There are striking examples in tomato and other plants where identified genes regulate the development of fruit shape. For example, the OVATE gene in tomato regulates the phenotypic transition from round to pear-shaped fruit . If large-effect mutations underlie differences in strawberry fruit shape, the ordinal classification system proposed here should enable the discovery of such effects. Furthermore, quantitative phenotypes were linked to genetic features that interact with large-effect genes, i.e., suppressors of OVATE , through bulk segregant analysis and quantitative trait locus mapping . In woodland strawberry , fruit size and shape are linked to the accumulation and complex interaction of auxin, gibberellic acid, and abscisic acid, mediated by the expression and activity of FveCYP707 and FveNCED, as well as other genes. Because of the high H2 estimates for several of the newly created phenotypic variables , we hypothesize that quantitative, nft hydroponic latent space phenotypes can yield a more comprehensive understanding of the underlying genetic mechanisms of fruit shape in garden strawberry through GWAS and other quantitative genetic analyses. We anticipate that the analyses in this study will enable us to discover and study the genetic determinants of fruit shape in strawberry and other specialty crops.
Over the past few decades, models of peach fruit growth and plant development have identified useful principles for assisting growers in making horticultural management decisions. For example, harvest-date prediction models are now available to aid in managing fruit crops . The unusually early harvest of California’s peach crop in 2004 — which had record high temperatures during bloom time — and attendant difficulties in attaining the fruit sizes desired by the market have increased interest in using physiological concepts to understand the effects of early-spring temperature on peach fruit growth and in anticipating fruit size at harvest. The dependence of peach fruit development on spring temperatures during the first 30 days after bloom has been established; there is a strong correlation between the sum of growing degree hours accumulated in the 30 days after bloom and the number of days between bloom and harvest for several stone-fruit cultivars . Traditionally, the California cling stone peach industry has used reference-date fruit size to predict what the fruit size potential will be for a given year, and then peach growers conduct fruit-thinning accordingly. Reference-date fruit sizes are known to vary from year to year, but the reasons for this variation were previously unclear.
Lopez and DeJong compared a 20-year cling stone-peach data set collected and archived by the California Canning Peach Association, which included full bloom date , reference date and fruit size at reference date from different locations in California. When the data — collected from orchards near the Central Valley cities of Kingsburg, Modesto and Yuba City — was correlated with seasonal weather data available through the California Irrigation Management Information System , a strong correlation was found between accumulated GDH30 and the number of days between full bloom date and reference date . The number of days between full bloom date and reference date decreased as accumulated GDH30 increased . There was also a strong correlation between the number of days from full bloom date to reference date, and fruit size at reference date. Fruit size at reference date increased with an increase in the number of days from full bloom date to reference date . This study indicated that peach trees apparently could not supply resources rapidly enough to support the potential maximum fruit growth rates when accumulated GDH30 was higher than a threshold value . Consequently, fruit size at reference date in years with very warm spring temperatures was less than in years when accumulated GDH30 was below that threshold value. Furthermore, previous research has documented that fruit growth potential unfulfilled in early spring cannot be compensated for later in the season .
Although the effects of early-spring temperature on fruit size have been quantified for cling stone peaches at reference date, and fruit size at reference date is thought to be a good indicator of fruit size at harvest, industry wide data on fruit size at harvest is not available from the canning cling stone peach industry. However, the industry wide data situation is the opposite for California fresh market peaches. This industry does not keep representative seasonal data on full bloom date or reference date, but general fruit-size data is available from industry records maintained by the California Tree Fruit Agreement . At the outset of this study, we anticipated that the environmental factors influencing fruit growth and development rates for canning cling stone peaches would be the same as for fresh-market freestone peaches. Thus we initiated a follow-up study using relationships we had established for cling stone peaches to analyze the seasonal environmental effects on industry wide data for the fruit size of freestone peach cultivars. When fresh-market peaches are packed for shipping, the fruit are separated into different size categories related to the number of fruit that will fit into a standard-size lug box. Fruit packed in a size 30 lug are larger than those in a size 40 lug, while the fruit in a size 40 lug are larger than those in a size 50 lug, and so on. The CTFA annually reports the percentage of the total number of lugs for specific fruit-size categories that are shipped for each major cultivar at harvest. Data from three different fresh market peach cultivars were used for this study and compared with full bloom and fruit reference-date data for cling stone canning peach cultivars . However, the average fruit size lug category of the fresh-market cultivars was not correlated with the number of days between full bloom date and reference date for the cling stone cultivars in a given year in the Kingsburg area . When we analyzed historical trends in fruit size, there was a clear trend toward lower average lug categories; over the 20 years of this study, the average size of the fruit packed for each cultivar increased significantly . Although improvements in cultural practices may account for some of the increases in packed fruit size, this long-term trend presumably can be attributed to marketing pressures. Consumer acceptance of California peaches has been related to soluble solid concentration, acidity or soluble solid concentration/acidity ratio, but the major quality factor is fruit appearance . Likewise, market pricing has consistently favored larger-sized fruit. The percentage distribution trends of average fruit-size categories over the 20 years were similar for the three cultivars, and there were no significant differences in the slope of the regressions between Elegant Lady and O’Henry, or between Elegant Lady and Flavorcrest. However, the slope of the response for Flavorcrest was steeper than for O’Henry .When the effect of the year on the percentages of four fruit-size lug categories at harvest was analyzed independently, different patterns were observed among the cultivars and categories . Although all the cultivars increased the percentages of larger fruit-size lug categories and decreased the percentages of the smaller fruit size lug categories , nft system the slopes of the 30s and 80s categories of Flavorcrest relationships were clearly different from those of Elegant Lady and O’Henry . The change in Flavorcrest peaches observed in figure 4 could be primarily explained by a drastic reduction in the percentage of fruit packed in the smallest fruit-size lug category . However, the change observed in Elegant Lady and O’Henry was mostly related to an increase in the percentage of fruit packed in the largest fruit-size lug category . Although industry wide data on fruit packed per acre is not available for these cultivars, one practical implication of these results is that the average yield of packed fruit has likely declined over the same 20-year period, since, on average, fruit size is generally correlated with crop load . For example, a California thinning study showed a substantial effect on yield for both O’Henry and Elegant Lady .
