High Outcrossing Rate Research Articles

Effect of forest fragmentation and altitude on the mating system of Eucalyptus pauciflora (Myrtaceae)

Habitat fragmentation is a key factor causing variation in important mating system parameters in plants, but its effect is variable. We studied mating system variation among 276 native trees from 37 populations of Eucalyptus pauciflora from Tasmania. We assayed 10 microsatellite loci from 1359 open-pollinated progeny from these trees. Across Tasmania the species’ mating system was characterised by a high outcrossing rate (tm = 0.90) but moderate bi-parental inbreeding (tm–ts = 0.16) and moderate correlated paternity (rP = 0.20) in comparison to other eucalypt species. Despite significant differences in outcrossing rate and correlated paternity among populations, this variation was not correlated with fragmentation. Nevertheless, fragmentation was inversely correlated with the number of germinants per gram of seed capsule content. Outcrossing rate had been reported previously to decrease with increasing altitude in mainland populations of E. pauciflora, but this was not the case in Tasmania. However, a small but significant decrease in correlated paternity occurred with increasing altitude and a decrease in bi-parental inbreeding with increasing altitude was evident in fragmented populations only. It is argued that strong, but incomplete self-incompatibility mechanisms may buffer the mating system from changes in population density and pollinators. While seed yields from highly fragmented populations were reduced, in most cases the seed obtained is unlikely to be more inbred than that from non-fragmented populations and, thus, is likely to be as suitable for use in local forest restoration.

Population genetic structure analysis of Sclerotinia sclerotio rum (Lib.) de Bary from different host plant species in northern Iran

The genetic structure of 65 Sclerotinia sclerotiorum isolates representing 52 field populations from three provinces in northern Iran were analyzed with Mycalial Compatibility Groupings (MCGs) and five polymorphic microsatellite loci. In total, 44 haplotypes were detected with 25 allele polymorphisms. A high level of genetic diversity was observed in about 67.6% (with clonal fraction = 0.077 to 0.20) of the regional populations studies, and the Shannon diversity index (Ho) for the whole region was found to be 0.86 (Htot). Partition of total diversity (Htot) showed that 64% corresponded to a variation in diversity within the S. sclerotiorum populations. By mycelial compatibility grouping (MCG) tests, the isolates were classified into 39 groups of which 26 MCGs were individual. Molecular and phenotypic analyses results of all of the isolates (except MCG4 and MCG23) were similar; however, the isolates in the MCG4 and MCG23 groups, with variable microsatellite haplotypes, were morphologically dissimilar. The results shown here were possibly due to high rates of outcrossing, as well as to the evolutionary potential within population of the pathogen in different locations in Iran. Nei’s genetic identity showed that populations from Golestan province and wild plants were the most diverse. <br><br><font color="red"><b> This article has been retracted. Link to the retraction <u><a href="http://dx.doi.org/10.2298/ABS160412035E">10.2298/ABS160412035E</a><u></b></font>

Erratum to: Unexpectedly high outcrossing rate in both dense and sparse patches in self-compatible Pedicularis rex (Orobanchaceae)

Pedicularis rex, a self-compatible alpine herb, depends exclusively on pollinators for reproduction. Previous study has revealed that 74.7 % of genetic variability occurs among populations in Yunnan, indicating a mixed mating system for the species. The large floral display also indicates high potential geitonogamy. Therefore, plant density and display size may be important factors influencing the realized mating system of P. rex. In the study reported here we explored the effects of plant density and floral display size on pollinator movements and thus outcrossing rate in two patches of in P. rex at low and high plant densities. We examined foraging behavior of bumblebees, measured reproductive outputs under hand and natural pollination, and estimated the outcrossing rates using RAPD markers. Floral display size was significantly larger and bumblebees visited significantly more flowers in sequence on individual plants in the sparse patch than in the dense patch. We found a significant positive correlation between floral display size and successive visits in the sparse patch, but not in the dense patch. Regression analysis revealed a significant inverse correlation between fruit production and flower production per plant with a theoretical maximum of 63 fruits per plant, but no relationship between seed production and flower production per plant. Contrary to previous studies on genetic structure, however, we found an unexpectedly high outcrossing rate in both the sparse and the dense patch (tm = 1.151 and 0.924, respectively). Resource limitation may intensify seed competition and result in selected seed abortion, which may largely explain the unexpectedly high outcrossing rate.

