The inheritance of anthracnose (Colletotrichum sublineola) resistance response in sorghum differential lines QL3 and IS18760

Anthracnose caused by the fungal pathogen C. sublineola is an economically important constraint on worldwide sorghum production. The virulence of C. sublineola pathotypes is determined by their capacity to colonize a set of eighteen diverse sorghum lines that exhibit variable resistance responses (named anthracnose-differentials) in the greenhouse. Understanding the genetic basis of these different resistance sources is necessary for its inclusion into sorghum breeding programs. In this study, 223 recombinant inbred lines (RILs) derived from crossing anthracnose-differentials QL3 (96 RILs) and IS18760 (127 RILs) with the common susceptible parent PI609251 were evaluated at four field locations in the United States (Florida, Georgia, Texas, and Puerto Rico) for their anthracnose resistance response. Both RIL populations were highly susceptible to Florida and Georgia pathotypes, while in Puerto Rico and Texas were segregating for anthracnose resistance response. A genome scan using a composite linkage map of 982 single nucleotide polymorphisms (SNPs) detected two genomic regions of 4.31 and 0.85 Mb on chromosomes 4 and 8, respectively, that explain 10-27% of the phenotypic variation in Texas and Puerto Rico. A subset of 43 highly informative RILs selected based on recombination events were evaluated against nine anthracnose pathotypes in the greenhouse. A genome scan showed that the 7.57 Mb region at the distal end of the short arm of chromosome 5 is associated with the resistance response against one pathotype from Arkansas. Comparative analysis identified the genomic region on chromosome 4 overlaps with an anthracnose resistance locus identified in another anthracnose-differential line, SC414-12E, indicating this genomic region is of interest for introgression in susceptible sorghum germplasm. Candidate gene analysis identified an R-gene cluster in a locus on chromosome 5 with high similarity to another R-gene cluster on chromosome 9 previously identified to be associated with anthracnose resistance.