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Strickler SR, Bombarely A, Munkvold JD, Menda N, Martin GB, Mueller LA.2014. Comparative genomics and phylogenetic discordance of cultivated tomato and close wild relatives. PeerJ PrePrints2:e377v1https://doi.org/10.7287/peerj.preprints.377v1
Background Studies of ancestry are difficult in tomato because it crosses with many wild relatives and species in the tomato clade have diverged very recently. As a result, the phylogeny in relation to its closest relatives remains uncertain. By using coding sequence from Solanum lycopericum, S. galapagense, S. pimpinellifolium, S. corneliomuelleri, and S. tuberosum and genomic sequence from two of cultivated tomato’s closest relatives, S. galapagense and S. pimpinellifolium, as well as an heirloom line, S. lycopersicum ‘Yellow Pear’, we have aimed to resolve the phylogenies of these closely related species as well as identify phylogenetic discordance in the reference cultivated tomato. Results Divergence date estimates suggest divergence of S. lycopersicum, S. galapagense, and S. pimpinellifolium happened less than 0.5 MYA. Phylogenies based on 8,857 coding sequences support grouping of S. lycopersicum and S. galapagense, although two secondary trees are also highly represented. A total of 29 genes in our analysis showed evidence of selection along the S. lycopersicum lineage. Whole genome phylogenies showed that while incongruence is prevalent in genomic comparisons between these accessions, likely as a result of incomplete lineage sorting and introgression, a primary phylogenetic history was strongly supported. Conclusions Based on analysis of these accessions, S. galapagense appears to be closely related to S. lycopersicum, suggesting they had a common ancestor prior to the arrival of an S. galapagense ancestor to the Galápagos Islands, but after divergence of the sequenced S. pimpinellifolium. Genes showing selection along the S. lycopersicum lineage may be important in domestication. Further analysis of intraspecific data in these species will help to establish the evolutionary history of cultivated tomato. The use of an heirloom line is helpful in deducing true phylogenetic information of S. lycopersicum and identifying regions of introgression from wild species.
A figure of SNPs and read coverage over all chromosomes for YP-1, S. galapagense, and S. pimpinellifolium.