Cytogenetics of two Indian varieties of Momordica charantia L. (bittergourd)

Momordica charantia L.commonly known as bitter gourd is a widely cultivated cash crop in India with immense medicinal values. India has been one centre of diversification of two prominent taxonomic varieties viz. long-fruited variety, M. charantia var. charantia (MCC) and small-fruited variety, M. charantia var. muricata (MCM). Momordica species have long been known not to be amenable to conventional cytological techniques. After thorough technical standardization, karyotype variation between the two varieties as well as different populations of the same variety was compared and we primarily structured karyotypes of MCC and MCM populations that conformed to diploid count of 2n = 22 with slightly greater chromosome size in MCM (1.32μm-3.24 μm) than MCC (1.27μm-3.07 μm). Significant differences in genome size between MCC and MCM was also confirmed by flow cytometry for the first time in the two varieties of the species. Pronounced intraspecific dissimilarity in somatic chromosomes was established by EMA-Giemsa method revealing four nucleolar chromosomes in MCC populations and six nucleolar chromosomes in MCM populations. This difference in varieties was substantiated by fluorochrome banding which revealed four and six distal CMA+ve signals in MCC and MCM respectively. Detailed inter- and intra- karyomorphometric evaluation ascertained higher tendency of karyotype asymmetry in MCC. EMA-DAPI technique was applied for meiotic analysis in MCC (n = 11) and MCM (n = 11) populations providing indications of regular meiotic behavior. These results will benefit the classification, the genetic basis of domestication and the genome studies of this widely cultivated cash crop.