Cytogenetical Studies of the Genus Sesbania Scop

II. Meiosis

Abstract

Out of the twelve taxa representing five species of the genus Sesbania, two varieties of S. aculeata, three varieties of S. sesban, three vaieties of S. macrocarpa and one variety of S. exasperata were found to be diploid with 2n=12 chromosomes, whereas one variety of S. macrocarpa and two varieties of S. grandtflora were found to be tetraploid with 2n=24 chromosomes.
The diploid taxa showed regular formation of six bivalents and tetraploid taxa showed the occurrence of twelve bivalents at meiotic metaphase-I except in S. macrocarpa ‘IL 1535’ (diploid) and ‘IL 89’ (tetraploid) in which two per cent cells show an early disjunctional bivalent and/or two univalents. The subsequent stages of meiosis were quite normal resulting into 85.0 to 99.0 per cent pollen stainability.
The minimum number of ring bivalents per cell (3.32) was found in S. macrocarpa ‘IL 1537’ and maximum (5.42) was recorded in S. macrocarpa ‘IL 1536’ in case of diploid taxa. The average number of ring bivalent per cell in tetraploid taxa varied from 7.9 to 9.7.
Chiasma frequency per cell at metaphase-I varied from 9.6 to 12.64 in diploid taxa while it varies from 21.1 to 23.8 in tetraploid taxa. On an average the number of chiasmata per bivalent varied from 1.6 in S. macrocarpa ‘IL 1537’ to 2.1 in S. macrocarpa ‘IL 1536’.
The average size of stainable pollen grains varied from 24.9μ to 28.8μ in diploid taxa, whereas it was found to vary from 28.8μ to 37.2μ in tetraploid taxa. However, the average size of stainable pollen grains in tetraploid S. macrocarpa was found to be 28.8μ which in turn was comparable to the size found in the diploid taxa.