Ergosterol as an indicator of mold resistance in white and colored grain sorghum hybrids

Grain mold is a serious disease of sorghum causing both qualitative and quantitative losses in grain production. There has been a drastic reduction in area and production in India due to the lack of resistant varieties to manage the disease. Genetic improvement for mold resistance has been suggested as a sole criterion for reducing losses associated with grain mold and several morphological and biochemical traits have been employed to aid screening for resistance. However, there is always a bias with visual scoring systems to rate disease severity; thus, ergosterol and flavan-4-ols content within the grain was evaluated as selection criteria. Twenty-five hybrids were selected based on their visual rating for grain mold resistance and grain color from replicated trials at two locations in India during 2004 and 2005 rainy seasons and grouped into colored resistant, white resistant, colored susceptible and white susceptible. The field grade score (FGS) and threshed grade score (TGS) were strongly and positively correlated with ergosterol content and weakly and negatively correlated with flavan-4-ols. Though the resistant hybrids had higher concentration of flavan-4-ols in methanol and acidified methanol extract compared to the susceptible hybrids, the white grained hybrids had negligible amounts indicating flavan-4-ols concentration is not a suitable selection criterion especially in white grained hybrids. The ergosterol content was higher in susceptible hybrids (19.49 μg/g) compared to resistant hybrids (9.96 μg/g) and it was marginally less in red hybrids (14.0 μg/g) compared to white (17.2 μg/g) hybrids. The highly significant correlation of ergosterol content with germination percentage, FGS and TGS validates the use of this trait for identification of grain mold resistant genotypes provided there is no delay in the estimation. Also the significant heterosis obtained for this trait indicates the existence of dominance gene action and suggests that further exploitation of this trait would benefit the development of grain mold resistant hybrids