Kiran Ghising, Juan M. Osorno, Phillip M McClean, Stephan Schroder, Kevin E. McPhee, Jose E Vasquez, Julie S Pasche and Robin Lamppa, North Dakota State University, Fargo, ND
Halo blight, caused by Pseudomonas syringae pv. phaseolicola (Burkn.) Downs (Psp), is an important seed-borne bacterial disease of common bean (Phaseolus vulgaris L.), particularly in regions with a moderately cool-wet climate. Under favorable conditions, disease can cause up to 45 % yield losses on susceptible cultivars. Nine races of Psp reported, being race 6 the most prevalent in the bean growing regions of world including North Dakota and Minnesota. Up today, only one source of genetic resistance to race 6 of Psp has been reported (US14HBR6). A total of 283 accessions of P. vulgaris from the USDA-NPGS core collection evaluated under greenhouse conditions, and a subset of 62 accessions showed resistance to race 6 of Psp when inoculated on primary leaves. Further evaluation of those 62 accessions in terms of trifoliate and pod infections showed 15 accessions (19%) as resistant on trifoliates with a mean score of 1.9, while 29 accessions (42%) showed highest levels of resistance on pods with a mean score of 2.4 when compared to USHBR6, a resistant pinto check with a mean score of 1.0 and 1.5 on trifoliate and pod infection, respectively. The results of correlation analysis revealed a significant but weak correlation (r = 16%) between the trifoliate and pod reactions within an individual plant, suggesting that leaf resistance does not always translate into pod resistance and therefore, independent mechanisms of resistance may be responsible. Of these resistant accessions reported, PI 313490, a black bean from Mexico, showed the highest levels of resistance with a mean score of 0.8, and 2.7 for trifoliate and pod infections, respectively. Using Genome-Wide Association Mapping approach, identification of genomic regions linked to higher levels of resistance to race 6 of Psp will be conducted.