Quantitative Trait Loci Controlling Resistance to Gray Leaf Spot in Maize

Abstract

Gray leaf spot (GLS) (caused Cercospora zeae‐maydis Theon & Daniels) is a fungal disease of the maize (Zea mays L.) that can cause significant grain yield reductions. Quantitative resistance to GLS does exist; therefore, one method of controlling the disease is to develop hybrids with genetic resistance. The objective of this study was to identify quantitative trait loci (QTL) and type‐of‐gene action for GLS resistance in segregating families of three single‐cross populations of maize using restriction fragment length polymorphisms (RFLPs). We also attempted to determine the consistency of QTL over environments and populations. Population 1 (POP1) consisted of 139 F2:3 families evaluated in three environments. Population 2 (POP2) consisted 193 F2:3 families and Population 3 (POP3) had 144 F2:3 families; POP2 and POP3 were considered as replicate populations evaluated in separate environments. Families were rated for GLS on a plot basis by a scale of 1 (susceptible) to 9 (resistant), and ratings were taken at 5‐ to 18‐d intervals in each environment. The QTL were identified on the basis of marker associations with GLS means over all ratings taken in an environment, as well as a GLS mean over environments for POP1 and over POP2 and POP3 for the replicate populations. Based on single‐factor ANOVA, detectable individual markers accounted for 4 to 26% of the phenotypic variation. The QTL associated with GLS were inconsistent over environments, but the cause of these differences could not be determined. One region on chromosome 2 was associated with GLS resistance in POP1, POP2, and POP3. Additive gene action was displayed for nearly all markers associated with resistance.