Heterosis and gene effects of multiplicative characters: theoretical relationships and experimental results from Vicia faba L.

Theoretical results were derived to relate the heterosis and the hybrid factor (ratio of hybrid performance to parental mean) of a complex character (seed yield) with the respective parameters of component subcharacters in a multiplicative model. A multiplication factor, which is a function of differences in the parents for subcharecters, was introduced to arrive at multiplicative relationships between the parameters in the model. Under certain assumptions, gene effects of a complex multiplicative trait can be expressed in terms of gene effects for the subcharacters. Data on seed yield and its components in two crosses between Vicia faba minor and major cultivars were used as a numerical example. Theoretical and experimental results indicate that with large complementary differences for subcharacters in the parents, it is possible to find substantial heterosis in the complex character without significant heterosis in its component traits. However, a review of results from the literature shows that multiplication effects are only of minor importance in most crops. Implications for the use of multiplication effects in the breeding of hybrid, synthetic, and line cultivars are discussed.