Proposed nomenclature for pathogenic races of Exserohilum turcicum on corn.
A new system of race nomenclature for E. turcicum (Setosphaeria turcica) similar to that used for races of Phytophthora infestans is proposed. In the new system race designations are assigned according to the resistance genes that their virulence matches. Thus, isolates currently designated Race 1 become Race 0, indicating their lack of virulence on maize with any of the Ht genes, Race 2 becomes Race 1 to indicate its virulence to Ht1, and Races 3 and 4 become Races 23 and 23N, respectively. It is concluded that the system is useful as long as the number of resistance genes used in race identifications does not become so large as to be unwieldy and that at the current rate of identification and utilization of major genes for resistance to northern leaf blight in maize, the proposed system should remain useful for many years. Conditions under which race identifications should be carried out are outlined.