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Gary E. Vallad, Kenneth L. Pernezny, Botond Balogh, Aimin Wen, Jose Francisco L. Figueiredo, Jeffrey B. Jones, Timur Momol, Rosa M. Muchovej, Nikol Havranek, Nadia Abdallah, Steve Olson, and Pamela D. Roberts

Bacterial spot is a major disease of tomato ( Solanum lycopersicum ) in Florida and worldwide ( Jones, 1991 ; Jones et al., 2004 ). The disease is associated with four species of Xanthomonas : X. euvesicatoria , X. vesicatoria , X. perforans

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Abbasali Ravanlou and Mohammad Babadoost

Bacterial spot of pumpkin, incited by X. cucurbitae (ex Bryan) Vauterin et al. (1995) [syn. Xanthomonas campestris (Pammel) Dowson pv. c ucurbitae (Bryan) Dye], has become one of the most important diseases of pumpkin [ Cucurbita pepo L. and

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Gary E. Vallad and Bielinski M. Santos

in tomato. Florida accounted for nearly 40% of the total U.S. gross sales ( USDA, 2010 ). Among the many diseases that affect tomato, bacterial spot is one of the most troublesome ( Bouzar et al., 1999 ; Jones et al., 2004 ; O'Garro and Charlemagne

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Sabin Khanal, Sarah R. Hind, and Mohammad Babadoost

Bacterial spot of tomato ( Solanum lycopersicum L.) was first identified in South Africa ( Doidge, 1921 ). Originally, bacterial spot was thought to be caused by only one species, Xanthomonas campestris pv. vesicatoria ( Stall et al., 1994

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Samuel F. Hutton, Jay W. Scott, and Jeffrey B. Jones

Bacterial spot of tomato is caused by as many as four species of Xanthomonas : X. euvesicatoria , X. vesicatoria , X. perforans , and X. gardneri ( Jones et al., 2000 , 2005 ); the former three species were previously named X. campestris

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Samuel F. Hutton, John W. Scott, and Gary E. Vallad

susceptibility to bacterial spot (J.W. Scott, unpublished data). Bacterial spot is also a major disease of tomato in Florida and in many regions of the world where the crop is grown in humid environments. The disease is caused by several species of Xanthomonas

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G. Cameron Somodi, J.B. Jones, J.W. Scott, and J.P. Jones

A `spray-inoculation seedling screening procedure was developed for detecting resistance to Xanthomonas campestris pv. vesicatoria (Doidge) Dye, causal agent of bacterial spot of tomato (Lycopersicon esculentum Mill.). Two-week-old transplants were preconditioned under 95% humidity for 16 hours before spray inoculation and then rated for bacterial spot 2 weeks later. Resistant plants could also be distinguished from susceptible genotypes using a modified bacterial speck [Pseudomonas syringae pv. tomato (Okabe) Young, Dye, and Wilkie] screening procedure (cotyledon-dip technique). When results of both screening methods were compared to field ratings from three previous seasons, significant correlations were more frequently observed for the spray-inoculation method. In Summer 1991, individual plants were evaluated by the spray-inoculation technique and then were placed in the field to determine susceptibility under field conditions. Correlations (r = 0.28 to 0.34) between spray-inoculation seedling screening ratings and field ratings, although low, were significant (P ≤ 0.0001). More than 90% of susceptible plants could be eliminated, saving labor, space, and time.

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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.

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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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Wencai Yang and David M. Francis

The lack of resistance to bacterial diseases increases both the financial cost and environmental impact of tomato (Lycopersicon esculentum Mill.) production while reducing yield and quality. Because several bacterial diseases can be present in the same field, developing varieties with resistance to multiple diseases is a desirable goal. Bacterial spot (caused by four Xanthomonas Dowson species) and bacterial speck (caused by Pseudomonas syringae pv. tomato Young, Dye and Wilkie) are two economically important diseases of tomato with a worldwide distribution. The resistance gene Pto confers a hypersensitive response (HR) to race 0 strains of the bacterial speck pathogen. The locus Rx3 explains up to 41% of the variation for resistance to bacterial spot race T1 in field trials, and is associated with HR following infiltration. Both Pto and Rx3 are linked in repulsion phase on chromosome 5. We made a cross between two elite breeding lines, Ohio 981205 carrying Pto and Ohio 9834 carrying Rx3, to develop an F2 population and subsequent inbred generations. Marker-assisted selection (MAS) was applied to the F2 progeny and to F2:3 families in order to select for coupling-phase resistance. Thirteen homozygous progeny from 419 F2 plants and 20 homozygous families from 3716 F3 plants were obtained. Resistance was confirmed in all selected families based on HR in greenhouse screens using bacterial speck race 0 and bacterial spot race T1 isolates. Resistance to bacterial spot race T1 was confirmed in the field for 33 of the selected families. All selected families were also resistant to bacterial speck in the field. MAS was an efficient tool to select for desirable recombination events and pyramid resistance.