Outcrossing rates in two self‐compatible, hybridising Rhinanthus species: implications for hybrid formation

The congeners Rhinanthus angustifolius and Rhinanthus minor, two annual hemiparasites pollinated by bumblebees, are known to hybridise in the wild. Both species are self-compatible, but the capacity for autonomous selfing is higher in R.minor. This suggests a difference in realized outcrossing rates, which have not been determined before in these species. Using microsatellites, both species turned out to have mixed mating systems, but with a much lower multilocus outcrossing rate (0.13) for R.minor compared to R.angustifolius (0.76). We hypothesised that a higher outcrossing rate should lead to a higher chance of heterospecific pollination, and we therefore determined the rate of hybrid formation on each species in an artificial mixed population. Hybrid seeds were produced at low frequency (4.5%), and no significant difference was found between the species. It is therefore likely that post-pollination processes influence hybrid seed formation to counteract the expected difference in heterospecific pollen deposition. We checked fruit set, seed set and the rate of autonomous selfing in controlled crosses in the greenhouse in 2 years, and found that fruit set (2003) or seed set (2010) were lower in R.angustifolius × R.minor crosses relative to the reciprocal cross. Hybrid seeds produced on R.angustifolius also had a much lower germination rate, so most of the established F1 hybrid plants have the R.minor cytoplasm. The formation of advanced hybrids depends on pollinator preference, which is biased towards R.angustifolius if present in sufficient numbers, because it offers more rewards.

Unexpectedly high outcrossing rate in both dense and sparse patches in self-compatible Pedicularis rex (Orobanchaceae)

Unexpectedly high outcrossing rate in both dense and sparse patches in self-compatible Pedicularis rex (Orobanchaceae)

Genetic Structure and Outcrossing Rates in Viola pedunculata (Violaceae), a California Endemic Violet Lacking Cleistogamous Flowers

Although most North American violet species (Viola, Violaceae) produce both showy chasmogamous (CH) flowers and inconspicuous cleistogamous (CL) flowers, some species lack the ability to manufacture the automatically self-pollinated CL flowers. Given that such flowers are considered beneficial as a back-up method of seed production when pollinators are scarce, the ecological and genetic implications of this absence remain unknown. In the current study, we focused on the California endemic violet, Viola pedunculata Torr. & A. Gray, which produces only CH flowers within its habitat in prairies and oak savannahs. Using microsatellites, we quantified the population genetic structure of three mainland populations and one island population in Southern California. We then used allozymes to estimate the outcrossing rate within a single population. Consistent with its production of CH flowers, levels of genetic variation were moderate to substantial within the species (Ap = 6.66, Ho = 0.39), with low but significant structure detected (Θ = 0.11). Furthermore, the high outcrossing rate (0.86) suggests that insect pollinators are frequent enough to ensure adequate seed set. These values were similar to those of a morphologically similar stemmed violet, Viola pubescens Aiton, which produces both CH and CL flowers. Overall, these results are consistent with substantial outcrossing occurring in V. pedunculata through CH flowers, leading to gene flow among populations and potentially counteracting effects of genetic drift.

