Histological study of post-pollination events in Spathodea campanulata beauv. (Bignoniaceae), a species with late-acting self-incompatibility

The reproductive biology of Spathodea campanulata was investigated by means of hand-pollination experiments, observations of pollen tube growth using fluorescence microscopy, and serial sections of ovules in selfed and crossed pistils. Only cross-pollinated flowers developed fruits, and all selfed flowers abscised within 3-4 d. However, self pollen tubes grew successfully to the ovary, penetrating and fertilizing the majority of ovules by 48 h, indicating that S. campanulata is a species with late-acting self-incompatibility. The incidences of ovule penetration, fertilization and endosperm initiation were all significantly slower in selfed vs. crossed pistils, although no other signs of malfunctioning were detected. The possible role of such slow self pollen tube effectiveness as a recognition event is discussed within the context of the slow but not entirely suppressed self pollen tube growth reported for some species with conventional homomorphic self-incompatibility.     

Contrasting breeding systems in six species of Tillandsia L. (Bromeliaceae) from woody areas of Santa Fe Province: Argentina

The reproductive biology of six native Tillandsia species that co-occurred in woody areas of Santa Fe Province (Argentina) was studied for floral biology, breeding systems and reproductive success. Flower longevity, floral phases, hand self- and cross-pollinations or natural pollinations and fluorescence microscopy observations of post-pollination events were analysed. Also pollen/ovule (P/O) ratio and pre-emergent reproductive success (PERS) were compared between species. In T. aëranthos, T. ixioides and T. meridionalis, self-pollinated flowers mostly failed to form fruits, and fluorescence microscopy studies showed that in selfed pistils pollen tube growth was arrested in the style. It is likely that these species have homomorphic, gametophytic self-incompatibility. In contrast, T. capillaris, T. tricholepis and T. recurvata regularly formed fruits following autonomous self-pollination. Floral traits, the P/O ratios and PERS indices correlate with the breeding systems found in these two groups of species: the three selfing species have inconspicuous closed flowers, and they have low P/O ratios and high PERS values. In contrast, the three self-incompatible (SI) species have conspicuous flowers with relatively high P/O and low PERS values. We described here three new cases of SI in Tillandsia species subgenera Anoplophytum and confirm the autogamous and cleistogamous status in three species of Tillandsia subgenera Diaphoranthema.     

Mating in the pseudogamic apomictic Anemopaegma acutifolium DC: another case of pseudo‐self‐compatibility in Bignoniaceae?

Self‐compatibility in apomictic pseudogamic species is considered fundamental to assure reproduction by seeds in extreme situations, making apomictic species more advantageous than sexual ones in these scenarios. Anemopaegma acutifolium is a polyploidy, apomictic sporophytic species with no endosperm development in ovules of unpollinated pistils, which indicates obligate pseudogamy. Thus, the aim of the present work is to study the breeding system and post‐pollination events to test if there is similar pseudogamous development irrespective of pollination treatment. We analysed fruit and seed set obtained in controlled experimental pollinations, as well as embryo number per seed, and the progress of ovule penetration, fertilisation and early endosperm development between self‐ and cross‐pollinated pistils. We found that the species is self‐fertile and that spontaneous selfing fruit set is also possible, although emasculated flowers never form fruits. Selfed pistils were as efficient as crossed ones for all parameters analysed, except for a delay in endosperm development observed in the former that may be an effect of the late‐acting self‐incompatibility. Therefore, the avoidance of selfed pistil abortion seems to be promoted by the presence of adventitious embryos and a normal endosperm. We conclude that A. acutifolium shows apomixis‐related pseudo‐self‐compatibility, as in other self‐fertile apomictic species of Bignoniaceae, which confer reproductive assurance and increases fruit‐set and persistence ability in fast‐changing tropical habitats.     

