Unilateral incompatibility: hypotheses,debate and its implications for plant breeding

Summary Unilateral incompatibility, its evolution and the hypotheses put forward to explain this phenomenon have been discussed. A new hypothesis is presented giving an easy explanation of the problems arisen and of the results obtained hitherto. The results to be expected from crosses between self-compatible and self-incompatible species and the crossability and (in)compatibility behaviour of their hybrids and segregating generations are elaborated. It has been shown how self-compatible hybrids and segregants could be selected and introduced into a breeding program aiming at combining characters from self-compatible and self-incompatible parents.