Mapping of Quantitative Trait Loci Controlling Resistance ofBrassica oleraceatoXanthomonas campestrispv.campestrisin the Field and Greenhouse

Abstract

Despite the existence of resistant cultivars, little is known about the genetic control of resistance of Brassica oleracea to Xanthomonas campestris pv. campestris. Quantitative trait loci (QTL) controlling juvenile and adult plant reactions of B. oleracea to X. campestris pv. campestris were mapped using restriction fragment length polymorphism loci and disease ratings of F 3 families from a resistant cabbage x susceptible broccoli cross. In the greenhouse, 2.5-week-old, plants were screened by inoculating the pathogen directly into the veins and measuring the diseased leaf area. In the field, 11-week-old plants were screened by inoculating intact plants and assessing the symptoms using an interaction phenotype scale. Two genomic regions on linkage groups 1 and 9 were associated with both young and adult plant resistance. These regions also were associated with variation for petiole length. Two additional QTL on linkage group 2 that were associated only with young plant resistance were found. For one of these, alleles from the resistant parent contributed to greater susceptibility. These results suggest that plants selected for resistance based on screening young plants in the greenhouse should exhibit adult plant resistance.