Pathotypes of Cochliobolus sativus on Barley in North Dakota

Spot blotch, caused by Cochliobolus sativus, has become an important disease on two-rowed barley cultivars in North Dakota. Information on the variability of virulence in C. sativus is essential for the development of spot blotch-resistant barley germ plasm. To establish the number and distribution of C. sativus virulence types in North Dakota, 22 isolates from the state were evaluated for their virulence on three differential barley genotypes: ND 5883, Bowman, and ND B112. Eleven additional isolates from Minnesota, South Dakota, Nebraska, Colorado, Japan, and China were included for comparison. Three pathotypes were identified from the thirty-three isolates tested based on the infection responses of the three host genotypes. These pathotypes were designated 0, 1, and 2 according to the coded triplet system of nomenclature. In North Dakota, pathotype 0 (exhibits low virulence on all three differentials) comprised 65%, pathotype 2 (exhibits high virulence on Bowman and low virulence on ND 5883 and ND B112) comprised 25%, and pathotype 1 (exhibits high virulence on ND 5883 and low virulence on Bowman and ND B112) comprised 10% of the total number of barley isolates examined. Within North Dakota, pathotype 1 was found in the east-central and northeastern region only, whereas pathotypes 2 and 0 were distributed throughout the state where samples were taken. Isolates with the pathotype 1 virulence pattern were identified in Colorado, Nebraska, Japan, and China. The remaining isolates collected outside North Dakota were pathotype 0. The information obtained from this study will facilitate the deployment of effective resistance to C. sativus in barley.