater as it flows downstream. This finding suggests that although the ag-MAR sites are located close to the Sacramento River, most of the recharged groundwater is not at a great risk of being diverted to the Sacramento River as surface water flow. We were able to construct the parent model and analyze the results to understand the regional groundwater flow in the parent model domain. These regional flow patterns and magnitudes were extracted to serve as the child model’s boundary conditions that were informed by the natural geography and hydrology of the region. Essentially, the parent model results were a credibility check for the child model. Since we successfully replicated the parent model’s flow patterns in the child model, we gained confidence in the results of our three recharge scenarios that were used to test different parameters using the child model. Despite the cone of depression observed in the parent model, the flow directions do make sense, but the magnitude of fluxes might be skewed because of how exaggerated the cone of depression is.Each of the three scenarios were run using the child model, and the flow in the child model domain was a direct result of the flow that occurred in the same area of the parent model domain. As such, the results and flow directions observed from the child model were influenced by the results of the parent model. It is important to note that each of the child model scenarios was affected in the same way by the cone of depression that occurs in the parent model, which was merely a systematic error in the parent model. Analyzing the flow direction and magnitudes of flux in the child model results from Scenario 1 make it clear that groundwater flows southwest, away from the Sacramento River and towards the cone of depression in the parent model.

Although the cone of depression occurs naturally, as seen in real-world data, we should reiterate that the cone of depression in our parent model is exaggerated, which may have influenced the magnitude of the groundwater flux in our child model scenarios. Scenario 1 was the baseline model run with unaltered deep percolation data. The one to-one plot of observed and simulated equivalent heads and residual map for the child model indicated that the model performed very well in the baseline scenario model run, since the simulated values are close to the observed head values. In Scenario 1, we noticed that proximity to the river affected the variation in simulated head values. For example, the hydrograph and recharge bar chart for Well_34 showed very little variation in groundwater elevation since that well is located so close to the Sacramento River. The hydrograph and recharge bar chart for Well_2b showed more of a response to recharge rates. In the child model run for Scenario 2, deep percolation rates were increased by one order of magnitude to assess whether a significant hydrologic response would be observed within the same time frame . From the combined hydrographs and recharge bar charts for Scenarios 1 and 2, we saw a significant difference in the water table elevation between the two scenarios. The simulated heads in Scenario 2 were consistently higher than the simulated heads in Scenario 1 . It is clear that increasing the magnitude of recharge, as we did in Scenario 2, shows a significant hydrologic response through a raised water table when compared to the simulated heads plotted from Scenario 1. In the case of Well_2b in Scenario 2, we even noticed that the simulated heads exceeded the observed values, unlike the simulated heads from Scenario 1.

We also want to clarify that for Well_2b, the spike in simulated head would realistically flood that monitoring well by approximately 2 m. However, since Scenario 2 is purely hypothetical, we want to emphasize that our goal was to test an extreme increase in recharge rates in order to see a significant response. The water budget component graphs of both Scenario 1 and Scenario 2 exhibited the same pattern, but as expected, the rates in Scenario 2 are extremely scaled up when compared to Scenario 1. In Scenario 1, we observed that as recharge rates increased, water levels rose in the model. When recharge rates declined,plant pots with drainage water began to drain out from the model cells and flow out to storage. In Scenario 2, we also noticed the same pattern of increased outflows from the model cells to storage after recharge rates started to decline. It was difficult to compare the results of Scenario 3 to the results of Scenarios 1 and 2, since the time discretization of Scenario 3 was ten times larger, and only simulated heads were analyzed since there were no projected groundwater elevation data that could be used as input observed heads. We initially hoped to see at least a slight and gradual increase in storage inflows and groundwater levels over the course of the ten years for Scenario 3, but the water budget graph indicated that just simply replicating the 2019 recharge program year did not provide enough variability to show any significant improvement in groundwater storage or water levels over time. Perhaps gradually increasing recharge rates with each consecutive year would have shown an overall positive hydrologic response by the end of the ten years. Although we did not observe the response we had hoped to see for Scenario 3, we learned what does and does not work for the context of designing that hypothetical scenario. What may work in a future scenario might be gradually increasing recharge rates with each consecutive year, which might show a significant hydrologic response by the end of the ten years. We also believe that the plots of the hydrographs and recharge bar charts for Scenario 3 did not show any changes in groundwater levels over time because the amount of recharge was so little. And unfortunately, the sites that have been flooded are located very close to the Sacramento River. This is an issue in the context of this model because the river package acts as a boundary condition, which does not allow for much movement of water near that boundary. Theoretically, Scenario 3 showed results that should have been expected, since it was essentially a ten-year replication of Scenario 1, which had such small deep percolation rates from flooding that we saw very little hydrologic effects. In a future scenario, replicating the design of Scenario 2 for ten years, instead of Scenario 1, might show a significant difference.After comparing the results of the three scenarios, it is evident that increasing deep percolation rates yields the most significant hydrologic response. The results of Scenario 2 yielded the most positive response, increasing the simulated equivalent heads at each of the four groundwater monitoring wells. Global climate change has increased extreme hydrological events, such as long-term drought, extreme precipitation, and frequent wet-dry cycles . This can lead to greater uncertainty in agricultural production globally . Improving soil water retention capacity can increase the resilience of agroecosystems and the soil microbial communities on which they depend . As a by-product of biomass pyrolysis under oxygen limited conditions, bio-char soil amendments provide a potential soil carbon sequestration technology to help mitigate global climate change .

