Genome Relations among Octaploid Species of Sesamum L.(Pedaliaceae).

Genome relations among 3 octaploid species of Sesamum namely S. radiatum, S. occidentale and S. schinzianum were analyzed. These 3 African wild species exhibited normal 32 bivalents at diakinesis and metaphase-I and showed high degree of pollen fertility and seed set. In S. radiatumXS. occidentale F 1 hybrids, mean chromosome pairing of 0.81 f +31.6 u per cell was found. About 86% of the pollen mother cells revealed 32 bivalents formation. This suggests that genomes of S. radiatum and S. occidentale are similar and homologous. Both these parental species are morphologically similar. F 1 and F 2 progenies are highly fertile. Based on these evidences it is proposed that S. occidentale be treated as a variety of S. radiatum. Mean chromosome pairing of 0.154 I +31.79 I I +0.11 I V per cell was found in S. radiatum×S. schinzianum hybrid. About 92% of the PMCs revealed 32 bivalents. This pairing behaviour indicates that genomes of S. radiatum and S. schinzianum are similar and homologous. These 2 species have diverged and differentiated by 2 translocations as evident from 2 quadrivalent formation in the hybrid. It is proposed that S. radiatum and S. schinzianum have descended from a common ancestral octaploid species. Isolating barriers preventing gene flow between species in nature is discussed.