QTL Mapping for Gray Leaf Spot Resistance in a Tropical Maize Population

A tropical gray leaf spot (GLS)-resistant line, YML 32, was crossed to a temperate GLS-susceptible line, Ye 478, to produce an F_2:3 population for the identification of quantitative trait loci (QTL) associated with resistance to GLS. The population was evaluated for GLS disease resistance and flowering time at two locations in Yunnan province. Seven QTL using GLS disease scores and six QTL using flowering time were identified on chromosomes 2, 3, 4, 5, and 8 in the YML 32 × Ye 478 maize population. All QTL, except one identified on chromosome 2 using flowering time, were overlapped with the QTL for GLS disease scores. The results indicated that QTL for flowering time in this population strongly corresponded to QTL for GLS resistance. Among the QTL, qRgls.yaas-8-1/qFt.yaas-8 with the largest genetic effect accounted for 17.9 to 18.1 and 11.0 to 21.42% of variations for GLS disease scores and flowering time, respectively, and these should be very useful for improving resistance to GLS, especially in subtropical maize breeding programs. The QTL effects for resistance to GLS were predominantly additive in nature, with a dominance effect having been found for two QTL on the basis of joint segregation genetic analysis and QTL analysis.