Abstract
The chromosome structures of eight strains of T. araraticum collected in southeastern Turkey and Northern Iraq were analyzed by hybridization with three chromosome type tester strains; the A type of araraticum 196-1, the B type of timopheevi 107-1 and the C type of araraticum 1908A. Concurrently, the chromosome pairings of hybrids of eight araraticum strains were observed.
Results of the present experiment clearly show that of the eight strains studied, four were the B type. The remaining four strains were classified into three chromosome types different from the A, B and C types. These were designated the D, E and F types. A tetravalent was formed in the PMCs of hybrids between the B and D types and between the B and E types. A hexavalent was observed in hybrids between the D and E types, between the E and F types and between the B and F types. Two tetravalents were recognized in hybrids between the A and D types and between. the C and E types. A hybrid between the D and F types showed an octavalent formation at meiosis. Both a tetravalent and a hexavalent were observed in a hybrid between the A and F types.
Reduced seed fertility in hybrids of the strains of T. araraticum seems to be caused by meiotic irregularities such as polyvalent formations. The seed fertilities of hybrids between the B type strains of T. araraticum and T. timopheevi varied from almost sterile to fully fertile. An araraticum strain collected near Hozat, Turkey, was found to be fully fertile when crossed with T. timopheevi. This provides evidence for the theory that T. araraticum is the ancestral species of cultivated T. timopheevi.
This study has clearly shown that chromosome differentiation in T. araraticum is more abundant in Northern Iraq than in Transcaucasus. This would indicate that the Timopheevi group of tetraploid wheats first originated in the eastern part of the Fertile Crescent and that later its distribution area was extended northward to the Transcaucasus.
