Spooner and van den Berg, 1992). Eleven of the putative hybrids are diploid, six triploid, three tetraploid, Twenty-seven of the 232 wild potato species (Solanum sect. Petthree pentaploid, and four hexaploid. Five of the seven ota ) have been hypothesized to be of natural hybrid origin. Prior cultivated species and 22 of the wild species accepted molecular data have failed to support hybrid origins involving two other wild potato species, Solanum raphanifolium Cárdenas and by Hawkes (1990) are of putative hybrid origin. Hawkes and S. chacoense Bitter, and hybrid speciation has never Many of these hybridization hypotheses have been been supported with molecular data in sect. Petota. This study was generated from intuitive methods involving intermediconducted to test the hybrid origin of Solanum 3 rechei Hawkes and ate morphology and inference from distributional data Hjert. It is a locally common and weedy wild potato species from (Hawkes, 1963, 1990). Others have been supported by Argentina, occurring at the extreme southern end of the range of artificial reconstruction of the putative hybrids (Okada S. microdontum Wittm., and near the northern end of the range of and Clausen, 1982; Okada and Hawkes, 1978), additivity S. kurtzianum Bitter, its two putative parents. Solanum 3 rechei is of flavonoids and/or tuber proteins (Cribb and Hawkes, diploid (2n 5 2x 5 24) with triploid (2n 5 3x 5 36) populations, 1986; Rickeman and Desborough, 1978), and by cytogeS. kurtzianum is diploid (2n 5 2x 5 24), and S. microdontum is diploid netic data (Matsubayashi, 1991). (2n 5 2x 5 24), with triploid populations at its extreme southern Solanum 3 rechei Hawkes and Hjert. is one of the range. A prior study supported the hybrid origin of S. 3 rechei by intermediate morphology of natural and synthetic hybrids, reduced better documented hybrids. It is endemic to the eastern pollen stainability of the natural and synthetic hybrids, and distribuslopes of the Sierra de Famatina in Argentina, Province tional evidence. Our studies of new collections and prior germplasm of La Rioja, Department of Chilecito. Eight populations collections fail to support the morphological intermediacy of S. 3 are scattered over a distance of 12 km, with populations rechei, but lack of morphological intermediacy is common for many containing hundreds of individuals (Okada and Hawkes, hybrids. Hybrid origin was instead verified by reduced pollen stainabil1978; Spooner and Clausen, 1993). Within this region, ity and additive parent-specific singleto low-copy nuclear restriction S. 3 rechei is common and weedy, growing along roadfragment length polymorphisms (RFLPs) in S. 3 rechei. These data sides in ditches and open fields, or under trees in orsuggest that other wild potato species also may be of hybrid origin, chards. The species was first collected in 1928, and has which may help explain some of the taxonomic confusion in the group. been persistent for at least 69 yr. Solanum 3 rechei was first described as a distinct species, and was hypothesized to be ancestral to S. magS L. sect. Petota Dumort., the potato and its lia Schltdl. (Hawkes, 1963). Subsequent field studies by wild relatives, contains seven cultivated and 225 Hawkes and Hjerting (1969) suggested that S. 3 rechei wild species, according to the latest taxonomic interprewas of hybrid origin between S. kurtzianum Bitter and tation (Hawkes, 1990). An alternative classification S. microdontum Wittm., with introgression from S. speg(Child, 1990), supported by morphological and chloroazzinii Bitter. plast DNA (cpDNA) data (Spooner et al., 1993), classiSolanum 3 rechei is narrowly restricted to the overlap fies all of the tuber-bearing species in sect. Petota, and zone of S. kurtzianum and S. microdontum. It grows the nontuber-bearing species in sect. Etuberosum (Bunear the northern end of the range of S. kurtzianum, kasov and Kameraz) A. Child, sect. Juglandifolium and at the extreme southern end of the range of S. mi(Rydb.) A. Child, and sect. Lycopersicum (Mill.) Wettst. crodontum (Fig. 1). All known populations of S. microHawkes (1990) classifies the 223 tuber-bearing species dontum are diploid (2n 5 2x 5 24), except for the into 19 series, distributed from the southwestern USA presence of triploid (2n 5 3x 5 36) populations in the to southern Chile, with a concentration of diversity in extreme southern end of its range (Okada, 1981). All the Andes. known populations of S. kurtzianum are diploid (2n 5 While well-developed crossing barriers prevent hy2x 5 24) (Hawkes and Hjerting, 1989; Hawkes, 1990). bridization between some species (Johnston and HanneSolanum microdontum, S. 3 rechei, and S. kurtzianum man, 1980, 1982; Hanneman, 1994), many others are are the only wild potato species recorded from the Defreely able to hybridize naturally and artificially partment of Chilecito where S. 3 rechei grows. The (Hawkes, 1978, 1990; Hawkes and Hjerting, 1969, 1989; closest other wild potato species are S. acaule Bitter Johnston and Hanneman, 1980; Ochoa, 1990). Natural ssp. acaule, S. acaule ssp. aemulans (Bitter and Wittm.) interspecific hybridization has been hypothesized to be Hawkes and Hjert., S. chacoense Bitter, and S. spegazcommon in sect. Petota (sensu Child, 1990). There are zinii, found in the Province of La Rioja in the Depart27 diploid or polyploid taxa of putative hybrid origin in ments of Capital, Famatina, and Sanagasta, at least 20 the group, involving both wild and cultivated species km away by air (Hawkes and Hjerting, 1969; Okada and Hawkes, 1978). A.M. Clausen, Estación Experimental Agropecuaria, Instituto Nacional de Tecnologı́a Agropecuaria (INTA), C.C. 276, 7620 Balcarce, Argentina; and D.M. Spooner, Vegetable Crops Research Unit, Abbreviations: BAL, Herbarium of the Instituto Nacional de TecnoUSDA-ARS, Dep. of Horticulture, 1575 Linden Dr., Univ. of Wisconlogı́a Agropecuaria (INTA), in Balcarce, Argentina; PCA, Principal sin, Madison, WI 53706-1590, USA Received 29 May 1997. *CorreComponents Analysis; PTIS, Herbarium of the Potato Introduction sponding author (email@example.com). Station of NRSP-6; NRSP-6, National Research Program-6, the USA Potato Genebank at Sturgeon Bay, WI. Published in Crop Sci. 38:858–865 (1998).