Adding bio-char can provide other agricultural benefits, such as reducing nutrient leaching and increasing soil cation exchange capacity .Because bio-char physical characteristics vary depending on feed stock and pyrolysis conditions , its capacity to modify soil water retention depends on the combination of bio-char and soil properties. Comparing bio-chars prepared from straw and pine wood at different temperatures, Burrell et al. found no consistent impact on plant available water in three agricultural soils. However, Hansen et al. found that two gasification bio-chars improved plant available water in two coarse-textured soils. Bio-char soil amendment can influence soil water retention properties by decreasing soil bulk density , increasing total soil pore volume and altering the pore-size distribution , increasing soil surface area, especially in coarse-textured soil , and increasing soil aggregation . However, many of these proposed mechanisms have not been validated based on direct evidence. Observation of soil moisture distribution in bio-char-amended soil at a finer resolution can provide direct information about potential mechanisms. The investigation of water movement and distribution in porous media using traditional methods, such as a pressure plate , is challenging since pressure plate can only measure water retention capacity when the internal moisture distribution has reached equilibrium. Neutron imaging technology, a non-destructive method, provides the possibility to observe moisture distribution in undisturbed porous media. Neutron imaging can measure the spatial and temporal moisture distributions with a high resolution and is sensitive to minute changes in soil volumetric water content. This tool enabled us to investigate bio-char’s potential impact on soil water retention and water movement between bio-char and supporting material in a defined system, e.g., organic matter free silica sand. An area that has not received much research attention is how bio-char aging after application to soil may lead to changes in its properties over time. Most studies of bio-char and soil water retention measure impacts in freshly amended systems; however, bio-char soil amendment is considered to be a long-term practice . Interactions between bio-char particles and soil components will gradually alter the bio-char surface, especially under field conditions . For example, fresh bio-char has a relatively high surface area associated with its internal micro- and macropores , however over time particles of soil organic matter fill bio-char pore space and decrease its specific surface area . Ren et al. found that bio-char surface area increased after aging for 0.5 year in an agricultural soil and decreased during the following 1.5 years. A three-month lab incubation experiment also showed application of in-situ aged bio-char had a greater impact on soil water holding capacity than did fresh bio-char . The results are inconsistent in part because they are conducted under different, sometimes artificial, conditions and do not reflect the realistic aging processes that occur in agricultural fields subjected to physical disturbance, UV exposure and wet-dry cycles. Thus, long-term field studies are needed to better understand impact of bio-char on soil water retention capacity in agricultural systems with different management practices.

One of the costlier forms of somatic investment in adulthood is immune function

Natural and controlled experiments provide evidence in favor of testosterone-mediated male survival, with castrated males living longer than intact males across many species including humans .Immune activation increases resting metabolism in humans and other species by 8%–56%, and can incur caloric costs of up to 2,000 kJ/day21 . The Immuno competence Handicap Hypothesis rose out of classical life-history theory and decades of research into costly signaling to become a dominant framework in the evolutionary ecology and behavioral endocrinology literature. It proposes that testosterone—as a critical mediator of male reproductive effort—suppresses immune function, and thus elaborate androgen based traits represent an honest signal of male quality since only high quality males can afford to incur such costs . While the ICHH is a dominant theoretical model in the life history literature, evidence in favor of this hypothesis is limited, and other lines of research have suggested alternative models to explain associations between androgens and immune function . The immuno suppressive effects of exogenously administered testosterone are well documented from experimental studies of nonhuman animal models . However,hydroponic containers recent studies and meta-analyses find mixed evidence that endogenous testosterone is an active immuno suppressant in free-living mammals .

In fact, naturalistic studies often show positive associations between endogenous testosterone and induced antibody response, suggesting that males in good condition can afford to maintain both high testosterone levels and robust immune responses . These findings are bolstered by experimental work in a reptile model showing that immune function is enhanced when exogenous testosterone is paired with food supplementation, but without food supplementation exogenous testosterone results in decreased innate immune function . Importantly, testosterone is down-regulated following infection and tissue injury, making it difficult to isolate the effects of testosterone on immune function in cross-sectional studies . While meta-analyses suggest that testosterone is overall immuno suppressive , there is still ambiguity depending on which aspects of immune function are studied, and whether the impacts of testosterone on immune function are direct or indirect. Another major issue is that most studies assessing trade-offs between immune function and testosterone rely on only a single biomarker of immune function, precluding the ability to examine a potential immuno modulatory role of testosterone. Immune function involves multiple coordinated responses, each with their own costs, benefits and interactions with other immune and endocrine responses. Numerous cytokines, for example, play critical roles in immune cell signaling and lymphocyte differentiation and have varying impacts on physiology and varying energetic costs . As an alternative to the ICHH, it has been proposed that testosterone is immuno-modulatory rather than immuno suppressive, that is, testosterone regulates trade-offs between different types of immune response . If only the energetically costlier forms of immunity are down regulated in higher testosterone males, then energetic availability may underlie some of the associations reported in the literature.

Indeed, evidence suggests that energetic costs can impact both testosterone levels and immune function . The ability to mount a rapid response to local infection or tissue injury is of particular utility, as high testosterone males more frequently engage in aggressive physical competition with other males . In mandrills, male–male competition in the form of physical aggression is a common route for spreading simian immunod eficiency virus , while physically aggressive interactions between wild rodent males increase transmission rates of hantavirus . Innate immune responses, which include pro- and anti-inflammatory cytokines, not only are crucial rapid responses to injury, but also play a role in subsequent wound healing . In free-ranging baboons, where success in male–male physical conflict determines males’ reproductive access to females, high status males—who have higher testosterone than subordinate males — heal faster than subordinates , perhaps because of positive phenotypic correlation. Thus, while there may be trade-offs between testosterone and some more energetically costly aspects of immune function , one would not expect that testosterone would down-regulate all aspects of immune function equally. Studying the role of testosterone in modulating immune function under naturalistic conditions is notoriously difficult in humans, where ethical concerns limit the use of various experimental protocols commonly used in nonhuman animal models. Observational studies demonstrate that testosterone decreases immediately following illness or injury , which is consistent with a life history framework which posits that energetic stress shunts caloric resources from investment in reproductive effort toward immune function.

