THE EFFECTS OF FIVE GENERATIONS OF ENFORCED SELFING ON POTENTIAL MALE AND FEMALE FUNCTION IN MIMULUS GUTTATUS

In prior work we detected no significant inbreeding depression for pollen and ovule production in the highly selfing Mimulus micranthus, but both characters showed high inbreeding depression in the mixed-mating M. guttatus. The goal of this study was to determine if the genetic load for these traits in M. guttatus could be purged in a program of enforced selfing. These characters should have been under much stronger selection in our artificial breeding program than previously reported characters such as biomass and total flower production because, for example, plants unable to produce viable pollen could not contribute to future generations. Purging of genetic load was investigated at the level of both the population and the individual maternal line within two populations of M. guttatus. Mean ovule number, pollen number, and pollen viability declined significantly as plants became more inbred. The mean performance of outcross progeny generated from crosses between pairs of maternal inbred lines always exceeded that of self progeny and was fairly constant for each trait through all five generations. The consistent performance of outcross progeny and the universally negative relationships between performance and degree of inbreeding are interpreted as evidence for the weakness of selection relative to the quick fixation of deleterious alleles due to drift during the inbreeding process. The selective removal (purging) of deleterious alleles from our population would have been revealed by an increase in performance of outcross progeny or an attenuation of the effects of increasing homozygosity. The relationships between the mean of each of these traits and the expected inbreeding coefficient were linear, but one population displayed a significant negative curvilinear relationship between the log of male fertility (a function of pollen number and viability) and the inbreeding coefficient. The generally linear form of the responses to inbreeding were taken as evidence consistent with an additive model of gene action, but the negative curvilinear relationship between male fertility and the inbreeding coefficient suggested reinforcing epistasis. Within both populations there was significant genetic variation among maternal lineages for the response to inbreeding in all traits. Although all inbred lineages declined at least somewhat in performance, several maternal lines maintained levels of performance just below outcross means even after four or five generations of selfing. We suggest that selection among maternal lines will have a greater effect than selecting within lines in lowering the genetic load of populations.     

Tests of two hypotheses concerning pollen competition in a self-compatible,long-styled species (Lobelia cardinalis: Lobeliaceae)

Using the long-styled, self-compatible species Lobelia cardinalis, I examined the relative abilities of self pollen and two outcross pollen sources to fertilize ovules when these three kinds of pollen were applied simultaneously to stigmas. Paternity was determined electrophoretically for 712 progeny of 25 seed parents. Two hypotheses were tested. First, it was hypothesized that self pollen would be less effective than outcross pollen at fertilizing ovules, as a means of reducing the selfing rate. Outcross pollen outperformed self pollen in eight of the 25 seed parents, self outperformed outcross in five, and they were competitively indistinguishable in 12. The mean proportion of offspring produced by self pollen was not significantly different from the value expected under random tube growth and fertilization. The rate of self-fertilization is therefore determined by prepollination events. Second, to test one stage of the sexual-selection process, it was hypothesized that the pollen of some individuals would outcompete that of others, across a range of maternal plants. The 25 maternal parents were divided into five groups of approximately five individuals. Each member of a group received pollen from the same two outcross pollen sources (as well as from itself). With offspring pooled across seed parents, one outcross pollen parent outcompeted the other in two of the five groups. In two other groups, pollen sources were competitively superior or inferior depending on the maternal parent. Overall, pollen donors were competitively indistinguishable in 13 of 25 maternal parents. There is thus no evidence for strong postpollination sexual selection. If such selection is present, it is weak, and its importance to the evolution of style length in Lobelia cardinalis requires other kinds of study.     

Variation of pollen limitation in the early flowering Mediterranean geophyte Narcissus assoanus (Amaryllidaceae)

A recent literature review indicates that pollen limitation of female fertility is a common feature of flowering plants. Despite the ecological and evolutionary significance of pollen limitation, most studies have only examined fertility in a single population at one time. Here we investigate pollen limitation of fruit and seed set in five populations of Narcissus assoanus, a self- sterile, insect-pollinated geophyte, over 2–3 years in southern France. In common with many early spring flowering plants, pollinator visitation to N. assoanus is often infrequent. Supplemental hand-pollination of flowers with outcross pollen significantly increased overall fruit and seed set by 11% and 19%, respectively. Four of the five populations experienced some pollen limitation during the study. For a given year, there was significant variation in pollen limitation among populations. Two of the populations were pollen limited in one year but not in other years in which they were studied. Seed:ovule ratios for open- and hand-pollinated flowers averaged 0.29 and 0.33, respectively. While hand pollination significantly increased the seed:ovule ratio, the low value obtained indicates that the majority of ovules in flowers do not mature seeds despite hand pollination. The role of genetic and environmental factors governing low seed:ovule ratios in N. assoanus is discussed. Received: 28 December 1999 / Accepted: 6 April 2000     

