Genetic reticulation and interrelationships amongcitrullusspecies as revealed by joint analysis of shared AFLPs and species-specific SSR alleles

Abstract

Thirty-one accessions ofCitrullusspp. belonging toCitrullus lanatusvar.lanatus,C. lanatusvar.citroidesandCitrullus colocynthiswere subjected to phylogenetic analysis using combined datasets of amplified fragment length polymorphisms (AFLPs) and simple sequence repeats (SSRs). Tree topologies inferred by neighbour-joining analysis have resolved the phylogenic relationships among the species with special reference to established taxonomic classification. In this study, we have clearly resolved species boundaries of various taxa ofcitroides,lanatusandcolocynthisinto three well-supported clusters. Clustering pattern of principal component analysis with the shared polymorphisms using the subsets of data between any two taxon combinations helped to elucidate the introgression and interrelationships among the species. We report two major groups ofC. lanatustaxa, one of which has undergone wide introgressions with the taxa ofC. lanatusvar.citroidesandC. colocynthis. In this paper, we identified 583 AFLP bands that are polymorphic within the var.lanatusofC. lanatus, which is the largest set ever reported. The species-specific diagnostic SSRs and polymorphic AFLPs that are informative within and between the taxa reported in this paper would be immensely useful for future studies of these economically important genera.