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Seed orchards are an important source of high-quality seeds for afforestation. Genetic composition of seed orchard crop was studied in a clonal seed orchard situated in Borovets, Rila Mts, which was designed for producing seed for high-mountain afforestations. Diversity in the seed orchard was comparable with the results of other similar studies. Both multilocus and single-locus outcrossing rates were relatively low - 0.867 and 0.782, respectively. Such low levels of outcrossing are not unprecedented in conifers, but the results indicate some degree of selfing in the seed orchard. The possible causes and factors influencing genetic aspects of the reproductive process in the seed orchard are discussed.

Many plants exhibit a mixed mating system. Published models suggest that this might be an evolutionarily stable rather than a transitional state despite the presence of inbreeding depression, but there is little empirical evidence. Through field experimentation, we studied the role of inbreeding depression in eliminating inbred progeny from the reproductive cohort of the forest tree Eucalyptus regnans, and demonstrate a stable mixed primary mating system over two successive generations. Two field experiments were conducted using seed from natural populations. We sowed open-pollinated seeds to simulate a natural regeneration event and determined isozyme genotypes of dominant and suppressed individuals over 10 years. We also planted a mixture of open-pollinated, outcross and selfed families with common maternal parentage; monitored survival of cross types over 29 years; and determined the percentage of outcrosses in open-pollinated seed from a sample of reproductively mature trees using microsatellite analysis. Both experiments demonstrated progressive competitive elimination of inbred plants. By 29 years, the reproductive cohort in the planted experiment consisted only of outcrosses which produced seed which averaged 66 % outcrosses, similar to the estimate for the parental natural population (74 %). Selective elimination of inbred genotypes during the intense intra-specific competition characteristic of the pre-reproductive phase of the life cycle of E. regnans results in a fully outcrossed reproductive population, in which self-fertility is comparable with that of its parental generation. The mixed mating system may be viewed as an unavoidable consequence of the species' reproductive ecology, which includes the demonstrated effects of inbreeding depression, rather than a strategy which is actively favoured by natural selection.

Abstract Gene dispersal processes shape demographic and microevolutionary dynamics of tree species. Gene dispersal patterns can be studied by spatially explicit methods. Spatial genetic structure (SGS), summarized in the Sp statistic, provides indirect estimates of gene dispersal across generations for a known or assumed population effective density. Sp is modulated by exogenous and endogenous factors including the mating system that can be assessed using outcrossing rates (tm). Knowledge on tm and Sp are particularly important for the conservation of species in fragmented biomes such as seasonally dry tropical forests (SDTF). The main aim of this review was to evaluate putative drivers of Sp and tm, and their consequences for gene dispersal in tree species from SDTF. We reviewed 59 genetic studies on SDTF tree species published between 2000 and 2020 and extracted data on propagule dispersal, successional stages, seasonality, mating system, population density, landscape features, type of molecular markers, pairwise kinship in the first distance class (F1), Sp statistic, mean gene dispersal distance (σg), and multilocus outcrossing rates (tm). Sp was significantly associated with the mating system where Sp(outcrossing) > Sp(mixed-mating), and population density where Sp was higher in high-density populations. Outcrossing rate was significantly associated with the type of propagule dispersal, where tm was higher in populations of plants pollinated by wind, and in those with animal-mediated seed dispersal, tm(zoochory) > tm(anemochory) > tm(autochory), and with successional stage where tm(late-successional) > tm(pioneer). These factors are relevant to inform management actions in conservation and restoration projects. Thus, the knowledge on the determinants of gene dispersal processes can help to rescue SDTF through sustainable management.

Previous reviews of plant outcrossing rate survey data have agreed that predominant selfing and predominant outcrossing are alternative stable states of mating system evolution. We reanalyzed the most recent data and plot outcrossing rates as a continuous variable rather than as a class variable. Wind‐pollinated species are indeed bimodal. However, the shape of the distributions for animal‐pollinated species reveals that intermediate rates of outcrossing are common (49% of species fall between 20% and 80% outcrossing). Consequently, we suggest that mating system is best considered a continuous rather than a discrete character of plant populations.

