Polyploidy and domestication: the origin and survival of polyploids in cytotype mixtures.

The origin and survival of a polyploid in a mixture of this polyploid and its parent(s) is reviewed. With several examples a picture is drawn of the interference of cytotypes in a mixture of cytotypes. Some natural polyploids, both wild and domesticated, are very successful. They, like bread wheat and banana, largely replaced their parents. The same is true for some artificial polyploids like autotriploid hybride sugar beet in Europe and autotetraploid perennial ryegrass. But when grown together with their parents for several generations they will disappear from this misture. Although in South America under primitive conditions, diploid, triploid, and tetraploid potatoes are grown, elsewhere only the tetraploids have survived. Various causes are presented to explain why the diploids and triploids succumbed. Autotetraploids of maize, rye, barley, and rice cannot maintain themselves in diploid/tetraploid mixtures. The maintenance of diploid or tetraploid rye varieties is less difficult as both are "self-cleaning" with respect to the other. Only two haploid cultivars exist but they can only maintain themselves with the help of man. It is concluded that the survival chances of a polyploid after its origination is low. Firstly, under conditions of random sampling a rare type has a very small chance of occurring in the next generation. Furthermore, seedset of triploids and tetraploids is often low which limits their survival. In addition, in mixtures of cross-fertilizing diploid and autotetraploids the n gamete has an advantage over the 2n gamete. This limits the survival of the autotetraploids again. It is concluded that our knowledge of the the mutual interference of cytotypes in a cytotype mixture is quite limited. Much more research is needed and some proposals concerning this research are made.