High Outcrossing Rate Research Articles

Gene flow among Hancornia speciosa (Apocynaceae) varieties and hybrid fitness

The fate of hybrids and the temporal and spatial dynamics of hybrid zones depend on hybrid fitness in comparison to non-hybrids. We studied cross-pollination among Hancornia speciosa varieties and compared progeny fitness in a nursery to address whether hybrid fitness differed from non-hybrids and whether maternal and paternal taxa contribute differentially to offspring fitness. This species has edible fruit pulp that is used as a raw material for candies, ice cream, and juice by small- and medium-sized enterprises in Central-West and Northeast Brazil. We genotyped 258 adults from a germplasm collection and 320 seeds using seven microsatellite loci to estimate genetic parameters and determine pollen donors. Fitness components, days to shoot, growth rate (mm/day), leaf width (mm), leaf length (mm), stem diameter (mm), and plant height (cm) were analyzed in 200 individuals. Genetic diversity and polymorphism did not differ neither between adults and progeny arrays nor among the four varieties. Genetic differentiation among varieties (F CT = 0.019, p < 0.001) and among populations within varieties (F SC = 0.053, p < 0.001) was significant but low. We detected mating among the four varieties, and no self-pollination was observed in parentage analysis, confirming that H. speciosa is self-incompatible with a high outcrossing rate (t m = 0.990, SE = 0.007). No significant effect of heterosis or exogamic depression was detected for any fitness component, but maternal contribution significantly affected plant height.

The long and the short of it: long-styled florets are associated with higher outcrossing rate in Senecio vulgaris and result from delayed self-pollen germination

Background: It has been reported that some plants of the self-compatible species Senecio vulgaris produce capitula containing long-styled florets which fail to set seed when left to self-pollinate, although readily set seed when self-pollinated by hand.Aims: To determine if production of long-styled florets is associated with higher outcrossing rate in S. vulgaris, and whether long-styles occur in non-pollinated florets, whereas short-styles are present in self-pollinated florets.Methods: The frequency of long-styled florets was compared in the radiate and non-radiate variants of S. vulgaris, known to exhibit higher and lower outcrossing rates, respectively. In addition, style length was compared in emasculated florets that were either self-pollinated or left non-pollinated.Results: Long-styled florets were more frequent in the higher outcrossing radiate variant. Following emasculation, long styles occurred in non-pollinated florets, while short styles were present in self-pollinated florets. The two variants did not differ in style length within the non-pollinated or within the self-pollinated floret categories.Conclusions: A high frequency of long-styled florets is associated with higher outcrossing rate in S. vulgaris and results from delayed self-pollination and pollen germination on stigmas.

Simulating the selfing and migration of Luehea divaricata populations in the Pampa biome to investigate the conservation potential of their genetic resources.

Computer simulations are an important tool for developing conservation strategies for forest species. This study used simulations to investigate the genetic, ecological, and reproductive patterns that contribute to the genetic structure of the tree Luehea divaricata Mart. & Zucc. in five forest fragments in the Brazilian Pampa biome. Using the EASYPOP model, we determined the selfing and migration rates that would match the corresponding genetic structure of microsatellite marker data (based on observed and expected heterozygosity parameters). The simulated reproductive mode was mixed, with a high rate of outcrossing (rate = 0.7). This was consistent with a selfing-incompatible system in this species, which reduced, but did not prevent, selfing. The simulated migration rate was 0.02, which implied that the forest fragments were isolated by distance, and that the inbreeding coefficients were high. Based on Nei's gene diversity analysis, 94% of the genetic variability was distributed within the forest fragments, and only 6% of the genetic diversity was caused by differences between them. Furthermore, the minimum viable population and minimum viable area genetic conservation parameters (which determine conservation potential in the short and long term) suggested that only the Inhatinhum forest fragment had the short-term potential to maintain its genetic diversity. However, in the long term, none of the forest fragments proved to be sustainable, indicating that the populations will require intervention to prevent a decline in genetic variability. The creation of ecological corridors could be a useful solution to connect forest fragments and enhance gene flow between them.

