Pathotypes of Cochliobolus sativus on barley in North Dakota.
Spot blotch, caused by C. sativus, is an important disease on 2-rowed barley cultivars in North Dakota, USA. The number and distribution of C. sativus virulence types in North Dakota were investigated. Twenty-two isolates were evaluated for their virulence on the barley genotypes ND5883, Bowman and NDB112. Eleven additional isolates from Minnesota, South Dakota, Nebraska, Colorado, Japan and China were included for comparison. Based on infection response of the genotypes, 3 pathotypes were identified and were designated 0, 1 and 2 according to the coded triplet system of nomenclature. In North Dakota, pathotype 0 (low virulence on the 3 genotypes), pathotype 2 (high virulence on Bowman and low virulence on ND5883 and NDB112) and pathotype 1 (high virulence on ND5883 and low virulence on Bowman and NDB112) comprised 65, 25 and 10% of the total number of isolates examined, respectively. Within North Dakota, pathotype 1 only occurred in the east-central and northeastern region, whereas pathotypes 0 and 2 were distributed throughout the state where samples were taken. Isolates with pathotype 1 virulence were identified in Colorado, Nebraska, Japan and China. The remaining isolates collected outside North Dakota were pathotype 0.