RAPD variation within and between natural populations of the wild rice Oryza rufipogon from China and Brazil

Genetic variation within and between eight natural populations of Oryza rufipogon from China and Brazil was investigated at the DNA level by analysis of RAPD fragments. Out of 60 random primers, which were initially screened against DNA from four individuals, 20 generated highly reproducible RAPD fragments which were then used for further population analysis. With these primers, 95 discernible DNA fragments were produced and 78 (82.1%) were polymorphic, which indicated that high levels of genetic variation existed in these natural populations. In addition, the Chinese populations showed greater polymorphism than those from Brazil at both the population and regional levels. This is noteworthy considering that the Chinese populations are from a relatively restricted area of China. The factors responsible for these findings include the contrasting mating systems in the Brazilian and Chinese populations, and gene flow from annual cultivated rice to perennial natural populations in China. An Analysis of Molecular Variance (AMOVA) was used to apportion the variation between individuals within populations, between populations within regions, and between regions. Results showed that 61.8% of the total genetic diversity resided between the two continents, whereas only 14.9% and 23.3% was attributable to population differences within regions and to individual differences within a population, respectively. The great genetic differentiation between the Chinese and Brazilian populations is in agreement with recent treatment of the American form of O. rufipogon as a separate species, O. glumaepatula.