Single-locus Outcrossing Rate Research Articles

Analysis of the Genetic Diversity and Mating System of the Endangered Plant Keteleeria davidiana var. calcarea

Keteleeria davidiana var. calcarea is an endangered plant endemic to China. It is mainly distributed in the karst areas of the Guangxi and Guizhou Provinces. It is characterized by small populations and intermittent distribution. This study aimed to explore the genetic diversity and mating system of wild populations of Keteleeria davidiana var. calcarea in fragmented habitats. To achieve this, we genotyped 46 maternal trees and 214 progenies from four fragmented populations of Keteleeria davidiana var. calcarea using nine pairs of microsatellite primers. The genetic diversity of Keteleeria davidiana var. calcarea (Ho = 0.68, He = 0.63) was lower than that of the species overall but higher than that of other Keteleeria plants. The incidence of unbiased expected heterozygosity (uHe) and allelic richness (Ar) was higher in the maternal generation than in the progeny. This suggests that the genetic diversity of the progeny was lower than that of the maternal generation. Keteleeria davidiana var. calcarea is divided into four populations, but there is significant genetic exchange between the populations according to STRUCTURE and gene flow analyses. The multilocus mating system analysis (MLTR) results indicate that the multilocus outcrossing rate (tm) was 0.902, the single-locus outcrossing rate (ts) was 0.606, the bimaternal inbreeding coefficient (tm-ts) was 0.295, and the coefficient of inbreeding depression(δ) was 0.904. These results suggest a certain degree of selfing and inbreeding in Keteleeria davidiana var. calcarea. To prevent problems associated with inbreeding and conserve the genetic diversity of Keteleeria davidiana var. calcarea, we recommend establishing seed gardens, using artificial pollination, and employing asexual propagation techniques for conservation intervention.

Outcrossing mating system in natural populations of the endangered aquatic fern Ceratopteris thalictroides in China as revealed by microsatellite markers: implications for conservation

In this study, the mating system of the endangered aquatic fern Ceratopteris thalictroides in China was investigated using microsatellite markers. The estimates of the multilocus outcrossing rate (tm) and single-locus outcrossing rate (ts) were high at the species level (tm = 0.701 and ts = 0.595, respectively), indicating that C. thalictroides is a predominantly outcrossing species. Negative F (inbreeding coefficient of the maternal parents) values (-0.137) at the species level indicated an excess of heterozygotes and low inbreeding in the populations analyzed. Our investigation revealed that some of the natural and ex situ conservation populations of C. thalictroides have a prolific capacity for vegetative growth. The results showed that the homosporous pteridophyte C. thalictroides in China predominantly favors gametophytic crossing with a certain level of inbreeding along with vegetative growth. Ten populations have been established for ex situ conservation in Wuhan, China, with a survival rate of more than 90%, and mature spores were collected from them. Several factors, including high dispersal of spores and gametophytes by flowing water, high gene flow, and the wide distribution of the species in China, with the occurrence of some large populations, may have resulted in a high outcrossing rate in Chinese C. thalictroides. The high outcrossing rate of C. thalictroides showed that ex situ plantings are most suitable for enhancing possible mixing of the different populations, thus minimizing inbreeding.

Mating system and population structure in the natural distribution of Toona ciliata (Meliaceae) in South China

Most initially perfect flowers of Toona ciliata Roem subsequently develop into functionally unisexual flowers and their relative positions in the same inflorescence could enhance the outcrossing system in this species. Here we investigated the mating system of this species. We used eight nuclear microsatellite markers and investigated the progeny of 125 mother trees from six populations naturally distributed in South China, with sample sizes ranging from 64 to 300 seeds. The multilocus outcrossing rate was 0.970 ± 0.063, and the single locus outcrossing rate was 0.859 ± 0.106, indicating the pattern of predominant outcrossing. Selfing was present in one population, but biparental inbreeding occurred in five populations. Inbreeding was absent in maternal parents, and correlations of selfing among families or among loci were generally insignificant. Positive correlation of paternity at multiple loci was significant in four populations, but was not consistent with the results at single loci. Population substructure occurred in male similarity between outcrosses only in one population. Population genetic differentaitaion was significant (Fst = 34.5%) and the effects of isolation-by-distance at the eight loci were significant among the six populations. These results provide evidence that self-comptability and inbreeding naturally occur in T. ciliata and indicate that inbreeding avoidance is necessary during genetic improvement and breeding of this endangered tree species.

