Cytogenetical studies in Sesamum. Part I. Cytology of the parents, Sesamum orientale Linn, and Sesamum prostratum Retz. and the cytology of the sterile hybrid between them and of the fertile amphidiploid

Abstract

Interspecific crosses between Sesamum orientale Linn, and Sesamum prostratum Retz. were effected reciprocally and the sterile hybrid was made fertile by artificial induction of amphidiploidy through colchicine. The cytology of the parents and the hybrids was studied in detail. Details of meiosis of Sesamum orientale, one of the parents employed have been worked out. The peculiar persistence of the nucleus and its movements during the meiotic cycle are recorded. The other parent Sesamum prostratum has also been cytologically studied. The irregular meiosis of the sterile hybrid and the occurrence of scattered bivalents and univalents in the metaphase plate, leading to the ultimate formation of abnormal sporads have been described fully. The regular meiosis of the fertile amphidiploid is compared with the irregular meiosis of the sterile hybrid and the cause of this regularity is explained. The nucleolus with behaviour of the special regard to its persistence and movements is discussed. Interspecific hybridisation as a guide to ancestral homology and the artificial synthesis of a new species are discussed in the light of cytological data gathered in the present investigation. The origin of the cultivated Til Sesamum orientale Linn. from a putative ancestor having haploid number 7 through allopolyploidy is traced with the help of cytological details obtained in the hybrid meiosis. The origin of the wild Sesamum prostratum Retz. is also traced to an ancestral form possessing haploid number of 8 chromosomes through autopolyploidy.