2000 Volume 44 Issue 2 Pages 115-122
Sesamum mulayanum NAIR distributed in the Indian subcontinent is a wild relative of cultivated sesame, S. indicum L. It was considered to be the wild ancestor of sesame, although there were different hypotheses on domestication. Two different ecotypes, the ruderal weed type and the associated weed type of S. mulayanum were observed in the field. The ruderal weed type was characterized by a deep pink-colored corolla with a strong purple pigmentation on the lowest lobe of the lip. The associated weed type resembled S. indicum in some characters, e.g., lighter coloration. Both types of S. mulayanum were crossed with S. indicum reciprocally in the present study. The F1 hybrids grew vigorously and exhibited intermediate characteristics between their parents. The F1 hybrids between the ruderal weed type of S. mulayanum and S. indicum showed a pollen semi-sterility of about 50% and produced a remarkably reduced number of seeds per capsule, while those between the associated weed type and S. indicum showed a normal pollen fertility and seed set. It was suggested that the sterility was neither cytoplasmic nor due to structural changes of chromosomes but caused by a gametophytic sterility gene. Judging from the present results, it is concluded that the associated weed type is closer genetically to the cultivated species than the ruderal one. Nevertheless, S. mulayanum and S. indicum are considered to belong to the same biological species, because they hybridized easily and no completely sterile hybrids were obtained in the study.
