Mapping QTL Controlling Southern Leaf Blight Resistance by Joint Analysis of Three Related Recombinant Inbred Line Populations

Southern leaf blight (SLB) is a foliar necrotrophic disease of maize (Zea mays L.) caused by the ascomycete fungus Cochliobolus heterostrophus (Drechs.) Drechs. It is particularly important in warm humid parts of the world where maize is cultivated, such as the southern Atlantic coast area of the United States and parts of India, Africa, and Western Europe. Quantitative trait loci (QTL) for resistance to SLB disease caused by C. heterostrophus race O were identified in three maize recombinant inbred populations assessed in two environments: Clayton, NC, in the summer and Homestead, FL, in the winter. The three populations were derived from the crosses B73 x CML254, CML254 x B97, and B97 x Ki14. Each of these populations was derived from a cross between a temperate maize line (B73 or B97) and a tropical maize line (Ki14 or CML254). Quantitative trait loci were identified by separate analysis of each population and by joint connected and disconnected analyses of all the populations. The most significant QTL identified were on chromosomes 3, 8, 9, and 10. Joint analysis led to more precise position estimates than separate analysis in each case. Results are discussed in the context of previous SLB QTL analysis studies and a recent flowering time QTL study that used the same populations. The chromosome 8 and 9 QTL colocalized with previously identified flowering time QTL, which suggested that the perceived effect on SLB resistance at these QTL may have been mediated through an effect on flowering time.