Mixed pollen load and late‐acting self‐incompatibility flexibility in Adenocalymma peregrinum (Miers) L.G. Lohmann (Bignonieae: Bignoniaceae)

• Mixed cross and self‐pollen load on the stigma (mixed pollination) of species with late‐acting self‐incompatibility system (LSI) can lead to self‐fertilized seed production. This “cryptic self‐fertility” may allow selfed seedling development in species otherwise largely self‐sterile. Our aims were to check if mixed pollinations would lead to fruit set in LSI Adenocalymma peregrinum, and test for evidence of early‐acting inbreeding depression in putative selfed seeds from mixed pollinations.
• Experimental pollinations were carried out in a natural population. Fruit and seed set from self‐, cross and mixed pollinations were analysed. Further germination tests were carried out for the seeds obtained from treatments.
• Our results confirm self‐incompatibility, and fruit set from cross‐pollinations was three‐fold that from mixed pollinations. This low fruit set in mixed pollinations is most likely due to a greater number of self‐ than cross‐fertilized ovules, which promotes LSI action and pistil abortion. Likewise, higher percentage of empty seeds in surviving fruits from mixed pollinations compared with cross‐pollinations is probably due to ovule discounting caused by self‐fertilization. Moreover, germinability of seeds with developed embryos was lower in fruits from mixed than from cross‐pollinations, and the non‐viable seeds from mixed pollinations showed one‐third of the mass of those from cross‐pollinations.
• The great number of empty seeds, lower germinability, lower mass of non‐viable seeds, and higher variation in seed mass distribution in mixed pollinations, strongly suggests early‐acing inbreeding depression in putative selfed seeds. In this sense, LSI and inbreeding depression acting together probably constrain self‐fertilized seedling establishment in A. peregrinum.

     

Effects of self-, chase and mixed self/cross-pollinations on pistil longevity and fruit set in Ceiba species (Bombacaceae) with late-acting self-incompatibility

BACKGROUND AND AIMS: Late-acting self-incompatibility (LSI), in which selfed flowers fail to form fruits despite apparently successful growth of the pollen tubes to the ovules, is a contentious and still poorly understood phenomenon. Some studies have indicated pollen tube-pistil interactions, and major gene control. Others favour an early acting inbreeding depression explanation. METHODS: Experimental pollinations, including selfs (in a subsample of which the style was cut before pollen tubes reached the ovary), chase self/cross-pollinations, crosses, and mixed self/cross-pollinations were used to study floral/pistil longevity and effect on fruit set and seed yield in two Ceiba species known to have LSI. RESULTS: Self-pollinations, including those with a cut style, had extended floral longevity compared with unpollinated flowers. Chase pollinations in which cross-pollen was applied up to 3 h after selfing set fruits, but with reduced seed set compared with crosses. Those with cross-pollen applied at 4 and 8 h after self-pollination all failed to set fruits. Flowers subjected to 1 : 1 and 2 : 1 self/cross-pollinations all produced fruits but again with a significantly lower seed set compared with crosses. CONCLUSIONS: Extended floral longevity initiated with self-pollen tubes growing in the style indicates some kind of pollen tube-pistil interaction. Fruit set only in chase pollinations up to 3 h implies that self-pollen tubes either grow more slowly in the style or penetrate ovules more slowly on arrival at the ovary compared with cross-tubes. This agrees with previous observations indicating that the incidence of penetrated ovules is initially lower in selfed compared with crossed pistils. However, the low seed yield from mixed pollinations indicates that self- and cross-pollen tubes arrive at the ovary and penetrate ovules more or less simultaneously. Possible explanations for these discordant results are discussed.     

Pollination biology and breeding system of Zeyheria montana (Bignoniaceae)

The reproductive biology of Zeyheria montana was studied through field observations of flower visitors and floral events, controlled manual pollinations, and observations of pollen tube growth and ovule penetration by fluorescence microscopy. Analysis of secretory areas of the nectar chamber was made by flower dissections and histology of serial sections. The flower lasted 6–8 days, but pollen exposure and stigma receptivity occurred only up to the end of the first and second days, respectively. Pollination was effected by several species of hummingbirds, especially Colibri serrirostris. The flowers present a rudimentary, non-functional disc, and secretion of nectar is performed by corolla-borne glandular trichomes. Only hand cross-pollinated and natural-pollinated flowers set fruits. Artificially self-pollinated and non-pollinated flowers dried off after anthesis without presenting any swelling of the ovary. Almost all the ovules in selfed and crossed pistils were penetrated 96 h after pollination. However, a delay in ovule penetration in self-pollinated pistils was verified, which indicates the occurrence of late-acting self-incompatibility.We are grateful to Fundo de Apoio ao Ensino e à Pesquisa (UNICAMP) for financial support, and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the fellowship granted to the first author (this work is part of a Ph.D. thesis presented to UNICAMP, Campinas, SP, Brazil).     

