Comparison of microsatellites and isozymes in genetic diversity studies of Oryza glumaepatula (Poaceae) populations.

The study of the genetic structure of wild plant populations is essential for their management and conservation. Several DNA markers have been used in such studies, as well as isozyme markers. In order to provide a better comprehension of the results obtained and a comparison between markers which will help choose tools for future studies in natural populations of Oryza glumaepatula, a predominantly autogamous species, this study used both isozymes and microsatellites to assess the genetic diversity and genetic structure of 13 populations, pointing to similarities and divergences of each marker, and evaluating the relative importance of the results for studies of population genetics and conservation. A bulk sample for each population was obtained, by sampling two to three seeds of each plant, up to a set of 50 seeds. Amplified products of eight SSR loci were electrophoresed on non-denaturing polyacrylamide gels, and the fragments were visualized using silver staining procedure. Isozyme analyses were conducted in polyacrylamide gels, under a discontinuous system, using six enzymatic loci. SSR loci showed higher mean levels of genetic diversity (A=2.83, p=0.71, A(p)=3.17, H(o)=0.081, H(e)=0.351) than isozyme loci (A=1.20, p=0.20, A(p)=1.38, H(o)=0.006, H(e)=0.056). Interpopulation genetic differentiation detected by SSR loci (R(ST)=0.631, equivalent to F(ST)=0.533) was lower than that obtained with isozymes (F(ST)=0.772). However, both markers showed high deviation from Hardy-Weinberg expectations (F(IS)=0.744 and 0.899, respectively for SSR and isozymes). The mean apparent outcrossing rate for SSR (t(a)=0.14) was higher than that obtained using isozymes (t(a)=0.043), although both markers detected lower levels of outcrossing in Amazonia compared to the Pantanal. The migrant number estimation was also higher for SSR (Nm=0.219) than isozymes (Nm=0.074), although a small number for both markers was expected due to the mode of reproduction of this species, defined as mixed with predominance of self fertilization. No correlation was obtained between genetic and geographic distances with SSR, but a positive correlation was found between genetic and geographic distances with isozymes. We conclude that these markers are divergent in detecting genetic diversity parameters in O. glumaepatula and that microsatellites are powerful for detecting information at the intra-population level, while isozymes are more powerful for inter-population diversity, since clustering of populations agreed with the expectations based on the geographic distribution of the populations using this marker.