Genetic Diversity in Watermelon Cultivars and Related Species Based on AFLPs and EST-SSRs

Abstract

The genetic relationships among 27 watermelon cultigens (Citrullus lanatus var. lanatus) from different countries of origin and with different horticultural characteristics and 5 related wild-type species and subspecies (Citrullus colocynthis, Citrullus lanatus var. citroides, and Citrullus rehmii) were assessed using amplified fragment length polymorphism (AFLP) and expressed sequence tag-simple sequence repeat (EST-SSR) markers. AFLPs were evaluated using 16 EcoRI-MseI primer combinations, and 862 alleles (an average of 53.8 alleles per primer combination) were scored. Polymorphisms were found in 806 (93.4%) alleles, whereas 56 monomorphic alleles were identified. Using 16 EST-SSR primer sets, 103 alleles were scored, and all 103 alleles were polymorphic among the 32 genotypes with an average of 6.4 polymorphic alleles per primer pair. However, the high polymorphic ratio among the AFLPs and EST-SSRs was largely due to the wild-type species, while little diversity was observed among the adapted cultivars. Genetic similarity coefficients were calculated based on the 965 polymorphic AFLP and EST-SSR alleles, and a phenetic tree was constructed. The dendrogram contained 2 major clusters. Cluster I included all adapted watermelon cultivars, and the similarity among these cultigens was very high (0.94-0.98), demonstrating cross relationships and a narrow genetic background. Cluster II was composed of 4 wild-type species. The genetic distance between the nodes that comprise these 2 clusters was approximately 0.63, indicating a high level of genetic dissimilarity between the adapted watermelon species and the other related species. The low level of marker polymorphism among the adapted cultivars implies that a severe bottleneck in genetic diversity existed in watermelon during the initial breeding practices.

Genetic diversity and population structure of core watermelon (Citrullus lanatus) genotypes using DArTseq-based SNPs

“…A similar distinct clustering pattern of wild and cultivated watermelon genotypes has also been reported by Hwang et al (2011), who clustered 32 watermelon genotypes into two major clusters based on AFLP and EST-SSR markers. In the present study, the genetic relationship based on three different approaches (NJ dendrogram, PCoA and population structure analysis) gave similar results.…”

Grouping and genetic diversity of different watermelon ecotypes based on agro-morphological traits and ISSR marker

“…According to high genetic similarity values and low private band among studied different watermelon ecotypes from different region this hypothesis was confirmed that watermelon ecotypes may have been originated from the common ancestry. High genetic similarity among watermelon ecotypes can be due to artificial selection by humans over a long duration breeding programs, improved by sequential selection of the best traits (Kwon et al 2010) and due to the asexual propagation of the species (Hwang et al 2011). Thus, the present results indicated the robustness of the ISSR technique in providing a higher degree of resolution for discriminating closely related genotypes within the species of watermelon.…”

Genetic Diversity of Colocynth (Citrullus colocynthis Schrader) Populations in the Eastern Desert of Egypt as Revealed by Morphological Variation and ISSR Polymorphism

“…lanatus ) and the wild C. colocynthis was very high (Hwang et al. ). The wild‐type accessions had round and white fruits in common and diverse rind colors, seed sizes, and seed colors.…”

“…Hwang et al. () used EST–SSR markers to differentiate six watermelon cultigens, Citrullus lanatus var. citroides and C. colocynthis based on fruit characteristics.…”