FITNESS CONSEQUENCES OF MIXED-DONOR POLLEN LOADS IN THE ANNUAL LEGUME CHAMAECRISTA FASCICULATA

We experimentally examined the effects of pollen composition on progeny fitness in the self-compatible, annual plant Chamaecrista fasciculata. Plants were hand-pollinated with single- and mixed-donor pollen loads and with various combinations of self- and outcross pollen. For outcrosses, pollen was obtained from two plants at each of two different distances within the same subpopulation as the female parent. Seedlings from all crosses were planted back into the maternal site. For single-donor crosses, seed weight, progeny fruit production, and overall relative fitness were significantly higher for outcross, as compared to self-treatments, but we found no significant differences among outcross sources. For all fitness components, the value observed for crosses derived from mixed loads was intermediate between the values for the singledonor crosses that comprised the mixed load. In a parallel experiment, an analysis of seed paternity of progeny which resulted from pollen mixtures of self- and outcross pollen showed random paternity in two maternal families, and significant excess of outcross in one family. Our results demonstrate that mixed pollen loads do not confer a fitness advantage to the maternal plant in this species, and that the fitness observed for progeny derived from mixed loads is generally consistent with a hypothesis of random paternity.     

Linkage Disequilibrium between Allozymes in Natural Populations of Lodgepole Pine

Pairwise linkage disequilibrium values (D) were estimated for 14 allozyme loci in two natural populations of lodgepole pine (Pinus contorta ssp. latifolia). Maternal multilocus genotypes were inferred from samples of (haploid) megagametophytic seed-endosperms. Coupling/repulsion double heterozygotes were distinguished for closely linked pairs of loci. Assays of seven of the loci in seed embryos allowed estimates of D for these loci in the outcross pollen pool (estimates of outcrossing rates indicate no significant departures from random mating in either population). No disequilibrium was observed between unlinked loci in either maternal genotypes or outcross pollen. However, significant disequilibrium was observed within and between gametes for some allelic combinations of four tightly linked loci; the assumption of random association of gamete types within individuals is thus invalid for some loci in lodgepole pine. Possible causes of the observed D were examined using the noncentrality parameter of the general noncentral chi square distribution. We concluded, from estimates of population size, linkage and measurements of population substructure, that neither drift nor population subdivision was responsible for the significant values of D which were observed and that epistatic selection was the most likely cause of the disequilibrium observed.     

Pollen source affects female reproductive success and early offspring traits in the rare endemic plant Polemonium vanbruntiae (Polemoniaceae)

Understanding the relative magnitudes of inbreeding and outbreeding depression in rare plant populations is increasingly important for effective management strategies. There may be positive and negative effects of crossing individuals in fragmented populations. Conservation strategies may include introducing new genetic material into rare plant populations, which may be beneficial or detrimental based on whether hybrid offspring are of increased or decreased quality. Thus, it is important to determine the effects of pollen source on offspring fitness in rare plants. We established pollen crosses (i.e. geitonogamous‐self, autonomous‐self, intrasite‐outcross, intersite‐outcross and open‐pollinated controls) to determine the effects of pollen source on fitness (seeds/fruit and seed mass) and early offspring traits (probability of germination, number of leaves, leaf area and seedling height) in the rare plant Polemonium vanbruntiae. Open‐pollinated, intrasite‐outcross and geitonogamous‐self treatments did not differ in fitness. However, plants receiving autonomous‐self pollen had the lowest fitness and the lowest probability of seed germination. Intersite‐outcross plants contained fewer seeds/fruit, but seeds germinated at higher frequencies and seedlings were more vigorous. We also detected heterosis at the seed germination stage. These data may imply that natural populations of P. vanbruntiae exhibit low genetic variation and little gene flow. Evidence suggests that deleterious alleles were not responsible for reduced germination; rather environmental factors, dichogamy, herkogamy and/or lack of competition among pollen grains may have caused low germinability in selfed offspring. Although self‐pollination may provide some reproductive assurance in P. vanbruntiae, the result is a reduction in germination and size‐related early traits for selfed offspring.     

