QTL MAPPING OF MAIZE RESISTANCE TO EAR ROT AND MYCOTOXIN CONTAMINATION CAUSED BY FUSARIUM VERTICILLIOIDES USING GENOTYPING BY SEQUENCING

Fusarium verticillioides (FV) is a fungal maize pathogen that causes Fusarium ear rot (FER) and contaminates the grains with fumonisins, a family of carcinogen mycotoxins. Maize genotypes show quantitative genetic variations for resistance to FER and fumonisin B1 (FB1) accumulation. Moreover both traits have moderate -high heritability. For these reasons Marker Assisted Selection of resistant genotypes is an attractive approach to reduce the losses derived from this fungal infection. The outcome of the infection is strongly influenced by environmental conditions and the disease severity vary greatly among years. A careful phenotyping of the population has a central role in a precise QTL mapping of traits related to resistance to FER and FB1 accumulation. The resistant (CO441) and the susceptible (CO354) lines to FV infection were crossed and generated 180 F2:3 segregant maize families. The population was evaluated for resistance to FER and FB1 accumulation in two sowing times, early and late, of both 2011 and 2012. Phenotyping was conducted on artificially inoculated F3 ears at 15 days after pollination with two methods (sideneedle, inoculation with spores, and toothpick, inoculation with mycelium). FER resistance was evaluated at maturity using a 1-7 rating of Fusarium infection on the ears, corresponding respectively to 0 and 100% of the infected ear. FB1 accumulation in the grains was predicted by NIR spectroscopy. In parallel, a molecular linkage map was constructed for the CO441xCO354 progeny (157 F3 DNA pools and the parents) using a Genotyping-by-Sequencing (GBS) approach (PLoS ONE 6(5):e19379). Initial analyses identified 16.236 SNP markers. Stringent criteria for SNP calling and filtering, segregation distortion and the setting of a threshold for missing data generated a set of 339 SNPs. These markers were integrated with genotyping data from 72 SSRs to construct a more dense linkage map. A total of 16 and 14 QTLs for FER resistance and FB1 accumulation were detected using MQM analysis, and 5 of them were overlapped between the two traits. These small-moderate effect QTLs were mainly detected in 1, 2, 4-9 maize chromosomes