SEX EXPRESSION,BREEDING SYSTEM,AND POLLEN BIOLOGY OF RICINOCARPOS PINIFOLIUS: A CASE OF ANDRODIOECY?

A population of 54 Ricinocarpos pinifolius (Euphorbiaceae) plants contained male plants, which produced only staminate flowers, and hermaphrodites, which produced staminate and pistillate flowers. The fraction of pistillate flowers ranged continuously from 0 to 0.68. Insect pollination was effective and fruit set virtually complete except for losses to herbivores. Self pollen, outcross pollen from male plants, and outcross pollen from hermaphrodites were all equivalent in viability, germination, tube growth, ovule penetration, and fruit setting ability. Inbreeding depression was manifested as late abortion of some selfed seeds. Geitonogamous selfing is largely prevented by temporal separation of male and female functions within plants. This temporal separation, combined with population-wide synchrony of flowering, may create unusual conditions allowing male plants at low frequency to match hermaphrodites in reproductive success.     

The role of pollination level on the reproduction of females and hermaphrodites in the gynodioecious plant Gypsophila repens (Caryophyllaceae)

In gynodioecious plant species, females are expected to have more resources available for maturing seeds because pistillate flowers are smaller, do not produce pollen, and are thus less costly that perfect flowers. The potential female advantage arising from more abundant resources is, however, likely to vary depending on whether seed production is limited by resource or pollen availability. Here we experimentally investigated the influence of pollen and resource limitation on female advantage in a gynodioecious species using two levels of pollination. Total seed production of females was always greater than that of hermaphrodites: females produced more flowers and more fruits that contained similar numbers of seeds of similar mass. Under low pollination, female and hermaphrodite plants allocated resources to increased flower production rather than to increased seed size or quality. We did not detect any influence of pollen or resource limitation on female advantage, which remained similar under low (= abundant resources) and full pollination. Outcrossed fruits performed better than selfed fruits when the same plant received both selfed and outcrossed pollen on different flowers. These differences were not greater under high pollination, possibly because resources available for each fruit did not differ between our pollen intensity treatments.     

Pollen dispersion, pollen viability and pistil receptivity in Leymus chinensis

BACKGROUND AND AIMS: Leymus chinensis is an economically and ecologically important grass that is widely distributed across eastern areas of the Eurasian steppe. A major problem facing its propagation by man is its low sexual reproductivity. The causes of low fecundity are uncertain, largely because many aspects of the reproductive biology of this species remained unknown or incomplete. This study aims to address some of these issues. METHODS: Pollen dispersion, pollen viability, pollen longevity and pistil receptivity were studied in a representative, natural population of L. chinensis growing in Inner Mongolia. KEY RESULTS: Flowering of L. chinensis occurred at the end of June and lasted for 5 d. Pollination peaked between 1600 h and 1700 h, and about 56.1 % of the total pollen grains were released at this time. Pollen density was highest towards the middle of flowering spikes and lowest at the bottom over the 5 d measurement period. Pollen viability (62.4 %) assessed using TTC was more accurate than using IKI (85.6 %); 50 % of pollen arriving on stigmas germinated. Pollen remained viable for only 3 h and the pollen : ovule ratio was 79 333 : 1. Pistil receptivity lasted for only 3 h and, overall, 86.7 % of pistils were pollinated. Within the spike, the relative fecundity of different positions was middle > lower > upper throughout the period of pollination; daily variation of fecundity was similar to that of the pollen flow. The spikes that opened on the day of highest pollen density exhibited the highest fecundity (36.0 %). No seeds were produced by self-pollination. CONCLUSIONS: The data suggest that low pollen viability, short pollen longevity and short pistil receptivity all appear to contribute to the low seed production typical of this important forage crop.     

Effect of pollination on floral longevity and costs of delaying fertilization in the out-crossing Polygala vayredae Costa (Polygalaceae)

Background and Aims

The effect of pollination on flower life span has been widely studied, but so far little attention has been paid to the reproductive consequences of delayed pollination in plants with long floral life spans. In the present study, Polygala vayredae was used to answer the following questions. (1) How does male and female success affect the floral longevity of individual flowers? (2) How does delaying fertilization affect the female fitness of this species?

