Horticulture

Plastic plant pots with drainage holes are widely available and commonly used for container gardening. These pots have small holes at the bottom or along the sides to allow excess water to drain out, preventing waterlogging and root rot. Here are some key points regarding plastic plant pots with drainage holes:

1. Material: Plastic pots are lightweight, durable, and cost-effective. They are available in various sizes, shapes, and colors, offering versatility for different plant species and aesthetic preferences.
2. Drainage Holes: The drainage holes in plastic pots allow water to flow freely, ensuring that excess moisture doesn’t accumulate around the plant roots. These holes prevent the soil from becoming waterlogged and promote healthy root development.
3. Sizes and Shapes: Plastic plant pots with drainage holes come in a range of sizes, from small pots suitable for herbs and small plants to large pots for shrubs and trees. You can find round, square, rectangular, and even specialized shapes to accommodate different planting needs.
4. Saucers and Trays: When using wholesale plant containers with drainage holes, it’s common to pair them with saucers or trays to catch the excess water that drains out. This helps protect your floors or surfaces and allows you to reuse the drained water if desired.
5. Considerations: While plastic pots with drainage holes are popular, it’s important to note that plastic doesn’t provide as much breathability as other materials like clay or terracotta. This can affect moisture retention and airflow to the roots. However, proper watering practices and appropriate soil choice can help mitigate these issues.

When selecting plastic plant pots with drainage holes, consider factors such as the size and type of plant you’re growing, the amount of drainage needed, and the overall aesthetic you desire. These pots are widely available at garden centers, nurseries, and online retailers, offering a convenient and practical option for container gardening.

Commercial NFT (Nutrient Film Technique) hydroponic systems are widely used in large-scale commercial agriculture for growing a variety of crops. These systems are designed to maximize productivity and efficiency while ensuring optimal plant growth and nutrient delivery. Here are some key features and considerations of commercial NFT hydroponic systems:

1. Scale and layout: Commercial NFT systems can cover large areas, utilizing multiple channels or gutters for growing plants. The layout is carefully planned to make the most efficient use of space and allow for easy access, maintenance, and harvesting.
2. NFT channels: The channels used in commercial systems are typically made of durable materials such as PVC or food-grade plastic. They are designed to provide a shallow film of nutrient-rich water that flows over the roots of the plants. The channels may have specific shapes or contours to optimize the flow and prevent pooling or uneven distribution of the nutrient solution.
3. Water and nutrient delivery: A high-capacity water pump is used to circulate the nutrient solution from a central reservoir to the NFT channels. The flow rate is carefully controlled to ensure a thin, uniform film of the solution along the channels. The nutrient solution is typically well-balanced and adjusted based on the specific requirements of the crops being grown.
4. Automation and control systems: Commercial NFT systems often incorporate advanced automation and control systems to monitor and regulate various parameters. These systems can control the nutrient solution flow, adjust pH and EC levels, manage lighting and climate control, and collect data for analysis and optimization.
5. Climate control: Commercial NFT systems often operate in controlled environments, such as greenhouses or indoor facilities. Climate control systems are employed to maintain optimal temperature, humidity, and ventilation levels for plant growth. This includes using heaters, fans, evaporative cooling, and dehumidifiers to create the ideal conditions for the crops.
6. Lighting: Depending on the location and natural light availability, commercial NFT systems may use supplemental lighting to ensure consistent and adequate light for plant growth. High-intensity discharge (HID) lamps or LED grow lights are commonly used to provide the specific light spectrum required by the plants.
7. Monitoring and maintenance: Commercial systems incorporate monitoring and sensor technologies to track important parameters such as pH, electrical conductivity (EC), temperature, and humidity. These systems help growers identify and address any issues promptly. Regular maintenance, including cleaning the channels, checking for clogs, and ensuring proper nutrient solution concentration, is critical for system performance and plant health.
8. Crop selection: Commercial NFT systems are versatile and can be used to grow a wide range of crops, including leafy greens, herbs, strawberries, and certain fruiting crops. The choice of crops depends on market demand, profitability, and the suitability of the system for the specific plants.
9. Workforce and management: Commercial NFT systems require skilled personnel for day-to-day management, including planting, crop maintenance, harvesting, and system maintenance. Additionally, a management team oversees the operation, monitors crop health, and ensures proper nutrient management and system optimization.

Commercial NFT hydroponic systems offer several advantages, such as high-density planting, water efficiency, reduced use of pesticides, and the ability to grow crops year-round in controlled environments. However, setting up and managing a commercial system requires significant investment, expertise, and a thorough understanding of the specific crop requirements and market dynamics.

Evidence is accumulating that root system collapse is involved with HLB-induced tree decline, especially with commercial sweet orange and grapefruit trees on Swingle and Carrizo. Maintaining root health is imperative for keeping trees productive in an HLB endemic environment. In an effort to improve tree health by focusing on the roots, we have been experimenting with polymer coated nutrients and more recently TigerSul micronutrients in the field and greenhouse. In the greenhouse, Orange 15 rootstock were side grafted with HLB-infected Valencia sweet orange. Treatments were established with 10 replications each. Control treatments received either 1) bi-annual Harrell’s UF mix, or 2) bi-weekly liquid fertilizer. Experimental treatments received bi-annual treatments of the following: Harrell’s UF mix supplemented with bi-annual treatments of 3x overdoses of individual polycoated essential minor elements , TigerSul micro-nutrients , or 2x overdoses of the individual polycoated essential macro-nutrients. The experiment was carried out for one year. Effects on tree health, tree growth, root mass, SPAD, leaf and root nutritional analysis, and leaf and root Liberibacter titers will be presented. There were clear differences among treatments. Several treatments significantly improved tree growth and health as compared with the controls,drainage collection pot especially the 3x TigerSul manganese and 3x polycoated sodium borate treatments.

Results suggest that trees in the HLB world have higher specific micronutrient requirements than what are currently being recommended. In the field, we have several experiments that involve controlled release, ground applied fertilizers; these include the St. Helena project near Dundee, where sweet orange trees on numerous rootstocks are being grown completely with CRF and daily irrigation. The trees will be 7 years old in April, and they are now more than 80% infected with HLB, yet the large majority of the trees across all rootstocks have remained productive. Evolution of the CRF formulas and effects on tree health from St. Helena and other minor field CRF experiments will be discussed. It is clear that a constant supply of nutrients year-round is required to maintain productivity in the HLB world. Additional fine tuning of fertilizer composition, type, and delivery method should lead to improved tree health and productivity. Improved ground nutrition will continue to play a key role in integrated approaches to controlling HLB. Genetic variability for HLB tolerance/resistance is being identified in existing experimental rootstock germplasm planted throughout Florida, with both sweet orange and grapefruit scions. New rootstocks are being identified in these trials that show a reduced infection frequency, and less severe symptoms once infected, as compared to commercial rootstocks. Rootstocks showing promise include complex tetraploids, diploid citranges, and diploid pummelo x mandarin hybrids. Several of these rootstocks have been ‘Fast Track’ released for large-scale commercial evaluation. Current focus is on the identification of rootstocks that can sustain or increase productivity under heavy HLB pressure.

Data on these promising rootstocks will be presented. The fact that there is genetic variability in rootstock germplasm not pre-screened for HLB tolerance/resistance suggests that even greater progress can be made by focused selection, especially from crosses utilizing emerging HLB tolerant/resistant parents. Thus, we have adjusted our rootstock breeding/greenhouse screening program to focus on HLB by developing the ‘Gauntlet’ screening program described below. Following a preliminary calcareous soil/Phytophthora screen, selected individual hybrid rootstock candidates are transferred to citripots in commercial potting soil. Tops of these trees are propagated by rooted cuttings to produce seed trees on their own roots. The remaining individual liners are grafted with HLB-infected budsticks of Valencia sweet orange. The remaining rootstock top is then removed, forcing flush from the HLB-infected budstick. Trees are monitored for HLB symptoms, and healthy appearing trees are entered into a ‘hot psyllid’ house until psyllid feeding damage is observed on their leaves , followed by field planting at a challenging field site .The oldest ‘Gauntlet’ trees have now been in the field for approximately 2 years, and 20 promising new rootstocks have been identified so far. Our goal is to develop rootstocks that will facilitate sustainable and profitable citriculture in an HLB-endemic Florida, and possibly eliminate the need for psyllid control. Huanglongbing is one of the most devastating citrus diseases in the world. In Florida, it is associated with a bacterium Candidatus Liberibacter asiaticus and transmitted by a psyllid, Diaphorina citri Kuwayama.

