INHERITANCE OF REACTION TO GRAY LEAF-SPOT IN A DIALLEL CROSS OF 14 MAIZE INBREDS

Gray leaf spot of maize (Zea mays L.), caused by Cercospora zeaemaydis Tehon & Daniels, is a limiting factor in some areas where continuous minimum tillage practices are followed. The inheritance of reaction to this pathogen was studied using a diallel of 14 elite inbreds. The 91 single crosses were grown in field nurseries in Montgomery and Wythe counties, Virginia, in 1987 and 1988 using randomized complete-block designs. Data on gray leaf spot disease ratings, plant lodging, grain yield, and grain moisture were taken during the growing season. Analyses of variance and combining-ability analyses were made on these data. Resistance was found to be highly heritable and controlled by additive gene action. Many widely used inbreds (B73, Pa91, Mo17, and A632) were susceptible to gray leaf spot, explaining why many of the commercially available hybrids do not show high levels of resistance. Inbreds that provide high yielding, resistant, and agronomically acceptable hybrids were identified (B68, NC250, Pa875, Va14, Va17, and Va85), and several hybrids between these lines had high levels of resistance, high yield, and good general agronomic characters (B68 X KB1250, KB1250 X Pa875, and NC250 X Pa875). The data suggest that inbred lines are available to produce agronomically acceptable hybrids with high levels of resistance to gray leaf spot. These inbreds could serve as a basis for breeding programs where leaf spot resistance is emphasized.