Isozyme Variation in Indian and Chinese Melon (Cucumis melo L.) Germplasm Collections

Genetic variation among 378 melon (Cucumis melo L.) germplasm accessions collected in India in 1992 and 26 accessions in China in 1994 was evaluated with 19 isozyme loci. ʻTop Markʼ and ʻGreen Flesh Honeydewʼ, which represented two distinct C. melo ssp. melo L. groups, Cantalupensis and Inodorus, respectively, were used as reference cultivars. Genetic distances among accessions were calculated, and an initial cluster analysis using these distances re- sulted in 148 groups of varying size, ranging from two to 47 accessions. One accession from each of the 148 groups was chosen at random and used in a second cluster analysis that identifi ed 11 accession groups. Group 1 was unique and consisted of only two C. melo ssp. agrestis (Naudin) Pangalo accessions. Two large branches were detected at cluster node 2. One branch was comprised of three groups of 3, 12, and 34 accessions, while the other branch contained seven groups of 2, 3, 14, 16, and 47 accessions, and the reference cultivars. Of the 148 accessions, 132 were from 41 sites in Rajasthan and Madhya Pradesh, India, which were distributed unequally across the 11 groups. The 14 Chinese ac- cessions originating from seven provinces were also dispersed unequally in the four major cluster groups. ʻTop Markʼ and ʻGreen Flesh Honeydewʼ were genetically distinct and uniquely clustered in the same group. These results indicate that additional collections of melon germplasm should be made in eastern and southern India. Cucumis melo is a morphologically diverse crop species consisting of two subspecies that are differentiated on the basis of ovary pubescence (Kirkbride Jr., 1993), C. melo ssp. agrestis and C. melo ssp. melo. Six subspecifi c groups of cultivated and wild types have long been recognized in the western literature (Robinson and Decker-Walters, 1997). A more recent treatment of melon taxonomy by Pitrat et al. (2000) using literature and analysis of melon germplasm available to western taxonomists and newly available germplasm from the former Soviet Union resulted in the provisional, albeit testable, classifi cation of melon into 16 groups, fi ve in subspecies agrestis and 11 in subspecies melo. Upon more rigorous analysis, these groups might be more accurately defi ned as "cultivar-groups" according to Spooner et al. (2003). Melon is a tropical, old world species that probably originated in Africa (Kerje and Grum, 2000). Afghanistan, China, India, Iran, Saudi Arabia, southern Russia, and Turkey were important second- ary gene centers that gave rise to cultivated melons (Jeffrey, 1980; Pangalo, 1930; Whitaker and Bemis, 1976; Whitaker and Davis, 1962). The primary center for diversity in melon is southwestern and central Asia, mainly Turkey, Syria, Iran, Afghanistan, north and central India and Transcaucasia, Turkmenistan, Tadjikistan, and Uzbekistan (Esquinas-Alcazar and Gulick, 1983). Second- ary centers of diversity for cultivated melons are found in China, Korea, Portugal, and Spain (Esquinas-Alcazar and Gulick, 1983). Today, melons are grown in many countries worldwide for local, national, and export markets (Robinson and Decker-Walters,