Origins, colonization, and lineage recombination in a widespread perennial soybean polyploid complex

Polyploidy is a dominant feature of flowering plant genomes, including those of many important crop species, implying that polyploidy confers evolutionary advantages on plant species. Recent molecular studies suggest that polyploids often originate many times from the same progenitor diploids. For this to provide a broader genetic base for a polyploid species, there must be lineage recombination in the genomes of polyploids having different origins, and this has rarely been documented in recently formed wild polyploid species. Glycine tabacina, a wild relative of soybean, forms a widespread polyploid complex in Australia and the islands of the Pacific Ocean. In a sample of 40 G. tabacina plants, DNA sequence variation at one homoeologous histone H3-D locus identified three alleles, each also found in Australian diploid Glycine species. These data agree with our previous studies of chloroplast DNA variation in suggesting that this polyploid has originated several times. Both the origins of the polyploid and several independent dispersals from Australia to oceanic islands appear to have occurred within the last 30,000 years. The distributions of histone alleles, chloroplast haplotypes, and alleles at two isozyme loci were uncorrelated, and 20 multilocus genotypes were found among the 40 plants sampled. Extensive lineage recombination is thus hypothesized in the polyploid, involving migration and occasional outcrossing in this predominantly inbreeding species. The combination of multiple origins with gene exchange among lineages increases the genetic base of a polyploid and may help explain the wide colonization of polyploid G. tabacina relative to its diploid progenitors.