Ploidy distinction in male and female plants of betelvine (Piper betle L.): a study by flow cytometry

Piper betle L. (betelvine) is a dioecious species which is a native of Central and South East Asia and it is cultivated in an area of about 50,000 ha in India. The basic chromosome number of this species is x = 13. Only fragmented work has so far been reported on chromosome numbers and ploidy status. The extremely small size and high number of chromosomes, interclonal variability and very dense cytoplasmic contents make critical analysis difficult. In India, a large number of germplasm has been collected and assembled in All India Co-ordinated Research Project on Betelvine centers by sustained efforts of betelvine workers over a period of two and half decades. Hybridization work was also initiated and a few hybrids have been developed in India. But hybrid depression was noticed in most of the hybrids. Hence a study was undertaken to determine compatible ploidy level of available male and female germplasm using flow cytometry. Cytological studies conducted in a selected male cultivar revealed 2n = 3x = 39 and female cultivar it was 2n = 4x = 52 chromosomes and these cultivars were used as control samples in the flow cytometry analysis. Flow cytometric study showed that all male accessions were grouped within the same ploidy level (triploid) while all females were grouped in another ploidy group (tetraploid). The present study also gave explanation for the observed hybrid depression due to the possibility of aneuploid hybrid formation by the fusion of unbalanced gametes developed from the triploid male parents. Flow cytometry could thus be utilized for the rapid screening and earlier detection of the aneuploids in hybrid seedlings in the species. Separation of sexes by ploidy difference is also a new report in P. betle.