Pollen mediated gene flow in a small experimental population of Moringa oleifera Lam. (Moringaceae)

Large-scale plantations of Moringa oleifera Lam. are carrying out in the dry-hot valley of Red River in Yunnan Province to make it the core cultivation area in China. Nevertheless, there is a deficient understanding of detailed pollen flow patterns, which leads to uncertainty in designing and managing seed orchards of M. oleifera to fit the breeding demand. In order to facilitate the design of breeding strategies for inbreeding lines, paternity analysis by SSR (Simple Sequence Repeat) was used to estimate the outcrossing rate and pollen mediated gene flow of M. oleifera. The analysis was carried out in an experimental population domesticated in the dry-hot valley area of Red River with two germplasms (India and Myanmar) of 60 trees, including 12 maternal trees and 60 pollen donors (bisexual flowers, maternal trees were also possible paternal trees in case of selfing). One hundred fifteen seeds out of 288 were confirmed pollen donors by 8 microsatellite loci at 95% strict confidence level. The multilocus outcrossing rate is tm = 0.797 ± 0.096, and single-locus outcrossing rate is ts = 0.742 ± 0.058. Pollen dispersal distance varied from 0 m (self-pollination) to 24.7 m, with an average of 11.9 m, and 95% of effective pollen was dispersed within 20 m, indicating that the effective pollen mediated gene flow is restricted to a limited distance. 50.3% of effective pollen was donated by 9 trees. Moreover, there was no apparent correlation between pollen dispersal distance and pollen contribution rate, as well as between germplasm and reproducibility. The maximum pollen dispersal distance between two trees estimated in this experimental stand is highly localized at current 3 × 3 m planting density, indicating that M. oleifera seed orchards and clones could be planted nearer to each other than previously thought (as far as kilometers).

Estimation of Outcrossing Rates in Biodiesel Species Pongamia pinnata Based on AFLP and Microsatellite Markers

Outcrossing rates in biodiesel species Pongamia pinnata were estimated using amplified fragment length polymorphism (AFLP) and microsatellite markers. Five AFLP primer combinations and eight pairs of microsatellite primers were used for fingerprinting of 55 open pollinated progenies derived from five mother trees. The multilocus out-crossing rate was quite high with AFLP (0.917; SD = 0.103) and comparatively low with microsatellite markers (0.748; SD = 0.127). The multilocus out-crossing rate was higher than single locus out-crossing rate in case of both marker systems (tm − ts = 0.203; SD = 0.090) which implies that biparental inbreeding occurred at significant levels. The estimated F was higher than the expected which also indicated towards high inbreeding in the progeny population analyzed. This is the first study on estimation of outcrossing rates using any kind of molecular marker systems in Pongamia. We expect an increasing use of such high throughput PCR-based technologies in mating-system studies in various other tree species.

Mating system and intrapopulational genetic diversity of Copernicia prunifera (Arecaceae): a native palm from Brazilian semiarid.

The aim of this study was to investigate the mating system and genetic diversity of the palm Copernicia prunifera using inter-simple sequence repeat markers. We found that the C. prunifera has multiple inflorescences with hermaphroditic flowers and pollen viability of 62%. Outcrossing rates at the population level (N = 267) produced a multilocus outcrossing rate (tm) of 0.878 and a single-locus outcrossing rate (ts) of 0.738, indicating that C. prunifera has a mixed mating system that is preferentially allogamous. The rate of mating among relatives (tm - ts) was low, indicating limited outcrossing between closely related individuals. The fixation index between seed trees (F) was negative (0.200), suggesting an absence of inbreeding, while the correlation of selfing (rs) was high (0.914). The values of the diversity indices among adults and progenies did not differ statistically (HE = 0.319 and I = 0.470; HE = 0.337 and I = 0.505, respectively). In testing for the presence of genetic bottlenecks using the infinite allele model and the stepwise mutation model, we observed a reduction in the effective population, as well as a deficit in heterozygosity (P < 0.0001). The results of this study inform management strategies for the conservation and genetic improvement of the C. prunifera palm.

