Genetic Diversity among Cucumis metuliferus Populations Revealed by Cucumber Microsatellites

Cucumis metuliferus E. Mey. ex Naud (African horned cucumber, horned melon) is endemic to Africa and is a relative of cultivated cucumber (C. sativus L.) and melon (C. melo L.). In the present study, genetic variation among the USDA C metuliferus collection was evaluated with microsatellite [simple sequence repeat (SSR)] markers derived from C sativus genomic DNA sequences. Of 564 cucumber SSRs tested, 51.8%, were able to produce polymerase chain reaction amplicons in C. metuliferus suggesting a high degree of DNA sequence homology between the two species. Forty-two cross-species SSRs were used to assess genetic variation among 36 C. metuliferus accessions. Genetic diversity among these accessions was relatively low. Of the 42 SSRs, 12 were monomorphic, and each marker, on average, was able to detect 3.3 alleles among the 36 accessions. Neighbor-joining clustering analysis revealed a positive relationship between genetic divergence and geographic distances among these accessions. Genetic distance of C. metuliferus to melon is smaller than that of C. metuliferus to cucumber.