The inheritance of anthracnose (Colletotrichum sublineola) resistance 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 most effective strategy to safeguard yield is through the introgression of resistance alleles. This requires elucidation of the genetic basis of the different resistance sources that have been identified. 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 anthracnose in Florida and Georgia, while in Puerto Rico and Texas they 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 explained 10-27% of the phenotypic variation in Texas and Puerto Rico. In parallel, a subset of 43 RILs that contained 67% of the recombination events were evaluated against anthracnose pathotypes from Arkansas (2), Puerto Rico (2) and Texas (4) 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 the pathotype AMP-048 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 for the resistance locus on chromosome 5 identified an R-gene cluster that has high similarity to another R-gene cluster associated with anthracnose resistance on chromosome 9.

Genomic Dissection of Anthracnose (Colletotrichum sublineolum) Resistance Response in Sorghum Differential Line SC112-14.

Sorghum production is expanding to warmer and more humid regions where its production is being limited by multiple fungal pathogens. Anthracnose, caused by Colletotrichum sublineolum, is one of the major diseases in these regions, where it can cause yield losses of both grain and biomass. In this study, 114 recombinant inbred lines (RILs) derived from resistant sorghum line SC112-14 were evaluated at four distinct geographic locations in the United States for response to anthracnose. A genome scan using a high-density linkage map of 3,838 single nucleotide polymorphisms (SNPs) detected two loci at 5.25 and 1.18 Mb on chromosomes 5 and 6, respectively, that explain up to 59% and 44% of the observed phenotypic variation. A bin-mapping approach using a subset of 31 highly informative RILs was employed to determine the disease response to inoculation with ten anthracnose pathotypes in the greenhouse. A genome scan showed that the 5.25 Mb region on chromosome 5 is associated with a resistance response to nine pathotypes. Five SNP markers were developed and used to fine map the locus on chromosome 5 by evaluating 1,500 segregating F2:3 progenies. Based on the genotypic and phenotypic analyses of 11 recombinants, the locus was narrowed down to a 470-kb genomic region. Following a genome-wide association study based on 574 accessions previously phenotyped and genotyped, the resistance locus was delimited to a 34-kb genomic interval with five candidate genes. All five candidate genes encode proteins associated with plant immune systems, suggesting they may act in synergy in the resistance response.

Genome-Wide Association Mapping of Anthracnose (Colletotrichum sublineolum) Resistance in NPGS Ethiopian Sorghum Germplasm.

The National Plant Germplasm System (NPGS) Ethiopian sorghum [Sorghum bicolor (L.) Moench] collection of the United States is an important genetic resource for sorghum improvement. Anthracnose (Colletotrichum sublineolum) is one of the most harmful fungal diseases in humid sorghum production regions. Although multiple resistance sources have been identified in temperate-adapted germplasm in the Sorghum Association Panel (SAP), these resistance loci explain a limited portion of the total variation, and sources of resistance from tropical germplasm are not available for breeding programs at temperate regions. Using a core set of 335 previously genotyped NPGS Ethiopian accessions, we identified 169 accessions resistant to anthracnose. To identify resistance loci, we merged the genotypic and anthracnose response data for both NPGS Ethiopian germplasm and the SAP and performed genome-wide association scans using 219,037 single nucleotide polymorphisms and 617 accessions. The integrated data set enabled the detection of a locus on chromosome 9 present in the SAP at a low frequency. The locus explains a limited portion of the observed phenotypic variation (r2 = 0.31), suggesting the presence of other resistance loci. The locus in chromosome 9 was constituted by three R genes clustered within a 47-kb region. The presence of multiple sources of resistance in NPGS Ethiopian germplasm and SAP requires the inclusion of other resistance response evaluation that could revealed others low frequency resistance alleles in the panel.