Gray Leaf Spot Of Maize Research Articles

Quantitative Trait Loci Controlling Resistance to Gray Leaf Spot in Maize

Gray leaf spot (GLS) (caused Cercospora zeae‐maydis Theon & Daniels) is a fungal disease of the maize (Zea mays L.) that can cause significant grain yield reductions. Quantitative resistance to GLS does exist; therefore, one method of controlling the disease is to develop hybrids with genetic resistance. The objective of this study was to identify quantitative trait loci (QTL) and type‐of‐gene action for GLS resistance in segregating families of three single‐cross populations of maize using restriction fragment length polymorphisms (RFLPs). We also attempted to determine the consistency of QTL over environments and populations. Population 1 (POP1) consisted of 139 F2:3 families evaluated in three environments. Population 2 (POP2) consisted 193 F2:3 families 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 (susceptible) 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 associations 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, detectable individual markers accounted for 4 to 26% of the phenotypic variation. The QTL associated with GLS were inconsistent over environments, but the cause of these differences could not be determined. One region on chromosome 2 was associated with GLS resistance in POP1, POP2, and POP3. Additive gene action was displayed for nearly all markers associated with resistance.

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 ✕ KB1250, KB1250 ✕ Pa875, and NC250 × 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.

Inheritance of Resistance to Gray Leaf Spot in Maize1

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.