While it is clear that any energetic stress, whether due to immune activation from infection or caloric restriction , results in decreased testosterone production, it is less clear that endogenous testosterone actively down-regulates human immune function. Indeed, a longitudinal study of Filipino males found a positive association between testosterone and immunoglobulin A , a marker of mucosal immunity .This study contributes to the literature with data from a free-living energy limited population living a relatively traditional lifestyle, use of multiple measures of immune activation, and measurement of biomarkers at baseline and following an ex vivo challenge. The analyses herein focus on 109 older adult men in a population of forager horticulturalists facing high pathogen burden . In this immunologically stressed population, we expect energetic trade-offs between testosterone and immune function to be stronger than that observed among energetically replete industrialized populations with lower infectious burden . Additionally, industrialized populations have significantly higher levels of testosterone at younger ages compared with subsistence populations, and steeper age-related declines . Most prior observational studies in humans have only measured circulating concentrations of immune markers under baseline conditions, as opposed to the immune response to challenge. Recent studies indicate that immune response to challenge is far costlier than baseline immune function, both in nonhuman animal models and humans . Given behavioral effects of androgens , individuals with higher testosterone may also engage in behavior that increases the likelihood of wounding or encountering pathogens . In this study, levels of urinary testosterone are examined in relation to 13 circulating cytokines following ex vivo whole blood antigen stimulation with a T-cell mitogen, phytohemagglutinin and a B-cell mitogen, lipopolysaccharides . PHA is a commonly used mitogen that activates the division and replication of T-cells, while LPS is a cell wall component of gram negative bacteria that binds to toll-like receptor 4 and initiates B-cell division and differentiation into plasma cells as well as activation of macrophages, monocytes, and dendritic cells . This study can therefore examine androgen mediated immuno-modulation in response to several common immune challenges facing humans. This experimental approach has major advantages; first, we are able to stimulate an immune response ex vivo which permits intra- and inter-individual comparisons in cytokine response to the same challenge controlling for baseline cytokine levels and other potential confounders. Additionally, while under normal physiological conditions circulating testosterone rapidly decreases following infection or tissue injury ,container raspberries using an ex vivo design we can examine the relationship between baseline testosterone and cytokine response to stimulation without any potential for steroidal down regulation post-infection. Given the advantages of this experimental design over previous observational studies, we hypothesize that we will have a level of contrast necessary to differentiate between broad immunosuppression versus immuno modulation of specific aspects of immune function. We hypothesize that higher endogenous testosterone will be associated with more down-regulation of energetically costly aspects of immune function, such as T-cell mediated immune responses, but not broad, generalized immunosuppression.Tsimane men came to the Tsimane Health and Life History Project’s clinic in San Borja, Beni, Bolivia to participate in THLHP protocols , and to receive a routine medical exam as part of the project’s behavioral–biomedical surveillance. All Tsimane aged 401 were invited to participate in this and other studies regardless of their health status, and approximately 85% of adults participated. Prior to the medical exam and interviews, men provided a first morning void urine specimen. Fasting blood was drawn, both with and without heparin as an anti-coagulant.

One vacutainer of blood without anticoagulant was allowed to clot, and then serum was separated via centrifugation and frozen in liquid nitrogen. Multiple 100 mL aliquots of heparinized whole blood were immediately added to separate round bottom microtiter wells in a sterile 96-well plate. The first aliquot received 100 mL of 20 mg/mL phytohaemagglutinin diluted in RPMI-1640, for a final concentration of 10 mg/mL PHA. The second aliquot received 100 mL of 20 mg/mL Lipopolysaccharides diluted in RPMI- 1640, for a final concentration of 10 mg/mL LPS. A third aliquot was mixed with 100 mL RPMI-1640 without mitogens. In all three cases, RPMI was supplemented with 100 IU/mL penicillin and 100 lg/mL streptomycin to prevent contamination. In the absence of a CO2 incubator in the San Borja clinic, the microtiter plate was sealed in a glass Tupperware with a lit candle, which burned the O2 in the container, thus enriching the CO2 concentration . The sealed plates were incubated at 378C for 72 hr. Following this, the supernatant was removed and frozen in liquid nitrogen for transport to UNM. Specimens were transported on dry ice and stored at 2808C for up to 2 years before assay.This study tested trade-offs among older Tsimane men between androgens and immune activation biomarkers by examining associations between endogenous testosterone and mitogen-stimulated cytokine levels. Our results indicate that endogenous testosterone is associated with immuno-modulation, or at least selectively suppressive as opposed to broadly immuno suppressive. Testosterone is associated with reduced cytokine responses following stimulation with a T-cell mitogen, PHA, while testosterone has no significant association with response to stimulation with a B-cell and monocyte mitogen, LPS. These results fit within a larger life-history and ecological immunology literature suggesting that men with higher levels of testosterone down regulate some, but not all aspects of immune activation. In this case we find an association suggesting that cytokine responses to T-cell mitogens are down regulated in higher testosterone males. Unlike B-cells, which can continue to produce relatively long lasting antibodies, cytotoxic T-cells must be continually produced and clonally expanded in large numbers. From an energetic perspective, T-cell mediated immune activation may be more costly than B-cell mediated immune activation due to this need to produce many cells . Thus, testosterone appears to selectively down regulate the most energetically expensive forms of immune activation, which is expected if testosterone serves an adaptive immuno-modulatory function, especially in energy-limited subsistence populations. Stimulation with PHA results in an immune response similar to that expected with exposure to viral infection , and tends to cause greater changes in IL-2, IL-4, IL-5, and IL-13 . In animal models, treatment with testosterone results in reduced response to viral infections, as measured by higher viral titers .Research on humans indicates that men are more susceptible to viral infections than women, and also that testosterone is down-regulated in men infected with diverse viruses ranging from influenza vaccinations to HIV . If men with higher testosterone have a decreased cytokine response to viral infection, then reducing levels of testosterone following infection would be an optimal response. Indeed, studies find decreases in testosterone following illness and tissue injury . Testosterone can be lowered by decreasing hypothalamicpituitary-gonadal production, or by increasing aromatization of testosterone to estrogen . Changes in testosterone and other biomarkers during and following illness may underlie some sickness behaviors like reduced physical activity and other depressive symptoms . Contrary to the results from PHA stimulation, cytokines produced by stimulation with LPS were not associated with testosterone. LPS stimulates B cells as well as macrophages, monocytes, and dendritic cells. Macrophages in particular may be important in response to injury, and so the maintenance of their activity with elevated testosterone might be important. However, B-cells are much more abundant in Tsimane blood compared with industrialized populations, while monocytes are very rare , so much of the LPS response is likely a B-cell response. Unlike T-cells that are lysed when destroying infections, B-cells that remain inactive are relatively low cost reservoirs that can be activated to produce antibodies as needed . While the developmental costs of producing B-cells and immunoglobulins can be high, the maintenance and activation costs are relatively low, as are the collateral costs in terms of tissue damage when activated . For a 10 kg human infant, the total cost of producing immunoglobulin G is approximately 0.043% of their daily protein budget, while the costs of B-cell proliferation during infection is estimated to be 0.00048% of this budget . Immunoglobulins have a half-life of approximately 25 days, and thus once produced, antibodies have protective effects that require little additional energetic maintenance or input .

A total of 3801 differentially expressed genes among all treatments were identified 

To evaluate the effect of GA, CPPU, and GA + CPPU treatment at berry set on the volatiles composition, berries of ‘Sable’ were sampled 51 and 70 d after the treatments. GC-MS analysis allowed identification of 58 and 67 volatile compounds with quantitative data calculated relative to the internal standard . Analysis of the differences in volatile content by ANOVA showed that 62 of the 68 compounds present at both time points differed in content by treatments or time . PCA indicated strong separation of the volatile compounds according to the harvest time with PC1 at 49.6% . PC2 contributed 26.5% of the total variance and reflected the effect of CPPU at 51 d, but at 70 d there was convergence of the variance and overall differences among the treatments seemed insignificant. VIP score analysis for the volatile compounds at 51 d pointed to 15 compounds having significant scores . CPPU suppressed the levels of the monoterpenes, α-terpineol, linalool, and limonene,plastic plant containers as well as the carotenoid derivative, β-cyclocitral and the fatty acid derivative, hexanal. However, GA + CPPU increased the levels of these compounds. The levels of 2-hexenal and pentanal were higher in CPPU-treated berries while GA increased the level of methyl geranate.

