Genetic diversity of Japanese melon cultivars (Cucumis melo L.) as assessed by random amplified polymorphic DNA and simple sequence repeat markers

The genetic diversity among 67 melon (C. melo L.) cultivars from five Japanese seed companies was assessed using 25 10-mer RAPD primers (56 bands) and nine SSR (36 alleles) markers. These cultivars belong to three horticultural varieties (synom. Groups) spanning eight melon market classes: Group Cantalupensis (market classes Earl's, House, Galia, Charentais, and Ogen), Group Inodorus [Honeydew and Casaba melons (market classes Amarillo, Piel de Sapo, Rochet, Negro, Crenshaw, and Tendral)], and Group Conomon (market class Oriental). Genetic variation among these cultivars was compared to variation in a reference array (RA) consisting of 34 selected melon accessions from previous studies. Cluster analysis resulted in 11 of 15 Japanese Oriental accessions forming a group with South African RA accessions. The remaining Group Conomon Japanese accessions grouped either with Casaba or with Honeydew cultivars. Japanese Group Conomon accessions and South African RA accessions formed a genetic group that was distinct from all other accessions studied, and suggests either an Asiatic origin for the South African melon germplasm examined or an independent domestication involving similar ancestors. The majority of Japanese House and Earl market class accessions shared genetic affinities, and were genetically different from the Japanese Group Inodorus accessions examined. These Japanese accessions were most similar to Casaba RA accessions. Japanese Galia accessions were similar to either House and Earl's market classes or to Galia, Ogen, Casaba, and Honeydew RA accessions. Genetic differences exist between melon types that were domesticated from wild, 'free-living' subspecies agrestis and from melo.