Identification of loci conferring resistance to four foliar diseases of maize.

Foliar diseases of maize are among the most important diseases of maize worldwide. This study focused on four major foliar diseases of maize: Goss's wilt (GW), gray leaf spot (GLS), northern corn leaf blight (NCLB) and southern corn leaf blight (SCLB). Quantitative trait locus (QTL) mapping for resistance to GW was conducted in four disease resistance introgression line (DRIL) populations with Oh7B as the common recurrent parent and Ki3, NC262, NC304, and NC344 as recurrent donor parents. Mapping results for GW resistance were combined with previous studies for GLS, NCLB and SCLB resistance in the same four populations. We conducted 1) individual linkage mapping analysis to identify QTL specific to each disease and population; 2) Mahalanobis distance analysis to identify putative multiple disease resistance regions for each population; and 3) joint linkage mapping to identify QTL across the four populations for each disease. We identified three lines that were resistant to all four diseases. We mapped 13 GW QTLs in the individual populations and an additional six using joint linkage mapping. All GW QTL had small effects, confirming that resistance to GW is highly quantitative. We report several potentially important chromosomal bins associated with multiple disease resistance including 1.02, 1.03, 3.04, 4.06, 4.08, and 9.03. Together, these findings indicate that disease QTL distribution is not random and that there are locations in the genome that confer resistance to multiple diseases. Furthermore, resistance to bacterial and fungal diseases are not entirely distinct, and we identified lines resistant to both fungi and bacteria, as well as loci that confer resistance to both bacterial and fungal diseases.