Pathogenicity, aggressiveness, and virulence of three species of Cercospora associated with gray leaf spot of maize

In the eastern United States, three genetically distinct species of Cercospora, the two sibling species of C. zeae-maydis (types I and II) and C. sorghi var. maydis, are routinely isolated from maize leaves exhibiting symptoms of gray leaf spot (GLS). To determine if resistance to GLS is species specific, we conducted field trials comparing four commercially available maize hybrids for resistance to four isolates of C. zeae-maydis type I, three isolates of C. zeae-maydis type II, two isolates of C. sorghi var. maydis, as well as isolates of C. sorghi from Sorghum spp., and C. kikuchii from soybean. Isolates within each of the two sibling species of C. zeae-maydis were highly variable in their aggressiveness on the hybrids. Resistance in maize to GLS appears to be equally effective against both type I and type II of C. zeae-maydis. Neither of the two isolates of C. sorghi var. maydis isolated from maize, the C. sorghi isolates, nor C. kikuchii were pathogenic on maize. These results indicate that aggressive isolates, regardless of which sibling species of C. zeae-maydis, should be used to select for GLS resistance in field trials.