Population study of Xanthomonas spp. from bean growing regions of Canada and response of bean cultivars to pathogen inoculation

Abstract

Common bacterial blight caused by Xanthomonas axonopodis pv. phaseoli and Xanthomonas fuscans pv. fuscans is a major disease of bean in Canada and elsewhere with limited disease management options. A population study was conducted to determine the diversity among strains isolated from bean plants, and to investigate whether different races exist in this population in Canada. A total of 49 strains, including reference strains from the USA and Mexico, were evaluated on seven bean accessions with different sources of resistance. A wide range of host responses was observed. Among the strains, 22 caused minute lesions on bean plants and were thus designated as non-pathogenic xanthomonads. Highest disease scores and the widest spread in score frequencies after inoculation with pathogenic strains were observed on the susceptible cultivar ‘CDC Pintium’ and the reportedly partially resistant cultivar ‘Weihing’, suggesting that the latter is not an effective source of resistance to the Canadian population. Low disease severities and score frequencies skewed towards resistance were observed on cultivars HR67, ICB-10, XR 235-1-1 and ‘OAC Rex’, whereas ‘OAC Seaforth’ showed intermediate reactions. Continuous distributions of disease severity scores of strains for each cultivar and detailed analyses of disease data revealed no evidence for a race structure in the population tested.