Structure of genetic diversity in marginal populations of black poplar (Populus nigra L.)

It has been hypothesized that populations at the margins of the distributional range of a species show reduced genetic diversity and increased inter-population differentiation compared to central populations. Here, we test this hypothesis by examining the structure of genetic diversity in marginal populations of black poplar, Populus nigra L. (Salicaceae). This species occurs mainly in Europe but its range extends to central Asia. We collected 117 individuals from 10 populations at the edge of the distributional range of the species in central Asia to examine the structure of genetic diversity based on genetic polymorphisms at 20 microsatellite markers. As expected, the genetic diversity within these marginal populations is relatively low, with an average observed heterozygosity Ho of 0.337 and an average expected heterozygosity He of 0.466, compared to the genetic diversity of populations from central distributions. However, we recovered very low genetic differentiation between populations, with an average Fst of 0.0745, a value similar to those reported for central populations. AMOVA analyses confirmed this result, showing that only 9.2% of the total variation could be attributed to between-population variance (P < 0.001). Our findings do not fully support hypotheses about the structure of genetic diversity in marginal populations formed from observations on other species. We suggest that a high rate of outcrossing and possible postglacial colonization at the edge of the distributional range of this long-lived poplar may explain the observed structure of the genetic diversity.

Genetic diversity, outcrossing rate, and demographic history along a climatic gradient in the ruderal plant Ruellia nudiflora (Acanthaceae)

Ruellia nudiflora has shown a high potential to easily invade disturbed areas. Outcrossing rate and genetic structure and diversity in this species were examined along a climatic gradient in the Yucatán Peninsula (Mexico) in order to understand the effects of environmental heterogeneity – isolation by environment (IBE) – as well as correlation in herkogamy on genetic structure, diversity, and demographic history in this species. Nine populations were sampled along a temperature-precipitation gradient with marked differences in vegetation, measuring the degree of herkogamy in each sampled plant. To evaluate genetic diversity and structure, amplified fragment length polymorphism (AFLP) markers from 76 plants in these populations were used, while the outcrossing rate was evaluated in 22 genetic families from six populations. All populations had high levels of within-population genetic diversity and high outcrossing rates. Virtually all populations were also undergoing demographic and spatial expansion. The partial Mantel test found a positive correlation between geographic and genetic distance, but none between mean temperature, precipitation, and herkogamy with genetic distance. In this context, R. nudiflora shows incipient evidence of genetic differentiation on a small geographical scale (isolation by distance, IBD) but not along the environmental gradient (IBE). Results suggest that under conditions of constant disturbance, R. nudiflora is able to continuously colonize new areas.

Effect of clonal growth on mating system of invasive plant Coreopsis lanceolata.

The main pollinator behaviors of Coreopsis lanceolata were observed. The average flight distance of native bees is 12. 71 cm,and the farthest distance is 60 cm in population. They usually stay on one florescence for 10 sec. It could visit 2. 59 plants between its come-and-go in population. Our results showed that high pollen viability and pollinator movement and a lot of visiting bees ensure high out-crossing rate( the yield of seeds is about 12000 per plant). In this paper,we simulated the distribution of different genetic ramets of C. lanceolata,the results showed that different genetic ramets mixing standard influence the seed-setting remarkably. High genetic diversity of population,the pollinator movement and the guerrilla growth strategy could disperse the ramets,these traits lower the rate of geitonogamy. Therefore,the disadvantage of clonal outbreeding mating system could be avoided effectively,C. lanceolata could keep a high outcrossing rate. This strategy could improve its invasive ability.