At 70 d, CPPU increased and GA or GA + CPPU decreased the levels of decanal and 5 other compounds . In contrast, GA increased the levels of trans and cis-rose oxide, β-bourbonene, and methyl geranate. Decanal, methyl geranate, ethyl acetate, and α-terpineol were common among the two time points and the first two compounds showed the same pattern.PGRs may have multiple immediate effects on gene expression, but, in this study, we were interested in understanding the long-term effects of GA and CPPU on the berries at harvest. To this end, RNA-seq was carried out on ‘Sable’ berries at 51 and 70 d after the treatments, the time points that can be defined as early and late ripening with respect to the untreated control.Venn diagram analysis of control vs. GA showed that there were hardly any differences between the control and GA treatments either at the early or late ripening, but there were significant differences in gene expression among the ripening stages . In contrast, the CPPU treatment imposed significant differences on gene expression at either the early or late stages of ripening . Six main clusters representing gene expression patterns were identified . KEGG pathway enrichment showed that only cluster 3 and cluster 4 contained significantly enriched pathways . Six out of the 13 processes related to cluster 3 were assigned to the phenylpropanoid pathway. The first process registered for cluster 3 was ‘circadian rhythms’ but analysis of the relevant KEGG map suggested that all the 20 enriched genes in this bin were actually family members of chalcone synthase which is a central flavonoid pathway.

The ‘ubiquinone and other terpenoid-quinone biosynthesis’ bin included 4CL, trans-cinnamate 4-monooxygenase, and isochorismate synthase. Other bins of cluster 3, excluding the large unspecific bins of ‘Biosynthesis of secondary metabolites’ and ‘Metabolic pathways’, will be discussed later. Cluster 4 contained 2 out of 5 bins assigned to ‘photosynthesis’ or ‘photosynthesis – antenna proteins’. The genes in these bins belonged to photosystem I, photosystem II, cytochrome b6/F complex, and LHC1 and LHC2 complexes. In the ‘Steroid biosynthesis’ bin, genes included squalene synthase, squalene monoxygenase, and other sterol biosynthesis genes upstream of brassinosteroid biosynthesis.Because GA did not contribute a significant number of genes to the DEG pool, it was eliminated from further analysis. There were major differences in ripening between the untreated grapes and grapes treated with CPPU, and this was also expressed in the number of DEGs at both early and late sampling. At the early and late sampling, there were 697 and 382 DEGs between the untreated and the CPPU-treated berries, respectively, and the reduction in the number of DEGs was mainly in the late sampling for genes with lower expression following CPPU treatment . KEGG analysis of these two groups did not show any functional bin enrichment. In a separate analysis, the treatments were compared on the basis of similar Brix; this comparison was possible because the untreated berries reached a Brix of 19.8 at 51 d while the CPPU-treated berries reached Brix of 19.6 at 70 d. Comparing these two groups resulted in 313 and 589 DEGs with higher and lower expression from the untreated and CPPU-treated berries, respectively . KEGG analysis demonstrated that in this ‘similar Brix’ group there was enrichment of 11 functional bins similar to those already present in cluster 3 .

A subset of 42 genes showed significant differences in three combinations: Control vs. CPPU at 51 d; Control vs. CPPU at 70 d; Control at 51 d vs. CPPU at 70 d . Interestingly, very few DEGs had higher expression in the untreated berries atsampling of 51 and 70 d. These genes were a germin-like protein, basic 7 S globulin , protein P21 , polyol transporter 5 , oleosin 1, and DMR6-like oxygenase 2 that functions in response to pathogens. The DEGs that had higher expression in response to CPPU could be assigned mainly to cell wall-related and stress-related functions. Gibberellin has been used to enlarge seedless grape berries for many years. Some cultivars are very sensitive to the treatment while others have a modest response. Sable Seedless can be assigned to the category of ‘modest response to GA’, with a significant effect on size at early sampling that is reduced at late harvest. The transcriptomic data for both 51 and 70 d after the treatment, corresponding to early and late commercial harvest, suggest that GA did not have long-term effects on biological processes and this was also confirmed in the profile of phenylpropanoid metabolites. However, GA did delay maturity as expressed by lower TSS and TA , and also had an effect on volatile compounds . In addition, when combined with CPPU, GA had some additive effects on fruit weight but it mitigated the response to CPPU with respect to acidity and reduction in some phenylpropanoid metabolites . It is likely that higher doses of GA than the concentration used in this study , but still considered in the range of commercial practice for this cultivar, or multiple applications, would further increase the size and delay the ripening as previously reported in many studies. Our data and the literature support the notion that GA can trigger quantitative effects on berry size, but does not have a major impact on ripening processes under standard practice. In contrast to GA, CPPU affected a wide range of phenotypic, biochemical, and molecular responses. Since the introduction of CPPU,blueberry container there have been a number of studies in grapes reporting beneficial effects on fruit size, and delays in maturity, abscission, rachis browning, decay, cuticle formation, volatile profile and gene expression. Our study on the colorless cultivar ‘Thompson Seedless’ pointed to the effect of CPPU on total tannin content resulting in higher astringency. It was therefore of interest to study how the interplay between the anthocyanin branch and the PA branch of the pathway is manifested in colored cultivars. Our data clearly shows that synthesis of PA is at the expense of anthocyanins with no particular effects on the type of anthocyanins produced . The fact that the level of flavonols was also reduced points to the possibility that either PA synthesis was induced by CPPU or that there was multiple repression of both the flavonol and anthocyanidin branches by genes such as MybA1 and MybF1. One interesting trend was the increase of -epicatechin during late ripening, both in the control and CPPU-treated berries , in contrast to previous results showing that flflavan-3-ols in the skins peak at 2–3 weeks after veraison. This increase can result from degradation of PAs, but there was no evidence for this in the total PA levels and the only PA monomer that decreased in content during ripening was ECG . Both flflavan-3-ols, -catechin and -epicatechin, had higher concentration in CPPU-treated grapes and, thus, it can be hypothesized that there was a concomitant induction of their biosynthetic genes, LAR and ANR by TFs such as MybPA1 and MybPA2. CPPU did not affect the expression level of VvMybPA1 at 51 d but the level of this gene was reduced at 70 d post treatment . It is not known if the gene was actually induced by CPPU before veraison. It should however be noted that PAs are synthesized prior to veraison while anthocyanins are synthesized during or after veraison, bringing up the possibility that the decrease in anthocyanins may be due to deficiency in substrates in the berry rather than repression of the ratelimiting genes.

