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Cytomorphological characteristics of Indian hexaploid S. nigrum and S. nodiflorum and of their F1hybrids were studied. The parents differed significantly in several morphological and cytological characters. The hybrids were highly sterile and did not set seed.They showed a wide range of meiotic irregularities. In several pollen mother cells, trivalents and quadrivalents were recorded, although in a very low frequency, in addition to a large number of univalents and bivalents. Occasionally bridges with or without fragments, were recorded. The results of these investigations show that chromosomal differences as well as genic differences have played an important role in reproductive isolation and morphological differentiation of the two species.
Khan et al. (Tue,) studied this question.