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Abstract
To determine whether cold hardiness of peach [Prunus persica (L.) Batsch] is affected by cultural practices, 2-year-old âCoronetâ trees growing in a peach tree short-life site were treated by soil fumigation with 1,2-dibromo-3-chloropropane (DBCP) late fall application of nitrogen, combination of fumigation and fall applied nitrogen, fall pruning (November), or usual grower practices (control). Cold hardiness was measured by determining the leakage of electrolytes from dormant terminal twig sections exposed to low temperatures, and visually by oxidative browning and ease of phloem-xylem separation. Fall-pruned trees were lower in cold hardiness and survival than controls. Nitrogen applied alone or in combination with fumigation reduced cold hardiness in early winter but increased vigor and survival. Trees grown in fumigated soil and winter-pruned were hardier than control trees and fall-pruned trees in nonfumigated soil. Differences in hardiness were greatest near bloom time. Cultural practices strongly affected cold hardiness of xylem, phloem, and cambium of treated trees, and cold hardiness was associated with tree longevity.
Bacterial leaf spot (BLS) caused by Xanthomonas campestris pv. vesicatoria is the scourge that has devastated and continues to limit expansion of both fresh-market and processing pepper production in Kentucky. Fourteen new BLS-resistant varieties and breeding lines were evaluated together with two standard (susceptible) varieties in 1995 at two locations. Twenty advanced lines and commercial varieties were tested at the same locations in 1996. All entries were exposed to an induced BLS epidemic at one location, but were kept disease-free at the second location. Epidemic development was slow and field resistance to four races of BLS was high for all but one of the lines tested, which claimed resistance to races 1, 2, and 3 in 1995. Six entries performed well both under BLS epidemic conditions and in the disease-free environment in 1995. Cultivars with resistance to only race 2 or races 1 and 2 of the pathogen were no different from susceptible checks in terms of yields and disease resistance and were not tested in 1996; combined results form 1995 and 1996 are discussed.
Virus and fungal disease pressures limit fall production of summer squash (Cucurbita pepo L.) in Kentucky. Twenty-five summer squash cultivars (nine zucchini, eight yellow straightneck, and eight yellow crookneck entries) were evaluated for marketable yield, appearance, and disease resistance in a late summer planting. Genetically engineered virus-resistant materials and new conventionally bred resistant or tolerant cultivars were compared with popular susceptible hybrids. Virus incidence was determined visually before and after final harvest and was also determined by enzyme-linked immunosorbent assay (ELISA). Watermelon mosaic virus (WMV) was most frequently detected and appeared to have caused most of the observed symptoms. Conventionally bred cultivars containing the precocious yellow gene and two transgenic lines were in the highest yielding group of yellow straightneck squash despite high virus incidence in precocious yellow cultivars. Among yellow crooknecks, transgenic cultivars were clearly superior for disease resistance and yields. Conventionally bred cultivars with virus tolerance were among the highest yielding zucchini types. Most transgenics were superior to their nontransformed equivalent cultivars for virus resistance and yield. Cultivars and breeding lines varied considerably in color, shape, and overall appearance. ELISA results revealed that some (but not all) transgenic cultivars tested positive for the coat protein corresponding to the virus resistance present in that cultivar. Also, mild virus-like symptoms were observed in transgenic squash plants after the conclusion of harvest.
Kentucky growers currently produce about 1300 acres of bell peppers worth $2 million for both fresh market and processing. Bacterial leaf spot (BLS) caused by Xanthomonas campestris pv. vesicatoria has been the scourge which continues to limit expansion of pepper production in the state. Fourteen new BLS-resistant varieties and experimental lines were evaluated together with two standard (susceptible) varieties in 1995 at two locations. All entries were exposed to an induced BLS epidemic at one location but were kept disease-free at the second location. Field resistance to four races of BLS was high for all but one of the lines tested, which claimed resistance to races 1, 2, and 3. Cultivars with resistance to only race 2 or races 1 and 2 of the pathogen were no different from susceptible checks in terms of yields and disease resistance. Six entries performed well at both locations; these will be included in further trials in 1996.