Growth Regulators Improve the Intercrossing Rate of Cucumber Families for Recurrent Selection

ABSTRACTCucumber (Cucumis sativus L.) populations for recurrent selection often are intercrossed after each cycle using bees (Apis mellifera) in isolation blocks to save the expense of hand labor. This experiment was conducted to determine whether the rate of natural outcrossing could be increased using growth regulators, plot size management, and node of fruit position for seed harvest. The experiment was a factorial in a randomized complete block design with 2 yr (1997 and 1998), two growth regulators (treated and none), two plot sizes (single plant hills and small plots), two nodes of harvest (crown and top), and four replications (six in 1998). Plots or hills were planted to white‐spined ‘Sumter’ and were surrounded by rows of black‐spined ‘Wisconsin SMR 18’ pollenizer. Plots or hills of Sumter were treated with ethrel to induce gynoecy, and pollenizer rows were treated with silver nitrate to induce androecy. Untreated isolation blocks remained monoecious. Progeny of the harvested white‐spined plants were planted the following year to evaluate spine color, with black‐spined plants indicating an outcross. Results showed that node of harvest had no effect on outcrossing rate. However, growth regulators and plot size had a significant effect. Treated small plots, treated hills, and untreated hills had high outcrossing rates (54%) relative to untreated plots (30%). Therefore, if families are to be intercrossed in isolation blocks, they should be treated with growth regulators for maximum outcrossing.

Outcrossing rate in olive assessed by microsatellite and inter simple sequence repeat (ISSR) markers

Olive is known to be an allogamous species. The aim of this study was to estimate the magnitude of cross-pollination rate using microsatellite simple sequence repeats (SSR) and inter simple sequence repeats (ISSR) molecular markers in olive genotypes. The DNA from maternal plants and 23 progenies of two different accessions, Ascolano USA and MGS GRAP541 were extracted and screened with two microsatellite and ten ISSR markers. The outcrossing rate and other related parameters were analyzed using the MLTR application. The set of estimates, individually and collectively, support the hypothesis of frequent allogamy in both olive genotypes evaluated, with high rates of outcrossing in both markers. Keywords: Olea europaea L., outcrossing rate, zygotic embryos, mating system, molecular markers

Fluxo gênico em milho geneticamente modificado com resistência a insetos

O objetivo deste trabalho foi estimar o fluxo gênico em milho transgênico com resistência a insetos, em lavouras comerciais. Amostras de grãos foram coletadas em lavouras com milho convencional e transgênico, nos municípios de: Itumirim, Uberlândia, Paracatu e Tupaciguara, MG; Itapetininga e Pedrinhas, SP; e Assaí e Ponta Grossa, PR. As amostras foram coletadas em lavouras de milho convencional, a partir de 5 m de distância da fonte com o milho transgênico. Foram coletadas dez espigas de plantas individuais por ponto, em quatro repetições, no total de 40 espigas para cada distância amostrada. As análises de fluxo gênico foram realizadas por meio da técnica de reação em cadeia da polimerase (PCR) em tempo real. Em média, 82% da fecundação cruzada ocorreu nos primeiros 30 m. Em Itapetininga, SP, foram observadas as maiores taxas de fecundação cruzada - acima de 10% até a distância de 50 m -, porém, inferiores a 1% na distância de 100 m. O isolamento de 20 m, com dez linhas de bordadura, não é suficiente para garantir taxas de fecundação cruzada inferiores a 1%.

Mating System Analysis of Alnus maritima (Seaside Alder), a Rare Riparian Tree

Abstract Effective conservation requires an understanding of the genetic interactions among populations and individuals of a species, particularly those with fragmented, isolated distributions. Alnus maritima (seaside alder) is a rare tree species with an extremely fragmented distribution of highly isolated populations in the Delmarva Peninsula, Georgia, and Oklahoma. We conducted a mating system study to estimate the outcrossing rate, inbreeding coefficient, biparental inbreeding rate, and correlation of paternity in progeny from a Georgia and an Oklahoma population to investigate the effects of isolation on the A. maritima mating system. Data from nine microsatellite loci showed similarly high multilocus outcrossing rates in both populations (tm = 0.94). Individual tree outcrossing rates were also high (tm = 0.873–1.047). There was no significant biparental inbreeding in either population, but there was significantly higher correlated paternity in the Oklahoma population. Results showed the high out...