We tested D. citri collected in many different venues over a period of 6 years for Las by molecular methods. Results surprised us. first, positive D. citri can be found long before symptoms develop on the plants at the site. Second, positive psyllids can ride on unprocessed fruit in trailers, even when there is no foliage. Third, about 10% of psyllid samples collected from plants for sale in Florida tested positive for Las. Finally, our data, and a related mathematical model, predict a form of transmission of Las that vastly increases the potential for spread of HLB. The mechanism now is known. The increase of infected vectors follows the growth of the insect population, independent of the incubation period in the plant. The implications of this new mechanism completely change our understanding of the epidemiology of HLB. It is possible to have positive D. citri throughout a grove before ever seeing a symptomatic plant. This mechanism has profound implications for disease spread, epidemiological research, early detection, long range dispersal, and grove management. Through utilizing the nutrient-rich phloem sap, sap feeding insects such as psyllids, leaf hoppers, and aphids can transmit many phloem-restricted pathogens. On the other hand, multiplication of phloem-limited, uncultivated bacteria such as Candidatus Liberibacter asiaticus inside the phloem of citrus indicates that the sap contains all the essential nutrients needed for the pathogen growth. Genome sequencing studies revealed that CLas can metabolize many sugars and amino acids found in the phloem sap. In addition, CLas can act as energy parasites and scavenge ATP from its host through the use of an ATP/ADP translocase. Furthermore, reduction in some minerals such as Zn and P in CLas-infected trees indicated that these minerals are required for the growth of CLas. The presence of gene in CLas genome also indicated that CLas can import Zn from its host. The phloem sap composition of many plants has been studied; however,drainage pot available data about citrus phloem sap is limited. In this study, we investigated the phloem sap composition of sweet orange. The phloem sap collected by EDTA or centrifugation method was derivatized with three different reagents and analyzed with GC-MS revealing 20 amino acids, 8 sugars, and 8 organic acids. Analysis of citrus phloem sap by inductive coupled plasma showed that it was rich in potassium, calcium, phosphorus, magnesium, and sulfur. Trace amounts of iron, copper, zinc, and boron were also detected. The ATP concentration in citrus phloem was 24.0 ± 4.0 ppm. Analysis of citrus phloem sap high performance liquid chromatography showed that citrus phloem sap was rich in nucleotides. Studies on seed transmission of ‘Candidatus Liberibacter asiaticus’ , the bacterium associated with Huanglongbing , described seedlings from infected trees which showed an abnormal growth phenotype but were free of CLas. We germinated populations of seeds of ‘Hamlin’, ‘Ridge Pineapple’, and ‘Valencia’ sweet orange from infected trees and observed chlorotic and stunted seedlings which failed to grow substantially. Tests detected no CLas DNA in these seedlings. These aberrant phenotypes were similar to symptoms expressed by infected trees, and persisted for 6 months or longer, at which point seedlings died or began to grow normally. Normal growth also was induced by grafting stunted seedling apices to healthy citrus seedlings. The absence of infection and their HLB-symptomatic phenotype suggest that extracellular factors produced by CLas in the mother tree affected the normal development of these seedlings, possibly through the alteration of normal gene expression. The similarity of these seedlings and symptomatic foliage suggest these factors are involved in disease development in infected trees. We propose these seedlings are a model system for understanding the molecular basis of symptom development in HLB-affected citrus trees.As Huanglongbing has continued to spread across the state, there is a growing body of evidence to support that in some instances, there are some off-flavors that can be detected in juice coming from fruit of HLB-infected trees compared to juice coming from the fruit of healthy trees.

The differences tend to be subtle but detectable in sensory evaluations by trained panelists, and in some instances by untrained panelists. Among the descriptors that have been used to describe HLB juice are bitter, sour, astringent, metallic, salty, umami, less orange aroma, less orange mouth feel, etc. Similarly, multiple studies have also identified several juice quality parameters, metabolites, or compounds that change with HLB infection; but, in all cases it has been changes in levels and not the presence or absence of a specific chemical. For instance, juice from HLB-infected fruit results in lower Brix, higher acid, and higher levels of limonin and nomilin. However, there is no one “smoking gun” parameter that can be measured that would indicate the potential for off flavors. In the present study, 14 different parameters were evaluated that encompassed sensory descriptors , basic juice chemistry , secondary metabolites , and harvest associated parameters . Samples were collected at random from fruit loads delivered to a commercial processing plant and were extracted using commercial equipment by the “USDA/State” lab that exists at commercial processing facilities. Sensory data were collected through the use of an electronic tongue. Basic juice chemistry data were collected using traditional wet chemistry techniques. Secondary metabolites were measured by HPLC and harvest date and fruit size were collected at the processing facility. Samples were collected from both Hamlin and Valencia varieties. Principal component analysis was used to reduce the number of variables considered for each of the varieties and the results were compared to a novel qPCR method to cross check the conclusions. Initial results indicated that a subset of parameters that include some sensory, basic juice chemistry, secondary metabolites, and harvest data can be used to identify fruit loads that have the potential to produce off flavors in Hamlin and to a lesser extent in Valencia varieties.Since its discovery in Florida in late 2005, citrus Huanglongbing , widely recognized as the most serious disease of citrus, has caused havoc in the Florida industry. Production costs have increased and production is down. Despite the apparent advances that growers and researchers have made in mitigating some of the symptoms of the disease, the statewide production continues to go down. All of the variables that go into the state forecast, tree number, fruit size, fruit per tree, and percent fruit drop are all trending in the wrong direction. This has led some growers to hold back on replanting in recent years which has further exacerbated the problem. The big question is how much lower will production go? Based on what we know, or in some cases based on our best guess, a model was created to estimate where we are in the HLB decline curve in the Florida industry. The model assumes that the industry focus will continue on the track of symptom mitigation instead of inoculum removal and management. Based on some conservative assumptions used in the model, the significant losses that have occurred the last several years should have been predicted. Going forward with the same assumptions, it appears that the production decline is near its predicted lowest significant drop and future losses will track the rate of replanting. That is to say, if tree attrition is greater than the rate of replanting, production will continue to decline. If the replanting rate is equal to or greater than the attrition rate, then the production will hold or increase slightly over time. Citrus is one of the most economically important and extensively grown fruit tree crops worldwide. Citrus production in most citrus producing countries, e.g., US, Brazil, and China, is facing an unprecedented challenge caused by Huanglongbing . Currently, no effective HLB management is available. Development of HLB resistant or tolerant citrus will provide a long-term, effective, and sustainable solution to HLB. Traditional plant breeding is unlikely to lead to HLB resistant or tolerant plants due to the lack of resistant varieties. Targeted genome engineering is expected to contribute significantly to future varietal improvement. Genome editing technologies using zinc finger nucleases , transcription activator-like effector nucleases , and clustered regularly interspaced short palindromic repeat /Cas9/single guide RNA have already been successfully used to genetically modify plants. Here, we reported our progress in modifying citrus genome suing Cas9/sgRNA technology.

A one percentage point increase in the unemployment rate raised the probability of receiving a bonus by 0.9 percentage points.We conducted five robustness checks. first, we estimated all three equations separately for documented and undocumented workers. That is, we allowed all the coefficients to vary between these two groups instead of only the recession dummies. The coefficients on our seven key recession variables were virtually unchanged . Second, we estimated all three regressions eliminating all newcomers , about 3,300 people or 7.5% of the sample, to see if compositional changes in the workforce during recessions are driving our results. However, the coefficients were virtually unchanged . Third, we estimated all three regressions leaving out the unemployment rate. Doing so had negligible effects on the other recession variable coefficients . Fourth, we excluded the crop dummies, in case they are endogenous. The recession variable coefficients were unaffected .There are multiple ways in which removal of infected host plant tissue can be employed as an element of disease management. These include removal of reservoir hosts to limit pathogen spillover onto a focal host , roguing of infected focal hosts to limit secondary spread ,pots with drainage holes and removal of localized infections within hosts to limit further infection or to retrain an unproductive plant .

Studies of bacterial pathogens in perennial crops have evaluated the utility of pruning as a disease management tool, with mixed results . The removal of infected plant tissues is analogous to measures used for management of trunk diseases, often referred to as “remedial surgery,” as an alternative to replacing infected plants . In this study, we investigated whether severe pruning of Xylella fastidiosa-infected grapevines in commercial vineyards could clear vines of existing infections. Pierce’s disease is a lethal vector-borne disease of grapevines caused by the bacterium X. fastidiosa . After susceptible plants are inoculated by X. fastidiosa, pathogen populations multiply and move through the xylem network, leading to symptoms of reduced water flow , including leaf scorch, cluster desiccation, vine dieback, and eventually death. There is no cure for grapevines infected with this bacterium; current strategies for management of PD in California vineyards involve limiting pathogen spread to uninfected vines by controlling vector populations, disrupting transmission opportunities, and eliminating pathogen sources in the surrounding landscape . PD is notable for the numerous sources of variability in infection levels and symptom severity in plants. X. fastidiosa infection levels vary among plant species , grapevine cultivars , seasons , and as a function of temperature . Like other bacterial plant pathogens , X. fastidiosa is often irregularly distributed within individual hosts.

For example, X. fastidiosa infection levels in grapevines may vary by more than 10-fold between grapevine petioles and stems ; in other hosts, infection levels may vary by more than 100-fold between basal and apical sections of shoots . This within-host heterogeneity may be epidemiologically significant if it affects pathogenacquisition efficiency . Moreover, if such variation is associated with protracted localized infection near inoculation points, such heterogeneity may facilitate other disease management tactics. In addition to grapevines, other plant species that are susceptible to X. fastidiosa infection include citrus in South America . Management of the resulting disease in C. sinensis relies on clean nursery stock, vector control, and pruning infected plant tissue from established trees or roguing young plants . The concept of pruning of infected plant material is based on the fact that, in established trees , tissue with early symptoms of infection can be pruned ~1 m proximal to the most symptomatic basal leaf, effectively eliminating infections, as the remaining tissue is free of X. fastidiosa. However, pruning is not adequate for young trees or for removing bacterial infections if any symptoms are present in fruit . X. fastidiosa multiplies and spreads through the xylem vessels, reaching the roots of perennial hosts such as citrus , peach , alfalfa , and blueberry . Nonetheless, under field conditions, chronic infection of grapevines is temperature and season dependent. In regions with freezing winter temperatures, infected plants can recover in winter, curing previously infected and symptomatic grapevines .

