Inheritance of Resistance to Gray Leaf Spot of Corn

Host plant resistance can play an important role in reducing the severity of gray leaf spot (caused by Cercospora zeae‐maydis Tehon & Daniels) on corn (Zea mays L.). Inheritance of resistance was studied using four generations (inbred, single cross, F2, and backcross) produced from inbred lines PA875, VA59, B68Ht, H93, PA887P, and PA76‐22. Four weekly estimates of percent leaf area affected were made on experiments planted at Shenandoah County, Virginia, and Franklin County, Pennsylvania. Disease progress curves were estimated for each genotype using orthogonal polynomial regression. There were significant differences (P < 0.05) among genotypes for the mean, linear, and quadratic regression response effects within the inbred, single cross, and backcross generations and for the mean response effect within the F2 generation. No differences were detected among cubic effects in any of the generations. General combining ability (GCA) and specific combining ability (SCA) mean squares were significant (P < 0.01) for and linear response effects in diallel analyses of single crosses; GCA sums of squares were from 1.8 to 11.5 times larger than SCA sums of squares for these effects. Prediction of single cross performance using information from per se evaluation of inbreds resulted in r2 values of 0.55 to 0.67 for mean response effects and 0.33 to 0.45 for linear responseffects. Prediction of backcross performance using information from diallel analyses resulted in r2 values of 0.81 to 0.90 for mean response effects and 0.61 to 0.89 for linear response effects. Regression of area under the disease progress carve data onto two models based on complete dominance indicated that dominance was important. For the genotypestudied, a model more complex than simple additivity was required to fully explain inheritance of resistance to gray leaf spot; however, screening of inbreds prior to testing them for combining ability should be effective in eliminating those that are most susceptible.