Cultural Characteristics and Pathogenic Variations among Cochliobolus carbonum Isolates in Yunnan Province of China

Northern leaf spot, caused by Cochliobolus carbonum, is an important corn disease that is favored by the temperate mountain climate, and is the most important factor limiting the production of corn in Yunnan Province, China. Cultural characteristics and pathogenic diversity of 25 isolates of C. carbonum from Yunnan were studied. The isolates showed some variation in colony morphology and sporulation on potato lactose agar (PLA) medium. Pathogenicity test of the isolates on 8 differential corn inbred lines demonstrated that races 2 and 3 of C. carbonum caused the greatest losses in maize production in Yunnan. However, lines MU-4 and W-8053 were resistant to all race 3 isolates, whereas line s37 showed resistance response to all race 2 isolates. The pathogencity and virulence of all isolates were studied on 40 cultivars. The virulence varied with the fungal isolates. In general, race 3 isolates were more virulent than race 2 isolates, but 2 isolates of race 2 proved to be highly virulent and could cause great damage to corn. This information will be useful in the selection of cultivars/lines with different resistance genes for use in designing resistant corn breeding programs.