REPRODUCTIVE SYSTEM AND POLLEN FLOW IN PROGENIES OF Qualea grandiflora Mart., A TYPICAL SPECIES OF THE BRAZILIAN CERRADO

This study analyzed the reproductive system and the pollen dispersion pattern of Qualea grandiflora progenies. This is a typical species from the Brazilian Cerrado about which there are not too many studies from the genetics point of view. The study was conducted in an area of 2.2 hectares located in the Conservation Unit managed by the Forest Institute of the state of São Paulo, Brazil (Assis State Forest). Total genomic DNA of 300 seeds from 25 plants (12 seeds from each plant) was extracted and amplified using specific primers to obtain microsatellite markers. Results showed that selfing is frequent among adults and progenies, and the species reproduces by outcrossing between related and unrelated individuals (0.913). The single-locus outcrossing rate was 0.632, which indicates that mating between unrelated individuals is more frequent than between related plants. The selfing rate was low (0.087), that is, the species is allogamous and self-fertilization is reduced. About 35% of the plants in the progenies were full-sibs, and about 57%, half-sibs. Besides, about 8% of the progenies were selfing siblings. The genetic differentiation coefficient within progenies was 0.139, whereas the fixation rate was about 27%. The estimate of the effective size revealed that the genetic representativeness of descent was lower than expected in random mating progenies: The analyzed samples corresponded to only 13.2 individuals of an ideal panmictic population. In environmental recovery programs, seeds, preferably from different fruits, should be collected from 95 trees to preserve the genetic diversity of the species.

Mating system patterns of natural populations of Pinus koraiensis along its post-glacial colonization route in northeastern China.

To understand the genetic mechanisms underlying the endangerment of Pinus koraiensis, we studied the mating system of 49 families of this species in 3 natural populations along its post-glacial colonization route across ~1500 km in northeastern China using the chloroplast simple sequence repeat technique. We analyzed 11 polymorphic loci with clear and repeating bands, and we calculated the multi-locus outcrossing rate (tm), single-locus outcrossing rate, inbreeding index, and fixation index (F). Intra-population variation was not observed, but a large inter-population variation was observed in the outcrossing rate, and the tm increased from 0.767 (the south population) to 0.962 (the north population) along the post-glacial colonization route. The tm values within a population did not change with time over 2 consecutive years. The F values for the 3 populations were <0, which indicates an excess of heterozygotes. The mean effective number of alleles, Shannon diversity index, and Nei's genetic diversity index did not show a south-north pattern. The north population had the highest outcrossing rate but the lowest genetic diversity. The average genetic differentiation of P. koraiensis populations was 0.1251, which was within the average range of woody plants with outcrossing and wind pollination. This study suggests that the current endangerment of P. koraiensis is not related to its genetic structure; perhaps it is mainly caused by man-made and natural disturbances such as deforestation and fire. Therefore, reducing disturbances and enhancing habitats, rather than the genetic aspects, play more important roles in the long-term protection of P. koraiensis.

Jatropha curcas L. (Euphorbiaceae) exhibits a mixed mating system, high correlated mating and apomixis

The hierarchical mating system among and within fruits of Jatropha curcas was investigated in a base population using five microsatellite loci, employing mixed mating and correlated mating models. Open-pollinated fruits were collected from 15 randomly selected seed trees, sampling seven fruits per tree for a total of 21 seeds from each tree. We detected multilocus genotypes identical to the mother tree in 13 % of offspring, implying the occurrence of apomixis in J. curcas. The presumed apomictic individuals were excluded from the analysis of the remaining results. Evidence of substantial selfing was provided by the average multilocus outcrossing rate (tm = 0.683), showing that the species exhibits a mixed mating system. The outcrossing rate showed a large variation among seed trees, ranging from 0.21 to 1.0, indicating that the species is not self-incompatible. Significant differences were detected between the multilocus and the single locus outcrossing rates (tm − ts = 0.347) that suggested mating among related individuals, possibly because of the presence of individuals from the same progeny (sibs) in the base population. The multilocus paternity correlation was extremely high for the population (rp(m) = 0.999), indicating that the progenies were manly composed of full-sibs. As a consequence of selfing and a high paternity correlation, the co-ancestry coefficient within the progeny was higher (Θ = 0.369) than expected for panmictic populations. Our results indicated that J. curcas produces seeds asexually by apomixis and sexually by a mixed mating system, combining selfing and outcrossing.

Molecular diversity, genetic structure and mating system of Calopogonium mucunoides Desv.

