Melon is a diploid (2n = 2x = 24), morphologically diverse crop of commercial importance as a dessert fruit. Melon was first used as food in ancient Egypt and Iran during the second and third centuries B.C.E. (Dhillon et al., 2011; Janick et al., 2007; Zeven and de Wet, 1982) and melon cultivation then spread to nearby areas. In 2010, 25 million tonnes of melon were produced on 1 million hectares [Food and Agricultural Organization of the United Nations (FAO), 2012]. According to some authors, wild-type melon originated from south and east Africa (Mallick and Masui, 1986). However, recent work suggests that melon originated in Asia (Sebastian et al., 2010). This idea is supported by the fact that the primary center of diversity of many commercially important melons is the Near East and central Asia (Jeffrey, 1980; Luan et al., 2008). Turkey is an important secondary center of diversity for melon and other cucurbits (Sari et al., 2008) and was considered by Harlan (1951) to be a microcenter for melon landraces. Turkey consistently ranks second behind China in worldwide melon production with 1.6 million tonnes produced in 2010 (FAO, 2012).
The Turkish national melon germplasm collection is housed at the National Seed Genebank at the Aegean Agricultural Research Institute (AARI), Menemen, Izmir, Turkey. The seed bank contains 571 accessions of Cucumis melo, many of which have been collected and submitted by farmers from throughout the country (Sari et al., 2008). Ex situ conservation of plant germplasm is expensive and labor-intensive. Although a collection may contain hundreds or thousands of accessions, these accessions may be redundant or genetically similar. In addition, depending on collection method, accessions may be mixtures of individuals with different morphologies. Such populations are difficult to fully characterize and may not be favored by breeders who prefer to work with homogeneous material. Therefore, at least preliminary morphological and molecular characterization is essential for efficient management and use of germplasm collections. Molecular genetic characterization of plant accessions has become routine and several molecular marker methods have been used for determination of genetic variability within melon accessions including isozymes (Akashi et al., 2002), restriction fragment length polymorphisms (Neuhausen, 1992), random amplified polymorphic DNA [RAPDs (Garcia et al., 1998; Luan et al., 2008; Nhi et al., 2010; Sensoy et al., 2007; Staub et al., 2004; Yildiz et al., 2011)], simple sequence repeats [SSRs (Danin-Poleg et al., 2001; Monforte et al., 2003)], intersimple sequence repeats [ISSRs (Perl-Treves et al., 1998; Yildiz et al., 2011)], AFLPs (Nimmakayala et al., 2009), and single nucleotide polymorphisms (Deleu et al., 2009; Szabo et al., 2005).
In this study, we characterized the molecular genetic diversity of a portion of the Turkish national melon germplasm collection (209 genotypes from 115 accessions) using AFLP markers. The AFLP technique was selected because it provides a high number of reproducible polymorphic fragments distributed throughout the genome. The genotypes represented eight morphotypes including both widely grown (Ananas, Casaba, Charentais, Winter) and regional (Altınbaṣ, Yuva-Hasanbey, Mollaköy, Topatan) types. The regional melons are Turkish in origin or are variants of more widely grown melons, which have been selected according to local preferences. Altınbaṣ is a Kırkaḡaç type of melon. This type is of Turkish origin and has yellow skin with dark green spots. Yuva-Hasanbey melons are Casaba types with dark green or gray–green skin. Mollaköy is a Charentais type with yellow skin and green sutures. Topatan is an Ananas type with yellow skin and less netting than Ananas. The AFLP data indicated the level of diversity present in the national collection and were used to select a core set of genotypes. This core set was then analyzed with SSR markers to confirm that it represented the molecular diversity present in the entire set of genotypes.
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Identities of Turkish melons used in the study including origin and morphotype. A total of 209 genotypes were used representing 115 different accessions from the national melon collection.
Cucurbit species used as outgroups in the study.
Primer sequences for the four simple sequence repeat (SSR) markers developed and used to measure molecular diversity of melon in the study.