Bacterial spot epidemics, caused by Xanthomonas campestris pv. vesicatoria (Doidge) Dye, continue to plague bell pepper (Capsicum annuum L.) growers in a number of southern and midwestern states. A 3-year study designed to compare cultivars and breeding lines under induced bacterial spot epidemic and bacterial spot-free conditions began soon after the first release of cultivars having the Bs2 gene for resistance to races 1 to 3 of the pathogen. Bacterial spot epidemics were created by transplanting `Merlin' plants (inoculated with races 1 to 3) into plots of each test cultivar at an isolated location in eastern Kentucky. Plots of the same trial entries at a second location were kept free of bacterial spot for 2 of the 3 years of trials; however, a moderate natural epidemic occurred at this location in 1996. Bacterial spot resistance had the greatest impact on yields and returns per acre in the inoculated trials. Cultivars with only Bs1 or a combination of Bs1 and Bs3 were highly susceptible in the inoculated trials. There were statistically significant and economically important differences in resistance among cultivars and breeding lines having the Bs2 gene; some were nearly as susceptible as susceptible checks. Although many Bs2-gene cultivars showed satisfactory levels of resistance, only a few were highly resistant, horticulturally acceptable, and comparable in yields to the best susceptible hybrids in a bacterial spot-free environment.
Farmers' field trials conducted in western Kentucky counties in 1995 and 1996 showed that dramatic reductions in insecticide usage are possible using scouting and action thresholds. Five-acre plots were scouted and treated according to action thresholds while adjacent 5-acre plots were treated weekly with insecticides. Seven out of 10 insecticide sprays were eliminated, saving $65/acre for the 1995 season. There were no differences in yield, insect damage, or fruit quality between the scouted plots and the plots that were treated weekly. Assuming similar low pest populations in all 885 acres of the company's contracted fields, savings could have amounted to nearly $31,000 for 1995 after deducting scouting costs. There were no yield or quality differences from three test plots treated according to regularly scheduled applications and three plots treated according to action thresholds for insect pests and according to Tomcast predictions for fungal disease control in 1996. We have demonstrated the value of using Tomcast as an aid in making fungicide spray scheduling decisions for processing tomatoes in Kentucky. Although we were able to greatly simplify the Tomcast-CR10 datalogger interface program in 1996, there were still difficulties in getting information from the university-based computer to the company making spray applications. The company will be able to access the datalogger and obtain the information directly in 1997. The further analyses of âSkybitâ satellite data collected in 1996 should also tell us whether this type of information might be used instead of a remote datalogger thus simplifying the process even further. We plan to build on the quick adoption of the Tomcast system and to make it sustainable by transferring âownershipâ to the growers and processing company in 1997.
We began trials of vine-ripened, staked tomato cultivars in 1998 to identify a variety suitable for marketing as a premium âKentucky Tomatoâ. In conversations with marketing specialists at the Kentucky Dept. of Agriculture and merchandising managers at the Kroger Company's regional distribution center, we identified essential qualities of our ideal Kentucky tomato. A carefully selected group of 16 varieties was evaluated at two locations for yields, appearance, quality, disease tolerance, and taste. New varieties were compared with commercial standards like `Mountain Spring'. Yields of different sizes and grades of marketable fruit were multiplied by appropriate real-market prices for a given harvest date and summarized in a single income-per-acre variable for each variety. Some of the highest yielding varieties in eastern Kentucky (`Fabulous' `Sunbeam') appeared to have some tolerance to early blight; other varieties in this highest-yielding group included `Emperador', `Enterprise', `Sunleaper', and `Sunbrite'. All of these had fruit quality we considered acceptable for commercial markets with the exception of `Sunbrite'. `Fabulous', `Emperador', `Sunleaper', `SunGem', and `Sunpride' were the highest yielding varieties in central Kentucky. `Sunleaper' and `Sunpride' appeared somewhat tolerant to tomato mosaic virus (ToMV), which occurred at this location. Preliminary taste tests identified six varieties that were evaluated further by consumers at a local farmers' market. `Mountain Fresh' and `Floralina' were considered the best tasting varieties overall. The search continues in 1999.
Bacterial spot epidemics, caused by Xanthomonas campestris pv. vesicatoria (Xcv), are still considered serious risks for commercial pepper (Capsicum annuum) growers in a number of eastern, southern and midwestern states. Newly released bell pepper cultivars with the Bs2 gene for resistance to Xcv races 1, 2, and 3 were compared in 2000 under bacterial spot-free and severe (natural) bacterial spot epidemic conditions in central and eastern Kentucky where similar trials had been conducted from 1995 to 1997. In addition to the replicated bell pepper trials, 49 hot and specialty pepper cultivars were grown for observation in single plots at the same two locations. As in previous trials, there were economically important differences in resistance and marketable yields among bell pepper cultivars having the Bs2 gene; some resistant cultivars were as susceptible as susceptible checks. Others were highly resistant in spite of the presence of Xcv races 3 and 6 in the eastern Kentucky trial. Only a few were highly resistant with excellent fruit quality. With a few notable exceptions, most of the hot and specialty cultivars were very susceptible to bacterial spot. Two of the three new jalapenĚo cultivars carrying Bs2 were highly resistant to bacterial spot and high yielding under severe epidemic conditions.