Calopogonium mucunoides Desv. is a species native of South and Central America that is used as green manure and a pasture crop. The molecular genetic diversity was characterized in 195 C. mucunoides accessions from a germplasm collection using 17 microsatellite markers. Outcrossing rate was estimated after the evaluation of six microsatellite loci in 200 genotypes originated from 10 open-pollinated progenies (20 genotypes per progeny). Six genetic clusters were identified in the germplasm collection by the STRUCTURE software analysis, neighbor-joining tree comparisons and principal component analysis, which highly correlated with the geographic locations where these accessions were originated or collected. These results were confirmed using AMOVA. The largest portion of the genetic variation was observed among clusters (64.38%). The results indicated that: multilocus outcrossing rate (tm) was 16.3%, suggesting a mixed mating system with a predominance of autogamy; single locus outcrossing rate (ts) was 11%; difference (tm−ts) was 0.054, indicating that only 5.4% of outcrossing occurred among related individuals; paternity correlation (rp) was 33% suggesting a low probability of finding full sibs among the progeny; parental coefficient of inbreeding (Fm) was 5.0%, indicating a low degree of inbreeding in each parent. A core collection for C. mucunoides was assembled to capture the allelic diversity found in this study. The complete allelic diversity was represented by only 15 accessions. These results should be useful for exploiting the genetic resources of C. mucunoides and could influence future conservation efforts and breeding programs.

Genetic studies in Centrosema pubescens benth, a tropical forage legume: the mating system, genetic variability and genetic relationships between Centrosema species

In this study, we used microsatellite loci to estimate the outcrossing rate of Centrosema pubescens in open-pollinated populations of 10 progenies that each contained 20 genotypes. The multilocus outcrossing rate was 27%, which suggested a mixed mating system with a predominance of autogamy. The single locus outcrossing rate was 13%. The difference was 0.040, which indicated that only 4% of outcrossing occurs in related individuals. A paternity correlation of 14% suggests that there is a low probability of finding full sibs in the progeny. Cross-amplification of the 26 microsatellite loci available for C. pubescens was evaluated across 11 different Centrosema species. Nineteen of the 26 tested microsatellites were successfully transferable across the Centrosema species. The polymorphism information content and discriminating power evaluated had averages of 0.64 and 0.77, respectively. A total of three clusters were assembled to demonstrate the genetic relationships between Centrosema species. The transferable microsatellite loci should be useful for exploiting the genetic resources of the Centrosema species and determining the outcrossing rate, which are essential for proposing effective approaches for conservation and for establishing strategies for the selection and improvement of Centrosema spp.

Study on Mating System of &lt;i&gt;Pinus koraiensis&lt;/i&gt; in Natural Population Based on cpSSR Technology

Chloroplast simple sequence repeat (cpSSR) technique was firstly used to study mating system of natural Pinus koraiensis population. Nine pairs of primers with clear spectrum bands, high stability and polymorphism were selected from 70 pairs of cpSSR primers to analyze the mating systems of 28 individuals. 14 polymorphic loci were detected in the nine pairs of primers. The multi-locus (tm) and single-locus (ts) outcrossing rate were 0.966 (SD=0.000) and 0.939 (SD=0.000), respectively, which were slightly higher than those of other tree species. The constant index (F=-0.035) was below zero, indicating the occurrence of excessive heterozygote. Moreover, inbreeding index (tm-ts=0.027; SD=0.000) was close to zero, indicating an insignificant inbreeding. MLDT analysis showed that multi-locus outcrossing rate differed from single-locus outcrossing rate in mating systems of 28 individuals, but the differences were not statistically significant.

An evaluation of small-scale genetic diversity and the mating system in Zostera noltii on an intertidal sandflat in the Wadden Sea

The dwarf eelgrass, Zostera noltii, is a predominant inhabitant of soft-bottom intertidal regions along the coasts of northern Europe. It is a monoecious, protogynous angiosperm in which the potential for self-fertilization and inbreeding are high, especially if clone sizes exceed pollen dispersal distances. The aim of the present study was to determine the relationship between mating system and clonal structure, examine the relative roles of geitonogamous selfing and biparental inbreeding, measure pollen availability (multiple paternities) and estimate pollen dispersal. A 100-m(2) plot was established in a large, intertidal Z. noltii meadow on the island of Sylt in the German Wadden Sea. A total of 256 adult shoots was sampled: one from the centre of 100 fixed 1-m(2) quadrats (large scale resolution) and an additional 156 from within eight randomly selected 1-m(2) sub-quadrats (small-scale resolution). DNA was extracted from seeds and leaf tissue of all samples and genotyped with nine microsatellite loci. Mating system analysis revealed high multilocus and single locus outcrossing rates. Average pollen dispersal distance was nearly the same as the average genet (clone) size. Multiple paternity was common and 20-30 % of mature seeds originated from matings within the plot. Among inbred seeds, most resulted from geitonogamy rather than biparental inbreeding. Moderate disturbances intrinsic to the intertidal habitat appear to facilitate seed recruitment by gap formation. Pollen dispersal distances are sufficient to maintain outcrossing and high clonal diversity.