In previous studies, cytokinins were shown to promote anthocyanin synthesis in shoots and leaves of Arabidopsis with concomitant transcriptional activation of the pathway. Likewise, introduction of a bacterial ipt gene to tobacco leaves increased the level of phenolic compounds. The inherent discrepancy of comparing gene expression by treatments that delay maturity was partially compensated by comparing differential expression of phenylpropanoid-related genes at similar Brix, i.e., control at 51 d and CPPU at 70 d after treatment . There is a remarkable reduced expression of 28 STSs in CPPU treated berries . The STS multigene family in grapes includes 48 annotated genes. Expression maps of STS genes suggest induction of gene expression by multiple biotic stresses including ethylene and jasmonate, while abiotic stresses had both suppressive and inductive effects. Therefore, according to our data cytokinin may contribute to long-term inhibition of VvSTS expression. Of the upstream genes in the phenylpropanoid pathway, 6 DEGs corresponded to PAL pointing to a trend of overall reduction in the pathway during ripening. Other genes included C4H, 4CL, CHS, UFGT , and 9 other structural genes of the pathway. Of the related transcription factors, MYB14 and MYB15 are considered as activators of STS gene expression and their low level is in agreement with the low expression of the STS genes. The expression of MYB14 and MYB15 was shown to increase with ripening in Pinot Noir grapes, and therefore delay in ripening mediated by CPPU may reduce their expression. MybA3 was shown to be a truncated non-functional protein. MYB136, MYB137, and MYB139 showed high expression in CPPU-treated berries, and it will be interesting to find out if they are targets for cytokinin signaling in plants and bona fide regulators of VvSTS genes. Of the WRKY genes, WRKY24 and WRKY43 are reported to be co-expressed with STS and MYB genes. For example, MYB14 and MYB15 were coexpressed with STS21, STS29, STS41, and STS48 in agreement with our data . Like MYB14 and MYB15, WRKY24 alone was shown to interact directly with the promoter of STS29. A previous study on the effect of CPPU in ‘Shine Muscat’ grapes focused on transcriptome changes 60 d after the treatment and volatile profile changes 80 d after the treatment. Similar to the previous report, our data showed that some genes of the phenylpropanoid pathway, e.g., PAL, 4CL, and UFGT had lower expression following CPPU treatment as well as fatty acid biosynthesis genes, amino acid biosynthesis, and volatile-related processes. Higher expression was observed for carotenoid-related genes, fatty acid metabolism genes, and auxin-related genes. In hormonal signaling, Wang et al. identified three accessions for TIFY 5A, two of which had higher expression at CPPU application level of 5 mg L−1 but with reduced expression at a level of 10 mg L−1 CPPU. This is consistent with our study where one of the TIFY 5A had increased expression at both 51 and 70 d . Another set of affected hormone-signaling genes in our study was that of the cytokinin receptor genes, of which ARR-5 was repressed by CPPU at the late stage . In contrast, in ‘Shine Muscat’ these genes were induced by CPPU. With respect to the volatile profile, similar reduction in terpenoids was encountered following CPPU treatment with respect to our sampling at 51 d . Several volatile compounds that were reduced after CPPU treatment in our study are consistent with reductions reported in Shine Muscat by Wang et al., i.e., α-terpineol, linalool, 2-hexenal at 51 d post treatment and cis geraniol at 70 d post treatment. Wang et al. also reported an increase in hexanol in ‘Shine Muscat’ following CPPU treatment but this was not the case for ‘Sable’ in our study .

Light and carbon availability follows a diurnal cycle creating different signaling inputs

Under sustained low-temperature stress, tissue acclimation fails, leading to exhaustion and the onset of severe PCI. Preharvest factors, including genotype, environmental variables, and agronomic practices, all interact to influence PCI severity. PCI is more severe in tissues harvested before reaching horticultural maturity , as the developmental pathways are incomplete and will be largely disrupted by chilling and rewarming. Although PCI is a significant problem, determining the PLW that can be ascribed to PCI is challenging because of the difficulty in identifying when it occurs. Most damage appears in retail outlets or in consumers’ homes, which is hard to monitor. Further, symptoms are internal in many species, for example, pineapple, nectarines, and so on, and some abnormalities in texture and flavor are only detected when the fruit or vegetable is eaten. PCI symptoms are also misdiagnosed. For example, PCI increases susceptibility to pathogens,plastic pots for planting which is often mistaken as the primary cause of loss, and poor-quality produce due to PCI may be attributed to early harvest or poor varietal selection. Given the above factors, quantifying economic losses due to PCI is also difficult.

The global trade of fresh fruits and vegetables was worth 115 billion USD in 2018. More than half of the 50 highest-traded global commodities are PCI-susceptible, and PLW globally is estimated at ∼33%. If PCI reaches even 0.5% of PLW, it could cost USD $144 M. Additional costs related to 1) shipping at temperatures higher than the commonly used 4°C, and 2) the complex logistics that factor in harvest date and storage life into transportation, are not included into this estimate, but they collectively reduce flexibility for growers and distributors. Periodically, the apparent benefits of extending shelf-life by storing produce at inappropriate temperatures may outweigh the negative impact on quality: if fruit are stored at non-PCI-inducing temperatures for the equivalent time, they may spoil and will be rejected, whereas fruit with invisible PCI symptoms are salable. This incentivizes refrigerating sensitive produce, which may be profitable in the short term, but leads to long-term consumer distrust in produce quality and value. The abnormalities associated with PCI that lead to consumer dissatisfaction, waste, and loss can be linked to specific cellular dysfunctions . Mealy texture, surface pitting, and fungal susceptibility are due to reduced pectin solubilization and depolymerization, and micro-fractures in the cell-wall network. Tissue browning is initiated when organelles lose their structural integrity in chilled tissues. Chilling leads to membrane disassociation that releases polyphenol oxidase, peroxidase, and their phenolic substrates into the cytosol where they react to form quinones.