Copaifera multijuga Hayne is an Amazonian species that has been the target of intense exploitation due to its oleoresin. This raw material has a high value in various economic segments such as perfumery and cosmetics. However, there are few investigations  aimed at characterizing the genetic parameters in native populations of this species. In this sense, our objective was to estimate the genetic diversity and characterize the mating system of C. multijuga found in a native population in the Western Amazon. Wood samples were collected from 48 adult trees for the population study. Among these, 15 trees were selected to compose the group of maternal parents of the reproductive system study, for which leaf samples were collected from 20 open-pollinated seedlings (offspring), which were obtained using natural regeneration (n = 300). Using five pairs of heterologous microsatellite primers, the main parameters of genetic diversity and mating system were estimated: observed (H o ) and expected (H e ) heterozygosity, total number of alleles (A), fixation index (f), multilocus (t m ) and single-locus (t s ) outcrossing rates, etc. The population showed levels of genetic diversity greater than 0.6 both in the adult trees (H o : 0.742; H e : 0.743) and in the offspring (H o : 0.685; H e : 0.685). Mating occurred predominantly by outcrossing (t m : 0.88–1.00), of which 4.1% corresponded to mating between relatives (t m –t s ). The results obtained in this study are fundamental for the investigation of the possible impacts of exploitation on the genetic diversity of native populations and, consequently, so that conservation strategies are properly planned.

Oryza rufipogon Griff. and O. nivara Sharma et Shastry are wild ancestors of Asian cultivated rice, harboring a wealth of genetic variation valuable for rice breeding. Mating systems play an important role in shaping genetic variation within species, and could shed light on germplasm conservation. Despite the importance, previous research on the mating systems of O . rufipogon and O. nivara has been hindered by limited sample sizes and the use of unsuitable genetic markers. In this study, by collecting a large number of maternal plants and seeds from representative populations of both species, we estimated their outcrossing rates using an extended mixed-mating model along with 12 simple sequence repeats markers. Our results revealed distinct mating strategies between the two species. Oryza rufipogon exhibited a mixed mating system with an average outcrossing rate of 0.478, while O. nivara was predominantly selfing, with an average outcrossing rate of 0.256. In addition, compared to O. nivara , O . rufipogon has a higher genetic diversity within populations and lower differentiation among populations. The contrasting genetic variation patterns between the two wild rice species could result from demographic bottlenecks and a shift from mixed mating to primarily selfing in O. nivara . Overall, through our geographically widespread sampling, we have obtained reliable outcrossing rate estimates for O . rufipogon and O. nivara , thus facilitating both in situ and ex situ conservation of their germplasm.

Synthetic hybrids is one of the ways to heterosis application in rapeseed, which can effectively solve the problems of the promotion of extra-early-maturing rapeseed varieties in high altitude areas. The flowering period, the yield and the outcrossing rate of the restorer lines, and the yield of their F1s crossed with the sterile line are crucial factors for breeding synthetic hybrids. In this study, one excellent extra-early-maturing Brassica napus sterile line and 28 restorer lines were used as plant materials. Three excellent restorer lines (2036, 137, and 52) were selected by investigating the flowering period, the genetic differences and the yield of each restorer line, and the yield of their hybrid F1 crossed with the sterile line. DNA fingerprinting was performed with SSR molecular markers. The three restorer lines had outcrossing rates from high to low as follows: 137 (59.00%) > 2036 (46.90%) > 52 (30.55%). In addition, the pollen tube germination of each restorer line was observed, and their hybridization and self-compatibility were explored to explain the rates of outcrossing. Collectively, our results suggest that the proportion of the three restorer lines was 137 > 2036 > 52 when using these three extra-early-maturing and sterile rapeseed lines to prepare synthetic hybrids.