Studying comparative suitability of CMS lines

Parental lines constitute the first and foremost step in a hybrid breeding program. In this context, developing a commercially viable cytoplasmic male sterile (CMS) line is considered to be a highly cumbersome process. In fact, the belated success of hybrid rice technology in India was basically due to the nonavailability of a CMS line suited to the tropics. Over the years, a large number of male sterile lines with different cytosterility sources have been developed in India and elsewhere. Only a few-such as IR58025A and IR62829A-are now used commercially in India. They possess all the essential traits-complete and stable male sterility, high outcrossing rate, better grain quality, easy restorability, good combining ability, and adaptability-of a commercially viable CMS line. Some 64 CMS lines from India, China, Malaysia, and IRRI were evaluated along with IR58025A, IR62829A, and standard checks in the wet season of 1995 and 1996 and dry season of 1994 and 1995 to assess their comparative suitability for commercial use.

No Evolutionary Shift in the Mating System of North American Ambrosia artemisiifolia (Asteraceae) Following Its Introduction to China

The mating system plays a key role during the process of plant invasion. Contemporary evolution of uniparental reproduction (selfing or asexuality) can relieve the challenges of mate limitation in colonizing populations by providing reproductive assurance. Here we examined aspects of the genetics of colonization in Ambrosia artemisiifolia, a North American native that is invasive in China. This species has been found to possess a strong self-incompatibility system and have high outcrossing rates in North America and we examined whether there has been an evolutionary shift towards the dependence on selfing in the introduced range. Specifically, we estimated outcrossing rates in one native and five invasive populations and compared levels of genetic diversity between North America and China. Based on six microsatellite loci we found that, like the native North American population, all five Chinese populations possessed a completely outcrossing mating system. The estimates of paternity correlations were low, ranging from 0.028–0.122, which suggests that populations possessed ∼8–36 pollen donor parents contributing to each maternal plant in the invasive populations. High levels of genetic diversity for both native and invasive populations were found with the unbiased estimate of gene diversity ranging from 0.262–0.289 for both geographic ranges based on AFLP markers. Our results demonstrate that there has been no evolutionary shift from outcrossing to selfing during A. artemisiifolia's invasion of China. Furthermore, high levels of genetic variation in North America and China indicate that there has been no erosion of genetic variance due to a bottleneck during the introduction process. We suggest that the successful invasion of A. artemisiifolia into Asia was facilitated by repeated introductions from multiple source populations in the native range creating a diverse gene pool within Chinese populations.

Mating system in natural populations of Taurus cedar (Cedrus libani A.Rich.)

The aim of this study was to estimate patterns of the mating system in 2 natural Cedrus libani A.Rich. populations in Elmalı, Antalya, with the aid of isozyme markers. Isozyme analysis was performed on both maternal and embryo tissues of the seeds collected from Avlankuzu and Çamkuyusu populations. Eleven loci encoding 8 enzyme systems were analyzed. The Avlankuzu and Çamkuyusu populations were a homogeneous and similar gene pool for the loci studied. Based on a multilocus estimator, the proportion of viable seeds originating from outcrossing (tm) was 0.940 for the Avlankuzu population and 0.944 for the Çamkuyusu population. In other words, selfing in the Avlankuzu and Çamkuyusu populations was 6% and 5.6%, respectively. A high outcrossing rate, relatively high heterozygosity, and a lack of significant levels of inbreeding in the study populations are important components of the adaptive strategy of this species. Therefore these populations are not at risk for inbreeding depression is an important finding for the conservation of gene resources of this species.

