The mechanism of 2n pollen formation in diploids of Costus speciosus (Koenig) J.E. Smith and role of sexual polyploidization in the origin of intraspecific chromosomal races.

Abstract

Microsporogenesis in the two diploid clones of C. speciosus was studied in detail. The absence of cytokinesis detected in some of the dyads at the close of the second meiotic division was the mechanism producing 2n pollen in both the diploids. The distinct variation in n and 2n pollen size indicated the possibility of its use as a reliable criterion for estimating the frequency of 2n pollen in large populations. In addition to the normally expected diploids, certain triploid and tetraploid genotypes were identified in the selfed progenies of both the diploids which confirmed the occurrence of functional 2n gametes in their parental diploid clones. The present study suggested that sexual polyploidization involving the function of 2n gametes might have played an important role in the origin of naturally occurring intraspecific chromosomal races of C. speciosus.