For O’Henry, the change in lug size from 1985 to 2004 required average fruit weights to increase from 0.48pound to 0.56 pound . To obtain these fruit weights, a typical tree would need to be thinned to 976 and 523 fruit in 1985 and 2004, respectively. Thus, yields would have dropped from 464 pounds per tree to 291 pounds per tree , a 37% decrease over the 20 years. The results for Elegant Lady were similar. However, the profitability of early cultivars such as Flavorcrest was probably affected more by market pressures than Elegant Lady and O’Henry, since decreases in the amount of fruit in small size categories were not offset as much by increases in fruit packed in the large-size categories . When the data in figure 4 was used to normalize the fruit-size lug data to account for the long-term general trend, the deviation of a given year’s average fruit-size lug category from the long term trend was clearly related to spring weather patterns. The average, long term, trend-adjusted fruit-size lug category for the fresh-market cultivars in a given year decreased, with an increase in the number of days of fruit growth between full bloom and reference date recorded in the same year for cling stone peaches . Although the variability in this relationship among the different cultivars could have been related to the inherent variability in sources of fruit that were packed, the similarity of the slopes of the relationships for the three cultivars indicates that the conditions driving the relationships were likely similar for all three cultivars .Previous research with cling stone peaches, combined with this analysis of fresh-market peach data, indicate that early fruit development rates are clearly related to heat accumulation, and that high early-spring temperatures tend to decrease the average size of fruit packed in a given year. This is apparently because in especially warm springs, the tree cannot supply resources rapidly enough to support the potential fruit growth rates associated with high rates of phenological development. The relationships between fruit developmental patterns, fruit growth potentials and spring temperatures are even more important in light of the clear long-term marketing trends toward packing larger-sized fruit. Grower success will depend upon the ability to anticipate yearly fruit-sizing potential for individual cultivars and make the appropriate, cost-effective adjustments in cultural practices. It is well documented that early and heavy fruit thinning can increase average fruit size, but may cost more and/or reduce overall yields . However, these practices may be particularly useful in difficult fruit sizing years in light of the increasing market pressure for large-size fruits.California’s coastal districts, where 86% of the nation’s strawberries are produced on 38,600 acres, are the most productive strawberry-growing areas in the United States . To achieve this level of productivity, California strawberry producers need effective soil disinfestation, productive varieties and cultural practices such as polyethylene mulch and drip irrigation . Strawberries are very sensitive to soil pathogens, and growers with these highly productive systems have become dependent on preplant fumigation. Traditionally, they used methyl bromide plus chloropicrin as the basis for soil pest control. Fumigation with these chemicals controls soilborne pathogens such as Verticillium dahliae, Phytophthora species, Pythium species, Rhizoctonia species, Fusarium oxysporum and Cylindrocarpon species, as well as nematodes, soilborne insects and weed seeds in the soil seedbank . In 1992 methyl bromide was classified as a Class I stratospheric ozone-depleting chemical. Since 2005, under the Montreal Protocol, the use of methyl bromide for fumigation in the United States has been permitted only through critical use exemption . The methyl bromide phase-out and other regulatory limitations make research on alternative pest control measures essential. Currently, some California strawberry fields can still be treated with methyl bromide under the critical use exemption, which is subject to annual review by the parties of the Montreal Protocol.However, methyl bromide costs have been increasing, and its use in strawberry production has been decreasing . In traditional fumigation of California strawberry fields, beginning in the 1960s and continuing until recently, growers applied methyl bromide plus chloropicrin to the total field area. This process was called flat fumigation; the entire field was covered with polyethylene film to hold the fumigant at the concentration needed to kill soil pests . In the last decade, a sizable portion of the strawberry acreage has been treated with fumigants applied to the strawberry bed by drip fumigation .