Phenotypic analysis of maize and maize-teosinte near isogenic lines for resistance to corn smut (<i>Ustilago maydis</i>)

Maize, a globally important staple crop, faces significant yield losses due to corn smut disease, caused by the fungal pathogen <i>Ustilago maydis</i>. Most cultivated maize lines lack genetic resistance, necessitating the identification of new resistance sources. This study evaluated resistance to <i>U. maydis</i> across diverse maize germplasm, including four maize inbred lines (B73, H95, Mo17, and Golden Bantam), three teosinte accessions (<i>Zea mays</i> ssp. <i>parviglumis</i>, <i>Z. mays</i> ssp. <i>luxurians</i>, and <i>Z. mays</i> ssp. <i>diploperennis</i>), and two maize-teosinte near-isogenic lines (NILs). Phenotypic resistance was assessed at the seedling and reproductive growth stages (ear and tassel) 7-, 10-, 14-, and 21-days post-inoculation with <i>U. maydis</i> at four inoculum concentrations. At the seedling stage, teosinte accessions demonstrated resistance to <i>U. maydis</i>, 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 <i>U. maydis</i> is based on genotype, developmental stage, and dose-dependent genetic resistance. The maize-teosinte NILs have genes associated with resistance to <i>U. maydis</i> that were derived from the teosinte parent, suggesting maize-teosinte NILs and teosinte are valuable genetic resources for enhancing <i>U. maydis</i> resistance in cultivated maize.