Restricted seed contribution and clonal dominance in a free-floating aquatic plant <Emphasis Type="Italic">Utricularia australis</Emphasis> R. Br. in southwestern Japan

Utricularia australis R. Br. is an aquatic angiosperm species common in natural and irrigation ponds in temperate regions. This species reproduces both sexually and vegetatively, but in southwestern Japan the occurrence of male-sterile populations, in which plants produce no pollen and propagate only vegetatively, has been recorded. We studied the reproductive contribution of seeds in normal pollen-producing populations using isozyme analyses, a pollination experiment under culture and field observations. Although seedlings obtained from controlled mating indicated segregation of isozyme, polymorphism of the isozyme genotype was detected mainly among populations, but rarely within each pond population. This suggested clonal dominance and rarity of seed or seedling survival in natural populations. In the pollination experiment, the mean seed set ratio in cross-pollination between plants of the same isozyme genotype (7.6%) did not differ significantly from self-pollination (7.6%), but was lower than cross-pollination between plants of different genotypes (45.7%). The low ratio in crossing between the same genotype plants was ascribed to the clonality of the parents. In general, these results corresponded with the low ratios in seed setting observed in natural populations (7.9–13.7%). All the male-sterile populations we surveyed showed the same genotype, thus male sterility in the study area was considered to have the same origin.     

Variation in breeding system among populations of the common woodland herbAnemone nemorosa (Ranunculaceae)

Recent studies of germination in natural habitats, of genetic variation within populations and of the relative proportion of vegetative and sexual reproduction in the clonal plant speciesAnemone nemorosa suggest that sexual recruitment by seeds from outcrossed flowers is important for the maintenance of this species' populations. Because published reports on its breeding system are controversial, pollination experiments were performed in five natural populations ofA. nemorosa. Differences in ovule number per flower were recorded among populations, but they were not related to obvious habitat differences. Seed/ovule-ratios were significantly higher after open pollination and artificial crossing than after either artificial or spontaneous selfing. Populations had no effect on seed/ovuleratios. Different breeding indices indicated thatA. nemorosa is mainly self-incompatible. Nevertheless, some seed set also occurred after selfing, and both artificial and spontaneous selfing exhibited higher variation in seed/ovule-ratios than open pollination and artificial crossing. Continuous variation in seed/ovule-ratios after selfing suggested that the expression and effectiveness of the self-incompatibility system ofA. nemorosa is influenced by both genetic variation and phenotypic plasticity.     

Fertility differences among floral morphs following selfing in tristylous Eichhornia paniculata (Pontederiaceae): inbreeding depression or partial incompatibility?

Reduction in seed set following self- vs. cross-pollination in flowering plants can result from abortion of selfed offspring owing to inbreeding depression and/or partial self-incompatibility. Previous studies on tristylous Eichhornia paniculata (Pontederiaceae) indicate that reduced seed set following self-pollination generally occurs in the short- (S), but not the long-(L) or mid-styled (M) morphs. To determine whether this pattern results from morph-specific differences in inbreeding depression owing to the sheltering of deleterious alleles at the S locus and/or partial self-incompatibility, we conducted controlled hand-pollinations of the floral morphs and measured seed set and levels of seed abortion. There were no significant differences in fertilization success and seed set following self-, illegitimate, and legitimate pollinations in the L and M morphs. In contrast, in the S morph self-, intramorph and intermorph illegitimate pollinations resulted in significant reduction in seed set in comparison with legitimate pollination. This indicates that the reduced seed set observed in self-pollination is the result of partial incompatibility rather than inbreeding depression. Significantly reduced fertilization success and low levels of ovule abortion in illegitimate pollinations of S plants also supported this conclusion. Reduced fertility in the S morph may have implications for the observed loss of this morph from natural populations and the evolutionary breakdown of tristyly.     

Pollination of the heterostylous Galápagos native, <Emphasis Type="Italic">Cordia lutea</Emphasis> (Boraginaceae)

The hypothesis of this study was that in the Galápagos Islands, fruit and seed set via nocturnal pollination would exceed that of diurnal pollination due to greater insect activity at night typical of hot, arid regions. Cordia lutea, a heterostylous member of the Galápagos flora, was submitted to pollination experiments, visitor observations, nectar sampling, pollen transfer studies, pollen-ovule ratio studies, and pollen measurements. Flowers set fruit and seed via open pollination, autonomous autogamy, facilitated autogamy, facilitated cross-pollination, diurnal pollination, and nocturnal pollination. There was a significant difference in fruit set between flowers experiencing legitimate cross-pollinations (pin × thrum) and those experiencing all other pollination treatments except facilitated autogamy. There was no significant difference in seed set among any of the treatments, but there was a trend toward greater seed set for flowers experiencing open-pollination, legitimate cross-pollination, and nocturnal pollination. There was no significant difference in fruit set or seed set between flowers experiencing diurnal pollination and nocturnal pollination, although there was a trend toward greater seed set resulting from nocturnal pollination. Carpenter bees were the most effective diurnal pollinators, whereas moths were the most effective nocturnal pollinators. Of the two, moths are more efficient at transporting pollen from plant to plant. Results indicate that an overall low productivity of this species is due to pollen limitation exacerbated by nectar robbing. Cordia lutea exhibits a mixed mating system, producing a relatively low level of fruits through a combination of self- and cross-pollination, facilitated by the relatively few insects that are available.     