Polymerization of quinone creates the brown pigments in chilling-injured tissues. Cold storage disrupts the finely-tuned ripening program that is modulated by the interplay of hormones, transcriptional factors , and epigenetic marks often, with negative consequences for fruit quality.Upon rewarming, increases in respiration and ethylene production are initiated, and visible chilling-injury symptoms develop, the magnitude of which is inversely proportional to the storage temperature. Even mild chilling injury in red tomato fruit triggers epigenetic changes in ripening TFs such as RIN, NOR, and CNR that down regulate the production of key volatiles responsible for hedonistic values. However, this is not always so, ‘abnormal chilling injury behavior’ occurs at milder storage temperatures and has been reported in peach and nectarine, plum, persimmon, and papaya. The mechanisms underlying ‘abnormal chilling injury’ are unknown, but the enhancement of sugar and energy metabolism may be relevant. Many economically important commodities, for example, zucchini, cucumber, and bell pepper, are harvested before reaching physiological maturity, and will thus have different cold-stress responses to those commonly studied such as tomato and banana, which are harvested when mature. Commodities harvested at immaturity typically have higher respiratory and deterioration rates, greater water loss because of incomplete cuticle development, and inefficient reactive oxygen species scavenging systems, which will influence their PCI response. In potato, chilling leads to cold-induced sweetening — starch breakdown and sugar accumulation, where the latter serves as protective compatible solutes. When these ‘sugared’ tubers are fried, baked, or roasted, they turn black as acrylamide forms, which is visually unappealing, bitter in taste, and harmful to human health.

The shelf-life of leafy greens is relatively short, given their limited energy reserves and high transpiration rate. Fresh basil is a popular herb with high export value, but chilling causes changes in leaf photosynthetic parameters and stimulates ethylene biosynthesis, which accelerates senescence. Loss of membrane permeability, suppression of the protective antioxidant system, tissue browning, and Botrytis attack, all lead to premature spoilage. Reducing the severity of the negative traits of PCI that lead to waste and loss could be achieved by inducing allelic diversity at single or multiple genes that directly regulate relevant pathways . Integration of multi-omics data of cold-injured tissue compared with non-chilled tissues, has helped identify gene targets that influence PCI . In tomato, two important discoveries were made from genes identified using functional genomics: over expressing the TF SlGRAS4 reduced fruit-surface pitting, and promoted a more uniform color due to increased β– carotene content after chilling. Likewise, over expression of SlCYP90B3, a key brass inosteroid biosynthetic gene, improved the antioxidant response of fruits during cold storage, reducing PCI. These genes coordinated multiple pathways to improve PCI tolerance . Candidate genes for improving PCI tolerance have also been found by applying physical and chemical treatments that alleviate symptoms, and by studying the associated changes in the signal-transduction pathway. This is an active area of research where the literature is expanding rapidly. For example, physical treatments such as dipping in hot water before chilling mitigated fruit PCI, and have been associated with the upregulation of heat-shock proteins in banana and in mango, among others. The MaAPY gene family and the ATP receptor MaDORN1.19 are likely to be important for maintaining ATP homeostasis under chilling, after exogenous application of ATP or GTP to banana fruit. TFs MabHLH060 and MabHLH183, which are associated with reduced cold-induced membrane rigidity, were induced by Ethrel®, an ethylene releasing agent, which also reduced banana fruit PCI visual symptoms. Melatonin reduced peel browning in bananas, by inducing miR528 expression, which in turn down regulated several ‘browning genes’, i.e., MaPPO1, MaPPO2, and MaPPO3.

In tomato fruit, melatonin improved surface pitting, increased the expression of FAD3 and 7, and reduced the expression of phospholipase Dand lipoxygenasegenes, which helped to maintain membrane integrity under cold stress. New insights into regulatory networks governing PCI can be gained through-omics profiling as shown in several examples. Treating peach fruit with methyljasmonate delayed internal browning , maintained fruit texture and aroma volatiles,plant pot drainage and the accompanying transcriptomic and methylomic changes were revealed. In bell pepper, MeJA reduced surface pitting, shriveling, discoloration, and seed browning, and differences in the transcriptome, proteome and metabolome compared with untreated fruit were detected. Other studies combined cold storage with additional factors such as varying carbon dioxide, or fruit harvested at different times, and identified differentially expressed transcripts by RNASeq. These differential transcripts, proteins, and metabolites may help to identify gene networks and their regulators for genetic engineering. Gene targets for minimizing CIS in potato have been identified. CIS has been extensively studied compared with PCI in fruit, because potato is a staple for one billion people, and in some production areas, tubers are stored at low temperature for up to eight months. During tuber storage, there are cycles of synthesis and degradation of both sucrose and starch, but at temperatures between 4 and 10°C, the degradative fluxes are activated, so that reducing sugars accumulate . This change in metabolism occurs via the upregulation of genes encoding the beta-amylase, glucan water dikinase, sucrose phosphate synthase, and invertase enzymes. Attempts to alleviate CIS by modulating the activity of core enzymes of carbohydrate metabolic pathways have been made, although the role of each enzyme isoform is still to be elucidated. Recently identified non-metabolic genes that regulate CIS , for example, A CBF/DREB transcription factor and ring finger protein 1, are good targets for developing new germplasm. There is an acute need for a greater foundational understanding of PCI. Several advances have been made in model species, where regulatory elements of the cold signal-transduction pathway response have been identified and functionally verified. Integrating the discrete ‘snapshot’ studies discussed previously into full models across tissues, developmental stages, and conditions, is the next step for developing functional biotechnological solutions. PCI is often assessed in a single tissue sampled from a defined region. Not only is valuable information about the spatial evolution of the process lost, but events occurring in all the tissues that are consumed are not captured. A few studies have addressed this gap and serve as a guideline for future work. In tomato, tissue specific development of PCI was detected, even though pericarp is usually the only tissue traditionally studied. In pineapple, scanning electron microscopy and histochemical staining of fruit revealed that IB starts at the phloem and diffuses throughout fruit tissues from the core.

