Characterizing pathotypes and haplotypes of Colletotrichum sublineolum in Arkansas

Sorghum anthracnose, caused by Colletotrichum sublineolum, is an important disease in nearly all grain sorghum production regions of the world. This disease is widely distributed in Arkansas and sporadic epidemics have occurred. Sorghum anthracnose can cause severe yield loss in susceptible grain sorghum hybrids by infecting and damaging leaves, stalks, peduncles, and panicles. It has been suggested that the most effective control strategies for sorghum anthracnose are crop rotation and disease resistance; however, disease resistance has often been unsuccessful because of high variability within the population of C. sublineolum. Little is known about the populations of C. sublineolum in Arkansas or their distribution within the state. The first objective of this study was to determine how many pathotypes exist in Arkansas and where these pathotypes are geographically located. Pathotypes 1 through 8 were previously described in the USA and Puerto Rico. These results show that two of the previous 8 pathotypes were found in Arkansas, but that 11 new pathotypes were discovered. Pathotype 9 is virulent to all 8 differentials and was found in all locations from which isolates were collected and comprised 53% of the total samples evaluated. The second objective examined the genetic diversity of these isolates by using amplified fragment length polymorphism (AFLP). Results show that genetic diversity is high and that the isolates were more closely related based on the year of collection rather than on where isolates were collected within the state. The third objective was to determine the level of resistance of grain sorghum hybrids grown in Arkansas to C. sublineolum pathotypes found in Arkansas. Results show that different levels of resistance exist in current grain sorghum hybrids to different pathotypes, but only one, Cargill 888Y, was resistant to all pathotypes in Arkansas. Asgrow A571, DEKALB DKS53-11, FFR 318, and Pioneer 84G62 were moderately susceptible to susceptible to every pathotype tested. The fourth objective determined the effect of crop rotations on the severity of sorghum anthracnose. Four rotations were evaluated: sorghum following sorghum, corn, soybeans, and rice. The results show that planting sorghum after corn, soybeans, or rice significantly reduced anthracnose severity. Resistance coupled with rotations provides an excellent management tool to control this disease. Overall these experiments should provide valuable information to growers and plant breeders to achieve higher yields and quality of the harvested crop.