Methods

Floral longevity was studied after experimental pollinations involving male and/or female accomplishment, bagging and open pollination. The reproductive costs of a delay in the moment of fertilization were evaluated through fruit set, seed–ovule ratio and seed weight, after pollination of flowers that had been bagged for 2–18 d.

Key Results

Senescence of the flowers of P. vayredae was activated by pollen reception on the stigmatic papillae, while pollen removal had no effect on floral longevity. Nonetheless, a minimum longevity of 8 d was detected, even after successful pollination and pollen dissemination. This period may be involved with the enhancement of male accrual rates, as the female accomplishment is generally achieved after the first visit. Floral life span of open-pollinated flowers was variable and negatively correlated with pollinator visitation rates. Delayed pollination had a major impact on the reproductive success of the plant, with fruit set, seed–ovule ratio and seed weight being significantly diminished with the increase of flower age at the moment of fertilization.

Conclusions

A strong relationship between pollination and floral longevity was observed. Flowers revealed the ability to extend or reduce their longevity, within some limits, in response to the abundance of efficient pollinators (i.e. reproductive fulfilment rates). Furthermore, with scarce or unpredictable pollinators, a long floral life span could maintain the opportunity for fertilization but would also have reproductive costs on production of offspring. Reduced female fitness late in the flower''s life could shift the cost–benefit balance towards a shorter life span, partially counteracting the selection for longer floral life span potentially mediated by scarce pollination services.Key words: Delayed pollination, endemic species, flower longevity, life span, pollen limitation, pollination, pollinator scarcity, Polygala vayredae, Polygalaceae, reproductive consequences, secondary pollen presentation     

毛翠雀花花序内的性分配和繁殖成功

两性花植物花序内不同位置的性分配和繁殖成功一般存在差异,通常认为资源竞争、结构效应和交配环境是形成这种差异的主要原因。为了研究雄性和雌性繁殖资源在花序内不同位置间的最优分配问题,该文以青藏高原高寒草甸典型高山植物毛翠雀花为材料,通过比较花序内不同位置的花部特征和种子性状,对其花序内的性分配模式和雌性繁殖成功进行研究,并通过观察传粉者运动特点以及人工去花和补授花粉实验,探讨花序内资源竞争和交配环境对繁殖资源分配的影响。结果表明:(1)不同位置间的雄蕊数、雄蕊鲜重/雌蕊鲜重、花粉数及花粉胚珠比从花序基部到上部显著增加,而雌蕊鲜重和胚珠数逐渐减少,表现出上部花偏雄的性分配;上部花的结籽率显著低于基部花和中部花,不同位置间的发育种子数/果实和发育种子重/果实随着花位置的升高而显著降低,说明基部花具有更佳的雌性繁殖成效。(2)去花处理后,剩余果实的单个种子重/果实显著增加,但发育种子数/果实没有显著增加;而给上部花人工补授异花花粉后,位置间结籽率的差异消失,说明传粉限制而非资源竞争导致了花序内位置依赖的种子生产模式。(3)毛翠雀花雄性先熟的开花特征,以及传粉者苏氏熊蜂从花序基部到上部的定向访花行为,导致了花序内交配环境的变化。综上结果表明,毛翠雀花花序内的性分配和繁殖成功差异是对交配环境适应的结果,对其在高山环境中实现雌雄适合度最优化具有重要意义。     

Pollination biology of Indotristicha ramosissima (Podostemaceae: Tristichoideae)

Floral morphology, phenology and mode of pollination have been studied in Indotristicha ramosissima (Wt.) van Royen. Although the plants are submerged, self-pollination (autogamy) occurs above water. This is aided by considerable elongation of the pedicel (20 mm) prior to pollination. The filaments of the stamens also elongate rapidly (∼6.5 mm/h) before and after pollination. The flowers are typically trimerous. Each anther contains 1743 ± 187 pollen grains. These are spherical, multiporate, 3-celled and ∼97% fertile at the time of shedding. Germination of pollen on the stigma and the growth of pollen tubes have been traced in both naturally and manually (self- as well as cross-) pollinated pistils. The pollen:ovule ratio is ∼72:1 and the ovule: seed ratio is ∼2:1. Mature fruits are 8 or 9 ribbed and open by 2 or 3 longitudinal slits that release ∼32 seeds.     