A breakthrough was made when a high resolution spatiotemporal transcriptome atlas in tomato was developed, which showed that ripening is not homogeneous. Because cold interferes with fruit ripening, some PCI symptoms would be expected to occur heterogeneously. Looking holistically at the chilling response across cells and tissues in harvested organs would uncover additional regulatory features of PCI. Uncontrolled and physiologically abnormal expression of genes through genetic engineering may severely disrupt the multiple finely-balanced gene-regulatory networks, resulting in deleterious phenotypes, especially if constitutively expressed in tissues where they do not normally occur. Regulated promoter systems to direct tissue gene expression in a highly controllable manner, with spatial and temporal precision, may be useful to study and design long-term solutions to PCI. Sequential changes in gene expression by promoter engineering are also a promising approach. Precise editing of chilling-associated cis-regulatory elements and differentially methylated regions due to chilling by Clustered Regularly Inter spaced Short Palindromic Repeats could promote ripening under chilling conditions and alleviate PCI . Achieving this precision is an immensely challenging prospect that likely depends on attaining the previously described holistic knowledge of chilling response. There are many longstanding challenges related to PCI that remain largely to be tackled, and which limit progress. The nature of research appears fragmented, and many species are studied with a substantial focus on symptom alleviation through exogenous treatments rather than development of endogenous/innate solutions. The importance of PCI is reflected in the number of papers published in Google Scholar using the search term ‘Postharvest chilling injury’, which has increased 7- fold over the past 20 years . This directly points to the urgency of developing biotechnological approaches to address PCI, and the immediacy with which solutions are needed. Environmental and management factors, both pre- and post harvest, influence whether a tissue will manifest PCI after cold storage. Time of year, time of day of harvest, and the growing environment are all documented to influence the trait. Experiments are by necessity, multi-factorial, and rely on large harvests of fruit, tubers, and so on, which limit the number of experiments that can be set up. In addition, plants must reach advanced developmental stages to obtain fruit or tubers, and this is followed by weeks of post harvest cold storage, limiting the number of experiments that can be performed in a year. This is exacerbated in perennial crops that fruit annually and may be biennial, offering fewer opportunities for experimentation. Replication of experiments may not be economically feasible, therefore, at a minimum, a thorough reporting of these factors should be included in PCI studies.There is a limit to which the data so derived can be translated to PCI. The growing plant may use avoidance, escape, and tolerance to cope with cold, while in contrast, options for surviving anthropogenic cold stress in stored tissues with limited nutrients are few. Cold responsive genes in Arabidopsis rosettes may have conserved functions in leafy greens, but genes and pathways from model crops, for example, cereals, will have limited relevance to the consumed tissues in horticultural crops. Therefore, post harvest studies must redescribe the behavior of these pathways under the conditions of each experiment, which is laborious and expensive or work with tempered assumptions about them.

Plant growth is heavily dependent on the continuous function of the SAM

Disregarding a poorly conserved insertion in CRM1 , all three modules are almost exactly the same size at 85-90bp long, further supporting the existence of a higher-order structure. Although the identity of this structure cannot be determined from the present data, its functional significance appears to be reflected in CRM1, where the ATG repeats/TGAT cores sequence appears to be reevolving in the ~36bp inserted sequence that displaced the original conserved block . Research in the Drosophila model suggests that the organizing proteins may in fact be PcG and/or TRX proteins, which are thought to be recruited to regulatory modules by a platform of multiple DNA binding proteins. In the Drosophila example however, the “platform” was spread over several hundred base pairs. In plants, a more comparable example might be the PcG binding site demonstrated in LEAFY COTYLEDONS2, where PcG proteins recognized an RLE motif that contained several cis-motifs in a region 50bp long. Interestingly, analysis of FERTILIZATION INDEPENDENT target sites found in A. thaliana found that they were enriched in four cis-motifs, and at least one of each can be identified in the three CRM’s revealed by the present study. The possibility of chromatin regulation also immediately suggests a plausible mechanism by which the 3’ enhancer region might repress CLV3 transcription.

The three CRM’s may serve as a nucleation site for a chromatin silencing mechanism,blueberry plants in pots allowing the silenced chromatin to spread in both directions until it blocks the 5’ promoter of AtCLV3, and presumably the promoter of the neighboring gene At2g27240 as well. However, this model is only weakly supported by the plant literature, as only as a single tenuous chain of evidence supports such an interaction: The TAAT core-motifs in CRM1 are bound by WUS protein, which in turn recruits TOPLESS, SAP18, and ultimately the histone deacetylase HDA19/SIN3-LIKE. This evidence is at least consistent with the repressive portion of WUS transcriptional activities. Although the biochemical details regarding how WUS activates transcription are not yet known, another example from the Drosophila model suggests that such bifunctional activity might be an emergent property of chromatin regulation. Transcription factors that recruit PcG proteins to transcriptional start sites were found to prefer H3K4me3 chromatin modifications. If interpreted correctly, this suggests that transcriptionally active promoters directly recruit their own repressor complex. When a similar model is extrapolated to plants, it is tempting to speculate that the reverse situation might also true: WUS as a repressive transcription factor, may recruit TRX proteins to silenced chromatin, thus activating CLV3 expression. The spread of chromatin silencing is also known to involve insulator motifs that limit the spread of such silencing, but the asymmetric structure of the three CRM’s makes it tempting to speculate that they have polarized activity.

Interestingly, such directional specificity has been observed in fission yeast centromeres, where strand specific repression depended on which Sin3 homolog was used to assemble a histone deacetylase complex. However, no comparable examples are known from plants. Another possible mechanism by which the 3’ enhancer region might affect AtCLV3 transcription is through chromatin looping. This typically involves 8-70kb stretches of DNA [98], all of which are considerably larger than the 1.5kb that separates the AtCLV3 promoter from the three cisregulatory modules. Considering that this small region only supports 5-8 nucleosomes, such short-distance looping might be difficult to achieve before transcriptional activation due to stearic interference. The possibility of looping with a distant enhancer element is also unlikely, as the previously identified 1.5kb +1.2 kb regulatory regions were sufficient to reproduce the AtCLV3 expression pattern. The presence of a potential miR414 site in the coding sequence of CLV3 is intriguing, as it may also offer another level of control. If this microRNA were to be expressed in the RM, its presence would be sufficient to explain the weak expression of AtCLV3 in L2-L4 tissues. This interpretation is consistent with the finding that miR414 is up regulated by cytokinin responses, and strong cytokinin responses are known to occur in the Rib Meristem. However, the putative target site in the 3rd exon is poorly conserved among the five orthologs , and others have suggested that the miR414 gene product itself does not fold properly. Still, it may be premature to dismiss miR414 as a pseudo-gene, as several additional target sites were also found in a naturally occurring transposon , just past the CLV3 regulatory region.

