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John C. Snyder

Breeding for resistance to insects and other arthropod pests in vegetables has been a difficult endeavor. Greater public awareness of health and environmental issues requires that we as horticultural scientists reexamine why breeding for resistance has been difficult. The literature clearly suggests the potential for a genetic solution, and the literature also reveals some reasons why achievement of genetic resistance to arthropod pests has not been as successful as the achievement of resistance to pathogens. The thesis of my presentation is that the complexity of plant-arthropod interactions often prevents simple genetic approaches to breeding for resistance. Data using Lycopersicon hirsutum and its interaction with spider mites will provide examples of the these complex interactions. L. hirsutum is a wild relative of L. esculentum, the common tomato, and is nearly immune to insect attack. However, there are few or no clear examples of this taxa contributing to the insect resistance of tomato. The complexity of the interaction between mites and trichomes on L. hirsutum will be highlighted as it pertains to environment and genetics of the plant, and the development of the arthropod.

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Brent Rowell and John C. Snyder

“We are a tobacco state” is frequently heard among farmers and agricultural leaders in Kentucky; the state's farm economy has always revolved around burley tobacco production. Tobacco, grown in Kentucky for nearly two centuries, remains the most valuable crop earning approximately $694 million in 1995. Even our unusual terminology of “alternative,” “supplemental,” or “opportunity” crops denotes the prime position of tobacco and attitudes toward vegetable crop production. This long tradition and attitudes associated with it contribute to a serious lack of confidence and low expectations when it comes to diversification with vegetable crops. These low expectations and the consequent circular pattern of experience with vegetable production were revealed in a multidisciplinary, 5-year research project designed to determine opportunities for and constraints to vegetable production in the state. The study showed that nearly half of Kentucky's commercial vegetable growers also were tobacco growers and that there were no fundamental incompatibilities in tobacco–vegetable cropping systems. Although farmers considered lack of markets a major constraint, economic research revealed that growers were often unwilling to use and take the risks associated with existing market structures and channels. As a result of these findings, a major on-farm demonstration program was implemented to raise expectations and break the “circular syndrome”. More recently, new partnerships and collaborative relationships have been established between university horticulture and marketing specialists and the Burley Tobacco Growers Cooperative Association for the promotion of “supplemental crops” among Kentucky's tobacco growers.

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Zhenhua Guo and John C. Snyder

Choice and non-choice bioassays were used to examine deterrence in vitro and in vivo of Tetranychus urticae Koch. In vivo deterrence of leaflets from 11 Lycopersicon hirsutum accessions as well as the tomato cultivar `Ace 55' was measured as was in vitro deterrence of their leaf hexane extracts. Leaf surface chemistry was examined by gas chromatography. All 6 accessions of L. hirsutum f. hirsutum contained sesquiterpene hydrocarbons. Each of these extracts also contained one or a few late eluting components. All were deterrent in vitro and 5 out of the 6 were deterrent in vivo. The one lacking in vivo deterrence had low density of type IV trichomes. All 5 accessions of L. hirsutum f. glabratum contained methyl ketones. These accessions were less deterrent in vitro and 4 out of the 5, less deterrent in vivo. The one accession having high in vivo deterrence also had high density of type IV trichomes. `Ace 55', having few hexane extractable compounds was neither deterrent in vitro nor in vivo. Within an accession, secretions from different types of trichomes shared similar chemical profiles and were similar to leaf profiles.

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Brent Rowell, William Nesmith, and John C. Snyder

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.

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John C. Snyder, George Antonious, and Richard Thacker

Many accessions of Lycopersicon hirsutum are highly resistant to insects. Trichomes and their secretions have been extensively indicated as factors of resistance. One mechanism of resistance mediated by secretions is repellency, a mechanism that is consistent with the observation that few insects visit plants of L. hirsutum. Trichome secretions from certain accessions of L. hirsutum f. typicum are repellent to spider mites. However, the composition of secretions from different accessions of f. typicum are chemically diverse. Sesquiterpene hydrocarbons are prevalent in secretions, but are structurally diverse. How structure may relate to repellency is of interest but difficult to address because isolation of pure sesquiterpene hydrocarbons from hydrocarbon mixtures is difficult. To begin examining relationships between structure and activity we determined how chain length of n-alkanes related to repellency of spider mites. n-Alkanes having chain lengths from 8 to 22 carbon atoms were assayed for repellency. The C16-C18 alkanes were most repellent. Smaller and larger hydrocarbons were less repellent. The EC50 for n-hexadecane was equal to that of the most repellent natural products we have isolated from trichome secretions of L. hirsutum.

