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Muhammet Tonguç and Phillip D. Griffiths

Black rot, caused by Xanthomonas campestris pv. campestris (Pam.) Dawson (Xcc), is a major bacterial disease of Brassica oleracea L. vegetables. In this study the related species Brassica carinata Braun (ethiopian mustard), which can be used to generate interspecific crosses with B. oleracea was evaluated for resistance to Xcc. Fifty-four accessions and susceptible control plants were wound inoculated with four isolates of Xcc race 4 at the juvenile stage. Of the 54 accessions tested, A 19182 and A 19183 exhibited no symptoms when inoculated with Xcc for all plants tested, and the accessions including PI 199947, PI 199949 and PI 194256 segregated for resistance to Xcc.

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David J. Norman, Qi Huang, Jeanne M.F. Yuen, Arianna Mangravita-Novo, and Drew Byrne

bacterial wilt by drench inoculation or by wound inoculation. Three strains of R. solanacearum were used for cultivar susceptibility screening, including two race 1, biovar 1 (R1B1) strains, P597 and P673, and a race 3, biovar 2 (R3B2) strain UW551

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Phillip D. Griffiths, Laura Fredrick Marek, and Larry D. Robertson

, IA) and NE-9 (Geneva, NY) USDA regional PI centers were inoculated and evaluated for resistance to race 1 and race 4 of Xcc using the wound inoculation technique ( Griffiths and Roe, 2005 ). Materials and Methods Plant material. The USDA crucifer

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Wojciech J. Janisiewicz, Robert A. Saftner, William S. Conway, and Philip L. Forsline

apples from the Kazak collection of Elite (PI) and seedlings (GMAL) wound inoculated with various concentrations of Penicillium expansum conidia and incubated for 5 d in air at 22 °C. For our experiments, fruit were harvested on 8 to 9 Aug

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Richard O. Nyankanga, Ocen Modesto Olanya, Hans C. Wien, Ramzy El-Bedewy, John Karinga, and Peter S. Ojiambo

diameter (millimeters) for tubers infected after wound inoculation assay ( B ). Estimation of tuber blight occurrence in field from tuber blight assessments based on in vitro assays. Estimation of tuber blight occurrence in field experiments

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Phillip D. Griffiths and Cathy Roe

Eighteen cabbage breeding lines and cultivars were evaluated for resistance to black rot caused by Xanthomonas campestris pv. campestris following wound and spray inoculations at the juvenile and mature stages. Plants were evaluated using four inoculation procedures (juvenile wound, juvenile spray, mature wound, and mature spray) in replicated greenhouse and field experiments. The breeding lines Badger #16, Cornell 101, Cornell 102, NY 4002 and accession PI 426606 exhibited high levels of resistance following all inoculation procedures. `Silver Dynasty' was the most resistant commercial cultivar based on the four tests, yet ranked 12th following the juvenile wound inoculation. The juvenile spray inoculation had a high correlation with both wound and spray inoculations in field experiments (0.89 and 0.86, respectively); however, the juvenile wound inoculation did not correlate well with mature wound and spray inoculations (0.58 and 0.51, respectively). The results indicate that the juvenile wound inoculation is not the most appropriate approach for determining field resistance in Brassica oleracea, and that resistant material could be selected against using this approach. A high correlation between juvenile spray inoculation disease severity ratings and mature plant resistance indicates that plants can be evaluated effectively at the juvenile stage for mature plant resistance to black rot.

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Fenny Dane

A genetically engineered, bioluminescent strain of Xanthomonas campestris pv. campestris (Xcc) was used to study the effectiveness of plant growth-promoting rhizobacteria (PGPR) as disease control agents. Black-rot-susceptible cabbage plants were wound-inoculated with PGPR and wound- or mist-inoculated with bioluminescent Xcc 10 days later. Growth of the bioluminescent strain in the plants was followed over time with a low-light, charge-coupled device camera. Several PGPR strains effectively reduced growth of the bioluminescent pathogen in the plants when bacteria were introduced into the plant by wound. PGPR inoculation was less effective when bioluminescent bacteria were introduced into the plant by mist inoculation. Little effect on symptom reduction was observed.

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Fenny Dane and Joe Shaw

The movement of genetically engineered, bioluminescent, Xanthomonas campestris pv campestris, causal agent of black rot in crucifers, was followed after wound or mist inoculation of susceptible and resistant host plants. Wound inoculation resulted in higher bacterial population levels in susceptible (Perfect Ball) as compared to resistant (Hancock) cabbage plants. More leaves became infected in the susceptible host and peak levels were reached after 4-8 days, but after 10-12 days in the resistant plants. Mist inoculation resulted in high levels of bioluminescent Xcc after 11-15 days in susceptible tissues only, unless entry was gained through damaged tissue of the resistant plant. In the field environment, Xcc was found endophytically after mist inoculation in susceptible cabbage only, but found to grow epiphytically for as long as 2 1/2 months to the same degree on resistant and susceptible host plants. Dispersal of the bacterium was limited and survival in the soil environment found to last for four months.

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P.G. Braun, P.D. Hildebrand, and A.R. Jamieson

Twenty-five cultivars of red raspberry (Rubus idaeus L.) and one purple raspberry (R. occidentalis L. × R. idaeus L.) were evaluated for their resistance to fire blight caused by Erwinia amylovora (Burr.) Winslow et al. Actively growing raspberry cane tips were wound inoculated with three isolates of the pathogen and disease development was assessed over 17 days. Three methods of evaluating resistance were used: area under the disease progress curve (AUDPC), a weighted AUDPC called the area under the disease severity curve (AUDSC), and lesion length. A wide range of resistance levels was observed, but no cultivars were symptomless. Primocane-fruiting cultivars tended to be more resistant than floricane-fruiting ones. Of the three E. amylovora isolates used in this study, one was significantly more virulent than the other two, but no cultivar × isolate interaction was detected.

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Fenny Dane and Marten H. Dane

A pathogenic strain of Xanthomonas campestris pv. vesicatoria, causal agent of bacterial spot of tomato (Lycopersicon esculentum Mill.), was genetically engineered to bioluminesce. In planta growth of the bioluminescent strain was similar to that of its parental strain. Movement and growth of the bioluminescent strain in susceptible tomato seedlings after wound inoculation was followed over time with a liquid-N-cooled, charge-coupled device camera. Highly significant differences in bioluminescent bacterial growth were observed in the four tomato cultivars used. Systemic bacterial movement was most pronounced in `Sunny', which showed population development not only at the inoculation sites but also on several sites in the leaves and at the leaf margins. Bacterial bioluminescence levels in `Campbell 28' remained significantly lower than those observed in `Walter' and `Sunny'. The technique offers unique possibilities for studying host-pathogen interactions and bacterial pathogenesis.