Inheritance Of Resistance To Gray Leaf Spot Of Corn

Twenty-four corn inbreds, selected for resistance to gray leaf spot (caused by Cercospora zeae-maydis) in 1989 and 1990, were crossed with the susceptible inbreds FR1141 and/or FR20 and populations of four to six generations were produced. In 1991, the populations were evaluated for gray leaf spot severity at Urbana, Illinois and at Andrews, North Carolina. Using generation mean analysis, additive genetic effects were found significant for most populations and dominance effects were found significant for eight populations. Significant parameter estimates for dominance effects were negative indicating dominance for resistance. Five inbred lines 061, 198, B37HtN, DS:74:1071, and (OH43x#8brbr) were selected for further evaluation based on their level of resistance, results from the generation mean analysis, and maturities useful for breeding in Central Illinois. The five inbred lines selected in 1991 were crossed with FR1141. The inbreds 061, B37HtN, and (OH43x#8brbr) also were crossed with the inbreds FR20, B37, and OH43 respectively. Eight populations of six to nine generations were produced from these crosses and evaluated for gray leaf spot severity in 1992 and 1993 at Urbana, Illinois and Andrews, North Carolina. Individual plants were rated for gray leaf spot severity by visually estimating the percent leaf area blighted in August and again in September. Analyses of variance indicated significant interactions between generations and environments and rating times for certain populations. Generation mean analyses indicated that pooled additive effects and pooled dominance effects were adequate to explain the inheritance of resistance for three populations, FR20 x 061, FR1141 x (OH43x#8brbr), and OH43 x (OH43x#8brbr). For the other populations there were significant deviations from the additive-dominance model at certain year-location-rating time combinations. For the FR1141 x DS:74:1071 population, additive effects were most important. Significant dominance effects were most frequently detected at early rating times and were most important for the FR1141 x 061, FR1141 x 198, FR1141 x (OH43x#8brbr), and OH43 x (OH43x#8brbr) populations. Epistatic effects were most important for the B37 x B37HtN population. Based on the level of resistance, heritability estimates, and estimates of effective factors for these populations, genes for resistance from these inbred lines should be useful in improving corn belt germplasm for resistance to gray leaf spot.