Mating system and pollen gene flow in Mediterranean maritime pine

Mating systems define the mode of gene transmission across generations, helping to determine the amount and distribution of genetic variation within and among populations of plant species. A hierarchical analysis of Mediterranean maritime pine mating system (61 mother trees from 24 plots, clustered in three populations) was used to identify factors affecting mating patterns and to fit pollen dispersal kernels. Levels of ovule and seed abortion, multi- and single-locus outcrossing rates and correlated paternity were estimated from progeny arrays and correlated with ecological stand variables and biometric tree measures. Pollen dispersal kernels were fitted using TwoGener and KinDist indirect methods and simulations were carried out to identify relevant factors affecting correlated paternity. Maritime pine showed high outcrossing rates (t(m) and t(s) approximately 0.96) and relatively low levels of correlated paternity [an r(p) of 0.018 (Ritland's estimate) or 0.048 (Hardy's estimate)], although higher than in other anemophilous tree species. Mating system parameters had high variation at the single-tree level (99-100%) but no stand or population effect was detected. At the single-tree level, outcrossing rates were correlated with tree (diameter and height) and crown size. In addition, correlated paternity showed a significant negative correlation with tree height, height to crown base and height to the largest crown width, probably reflecting the importance of the trees' 'ecological neighborhoods'. Indirectly estimated pollen dispersal kernels were very leptokurtic (exponential-power distributions with beta<<0.5), with mean dispersal distances from 78.4 to 174.4 m. Fitted dispersal kernels will be useful in building explicit simulation models that include dispersal functions, and which will contribute to current conservation and management programs for maritime pine. Nevertheless, the numerical simulations showed that restricted dispersal, male fertility and phenological overlap could only partially explain the observed levels of correlated paternity; so other factors may also be relevant for the management of this valuable forest tree species.

Quantitative estimates of outcrossing rates in a natural population of Caldesia grandis (Alismataceae)

Outcrossing rate in a natural population of Caldesia grandis was estimated by the dominant random amplified polymorphism DNA (RAPD) marker using 10 open-pollinated progeny arrays of 24 individuals. The multilocus outcrossing rate estimated based on all 25 RAPD loci was 0.872±0.033 and the single-locus outcrossing rate was 0.795±0.032. Multilocus estimates did not differ significantly from the single-locus estimates. The fixation index, F, in the progeny estimated from RAPD data was -0.142±0.000. The estimates of multilocus outcrossing rates (t(subscript m)) and single-locus outcrossing rates (t(subscript s)) obtained from MLDT clearly indicate that outcrossing is predominant in the open-pollinated C. grandis population. An empirical analysis suggests that 15 should be the minimum number of dominant marker loci necessary to achieve robust estimates of t(subscript m).

Sistema de reprodução em populações de Eschweilera ovata (Cambess.) Miers

O sistema de reprodução de duas populações de Eschweilera ovata foi quantificado por análise de isoenzimas em estrutura de progênies usando os modelos misto de reprodução e cruzamentos correlacionados. Desvios do modelo misto de reprodução foram evidenciados entre as freqüências alélicas dos óvulos e do pólen e pela heterogeneidade nas freqüências alélicas do pólen que fecundou as diferentes árvores. A taxa de cruzamento multilocos foi alta em ambas populações Camarugipe (t m =0,999±0,004) e Itaparica (t m=0,985±0,023). A alta variação na taxa de cruzamento individual (t variando de 0,320 a 1,000) indicou que a espécie não é auto-incompatível. Diferenças positivas e significativamente diferentes de zero foram detectadas entre a taxa de cruzamento multiloco e uniloco, indicando cruzamentos endogâmicos em ambas populações Camarugipe (t m-t s =0,066±0,014) e Itaparica (t m-t s =0,073±0,016) e possível estruturação genética espacial. Valores altos de cruzamentos biparentais foram detectados nas populações (Camarugipe, r p=0,577±0,088; Itaparica r p =0,423±0,070), demonstrando que as progênies são constituídas principalmente por misturas de meios-irmãos e irmãos-completos. O coeficiente de coancestria nas progênies de ambas as populações (Camarugipe, tetaxy=0,211; Itaparica tetaxy =0,191) foi superior ao esperado em progênies de meios irmãos (0,125). Os resultados foram discutidos sob a ótica de amostragens para melhoramento, conservação genética e coleta de sementes para recuperação ambiental.

