Cytogenetic studies of Trifolium spp. Related to berseem : IV. The relationships in the alexandrinum and vavilovi crossability groups, and the origin of the cultivated berseem.

The interspecific cytogenetic relationships among T. alexandrinum L., T. berytheum Boiss., T. salmoneum Mout., T. apertum Bobr., T. meironense Zoh. et Lern, and T. vavilovi Eig. were studied in several hundreds of intraspecific (WS) and interspecific (BS) F1 hybrids in all possible combinations, and in many of their progenies.Seed germination and development of F1 BS hybrids were normal, except in crosses involving T. vavilovi. Their pollen fertility and seed set was subnormal, with somewhat lower values in T. vavilovi progenies. No multivalents were observed in any F1 BS hybrid, but in some plants, four and also six chromosomes did not pair to form bivalents. B chromosomes were common in hybrids involving T. berytheum or T. salmoneum.Some BS F1 hybrids set ample seeds when selfed, and most of them originated from either one of two self-incompatible T. berytheum plants.The six taxa studied form three groups: (i) T. vavilovi, which is quite remote from the other five; (ii) T. meironense and T. apertum; and (iii) T. alexandrinum, T. berytheum and T. salmoneum. The two last species, especially T. salmoneum, seem to be the progenitors of the cultivated berseem.