QUANTITATIVE TRAIT LOCI CONTROLLING RESISTANCE TO GRAY LEAF-SPOT IN MAIZE

Gray leaf spot (GLS) (caused by Cercospora zeae-maydis Theon & Daniels ) is a fungal disease of the maize (Zea mays L.) that can cause signif icant grain yield reductions. Quantitative resistance to GLS does exis t; therefore, one method of controlling the disease is to develop hybr ids with genetic resistance. The objective of this study was to identi fy quantitative trait loci (QTL) and type-of-gene action for GLS resis tance in segregating families of three single-cross populations of mai ze using restriction fragment length polymorphisms (RFLPs). We also at tempted to determine the consistency of QTL over environments and popu lations. Population 1 (POP1) consisted of 139 F2:3 families evaluated in three environments. Population 2 (POP2) consisted of 193 F2:3 famil ies 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 (suscept ible) 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 as sociations 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, detectabl e individual markers accounted for 4 to 26% of the phenotypic variatio n. The QTL associated with GLS were inconsistent over environments, bu t the cause of these differences could not be determined. One region o n chromosome 2 was associated with GLS resistance in POP1, POP2, and P OP3. Additive gene action was displayed for nearly all markers associa ted with resistance.