Genetic dissection of sorghum [Sorghum bicolor (L.) Moench] grain antimicrobial activity against Clostridium perfringens and its relationship with grain composition and field performance.

In the poultry industry, there is a growing interest in finding alternatives to synthetic antibiotics to maintain gut health, given the growing problems with antibiotic resistance in several pathogenic species. Antibiotics are especially used to control one of the most widespread and problematic diseases of poultry, necrotic enteritis, which is caused by Clostridium perfringens. Sorghum grain is known to have bioactive compounds that can provide antimicrobial (AM) activity, with most of these compounds being phenolics. Condensed tannins are produced by sorghum and known for their potent antioxidant and AM activity; however, they also have antinutritional effects in the poultry gut. Thus, the AM potential of non-tannin sorghum grain against C. perfringens was examined. Two distinct analyses were performed on a non-tannin recombinant inbred line (RIL) population to measure AM activity of the grain against C. perfringens: 1) a minimum inhibitory concentration (MIC) analysis with phenol extract of the grain, and 2) a qPCR-based approach to measure inhibition of C. perfringens in monoculture with in vitro enzymatically digested grain. It was found that the RIL population exhibited different levels of AM activity against the bacteria, with some lines having activity comparable to that of tannin sorghums, indicating that genotypes lacking functional Tan1 and Tan2 genes maintain a sufficient level of AM activity. Additionally, no negative impact on agronomic performance, grain productivity or quality traits was observed, while positive correlations were found with desirable traits such as grain yield and grain mold resistance. Furthermore, through QTL mapping, novel loci were identified associated with AM activity, with a major-effect QTL on chromosome 1 that was distinct from the location of the pericarp color gene YELLOWSEED1. Three other loci were identified on chromosomes 3, 4 and 6, having additive and interaction effects. This suggests that, although the AM activity is controlled by multiple interacting genes, there are some major-effect genes that could be targeted to increase this trait in breeding lines. In this biparental population, 23 RILs possessed optimal haplotypes to serve as AM activity donors for introgressing this trait into sorghum improvement programs.