HETEROSIS AND GENE EFFECTS OF MULTIPLICATIVE CHARACTERS - THEORETICALRELATIONSHIPS AND EXPERIMENTAL RESULTS FROM VICIA-FABA L

Theoretical results were derived to relate the heterosis and the hybri d factor (ratio of hybrid Introduction performance to parental mean) o f a complex character (seed yield) with the respective parameters of c omponent subcharacters in a multiplicative model. A multiplication fac tor, which is a function of differences in the parents for subcharecte rs, was introduced to arrive at multiplicative relationships between t he parameters in the model. Under certain assumptions, gene effects of a complex multiplicative trait can be expressed in terms of gene effe cts for the subcharacters. Data on seed yield and its components in tw o 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 rev iew of results from the literature shows that multiplication effects a re 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.