QTL Mapping of Quantitative and Qualitative Measures of Resistance to Fusarium Ear Rot in Maize

Infection by Fusarium verticillioides in maize can cause Fusarium ear rot (FER) and subsequent accumulation of the mycotoxin fumonisin in the grain, which can result in devastating yield losses and serious health risks for humans and animals. Resistances to FER and fumonisin contamination are quantitative in nature, moderately to highly heritable, and strongly genetically correlated with each other, indicating that selection for resistance to fumonisin contamination can be indirectly and effectively accomplished via selection for resistance to FER, which is less costly to phenotype. In this study, four families of recombinant inbred lines (RILs) from the maize nested association mapping (NAM) population were used to identify quantitative trait loci (QTL) associated with both quantitative and qualitative measures of resistance to FER. The NAM, consisting of 25 families of RILS, was screened for FER in 2012, and the four families with the best performance and the highest levels of segregation for FER were chosen for further evaluation in 2013. These families included the CML52xB73, CML69xB73, CML333xB73, and NC358xB73 RILS. In 2012, FER was quantitatively measured based on the percentage of the ear presenting disease symptoms (0-100% scale with 5% increments). In 2013, FER was both quantitatively and qualitatively measured. Qualitative scoring was based on the primary FER type per plot (moldy, severe discoloration, starbursting, brown staining, blushing, or asymptomatic). The inclusion of FER type as a covariate in QTL mapping of the quantitative measure of FER resistance was also assessed.