Inter- and Intracultivar Effects of Selection on Heterosis
- Chang-jian Jiang,
- C. Clark Cockerham and
- R. H. Moll
The effect of selection on heterosis depends on the gene action and the type of selection. Intracultivar (W) selection, full-sib family selection within each of two cultivars, and intercultivar (R) selection, reciprocal recurrent selection between the two cultivars, were contrasted for their effects on heterosis. The cultivars were considered to be random replicate populations from an ancestral population. The relatedness of individuals within cultivars and the degree of divergence between cultivars were formalized in terms of identity by descent (IBD) measures for two, three, two-pair, and four genes a locus and joint IBD measures for genes at each of two loci. Quantitative genetic components for a model that is general for additive, dominance, and additive by additive (a ✕ a) effects with an arbitrary number of alleles were defined for the ancestral population, and selection responses were formulated for the cultivars and the hybrid for each selection method with the aid of the IBD measures. A further analysis was made utilizing a biological building block model of gene effects. The contribution of a ✕ a effects was such that they reduced heterosis from W selection, but slightly increased heterosis from R selection. It was concluded that R selection always increased heterosis while W selection could increase or decrease heterosis, but decreased heterosis for a preponderance of the genetic parameters considered.
Copyright © 1990.