Infections that occur during spring lead to chronic disease ; however, infections that occur during late summer and fall may cause disease symptoms in the current year, but a high proportion of vines lack symptoms of X. fastidiosa infection in the following year .Nonetheless, models that incorporate low temperatures have substantial explanatory power in predicting rates of winter curing of X. fastidiosa infections in grapevine . Infections that occur early in the season may have a longer period during which X. fastidiosa can colonize and reach high infection levels, which may increase the likelihood of the disease surviving over the winter. Following this rationale, if most late-season infections remain in the distal ends of shoots and have lower infection levels, removing the symptomatic portion of the vine might eliminate X. fastidiosa. In other words, the efficacy of pruning infected grapevine tissue could depend on both the time of year in which the plant was infected and on winter temperature. A potential benefit of severe pruning versus replanting is that pruning leaves a mature root stock in place, which is likely to support more vigorous regrowth compared to the developing root stock of a young transplant . Recent attempts to increase vine productivity by planting vines with more well-developed root systems are based on this presumption. However, even if severe pruning can clear vines of infection,drainage pot it removes a substantial portion of the above ground biomass of the vine. Thus, a method for encouraging rapid regrowth of the scion after aggressive pruning is needed. We studied the efficacy of pruning infected vines immediately above the root stock graft union—the most aggressive pruning method—for clearing grapevines of infection by X. fastidiosa. We reasoned that if such severe pruning was ineffective at clearing vines of infection, less severe pruning would not be warranted; if severe pruning showed promise, less severe pruning could then be tested. We use the term “severe pruning” to refer to a special case of strategic pruning for disease management, analogous to the use of “remedial surgery” for trunk diseases . To test the efficacy of clearing vines of X. fastidiosa infection, we followed the disease status of severely pruned versus conventionally pruned vines over multiple years, characterized the reliability of using visual symptoms of PD to diagnose infection, and compared two methods of restoring growth of severely pruned vines.Pruning trials were established in Napa Valley, CA in commercial vineyards where symptoms of PD were evident in autumn of 1998. The vineyards used for these trials varied in vine age, cultivar, and initial disease prevalence . All study vines were cordon-trained and spur-pruned. We mapped the portions of the six vineyards selected for study according to evaluation of vines for disease symptoms. The overall severity of PD symptoms for each vine was recorded as follows: 0 = no symptoms, apparently healthy; 1 = marginal leaf scorch on up to four scattered leaves total; 2 = foliar symptoms on one shoot or on fewer than half of the leaves on two shoots on one cordon, no extensive shoot die back, and minimal shriveling of fruit clusters; and 3 = foliar symptoms on two or more shoots occurring in the canopy on both cordons; dead spurs possibly evident along with shriveled clusters.

To test the reliability of the visual diagnosis of PD, petiole samples were collected from the six vineyard plots when symptom severity was evaluated for vines in each symptom category; these samples were assayed using polymerase chain reaction . Petioles were collected from symptomatic leaves on 25, 56, and 30 vines in categories 1, 2, and 3, respectively. Next, severe pruning was performed between October 1998 and February 1999 in the six vineyard plots by removing trunks of symptomatic vines ~10 cm above the graft union. Cuts were made with saws or loppers, depending upon the trunk diameter. During a vineyard survey, severe pruning was conducted on 50% of vines in each symptom category; the other 50% of vines served as conventionally pruned controls. Sample sizes for control and severely pruned vines in each disease category ranged between six and 62 vines depending on the plot, with at least 38 total vines per plot in each control or pruned treatment. In spring 1999, multiple shoots emerged from the remaining section of scion wood above the graft union on severely pruned vines. When one or more shoots were ~15 to 25 cm long, a single shoot was selected and tied to the stake to retrain a new trunk and cordons, and all other shoots were removed at this time. We evaluated the potential of severe pruning to clear vines of infection, by reinspecting both control and severely pruned vines in all six plots for the presence or absence of PD symptoms in autumn 1999 and 2000. In all plots, category 3 vines were inspected in a third year ; in plot 6, vines were inspected an additional two years . Finally, in plot 6 we investigated chip-bud grafting as an alternate means of ensuring the development of a strong replacement shoot for retraining. To do this, 78 category 3 vines were selected for severe pruning, 39 of which were subsequently chip-bud grafted in May 1999. An experienced field grafter chip budded a dormant bud of Vitis vinifera cv. Merlot onto the rootstock below the original graft union, and the trunk and graft union were removed. The single shoot that emerged from this bud was trained up the stake and used to establish the new vine. The other 39 vines were severely pruned above the graft union and retrained in the same manner as vines in plots 1 to 5. Development of vines in plot 6, with and without chip-bud grafting, was evaluated in August 1999 using the following rating scale: 1) “no growth”: bud failed to grow, no new shoot growth; 2) “weak”: multiple weak shoots emerging with no strong leader; 3) “developing”: selected shoot extending up the stake, not yet topped; and 4) “strong”: new trunk established, topped, and laterals developing. All analyses were conducted using R version 3.4.1 . We used a generalized linear model with binomial error to compare the relative frequency of X. fastidiosa-positive samples from vines in the different initial disease severity categories . Next, we analyzed the effectiveness of chip budding versus training of existing shoots as a means for restoring vines after severe pruning. This analysis used multinomial logistic regression that compared the frequency of four vine growth outcomes the following season: strong, developing, weak, or no growth. This main test was followed by pairwise Fisher exact tests of the frequency of each of the individual outcomes between chip budded-trained and trained vines . We analyzed the effect of severe pruning on subsequent development of PD symptoms using two complementary analyses. first, we compared symptom return between severely pruned and control vines in the three symptom severity categories for two years after pruning. To appropriately account for repeated measurements made over time, our analysis consisted of a linear mixed-effects model with binomial error, a random effect of block, and fixed effects of treatment , year , and symptom severity category . Next, we analyzed the rate at which PD reappeared in only severely pruned vines from category 3 in subsequent years using a survival analysis. Specifically, we used a Cox proportional hazards model with a fixed effect of plot .Accurate and time- or cost-efficient methods of diagnosing infected plants are important elements of a disease management program, both with respect to roguing to reduce pathogen spread , and the efficacy of pruning to clear plants of infection . Accurate diagnosis of PD in grapevines is complicated by quantitative and qualitative differences in symptoms among cultivars and other aspects of plant condition . Our results suggest that a well-trained observer can accurately diagnose PD based on visual symptoms, particularly for advanced cases of the disease. The small number of false positives in disease category 1 and 2 vines may have been due to misdiagnosis of other biotic or abiotic factors . Alternatively, false positives might indicate bacterial populations that are near the detection limit; conventional PCR has at least as low a detection threshold as other methods that rely on the presence of live bacterial cells .

Transcription factors act as master switches of transcriptional reprogramming, inducing diverse protective mechanisms in response to abiotic stresses.We identified a large number of TFs responsive to dehydration, and 287 TFs were responsive to rehydration from among the DTGs . Among these TFs, the bHLH, MYB, and WRKY families were the largest groups during both dehydration and rehydration . Members of these three TF families are implicated in stress responses in model plants. In Arabidopsis, bHLH-type genes AtMYC2 and AtAIB are involved in ABA signaling, and overexpression of AtMYC2 or AtAIB enhances the drought tolerance of transgenic plants.Multiple MYB genes have also been implicated in stress responses. For example, AtMYB2 is involved in the ABA-dependent drought tolerance pathway,and AtMYB108 is associated with both biotic and abiotic stress responses.WRKY TFs are well known for their involvement in the regulation of plant development and in response to abiotic stresses.Functional analyses of rice OsWRKY11 and soybean GmWRKY54 demonstrated that WRKYs are involved in drought signaling pathways.Our results revealed that 9 SBP and 5 TCP type TFs also showed a response to dehydration in M. flabellifolia . Further functional characterization of these TFs may shed light on their roles in desiccation tolerance. PKs are essential signaling regulators in the acquisition of desiccation tolerance. Among the DTGs,vertical grow system we identified strikingly large numbers that respond to dehydration and rehydration .

PKs may play a key regulatory role in drought stress adaptation in M. flabellifolia, as corroborated by comparison of our data with Arabidopsis and chrysanthemum drought stress expression profile data.In Arabidopsis, only 121 PKs were found to be responsive to osmotic stress.Xu et al. identified only 229 differentially expressed PKs during drought stress in chrysanthemum, a species with a large and complex polyploid genome and high heterozygosity.Protein family distribution analyses showed that three receptorlike kinase type families – leucine-rich repeat kinases, domain of unknown function DUF, and receptor like cytoplasmic kinases – were the largest groups of DTGs in both the dehydration and rehydration treatments . RLKs constitute the largest PK family in plants and have been implicated in the regulation of meristem proliferation, organ specification, reproduction, and hormone signal transduction.Drought transcript profiling in Arabidopsis has revealed that the transcript abundance of many RLK genes peaks 1 h after the start of drought treatment, indicating that RLKs may also be part of a rapid drought response.Several functional studies have also confirmed roles of RLKs in drought tolerance.In Arabidopsis, an LRR kinase, receptor protein kinase 1 , is induced by ABA. Repression of RPK1 decreases sensitivity to ABA, suggesting that RPK1 is involved in ABA perception.A DUF type kinase, CRK, and a receptor-like cytoplasmic type kinase, ARCK1, form a complex that negatively controls ABA and osmotic stress signal transduction.