Between the three CRM’s identified in this study, it is possible that they can recruit up to 20 different transcription factors simultaneously. Currently, only WUS proteins have clearly been demonstrated to be part of this group, though a few other candidates can be inferred based on known protein interactions. The recognition that SAP18 binds to the EAR-domain of ERF3 for example, clearly suggests that WUS can interact with SAP18 through its own EAR-like domain, in addition to the previously established WUS-TPL interaction. Although TPL did not bind to HDA19, the observation that TOPLESS RELATED1 and HDA19 coimmuno precipitated suggests that they are at least part of the same protein complex. Thus it would be interesting to identify the proteins that co-immuno precipitate with WUS, as these may include the adjacent transcription factors and the higher order protein complexes. Among transcription factors, one likely candidate might be HAIRY APICAL MERISTEM1 At2g45160, a GRAS domain transcription factor. Originally identified in Petunia hybrida, the GRAS domain HAM1 is known to cooperate with the WUS ortholog TERMINATOR, and was later shown to physically interact with WUS in A. thaliana. This pattern is consistent with the structure of the cis-regulatory modules, particularly if HAM1 should bind to one of the cis-motifs on either side of the conserved +970 WUS binding site. It is also possible that STM might be another co-factor, as both WUS and STM were required to ectopically express AtCLV3 in leaf tissue. The WUS-CLV3 feedback loop has long been predicted to be an essential part of meristem structure within A. thaliana, yet evidence from the present study suggests that CLV3 orthologs are rather poorly conserved outside of the Brassicaceae. The lack of conservation may be related to the size of the CLE gene family, where current evidence suggests that most plant species have twenty or more paralogs. Many of these are co-expressed in the same tissues, and at least some are functionally interchangeable. However, it is also difficult to reconcile the WUS-CLV3 feedback loop with the number of evolutionary clades in each gene family, which would be expected to closely correspond if they represent a conserved feedback loop. Instead, the WOX gene family is organized into 3 recognizable clades, whereas CLE genes are divided into 13 distinct groups.

Their functions are also diametrically opposed, as WOX genes tend to be expressed in or near stem cells, while CLE genes are typically expressed in tissues that display terminal differentiation, such as trichomes, vasculature, stamens, the placenta, and abscission zones. If WUS is an activator of CLV3, it is also difficult to explain why CLV3 expression occurs as much as 24 hours after the appearance of WUS, a phenomenon that has been repeatedly observed plant embryos, and callus tissue studies. Although WUS and CLV3 do have reciprocal phenotypes in mutant backgrounds, and when ectopically expressed, it is surprising that the importance of the hypothesized feedback loop has not left a stronger evolutionary imprint. Instead, there are hints that the two genes may actually operate in different, but related pathways. One such pathways appears to involve an auxin-CLE connection, which is supported by the similarity of auxin responsive tissues and CLE gene family expression patterns in vasculature tissue, leaf tips, guard cells, and trichomes. This is consistent with the proposed CLV3 regulation by an auxin response element,draining plant pots and is futher supported by the synergistic interaction between auxin and exogenous CLE oligopeptides found in developing Zinnia elegans tracheids. Another pathway appears to involve a WUS-cytokinin connection, as WUS has been found to directly regulate cytokinin signaling by repressing A-type ARRs, and potentially has a role in activating cytokinin biosynthesis in A. thaliana and rice . In turn, these two mechanisms might be linked by the mutually exclusive pattern of auxin and cytokinin responses, which seem to be involved in pattern formation in different parts of the plant. Together these observations suggest that WUS and CLV3 might simply respond to the patterns produced by these hormones, providing sharper boundaries between zones and imparting tissue-specific cell identities. In the present study, the fortuitous finding that several significant CLV3 regulatory regions lie entirely within a naturally occurring transposon immediately suggests a novel hypothesis that could unite many different observations. A transposition event that introduced the cis-regulatory modules to AtCLV3 could easily explain the difficulty of identifying CLV3 orthologs outside of the Brassicaceae, as it implies that it occurred independently in other lineages, where similar transpositions may have involved other CLE paralogs. Repression of the transposon via siRNA pathways might also trigger chromatin silencing, leading to the repression of nearby genes, while replicative transposition might explain why the 13-bp TAATnnWnnTGAT motif seems to be widespread in the A. thaliana genome. On a more macroscopic level, the sudden introduction of the cis-regulatory modules might also immediately reduce the size of the SAM, as ectopic activation of CLV3 in the CZ would partially stimulate terminal differentiation by the CLE pathway, and thus indirectly suppress WUS expression. Such a mechanism would produce smaller plants overall, which is consistent with the size of A. thaliana and related species.In order to maintain the dynamic structure of the SAM, a feedback loop between WUSCHEL and CLAVATA3 has been proposed to be an integral part of meristem maintenance. Research over the past decade has successfully clarified many aspects of this model by identifying some of the intermediate steps between CLV3 transcription, perception and signal transduction pathways, though it is not yet known how this controls WUS transcriptional repression.

In contrast, studies of WUS regulated genes have identified several hundred candidates, and have shown that WUS binding to CLV3 regulatory sequences is necessary for CLV3 expression. However, there is an increasing amount of evidence to suggest that this feedback loop is at least partially influenced by hormone signaling pathways. One of the most striking examples of this occurs in rice, where cytokinin biosynthesis mutants produce a flower phenotype that is almost identical to the wus-1 mutant phenotype in A. thaliana. A more direct route of cross-talk was found through microarray experiments, which found that WUS repressed ARABIDOPSIS RESPONSE REGULATOR7 and ARR15,both of which are negative regulators of the cytokinin response pathway. This interaction is fully consistent with the strong pattern of cytokinin responses that occurs in the RM, and suggests that this pattern might be a result of WUS repression of a repressor, leading to activation. In addition, exogenous cytokinin treatments can increase WUS transcript levels, and WUS transcripts are increased when cytokinin catabolism is reduced in ckx3/ckx5 double mutant. Similar positive correlations have also been found in callus tissues and in microarray studies. More directly, WUS has evenbeen found to activate ARR1 transcription, a positive regulator of cytokinin responses, which in turn might explain why both WUS and ARR15 are simultaneously up regulated in SAM regeneration studies. However, this interpretation is somewhat inconsistent with the expression pattern of ARR7 and ARR15, which have been found to strongly overlap with the RM in numerous studies. How this is possible in a tissue that also expresses their direct negative regulator indicates that this system is not well understood. Auxins are involved in the WUS-CLV3 feedback loop, as this hormone has repeatedly been found to reduce WUS transcript levels. There also appears to be a tight correlation between the auxin transporter PIN1 and WUS induction during somatic embyogenesis, while mutation alleles of the auxin-sensitive POPCORN gene are known to disrupt WUS expression patterns. This relationship is perhaps most strongly supported by studies in root meristems, where the closely related WOX5 gene is known to participate in a complex feedback loop involving auxin biosynthesis with YUCCA6, auxin signal transduction with IAA17, auxin efflux with PIN1, and auxin influx with LAX3 carriers. In SAM tissues, the close juxtaposition of WUS and the YUC4 biosynthesis domain in the overlying CZ is also at least reminiscent of the activation of YUC1 by pWOX5:WOX-GR in the root meristemss.