Observed and predicted phenotypic effects of inbreeding in the BS13(S)C0 maize population

Edwards, Jode
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Inbreeding occurs at both the individual level and the population level in most plant breeding programs. Modeling systems that include inbreeding requires knowledge of how inbreeding affects genetic variance. The objectives of this work were to model the effects of inbreeding on variances of genetic effects in individuals and repartitioning of genetic variance within and among subpopulations derived from a common metapopulation. Two hundred random inbred lines were developed in the BS13(S)C0 maize population by four generations of self-pollination to study the effects of inbreeding at the individual and population level in BS13(S)C0. The 200 lines along with a set of related half-sib families were evaluated in replicated yield trials. Genetic covariances of inbred relatives were estimated for six agronomic characters. Inbreeding caused a significant change in the mean of all six traits, and an increase in the variance of dominance deviations for five of six traits demonstrating that both the mean and variance of dominance deviations are larger in inbred individuals (F = 1) than in noninbred individuals. Additionally, dominance deviations became negatively correlated with breeding values in inbred individuals. The correlation between dominance deviations and genotypic values in inbred individuals was 0.37 or less for all traits except grain yield, which had a correlation between dominance deviations and genotypic values in inbred individuals of 0.63. The average degree of dominance was found to be greater than 2 (0 is no dominance, 1 is complete dominance) for all traits except grain yield. Based on predicted effects of inbreeding on variance component structure in BS13(S)C0, additive variance for grain yield will change very little at average inbreeding coefficients less than 0.5. Other traits will lose genetic variance roughly in accord with neutral additive expectations based on estimates of additive variance in the base population. Pseudo-overdominance, combined with the high correlation between inbred dominance deviations and genotypic values may explain the lack of response to inbred-progeny recurrent selection for grain yield in the BS13(S) population. Furthermore, our results predict that genetic variance will not be exhausted in this population, a result in accord with the observed long-term maintenance of genetic variance in recurrent selection programs in the Iowa Stiff Stalk Synthetic population.

Agronomy, Plant breeding