INDIVIDUAL VARIATION IN THE VIGOR OF SELF POLLEN AND SELFED PROGENY IN HIBISCUS MOSCHEUTOS (MALVACEAE)

In some self-compatible species, self pollen tubes grow more slowly than outcross pollen, presumably leading to low selfing rates when mixtures of self and outcross pollen reach the stigma simultaneously. Here we show that the competitive ability of self pollen differed among individuals of Hibiscus moscheutos. Self pollen tubes grew slower than outcross pollen in three plants, faster than outcross pollen in four plants, and showed no difference in five other plants (based on rates of callose plug formation). Levels of inbreeding depression were examined by comparing progeny from self and outcross pollinations in seven maternal families. Self pollination led to reduced seed number in only one maternal family, and a slight decrease in seed size was seen in two maternal families. Considerable inbreeding depression occurred later in the life cycle, and the degree of inbreeding depression varied among maternal families of 6-week-old plants. Our results demonstrate the potential for unpredictable effects of pollen competition on individual selfing rates, which in turn may affect progeny vigor. This complex situation contrasts with previous reports of species in which outcross pollen consistently outcompetes self pollen (cryptic self-incompatibility).     

Resource limitation and pollen source (self and outcross) affecting seed production in two louseworts, Pedicularis siphonantha and P. longiflora (Orobanchaceae)

Two animal-pollinated hermaphrodite plants, Pedicularis siphonantha and P. longiflora , have been used to investigate factors limiting seed production in natural populations. To evaluate the potential seed abortion due to resources limitation, seed development has been observed and seed count conducted twice. Seed production per capsule has been compared when flowers have been removed and in a control group. Open pollination has been investigated and pollen supplementation undertaken to estimate the possibility of pollen limitation. Results show that seed abortion is frequent. Stigmatic pollen load is significantly higher than ovule number per ovary under open pollination for both species. Additional self and outcross pollen did not affect seed production. Flower removal significantly increases seed production per capsule, which indicates that seed production of the studied species is limited by available resources. To detect differences in seed production between flowers pollinated by self and outcross pollen, hand pollination of bagged flowers has also been conducted in natural populations of the two Pedicularis species. Compared with open pollination, hand-pollinating self-pollen decreases, while outcross pollen increases seed production per capsule. Such results suggest that inbreeding depression in the two self-compatible species may also result in partial seed abortion under open pollination if mixed pollen is deposited on the stigma. Our results also suggest that pollen interference plays an important role in low female fertility in the two Pedicularis species.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 83–89.     

Limiting inbreeding in disjunct and isolated populations of a woody shrub

Pollen movements and mating patterns are key features that influence population genetic structure. When gene flow is low, small populations are prone to increased genetic drift and inbreeding, but naturally disjunct species may have features that reduce inbreeding and contribute to their persistence despite genetic isolation. Using microsatellite loci, we investigated outcrossing levels, family mating parameters, pollen dispersal, and spatial genetic structure in three populations of Hakea oldfieldii, a fire‐sensitive shrub with naturally disjunct, isolated populations prone to reduction in size and extinction following fires. We mapped and genotyped a sample of 102 plants from a large population, and all plants from two smaller populations (28 and 20 individuals), and genotyped 158–210 progeny from each population. We found high outcrossing despite the possibility of geitonogamous pollination, small amounts of biparental inbreeding, a limited number of successful pollen parents within populations, and significant correlated paternity. The number of pollen parents for each seed parent was moderate. There was low but significant spatial genetic structure up to 10 m around plants, but the majority of successful pollen came from outside this area including substantial proportions from distant plants within populations. Seed production varied among seven populations investigated but was not correlated with census population size. We suggest there may be a mechanism to prevent self‐pollination in H. oldfieldii and that high outcrossing and pollen dispersal within populations would promote genetic diversity among the relatively small amount of seed stored in the canopy. These features of the mating system would contribute to the persistence of genetically isolated populations prone to fluctuations in size.     