Mating Patterns and Pollinator Communities of the Invasive ShrubLonicera maackii: A Comparison between Interior Plants and Edge Plants

Premise of research. It is known that outcrossing rates and mating structure are important factors determining the genetic structure of populations. Moreover, the composition and abundance of pollinator communities visiting flowers determine the distances over which the pollen is likely to be dispersed, which in turn affects the genetic structure of plant populations. For invasive plants, high outcrossing rates produce genetically diverse propagules for the colonization of uninvaded areas and facilitate the establishment of novel gene combinations that may affect their invasive ability. Here, we examine how differences in pollinator communities visiting flowers of the invasive shrub Lonicera maackii (Caprifoliaceae), growing along the edge and in the interior of a woodlot, affect their outcrossing rates and mating structure. Methodology. Five microsatellite marker loci were used to determine the outcrossing rates, levels of biparental inbreeding, and effective number of pollen donors siring the seed crop of plants growing along the edge and in the interior of an invaded woodlot. Pivotal results. We found that L. maackii is a predominantly outcrossing plant. Despite dissimilarities in composition and abundance of pollinator communities, there were no differences in outcrossing rates and biparental inbreeding between plants along the edge of the woodlot and those in the interior. However, the seed crop of plants in the interior was sired by more pollen donors than that of plants along the edge. Our findings suggest that plants differ in their ability to sire seeds, as maternal allele frequencies are different from those that sired their seeds. Conclusions. Lonicera maackii plants showed high outcrossing rates regardless of their position in the woodlot. Differences in the number of donors siring the seed crop between plants in the interior of the woodlot and those along the edge are most likely due to disparities in the abundance and composition of the pollinator communities.

Genetic diversity and population structure of the mangrove lime (Merope angulata) in India revealed by AFLP and ISSR markers

The mangrove lime, Merope angulata (Willd.) Swingle (Rutaceae) is a threatened mangrove associate species occurring sporadically in the tidal forests from Papua New Guinea to the east coast of India. It is an underutilized salt tolerant plant related to Citrus. We have applied AFLP and ISSR markers to estimate the extent of genetic diversity among 55 individuals of M. angulata, sampled from two natural populations (Bhitarkanika Wildlife Sanctuary) and one ex situ population (Jharkhali Mangrove Ecological Garden) in India. A combined analysis of both AFLP and ISSR markers revealed low polymorphism (42.93%) and a moderate heterozygosity and Shannon diversity index (H=0.393, I=0.571) in the species. The Jaccard genetic distance among 55 accessions ranged from 0.16 to 0.74 (average 0.43). Analysis of population genetic structure using Bayesian method in STRUCTURE software identified two genetic clusters. FST statistics and AMOVA results indicated low population differentiation with high gene flow. Haplotype indices and mismatch distributions indicated some evidence of expansion in the two natural populations. Outcrossing test revealed a predominantly out-breeding system with high outcrossing rate. The high gene flow detected among the populations indicates that M. angulata does not face any genetic drift, and hence no local genetic differentiation and population divergence. The highly fragmented state of its habitats warrants adequate measures for maintenance of genetic diversity in this species without further depletion. This is the first report on molecular analysis of genetic diversity and population structure of M. angulata from its native distributional range in India.

Floral traits to enhance outcrossing for higher hybrid seed production in rice: present status and future prospects

High seed cost is a major factor limiting the adoption of hybrid rice in South and Southeast Asian countries. A practical way to improve hybrid seed production is to increase the outcrossing rate in rice. Several studies reveal that perennial wild Oryza species have a higher outcrossing rate than annual species. Among various traits that influence outcrossing, pistil characteristics are the most crucial in improving the seed set on the male sterile parent in hybrid seed production. Wild species are known to have wide genetic variability for stigma length, anther length, and percent stigma exsertion. This review establishes the need to exploit new genetic resources, through both classical and molecular breeding approaches, to improve seed production. It also reviews the genetic variability of floral characteristics, the genetics of floral traits that influence outcrossing, and progress made in understanding these traits using biotechnological approaches, the effect of environment on floral traits and the resulting prospects for improving hybrid rice seed production.

