Effects of pollination and plant genotype on Ustilago maydis disease development on the ears of maize inbreds and maize-teosinte near-isogenic lines

Ustilago maydis, the fungus that causes corn smut disease, leads to significant economic losses in maize cultivars. A key feature of successful plant pathogens is their ability to utilize the plant–pathogen relationship to influence disease progression. Greenhouse experiments examined how pollination and plant genotype affect disease incidence and severity of U. maydis infection. Four U. maydis susceptible maize inbreds (B73, H95, Mo17, and Golden Bantam), and two U. maydis resistant maize-teosinte near-isogenic lines (NIL1 and NIL2) were utilized for this work. Three-hundred and sixty plants (pollinated and unpollinated) from the six plant genotypes were inoculated with U. maydis and assessed based on five phenotypic traits [(1) disease incidence, (2) gall number, (3) gall weight, (4) disease severity, and (5) area under disease progress curve]. All pollinated plants demonstrated significantly (p < .001) lower disease incidence, gall number, gall weight, area under the disease progress curve, and severity in comparison to the unpollinated plants. Both pollinated resistant NILs demonstrated significantly (p < .001) less disease development than the pollinated susceptible maize plants and two unpollinated NILs. Therefore, disease resistance to U. maydis was dependent upon pollination and plant genotype. This provides novel evidence that pollination can significantly improve resistance to U. maydis in different plant genotypes. Enhanced disease resistance observed in the resistant NILs after pollination indicates pollination-mediated resistance is one of the resistance mechanisms functioning in the resistant NILs. Integration of pollination-mediated resistance and resistance introgressed from a maize progenitor will be useful for improving resistance to U. maydis and management of the disease.