Breeding system and pollen limitation in the masting tree Sorbus aucuparia L. (Rosaceae) in the NW Iberian Peninsula

Mast seeding or masting is the supra-annual periodic production of a large number of seeds by long-lived plants. It has been suggested that this may be a strategy to increase pollination efficiency. Sorbus aucuparia is a masting tree typically showing rather low fruit set, though with some variation among years and populations, together with marked among-year variation in flower and fruit production. Here we report a study of the reproductive biology and insect-visitor spectrum of S. aucuparia in the NW Iberian Peninsula. Results obtained over a 4-year period indicate marked self-incompatibility, so that fruit set is strongly dependent on pollinator service. Nevertheless, fruit and seed set were not limited by pollen supply in any of the years of study, since fruit and seed set after manual cross-pollination were no higher than after natural pollination. Inflorescences were visited by diverse insect species. There was no significant correlation between fruit set and insect visit frequency. Taken together, these findings indicate that the rather low fruit and seed sets observed in this species, and the spatiotemporal variation in these parameters, must be attributed to other factors, such as abiotic resource availability. We conclude that masting in S. aucuparia is probably not a strategy for increasing pollination efficiency.     

How selfing and intra- and interspecific crossing influence seed set, morphology and ploidy level in Euphrasia: An experimental study of species occurring in the Alps of Switzerland

Annual alpine species rely on selfing rather than on cross-pollination for successful reproduction. However, insect visits may occasionally cause cross-pollination not only within but also between closely related species. The aim of this study was to investigate four species of Euphrasia for their efficiency in spontaneous selfing and their success in intra- and interspecific crossing. We used the seed sets that followed spontaneous selfing and artificial cross- and selfpollination to measure the breeding success. We compared the morphological characters of species and hybrids and determined their ploidy level using flow cytometry. We verified the hybridogenous origin of plants resulting from interspecific crosses using RAPD banding patterns. While spontaneous seed set was high in the two small-flowered species, seed set in the large-flowered species was small and affected by external circumstances. We obtained F1 and F2 hybrids from interspecific crosses of two diploid species and detected polyploid individuals in both generations.     

Quantitatively determined self-incompatibility

Summary It has been reported that incomplete self-incompatibility could be determined in Borago officinalis by many genes. Simple ten-gene models for such enforced cross-fertilization have been developed and their properties examined by computer simulation. Mutation rates necessary to maintain a given level of variability in small populations are high, as already determined theoretically for oligogenic self-incompatibility systems. However, the extent of ineffective pollination is very much greater in the ten-gene system. This finding may be verifiable in borage if it is indeed self-incompatible.     

授粉方式对铁皮石斛种质座果及种子萌发的影响

为进行铁皮石斛(Dendrobium officinale)的良种选育和种苗生产,对46个铁皮石斛种质进行人工授粉试验,研究了不同授粉方式的授粉成功率、座果率和种子的萌发能力。结果表明,4种授粉方式的授粉成功率明显不同,不同种质间的授粉成功率可达100%,且座果率普遍较高。只有31.3%的种质可以成功自花授粉,且座果率相差较大。同株异花授粉和种质内异株授粉的成功率和座果率均介于上述二者之间。授粉后所得种子的萌发率和萌发速度在4种授粉方式间也呈现与授粉成功率和座果率一致的趋势。这表明在铁皮石斛种质中存在自交不亲和现象,因此以不同产地来源的铁皮石斛种质为亲本进行人工授粉,可大大提高授粉的成功率和座果率,以及后代种子的萌发能力。     

Ovule pre-emption and pollen limitation in a self-fertile perennial herb (Blandfordia grandiflora,Liliaceae)

