Expression of nuclear-cytoplasmic interactions on quantitatively inherited traits from interspecific matings of oat (Avena sativa L. and A. sterilis L.)

Beavis, William
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From a biological perspective, cytoplasmic effects are probably due to interactions of nuclear and cytoplasmic factors. For example, an enzyme involved in photosynthesis, ribulose-1,5-biscarboxylase, is encoded by both cytoplasmic and nuclear DNA. In this study, the phenomena of cytoplasmic and nuclear-cytoplasmic interaction effects on quantitatively inherited traits of oats (Avena sativa L. and A. sterilis L.) were investigated;Genetic models were fit to generation means of isopopulations from four matings involving A. sterilis accessions and the Cornbelt oat (A. sativa) variety 'CI 9170'. One mating had an isopopulation that exhibited nuclear-cytoplasmic heterosis. The models accurately described generation means in three matings and included additive nuclear and cytoplasmic interaction effects. It appeared that assumptions that simplified the algebra of the genetic models caused a lack of fit in one mating, and that alternative models should be developed. Based upon the best fitting model for each mating, predicted graing yield of advanced backcross generations was calculated. Actual grain yields of advanced backcross populations did not agree with the predicted values;The failure of the genetic models to describe generation means from all four matings prompted the development of an alternative model based upon molecular studies of cytoplasmic genetics. Unlike the nuclear genome, the cytoplasmic genome (a) consists of single, circular, duplex molecules of DNA, (b) is transmitted solely through the maternal parent in oats, and (c) exhibits little or no variability within cytoplasmic lines of descent. These biological features were incorporated into a quantitative genetic model which describes the genotypic value of an individual. The model was used to derive theoretical components of genetic variability in random mating population. Estimation of some variance components from the model is possible with a reciprocal mating design;Twelve F(,2)-derived lines of 76 cytoplasmic isopopulations were evaluated for seven traits. All traits exhibited significant nuclear-cytoplasmic interactions, but none exhibited consistent cytoplasmic effects. Nuclear-cytoplasmic heterosis was detected for each trait in 5 to 20% of the isopopulations with A. sterilis cytoplasm.

Agronomy, Plant breeding and cytogenetics