In addition,DTGs encoding mitogen-activated protein kinases were identified during dehydration stress in M. flabellifolia . MAPK cascades function in transducing environmental and developmental cues to intracellular responses.In Arabidopsis, several MAPKs are involved in abiotic stress signaling pathways including MEKK1,MPK1,MPK3,MPK4,MPK6,MAP9,and MAP12.The transcript abundance of homologs of all these MAPKs, apart from MPK6 and MAP12, was altered in response to dehydration in M. flabellifolia . To identify early responsive regulatory genes, the expression pattern of differentially transcribed TFs and PKs was analyzed by hierarchical clustering . The transcript abundance of 53 TFs and 91 PKs peaked early in dehydration , indicating that broad regulatory networks are quickly employed to coordinate global transcriptional reprogramming during desiccation of M. flabellifolia. Among the up-regulated TFs during early dehydration, the strongest induction was observed for genes encoding putative DREB family members . The DREB TFs are well-known regulators of ABA-independent drought stress signaling pathways in other plant species.In addition, a total of nine genes encoding WRKY family members were included among the up-regulated TFs in early dehydration, making the WRKY family the biggest group of early dehydration up-regulated TFs . Furthermore, among the up-regulated PKs, the LRK10 L kinase family is one of the largest groups in during early dehydration , suggesting that LRK10 L kinases may be important upstream regulators of rapid responses to water deficit. For example, the transcript abundance of a DTG encoding an LRK10 L kinase increased nearly 120-fold in early dehydration .

LRK10 L genes have previously been reported to be associated with resistance to pathogen infection.Functional characterization of these LRK10 L kinases will be an important step toward elucidating their roles in desiccation tolerance.Various genetically encodable reporters have been developed to monitor gene expression, protein subcellular localization, protein stability, hormonal signaling, and impacts of environmental signals. The green fluorescent protein and its derivatives such as RFP, mCherry, and YFP have many applications as reporters for gene expression or as fusion proteins. Although GFP is easy to use, it needs light sources to visualize the fluorescence signals. The β-glucuronidase reporter has been widely used in plants for monitoring gene expression patterns and as a reporter for hormonal signaling. For example, DR5-GUS transgenic lines are commonly used to monitor auxin distribution and auxin signaling. Luciferase is another broadly used reporter in both animals and plants. Both GUS and luciferase require the addition of expensive substrates X-Gluc and luciferin, respectively. Whereas the traditional reporters have been very useful, they have limitations. Fluorescent proteins are often monitored under a microscope, rendering it less useful in analyzing plants in natural growing fields or analyzing large samples such as a tree. GUS staining is invasive and often requires sacrifice of the plants. Luciferase can be used non-invasively, but it requires a special camera and spraying the expensive substrate. It is also not very practical to use them in fields. GUS and luciferase may not be optimal for sterile conditions such as tissue culture because addition of substrates increases the chance for contamination of microbes. Therefore, there is a need to develop new reporter systems that can be widely used to monitor cellular activities noninvasively, continuously, and cost effectively. For the past few years,strawberry pots gene editing has been widely used in basic research and crop improvement. A visible marker for transgenes will greatly accelerate the isolation of edited plants that no longer harbor the gene editing machinery. Plants produce many colorful compounds that potentially can serve as reporters. For example, anthocyanins display bright red-blue colors and anthocyanin-producing rice plants have been used to generate interesting patternsin rice field. However, synthesis of anthocyanins requires multiple enzymes and varies greatly among different plants. It is difficult to use anthocyanin biosynthesis pathways as a universal visible reporter. Betalains are a class of plant natural products derived from the aminoacid tyrosine. The bright red color seen in beets, dragon fruit, Swiss chard, and other plants is resulted from accumulation of betalains. Biosynthesis of betalains has been well studied and only needs three enzymatic reactions to convert tyrosine into betalain. Tyrosine is first hydroxylated on the benzene ring, resulting in L-3,4-dihydroxyphenylalanine . The reaction is catalyzed by the P450 oxygenase CYP76AD1 . L-DOPA can be further oxidized into cyclo-DOPA by CYP76AD1 . Alternatively, LDOPA is catalyzed by L-DOPA 4,5-dioxygenase into betalamic acid, which is subsequently condensed with cyclo-DOPA into betanidin. The condensation reaction does not require an enzyme . Finally, a sugar moiety is added to betanidin by a glucosyltransferase to generate the colorful betalain . Betalain has a very bright red color, which potentially can serve as a reporter to track gene expression or to visualize transgenic events. Because every cell contains the amino-acid tyrosine, exogenous application of tyrosine to tissues may not be required. We hypothesized that betalain would be a more convenient reporter than the aforementioned reporters. It is visible to naked eyes without any needs for special equipment. It does not require processing samples and it allows continuously monitoring events throughout the life cycle of an organism. Moreover, it is applicable to large plants grown under normal field conditions. Herein, we synthesize an artificial open reading frame named RUBY that when expressed can produce all of the enzymes required for betalain biosynthesis. We show that RUBY is a very effective marker for noninvasively selecting transformation events in both rice and Arabidopsis. Moreover, we show that RUBY can be used to visualize gene expression without any chemical treatments or special equipment, providing useful tools for visualizing gene expression in large plants under natural field growth conditions.Heterologous expression of CYP76AD1, DODA in tobacco, and other plants demonstrated that the betalain biosynthetic pathway can be re-constituted in plant cells. In order to use betalain as a visual reporter, we need to effectively co-express the entire pathway using a single promoter. We organized CYP76AD1, DODA, and Glucosyltransferase into a single open reading frame . The stop codons of CYP76AD1 and DODA were removed. The three genes were linked by sequences that encode 2A peptides. Upon transcription, the single transcript, which includes the coding regions of the three enzymes, produced the three separate enzymes through either 2A-mediated self-cleavage or ribosomal “skipping”.

The 2A system enables the expression of multiple proteins under the control of a single promoter. We name the 2A-linked unit of CYP76AD1, DODA, and Glucosyltransferase RUBY . RUBY can be expressed when a promoter is placed in front of it. The expression pattern and level of a particular gene may be inferred from the red color of betalain if the gene’s promoter is used to drive RUBY expression.We first placed RUBY under the control of Cauliflower Mosaic Virus 35S promoter, which is a widely used constitutively strong promoter. To test whether RUBY can produce functional enzymes for betalain synthesis, we infiltrated tobacco leaves with Agrobacteria that contain RUBY-expressing plasmid.Transient expression of RUBY led to the production of betalain in tobacco leaves, suggesting that the synthetic open reading frame RUBY can produce the functional enzymes for the synthesis of betalain. Moreover, we observed that betalain was not transported from the spots of Agrobacterium-infiltration spots to other leaves of the plant .We transformed the 35S:RUBY construct into Arabidopsis using Agrobacterium-mediated floral dipping. Two days after floral dipping, we noticed that the transformed plants displayed patches of red color , indicating that the RUBY cassette was functionally expressed and that RUBY may be used to monitor transient Arabidopsis transformation. Once the seeds from the Agrobacterium-dipped plants were harvested, transgenic seeds could be easily differentiated from non-transgenic seeds . The transformed seeds had a dark red color , demonstrating that RUBY can be used as a visual selection marker for transgenic events in Arabidopsis. We previously used mCherry as a very effective marker to select transgenic events , which requires a dissecting microscope with fluoresence capability. RUBY is a better option because it does not require special equipment. The 35S:RUBY plants produced sufficient amount of betalain to become visually evident . Consistent with previous reports that CaMV 35S promoter is constitutively active, we observed red color in all tissues throughout the plant life cycle . We also expressed RUBY reporter under the control of the Maize UBIQUITIN promoter, which has been widely used to over express genes in monocots. Similar to 35S:RUBY plants, UBQ:RUBY plants were also visibly red in leaves, stem, and flowers . These results clearly demonstrated that RUBY could be expressed in Arabidopsis and that our RUBY reporter was able to functionally re-constitute the betalain biosynthetic pathway. We expressed RUBY using the seed specific At2S3 promoter, which we previously used to drive mCherry expression in Arabidopsis to facilitate the selection of transgenes. As shown in Fig. 2c, the transgenic plants were indistinguishable from wild type plants. When we checked the seeds in a silique from an At2S3:RUBY T1 plant, RUBY-expressing seeds displayed strong red color, whereas the non-transgenic seeds were green . RUBY can be conveniently used to select single T-DNA insertion events by analyzing the ratio of red seeds to green seeds, which should be ~3:1 for single insertions. The At2S3:RUBY results demonstrate that RUBY could be an effective marker for Arabidopsis transformation. Furthermore, betalain was not widely transported from the sites of synthesis to other tissues as we did not see any red color in leaves . We also expressed RUBY under the control of the Arabidopsis YUC4 promoter . YUC4, which encodes a key enzyme in auxin biosynthesis, was shown to express in small regions of embryos, leaves, and flowers. GUS signals were observed in leaf tips and apical region of a gynoecium in YUC4 promoter:GUS transgenic plants. We observed similar patterns of betalain production in YUC4:RUBY lines .Unlike Arabidopsis, rice and many other plants are transformed through tissue culture and the formation of calli, which are often mosaic.

Environmental cues, especially temperature and light, have huge impacts on organ abscission. It has been reported in various plant species that high temperature accelerates reproductive organ abscission. In cotton, day temperatures above 40 °C can induce flower abscission. In soybean, flower abscission was found to increase with the elevated temperature treatment in three different soybean varieties, while no significant difference was found between control and cool temperature treatments. In addition, the light quality is also critical for organ abscission. Shading, as well as dark treatments, induced reproductive organ abscission in several plants. In pepper, shading treatment enhanced flower abscission in several cultivars. In apple, periods of darkness, shading, or cloudy weather have been showed to increase fruit abscission leading to early fruit drop. Nineteen days of shading treatment caused 98% of the fruit to abscise. In grape, five days of shading at bloom reduced the percentage of fruit set. However, the mechanisms of high temperature, or dark/low light-induced abscission and whether auxin is involved in these processes are still unknown. The DR5::GUS reporter system provides a visual indication of the activity of the auxin response in the auxin signal transduction pathway. We used tomatoes transformed with this reporter to investigate dynamics of the auxin response system during the different developmental stages and in response to environmental cues in pedicel AZ of tomato and to test the hypothesis that changes in the auxin response system are important in the regulation of abscission.

