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 (r(2) = 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.