Patterns of nuclear and chloroplast genetic diversity and structure of manioc along major Brazilian Amazonian rivers.

Background and Aims: Amazonia is a major world centre of plant domestication, but little is known about how the crops were dispersed across the region. Manioc (Manihot esculenta) was domesticated in the south-western Amazon basin, and is the most important staple food crop that originated in Amazonia. Current contrasting distributions may reflect distinct histories of dispersal of bitter and sweet manioc landraces. To produce new insights into the evolutionary history of the crop, we investigated the contemporary genetic diversity and structure of bitter and sweet manioc along major Amazonian rivers. Methods: The patterns of genetic structure and diversity of wild and cultivated sweet and bitter manioc with four chloroplast and 14 nuclear microsatellite markers were evaluated. Results were interpreted in terms of the crop's dispersal. Key results: No phylogeographic patterns among rivers were detected, and genetic structure among rivers was confounded by the bitter-sweet divergence. However, differences in the distribution of nuclear diversity and somewhat distinctive patterns of genetic structure across rivers were observed within bitter and sweet manioc. Conclusions: Various pre-Columbian and post-European conquest events in the history of Amazonian occupation may explain the absence of clearer patterns of genetic structure. However, the wide distribution of the most common chloroplast haplotype agrees with an early dispersal of manioc across Brazilian Amazonia. Furthermore, differences in genetic structure and in the spatial distribution of genetic diversity suggest that bitter and sweet manioc had distinct dispersal histories. Knowledge about how prehistoric and contemporary Amazonian peoples manage their crops is valuable for the maintenance and conservation of the impressive diversity of their native crops.

Pollen and seed flow patterns of Carapa guianensis Aublet. (Meliaceae) in two types of Amazonian forest.

Various factors affect spatial genetic structure in plant populations, including adult density and primary and secondary seed dispersal mechanisms. We evaluated pollen and seed dispersal distances and spatial genetic structure of Carapa guianensis Aublet. (Meliaceae) in occasionally inundated and terra firme forest environments that differed in tree densities and secondary seed dispersal agents. We used parentage analysis to obtain contemporary gene flow estimates and assessed the spatial genetic structure of adults and juveniles. Despite the higher density of adults (diameter at breast height ≥ 25 cm) and spatial aggregation in occasionally inundated forest, the average pollen dispersal distance was similar in both types of forest (195 ± 106 m in terra firme and 175 ± 87 m in occasionally inundated plots). Higher seed flow rates (36.7% of juveniles were from outside the plot) and distances (155 ± 84 m) were found in terra firme compared to the occasionally inundated plot (25.4% and 114 ± 69 m). There was a weak spatial genetic structure in juveniles and in terra firme adults. These results indicate that inundation may not have had a significant role in seed dispersal in the occasionally inundated plot, probably because of the higher levels of seedling mortality.

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, Ho=0.081, He=0.351) than isozyme loci (A=1.20, p=0.20, A P=1.38, Ho=0.006, He=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 ( =0.14) was higher than that obtained using isozymes ( =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 ...

