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Reaction in Diallel Crosses of Corn Inbreds (Zea mays L.) to Maize Dwarf Mosaic Virus¹

Two six-parent sets of crosses, each consisting of three resistant inbreds and three susceptible inbreds, were grown under heavy natural infections of maize dwarf mosaic virus (MDMV) in two locations in Tennessee in 1968. Highly significant differences among genotypes were obtained in all experiments for reaction to the virus. White inbred Ga209 and yellow inbred T232 were the most resistant both as inbreds and in F₁ crosses. Mean MDMV ratings for R x R, R S, and S x S crosses were 1.09, 1.78, and 3.41, respectively. The data showed that resistance to MDMV was largely dominant and was controlled by only a few major genes. Indications were that minor genes also were necessary for a high degree of resistance. General combining ability effects for reaction to MDMV were highly significant and were more important than specific effects. Significant specific effects were associated with crosses involving highly susceptible inbreds. Hybrids having high tolerance are obtainable from crosses involving these resistant inbreds. The data indicate that a backcrossing procedure can be used to transfer the resistance factors into elite lines. Alternating generations of backcrossing with selfing or sib-pollination of resistant plants will facilitate incorporation of any minor genes necessary for a high degree of resistance. Some form of recurrent selection in populations having a degree of resistance also is suggested.

Key Words: Inheritance • Dominance • Resistance • Susceptibility

² Research Agronomist, Plant Science Research Division, ARS, USDA, Knoxville, Tenn. 37901, and USAID Graduate Student (India).

Received for publication February 24, 1971.