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Genetics

Type of Gene Action in the Resistance to Maize Chlorotic Dwarf Virus in Corn. Eugen Rosenkranz, Plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, and professor, Department of Plant Pathology and Weed Science, Mississippi State University, Mississippi State 39762; Gene E. Scott, Supervisory agronomist, ARS, USDA, and professor, Department of Agronomy, Mississippi State University, Mississippi State 39762. Phytopathology 77:1293-1296. Accepted for publication 26 January 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1987. DOI: 10.1094/Phyto-77-1293.

A six-parent diallel cross, comprised of three maize chlorotic dwarf virus (MCDV)-resistant (Ky122, Mp444, and Tx29A) and three MCDV-susceptible (AR234, Ky21, and T131) corn inbred lines, was chosen to estimate the genetic variance of host response to MCDV, and thus gain information on the type of gene action involved in the resistance to MCDV in corn. The 15 possible crosses (without reciprocals) were grown during 2 yr in a screenhouse into which leafhoppers from viruliferous colonies of Graminella nigrifrons were released at the rate of six and 12 insects per plant in 1984 and 1985, respectively. Each year, about 125 plants of each cross were evaluated for the presence of tertiary vein clearing, the diagnostic symptom of maize chlorotic dwarf. The results were consistent under the two levels of inoculum pressure. In both years, the mean disease incidence of the nine resistant (R) × susceptible (S) crosses was equal or similar in magnitude to the mean disease incidence for the combined three R × R and the three S × S crosses. The diallel analysis of the disease incidence data showed a relatively large and highly significant mean square for general combining ability and a relatively small and statistically nonsignificant mean square for specific combining ability. Thus, our results indicate that the total genetic variance in host response to MCDV among the 15 crosses was contained in the general combining ability, suggesting additive gene action, and that nonadditive gene action (dominance variance) was absent because the variance for specific combining ability was insignificant.