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 ruf ipogon 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 fr agments which were then used for further population analysis. With these pr imers, 95 discernible DNA fragments were produced and 78 (82.1%) were polym orphic, which indicated that high levels of genetic variation existed in th ese natural populations. In addition, the Chinese populations showed greate r polymorphism than those from Brazil at both the population and regional l evels. This is noteworthy considering that the Chinese populations are from a relatively restricted area of China. The factors responsible for these f indings include the contrasting mating systems in the Brazilian and Chinese populations, and gene flow from annual cultivated rice to perennial natura l 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 regi ons and to individual differences within a population, respectively. The gr eat genetic differentiation between the Chinese and Brazilian populations i s in agreement with recent treatment of the American form of O. rufipogon a s a separate species, O. glumaepatula.