Effect of pollen load size and source (self, outcross) on seed and fruit production in highbush blueberry cv. 'Bluecrop' (VACCINIUM CORYMBOSUM; Ericaceae)

Reproductive fitness of a plant is ultimately determined by both number and quality of seed offspring. This is determined by sexual selection of pollen microspores and ovules during pollination and fertilization. These processes may include pollen competition and seed abortion, which reduce the number of microspores and ovules available for final seed production. Thus, even an excess of pollen microspores to ovules does not result in fertile seeds equal to ovule number. We investigated pollen requirements of highbush blueberry (Vaccinium corymbosum cultivar 'Bluecrop') for maximal seed production and how fertile seed number translates into fruit quality, since fruit quality would ultimately determine the dispersal of its offspring. We demonstrate that individual blueberry flowers with a mean of 106 ovules reach their maximum fruit set and mass and minimum time to ripen when 125 outcross pollen tetrads pollinate a flower, compared to 10 or 25. Three hundred tetrads resulted in the increase of fertile seeds, but did not result in a further increase of fruit mass or fruit set, or decrease in time to ripen. We also examined the effect of pure and mixed loads of self and outcross pollen (25 and 125 tetrads), and found no differences in fertile seed number, fruit mass, or percentage fruit set when pollen loads were either 25 self or outcross pollen tetrads, although number of days to ripen was significantly shorter by 8 d with 25 outcross tetrads. When the pollen load of 125 tetrads consisted of self or a 50:50 mixture of self and outcross pollen, fruit mass, days to ripen, and percentage fruit set were not different from loads of 125 outcross pollen. In addition, a pollen load of 25 outcross tetrads resulted in fertile seed number and fruit quality in between that of 25 self, and 125 self, 125 mixed, or 125 outcross tetrads. Large, small, and flat seed types were identified, and only large seeds (length = 1.7 mm) were fertile. These results improve our understanding of pollen load size and source requirements of a crop plant and the limits to pollen transfer when translated to fruit growth.     

Limited seed dispersal and microspatial population structure of an agamospermous grass of West African savannahs, Hyparrhenia diplandra (Poaceae)

We studied the microspatial population structure of the perennial tussock grass, Hyparrhenia diplandra (Poaceae), a facultative agamospermous species of West African savannahs. The microspatial population structure of H. diplandra was investigated by choosing two 100-m(2); quadrats at random from which all individuals were mapped. The genotype of every individual was determined using two highly polymorphic microsatellite loci. A chloroplast locus was also used to investigate the role of seed dispersal on the genetic structure of populations. The genetic diversity index (0.85) was high for a clonal species. Significant genetic differentiation over short distances was detected by F statistics, and spatial autocorrelation analyses within both quadrats showed significant isolation-by-distance patterns, both with the cytoplasmic locus and the nuclear loci. Some clones formed large patches (up to 5 m in diameter) whereas others were more scattered. However, the genetic differentiation between quadrats was much higher when studied with the cytoplasmic locus than with the nuclear loci, indicating that gene flow via pollen, but not seeds, may frequently occur between quadrats. The maintenance of genetic diversity in this facultative agamospermous species most likely results from several factors, such as low seed dispersal ability, nonnegligible gene flow through pollen, and selective pressures induced by regularly occurring fires in this ecosystem.     

Optimal sampling strategy for estimation of spatial genetic structure in tree populations

Fine-scale spatial genetic structure (SGS) in natural tree populations is largely a result of restricted pollen and seed dispersal. Understanding the link between limitations to dispersal in gene vectors and SGS is of key interest to biologists and the availability of highly variable molecular markers has facilitated fine-scale analysis of populations. However, estimation of SGS may depend strongly on the type of genetic marker and sampling strategy (of both loci and individuals). To explore sampling limits, we created a model population with simulated distributions of dominant and codominant alleles, resulting from natural regeneration with restricted gene flow. SGS estimates from subsamples (simulating collection and analysis with amplified fragment length polymorphism (AFLP) and microsatellite markers) were correlated with the 'real' estimate (from the full model population). For both marker types, sampling ranges were evident, with lower limits below which estimation was poorly correlated and upper limits above which sampling became inefficient. Lower limits (correlation of 0.9) were 100 individuals, 10 loci for microsatellites and 150 individuals, 100 loci for AFLPs. Upper limits were 200 individuals, five loci for microsatellites and 200 individuals, 100 loci for AFLPs. The limits indicated by simulation were compared with data sets from real species. Instances where sampling effort had been either insufficient or inefficient were identified. The model results should form practical boundaries for studies aiming to detect SGS. However, greater sample sizes will be required in cases where SGS is weaker than for our simulated population, for example, in species with effective pollen/seed dispersal mechanisms.     

