Population structure and genetics of host resistance in the barley leaf spot pathogen Bipolaris sorokiniana

Spot blotch, caused by Bipolaris sorokiniana is one of the most damaging foliar diseases of barley in Canada, especially in Manitoba. This research project was undertaken to evaluate the virulence and genetic diversity of the pathogen in Canada, as well as the genetics of resistance in the spot blotch resistant barley line TR 251.;Based on molecular analysis, low virulence isolates and those with differential virulence were clearly discernable from isolates in the other six virulence groups (pathogenic group 3). The molecular analysis did not provide a robust differentiation between isolates of the latter six virulence groups identified by the classical method of pathotype designation. However, the groupings based on molecular analysis were concordant with those made by quantitative analyses of virulence data.;A doubled haploid population derived from a cross with TR 251 was used to evaluate the genetics of the resistance to spot blotch. Four putative loci on chromosomes 1H, 3H, 5H, and 7H were associated with spot blotch resistance in line TR 251, of which two, located on chromosomes 1H and 5H, have not been reported previously. These loci are both likely unique, and presumably contribute to the superior resistance of line TR 251 to B. sorokiniana.;The infection responses of 12 differential barley genotypes inoculated with 127 B. sorokiniana isolates were used to characterize the virulence pattern of the pathogen in Canada and compare this to that previously reported for the USA (i.e. pathotypes, '0', '1' and '2'). Using the classical (qualitative) method of pathotype designation isolates were classified into eight virulence groups. A quantitative analysis of the data showed that these eight groups can be categorized into 3 distinct pathogenic groups, of: (1) low virulence (equal to pathotype '0'); (2) differential virulence (equal to pathotype '2'); and (3) virulence with varying levels of aggressiveness (the other 6 virulence groups). Considerable virulence diversity among isolates in the third major group did not allow for the incorporation of all these isolates into a single unique virulence group (i.e. pathotype '1').