Genome-wide association mapping of grain mold resistance in the U.S. sorghum association panel

Authors: Cuevas, Hugo; FERMIN-PEREZ, RAMON - University Of Puerto Rico; Prom, Louis; COOPER, ELIZABETH - University Of North Carolina; Bean, Scott; ROONEY, WILLIAM - Texas A&M University

Submitted to: The Plant Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2019
Publication Date: 4/11/2019
Citation: Cuevas, H.E., Fermin-Perez, R.A., Prom, L.K., Cooper, E., Bean, S.R., Rooney, W.L. 2019. Genome-wide association mapping of grain mold resistance in the U.S. sorghum association panel. The Plant Genome. 12:180070.

Interpretive Summary: The identification of sorghum accessions resistant to grain mold in temperate-adapted germplasm is imperative to sustain productivity and profitability in the United States. Therefore, 335 temperate-adapted accessions representing genetic diversity of public and private breeding programs were evaluated for grain mold resistance based on seed mold deterioration and germination rate for three consecutive years. Eighteen accessions exhibited grain mold resistant response while phylogenetic analysis suggests the presence of multiple resistance sources. Two resistance loci at chromosome 1 and 8 were associated with less seed deterioration and another at chromosome 10 associated with germination rate. These loci and the grain mold resistance germplasm identified herein could be used in breeding programs to develop new resistant cultivars.

Technical Abstract: Sorghum [Sorghum bicolor (L.) Moench] production include warm and humid regions, but its productivity and profitability in these regions is being limited by grain mold disease. Because grain mold can be caused by a complex of more than forty pathogenic and opportunistic fungi. Many cultivars are affected, thus the identification of resistant plants within temperate-adapted germplasm is imperative to the development of better adapted varieties. We evaluated the performance of 331 accessions available to breeders from the previously genotyped Sorghum Association Panel (SAP) in four tropical environments, and found that only eighteen accessions were either partially or totally resistant. Resistant accessions showed both high and low tannin content in their seed along with phenotypic variation in panicle shape, indicating that grain mold resistance is not associated with any single phenotypic trait. Seed mycoflora analysis recovered pathogenic fungi in both resistant and susceptible accessions suggesting that the resistance mechanisms in these accessions function by limiting pathogen growth instead of preventing infection or completely destroying the fungi from the seed. Genome-wide association scans were conducted using 268,289 single-nucleotide polymorphisms to identify three loci; two associated with less seed deterioration on chromosomes 1 and 8, and another associated with germination rate on chromosome 10. Candidate genes within these loci include one R-gene and two genes with domains associated with Systematic Acquired Resistance (SAR) proteins, suggesting the resistance response involved both pathogen recognition and downstream signaling cascades. Our study provides insight into the genetic basis of grain mold resistance and identifies valuable accessions to enhance breeding programs in temperate environments.