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J.D. Norton, G.E. Boyhan, D.A. Smith and B.R. Abrahams

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Unaroj Boonprakob and David H. Byrne

Six controlled crosses of cultivated and advanced selection Japanese-type plums adapted to southeast and southwest regions of the United States were made in 1990 and 1991. Over 800 seedlings from these crosses along with open pollinated seedlings of the parents were established in Suiting nurseries. The long range objective of this study is to determine linkage relationships between RAPD markers and commercially important traits (soluble solid, resistance to bacterial leaf spot, chilling requirement, fruit development period). The first step in the projects to characterize RAPD genotypes in the progenies. Eighty oligodecamers have been screened and 57 yielded successful reactions with an average of two to three bands per primer. The variability and inheritance of the RAPD markers in these plum populations will be described.

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Jude Boucher, Gianna Nixon and Richard Ashley

In 1995, we compared the horticultural characteristics of one Phytophthora blight, one cucumber mosaic virus, and 12 bacterial leaf spot–resistant varieties to two popular commercial peppers in a replicated trial at the University of Connecticut. Fruit were graded for size and shape and yields were separated into early and late-season harvests. Other parameters measured were plant height, canopy width, and fruit wall thickness, length to diameter ratio, number, weight, and the percent marketable. Unreplicated demonstration plantings with three or four resistant varieties each were conducted at 12 commercial farms in 1994–95 and at the university's research farm in 1994. Several resistant varieties were judged to be equal or superior to the two popular cultivars based on a combination of characteristics, including observations on disease susceptibility at local farms. Resistant varieties recommended for New England conditions include Boynton Bell (Harris Moran), King Arthur and PSX 271092 (Petoseed), Admiral and Reinger (Roger NK).

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Freddi A. Hammerschlag, Ghazala Hashmi, Robin Huettel, Dennis Werner and David Ritchie

One approach for obtaining useful genetic variation is to select for somaclonal variants generated by tissue culture techniques. Increased levels of resistance to bacterial leaf spot (Xanthomonas campestris pv. pruni) have been observed in toxin-selected and unselected peach regenerants in vitro, in the greenhouse and under field conditions. Peach regenerants have also demonstrated increased levels of bacterial canker (Pseudomonas syringae pv. syringae) and root-knot nematode (Meloidogyne incognita) resistance. Random amplified polymorphic DNA (RAPD) primers have been used to study genetic variation at the DNA level among the somaclonal variants. Sixty RAPD primers (10-mers) were screened and 10 proved useful as markers to detect polymorphisms, thus establishing a genetic basis for somaclonal variation. These studies demonstrate the feasibility of using tissue culture techniques to generate fruit trees with increased levels of disease resistance.

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

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 jalapeño cultivars carrying Bs2 were highly resistant to bacterial spot and high yielding under severe epidemic conditions.

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Allen Owings, Gordon Holcomb, Andrew Bates, Peggy Cox, Stephen Crnko and Anthony Witcher

In 1999, LSU Agricultural Center landscape trials of herbaceous ornamental plants included zinnias, ornamental sweet potatoes, vinca, and perennial verbenas. Based on growth habit, flowering and disease observations from 1999 and previous years, `Homestead Purple', `Tiger Rose', `Rose King', `Taylortown Red', and `Blue Princess' (`Biloxi Blue') are recommended perennial verbena cultivars for Louisiana landscapes. Zinnias evaluated included Zinnia angustifolia and Z. elegans cultivars. `Crystal White', `Profusion Orange', and `Profusion Cherry' (all Z. angustifolia cultivars) were superior landscape performers. Major incidence of bacterial leaf spot was reported on all Z. elegans cultivars in 1999. Over the last several years, the Pacifica series of vinca had significantly improved visual quality ratings in landscape trials when compared to the Heat Wave and Cooler series. In 1999, Mediterranean Deep Rose had visual quality ratings similar to Pacifica but had increased incidence of disease problems. Ornamental sweet potato cultivars recommended for landscape use in Louisiana based on trials in 1999 are `Blackie', `Black Beauty', `Margarite', and `Pink Frost' (`Tricolor'). `Summer Frost' is not recommended.

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Joseph R. Heckman, Steve Johnston and Win Cowgill

Field experiments were conducted with Cucurbita pepo L. `Howden' pumpkin in 2000 to 2001 to study the effects of silicon (Si) amendment of soil with and without the use of fungicides on yield and powdery mildew suppression. A Quakertown silt loam soil (fine-loamy, mixed, mesic Typic Hapludult) with an initial soil pH of 5.7 was amended with either CaCO3 or CaSiO3 at the rate of 7840 kg·ha-1 of calcium carbonate equivalent. Fungicides were applied on a 7-10 day schedule to half of the plots as a 2 × 2 factorial, beginning when the first powdery mildew lesions were detected in the field. Silicon amendment increased pumpkin yield by 60% in 2000 but Si did not influence yield in 2001. Infection with bacterial leaf spot reduced yield on all plots in 2001. Fungicide applications increased yield only in 2001. In 2000, Si amendment had the effect of delaying foliage senescence but it was not clear if this was the result of an effect of Si on disease activity or crop physiology. In Aug. 2001, Si amendment generally reduced powdery mildew severity, but only at the 10% level of significance. In Sept. 2001, the combination of Si amendment plus fungicide application was more effective in reducing powdery mildew severity than either Si or fungicide alone. Silicon amendment resulted in a 5-fold increase in plant Si concentration. Soil pH measured after harvest in 2001 indicated no significant difference in pH between plots amended with CaCO3 (pH = 6.8) and CaSiO3 (pH = 6.9). In New Jersey, the cost of these liming materials is similar. Thus, the selection of CaSiO3 as a liming material as needed for soil pH correction has the potential benefits of suppressing powdery mildew and increasing pumpkin yield without increasing the cost of production.

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. This breeding line, however, can be used in breeding programs because it combines high level resistances to downy mildew, bacterial leaf spot, Verticillium wilt race 1, and lettuce dieback. Two (SM13-R2, SM13-R3) of the four romaine breeding lines are

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Ivan Simko, Ryan J. Hayes, Carolee T. Bull, Beiquan Mou, Yaguang Luo, Mark A. Trent, Amy J. Atallah, Edward J. Ryder and Rebecca G. Sideman

heads assigned each respective score and N T is the total number of lettuce heads examined for the accession. Resistance to bacterial leaf spot. Evaluations of seedlings for resistance to bacterial leaf spot caused by Xanthomonas campestris pv

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lower grade point average students. Shoot Pruning Has No Effect on Bacterial Leaf Spot in Tomato Bacterial leaf spot in tomato is controlled by cultural practices such as exclusion of the pathogen from production areas, use of resistant varieties, and