Potato is an important world crop with an abundant diversity of wild relatives for research and breeding. About 200 tuber-bearingSolarium relatives of the cultivated potato are distributed from southern Chile to the southwest USA. Only five of these have been reported in the USA, and only two exist with certainty (S. fendleri andS. jamesii). This paper reviews the procedures and outcome of 12 expeditions by the authors to the Southwest USA from 1992 to 2001 that resulted in 132 new germplasm accessions. Previously published information allowed successful collection from many documented sites, and many new sites were discovered and sampled. Incomplete or inaccurate records were improved and refined, making it possible for others to easily find these sites. When assessed for genetic diversity, re-collections from the same site were found to be nearly as genetically different as samples from different sites, and genetic differences between sites could not be linked with any ecogeographic parameter, even physical distance of separation. In conclusion, wild potato germplasm from the USA and associated knowledge was greatly expanded, but reaching the goal of obtaining and keeping the most complete sample possible of the genetic diversity will involve additional collecting and continued research on the reproductive behavior of these plants.
