Pathotypes of Colletotrichum sublineolum in Arkansas

Sorghum anthracnose, caused by Colletotrichum sublineolum, is widely distributed in most grain sorghum-producing areas in Arkansas, and localized epidemics continue to occur across the state. The objectives of this research were to determine the number of pathotypes of C. sublineolum in Arkansas and to determine where these pathotypes are located within the state. Ninety-eight isolates were collected from research stations and production fields located in the Delta region of Arkansas from 2003 through 2005 and were tested for virulence to eight differential grain sorghum breeding lines. Of these, 11 isolates produced conflicting and unreliable results and were excluded from further analysis. Among the remaining 87 isolates, 13 pathotypes were identified. Eleven of these pathotypes were previously unreported, with 53% of the isolates consisting of pathotype 9. Pathotype 9 was distinguished from all other pathotypes by its virulence to all eight differential lines. Pathotype diversity appeared to be more closely associated with the year than with the locations where isolates were collected. Although all host differential lines were susceptible to at least 50% of the isolates evaluated, inbred lines SC326-6, TAM428, and TX2536 were susceptible to more than 90% of the 87 isolates evaluated. These results showed that the C. sublineolum populations in Arkansas are diverse based on the comparisons of pathogenicity to previously published host differentials, and it appears that these field populations varied from year to year.