Mining alleles for tar spot complex resistance from CIMMYT's maize germplasm bank

Authors: WILLCOX, MARTHA - University Of Wisconsin; BURGUEÑO, JUAN - International Maize & Wheat Improvement Center (CIMMYT); Jeffers, Dan; RODRIGUEZ-CHANONA, ENRIQUE - International Maize & Wheat Improvement Center (CIMMYT); GUADARRAMA-ESPINOZA, ARMANDO - Corteva Agriscience; KEHEL, ZAKARIA - The International Center For Agricultural Research In The Dry Areas(ICARDA); CHEPETLA, DANIEL - International Maize & Wheat Improvement Center (CIMMYT); SHRESTHA, ROSEMARY - International Maize & Wheat Improvement Center (CIMMYT); SWARTS, KELLY - Austrian Academy Of Sciences; HEARNE, SARAH - International Maize & Wheat Improvement Center (CIMMYT); Buckler, Edward - Ed; CHEN, N - Oklahoma State University

Submitted to: Frontiers in Sustainable Food Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2022
Publication Date: 8/2/2022
Citation: Willcox, M.C., Burgueño, J.A., Jeffers, D., Rodriguez-Chanona, E., Guadarrama-Espinoza, A., Kehel, Z., Chepetla, D., Shrestha, R., Swarts, K., Hearne, S., Buckler IV, E.S., Chen, N.C. 2022. Mining alleles for tar spot complex resistance from CIMMYT's maize germplasm bank. Frontiers in Sustainable Food Systems. 6:937200. https://doi.org/10.3389/fsufs.2022.937200.
DOI: https://doi.org/10.3389/fsufs.2022.937200

Interpretive Summary: Tar spot complex (TSC) is a devastating disease of corn occurring in 17 countries throughout Central, South and North America and the Caribbean which can cause grain yield losses of up to 80%. As yield losses from the disease continue to intensify in Central America, the first report of the disease in the United States occurred in 2015, followed by detection in Ontario, Canada, in 2020. Both the distribution and yield losses due to TSC are increasing, and there is a critical need to identify the genes for resistance to this disease. The Seeds of Discovery Initiative at the International Corn and Wheat Improvement Center (CIMMYT), has sought to combine cutting edge molecular biology tools and traditional disease resistance evaluations to identify valuable genes in historical farmer's corn varieties, to use in corn breeding programs. A subset of key traditional varieties were used to pollinate CIMMYT hybrids to form 918 combinations that were evaluated during 2011 and 2012 for TSC disease reaction. A total of 16 unique genes were identified for TSC disease resistance that also had high grain yield. These genes were confirmed by evaluating disease resistance in new combinations. We demonstrated the usefulness of using modern genetic tools with traditional disease resistance evaluations to identify unique sources of valuable genes found in traditional corn varieties, which can be critical in finding resistance to new corn diseases.

Technical Abstract: Tar spot complex (TSC) is a devastating disease of maize occurring in 17 countries throughout Central, South and North America and the Caribbean which can cause grain yield losses of up to 80%. As yield losses from the disease continue to intensify in Central America, the primary pathogen of the complex, Phyllachora maydis, was first detected in the United States in 2015, and in 2020 in Ontario, Canada. Both the distribution and yield losses due to TSC are increasing, and there is a critical need to identify the genetic resources for TSC resistance. The Seeds of Discovery Initiative at CIMMYT has sought to combine next-generation sequencing technologies and phenotypic characterization to identify valuable alleles held in the CIMMYT Germplasm Bank for use in germplasm improvement programs. Individual landrace accessions of the “Breeders' Core Collection" were crossed to CIMMYT hybrids to form 918 unique accessions-topcrosses (F1 families) which were evaluated during 2011 and 2012 for TSC disease reaction. A total of 16 associated SNP variants were identified for TSC disease resistance and increased grain yield. These variants were confirmed by evaluating TSC reaction of previously untested selections of the larger F1 testcross population based on presence of identified favorable SNPs. We demonstrated the usefulness of mining for donor alleles in germplasm bank accessions for newly emerging diseases using genomic variation in landraces.