Poster: Biology & Disease Mgmt: Genetics of Resistance
Exserohilum turcicum races causing northern leaf blight of corn in the North Central United States
J. Weems (1), C. Bradley (1) (1) University of Kentucky, U.S.A.
Northern leaf blight of corn, caused by Exserohilum turcicum, is a yield- reducing foliar disease that commonly occurs across the North Central U.S. Previous race population distribution studies identified five physiological races in the U.S. prior to 1995. For this study, 156 E. turcicum isolates from Illinois, Indiana, Iowa, Minnesota, North Carolina, Ohio, and Wisconsin were screened against corn differential lines containing Ht1, Ht2, Ht3, Htm1, and Htn1 resistance genes. Isolates were collected between 1979 and 1985 (n=13) and between 2007 and 2014 (n=143). Twenty physiological races were observed based on the responses of the differential corn lines. Races 0, 1, and 1mn were the most prevalent races, comprising 21%, 27%, and 13% of the isolates, respectively. Races were diverse within all states and years. Virulence to multiple Ht resistance genes within individual isolates was observed in 47% of those tested, with 3% of the isolates conferring virulence to all Ht resistance genes tested. Virulence to the Ht1, Ht2, Ht3, Htm1, and Htn1 resistance genes was present in 64%, 20%, 18%, 32%, and 27% of the E. turcicum isolates, respectively. Virulence to Ht resistance genes was fairly evenly distributed across states in isolates collected after 2008. Although Ht genes were still effective against several isolates, the use of quantitative resistance in conjunction with Ht genes would likely improve management of northern leaf blight in the North Central U.S.