Genetic Diversity Studies in Cucurbits Using Molecular Tools

Abstract

Cucurbits are of tremendous economic importance and are cultivated throughout the world from tropical to sub-temperate zones. China, Turkey, India and Iran are important cucurbit growing countries. Pumpkin may have been domesticated in Mexico and northern South America. Then it migrated to the Caribbean islands and from there reached Florida, the native Americans developed a distinct landrace called Seminole pumpkin. More diversifi cation on pumpkin has taken place in Asia and Africa. Bitter gourd is a very important crop of India, the Phillipines, Malaysia, China, Australia, Africa, the Middle East, Latin America and the Caribbean. Momordica charantia was domesticated in eastern India or southern China. Luffa cylindrica (smooth gourd) contains wild populations distributed from southern Central Asia to north-eastern Australia and the South Pacifi c. The domestic variety is cultivated in Asia, Africa and tropical America. Luffa acutangula is mostly grown in South-eastern Asia and other tropical countries (Table 2-1). In India, this diversity is concentrated in the IndoGangetic plains, north-eastern regions, north-western Himalayas, the Western and Eastern Ghats and sporadically in the tribal dominant belts of Central India. More diversity occurs in Cucurbita spp. in the north-east as also for ash gourd, bottle gourd while for Luffa, it is more concentrated in the eastern peninsular tract. In case of Cucumis melo and round gourd, it is more confi ned to north-western and Indo-Gangetic plains. In pointed gourd, diversity is concentrated more in eastern part of the Indo-Gangetic plains particularly in West Bengal and adjoining Bihar along eastern Uttar Pradesh. Coccinia cordifolia (growing wild throughout India, raw fruits used as vegetables), Cucumis sativus (distributed throughout India, in the Himalayas as well), Lagenaria siceraria (African origin but domesticated throughout India, tender fruits used as vegetables), Luffa cylindrica (indigenous to India whereas acutangula found in western, Central and southern India and is regarded as a wild form of cultivated species-tender fruits used as vegetables), L. acutangula var. amara (occurs in peninsular India and is a wild relative of cultivated spongegourd), L. echinata (western Himalayas, Central India Gangetic plains) and L. graveolans (considered as wild progenitor of L. hermaphrodita in Bihar and Sikkim) are potential species. In addition, Momordica, M. balsamina occurs in semi-dry northwestern plains, northern parts of Eastern and Western Ghats, M. dioica and M. cochinchinensis occur as wild/semi-wild in the Gangetic plains. Trichosanthes has 21 species occurring in India and the major zones of species concentration are (a) along the Malabar coast in the Western Ghats, (b) low and medium elevation zones in the Eastern Ghats and the north-eastern19 Table 2-1 Origin and geographical distribution of cultivated species of minor cucurbits of regional or local importance*.