Estimating seed vs. pollen dispersal from spatial genetic structure in the common ash

Spatial genetic structure was analysed with five highly polymorphic microsatellite loci in a Romanian population of common ash (Fraxinus excelsior L.), a wind-pollinated and wind-dispersed tree species occurring in mixed deciduous forests over almost all of Europe. Contributions of seed and pollen dispersal to total gene flow were investigated by analysing the pattern of decrease in kinship coefficients among pairs of individuals with geographical distance and comparing it with simulation results. Plots of kinship against the logarithm of distance were decomposed into a slope and a shape component. Simulations showed that the slope is informative about the global level of gene flow, in agreement with theoretical expectations, whereas the shape component was correlated with the relative importance of seed vs. pollen dispersal. Hence, our results indicate that insights into the relative contributions of seed and pollen dispersal to overall gene flow can be gained from details of the pattern of spatial genetic structure at biparentally inherited loci. In common ash, the slope provided an estimate of total gene dispersal in terms of Wright's neighbourhood size of Nb = 519 individuals. No precise estimate of seed vs. pollen flow could be obtained from the shape because of the stochasticity inherent to the data, but the parameter combinations that best fitted the data indicated restricted seed flow, sigmas pound 14 m, and moderate pollen flow, 70 m pound sigmap pound 140 m.     

Variation in self-fertility and the reproductive advantage of self-fertility for an invading plant (Spartina alterniflora)

The factors responsible for the reproductive success or failure of individuals in small, founding populations have received little attention. Previous work on a small population of smooth cordgrass (Spartina alterniflora) invading San Francisco Bay, California found that most clones flower prolifically but set little or no seed, while a few clones have high rates of viable seed set, producing most of the seeds in the population. This study first identifies recruitment from seeds as the main source of new smooth cordgrass plants during invasion and then tests the influence of growing conditions and pollination treatment on viable seed set among clones established in San Francisco Bay. Field transplants indicated that a clone's seed set rate was not strongly dependent on its site of establishment. Low and high nutrient greenhouse treatments also had little effect on viable seed set rates within most clones. In contrast, pollination treatment (self-pollination or outcrossing) had a major effect on viable seed set rates. Most clones had high seed set rates after outcross-pollination, but clones varied widely in their selfing capacity. Zero or low viable self-seed set rates were most common; however, a few clones had high viable self-seed set rates, comparable to outcross seed set rates. A clone's selfing capacity was significantly correlated across years (r=0.89, P<0.001), and capacity to set viable self-pollinated seeds in the greenhouse was significantly correlated with the clone's rate of viable seed set in the field . In this growing population where cross-pollination is limited, only the clones with high selfing ability had high viable seed set rates in the field. Among primarily outcrossing plant invaders, variation in self-fertility among individuals may be a common phenomenon, with important implications for genetic differentiation, effective population size and patterns of spatial spread during an invasion.     

COSTS OF SELF-POLLINATION IN A SELF-INCOMPATIBLE PLANT,POLEMONIUM VISCOSUM

Plants of Polemonium viscosum are strongly self-incompatible, yet have floral features that enforce spatial and temporal separation of pollen and stigma presentation. In this study, we address the widely held view that such barriers to selfing are maintained because they reduce interference by self pollen in performance of outcross grains. In the first year of the study we found that 24 hr precedence of self pollen on the stigma (24S), reduced outcross pollen germination by 32%, and seed set by 40% in flowers of P. viscosum. In the second year significant negative effects of self pollen on compatible pollen germination were seen when self pollen was applied four hours before (4S) or immediately prior (S×) to outcross pollen. Surprisingly, however, in the second year of study, seed set was not reduced with as much as 50% inhibition of compatible pollen germination. Results suggest that by interfering with normal functioning of outcross grains, incompatible self pollen can increase pollen limitation in P. viscosum. Reduction in seed production as a result of this phenomenon should select for displacement of pollen presentation from stigma receptivity.     

利用等位酶对油松无性系种子进行父本分析

利用水平淀粉凝胶电泳8种酶10个位点34个等位基因,对辽宁兴城油松无性系种子园中17个无性系20个单株的200粒种子作了父本分析。无性系雄花量的多少与授粉果率并不成正比;不同无性系对花粉的接受存在一定的选择性,分析试样单株与周围的无性系并没有构成固定的授粉组合,说明授粉期风向等气象因子,无性系的雌雄花器的构造,受精等对受粉的成败都有作用,种子园结实初期自交现象并不明显,在分析试样中只有16＃,17＃,19＃无性系存在自交现象;种子园内花偻的有效传播一般在半径30m范围内,同时,分析了种子园子代的等位酶变异和空间遗传结构,从另一侧面反映出采种母树周围花粉分布比较均匀,并说明散粉期间风向等气象因子对授粉成败影响较大。     

Molecular mapping of the rf1 gene for pollen fertility restoration in sorghum (Sorghum bicolor L.)