• Premise of the study: Crop wild relatives represent important genetic resources for crop improvement and the preservation of native biodiversity. Eggplant (Solarium melongena), known as brinjal in India, ranks high among crops whose wild gene pools are underrepresented in ex situ collections and warrant urgent conservation. Knowledge of outcrossing rates and patterns of genetic variation among wild populations can aid in designing strategies for both in situ and ex situ preservation. • Methods: We used 14 microsatellite (simple sequence repeat) markers to examine genetic diversity, population structure, and outcrossing in 10 natural populations of wild/weedy eggplant (S. insanum = S. melongena var. insanum) and three cultivated populations in southern India. • Key results: Multilocus FST analyses revealed strong differentiation among populations and significant isolation by distance. Bayesian model-based clustering, principal coordinate analysis, and hierarchical cluster analysis grouped the wild/weedy populations into three major clusters, largely according to their geographic origin. The three crop populations were similar to each other and grouped with two wild/weedy populations that occurred nearby. Outcrossing rates among the wild/weedy populations ranged from 5-33%, indicating a variable mixed-mating system. • Conclusion: Geographic isolation has played a significant role in shaping the contemporary patterns of genetic differentiation among these populations, many of which represent excellent candidates for in situ conservation. In two cases, close genetic affinity between cultivars and nearby wild/weedy populations suggests that gene flow has occurred between them. To our knowledge, this is the first study investigating population-level patterns of genetic diversity in wild relatives of eggplant.

Pollinator taxa may vary in their contribution to plant outcrossing rates and hence differ in their influence on plant fitness. In plants that have ornithophilous floral traits (large, deep-tubed orange-red flowers with dilute nectar), it is expected that birds should be the most effective agents of outcrossing. However, bees often pollinate plants with ornithophilous floral traits and may contribute to their outcrossing. To assess the contribution of bees to outcrossing rates and inbreeding in the rare self-compatible treelet Aloe thraskii , we compared outcrossing rates ( t ) and adult inbreeding coefficients ( F ), in bird-excluded and open-pollinated plants. We then tested whether outcrossing rates, and inbreeding depression ( δ ) estimated using Ritland’s genetic marker-based approach, varied according to bee and bird visitation rates, plant height, flowering population size, population density, and isolation distance across eight populations. Outcrossing rates did not differ between progeny from open-pollinated and bird-excluded inflorescences. Outcrossing rates increased with bee visitation, but not bird visitation. Adult inbreeding coefficients were low ( F  = 0–0.1), and inbreeding depression estimates were high ( δ  = 0.59–1). Estimates of inbreeding depression did not vary according to population aggregation. These results highlight the contribution to outcrossing that insect pollinators can make to outcrossing rates of rare plant species that are seemingly adapted for bird pollination.

Kochia [Bassia scoparia (L.) A.J. Scott] is an invasive species in the High Plains of the United States that poses formidable management challenges in agricultural systems, primarily due to its evolution of resistance to glyphosate. Resistance is due to a transposon-associated increase in 5-enolpyruvyl-3-shikimate phosphate synthase (EPSPS) gene copy number relative to the sensitive biotype. Factors behind the rapid spread of glyphosate-resistant biotypes are likely associated with certain aspects of B. scoparia biology, such as a protogynous flower morphology producing large amounts of pollen, that encourages outcrossing and favors high genetic diversity. Furthermore, its ability to tumble over long distances ensures a rapid spread of the resistance trait. Herein, we explore glyphosate resistance in B. scoparia in Colorado. There was no difference in EPSPS gene (Type I, Type II) and FAR1 copy numbers between parent and progeny B. scoparia populations across multiple years (2018, 2020, and 2022), suggesting stable inheritance of glyphosate resistance. Further, the inheritance of glyphosate resistance was investigated using three specific microsatellites or simple sequence repeat (SSR) markers viz. 2656, 2896, and 1792. SSR marker analysis revealed an outcrossing rate of 78% and a selfing rate of 22% in B. scoparia progeny. By investigating the complex interplay between B. scoparia’s biology and genetics, this study investigates the inheritance of glyphosate resistance in B. scoparia, estimates the outcrossing rate under field conditions, and underscores the importance of developing effective management strategies to mitigate its impact on agricultural ecosystems.