Use of Native Potatoes for Research and Breeding

Potatoisanimportantworldcropwithanabundantdiversityofwildrelativesforresearchandbreeding.Over100 tuber-bearing Solanum relatives of the cultivated potato occur naturally from southern Chile to the southwest United States. Only five of these have been reported in the United States, and only two exist with certainty (S. stoloniferum/fendleri and S. jamesii). The authors and colleagues have conducted expeditions in the southwest United States each season since 1992, collecting over 200 new germplasm samples. This work has greatly improved the representation of these species in the genebank with respect to geography and genetic diversity available to germplasm users worldwide. Corrected or refined collection site information now makes it possible to easily find these typically small populations for continued in situ study and sampling. Collecting experiences, often in contrast with conventional wisdom, have been documented for the benefit of future collectors. A broader sampling of the region has allowed studies of the association of eco-geo parameters with patterns of genetic diversity in an attempt to predict ''hot spots'' of diversity for future expeditions. Evaluation of these materials has resulted in the discovery of new useful traits—novel mutants, disease and pest resistances, and human nutritional compounds. Potatoes are native to the Americas, con- centrated in the western mountains extending from southern Chile to southern Utah and ColoradointheUnitedStates.Theauthorshere describetheireffortstocollectandstudypop- ulations of the two wild species originating in the United States. The diploid, Solanum jamesii ,i s assumed to be an obligate out- crosser and is very heterozygous and hetero- geneous. This is the most northern of all the potatoes. In fact, nearly all of the known pop- ulationsof this species originate in theUnited States. The tetraploid, historically known as Solanum fendleri, and referred to assuch here, has recently been reclassified under Solanum stoloniferum,aspeciesnamethatnowincludes expedition also sought specifically to recol- lect samples from sites originally collected in1958and1978.Thus,these materialswould alsoservetoansweracollectingresearchques- tion: Are populations in the genebank, some- times collected decades earlier, still genetically representative of the corresponding plants liv- ing in the wild? We found that they were not (del Rio et al., 1997). Thus, we gained insights about the status of old collections and recol- lections: Although it is a negative to find that the old collections cannot be assumed to be backed up in nature, it is positive to find that the provenance data are a handy guide to the location of sites from which new diversity can be collected. Germplasm managers wouldlike toknow if stocks from the wild seem to have new geneticdiversityonlybecausetheyareinsome waysubjectedtoselectioninthegenebankthat ''domesticates'' them. We found that this was not the case (del Rio and Bamberg, 2003). For example, plants of S. jamesii collected in the wild may appear to be uniform for dominant markers, but they do possess the recessive allelesthatbecomeevidentwhentheaccession is converted to botanical seeds in the gene- bank.Sothesamegeneticsarepresentinboth locations, if not the same phenotypes. This observation also illustrates that traits noted in genebank-derived seedlots may not be pres-