We report the molecular mapping of a gene for pollen fertility in A1 (milo) type cytoplasm of sorghum using AFLP and SSR marker analysis. DNA from an F₂ population comprised of 84 individuals was screened with AFLP genetic markers to detect polymorphic DNAs linked to fertility restoration. Fifteen AFLP markers were linked to fertility restoration from the initial screening with 49 unique AFLP primer combinations (+3/+3 selective bases). As many of these AFLP markers had been previously mapped to a high-density genetic map of sorghum, the target gene (rf1) could be mapped to linkage group H. Confirmation of the map location of rf1 was obtained by demonstrating that additional linkage group-H markers (SSR, STS, AFLP) were linked to fertility restoration. The closest marker, AFLP Xtxa2582, mapped within 2.4 cM of the target loci while two SSRs, Xtxp18 and Xtxp250, flanked the rf1 locus at 12 cM and 10.8 cM, respectively. The availability of molecular markers will facilitate the selection of pollen fertility restoration in sorghum inbred-line development and provide the foundation for map-based gene isolation. Received: 22 August 2000 / Accepted: 18 October 2000     

Prediction of genetic gain and gene diversity in seed orchard crops under alternative management strategies

Genetic gain and the gene diversity of seed crops from clonal seed orchards were formulated considering genetic selection, fertility variation and pollen contamination, and compared for five different management strategies. Genetic response was studied as a function of orchard management tactics. Management variables included the proportion of clones left after genetic thinning and/or selective seed harvesting. Formulae were derived to calculate gene diversity (expressed as group coancestry or status number) based on the sex ratio in an orchard population. The influence of having different sets of clones serving as seed parents, or pollen parents, or as both, was analysed. In addition, the impact on genetic gain and the gene diversity of seed crops was studied quantitatively as a function of the quantity and quality of gene flow from outside the orchard. The negative impact of fertility variation among orchard genotypes on the gene diversity of the seed crop was quantified. Numerical examples were given to illustrate the impact of orchard management alternatives on genetic gain and gene diversity. The formulae and results of this study can be used for identifying favourable alternatives for the management of seed orchards. Received: 16 December 2000 / Accepted: 13 March 2001     

REALIZED GENE FLOW VIA POLLEN IN ARTIFICIAL POPULATIONS OF MUSK THISTLE,CARDUUS NUTANS L.

Realized gene flow via pollen was measured in four adjacent, artificial populations of musk thistle, Carduus nutans L. by observing the distribution of electrophoretic markers at two allozyme loci. Realized gene movement declined exponentially with distance. Dispersal distances of the marker alleles averaged 5.0 m. Estimates of effective neighborhood sizes based on the movement of these genetic markers ranged from 126 to 378 individuals. When measures of seed movement were included, estimates of effective population sizes range from 1,281 to 3,844 individuals. It is, therefore, unlikely that chance effects play a major role in shaping the genetic structure of well-established musk thistle populations.     

Early-acting inbreeding depression in three species of Vaccinium (Ericaceae)

Greenhouse pollinations were performed to determine whether early-acting inbreeding depression is contributing to low levels of self-fertility in three Vaccinium species: V. myrtilloides Michaux, V. angustifolium Aiton, and V. corymbosum L. All three species showed a significant reduction in self fruit set and in the proportion of fertilized ovules that developed into mature seed in self compared to outcross fruit. Reductions were more severe in V. myrtilloides and V. angustifolium than in V. corymbosum; however, early-acting inbreeding depression appeared to be the primary factor limiting self-fertility in all three species. Evidence for early- acting inbreeding depression included the presence and higher proportion of aborted ovules in self fruit than in outcross fruit, a correlation between levels of self and outcross seed set, and pollen chase experiments demonstrating that self-pollen does fertilize the ovules. Self-fertility in the three species was probably influenced by levels of genetic load, ploidy level and outcrossing rates. Received: 10 December 1999 / Revision accepted: 20 June 2000