Inheritance of Resistance to Gray Leaf Spot in Maize1

Abstract

Gray leaf spot disease (caused by Cercospora zeae‐maydis Tehon and Daniels) of maize (Zea mays L.) has the potential to become an important problem in U.S. maize production. Inheritance of resistance in maize to gray leaf spot disease was investigated using plant ratings from three experiments in naturally occurring field epiphytotics: Generation mean analysis of four populations, diallel analysis of all possible single crosses, and correlation comparison between 16 inbreds per se and their crosses with a common parent. Plants were rated just prior to leaf death on a plot basis utilizing a scale of 1 (resistant) to 5 (susceptible). In the generation mean experiment the susceptible parents, B73 and B73rhm, were rated 4.1 to 4.3 and resistant parents, H99 and NC250, 1.4. For populations from susceptible ✕ resistant parents, estimates of pooled additive effects were large. In the diallel experiment, the eight parents (N28rhm, B73rhm, B73, B73ARB, H99, NC250, Va59, and T234) were rated 4.4, 4.0, 4.1, 2.6,1.4,1.4,1.2, and 1.2 as inbreds per se and 3.3, 3.2, 3.2, 2.5, 2.5, 2.3, 2.3, and 1.8 in crosses, respectively (1985). Mean squares for general combining ability in analyses of variance were significant (P < 0.01) but those for specific combining ability were not (P > 0.05). The 16 inbreds per se were correlated with their ratings in crosses at 0.69 (P < 0.01). Resistance to gray leaf spot in the maize genotypes tested was conditioned mainly by additive effects, was not very complex, could be evaluated effectively using inbreds per se, and may be transferred by usual backcrossing and selection techniques.