Cytogenetics of Tephrosia

VI. Meiotic systems in some taxa

抄録

Male meiosis was studied in sixteen species. Thirteen species were diploids. In T. purpurea and T. hamiltonii both diploid and tetraploid races were meiotically investigated. The present data together with the earlier data show that the gametic numbers recorded in the genus so far are n=10, 11, 18 and 22. Taking mitotic data also into consideration the series runs as n=10, 11, 12, 16, 18 and 22. It is important to note, however, that barring T. hookeriana all the 32 species, inves-tigated have one gametic number n=11 in common. The unrelated numbers (n=10, 12, 16, 18) are considered to be wrong reports or at the most study of one time aberrant plants and it is concluded that the genus Tephrosia is monobasic with x=11.
The occurrence of 2-6 univalents in a few PMCs in eight species has been ascribed to early separation of synapsed homo/homeologues and/or precocious separation of rod bivalents. The presence of 0-22 univalents and their overall average of 5.37 per cell in T. uniflora ssp. petrosa has been attributed to desynapsis. Very low quadrivalent average and high bivalent frequency per cell in the three tetraploid species (T. purpurea, T. pumila, T. hamiltonii) is indicative of their hybrid origin.
Besides gene mutation, the divergence and evolution of Tephrosia species was accompanied by chromosomal repatterning. The mechanisms responsible for detectable and undetectable chromosomal repatterning are peri- and paracentric inversions, cryptic structural hybridity, deletion and translocations. Hybridization is another important factor responsible for divergence. Polyploidy, present only in a few taxa, has played role in the stabilization of hybrids.