Origins, colonization, and lineage recombination in a widespread perennialsoybean polyploid complex

Polyploidy is a dominant feature of flowering plant genomes, including thos e of many important crop species, implying that polyploidy confers evolutio nary advantages on plant species. Recent molecular studies suggest that pol yploids often originate many times from the same progenitor diploids, For t his to provide a broader genetic base for a polyploid species, there must b e lineage recombination in the genomes of polyploids having different origi ns, and this has rarely been documented in recently formed wild polyploid s pecies. Glycine tabacina, a wild relative of soybean, forms a widespread po lyploid complex in Australia and the islands of the Pacific Ocean. In a sam ple of 40 G. tabacina plants, DNA sequence variation at one homoeologous hi stone H3-D locus identified three alleles, each also found in Australian di ploid Glycine species. These data agree with our previous studies of chloro plast DNA variation in suggesting that this polyploid has originated severa l times. Both the origins of the polyploid and several independent dispersa ls from Australia to oceanic islands appear to have occurred within the las t 30,000 years. The distributions of histone alleles, chloroplast haplotype s, and alleles at two isozyme loci were uncorrelated, and 20 multilocus gen otypes were found among the 40 plants sampled. Extensive lineage recombinat ion is thus hypothesized in the polyploid, involving migration and occasion al outcrossing in this predominantly inbreeding species. The combination of multiple origins with gene exchange among lineages increases the genetic b ase of a polyploid and may help explain the wide colonization of polyploid G. tabacina relative to its diploid progenitors.