El estudio de la estructura genética de poblaciones de plantas silvestres es esencial para su manejo y conservación. Varios marcadores de ADN e isoenzimas se han utilizado en este tipo de análisis. Con el fin de proporcionar una mejor comprensión de los resultados obtenidos y saber que marcador codominante elegir para futuros estudios en poblaciones naturales de Oryza glumaepatula, este trabajo busco evaluar y comparar dos marcadores de ADN, isoenzimas y microsatélites, en la diversidad y estructura genética de 13 poblaciones, destacando las similitudes y divergencias de cada marcador, así como la importancia relativa de los resultados en genética de poblaciones y conservación. Para los SSR, ocho loci SSR fueron evaluados, y los fragmentos se visualizaron utilizando el procedimiento de coloración con plata. Los análisis de isoenzimas se realizaron en geles de poliacrilamida, en los seis loci enzimáticos. Los loci SSR mostraron mayores niveles de diversidad genética que los loci isoenzimáticos, en promedio. La diferenciación genética entre los loci SSR (R ST=0.631, equivalente a F ST=0.533) fue inferior a la obtenida con las isoenzimas (F ST=0.772). Ambos marcadores mostraron alta desviación del equilibrio de Hardy-Weinberg (F IS=0.744 y 0.899, respectivamente, para SSR e isoenzimas). La tasa media aparente de cruzamiento para SSR ( =0.14) fue mayor que la obtenida con isoenzimas ( =0.043), aunque ambos marcadores detectaron niveles más bajos en la tasa de fecundación cruzada para la Amazonia, en comparación con la región del Pantanal. La estimación de número de migrantes también fue mayor para los SSR (Nm=0.219) que en isoenzimas (Nm=0.074). No se obtuvo ninguna correlación entre las distancias genéticas y geográficas para los SSR, y para las isoenzimas se obtuvo una correlación positiva entre las distancias genéticas y geográficas. Llegamos a la conclusión de que estos marcadores son divergentes en la detección de los parámetros de la diversidad genética en O. glumaepatula y que los microsatélites son más eficientes para detectar la información a nivel intra-poblacional, mientras que las isoenzimas son más potentes para detectar la diversidad entre poblaciones.

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.

New microsatellite loci for water yam (Dioscorea alata, Dioscoreaceae) and cross-amplification for other Dioscorea species.

PREMISE OF THE STUDY: Dioscorea alata L. is one of the most widely distributed species of the genus in the humid and semihumid tropics and is associated with traditional agriculture. Only a few microsatellite markers have been developed so far for this and other Dioscorea species. METHODS AND RESULTS: We isolated 14 codominant polymorphic microsatellite markers using a microsatellite-enriched genomic library technique. Ten microsatellite loci were selected, and 80 D. alata accessions from different regions in Brazil were evaluated with nine polymorphic loci. The polymorphism information content (PIC) varied from 0.39 to 0.78 and the power discrimination (PD) ranged from 0.15 to 0.91. Six of the markers showed transferability for the species D. bulbifera, D. cayenensis-D. rotundata, and D. trifida. CONCLUSIONS: The SSR markers obtained are an important tool for further studies aiming to characterize the genetic diversity in D. alata and other Dioscorea spp. accessions.

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

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 percent 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 (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. 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.

Mating system of Brazilian Oryza glumaepatula populations studied with microsatellite markers.

BACKGROUND AND AIMS: A knowledge of natural populations' breeding systems is important in order to implement in situ and ex situ management and conservation practices. Using microsatellite markers, three Oryza glumaepatula populations from Brazil were studied to determine the breeding system and genetic structure parameters of this species. METHODS: Each population represented by ten families with ten individuals per family was studied using eight microsatellite primers. Families of the Rio Xingu population (XI) were obtained from the greenhouse, whereas families from Rio Solimoes (SO) and Rio Paraguay (PG) were collected from the wild. Amplified products electrophoresed on non-denaturing polyacrylamide gels were visualized with a silver staining procedure. The mating system parameters were analysed based on the mixed mating model (software MLTR) while genetic structure analyses of the three populations and their families were performed using the FSTAT software. KEY RESULTS: The mean numbers of alleles per loci were 2.5, 3.9 and 2.5, respectively for the XI, PG and SO populations. Compared with their families, higher values for the observed heterozygosity and gene diversity were estimated for the parental populations. The subdivision (based on R(ST)) and inbreeding (F(IS)) in the SO and PG populations had similar effects, while inbreeding was the main effect in the families. Multilocus outcrossing rates varied from 0.011 to 0.223 in the three populations, indicating divergence in the outcrossing rates among O. glumaepatula populations. For the species (considering SO and PG populations together) an intermediate value was observed (tm = 0.116). Biparental inbreeding varied from 0.008 to 0.123, contributing to the selfing rate in these populations. More than 50 % of the outcrossing occurred between related individuals. CONCLUSIONS: The results indicated divergence in the mating system among O. glumaepatula populations, with consequences for conservation practices. The mating system of this species was classified as mixed with a predominance of self-fertilization.