The Reproductive Biology of Two Species of Diplusodon Pohl (Lythraceae) from Serra do Cipó, Southeastern Brazil

Abstract: The reproductive biology of two shrub species of Diplusodon (Lythraceae), D. hirsutus and D. orbicularis, was studied. Their distribution is restricted, mainly associated with "campos rupestres", a montane biome in SE Brazil. Both species proved to be self-compatible but because of herkogamy they are greatly dependent on visitors to effect pollination. The main pollinators are medium-sized bees. In experiments where pollinators were excluded or discouraged the percentage of abscised fruits was total or extremely high; most of these fruits dropped within the first two weeks after pollination in D. orbicularis and three weeks in D. hirsutus. The percentage of surviving fruits from control or manual pollination was higher in D. orbicularis ( ca. 70 %) than in D. hirsutus ( ca. 50 %). Seed set was very variable, with slightly lower means in D. hirsutus. Within each species the mean seed set was similar in self-, cross-pollinated fruits, and controls. In both species, the similarity between control and manual pollination fruit survival curves suggests that factors other than pollen limitation are the cause of abortion in the study area. The high rate of abscission, which was also observed in unmanipulated fruits, was attributed to resource limitation. In D. hirsutus this was caused by drought during seed development. In D. orbicularis it was enhanced by nutrient drain by shoot-galling flies. The lack of selective abortion of either selfed fruits or fruits with a small number of seeds may be a useful mechanism to overcome this detrimental effect which is felt later during fruit development.     

Reproductive systems and low outbreeding barriers between Jacaranda cuspidifolia and J. mimosifolia (Jacarandeae,Bignoniaceae)

The genus Jacaranda shows notable karyotype stability and a prevailing self‐sterile breeding system with evidence of late‐acting self‐incompatibility in several species. However, some studies have indicated self‐compatibility in J. mimosifolia, a species cultivated worldwide in tropical and subtropical areas. Jacaranda cuspidifolia is a closely related species with natural distribution broadly overlapping with that of J. mimosifolia, and manual heterospecific pollination studies have indicated that these species are interfertile, but there is no report on the breeding system of the former. In this study, we used hand‐pollination experiments, pistil longevity, epi‐fluorescence and histological analysis of post‐pollination events to determine the breeding system of J. cuspidifolia. We also employed intra and interspecific crosses and seed germination tests to reevaluate the breeding system of J. mimosifolia and the inter‐fertility between the two species. Some fruits were initiated from self‐pollinated pistils in J. mimosifolia, but none of them reached maturity. On the other hand, complete absence of fruit development by self‐pollination was verified in J. cuspidifolia, while in situ pollen tube growth and histological analysis of post‐pollination events in selfed pistils revealed the characteristic ovule penetration, fertilization and endosperm initiation also observed in other bignoniaceous species with late‐acting self‐incompatibility. Low outbreeding barriers seem to operate between these species because reciprocal interspecific crosses and hybrid seed germination tests indicated they are bilaterally interfertile. However, fruit/seed production and seed germinability were significantly lower when pistils of J. cuspidifolia were pollinated with pollen of J. mimosifolia, compared with crosses in the opposite direction, which indicates a partial unilateral incompatibility. This result is discussed in the context of the possible occurrence of self‐compatibility in J. mimosifolia. The low level of incongruity operating between the two species also points to their recent evolutionary divergence.     

