Population genetic structure of wild rice Oryza glumaepatula distributed in the Amazon flood area influenced by its life-history traits

Wild plant species develop their own way of living to adapt to the specific environment of their habitats. Their life-history traits strongly affect the genetic structure of the population. The wild species Oryza glumaepatula Steud. growing in the Amazon basin seems to have characteristic life-history traits suited for the flood condition. At the vegetative growth stage, the culms frequently break at internodes. With no roots anchoring on the ground, plant bodies floating in the water move downriver by water current and wind. To examine the association between the life-history traits and genetic population structure of Amazonian O. glumaepatula, we analysed allozyme variability at 29 loci of 16 enzymes using 37 populations from five regions. Allozymes were not so variable (total gene diversity H-E = 0.044) compared with Asian wild rice, O. rufipogon Griff. The bottleneck effect and rare opportunity of interspecies gene flow may prevent the development of allozyme variability. Population genotypes tended to be differentiated among geographically isolated regions. Observed heterozygosities were much lower than expected heterozygosities, or gene diversity (H-O = 0.003 for whole population) and F-IS over polymorphic loci was 0.931, indicating that O. glumaepatula has developed an inbreeding system. But, the intrapopulation gene diversity (H-S) was higher than interpopulation gene diversity (D-ST), as generally observed in outbreeding populations. The migration ability of O. glumaepatula makes long-distance seed dispersal possible. This might have led to frequent gene flow among populations.