Karyological Studies in the Genus Sesbania

Abstract

Detailed somatic karyotype analysis was carried out in 6 species of Sesbania. Of these, four species namely aculeata, rostrata, aegyptica and speciosa were diploid with 2n=12 chromosomes, while the species grandiflora was a tetraploid with 2n=24 chromosomes. The other species, sesban has both diploid (2n=12) and tetraploid (2n=24) cytotypes. Considerable differences were observed among the different species in terms of total chromatin length and volume with the values ranging from as high as 47.07μm and 31.98μm³ in S. qrandiflora to as low as 18.31μm and 8.98μm₃ in the species S. aegyptica. All diploid cytotypes except aculeata, exhibited one pair of SAT-chromosomes each, usually the second longest in the complement. In tetraploid forms two pairs of chromosomes (chro. 1, 2) carried secondary constriction in their long arms. The karyotypes of all species except aculeata were found to be symmetric with predominanty metacentric chromosomes. S. aculeata, however, had an asymmetric karyotype with 2 pairs of sub-metacentric and 1 pair of sub-telocentric chromosomes in addition to 3 metacentric pairs. Relative lengths, S% and TF% estimations also support the above view. The occurence of diploid and tetraploid forms in S. aculeata and S. sesban suggests the possibility of the existence of tetraploid forms in other Sesbania species also.