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Epistatic and Other Genetic Variances in Two Varieties of Maize¹

We obtained full-sib and half-sib covariances in two open-pollinated varieties of maize, ‘Jarvis’ and ‘Indian Chief,’ from families derived from both inbred and noninbred parents. These covariances provide estimates of additive, dominance, and certain estimable functions of epistatic variances, and are useful to investigate the relative importance of the different types of genetic variation in these varieties.

Seven characters were studied in both varieties, and no evidence of epistatic variance was noted except possibly for yield in Indian Chief. During development of the random inbred lines natural selection increased ear number and yield in both varieties. It may also have reduced the total genetic variance for characters that showed no change in the mean.

Both the observed and "expected" standard errors were smaller for estimates of variance components obtained from the Design II than from the Design I experiments. Observed standard errors of the experimental error variances were larger than "expected standard errors" for both Designs.

Additive variance appeared to account for the largest proportion of the total genetic variance for all characters in both varieties. Hence, recurrent selection should be effective in improving these varieties.

² Formerly graduate assistant and Geneticist Crops Research Division, ARS, USDA, Raleigh, N.C. (now Research Geneticist, Crops Research Division, ARS, USDA, Kitale, Kenya); Professor of Genetics; Administrative Dean for Research and Professor of Genetics; and Professor of Statistics, respectively.

Received for publication November 30, 1965.

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