Phenotypic Analysis of Maize and Maize-Teosinte Near-Isogenic Lines for Resistance to Corn Smut (Ustilago maydis)

Maize, a globally important staple crop, faces significant yield losses due to corn smut disease, caused by the fungal pathogen Ustilago maydis. Most cultivated maize lines lack genetic resistance, necessitating the identification of new resistance sources. This study evaluated resistance to U. maydis across diverse maize germplasm, including four maize inbred lines (B73, H95, Mo17, and Golden Bantam), three teosinte accessions (Zea mays ssp. parviglumis, Z. mays ssp. luxurians, and Z. mays ssp. diploperennis), and two maize-teosinte near-isogenic lines (NILs). Phenotypic resistance was assessed at the seedling and reproductive growth stages (ear and tassel) at 7, 10, 14, and 21 days postinoculation with U. maydis at four inoculum concentrations. At the seedling stage, teosinte accessions demonstrated resistance to U. maydis, while maize inbreds showed varying levels of susceptibility. The maize-teosinte NILs had better resistance than maize genotypes at the seedling and reproductive stages, with up to 75% fewer ear/tassel galls and 65% less area under the disease progress curve. This enhanced resistance likely stems from introgressed teosinte genomic segments, particularly a 3.9-Mbp region on chromosome 9. Resistance differed across developmental stages and exhibited dose-dependent responses to inoculum concentration. These results suggest that resistance to U. maydis is based on genotype, developmental stage, and dose-dependent genetic resistance. The maize-teosinte NILs have genes associated with resistance to U. maydis that were derived from the teosinte parent, suggesting maize-teosinte NILs and teosinte are valuable genetic resources for enhancing U. maydis resistance in cultivated maize.