Introduction
Momordica charantia L. (Cucurbitaceae) is commonly known as bitter gourd or bitter melon. It is an economically important species that belongs to the Joliffieae tribe and the Thladiantinae subtribe (Din et al., Reference Din, Bukhari, Salam and Ishfaq2011). Bitter gourd is widely distributed in China, Malaysia, India, Pakistan, tropical Africa, and North and South America. The immature fruits of bitter gourd are eaten as a vegetable and are a good source of calcium, iron, magnesium, phosphorus, sulphur, and vitamins A and C (Ullah et al., Reference Ullah, Chy, Sarkar, Islam and Absar2011). Bitter gourd contains a range of pharmaceutically active compounds such as momordicin and charatine (Mahmood et al., Reference Mahmood, Raja, Mahmood, Gulfraz and Khanum2012), so it has long been a focus of research. The cytogenetics of M. charantia have been poorly studied, with knowledge being limited to the somatic chromosome number (Lenzi et al., Reference Lenzi, Orth and Guerra2005). This may reflect technical difficulties arising from the small size of the chromosomes and difficulties in staining them (Bharathi et al., Reference Bharathi, Munshi, Chandrashekaran, Behera, Das, John and Vishalnath2011). Some karyological information has been provided by Bharathi et al. (Reference Bharathi, Munshi, Chandrashekaran, Behera, Das, John and Vishalnath2011). The objective of the present study was to investigate the extent of intraspecific karyological variation among accessions of bitter gourd grown in South and Southeast Asia.
Experimental design
Seeds of 30 accessions of M. charantia were obtained from The World Vegetable Center, Taiwan (Asian Vegetable Research and Development Center), along with seeds of four accessions from Pakistan. The seeds of all the 34 accessions (Table S1, available online) were germinated on moist filter paper and held at 30–35°C to obtain young root tips. The protocol for producing root tip squashes was modified from that given by Mirzaghaderi (Reference Mirzaghaderi2010). Roots that were 1–2 cm long were excised and held in 0.05% colchicine solution for 3 h, then fixed in 3:1 ethanol: acetic acid for 24 h, hydrolysed in 1 M HCl at 60°C for 12–15 min, and finally stained with 45% acetocarmine. Each root tip was squashed in a drop of 45% acetic acid and subjected to light microscopy examination.
A minimum of five metaphase cells per accession were scored. The chromosomes were classified according to the method proposed by Leven et al. (Reference Leven, Fredga and Sandberg1964). Karyological analysis was carried out using the computer software MicroMeasure 3.3 (available at http://micromeasure.software.informer.com/3.3/).
Discussion
The following three ploidy levels were observed: diploid (2n= 22), tetraploid (2n= 44) and hexaploid (2n= 66) (Tables 1 and 2). The diploids were represented by 13 accessions originating from all the four countries; diploidy has been recorded by Beevy and Bai (Reference Beevy and Bai2013) and Bharathi et al. (Reference Bharathi, Munshi, Chandrashekaran, Behera, Das, John and Vishalnath2011). Four accessions from Bangladesh (Fig. S1, available online), one accession from India (Fig. S3, available online), three accessions from Thailand (Fig. S2, available online) and two accessions from Pakistan (Fig. S3, available online) were tetraploid; this ploidy level has been observed by Zaman and Alam (Reference Zaman and Alam2009). Hexaploidy was observed in 11 accessions (six from Thailand, one each from India and Pakistan, and three from Bangladesh; Tables 1 and 2); this ploidy level has not been reported previously.
Table 1 Karyological data of Momordica charantia accessions originating from Bangladesh, India and Pakistan
sm, submedian; m, median.
Table 2 Karyological data of Momordica charantia accessions originating from Thailand
m, median; sm, submedian; st, subterminal.
Chromosome length was also variable. The chromosomes were small (0.8–2.9 μm), similar to the length range observed by Bharathi et al. (Reference Bharathi, Munshi, Chandrashekaran, Behera, Das, John and Vishalnath2011). The chromosomes harboured by the hexaploid accessions were smaller than those harboured by the lower-ploidy accessions, varying in length from 0.8 to 1.5 μm. The majority of accessions had a symmetrical karyotype, comprising median and submedian chromosomes, in accordance with that reported by Zaman and Alam (Reference Zaman and Alam2009). Only one accession (TOT1140, hexaploid) had chromosomes with a subterminal centromere.
Supplementary material
To view supplementary material for this article, please visit http://dx.doi.org/10.1017/S147926211400077X
Acknowledgements
The authors thank Dr. David M. Spooner, Professor (USDA), Department of Horticulture, University of Wisconsin, Madison, WI, USA, for technical review of the manuscript.
