Host-pathogen interactions among barley genotypes and Bipolaris sorokiniana isolates

Spot blotch, caused by Bipolaris sorokiniana, is a damaging foliar disease of barley (Hordeum vulgare) and other cereal grains in Canada. In order to deploy resistance as an effective management tool, information on the virulence diversity present in the local population of the pathogen is necessary. Speculation regarding the presence of differential virulence versus continuous aggressiveness in B. sorokiniana isolates was begun when isolates with differential virulence on the barley cv. Bowman and its derivatives were reported in North Dakota. To further evaluate the H. vulgare-B. sorokiniana interaction model, the infection responses induced by 127 isolates of the pathogen collected from Canada and other parts of the world were analyzed on 12 differential barley lines using quantitative approaches. Analysis of the data based on infection response elicited on the barley differentials resulted in an enhanced understanding of the host-pathogen interactions and in the relationships among isolates, compared with the classical method of pathotype identification. The population of B. sorokiniana was determined to consist of three distinct pathogenic groups (having low virulence, differential virulence, and virulence with varying levels of aggressiveness). The results of the various quantitative approaches indicated that complex interactions exist among barley genotypes and B. sorokiniana isolates of the third pathogenic group which cannot be analyzed easily using the classical method of pathotype identification. It also was inferred that the gene-for-gene model is not the principal system operating in the H. vulgare-B. sorokiniana pathosystem, although this plays a role in some interactions.