Darwin, S.C. (2009) The systematics and genetics of tomatoes on the Galápagos Islands (Solanum, Solanaceae). Doctoral thesis, UCL (University College London).
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Galápagos tomatoes (Solanum section Lycopersicon) have long interested scientists and plant breeders. Several morphological and physiological characters found in the endemic Galápagos tomatoes have been bred into the cultivated Solanum lycopersicum, making the native plants an invaluable resource for the development of this important global crop. Extensive fieldwork was carried out on twelve islands, old records were confirmed, new records added, but several previously recorded populations of endemic tomatoes could not be confirmed. I collected tomatoes from 12 islets and Islands. Detailed morphometric analysis on c.400 plants and extensive genetic studies on c.1,200 plants were carried out in addition to fieldwork and natural history studies. Observations and experiments were carried out on herbarium specimens, field collected and green house grown accessions. I confirmed the presence of four taxa in the Galápagos Islands – two endemic species S. cheesmaniae and S. galapagense, the latter here described as new, and two introduced species S. pimpinellifolium and S. lycopersicum. Hybrids were found involving all taxa growing in the Galápagos Islands. Of particular interest is an extensive hybrid zone between S. cheesmaniae and S. pimpinellifolium spanning 20km along the Baltra Road on Isla Santa Cruz. Hybridization raises the threat of extinction by introgression and the possibility of the evolution of a serious invasive species. Conservation recommendations are proposed. In addition, a genetic analysis was undertaken of 60 seed bank accessions of all four tomato species from the Galápagos. Again, indications of hybridization were found, raising the potential of introgression within the seed bank collections, occurring potentially during rejuvenation cycles. Furthermore, I propose a new outline for a generic invasive species threat/impact scoring system. Applying this new system I class Solanum pimpinellifolium as an alien invasive species and assess its impact on Isla Santa Cruz in the Galápagos Islands.
|Title:||The systematics and genetics of tomatoes on the Galápagos Islands (Solanum, Solanaceae)|
|Open access status:||An open access version is available from UCL Discovery|
|UCL classification:||UCL > School of Life and Medical Sciences > Faculty of Life Sciences > Biosciences (Division of) > Genetics, Evolution and Environment|
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