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George H. Snyder and John L. Cisar

Field and laboratory studies were conducted to evaluate the K retention properties of several resin-coated (RC), sulfur-coated (SC), and plastic-coated (PC) K fertilizers. Substantial differences in K release were found among the controlled-release K materials, based both on the K content of `Tifgreen' bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burt-Davvy] clippings and on direct measurement of K remaining in fertilizer granules in the field over time. One SC material appeared to release K too rapidly, and one RC material appeared to release K too slowly to be useful for providing extended plant-available K to turfgrass. The other sources appeared to have release characteristics that would be favorable for turfgrass maintenance. Because differences in K release were observed among the sources, a laboratory method for assessing K release would be useful. Toward this-end, models were developed relating K retention of sources in hot water (70C) to K retention under field conditions.

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John L. Cisar and George H. Snyder

The objective of this experiment was to determine the suitability of a compost obtained from a commercially available solid-waste processing plant for sod production when placed over a plastic barrier. Comparisons were made between compost-grown sod with and without fertilizer and between compost-grown sod and commercially grown sod. Six weeks after seeding or sprigging, both fertilized and nonfertilized compost-grown `Argentine' bahiagrass (Paspalum notatum Flugge), `Tifway' bermudagrass (Cynodon transvaalensis × C. dactylon), and `Floratam' St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze.] had discolored leaf blade tissue and poor growth. At 6 weeks, bahiagrass leaf tissue had a low N concentration, which suggested that the compost immobilized fertilizer N. Additionally, initial high salinity of the compost (2.85 dS·m-1) may have contributed to turf discoloration and lack of vigor. However, poor growth and discoloration were temporary. At 3 and 5 months, fertilized compost-grown turfgrasses had higher quality and coverage than nonfertilized sod. At 5 months, fertilized sod had sufficient coverage for harvest, whereas for conventional field production 9 to 24 months generally is required to produce a harvestable product. Compost-grown sod pieces had similar or higher tear resistance than commercially grown sod. One and 3 weeks after transplanting on a sand soil, compost-grown sod produced higher root weight and longer roots in the underlying soil than did commercially grown sod. The solid-waste compost used in this study offers a viable alternative material for producing sod that will benefit solid-waste recycling efforts.

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Karen E. Williams, John L. Cisar, and George H. Snyder

Current interest in the fate of agrochemicals applied to turf is encouraging many turf scientists to contemplate renovation of existing field plots for soil-water monitoring studies. Ceramic cup samplers are used for these studies and result in little soil profile disturbance. However, a limitation to using this tool is frequent sampler failure caused by frequent system air leaks. Also, conventional installation and sampling require that samplers be accessible from above the soil line. This imposes a constraint on turf maintenance and increases traffic and wear to turf plots. Herein, an inexpensive offsite soil-water sampling method using permanently installed ceramic cup samplers that allows for routine turf maintenance without system failure is described. Thirty-six separately irrigated 4 m2 plots each with an installed sampler provided daily data over 1988-1989, from which the effects of a range of irrigation, N, K, and propoxur treatments on soil-water concentrations were evaluated. These data, plus calculated percolation provided an estimate of groundwater loading.

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John L. Cisar, George H. Snyder, and Karen E. Williams

For only the second time, the United States will host The International Turfgrass Society's (ITS) International Turfgrass Research Conference (ITRC). The VII ITRC will be held July 18-24, 1993 at The Breakers in Palm Beach, FL. Since its inception, the ITS has been devoted to addressing problems that effect turfgrass and improving the standards of turfgrass science through international communication. The Conference will offer two symposia entitled “Pesticide and Nutrient Fate in Turfgrass Systems” and “Quantification of Surface Characteristics of Sports Fields”. Additionally plenary and volunteered oral and poster presentations on all topics of turfgrass science and related horticultural landscape management tours of the local horticultural industries will be offered. Volunteered papers will be published in a proceedings as either original research papers or as technical papers. Papers submitted as original research will undergo refereed peer review prior to acceptance. See poster for further details or contact authors at above address (phone: 305-475-8990).

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Brent Rowell, R. Terry Jones, William Nesmith, and John C. Snyder

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.