Estimating Genetic Variance in Maize by Use of Single and Three‐way Crosses among Unselected Inbred Lines¹

Abstract

Unweighted least squares and maximum likelihood procedures were used and compared for the estimation of genetic variance for eight quantitative traits in maize (Zea mays L.). The genetic material was developed from unselected inbred lines isolated from a strain of Krug Yellow Dent maize. All possible single and 3‐way crosses were produced from 60 inbred lines, which traced back to 51 S0 plants. The mean squares from the diallel and triallel analyses were used in estimating the genetic components of variance.Fitting the error and a six‐parameter genetic model showed that: 1) it was not possible to obtain realistic estimates of the epistatic components, although significant effects were detected in the analyses of variance; 2) the estimates of additive geuetic variance were significant for all traits for both estimation procedures; 3) the nonadditive components accounted for only a small proportion of the total genetic variance; 4) three iterations of the maximum likelihood procedure were sufficient to stabilize the estimates; and 5) the maximum likelihood procedure generally reduced the errors of the estimates.For the two‐parameter genetic model the largest proportion of the total genetic variance was additive for all traits. The estimates of deviations due to dominance were larger than twice their standard errors for all traits in the two‐parameter model for the combined single and three‐way cross data. The frequency of significant interactions with environments was higher for the additive than for the dominance effects.

Combining ability for femaleness and yield in single and 3-way crosses of pickling cucumbers intended for once-over harvest

“…In our study, additive effects (GCA) were found to be relatively more important than nonadditive effects (SCA) for female expression and yield . This agreed with results obtained in agronomic crops, e .g ., Zea mays (SPRAGUE & TATUM, 1942 ;WRIGHT et al ., 1971) and Medicago sativa (CARNAHAN et al ., 1960) ; and in horticultural crops, e .g ., Lycopersicon esculentum (CURRENCE et al ., 1944 ;IBARIA et al ., 1969 ;PUNZALAN & LAMBETH, 1970), Cucumis melo (LIPPERT & LEGG, 1972a ;1972b), Cucumis sativus (SMITH et al ., 1978), Brassica oleracea (JOHNSTON, 1968) ; and Pisum sativum (KRAUP & DAVIS, 1970) in the situation where inbred parental lines had not been previously subjected to selection for GCA . However, EL-SHAWAF & BAKER (in press) found that pickling cucumber lines previously selected for yield displayed lower SCA than GCA for yield, probably due to inadequate selection pressure or limited genetic diversity in the parental population .…”

Relation among full-sib progenies of maize (Zea mays L.) for different generations of inbreeding

“…Eberhart et al C1966) emphasized that reliable estimates of genetic variances with small standard errors can only be obtained from large experiments, repeated over an adequate sampling of environments. Wright et al (1971) reported that regardless of the estimation procedure used, the largest proportion of the total genetic variance was additive for all traits, and in general, these results agree with those obtained by using simpler mating designs for maize populations. Obilana and Hallauer (1977) concluded that valid estimates of genetic variability can be obtained in less time and at a cheaper cost from nonlnbred materials.…”

Comparison of half-sib and S1 recurrent selection in 'Krug Yellow Dent'

“…Second, the predicted gains based on estimates of the additive genetic variance in Krug (Wright et al, 1971) resulted in similar values to those given by Burton et al (1971) and those reported here.…”