Genetic relationships within the Cucurbitaceae as assessed by consensus chloroplast simple sequence repeats (ccSSR) marker and sequence analyses

Abstract

To investigate genetic relationships in Benincaseae (19 accessions), Cucurbiteae (1), Joliffieae (2), Melothrieae (2), and Sicyeae (3) tribes of the family Cucurbitaceae, consensus chloroplast simple sequence repeats (ccSSR) primer pairs obtained from tobacco (Nicotiana tabacum L.) chloroplast DNA were used. Variation in the length and putative sequence substitution events of polymerase chain reaction (PCR) products were analyzed. Sequencing of four fragments (ccSSR-1, -7, -8, and -19) revealed that convergence in fragment length occurs in more distant species comparisons. In ccSSR-1 and -8, the same fragment lengths occurred as the result of different insertion and deletion events. Nevertheless, the examination of a large number of ccSSR fragments suggested that this apparent homoplasy could be overshadowed by evolutionary relationships among taxa. This hypothesis is supported by the relative degree of positive congruence of taxon groupings after cluster and principal components analyses performed on both base pair length and sequence substitution data. Moreover, these analyses support previous biochemical and morphological data indicating that distinct lineages exist within the Benincaseae. Likewise, data support the hypotheses that the genus Benincasa is descended from an ancient African ancestor and that the progenitor of the New World Sicyeae tribe shares a common ancestor with the genus Luffa of the Old World Benincaseae.Key words: Benincaseae, chloroplast, consensus, homoplasy, microsatellite, simple sequence repeats.