Bayesian approach reveals confounding effects of population size and seasonality on outcrossing rates in a fragmented subalpine conifer

Mating systems have long been recognized as key factors determining genetic structure within and between pop- ulations. Outcrossing promotes genetic diversity and gene flow between populations, while inbreeding, on the other hand, decreases recombination rates, facilitating fixation of co-adapted genes. In small populations, selfing moderates pollen limitation because of low mate availability, but at the cost of increased inbreeding depression. These conflicts are of more than theoretical interest; they are critical for the man- agement of endangered species. In order to help designing conservation strategies for the management of the gene pool of fragmented populations of Pinus cembra, a protected spe- cies in Poland, we have characterized pollen flow and mating structure using nuclear microsatellite markers. We demon- strated that P. cembra in the studied stands of the Tatra Mts. is characterized by an average outcrossing rate (t )o f 0.72. Unlike with the existing approaches, using the newly devel- oped Bayesian method, we found that population size and seasonal variation had confounding effects on outcrossing rates. In concordance with predictions, large populations showed significantly higher outcrossing rates (t=0.89) than smaller ones (t=0.51). Temporal variation revealed in the outcrossing rate might be linked with masting behavior of the species. On the other hand, we showed that outcrossing rates were not associated with a trunk diameter of a mother tree. Our study also demonstrated that biparental inbreeding is a significant component of mating system. However, we further show that pollen dispersal follows a fat-tailed distribu- tion (with the average dispersal distance of 1,267 m) so that at least some long-distance pollen dispersal must be occurring. Overall, we conclude that the high inbreeding (both selfing and mating between relatives) found in P. cembra buffers for

High but variable outcrossing rates in the invasive Geranium carolinianum (Geraniaceae).

• Premise of the study: Mating system plays an important role in population establishment and persistence, maintenance of genetic variation, and adaptive ability, especially for invasive species that colonize new environments to which they may be poorly adapted. In mixed-mating species, population differences in self-fertilization rates often arise due to variation in local ecological conditions (e.g., pollinator or mate availability) or genetic variation in traits promoting selfing or outcrossing. Knowledge of how and why selfing rates vary can help us understand how populations respond to different environments, how this affects patterns of genetic variation, and the role of mating systems in biological invasions.• Methods: We determined outcrossing rates in invasive (China) and native (US) populations of the weedy annual Geranium carolinianum in natural populations and an open-pollinated common garden to answer the following questions: To what extent do populations vary in mating system? Do invasive populations differ from native populations? Is interpopulation variation in mating system under genetic control?• Key results: Despite having many characteristics of selfing species, we found high variation in outcrossing rates (tm from 0.1 to 1.0) resulting from both environmental and genetic variation. Outcrossing rates were generally high and plastic in the Chinese populations.• Conclusions: A delayed selfing mechanism provides reproductive assurance while allowing facultative outcrossing when mates are not limiting. In invasive populations, high outcrossing rates were facilitated by large admixed founding populations, promoting local adaptation and the maintenance of genetic diversity.

Selfing and Outcrossing Fertility in Common Bermudagrass under Open‐Pollinating Conditions Examined by SSR Markers

ABSTRACTC. dactylon (L.) Pers. var. dactylon is a cosmopolitan grass species with significant economic value for turf, forage, and soil conservation in the southern United States. The species has long been characterized as an outcrossing species based on heterogeneity of natural populations, comparison of seed set rates under self‐ and cross‐pollination, and assumption of widespread self‐incompatibility. However, reproductive behavior of plants in breeding populations based on definitive characterization of their progeny as to self‐ or cross‐pollinated origin is not available. The objective of this experiment was to quantify selfing and outcrossing rates of common bermudagrass plants grown in field environments conducive to interbreeding. Twenty‐five clonal common bermudagrass plants grown at Stillwater and Perkins, OK in a randomized complete block design with three replications were used in the study. Ten progeny from open‐pollinated seed harvested from each field plot of the maternal plants were grown in a greenhouse at the Agronomy Research Station, Oklahoma State University. Plant DNA samples were isolated from 1439 progeny from both sites along with the 25 seed parents. Eleven polymorphic simple sequence repeat (SSR) markers were chosen to identify breeding origin of the progeny by comparing SSR marker genotypes of the progeny with their respective maternal parents. Among the progeny examined, only two progeny plants from accessions A12281 and A12363 were identified to be selfed, indicating an extremely high outcrossing rate of 99.86%. The finding of complete or near complete outcrossing behavior in this experiment should assist in a fuller understanding of the sexual reproduction characteristics of common bermudagrass.

