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Reciprocal Differences and Combining Ability for Corn Earworm Injury among Maize Single Crosses¹

Reciprocal differences and combining abilities for corn earworm [Heliothis zea (Boddie)] injury were determined for single crosses among ten southern adapted maize (Zea mays L.) inbreds. Specific combining ability effects approached general combining ability effects in terms of their relative importance in conditioning resistance to injury by the corn earworm. Highly significant genotype-environment interactions occurred for both general and specific combining abilities. Reciprocal effects were highly significant during one of 2 years but nearly disappeared in the combined analysis by way of a genotype-environment interaction.

Constant parent regression (c.p.r.) analysis revealed significant amount of dominance for earworm injury, nearing the complete dominance level. The size of negative c.p.r., values for some inbreds suggested the presence of overdominance for resistance to earworm injury. In general, nonadditive effects appear to be nearly as important as additive effects in producing plant resistance. Reciprocal effects may interfere with identification of resistant genotypes through their interaction with specific enviromnents, but may normally be ignored as important genetic determinants. Consideration of the reciprocal differences and combining abilities obtained for these inbreds and crosses as selection criteria are discussed.

Key Words: Zea mays (L.) • Host plant resistance • Heliothis zea (Boddie) • Dominance • Gene action

² Research Geneticist, Plant Science Research Division, Agricultural Research Service, U.S. Department of Agriculture, Tifton, Ga. 31794.

Received for publication October 8, 1971.