Population structure and phylogeography ofSolanum pimpinellifoliuminferred from a nuclear gene

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Abstract
Phylogeographical studies are emerging as a powerful tool for understanding the population structure and evolution of wild relatives of crop species. Because of their value as genetic resources, there is great interest in exploring the distribution of variation in wild relatives of cultivated plants. In this study, we use sequence variation from the nuclear gene, fruit vacuolar invertase (Vac), to investigate the population history ofSolanum pimpinellifolium.Solanum pimpinellifoliumis a close relative of the cultivated tomato and has repeatedly served as a source of valuable traits for crop improvement. We sequenced the second intron of theVacgene in 129 individuals, representing 16 populations from the northern half of Peru. Patterns of haplotype sharing among populations indicate that there is isolation by distance. However, there is no congruence between the geographical distribution of haplotypes and their genealogical relationships. Levels of outcrossing decrease towards the southernmost populations, as previously observed in an allozyme study. The geographical pattern ofVacvariation supports a centre of origin in northern Peru forS. pimpinellifoliumand a gradual colonization along the Pacific coast. This implies that inbreeding populations are derived from outcrossing ones and that variation present at theVaclocus predates the spread ofS. pimpinellifolium. The expansion of cities and human agricultural activity in the habitat ofS. pimpinellifoliumcurrently pose a threat to the species.