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Two subspecies of Barbarea vulgaris are taxonomically recognized as ssp. vulgaris and ssp. arcuata. In addition, two types of Barbarea vulgaris ssp. arcuata occurs in Denmark. The G-type is resistant to an herbivorous flea beetle (Phyllotreta nemorum) whereas the P-type is susceptible. A previous study suggested that the P-type evolved by a loss of resistance from a resistant progenitor. We analyzed the genetic relatedness among eight Barbarea taxa: B. vulgaris spp. vulgaris, B. vulgaris ssp. arcuata G- and P-types, hybrids between the types, B. verna, B. intermedia, B. stricta, B. orthoceras and B. australis, using AFLP and SSR markers. A clear distinction between the G- and P-types was revealed. Both were distinct from B. vulgaris ssp. vulgaris, the G-type less so than the P-type. Barbarea verna and B. intermedia formed unambiguous clusters, whereas the remaining taxa produced less discrete groupings. Possible evolutionary scenarios for flea-beetle resistance and susceptibility are discussed, including lineage sorting from a polymorphic ancestral population, and de novo loss of resistance in the P-type of B. vulgaris ssp. arcuata. |
