Comparison of gSSR and EST-SSR markers for analyzing genetic variability among tomato cultivars (Solanum lycopersicum L.).

In order to study genetic variability and develop better strategies for the utilization of 48 tomato cultivars from America, China, the Netherlands, and Portugal, genomic simple sequence repeat (gSSR) and EST-derived SSR (EST-SSR) markers were applied. In all, 15 of 82 gSSR and 18 of 115 EST-SSR markers showed polymorphic loci. There were 995 and 2072 clear fragments amplified by polymorphic gSSR and EST-SSR markers, respectively. The total and average number of alleles detected by EST-SSRs (75, 4.2) was more than gSSRs (54, 3.6) as a result of some multi-locus EST-SSRs. A lower polymorphism information content value was found in gSSRs (0.529) compared to EST-SSRs (0.620). Similarity coefficient matrixes of the 48 tomato cultivars were established based on the gSSRs and EST-SSRs, and UPGMA dendrograms were constructed from the gSSRs and EST-SSRs similarity coefficient matrixes. A high similarity was observed between the gSSRs and EST-SSRs dendrograms. Genetic variability of four tomato populations from different countries showed that the observed number of alleles and Nei's genetic diversity were highest in the American population, and the effective number of alleles was highest in the Dutch population. The estimated genetic structure showed some tomato cultivars from different countries shared a common genetic background, which might be related to gene flow. It was inferred that both gSSR and EST-SSR markers were effective to assess genetic variability of tomato cultivars, and the combination of both markers could be more effective for genetic diversity analysis in tomato.