Development and characterisation of SSR markers in the potato rot nematode Ditylenchus destructor

The potato rot nematode, Ditylenchus destructor, causes serious disease limiting the production of many crops. This disease usually decreases sweet potato yield by 20-50%, and in heavily infested fields the crop may be completely lost. Although the nematode has economic importance in China, its transmission route and genetic diversity are unknown. In this study, a collection of 1761 contigs of the D. destructor genome was mined for simple sequence repeat (SSR) markers, which resulted in the identification of 9745 SSRs. A total of 150 pairs of SSR primers were further developed and used for validation of the amplification rate and assessment of the polymorphism. Nine SSR markers were finally identified and analysed using 96 individual specimens of D. destructor sampled from four provinces in China. These loci were found to be moderately polymorphic with 2-8 alleles per locus. The observed and expected heterozygosity across the four populations ranged from 0.000 to 0.833 and from 0.000 to 0.666, respectively. This is the first report of the development and characterisation of genomic SSR markers in D. destructor. Our study demonstrated the obvious gene differentiation among different populations of D. destructor in China. This suggests that D. destructor in China may have been introduced from multiple origins. Much more work is needed on this species to identify patterns of spread, and the microsatellite loci we develop here should be useful in many regions for modelling range expansion, studying the evolution of resistance, and increasing the effectiveness of pest management strategies.