To investigate the dynamics of the auxin response system in pedicel during flower development,vertical plant growing we collected pedicels two days before anthesis , at anthesis, and 5 and 10 days post anthesis/pollination . We examined the distribution of the auxin response activity using the DR5::GUS reporter system. GUS activity was concentrated in the vascular tissues, with the majority of activity, particularly in the young flowers and those at anthesis, on the distal side of the abscission zone , a clear disjunction or ‘step’ in the auxin response activity at the abscission zone. At anthesis the GUS activity seen in the proximal zone of the younger flowers had disappeared, increasing the difference in the auxin response across the AZ. GUS staining in pedicels at 5 and 10 DPA was considerably enhanced, particularly in the abscission zone and in the vascular tissues of the proximal portion of the pedicel . To examine the relationship between these auxin response changes on the control of abscission, we removed flowers 2 DBA, at anthesis, and 5 DPA. All of the pedicels whose flowers had been removed at anthesis had abscised 12 h after flower removal, but there was no abscission of flowers from young and older flowers .Following flower removal, pedicels were treated at the distal end, or at the junction between the pedicel and the peduncle with lanolin containing 1 mM auxin. Four hours after the start of the experiment there was little obvious change in distribution or intensity of the GUS staining , indicating that the response system was not rapidly responsive to changes in auxin concentration.Eight hours after flower removal pedicels began to separate and most had abscised by 12 h. . We tested the changes in the distribution of the auxin response after flower removal using the DR5::GUS reporter system.

Four hours after flower removal GUS staining in the pedicels was similar to that in the controls . RT-PCR visualization of GUS expression in the tissues confirmed that there was little change in expression in the early stages of the abscission process . There was a perceptible decrease in the sharp ‘step’ in GUS staining across the abscission zone 8 h after flower removal, and even more in pedicels that had not yet abscised 12 h after flower removal, suggesting a reduction in auxin response adjacent to the abscission zone in the later stages of abscission. GUS expression in pedicels 16 h after flower removal was confined to the distal portion of the pedicel .Treatment with the aubegan to abscise and most had abscised by 12 h . We tested the changes in the xin transport inhibitor mimicked the effect of flower removal on pedicel abscission. Eight hours after the treatment pedicels distribution of the auxin response after NPA treatment using the DR5:: GUS reporter system. Four hours after flower removal GUS staining in the pedicels was similar to that in the controls . There was a perceptible decrease in the sharp ‘step’ in GUS staining across the abscission zone 8 h after flower removal , suggesting a reduction in auxin response adjacent to the abscission zone in the later stages of abscission.Treatment with 10 ppm ethylene accelerated flower abscission following flower removal , while pretreatment for 24 h with 1-methylcyclopropene completely inhibited abscission . GUS activity in ethylene- and 1-MCP-treated pedicels 4 and 8 h after flower removal showed similar patterns to those seen in the controls . The sharp reduction in activity at the abscission zone showed little change 4 h after flower removal, even in ethylene-treated pedicels that had already abscised but was somewhat reduced after 8 h both in ethylene-treated and in 1-MCP-treated pedicels .Auxin is considered to be a key hormone in the initiation of abscission; the accepted model suggests that reduced transport of auxin through the AZ results in sensitization of the AZ to ethylene, which induces the chain of hydrolytic and other processes that lead to cell separation.

In a previous study, we demonstrated that a knotted homeobox transcription factor, KD1, plays a role in abscission, apparently by modulating transport of auxin through the AZ. Silencing KD1 increased auxin in the abscission zone, and microarray analysis suggested that this was associated with the down regulation of auxin efflux transporters, particularly PIN9. The study also suggested that the change in auxin distribution across the abscission zone resulting from KD1 activity was associated with a change in the activity of the auxin response pathway, and the experiments reported here were designed to test that hypothesis.High activity was seen in the distal portion of the pedicel during flower opening, with a marked disjunction or ‘step’ on the distal side of the AZ. Following pollination, response activity increased substantially, particularly in the young fruit, the AZ, and in the proximal region of the pedicel. Our data did not support the hypothesis that changes in distribution or activity of the auxin response system play an important role in the regulation of abscission. Removing the flowers at anthesis, which induces pedicel abscission within 8 h had little effect on the distribution or activity of auxin response , particularly in the early hours after excision,vertical farming when the abscission process is initiated. The visual results from GUS staining of the pedicels are supported by RT-PCR analysis of the expression of GUS transcripts , which shows a marked ‘step’ in transcript abundance across the abscission zone, and a change in expression pattern only at 12 h after excision, when most pedicels have already abscised.The conclusion that a change in distribution or activity of the auxin response system plays no regulatory role in pedicel abscission is supported by our additional data. None of the other manipulations that affected the occurrence or timing of abscission had a marked effect on GUS staining. Placement of auxin distal or proximal to the abscission zone, treatment with NPA, treatment with ethylene, or 1-MCP , placing inflorescences in the dark, or at high temperature, all had significant and varied effects on abscission, but the distribution of auxin response system as indicated by GUS activity was remarkably stable. In contrast, the data presented here demonstrated that the early stages of abscission were associated with marked changes in the distribution and activity of genes involved in auxin transport. This is in agreement with our earlier results. Application of the auxin transport inhibitor, NPA, resulted in a marked reduction of expression of genes encoding enzymes involved in auxin transport . Particularly striking decreases were seen in the expression of PIN1, PIN6, PIN9, and AUX/LAX2 in the abscission zone itself. This general pattern was also seen following flower removal, although the reduction in expression of the PIN genes appeared to be less tissue specific .

These changes are consistent with the observations of Shi et al, who also found a substantial reduction in SlPIN1 expression following flower removal, and suggested that it might play a role in modulating the auxin content of the AZ. Silencing of SlPIN1 expression accelerated pedicel abscission by simultaneously increasing auxin accumulation in the ovary and decreasing the auxin levels in the AZ, suggesting that auxin transport modulates auxin balance to influence pedicel abscission. Interestingly, PIN2/5/10 were not expressed in pedicels . This is different from other reports that down regulation of PIN5 in the flower pedicel reduces intracellular auxin accumulation in the endoplasmic reticulum , which is expected to control auxin availability for auxin signaling/response in the nuclei of AZ cells. The exact regulatory roles of these auxin transporters in the induction of abscission need further investigation in the future. Auxin and abiotic stress work together affecting plant growth and development. In Arabidopsis, the shoot ward auxin transport can be inhibited by the reduction of PIN1/ 3 transcripts under low temperature and increased by the upregulation of PIN2 under high temperature. In addition, high temperature induces hypocotyl elongation by regulating PIF4-mediated auxin biosynthesis. Our data showed that both high temperature and darkness can accelerate abscission . However, the intensity and distribution of the auxin response were almost little affected by these substantial changes in environmental conditions . It is still unknown if auxin transport can affect the pedicel abscission in tomato under these environmental conditions and would require further investigation. Our results are consistent with a model that places the primary control of abscission on the concentration of auxin in the abscission zone. Concurrent changes in the relative rates of influx and efflux might plausibly result in marked changes in auxin concentration, triggering the sensitivity to ethylene that results in the onset of the abscission process. Our data indicate that at 4 h after flower removal, expression of genes encoding auxin efflux enzymes fell while the expression of genes encoding influx enzymes increased. We can imagine a scenario where the activity of KD1 is controlled by auxin transported from the flower. When auxin flow falls, KD1 might modulate the expression of genes involved in auxin influx and efflux, amplifying the effect of small changes in auxin flow, and resulting in a marked fall in auxin content of the abscission zone, triggering the changes that result in separation. In this scenario, the auxin response system is an important factor, but it functions as a reporter of auxin content, and does not rapidly change activity or distribution in response to changes in auxin supply from the flower.Tomato inflorescences were harvested at 10 AM from plants grown in the greenhouse at the University of California Davis. inflorescences with at least two newly opened flowers at anthesis , two days before anthesis and five days post anthesis were cut on the proximal side of the AZ and placed in vials, and held in a chamber into which humid air was continuously flown through. For testing abscission triggered by auxin depletion via flower removal, flowers were removed with a sharp razor blade by cutting on the distal side of the AZ, and abscission of the remaining pedicel from the peduncle was monitored at intervals. For testing abscission triggered by auxin transporter inhibitor, N-1- naphthylphthalamic acid , the inflorescences were placed in vials containing 10 ml of 25 μM NPA solution. Flowers were not removed for NPA treatments. Control inflorescences were placed in a vial containing a solution of the equivalent concentration of dimethyl sulfoxide. For testing temperature-dependent abscission, the inflorescences were harvested at the anthesis stage. The pedicels with/out flowers were placed in the testing chambers in temperature-controlled rooms with indicated temperatures. For dark-induced pedicel abscission, the inflorescences were harvested at the anthesis stage with/ out flower removal and placed in the chambers under the dark conditions at 20 °C. For testing ethylene-triggered pedicel abscission, the inflorescences were harvested at the anthesis stage with flower removal and placed in the ethylene chambers. All the experiments were carried out with at least three biological replicates.

Benefit transfer approaches, SFA, and DEA yield results that can evaluate how well an NTS site is performing and how to improve their functioning, but have associated advantages and disadvantages . Benefit transfer approaches can provide an estimate for ecosystem services value, which can be used in cost-benefit analyses to determine net changes to well-being. In addition, benefit transfer can identify drivers of change through the application of regression models. Regardless of net costs or benefits, there exists a maximum level of ecosystem services provision that can be provided with given inputs. SFA and DEA can help determine whether systems are performing at this maximum level and where improvements can be made. Both methods apply somewhat similar regression models to benefit transfer approaches, yielding quantitative relationships among variables. Other options include a fixed effects model to estimate the best-practice frontier , and the multi-product distance function which allows for a stochastic error term and multiple outputs including negative externalities . In prioritizing ecosystem services,vertical hydroponic farming geographic location can dictate physical and social factors that can influence their value. For example, water issues have long been important in southern California and they are predicted to become more contentious due to climate change.