Fruit abortion in the Chihuahuan-Desert endemic cactus <Emphasis Type="Italic">Opuntia microdasys</Emphasis>

Resource and pollen limitation, as well as pollen/ovule incompatibility, have been proposed as causes to explain fruit abortion. To assess whether abortion in Opuntia microdasys was due to resource and/or pollen limitation and could therefore be reversed fruit set and seed set were studied using controlled pollination experiments on 60 plants that had been randomly assigned a combination of watering and fertilization treatments. On the other hand, to test whether fruit abortion was irreversible, due to pollen/ovule incompatibility, we examined the reproductive biology of the species. This included observations on floral phenology, nectar production, flower visitors, numbers of pollen grains and ovules, and self-pollination experiments. Results showed that O. microdasys is a fully self-incompatible species and its floral biology and the activity of the main pollinator allow constant deposition of incompatible pollen onto stigmas, which may contribute to fruit abortion. Reproductive success was limited by nutrients and pollen, but the fruit set increased only by 58%, compared to 47% of the control, after the experimental addition of pollen, nutrients and water. The magnitude of pollen and resource limitation suggests that similar levels of abortion will be present in good as well as in bad years. Selfing as well as incompatibility between ramets from the same clone and between closely related plants seem plausible candidates to explain the large proportion of fruit abortion, and experimental cross pollination between genotypes identified through molecular markers are necessary to fully understand the considerable abortion rate that remains unexplained after pollen and resource addition. Interestingly, the possible reason why the abortion of energetically expensive fruits has not been eliminated by natural selection is that the aborted fruits are propagules able to root and produce new plants with the same genotype of the mother. Abortion would have a dramatic effect on cross-fertilized genotypes because they result in zero fitness, but it would have a positive effect on the fitness of the maternal genotype because a clonal offspring is produced. Evidently, the exact fitness consequences to the maternal plant will depend on the differences in survival and reproduction of these different offspring types.     

Flowering and pollination patterns of Magnolia denudata with emphasis on anatomical changes in ovule and seed development

Magnolia denudata is an excellent ornamental and ecologically important tree that exhibits low fecundity because of seed abortion. To better understand the cause of this low sexual reproduction, pistil receptivity, and pollen quality were investigated using culture medium and histochemical staining, with emphasis on pollen viability at different flowering stages. Cross-pollination, geitonogamy, and self-pollination were undertaken on flowers of sample trees. We found that flowers produce a large number of pollen grains available for effective pollination. Pollen viability varied at different stages, but was highest during stage 3, in which the stamens detach from the axis, the anthers dehisce, and the gynoecium stigma starts to fade. The duration of pistil receptivity was approximately 5 h. These results indicate that poor fertilisation may occur if the optimum period for pollination is missed or the stigma receives poor-quality pollen grains from stages other than stage 3. Although dichogamy avoids selfing, it has led to considerable geitonogamy. Our anatomical analysis of ovule and seed development further revealed that fertilisation occurred in samples with geitonogamy, but that the embryo degenerated in the torpedo stage, demonstrating that aborted seeds were produced by fertilisation, rather than by pseudogamy. Our results provide new insights into the mechanism of reduced seed set under natural conditions.     

The effect of timing of pollination on the mating system and fitness ofKalmia latifolia (Ericaceae)

Plant mating systems are known to vary within species and some immediate ecological factors have been found to be associated with the geographic distribution of selfing. The environmental condition of the maternal plant may influence the production of selfed seed relative to outcrossed seed. This study investigated the effect of late pollination on the mating system of Kalmia latifolia, a long-lived perennial shrub. A 2 × 2 experimental design was used to determine whether reproductive success declines over the course of the flowering season and whether there was an interaction between pollination time (early vs. late in the season) and pollen type (self-fertilized vs. outcrossed). An interaction of this sort would indicate context-dependent fitness of selfed seeds compared to outcrossed seeds and, thus, show an ecological influence over a plant's mating system. Relative fitness was assessed in terms of female reproductive success. Timing of pollination did not affect abortion of outcrossed seeds; however, delay in pollination increased abortion of selfed seeds by 34.7%. Thus, it appears that plants selectively aborted selfed seeds rather than outcrossed seeds and this selection was more intense at the end of the season. An ecological factor such as time of pollination may affect the mating system of K. latifolia.     

The breeding system of Fumana ericifolia: first evidence of autogamy in woody Cistaceae

Fumana ericifolia belongs to the family Cistaceae, in which all perennial species previously studied have been reported to be self-incompatible and xenogamous. Here we show that F. ericifolia is self-compatible and autogamous. Its flowers last only four to eight hours and produce a small amount of pollen and ovules. Self-pollination depends on changes in the relative position of the stigma and the anthers, triggered by the abscission of the petals; this in turn causes closing of the sepals, which push the anthers onto the stigma. Pollen remains highly viable and germinable, and the stigma keeps its receptivity several hours after the loss of the petals. Hand pollination treatments revealed that fruits are produced both in selfed and crossed flowers. The germination of pollen grains on the stigma, the rate of pollen tube growth along the style, and the penetration into the ovules were similar in self-and cross-pollinations; also, there were no significant differences in fruit set, seed set and weight of seeds. Thus, we report the first evidence of autogamy in a woody Cistaceae and suggest that selfing may ensure reproductive success when pollinators are limited.     

