Differences in ergot vulnerability among sorghum genotypes and the relationship between stigma receptivity and ergot vulnerability

Abstract

The arrival of sorghum ergot (Claviceps africana) to the Americas poses a new threat to sorghum production. Reported for the first time in Brazil in 1995, the disease quickly moved to North America in less than two years. By determining if there are differences in ergot vulnerability between and among types of sorghum germplasms, and determining the reasons for such differences, researchers might be able to develop more effective ergot control strategies, such as ergot resistant germplasm for the future. The objectives of this research were (1) to characterize the relative rate of ergot vulnerability of a set of publicly available and commercially used A, B, R-lines, and hybrids; (2) to determine the relationship between the duration of stigma receptivity and ergot vulnerability; and (3) to determine the stability of ergot resistance among the inbred lines and hybrids evaluated. Ergot vulnerability ratings were determined for twelve pairs of sorghum A/B-lines, twelve R-lines, and twelve hybrids at seven environments in four locations during 1998. A-lines were the most vulnerable to the disease, followed by hybrids, R-lines and B-lines. Variation in ergot vulnerability among types of sorghum germplasm was detected as well; however, all genotypes evaluated were vulnerable to the disease. To determine the relationship between stigma receptivity and ergot vulnerability, sixteen sorghum genotypes that resulted from crossing four sorghum B-lines in all possible combinations (n² diallel) were evaluated. It was determined that stigma receptivity is not the only factor that influences ergot infection, since the data indicate that ovules no longer receptive to pollen can still be infected by ergot. Also, inconsistency across environments of the genetic effects related to the "resistance" of the genotypes evaluated, indicated a possible "pseudoresistance" mechanism that is operating accordingly to specific environmental conditions, which allow certain germplasms to escape disease infection.