Further, new policies in California put an emphasis on climate-regulating services. The region is also a biodiversity hot spot at risk of alteration . Urbanization has reduced the amount of suitable habitat for organisms as natural ecosystems are replaced by human structures. Urban green spaces such as NTS can be important patches of habitat and act as corridors for organisms seeking refuge . One of the biggest challenges in characterizing and valuing ecosystem services associated with NTS is the lack of accessible data. There is no standard monitoring program for NTS, which makes it difficult to compare across time and across sites, and there is no monitoring of ecosystem services associated with NTS. Monitoring could help identify effective management strategies, e.g. timing of maintenance, and improve the above quantitative models for more accurate estimates of value and efficiency. In situ, mesocosm studies are also needed to evaluate NTS performance under actual environmental conditions . Other questions that still need to be addressed include how networks of NTS compare to single systems regarding both targeted and non-targeted ecosystem services, and how NTS operate over time. Prior to the widespread use of soil fumigants, Verticillium dahliae Kleb. was considered among the most important pathogens affecting commercial strawberry production in California . Plantations established in infested soils often suffered 50% or greater mortality , and wilt from this pathogen continues to be a major concern where strawberries are managed in perennial planting systems .

Breeding for resistance has been an important strategy for minimizing damage caused by V. dahliae in strawberry for several decades, and genetic variation for resistance to this pathogen has been demonstrated in many breeding populations . The University of California strawberry breeding program was initiated in 1930, and its goal since initiation has been to release cultivars specifically adapted to California production environments. In part due to concerns about the continued availability of effective soil fumigants, researchers in the UC strawberry breeding program began to develop a field-based resistance screening method in 1992 , and an ongoing resistance evaluation program has been conducted for this disease since 1994. Preliminary experimental results demonstrated substantial genetic variation for an overall low level of resistance to V. dahliae in the UC breeding population . Researchers also verified that resistance to the pathogen in this population has polygenic inheritance, is conditioned by both additive and dominance genetic effects, and that genotypes with high resistance were rare in the germplasm at that time. These results suggested that the infusion of non-California germplasm was not needed to obtain genetic progress, but that substantial time and effort would be needed to change the genetic composition of the breeding population and generate Verticilliumresistant strawberry cultivars with adequate frequency.Two broad strategies have been used to improve genetic resistance to soil disease in crop plants. One common approach is to first identify resistant germplasm and generate highly resistant lines, then back cross the resistance into elite cultivars.

This method works well when the inheritance of resistance is conditioned by one or a few genes and the crop-specific breeding system permits back crossing and self-fertilization for rapid genetic transfer and stabilization. Intensive selection for resistance within the UC germplasm base has resulted in genotypes that exhibit few symptoms following inoculation with V. dahliae , and these genotypes have been useful in evaluating selection limits and the mechanisms of resistance within this genetic base . However, even asymptomatic plants suffer some yield loss under conditions of high disease pressure . Furthermore, due to the intensified focus on resistance in generating these genotypes, they all express substantial deficiencies for horticultural or productivity traits, and as a consequence this strategy has not been successful in generating cultivars that meet the commercial standards required of modern strawberry cultivars in California.An alternative breeding strategy is to obtain incremental increases in resistance through population improvement, by inclusion of V. dahliae–screening results in a multiple-trait selection system to choose the parents of elite breeding populations. This strategy is generally a superior alternative for developing resistance in cross-fertilized crops such as strawberry. This system is especially useful when inheritance of the resistance is polygenic, or determined by many genes, and back crossing systems are consequently less effective. Furthermore, with multiple-trait selection, Verticillium resistance is considered as one among the many characteristics required to render a cultivar useful to strawberry growers in commercial production. This selection system permits flexibility in the relative weighting of selection intensity for resistance and horticultural traits, and can result in cultivars of balanced commercial utility. Back crossing methods for resistance can be combined with multiple-trait selection for horticultural traits, but this strategy is generally most effective for inbred crops. UC has conducted strawberry breeding continuously since 1930 , and the improvement of traits important for commercial productivity has been substantial . The choice of parents for the population-improvement component of this program has depended in part on resistance to important pathogens,vertical gardening systems and the longest continuous screening effort has been dedicated to Verticillium dahliae Kleb. resistance. This study reports on progress in developing resistance to V. dahliae within the UC strawberry breeding program obtained through parent selection and population improvement since 1994.Between 1994 and 2008, 481 genotypes from the UC strawberry breeding program were screened for resistance to V. dahliae. This sample included 461 advanced selections, genotypes identified with superior characteristics and which might either serve as parents for future generations or eventually be released to growers as cultivars. These selections were obtained from controlled crosses conducted over 18 years , with 11 to 49 genotypes from each cross year. Twenty genotypes were tested from the original germplasm base present prior to 1988. Strawberry breeding proceeds with overlapping generations, but the yearly changes in resistance for the genotypes used as parents from 1988 to 2005 provided a reliable empirical index of genetic progress for this population. The advanced selections tested for resistance in each trial year included those genotypes considered most promising based on their performance in fruiting trials conducted at either the UC South Coast Research and Extension Center near Irvine, Calif. , or the Watsonville Strawberry Research Facility . The genotypes included from any cross year had not been evaluated for resistance prior to their selection for horticultural and productivity traits, and they provide a representative sample of the variation for resistance in that cohort. Changes in resistance parameters over time reflect the outcome of including resistance in the multitrait selection strategy for prior parent choice.

The selection intensities — which reflect the relative importance of the selected trait — applied to the improvement of Verticillium wilt resistance during the study period are impossible to quantify with precision, but the genetic progress reportedhere results from two sources. first, the most susceptible genotypes usually were eliminated entirely, and the participation of moderately susceptible genotypes as parents was limited to a few crosses. Moderately susceptible genotypes were included if they expressed outstanding horticultural characteristics, but they usually served as parents in crosses for just one year. Second, individual genotypic selections were made with knowledge of parental resistance scores, and fewer genotypes were retained from crosses expected to contain high frequencies of susceptible individuals.Runner plants from each tested genotype were immersed in an aqueous suspension of 1.0 x 106 V. dahliae spores per milliliter. All evaluations were conducted at the Wolf skill Experimental Orchard near Winters, Calif. . The inoculum included spores from one to three isolates originally obtained from symptomatic plants found in commercial production fields in California . Each genotype was represented by two plots of five inoculated runner plants per trial year; two noninoculated plants of the test genotype were placed adjacent to each plot, and disease ratings were made relative to these control plants. Plots were distributed between two replicates, and each year’s trial comprised a randomized complete block design. Inoculated plants and controls were established in the field from Oct. 5 to 18 each year. Many of the individual genotypes, 204 of the 481, were tested in more than one year, and the average number of test years per genotype was 1.7. In general, genotypes under consideration for release as commercial cultivars were tested with greater replication over years, and these superior genotypes were also heavily represented in crosses conducted to facilitate population improvement. Genotypes were evaluated in the spring following inoculation, by rating plants for symptoms of Verticillium wilt on a scale of 1 to 5, where 1 =severely diseased and 5 = no symptoms of disease . Individual plots were evaluated four to seven times in each trial year at approximately 3-week intervals beginning with the first symptoms on susceptible genotypes , and a combined score was obtained as the arithmetic mean of scores for all dates . An average resistance score was calculated for each genotype and year combination as the mean for the two replicates.Variation in resistance scores over trial years due to environmental factors — such as differences in ambient temperature, isolate source or inoculum quality — was confounded with genetic differences generated due to selection over years. Several of the genotypes were tested in most of the evaluation years, and the examination of these samples demonstrated relatively small yearly fluctuations in genotypic score. For example, on a resistance scale of 1 to 5, the relatively susceptible cultivar Camarosa had an average score of 2.52 and a standard deviation of 0.46 over all years, and the moderately resistant cultivar Camino Real had an average score of 4.25 and a standard deviation of 0.41 for trials conducted in 11 of the 15 years. This suggests that more than two-thirds of the samples will vary by no more than about 0.435 scoring units from year to year. The effect of trial year was not considered further, but is reflected as part of the error variation in our analyses. Changes in the Verticillium resistance scores due to selection were evaluated by first calculating a composite genotypic score as the average for each genotype over all trial years in which it was tested, then plotting and regressing these composite scores by cross year. The 20 genotypes from the original germplasm sample were considered representative of a base population present in 1987, and are included as such in plots and regression analyses. The average resistance scores were further resolved by calculating the percentage of genotypes in each cross-year population with a composite score greater than 3.0, and thus exhibiting at least moderate resistance. The percentages calculated for each cross year were plotted and treated by regression analysis as described for the resistance scores.The absence of reliable estimates for selection intensities and the presence of overlapping generations precludes precise determinations of the genetic response; however, the general trends for inclusion of Verticillium resistance in the population improvement program are evident from the steady increase in resistance scores over cross years . Regression of resistance scores for the 481 genotypes on their cross year demonstrated a highly significant increase over time, with b = 0.061 ± 0.007 . The predicted change in resistance score from this regression analysis over 18 cross years affected by selection is 1.10 resistance-score units, or a 46.3% improvement over the average resistance score for the original germplasm .

