P-253 - Identification of quantitative trait loci for resistance to tar spot in corn

Tar spot, caused by the fungus Phyllachora maydis, is a foliar disease of corn that is endemic to Latin America and the Caribbean. Since its first detection in the U.S. during 2015, it has now spread throughout most corn-producing regions to become the most significant pathogen of the crop, causing an estimated $1.2 billion in losses during 2024 alone. Due to its recent appearance, little is known about resistance in adapted corn germplasm and most cultivars are highly susceptible. To identify potential new sources of resistance, parents and progeny of two corn populations were tested for tar spot severity over two years of field trials at the Purdue Pinney Agriculture Center in Wanatah, Indiana. Analysis of 199 progeny from the Nested Association Mapping (NAM) population CML52 by B73 identified quantitative trait loci (QTL) for resistance on corn chromosomes 5 and 9, although the latter was only identified in one of the two years. Analysis of 100 progeny from the Intermated B73 × Mo17 (IBM) population identified a QTL on chromosome 1. Interestingly, Inbred B73 was more susceptible than CML52 but less susceptible than Mo17. All of these QTL appear to be previously unreported. Candidate genes, some of which had possible functions in disease resistance, were identified in the genomic regions spanning the QTL peaks. Future research involves validating these QTL in additional populations and testing likely candidates by functional analysis in corn. Once validated, these QTL could help to protect U.S. corn crops in the future.