Assessment of population differentiation and linkage disequilibrium in Solanum pimpinellifolium using genome-wide high-density SNP markers

To mine new favorable alleles for tomato breeding, we investigated the feasibility of utilizing Solanum pimpinellifolium as a diverse panel of genome-wide association study through the restriction site-associated DNA sequencing technique. Previous attempts to conduct genome-wide association study using S. pimpinellifolium were impeded by an inability to correct for population stratification and by lack of high-density markers to address the issue of rapid linkage disequilibrium decay. In the current study, a set of 24,330 SNPs was identified using 99 S. pimpinellifolium accessions from the Tomato Genetic Resource Center. Approximately 84% PstI site-associated DNA sequencing regions were located in the euchromatic regions, resulting in the tagging of most SNPs on or near genes. Our genotypic data suggested that the optimum number of S. pimpinellifolium ancestral subpopulations was three, and accessions were classified into seven groups. In contrast to the SolCAP SNP genotypic data of previous studies, our SNP genotypic data consistently confirmed the population differentiation, achieving a relatively uniform correction of population stratification. Moreover, as expected, rapid linkage disequilibrium decay was observed in S. pimpinellifolium, especially in euchromatic regions. Approximately two-thirds of the flanking SNP markers did not display linkage disequilibrium. Our result suggests that higher density of molecular markers and more accessions are required to conduct the genome-wide association study utilizing the Solanum pimpinellifolium collection.