Assuming all of the roughly 16 000 smallholder farmers currently growing tobacco were to produce an average of 400kg of paprika, for example, this would result in a total yield of just 6 400 tons, equal to less than half of Zimbabwe’s record crop. Although it is not unreasonable to expect this could lead to lower international prices, smallholder farmers appear well positioned to cope. To the extent this provides a window of opportunity for Zimbabwe’s buyers to focus on lower-value smallholder paprika, there could be good potential for a gradual shift away from tobacco. Whether or not this potential can be realised, however, still depends on the development of crop extension services and input supply arrangements. As with all other enterprises, more comprehensive modelling is needed to assess the conditions under which such an investment would make financial and economic sense. Marigold flowers are a relatively new niche product in Zimbabwe and are grown almost exclusively by LSC farmers for their value as a colour extract. Marigold is a much lower-value commodity than either coffee or paprika,vertical plant rack but grows well on most soil types and is forgiving to management input.

As a bulky and relatively low-value commodity the returns to marigold are highly sensitive to transportation costs and most LSC farmers dry the crop in a cement-lined silage pit before delivery to Harare for processing. Dry flowers are converted to a compact pellet form for export or for domestic use either as an industrial food colour or ingredient in stock feed. Research is ongoing in Zimbabwe to determine an optimal pest control strategy and fertiliser recommendations for LSC marigold. Current production is around 700mt of dry flowers annually. Horticulture is Zimbabwe’s second most valuable agricultural export sector after tobacco and earned over USD 124.9 million in gross foreign income in the 1999/00 season, equal to approximately 1.5% of total GDP and 22% of the revenue generated by tobacco.An overview of sector performance by export season is given in Table 33 and shows that horticulture has grown rapidly in the past ten years with total value now five times greater than in 1990. But unstable political and macroeconomic conditions have slowed these growth rates and it is projected that total exports in the 2000/01 season could decline by 10% or more. Roses require a large expenditure on imported inputs, especially during establishment, for irrigation equipment, planting materials and greenhouse construction, and the total export values listed below would be considerably less if measured in net terms.

More than 80% of Zimbabwe’s horticultural exports are grown on LSC tobacco farms and were first developed using tobacco revenue. For most farmers, the main objective behind the introduction of roses and other horticultural exports was to lessen their dependence on tobacco. Not only can horticultural crops be extremely profitable, but like tobacco, they also earn foreign exchange and so have the potential to play a similar anchor role in a mixed farm system. Furthermore, although horticultural crops tend to be expensive because of high costs for pest and disease control, export vegetables and roses both provide a steady cash flow in their own right with weekly and even daily sales throughout the export season. From the social point of view, a further advantage of horticulture is that these crops are extremely labour intensive and create more jobs on a per hectare basis than any other farm enterprise including tobacco. These characteristics all make horticulture a very attractive sector, both for farmers and for Zimbabwe as a whole in terms of more diverse export earnings, employment creation and potential for growth linkages.Despite these advantages, the production and marketing of horticultural crops is a highly specialised business that cannot be entered into lightly. At the field level, success demands unparalleled attention to quality control and strict adherence to European standards governing the use of pesticides, fertilisers and other inputs.

It is not unusual for more than 30% of a vegetable crop to be rejected because of quality and this risk has discouraged many LSC farmers from continuing with production. Marketing, therefore, is one of the biggest obstacles to success. Although cut flowers can still be sold independently on the Dutch auction, most other produce must be sold as part of a forward contract negotiated by a central agent or export consortium with the capacity to supply the specific volumes and varieties of produce European buyers demand. 145. High freight costs and the availability of direct flights to Europe further add to the challenge of success with horticulture and are currently among the most pressing constraints facing Zimbabwe’s export sector. Over the past 12 months, direct flights from Harare to the UK, Europe and Australia have been reduced from 32 to 14 per week, resulting in a shortfall of approximately 150 tons of cargo space per week with a potential value USD 17 million over the 25-week peak export season.As a result, many flower exporters have been forced to drive their produce by road to Johannesburg nearly 1 200 kilometres away simply to find cargo space. Zimbabwe also has some of the highest costs for aviation fuel in the region leading to high air freight prices which now account for as much as 40% of total production costs for both vegetables and roses.For these and other reasons, more than 95% of vegetable exports and 100% of cut flowers are grown on individual LSC and large corporate farms, mainly within 200km of the International Airport in Harare. Smallholder farmers are only marginally involved in the export sector with fewer than 3 000 vegetable growers linked to established agents. This is in sharp contrast with the experience in Kenya where there are perhaps 60 000 to 75 000 smallholders involved in export-oriented vegetables, including production for canners and freezers. Despite more stringent marketing standards that apply today than when Kenyan horticulture first developed, there is still considerable scope for increased participation of Zimbabwean smallholders on an out grower basis in some of the high potential farm areas near Harare. Three indicative export vegetables are considered for this analysis including mangetout , baby carrots and baby corn. Other important export crops for LSC farmers include sugar snaps, fine beans,growing strawberries vertical system cherry tomatoes, courgettes and asparagus. Each vegetable crop is typically grown over an 8 to 9 week period with most LSC farmers producing three crops in rotation each season. Although some growers have tried to form local export associations with neighbouring producers, most vegetable crops are farmed on an out grower basis for a local contractor who collects, washes, grades and packs the produce as a shelf-ready product for delivery to a UK or other European supermarket chain. Individual farmers simply cannot guarantee the variety and continuity of supply needed to negotiate export contracts with supermarket buyers and this system is a vital link to the international market. To ensure a steady supply of good quality produce, most export agents also grow vegetable crops themselves, especially during the rainy season when many LSC farmers switch away from commodities that are difficult to grow.

Mangetout and baby carrots, for example, are almost impossible to produce during the heavy rains, but baby corn is more forgiving and better suited to production throughout the year. In some cases, this means that export agents have even found it necessary to grow mangetout and other crops in plastic houses just to meet the conditions of regular supply demanded by European buyers. This can be justified for a few months each year, but is only feasible for a large supplier with effective economies of scale.Unlike roses, one important advantage of export vegetables is that these crops do not require a major investment in green houses and other specialised equipment by LSC farmers. Although most crops do best with drip line irrigation, it is perfectly acceptable to use existing overhead spray systems already available on most farms. For export agents, on the other hand, total investment costs can be very high and include the establishment of rural depots, grading and packing sheds, heat extraction units and cold rooms. Generators as well as insulated and refrigerated trucks are also required to ensure the cool chain to Europe is never broken.Large-scale commercial farmers. Per hectare results for each of the LSC vegetable crops covered here are summarised in Table 34. These calculations are based on delivery to a nearby depot where an agent collects the produce for final grading and export presentation. Importantly, LSC farmers are only paid for produce actually exported and yield assumptions are estimated on this basis. Unsurprisingly, this system has led to suspicions by LSC farmers that they are not always paid for all of the produce actually shipped abroad. Certainly, the grading system is not entirely transparent and this problem has caused some farmers to switch away from export vegetables in favour of other crops with more certain terms of payment. Because vegetable crops are all grown to a uniform standard, only one management level for each product is considered.Taken together, the results below are encouraging and show that, under the right conditions, export vegetables can be an important source of steady income for LSC farmers. Although per hectare profits are perhaps somewhat low compared with other enterprises on a single crop basis, export vegetables are normally triple cropped throughout the year and so easily rival flue-cured tobacco and other high-value enterprises in terms of total annual income. Assuming the three crops covered here were grown in rotation, for example, total annual income would be ZWD 102 503 per hectare, which is almost identical to the estimated profits for medium-input dryland flue-cured tobacco. Unlike tobacco, however, one the most important advantages of export vegetables is that these crops provide a steady cash flow in their own right. Not only are export vegetables planted in three to four cycles throughout the year, but most producers also aim to stagger their plantings on a weekly basis to produce a steady harvest throughout the season. This helps minimise the need for large cash expenditure at any one time and also provides a more regular income than almost any other farm enterprise. In terms of employment creation, the data show that an important advantage for Zimbabwe is that export vegetables are all very labour intensive and, on a per hectare basis, easily create more jobs than tobacco. Again assuming the three crops listed above were grown in rotation, a total of 760 days labour would be required per hectare, which is considerably more than for any other enterprise except roses. Although the precise situation will vary from farm to farm, casual workers normally fill more than 50% of the total labour requirement and vegetable exports can be an important source of employment and supplemental income for local residents. It should be stressed, however, that vegetable crops and other horticultural products could never substitute entirely for tobacco, which is grown on a much larger scale. Furthermore, crops with a large labour requirement are not always attractive from the farmer’s perspective because of potential management problems and incremental costs of housing and other benefits for permanent staff.Smallholder farmers. Vegetable crops have long been an important part of most smallholder farm systems and are grown both for household consumption and for sale in local markets. Crops including tomatoes, cabbage, onion, kale and okra all enjoy good demand in rural and urban markets and are an important part of many Zimbabwean diets.Domestic production, however, is entirely different from growing vegetables for the export market and there are currently fewer than 1 700 smallholder farmers within 100km of Harare producing baby corn, mangetout, butternut squash and sweet corn on an out grower basis for one leading export company. These farmers include established SSC producers also growing tobacco; irrigation scheme participants; and individual communal farmers with limited access to other sources of cash income. Depending on the time of year, these farmers produce from 50% to 90% of all baby corn and up to 5% of the mangetout shipped by the export company. Success with smallholder export horticulture depends heavily on technology transfer and the exporter provides extension agents to give advice and ensure that each crop is being grown to the required standards. A network of rural depots has been established to collect the produce and the out grower company itself does crop spraying with the cost deducted from each farmer’s final payment.

