Molecular support for the hybrid origin of the wild potato species Solanum x rechei

Twenty-seven of the 232 wild potato species (Solanum sect. Petota) have been hypothesized to be of natural hybrid origin. Prior molecular data have failed to support hybrid origins involving two other wild potato species, Solanum raphanifolium Cardenas and Hawkes and S. chacoense Bitter, and hybrid speciation has never been supported with molecular data in sect. Petota. This study was conducted to test the hybrid origin of Solanum x rechei Hawkes and Hjert. It is a locally common and weedy wild potato species from Argentina, occurring at the extreme southern end of the range of S. microdontum Wittm., and near the northern end of the range of S. kurtzianum Bitter, its two putative parents. Solanum x rechei is diploid (2n = 2x = 24) with triploid (2n = 3x = 36) populations, S. kurtzianum is diploid (2n = 2x = 24), and S. microdontum is diploid (2n = 2x = 24), with triploid populations at its extreme southern range. A prior study supported the hybrid origin of S. x rechei by intermediate morphology of natural and synthetic hybrids, reduced pollen stainability of the natural and synthetic hybrids, and distributional evidence. Our studies of new collections and prior germplasm collections fail to support the morphological intermediacy of S. x rechei, but lack of morphological intermediacy is common for many hybrids. Hybrid origin was instead verified by reduced pollen stainability and additive parent-specific single- to low-copy nuclear restriction fragment length polymorphisms (RFLPs) in S. x rechei. These data suggest that other wild potato species also may be of hybrid origin, which may help explain some of the taxonomic confusion in the group.