Do s genes or deleterious recessives control late-acting self-incompatibility in Handroanthus heptaphyllus (Bignoniaceae)? A diallel study with four full-sib progeny arrays

Background and AimsGenetically controlled self-incompatibility (SI) mechanisms constrain selfing and thus have contributed to the evolutionary diversity of flowering plants. In homomorphic gametophytic SI (GSI) and homomorphic sporophytic SI (SSI), genetic control is usually by the single multi-allelic locus S. Both GSI and SSI prevent self pollen tubes reaching the ovary and so are pre-zygotic in action. In contrast, in taxa with late-acting self-incompatibility (LSI), rejection is often post-zygotic, since self pollen tubes grow to the ovary, where fertilization may occur prior to floral abscission. Alternatively, lack of self fruit set could be due to early-acting inbreeding depression (EID). The aim of our study was to investigate mechanisms underlying the lack of selfed fruit set in Handroanthus heptaphyllus in order to assess the likelihood of LSI versus EID.MethodsWe employed four full-sib diallels to study the genetic control of LSI in H. heptaphyllus using a precociously flowering variant. We also used fluorescence microscopy to study the incidence of ovule penetration by pollen tubes in pistils that abscised following pollination or initiated fruits.Key ResultsAll diallels showed reciprocally cross-incompatible full sibs (RCIs), reciprocally cross-compatible full sibs (RCCs) and non-reciprocally compatible full sibs (NRCs) in almost equal proportions. There was no significant difference between the incidences of ovule penetrations in abscised pistils following self- and cross-incompatible pollinations, but those in successful cross-pollinations were around 2-fold greater.ConclusionsA genetic model postulating a single S locus with four S alleles, one of which, in the maternal parent, is dominant to the other three, will produce RCI, RCC and NRC full sib situations each at 33 %, consistent with our diallel results. We favour this simple genetic control over an EID explanation since none of our pollinations, successful or unsuccessful, resulted in partial embryo development, as would be expected under a whole-genome EID effect.     

Identifying population thresholds for flowering plant reproductive success: the marsh gentian (<Emphasis Type="Italic">Gentiana pneumonanthe</Emphasis>) as a flagship species of humid meadows and heathland

The threshold below which population declines impact the effectiveness of plant reproduction is essential for the identification of populations that can no longer spontaneously recover following habitat management or restoration, below the minimum viable population (MVP) size. We hypothesized that risk of reproductive limitation can be evaluated from combined analysis of pollen activity, ovule fertilization and germination in the context of population demographics and fragmentation. The marsh gentian (Gentiana pneumonanthe), a rare emblematic species of European heathland and fen, was investigated at the southern limit of its range in eighteen populations encompassing one to several hundred thousand individuals, spanning small fragments to extensive well-preserved areas. An index of habitat fragmentation was determined from GIS; field surveys determined the ratio of juvenile to reproductive age states; fluorescence microscopy of pistils determined, for each population, the proportion of flowers exhibiting active pollen tube growth. Analysis of seed lots determined the ovule fertilization rate and seed germination capacity. Some of the small populations occupying restricted habitat fragments showed high rates of pollination (100%) and ‘normal’ age state demographics. However, reproductive characters all exhibited exponential rise to maximum relationships with population size, indicating clear tipping points (for pollination, at a threshold of 7 reproductive adults, and for ovule fertilization rate and germination at 42 reproductive adults). Thus although small populations may set seed, exhibit a ‘normal’ age state structure, and may appear viable, reproductive effectiveness declines when population size falls below 42 generative individuals and < 7 is an indicator of strong limitation. Although many remnant populations of G. pneumonanthe are in the order of 50–150 individuals these should be not be considered as MVPs; they are on the brink of calamity.