Zimbabwe exports most of her tobacco crop, however, so if global demand for tobacco were to fall in future , the impact on employment would depend on the extent to which commercial farmers were able to switch to other export crops such as roses, paprika, coffee and vegetables which are also highly labor intensive. Many other crops have similar per hectare labor requirements to tobacco, and some have further opportunities for downstream processing and growth linkages. Most of these crops are currently grown on a fairly limited scale, however, so the question would be how quickly and successfully farmers would be able to scale up exports and production of these crops, in the face of declining tobacco markets. This paper considers the financial costs and returns for tobacco and twelve other important crops grown by commercial and smallholder farmers in the intensive farming areas of northern and central Zimbabwe. Tobacco is of critical importance to the Zimbabwean economy and typically generates around USD 600 million in foreign revenue annually,vertical farming supplies equal to almost 10 percent of GDP and 30 percent of total exports.

Although global demand for tobacco is still strong, pressure from international health organisations, anti-smoking groups and new trade protocols all threaten the long-term prospects of this important crop. As Zimbabwe looks to the future, therefore, it is important to consider diversification options and growth strategies in which other crops could play an increasingly important role and eventually substitute for some of the foreign earnings and employment currently accounted for by tobacco.Towards this end, the primary aim of this analysis to provide an improved understanding of the trade-offs individual growers face in deciding which crops to grow. Agricultural production begins with the decisions farmers make and any successful diversification strategy must have the costs and returns for individual producers in mind. More specifically, at this critical juncture in the development of Zimbabwe, how do different crops and production technologies now compare in terms of total production costs, investment requirements, farmer profitability, employment creation, demand for credit and other matters of private and social importance? Are there attractive crop options that would justify farmers making a shift away from tobacco and what would be the implications for Zimbabwe’s trade balance and local employment opportunities? This paper has been prepared to help answer some of these questions and to provide an improved basis for discussion of recent development trends and future growth strategies. In geographic terms, it is first important to note that tobacco is grown almost exclusively in high-potential farm areas of Natural Region II in northeastern and central Zimbabwe.

This zone accounts for less than 15% of Zimbabwe’s total land area , but is ideally suited to intensive farming with a more or less reliable 750 to 1 000 mm of rainfall coming in the summer months from late-October until the end of March.By contrast, Natural Regions III, IV and V are much less suited to intensive farming with progressively arid conditions less suited to tobacco and other crops. Smallholder farmers occupy about 71% of the farmland in these lower-potential areas equal to about 18.7 million hectares in total. Natural Region I is mostly in the Eastern Highlands with a mild climate suited to specialised farming and forestry. Maps showing the location and rainfall expectations of each Natural Region and also the location of Zimbabwe’s 15 main flue-cured tobacco growing districts are given in Appendix 1. Further details on the breakdown of land classification by farm sector and area planted to different crops in each Natural Region are given in Appendix 2. In interpreting the discussion that follows, it is also important to bear in mind that large-scale commercial farmers dominate Zimbabwe’s tobacco sector. Although there are fewer than 2 000 commercial tobacco growers, these producers account for about 87% of area planted and 95% of the total crop equal to some 180 to 240 million kilos of flue-cured tobacco annually. Furthermore, most commercial farmers already have diversified sources of income. Although tobacco is still the backbone of commercial agriculture in most locations, other important crops for large-scale farmers include wheat, soybeans, maize, groundnuts and livestock, which are typically grown in rotation with tobacco.

Most commercial tobacco farmers practice a 5-year rotation and these crops are an important part of the overall land use system and help provide a steady cash flow. More recently, many commercial growers have also introduced other high-value crops including export roses, supermarket vegetables, paprika and coffee as part of their farm system specifically to lessen their dependence on tobacco. More than 80% of all horticultural exports, for example, are grown on tobacco farms and were first developed using tobacco revenue. Smallholder farmers, by comparison, are only marginally involved in the direct production of tobacco. Although there are roughly eight times as many smallholder tobacco growers compared with large commercial farmers, these account less than 1.5% of all smallholder households and just 7% of those in suitable agro-ecological areas. Certainly, the importance of tobacco as a high profit crop with fully developed market outlets cannot be overlooked for these producers, but it should also be noted that maize, cotton and groundnuts are all more important for smallholder farmers in most locations. In this respect, the greatest threat from shrinking tobacco markets for the smallholder sector is not so much the potential loss of direct farm enterprise income, but rather the loss of remittances sent by family members employed on large-scale commercial farms. Before proceeding, it should also be noted that this analysis has been prepared at a critical time in the development of Zimbabwe. Apart from the pressure on tobacco from international health organisations, new trade protocols and other sources, the overall future of the agriculture sector is now facing great uncertainty in terms of the controversial program of land acquisition and resettlement.

Although this paper has no interest to enter the political debate over land or to predict the outcome of current events, it is not possible to overlook the present situation and implications for development opportunities in agriculture. No matter how one interprets recent events, for example, it is clear that current conditions in Zimbabwe not only discourage new investment but also make it difficult to sustain existing farm production in terms of access to seasonal credit,vertical lettuce tower fuel shortages, high inflation, land occupations and foreign exchange controls that distort the cost of imported inputs. For large-scale commercial farmers, the strategy now is mainly one of survival and bracing for the worst rather than to invest in new technologies and infrastructure as part of a drive towards crop diversification. Smallholder farmers have likewise been affected by the poor investment climate and are perhaps even more dependent on improved conditions than commercial growers. One of the key findings from the analysis is that that the most profitable crops and management systems depend on specialised infrastructure and technical support services. Quite simply, until the economic and political situation improves, few entrepreneurs are willing to invest in these services, thereby limiting the opportunities for broad-based growth and diversification. Putting aside current political and economic constraints, the overall results of the analysis are encouraging and show that several crops apart from tobacco offer an opportunity for high producer profits and attractive rates of return. Other crops that rival and/or surpass tobacco in terms of potential net profit include roses, paprika, coffee and supermarket vegetables for large-scale commercial farmers and paprika, coffee and cotton for smallholder growers. These crops can all be grown in the same areas as tobacco and provide excellent rates of return to total production costs. On the other hand, these crops are also relatively expensive to produce and, with high-input management, are sometimes more costly than tobacco. This is especially true for high-value horticultural crops and long-season irrigated paprika on commercial farms. The analysis also shows that many traditional agricultural crops including wheat, soybeans, groundnuts and maize are now marginal activities for large-scale commercial farmers and, in some cases, even return a net loss and fail to cover the long-run depreciation cost of fixed assets. On the other hand these traditional crops do, in most cases, provide a positive gross income and are therefore important in terms of helping to finance other more profitable and expensive crops like tobacco, paprika and coffee. In turn, the very good financial returns from these high-value enterprises help offset the net losses from traditional field crops and the analysis shows these are still a fundamental ingredient to most successful farm strategies. In the case of paprika, for example, which is the most profitable smallholder crop apart from tobacco, yields are highly dependent on rainfall and can easily be wiped out by adverse growing conditions. Whereas large-scale farmers are able to protect themselves from some of these risks through irrigation, most smallholder farmers do not have access to this technology and paprika is typically considered a risky enterprise for smallholder growers.

Coffee is likewise an attractive possibility and can provide a net income that rivals many tobacco scenarios, but is a relatively new crop in tobacco areas and would require a substantial investment in farmer training and also pulping and processing facilities before it can be widely promoted in these locations. With respect to cotton, this enterprise generally provides a much lower income that tobacco , but does offer an excellent rate of return to cash and total production costs. At the national level, cotton is the most widely grown smallholder cash crop. Importantly, for all categories of farmer, the analysis shows that the most profitable crops and production technologies require specialised infrastructure, processing facilities and other support services. This is especially true with respect to roses and vegetable exports, which can be very profitable but are also extremely expensive to grow and extraordinarily skill intensive. These enterprises also require a large capital investment in processing and packing facilities, special irrigation equipment and other infrastructure including greenhouses and insulated trucks for roses. Some large vegetable exporters have been working with smallholder farmers near Harare to provide inputs and develop a network of collection points for baby corn and mangetout, but these programs are expensive to establish and are still relatively small with only limited farmer participation. In this respect, marketing constraints are one of the main obstacles to success with most high-value crops that could compete with tobacco in terms of profitability and potential export earnings. Again, this is most obvious in the case of roses and export vegetables, which must be grown to exacting European standards and delivered in fresh condition according to a tight time schedule. Paprika, on the other hand, is far more forgiving and can be sold to local export agents and processing companies on forward contract. Although this helps to minimise some production and marketing risks, relatively small world demand for paprika means that prices are highly sensitive to increased production and the crop could never substitute for tobacco on its own. In terms of labour requirements, the data show that tobacco generates more employment opportunities per hectare than nearly every other enterprise analysed. This is one factor often noted by proponents of tobacco to illustrate the overall importance of the crop to the national economy and the calculations here suggest that the total wage bill for tobacco grown on large-scale commercial farms could be as high as ZWD 2 600 million .To the extent that a share of this income is sent as remittance payments to family members in communal areas, tobacco can play a major role in helping to finance the inputs needed for improved management of major smallholder crops including maize and cotton. Although these benefits of tobacco cannot be ignored, the data show that many other crops are also very labour intensive and so offer similar opportunities for employment creation on a per hectare basis. Roses are perhaps the best example of this where just one hectare generates almost as many jobs as 25 hectares of flue-cured tobacco. Of the other field crops, paprika, coffee and export vegetables all demand a similar amount and sometimes more labour than tobacco with further opportunities for downstream processing and growth linkages. Because of limited market outlets and intensive management requirements, however, these crops are mostly grown on a much smaller-scale than tobacco and it is unlikely any single enterprise could ever substitute for a loss of tobacco employment without growth in other economic sectors including industry and tourism.