Genetic structure of Brazilian wild rice (Oryza glumaepatula Steud., Poaceae) populations analyzed using microsatellite markers

Abstract

Knowledge of the genetic structure and diversity of natural populations is important in developing strategies for in situ and ex situ conservation. We used eight microsatellite loci to estimate genetic structure and investigate within and between population genetic variation in eleven Brazilian wild rice (Oryza glumaepatula) populations. The study showed the following genetic diversity parameters: average number of 3.1 alleles per locus; 77.3% polymorphic loci; 0.091 observed heterozygosity and 0.393 gene diversity. F-statistics detected by microsatellite loci were: F ST = 0.491 (and R ST = 0.608), F IS = 0.780 and F IT = 0.888. No population was in Hardy-Weinberg equilibrium. The estimated apparent outcrossing rate (t a = 0.143) indicated a predominance of self-fertilization. The gene flow values were low (Nm = 0.259 and 0.161 for F ST and R ST , respectively). Populations were spatially structured but without a correlation between genetic and geographic distances. Five populations (PG-4, PG-2, PU-1, SO-4, NE-18) were identified as priorities for conservation strategies. Populations from the Amazon biome showed heterogeneity with respect to intrapopulation diversity (H e ). The high level of genetic differentiation between populations and the high number of private alleles suggested that sampling should be carried out on a large number of O. glumaepatula populations for ex situ conservation purposes.

Assessing the genetic structure of Oryza glumaepatula populations with isozyme markers

“…Thus, considering six loci and four enzymatic systems, the mean number of alleles per locus ranged from 1.00 to 1.50, with a mean of 1.21 alleles per locus (Table 3), in agreement with the previous studies with isozyme (Akimoto et al, 1998;Buso et al, 1998) and microsatellite markers (Brondani et al, 2005) in O. glumaepatula. Karasawa et al (2007), however, observed a mean of 3.09 alleles per locus with microsatellites for this species. The percentage of polymorphic loci ranged from 0.0 to 50.0%.…”

“…However, the authors observed greater intrapopulational than interpopulational variability, a pattern usually found in the crossfertilized populations, which was explained considering the life history characteristics of this species. Studies of the genetic structure of O. glumaepatula populations were also recently conducted with microsatellite markers (Karasawa, 2005;Karasawa et al, 2007;Brondani et al, 2005;Silva et al, 2007), showing high values for F ST and R ST , suggesting a higher interpopulational variability, as well as the predominance of a selffertilizing breeding system. The purpose of this study, using isozymic markers, was to provide further information on the genetic diversity and genetic structure of 14 O. glumaepatula populations, originated from the hydrographic basins of the Amazon and of Rio Paraguay in the Pantanal ecosystem.…”

Elevada diversidade genética interpopulacional em Oryza glumaepatula Steud. (Poaceae) avaliada com microssatélites

“…Este número foi inferior aos obtidos por outros autores na mesma espécie. Karasawa et al (2007), utilizando oito locos de microssatélites, amplificaram 80 alelos em 11 populações de O. glumaepatula (total de 330 indivíduos), sendo a média de dez alelos por loco, enquanto Brondani et al (2005) analisando 10 locos SSR obtiveram 103 alelos em 30 populações de O. glumaepatula (total de 440 indivíduos), uma média de 10,3 alelos por loco observado.…”

“…Karasawa et al (2007), estudando 11 populações com maior número de indivíduos amostrados por população (variando de 17 a 35) e utilizando oito locos de SSR, observaram alelos privados em nove populações, variando de 1,0 a 8,0 por população. Por outro lado, Brondani et al (2005) (Slatkin 1995) em Oryza glumaepatula.…”

“…(Gao et al 2000a(Gao et al , 2002aGao 2004), espécie de arroz selvagem de origem asiática e reconhecida como ancestral da espécie cultivada O. sativa L. (Khush 1997 (Ishii & McCouch 2000;Gao et al 2000bGao et al , 2005Gao 2005;Zhou et al 2003). Para a espécie O. glumaepatula, podem ser citados, em especial, os trabalhos realizados por Brondani et al (2001Brondani et al ( , 2002, que apresentam iniciadores selecionados e testados para esta espécie, Brondani et al (2005) e Karasawa et al (2007) que obtiveram estimativas da estrutura genética e do sistema reprodutivo em populações brasileiras de O. glumaepatula.…”