Tree density and population size affect pollen flow and mating patterns in small fragmented forest stands of pedunculate oak (Quercus robur L.)

In many parts of the world, once large and continuous forests have been replaced by a mosaic of isolated forest fragments embedded in an agricultural or urban landscape matrix. At the same time, stand characteristics such as tree population size and tree density have been strongly modified as a result of anthropogenic activities. Because increased geographical isolation can impede gene flow among forest fragments, and because decreased population size and tree density may reduce the number of local mating partners, this can be expected to lower the opportunity to trees for outcrossing, and to result in increased inbreeding, negatively impacting the viability of fragmented tree populations. In this study, we examined eight isolated stands of the wind-pollinated tree species Q. robur that strongly differed in population size, tree density and spatial isolation. In the centre of each Q. robur stand, adult leaves and seeds were collected in a circular plot, in which we evaluated the diversity and differentiation of the local pollen pool, and examined mating patterns. Most forest stands showed high proportions of out-of-plot pollen flow (range: 0.24–0.77), which were positively correlated with the number and density of adult trees within the forest stands. Despite high outcrossing rates (>0.998), seeds within seed families were stronger related than what could be expected under panmixia, which could be attributed to small but significant levels of correlated paternity (0.018–0.107) and biparental inbreeding (0.025–0.118) within the study plots. Next to increased coancestry coefficients, deviations from random mating also resulted in significant pollen pool differentiation (0.008–0.059) among seed parents. We also found that stand population size and tree density were significantly correlated to the relatedness of the seedlings and the degree of pollen differentiation within the study plots. These results suggest that, in small and isolated low density forest stands, reduced mate availability may decrease local pollen pool diversity, increasing the likelihood of consanguineous mating and pollen pool differentiation in the next generations. We conclude that preserving high levels of pollen flow within and between forest fragments may be more important in wind-pollinated tree species than what was previously thought.

Relative impact of mate versus pollinator availability on pollen limitation and outcrossing rates in a mass-flowering species.

Plant mating systems are driven by several pre-pollination factors, including pollinator availability, mate availability and reproductive traits. We investigated the relative contributions of these factors to pollination and to realized outcrossing rates in the patchily distributed mass-flowering shrub Rhododendron ferrugineum. We jointly monitored pollen limitation (comparing seed set from intact and pollen-supplemented flowers), reproductive traits (herkogamy, flower size and autofertility) and mating patterns (progeny array analysis) in 28 natural patches varying in the level of pollinator availability (flower visitation rates) and of mate availability (patch floral display estimated as the total number of inflorescences per patch). Our results showed that patch floral display was the strongest determinant of pollination and of the realized outcrossing rates in this mass-flowering species. We found an increase in pollen limitation and in outcrossing rates with increasing patch floral display. Reproductive traits were not significantly related to patch floral display, while autofertility was negatively correlated to outcrossing rates. These findings suggest that mate limitation, arising from high flower visitation rates in small plant patches, resulted in low pollen limitation and high selfing rates, while pollinator limitation, arising from low flower visitation rates in large plant patches, resulted in higher pollen limitation and outcrossing rates. Pollinator-mediated selfing and geitonogamy likely alleviates pollen limitation in the case of reduced mate availability, while reduced pollinator availability (intraspecific competition for pollinator services) may result in the maintenance of high outcrossing rates despite reduced seed production.

Non-Density Dependent Pollen Dispersal of Shorea maxwelliana (Dipterocarpaceae) Revealed by a Bayesian Mating Model Based on Paternity Analysis in Two Synchronized Flowering Seasons

