The Host Pathogen Interaction And Breeding And Genetics Of Resistance For Common Bacterial Blight Of Common Bean Phaseolus Vulgaris L Caused By Xanthomonas Campestris Pv Phaseoli And X C Pv Phaseoli Var Fuscans

Common bacterial blight (CBB) caused by Xanthomonas campestris pv. phaseoli Smith (Dye) (Xcp, synonym: X. axonopodis pv. phaseoli [Smith] Vauterin et al.) and X. c. pv. phaseoli var. fuscans (Burkholder) Starr & Burkholder (Xcpf, synonym: X. fuscans subsp. fuscans sp. nov.) is the most important bacterial disease of common bean (Phaseolus vulgaris L.). Host resistance is the best method of management for this seed-borne disease. The first objective of this research was a host-pathogen diversity study, where new Xcp and Xcpf genotypes associated with CBB in Wisconsin were identified. These new genotypes, along with five previously reported genotypes, were inoculated onto 27 common bean genotypes having different combinations of CBB resistance QTL and markers. Eight host genotypes were identified that were resistant to all pathogen genotypes. The second objective was to compare direct disease selection (DDS) with marker-assisted selection (MAS) for the development of CBB resistant breeding lines, and the cost-effectiveness of the two selection methods. More CBB-resistant breeding lines were generated with DDS under conditions of high disease pressure in the greenhouse. However, under moderate disease pressure in the field, there were no significant differences between the two selection techniques. Under the parameters of this study, DDS was more cost-effective than MAS. Finally, the relationship between flower and seed color, CBB resistance, a CBB resistance SCAR marker (BC420) and the SOD12490 marker associated with the V pigmentation locus was investigated. In an F2 population and in the F3 progeny test, no recombination was found between colored flowers (purple [P] and lilac [L]), a dark undesirable DRK seed coat color and presence of the BC420 marker. All plants in the F2 and F3 that lacked the BC420 marker had white/lilac-striped (wl) flower color and the desirable DRK seed color. The SOD12490 marker was not linked with CBB resistance. Some plants with wl flowers were resistant but lacked the BC420 marker, indicating unidentified QTL in the CBB-resistant donor germplasm (VAX 3, Wilkinson 2, or I9365-25). Together, this information will facilitate the improvement of CBB resistance in all market classes of common bean.