Cytological basis of sex expression in Trichosanthes L.

Abstract

Cytogenetic analyses have been carried out to elucidate the mechanism of sex expression in T. anguina cv ‘Long Green’, and in sex forms of cultivated and wild T. dioica.A uniform number of 22 chromosomes has been recorded in the somatic complements of all the taxa investigated. Three or more pairs of chromosomes with secondary constrictions have been recorded in the taxa investigated. Androecious representative of T. dioica cv ‘Kalyani’ is characterized by the presence of a heteromorphic pair. A similar heteromorphic pair is represented not only in the androecious form of wild T. dioica but also in T. anguina. A heteropycnotic chromatin body in some interphase cells of somatic tissues has been observed in the androecious members of both wild and cultivated T. dioica.The gametic number of eleven chromosomes is uniformly represented in all the taxa studied. Regular bivalent formation is noted in most of the male meiocytes analysed. Structural and functional heterogeneity are reflected in the occurrence of a heteromorphic bivalent and in the asynchrony of first anaphasic separation in the androecious members of both wild and cultivated T. dioica.Giemsa C-banding studies have been carried out in T. anguina cv ‘Long Green’ and two sexes of T. dioca cv ‘Kalyani’. The banded karyotypes of somatic complements are characterized by distinct telomeric bands. The gynoecious form of T. dioica shows diffuse banding in a pair of chromosomes, while the androecious sex is characterized by one member of the pair without any band. Such chromosomes are completely absent in T. anguina.