Environmental effects on long-range outcrossing rates in maize

With the aims of clarifying the effects of genetically modified crops on the environment, along with investigating the coexistence rules for genetically modified (GM) crops and existing non-GM crops, we carried out outcrossing experiments with maize. To clarify the actual conditions and characteristics of long-range outcrossing rates in particular, the present research conducted over the 3-year period of 2006–2008 involved performing outcrossing experiments using large-scale plots and obtaining data on meteorological observations, outcrossing rates, and pollen observations. These experiments significantly expanded the scale of the test plots from previous work on this subject, with measurements of outcrossing rates at long distances and investigations of the effect of meteorological elements and pollen count. The outcrossing rate was estimated as the percentage of yellow kernels produced among the white kernels due to the pollination of the recipient female flowers of the white-kernel cultivar by the donor flower pollen of the yellow-kernel cultivar. The following was clarified from these results. (1) Precipitation from the date of flowering to the day before the peak pollen dispersion period suppressed the amounts of pollen dispersed during the peak period, and was one of the factors that determined the pattern of pollen dispersal. (2) Outcrossing did not occur in a spatially homogeneous manner, and the distribution produced isolated islands of high outcrossing rate. Even in locations that were several hundred meters from the donor, outcrossing did not occur in a spatially homogeneous manner. (3) The outcrossing rate decreased exponentially as a function of distance from the donor field, but did not reach zero even at points 800 m distant, nor did the values become uniform. They continued to decrease in an extremely gradual manner. (4) In the relationship between outcrossing rate and distance from the donor, the higher the mean wind speed, the smaller the reduction of outcrossing rate with distance. In addition, the greater the amount of solar radiation, the larger the reduction of outcrossing rate with distance.

Genetic population structure of cacao plantings within a young production area in Nicaragua.

Significant cocoa production in the municipality of Waslala, Nicaragua, began in 1961. Since the 1980s, its economic importance to rural smallholders increased, and the region now contributes more than 50% of national cocoa bean production. This research aimed to assist local farmers to develop production of high-value cocoa based on optimal use of cacao biodiversity. Using microsatellite markers, the allelic composition and genetic structure of cacao was assessed from 44 representative plantings and two unmanaged trees. The population at Waslala consists of only three putative founder genotype spectra (lineages). Two (B and R) were introduced during the past 50 years and occur in >95% of all trees sampled, indicating high rates of outcrossing. Based on intermediate allelic diversity, there was large farm-to-farm multilocus genotypic variation. GIS analysis revealed unequal distribution of the genotype spectra, with R being frequent within a 2 km corridor along roads, and B at more remote sites with lower precipitation. The third lineage, Y, was detected in the two forest trees. For explaining the spatial stratification of the genotype spectra, both human intervention and a combination of management and selection driven by environmental conditions, appear responsible. Genotypes of individual trees were highly diverse across plantings, thus enabling selection for farm-specific qualities. On-farm populations can currently be most clearly recognized by the degree of the contribution of the three genotype spectra. Of two possible strategies for future development of cacao in Waslala, i.e. introducing more unrelated germplasm, or working with existing on-site diversity, the latter seems most appropriate. Superior genotypes could be selected by their specific composite genotype spectra as soon as associations with desired quality traits are established, and clonally multiplied. The two Y trees from the forest share a single multilocus genotype, possibly representing the Mayan, ‘ancient Criollo’ cacao.

Estimation of outcrossing rates at small-scale flowering sites of the dwarf bamboo species, Sasa cernua

We estimated the outcrossing rates at small-scale flowering sites of an endemic dwarf bamboo species, Sasa cernua. The multi-locus estimation of the outcrossing rate of the dwarf bamboo population was 0.148 (SD 0.118). Two culms with the highest outcrossing rates had heterozygous genotypes at one locus, but other culms in the locus were homozygotes. Five culms with high outcrossing rates bore 2-17% seeds with homozygous genotypes. Due to predominant selfing, the overall inbreeding coefficient of seeds was high, although it declined in seedlings. This suggests that selection against inbred progenies began early in the establishment process in the natural habitat.

Mating system and pollination biology of a high-mountain perennial plant, Rhodiola dumulosa (Crassulaceae)

