Comparative analysis of genetic diversity among Chinese watermelon germplasmsusing SSR and SRAP markers, and implications for future genetic improvement

Abstract

The genetic diversity of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] in China, the world's largest producer of watermelon fruits, has not been examined. Two molecular markers, sequence-related amplified polymorphism (SRAP) and simple sequence repeat (SSR), were used to investigate the genetic variation and genetic relationship among 54 Chinese watermelon accessions, as well as 7 accessions from Africa, the United States, and Japan. SRAP assay generated 312 bands, of which 163 were polymorphic, while SSR assay detected 101 alleles with 87 polymorphic alleles and 114 genotypes. A comparative analysis of the diversity index, effective multiplex ratio, and marker index of the 2 markers showed higher efficiency of SRAP markers in watermelon germplasm fingerprinting. The Mantel test resulted in a high correlation between SRAP and SSR data with a value of γ = 0.863, revealing a good fit between the 2 marker systems. Genetic diversity among the accession set was estimated by a construction of dendrograms using SRAP, SSR, or SRAP-SSR combined data. There was clear consistency between the 3 dendrograms on the positioning of most accessions. The study demonstrated that most Chinese cultivated germplasms (CCGs) were clustered independently of their geographical distribution and horticultural classification, and had a narrow genetic base; most CCGs and foreign cultivars had a high genetic closeness and showed similar lineages; and the 4 wild accessions were the most genetically diverse, followed by the small-fruited accessions from northern China and edible-seeded accessions. We concluded that CCGs lacked genetic variation, and we offer a means of introducing new genetic diversity into the watermelon germplasm pool in China, which is essential to maximizing productivity in watermelon.

Genetic analyses of Turkish watermelons based on SRAP markers

“…In addition, the Turkish watermelons were slightly different from four popular cultivars (36, Sugar Baby; 39, Crimson Sweet; 233, Calhoun Gray; and 235, Charleston Gray) (Figure 1). Geography-based clustering among the Turkish watermelons did not exist in this study, which was also consistent with previous reports of watermelons (Solmaz et al, 2010;Ocal et al, 2014;Wang et al, 2015).…”

“…For example, data produced with SRAP, inter-simple sequence repeat (ISSR), random amplified polymorphic DNA (RAPD), and peroxidase gene-based polymorphism markers had a correlation value of 0.81 as verified by the Mantel test, but data of RAPD markers always had lower correlation values (about 0.7). Hence, SRAP-based estimation of relationships highly correlates with the results of most marker systems such as simple sequence repeat, amplified fragment length polymorphism, and ISSR (Wang et al, 2015). For estimating genome sampling size, one approach is to use a set that covers the genome.…”

Assessment of the genetic diversity of dessert watermelon (Citrullus lanatus var. lanatus) landrace collections of South Africa using SSR markers

“…Sheng et al (2012) detected a total of 94 putative alleles, similar to the current study. However, this was lower than 133, 101 and 795 alleles detected by Zhang et al (2016), Wang et al (2015) and Reddy et al (2015) among watermelon accessions, respectively. Nimmakayala et al (2009) reported a total of 169 alleles amplified in watermelon accessions.…”

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

“…In a comparative study of genetic diversity between C. lanatus germplasms using SSR and SRAP markers, Wang et al. () found that the most germplasms were grouped separately based on their geographical distribution and horticultural classification and have low genetic variations.…”