A green fluorescent protein-engineered haploid inducer line facilitates haploid mutant screens and doubled haploid breeding in maize

Northern corn leaf blight (NCLB) is a prevalent foliar disease in maize. Deployment of resistant cultivars is an effective way to control NCLB. In this study, 207 recombinant inbred lines derived from a K22 × By815 cross were planted in Yangling, China, in 2012 and 2013. NCLB score and lesion size were investigated after artificial inoculation. Significant phenotypic variation in NCLB resistance was observed in both years. Using a genetic map containing high-density single-nucleotide polymorphisms with average genetic distance of 0.74 cM, quantitative trait loci (QTL) for NCLB score and lesion size were analyzed. For NCLB score, four and three QTL were identified in 2012 and 2013, respectively. Two stable QTL were identified in both years. Of these, qNCLB5.04, located on chromosome 5 (bin 5.04), had the largest resistance effect, accounting for 19 and 20 % of the phenotypic variation in 2012 and 2013, respectively. For lesion size, six QTL were identified. Of these, one consensus QTL was associated with both lesion length and width, and the other five were associated only with lesion width. Among all QTL identified, only qNCLB5.04 was associated with both NCLB score and lesion size. Thus, our mapping results suggest that qNCLB5.04 could be a desirable target for marker-assisted selection for NCLB resistance in maize breeding programs.