Rhodiola dumulosa is a perennial herb growing in a naturally fragmented habitat of high-mountain rocks. This research aims to (i) investigate the mating system characteristics and pollination biology of R. dumulosa, (ii) study the effects of ecological factors on the mating system and pollination biology of R. dumulosa and (iii) assess the relationship between its pollination and mating system. Mating system parameters were analysed using allozyme markers. Growth of pollen tubes from artificial self- and cross-pollination was also examined. Field investigations were conducted on insect flower visitation during the blooming period of R. dumulosa. Relationships among mating system, insect flower visitation frequency and environmental factors were assessed. The results showed that (i) R. dumulosa has a mixed-mating system: it is self-compatible and primarily outbreeding, with the multilocus outcrossing rate (tm) ranging from 0.589 ± 0.078 (± standard deviation) to 0.846 ± 0.077; inbreeding coefficients of maternal parents (F) were zero, indicating that inbreeding depression was intense. (ii) Light intensity and temperature impacted the visitation of the principal pollinators, the syrphid Eristalis tenax and the bumblebee Bombus pyrosoma. (iii) Population size plays an important role in the mating system and pollination. Populations received more frequent visits by the principal pollinators usually had higher outcrossing rates. Pollination to some extent affects the mating system of R. dumulosa and it is important to maintain large populations to prevent further inbreeding and to maintain pollinators to facilitate outcrossing.

Yeast Sex: Surprisingly High Rates of Outcrossing between Asci

Background Saccharomyces yeasts are an important model system in many areas of biological research. Very little is known about their ecology and evolution in the wild, but interest in this natural history is growing. Extensive work with lab strains in the last century uncovered the Saccharomyces life cycle. When nutrient limited, a diploid yeast cell will form four haploid spores encased in a protective outer layer called the ascus. Confinement within the ascus is thought to enforce mating between products of the same meiotic division, minimizing outcrossing in this stage of the life cycle.Methodology/Principal FindingsUsing a set of S. cerevisiae and S. paradoxus strains isolated from woodlands in North America, we set up trials in which pairs of asci were placed in contact with one another and allowed to germinate. We observed outcrossing in ∼40% of the trials, and multiple outcrossing events in trials with three asci in contact with each other. When entire populations of densely crowded asci germinated, ∼10–25% of the resulting colonies were outcrossed. There were differences between the species with S. cerevisiae having an increased tendency to outcross in mass mating conditions.Conclusions/SignificanceOur results highlight the potential for random mating between spores in natural strains, even in the presence of asci. If this type of mating does occur in nature and it is between close relatives, then a great deal of mating behavior may be undetectable from genome sequences.

Introgression of fitness genes across a ploidy barrier

Gene flow from diploid to polyploid species could have significant effects on the morphology and ecology of polyploids. The potential of such introgression for bringing about evolutionary change within polyploids has long been recognized, although there are few examples of the process in the wild. Here, we focus on introgression between the diploid species, Senecio squalidus, and the tetraploid, S. vulgaris, which resulted in the origin of a variant form of S. vulgaris that produces radiate rather than nonradiate flower heads. The radiate variant of S. vulgaris is more attractive to pollinators and has a higher outcrossing rate. We review recent work that has isolated and characterized two regulatory genes, RAY1 and RAY2, that control presence of ray florets in radiate flower heads, and which have been introgressed into S. vulgaris from S. squalidus in the recent past. We identify a copy of RAY2 in S. vulgaris (RAY2b) homeologous to the copy (RAY2a) previously isolated, thus providing further evidence that S. vulgaris is allotetraploid. We also show that the RAY2a-R allele, which is fixed in radiate S. vulgaris, occurs at intermediate frequency in S. squalidus. Thus, based on this result, it is not possible to distinguish whether radiate S. vulgaris originated once or multiple times following hybridization between nonradiate S. vulgaris and S. squalidus.

Genetic polymorphism of plus-tree clones and their seed progeny in the scotch pine clone plantation

Genetic variation at 12 allozyme loci (10 of them being polymorphic ones) has been studied in the archive-clone plantation of 23 Pinus sylvestris plus-trees and their seed progeny in the south-east of Ukraine. More than a half of clones had 4-8 heterozygous loci, whereas their seed progeny was marked by a lower variation than maternal trees. Seed progeny was obtained at a high outcrossing rate (t(m) = 95%). The clone progeny was characterized by a high percentage of abnormal allele segregation in megagametophytes. There was also a high frequency of significant deviation in distribution of seed embryo genotypes from the theoretically expected one according to the Hardy-Weinberg law.