Browsing by Author "Donahue, Patrick J."

Now showing 1 - 2 of 2
  • Thumbnail Image
    A diallel study of stalk rot resistance in elite maize and its interaction with yield
    Donahue, Patrick J. (Virginia Polytechnic Institute and State University, 1986)
    Stalk rot reaction of maize (Zea mays L.) and its effect on yield was studied using 12 elite inbred parents (A619, A632, B73, H60, H93, H96, Mo17, Oh7B, Pa91, Va17, SS419, Va85) and all possible single crosses among them. The diallel study was conducted at Warsaw, Virginia in 1985. The experimental design was a split-plot with two stalk rot pathogens (Diplodia maydis and Fusarium moniliforme) and a control being the three whole plots and the inbreds described above and their single cross hybrids being the sub-plots. Plots were inoculated with the pathogens approximately three weeks following silking. Stalk rot scores and yield was taken four weeks following inoculation. Analyses of variance and combining ability analyses were performed on stalk rot scores and grain yield. There were no significant differences between the two pathogens for mean stalk rot score, but both were significantly higher in score than the control. Differences among the whole plots for mean yield were not significant. Hybrid/line by pathogen interactions were not significant for yield or stalk rot scores, indicating that the inbreds and their hybrids performed consistently across the pathogens and control. The estimates of GCA and SCA effects for stalk rot score both were significant with the GCA effects being the greater. This should indicate that stalk rot reaction would respond readily to selection in a breeding population. Per plant yields were not affected by the stalk rot treatments. Two Virginia lines, Val7 and Va85, were found to have both high yield and high levels of resistance to stalk rot, and should be good candidates for a breeding program stressing stalk rot resistance.
  • Thumbnail Image
    Inheritance of reactions to gray leaf spot and maize dwarf mosaic virus in maize and their associations with physiological traits
    Donahue, Patrick J. (Virginia Polytechnic Institute and State University, 1989)
    Gray leaf spot, caused by Cercospora zeae-maydis, can be a yield-limiting factor in maize where continuous minimum tillage practices are followed. Commercial corn hybrids were evaluated for response to gray leaf spot for seven years at two Virginia locations (Shenandoah and Wythe Counties) and one year at a third location in Virginia (Montgomery County). Yield losses, when comparing resistant to susceptible classes, were approximately 2,000 kg ha⁻¹ at Wythe County in 1982, 750 kg ha⁻¹ at Shenandoah County in 1984, and 2,150 kg ha⁻¹ at Montgomery County in 1988. The inheritance of reaction to gray leaf spot was studied using a 14 inbred diallel in Montgomery and Wythe Counties, Virginia in 1987 and 1988 planted in randomized complete block designs. Resistance was found to be highly heritable and controlled by additive gene action. Inbreds producing high yielding, resistant, and agronomically superior 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). Currently available inbreds could be used to produce hybrids with higher levels of resistance than hybrids currently available to growers, and these could serve as a basis for gray leaf spot breeding programs. Lesion size measurements were not correlated with disease scores. Late-season photosynthesis rates were associated positively with resistance. The hybrids of some inbreds were found to produce high levels of pigment (believed to be anthocyanins) around the gray leaf spot lesions. These did not limit the size of the individual lesion later in the season. Some pigment(s)-producing genotypes were found to be resistant when the pigment character was expressed. This type of resistance must prevent or inhibit infection of the leaf but not later colonization, once established. Maize dwarf mosaic virus (MDMV) also limits maize production in some areas where johnsongrass (Sorghum halepense L.) is a problem. Resistance to MDMV was found to be mainly additive and highly heritable. However, a strong specific combining ability component was found, indicating that the background of the material receiving resistance genes may have a strong effect on the expression of resistance. Inbreds capable of producing high-yielding, resistant, and agronomically acceptable hybrids are available (B68, NC250, A632, Pa875, Va17, and Va85); and several hybrids between these lines have high levels of resistance, high yield, and good general agronomic characters (B68 x KB1250, KB1250 x Pa875, and NC250 x Pa875).