Pollinator syndrome is one of the most important determinants regulating pollen dispersal in tropical tree species. It has been widely accepted that the reproduction of tropical forest species, especially dipterocarps that rely on insects with weak flight for their pollination, is positively density-dependent. However differences in pollinator syndrome should affect pollen dispersal patterns and, consequently, influence genetic diversity via the mating process. We examined the pollen dispersal pattern and mating system of Shorea maxwelliana, the flowers of which are larger than those of Shorea species belonging to section Mutica which are thought to be pollinated by thrips (weak flyers). A Bayesian mating model based on the paternity of seeds collected from mother trees during sporadic and mass flowering events revealed that the estimated pollen dispersal kernel and average pollen dispersal distance were similar for both flowering events. This evidence suggests that the putative pollinators – small beetles and weevils – effectively contribute to pollen dispersal and help to maintain a high outcrossing rate even during sporadic flowering events. However, the reduction in pollen donors during a sporadic event results in a reduction in effective pollen donors, which should lead to lower genetic diversity in the next generation derived from seeds produced during such an event. Although sporadic flowering has been considered less effective for outcrossing in Shorea species that depend on thrips for their pollination, effective pollen dispersal by the small beetles and weevils ensures outcrossing during periods of low flowering tree density, as occurs in a sporadic flowering event.

High genetic diversity in a potentially vulnerable tropical tree species despite extreme habitat loss.

Over the last 150 years, Singapore’s primary forest has been reduced to less than 0.2% of its previous area, resulting in extinctions of native flora and fauna. Remaining species may be threatened by genetic erosion and inbreeding. We surveyed >95% of the remaining primary forest in Singapore and used eight highly polymorphic microsatellite loci to assess genetic diversity indices of 179 adults (>30 cm stem diameter), 193 saplings (>1 yr), and 1,822 seedlings (<1 yr) of the canopy tree Koompassia malaccensis (Fabaceae). We tested hypotheses relevant to the genetic consequences of habitat loss: (1) that the K. malaccensis population in Singapore experienced a genetic bottleneck and a reduction in effective population size, and (2) K. malaccensis recruits would exhibit genetic erosion and inbreeding compared to adults. Contrary to expectations, we detected neither a population bottleneck nor a reduction in effective population size, and high genetic diversity in all age classes. Genetic diversity indices among age classes were not significantly different: we detected overall high expected heterozygosity (He = 0.843–0.854), high allelic richness (R = 16.7–19.5), low inbreeding co-efficients (FIS = 0.013–0.076), and a large proportion (30.1%) of rare alleles (i.e. frequency <1%). However, spatial genetic structure (SGS) analyses showed significant differences between the adults and the recruits. We detected significantly greater SGS intensity, as well as higher relatedness in the 0–10 m distance class, for seedlings and saplings compared to the adults. Demographic factors for this population (i.e. <200 adult trees) are a cause for concern, as rare alleles could be lost due to stochastic factors. The high outcrossing rate (tm = 0.961), calculated from seedlings, may be instrumental in maintaining genetic diversity and suggests that pollination by highly mobile bee species in the genus Apis may provide resilience to acute habitat loss.

Gene flow and genetic diversity in cultivated and wild cacao (Theobroma cacao) in Bolivia

The role of pollen flow within and between cultivated and wild tropical crop species is little known. To study the pollen flow of cacao, we estimated the degree of self-pollination and pollen dispersal distances as well as gene flow between wild and cultivated cacao (Theobroma cacao L.). We studied pollen flow and genetic diversity of cultivated and wild cacao populations by genotyping 143 wild and 86 cultivated mature plants and 374 seedlings raised from 19 wild and 25 cultivated trees at nine microsatellite loci. A principal component analysis distinguished wild and cultivated cacao trees, supporting the notion that Bolivia harbors truly wild cacao populations. Cultivated cacao had a higher level of genetic diversity than wild cacao, presumably reflecting the varied origin of cultivated plants. Both cacao types had high outcrossing rates, but the paternity analysis revealed 7-14% self-pollination in wild and cultivated cacao. Despite the tiny size of the pollinators, pollen was transported distances up to 3 km; wild cacao showed longer distances (mean = 922 m) than cultivated cacao (826 m). Our data revealed that 16-20% of pollination events occurred between cultivated and wild populations. We found evidence of self-pollination in both wild and cultivated cacao. Pollination distances are larger than those typically reported in tropical understory tree species. The relatively high pollen exchange from cultivated to wild cacao compromises genetic identity of wild populations, calling for the protection of extensive natural forest tracts to protect wild cacao in Bolivia.