Sistema de reprodução em Caesalpinia echinata Lam. implantada em arboreto experimental

The mating system of Caesalpinia echinata Lam. implanted in arboretum was studied by allozymes analysis of progeny arrays using the mixed-mating model and correlated-mating model. Deviations from mixed-mating model were observed from heterogeneity of pollen pools allele frequencies that fertilized different trees. The multilocus outcrossing rate was high (tm = 0.969), indicating that the species is predominantly allogamous. The high variation observed in the individual outcrossing rate (tranged from 0.77 to 1.00) shows that the species is not auto-incompatible. It was detected significant positive difference between multilocus and single locus outcrossing rate suggesting that biparental inbreeding has occurred (tm - ts = 0.078). High value of paternity correlation was detected (rp = 0.822), demonstrating that families are composed by full sibs, mainly. The coefficient of coancestry within families (qxy = 0.269) was higher than expected in half-sibs families (0.125). The results are discussed in the viewpoint of the sampling to genetic conservation and environmental recovering.

Mating system of wild Phaseolus lunatus L. and its relationship to population size

Using isozyme variation in a naturally pollinated seed family for 10 wild Phaseolus lunatus L. (Lima bean) populations, ranging in sizes from 10 to 60 reproductive individuals, we estimated levels of outcrossing (t) and parental inbreeding coefficient (F). We also examined the relationship between outcrossing rate and population size. Average estimates of the single-locus outcrossing rate (ts) ranged from 0.024 to 0.246 (mean=0.091+/-0.065). Estimates of the multilocus outcrossing rate (tm) ranged from 0.027 to 0.268, and averaged 0.096+/-0.071. Inbreeding coefficients based on genotypic frequencies of maternal plants were positive and significantly greater than zero (F=0.504), suggesting an excess of homozygotes in all the populations studied. There was indirect evidence of nonrandom mating for outcrosses and this was mainly attributed to self-fertilisation since the averaged difference between tm and ts, which provides a measure of biparental inbreeding, represents only 1% of the autogamy rate. No significant correlation was observed between outcrossing rate and population size. Estimates of t showed significant heterogeneity among populations and factors explaining this tendency are suggested.

Mating system parameters in species of genus Prosopis (Leguminosae).

The section Algarobia of genus Prosopis involves important natural resources in arid and semiarid regions of the world. Their rationale use requires a better knowledge of their biology, genetics and mating system. There are contradictory information about their mating system. Some authors claim they are protogynous and obligate outcrosser. However, some evidence have been shown indicating that they might not be protogynous and that they might be somewhat self-fertile. The current paper analyses genetic structure and mating system parameters in populations of seven species of this section from South and North America based on isozyme data. In all species a significant homozygote excess was found in the offspring population but not in mother plant genotypes. Multilocus and mean single locus outcrossing rates (tm, ts) indicated that about 15% selfing can occur in the studied populations. The heterogeneity between pollen and ovule allele frequencies was low suggesting population structuration, in agreement with the estimates of correlation of tm within progeny (rt) and correlation of outcrossed paternity (rp). The difference of FIS estimates between offspring and mother plants suggest some selection favouring heterozygotes between seedling and adult stages.

Mating system in a natural population of Theobroma grandiflorum (Willd. ex Spreng.) Schum., by microsatellite markers

The aim of this research was to study the mating system of a natural population of Theobroma grandiflorum (cupuassu) from Nova Ipixuna, Para state, using microsatellite markers. Eight polymorphic microsatellite loci were analyzed in eight families, each represented by 10 six-month old seedlings derived from open-pollinated pods. The estimation for the multilocus outcrossing rate (m = 1.0) and individual outcrossing rate ( = 1.0) for this population suggests that T. grandiflorum may be a perfect outbreeding (allogamous) species. Likewise, for the studied population the estimate for single locus outcrossing rate (S) was elevated (0.946), but lower than m, confirming the likely outcrossing character of the species and suggesting the occurrence of 5.4% biparental inbreeding rate (m - S). The estimation of genetic divergence (st) between allelic frequencies in ovules and pollen revealed a deviation from random mating in 75% of the evaluated loci. Likewise, the estimate of correlation of paternity (P = 0.930) and the mean coefficient of co-ancestrality within families (XY = 0.501) indicated that the outcrossings were predominantly correlated, and the offspring were full-sibs. These results suggested that for this particular population of T. grandiflorum, the sampling strategy for genetic conservation and breeding should adopt specific models for families derived from correlated outcrossing (full-sibs) and not the ones usually adopted in classic outcrossing species breeding programs (half-sibs).