Incompatibility in Autotetraploid Trifolium Pratense.

RIFOLI U M pratense L. is a highly self-incompatible species. An oppositional Tsystem of incompatibility has been established in this species by WILLIAMS and SILOW (1933). Artificially induced autopolyploids have been produced by LEVAN (1948) and FRANDSEN (1948) and selections have been carried out for several generations to improve their fertility. But no work has been done to study the effect of polyploidy on self-incompatibility in T . pratense. The effect of polyploidy on incompatibility has been reviewed in detail by LEWIS (1947) and ATWOOD and BREWBAKER (1953). After working with the known genotypes of autotetraploids in Oenothera orgunensis, LEWIS stated the following three principles which explain the results in most species that have been adequately tested. (1) Some pairs of different S alleles compete in diploid pollen grains. The interaction results in compatibility of the pollen grain in a style carrying both the alleles. (2) Pairs of S alleles which do not show competition may show dominance of one allele over another in the pollen grain. (3) These two effects differ according to the species in their power to alter the incompatibility reaction. Recently, the observations on the induced autopolyploids of Trgolium repens (ATWOOD and BREWBAKER 1953) and T . hybridum (BREWBAKER 1953) have been adequately explained on the above principles. As most of the previous work has only dealt with the allelic interaction in the diploid pollen, other effects of polyploidy on the incompatibility cannot be ruled out. The present experiments on the tetraploid Trgolium pratense were taken up to find out whether the same principles could be applied to explain the results obtained in this species, and also to discover any new effects of polyploidy on the incompatibility mechanism. Such a study would seem to be a prerequisite for an efficient breeding programme with autoploids in clovers.