Gene action in the inheritance of agronomic traits in intervarietal diallel crosses and relative importance of gene effects for quantitative characters in Zea mays L
An investigation was undertaken to determine gene action in the inheritance of agronomic traits in a diallel set of eight inbred lines of sweet corn and all possible Fl hybrids, including parents. Data were analyzed by Jinks and Hayman's diallel analysis for plant and ear height, weight with and without husk, shank and ear length, ear and cob diameter, kernel depth, and mid-silking days. Additive effects and environmental variations were significantly different from zero for April, June, and Combined dates of planting. Estimates of the component of variation due to dominance effects were significantly different from zero except for shank length and cob diameter in June and ear length in April planting. The parents carried an excess of dominant genes for plant height, ear length, weight with and without husk, mid-silking days, and an excess of recessive genes for shank length. Dominant and recessive alleles of each gene were distributed nearly equal among the parents for ear diameter, cob diameter, and kernel depth. Ear length, shank length, cob diameter, and mid-silking days for the June planting and ear height in Combined dates of planting were within the partial dominance range. Heritability estimates supported the conclusion that selection for weight with and without husk, mid-silking days, and ear height would be most effective and that selection for ear diameter, plant height, ear length, shank length, and kernel depth would be least effective. Eight inbred lines of sweet corn, including parents, Fl's, F2's, and first backcrosses were tested at two locations in one year. The population means obtained were used to estimate additive, dominance, additive x additive, additive x dominance, and dominance x dominance gene effects for nine quantitative agronomic traits. Additive gene effects appeared to be the most constant over locations for plant and ear height. Dominance gene effects for weight with and without husk, and ear length were more important than those of additive effects. The remaining types of gene effects indicated very little stability over locations for most of the agronomic traits studied. The relative magnitude of expected genetic gain expressed as a percentage F2 mean would suggest that rapid progress should be accomplished by selecting and recombining in early generations for plant height in the crosses AA 11 x AA 18 and AA 8 x 190a. Slower progress should be expected from crosses AA 18 x 190a, AA 11 x 245, AA 2 x AA 11, and AA 20 x P 39. For ear height, rapid progress should be expected from crosses AA 18 x AA 20, AA 11 x AA 18, AA 8 x 190a, and AA 2 x AA 11. For weight with husk, good progress should be expected from crosses AA 11 x AA 18, AA 11 x 245, AA 8 x 190a, AA 2 x AA 11, and AA 20 x P 39. For ear length, rapid progress should be expected from crosses AA 18 x 190a, AA 11 x AA 18, and AA 20 x P 39. For the nine crosses considered, it was concluded that most of the variation was due to additive and dominance gene effects with epistasis being some importance.
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