Identification of Teosinte Alleles for Resistance to Southern Leaf Blight in Near Isogenic Maize Lines

Southern leaf blight ([SLB], causal agent Cochliobolus heterostrophus) is an important fungal disease of maize (Zea mays L.). Teosinte (Z. mays ssp. parviglumis), the wild progenitor of maize, offers a novel source of resistance alleles that may have been lost during domestication. The aims of this study were to identify teosinte alleles that, when present in a temperate maize background, confer a significant level of resistance to SLB. Ten populations of BC4S2 near isogenic lines (NILs), developed by crossing 10 different teosinte accessions to the maize inbred B73, comprising 774 lines in total, were screened for SLB resistance. Quantitative trait locus (QTL) analysis identified four significant QTL associated with SLB in bins 2.04, 3.04, 3.05, and 8.05. Sixteen individual NILs which were significantly different to the susceptible recurrent parent, B73 and which were carrying at least one of the teosinte-derived resistance alleles were used to develop F-2:3 populations by crossing each to B73 followed by two rounds of self-pollination. These F-2:3 populations were evaluated for SLB resistance and genotyped at the loci of interest. In 13 of 19 cases single marker analysis validated allelic substitution effects predicted from the original NIL population analysis, while in five cases we were not able to validate the effects and in one case a significant effect was detected in the opposite to the predicted direction. An allele at the QTL in bin 2.04 was shown to confer resistance to both SLB and a second maize foliar disease, gray leaf spot (GLS).