Genetic changes under domestication in Vicia faba.

The components of variation within each one of two sets of landraces and/or cultivars of Vicia faba, respectively constituted of primitive and advanced morphological types, were studied by means of two sets of 8 × 8 diallel crosses with two repetitions. The results show that primitive and modern forms differ from each other in both the intensity and the kind of selective pressures acting on them, mainly on those characters more modified through the domestication process: i.e., seed morphology and the number of flowers per node. Because of the paramount importance of the additive component in the primitive forms, it is suggested that the most important type of selection on them is the stabilizing one. On the contrary, in the most advanced forms the selection is directional and disruptive : directional towards greater yields, and disruptive separating two morphological types, 'major' and 'equina'. The plant response to these different selective pressures has been to modify the genetic control of different characters: thus the primitive forms generally show only additivity while the most advanced forms show additivity as well as directional and asymmetrical dominance.