Outcrossing rates and reproductive success inXanthorrhoea johnsonii(Xanthorrhoeaceae), in south east Queensland, Australia

Outcrossing rates and seed set were estimated at both the population and individual plant scale within four populations of Xanthorrhoea johnsonii. Sites differed with respect to habitat disturbance (time since fire), plant density, mean plant height, and mean inflorescence length. Allozyme data from progeny arrays of 24 seeds per plant from ten plants at each site were used to determine maternal outcrossing rates, which were found to be consistently high at all sites (> 90%). Small but significant levels of inbreeding were recorded at three of the four sites. There was close agreement between tm and ts measures, which indicated that most inbreeding was a result of within plant selfing rather than biparental inbreeding. Outcrossing rates were estimated within top, middle, and bottom thirds of spikes on six plants at a fifth site. Significant differences from complete outcrossing were recorded in the middle and/or bottom sections of three plants. Total seed set per plant and seed set per flower varied significantly among the four sites. Xanthorrhoea johnsonii appears to be able to maintain relatively high outcrossing rates under different ecological conditions, although levels of both seed set per plant and seed set per flower are much more variable. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110, 335–345.

Estimation of in situ mating systems in wild sorghum (Sorghum bicolor (L.) Moench) in Ethiopia using SSR-based progeny array data: implications for the spread of crop genes into the wild

Because transgenic sorghum (Sorghum bicolor L.) is being developed for Africa, we investigated the potential for transgenes to spread to conspecific wild/weedy sorghum populations in Ethiopia, which is considered the centre of origin of cultivated sorghum. In the current study, the extent of outcrossing, and uniparental and biparental inbreeding were investigated in seven wild/weedy sorghum populations collected at elevations ranging from 631 to 1709 m. Based on allele frequency data of 1120 progenies and 140 maternal plants from five polymorphic microsatellite markers, outcrossing rates were estimated using standard procedures. The average multilocus outcrossing rate was 0.51, with a range of 0.31-0.65 among populations, and the family outcrossing rate was in the extreme range of 0 to 100%. The highest outcrossing (t(m) = 0.65) was recorded in a weedy population that was intermixed with an improved crop variety in Abuare (Wello region). It was also observed that the inbreeding coefficient of the progenies (F(p)) tend to be more than the inbreeding coefficient of both their maternal parents (F(m)) and the level of inbreeding expected at equilibrium (F(eq)), which is a characteristic of predominantly outbreeding species. Biparental inbreeding was evident in all populations and averaged 0.24 (range = 0.10-0.33). The high outcrossing rates of wild/weedy sorghum populations in Ethiopia indicate a high potential for crop genes (including transgenes) to spread within the wild pool. Therefore, effective risk management strategies may be needed if the introgression of transgenes or other crop genes from improved cultivars into wild or weedy populations is deemed to be undesirable.

Comparison of mating system parameters and genetic structure in three natural scenarios of Acacia visco (Leguminosae, Mimosoideae)

Acacia visco is a native South American tree species that has been extensively used for ornamental purposes and in carpentry, bodywork and parquet due to the hardness and durability of its wood. Little is known about genetic diversity and mating system of A. visco. The main aims of this study were to (1) estimate outcrossing rates in natural Argentinean populations using AFLP markers, (2) test for any difference in mating patterns among a large a patchy and relict population, and (3) compare the mating system of A. visco with other Acacia species. The three primer pairs used in the AFLP analysis revealed a total of 569 variable loci. Most genetic variation was observed among individuals within families (61.2 %). The estimate of multilocus outcrossing rate (t m) was high (≥0.971) in all populations. Average pairwise coancestry between progenies within families for each population ranged from 0.082 to 0.105 or from 0.125 to 0.136, depending on the method θ was estimated. In the three populations studied, the progenies of open pollination were constituted mainly for half-sibs (94.3 %). This work shows a similar mating system in all populations of A. visco in spite of their size differences, hypothesizing that the entire species has a similar mating system of outcrossing preferential. Considering the results obtained here where a high percentage of individuals were half-sibs, sampling large numbers of pods from individual trees for ex situ conservation will result in a genetically diverse sample as a consequence of high outcrossing rates.