Morphometric and Cytological Analysis of Different Cytotypes of Dioscorea deltoidea Wall., 1850 (Dioscoreaceae) from North-Western Indian Himalayas

Abstract

Dioscorea deltoidea Wall. (Dioscoreaceae), commonly called “Nepal Yam,” is distributed in the Himalayas, from Kashmir to Assam at altitudes of 450–3100 m. It is an important medicinal plant commercially exploited for the extraction of diosgenin, a pioneer for steroid drugs. This valuable species of the Indian Himalayas faces a serious threat of extinction due to over-exploitation of its tubers and gradual shrinkage of its natural habitat. The species shows considerable intraspecific morphological and cytological variations involving polyploidy and hybridization. In the present study, we examined the meiotic course, microsporogenesis, pollen fertility, and morphological characters of 12 populations of diploid (2x) and four populations of tetraploid (4x) cytotypes of Dioscorea deltoidea. The majority of populations exhibit normal course of meiosis with 100% pollen fertility. However, in six populations (four diploid cytotypes and two tetraploid cytotypes), the individuals show inter-PMC transfer of chromatin material at various stages of meiosis and associated meiotic irregularities such as chromosome stickiness, unoriented bivalents, laggards, micronuclei, and chromatin bridges at different stages of meiosis. Consequently, these populations exhibited varying degree of pollen sterility and heterogenous-sized pollen grains. Analysis of various morphological characteristics of diploid and tetraploid cytotypes revealed that increase in ploidy level in the species is correlated with gigantism of some vegetative characteristics.