The extent, frequency and causes of pollenlimited seed production were examined in partially selffertile populations of Blandfordia grandiflora for 2 years. Percentage seed set of open-pollinated plants (50–57%) did not differ within or between years, and was about 19% less than experimentally cross-pollinated plants (70–75%). Floral visits by honeybees did not differ through the flowering season and the number of pollen grains deposited on stigmas within 12 h of flowers opening exceeded the number of ovules per flower, indicating that the quality rather than the quantity of pollination limited seed set. Pollen limitation was caused by concurrent self- and cross-pollination and the subsequent abortion of some selfed ovules due to inbreeding depression. Natural seed set (55%) was intermediate between selfed (43%) and crossed (75%) flowers and was not increased when flowers that had been available to pollinators for 24 h were hand cross-pollinated, suggesting that ovules were already fertilized. Similarly, experimental pollination with both cross and self pollen within 24 h of flowers opening did not increase seed set relative to natural seed set, indicating that both cross- and self-fertilizations had occurred. In contrast, when selfing followed crossing by 48 h, or vice versa, seed set did not differ from crossed-only or selfed-only flowers, respectively, indicating that ovules were pre-empted by the first pollination. Collectively, these results indicate that under natural conditions self pollen pre-empts ovules, rendering them unavailable for cross-fertilization. This selfing reduces fecundity by 50%, as estimated from the natural production of cross seeds when selfing was prevented. Consequently, selection should favour floral traits, such as increased stigma-anther separation or protandry, that reduce interference between male and female functions that leads to selfing.     

Effects of pollination and pollen source on the seed set ofPedicularis palustris

Habitat alteration can deteriorate plant-pollinator interactions and thereby increase the risk of population extinction. As part of a larger study on the effects of changes in land use on fen grassland vegetation, factors influencing the seed set of a short-lived, endangered wetland plant,Pedicularis palustris, were studied. We conducted field pollination experiments in one large and one small population. To investigate the effect of pollen source on seed set, individual flowers of caged plants were left unpollinated or were pollinated with pollen from the same flower, the same population or another population. To study pollen limitation and flower display, whole plants were subjected to pollinator exclosure, hand pollination or natural pollination. Self-compatibility was high, but differed between populations (61% and 97% of seed set after cross-pollination within populations). Cross-pollination between populations did not significantly alter seed number per capsule. Pollinator exclosure resulted in a very low seed set (<15% of natural seed set), despite high self-compatibility. The most likely explanations for high self-compatibility in combination with low autofertility are geitonogamy as reproductive assurance, selective neutrality of self-compatibility and phylogenetic constraints. Because of low autofertility, the seed set inP. palustris depends on pollinators. In the study populations, natural pollination was clearly sufficient for maximum seed production per plant, but seed set per capsule was significantly pollen-limited in the smaller population. Plants in this population also had a higher maximum percentage of simultaneously open flowers than those of the large population (31% vs. 13%), while flower longevity was generally extended without pollination. It is concluded thatP. palustris may influence pollinator behaviour and therefore the risk of pollen limitation by flower display.P. palustris showed a flexible reaction to differing pollination regimes without losses in overall seed set in the study populations.     

The interplay of pollination,costs of reproduction and plant size in maternal fertility limitation in perennial <Emphasis Type="Italic">Paeonia officinalis</Emphasis>

Although several factors can limit female fertility in perennial plants, rarely have they been jointly studied in a single species over several years. In this study we experimentally manipulate seed production and simultaneously analyse the potential contribution of pollen limitation, costs of reproduction and plant size to variation in seed output over a 3-year period in the perennial herb Paeonia officinalis, in southern France. Since this rare species is threatened by forest closure in many sites we also examine the causes of female fertility variation in relation to habitat closure (open habitat vs. woodland). P. officinalis has a partial self-incompatibility system and only very low ability for autonomous self pollination in the absence of pollinators. However, supplementary pollination of individual plants in three consecutive years did not significantly increase seed production above natural levels. Forest closure was associated with a decline in ovule and seed production, which again was not due to pollen limitation since supplementary pollination had no significant effect on seed set in the woodland habitat. Comparison of the maternal fertility of plants which were previously excluded from reproduction with those which were hand pollinated to maximise seed set in two previous years produced no evidence that seed production in year three is limited by costs associated with prior reproduction. Likewise, flowering probability was not related to prior seed production but was however positively related to plant size. The absence of any influence of pollen limitation or prior reproduction on seed production suggests that sub-maximal seed production in long-lived perennial herbs may be part of a size-dependent strategy that maximises life-time seed production and fitness without compromising survival.     

Differential ovule development following self- and cross-pollination: the basis of self-sterility in Narcissus triandrus (Amaryllidaceae)

Self-pollination results in significantly lower seed set than cross-pollination in tristylous Narcissus triandrus. We investigated structural and functional aspects of pollen–pistil interactions and ovule–seed development following cross- and self-pollination to assess the timing and mechanism of self-sterility. Ovule development within an ovary was asynchronous at anthesis. There were no significant differences in pollen tube behavior following cross- vs. self-pollination during the first 6 d of growth, regardless of style morph type. Double fertilization was significantly higher following cross- vs. self-pollination. Aborted embryo development was not detected following either pollination type up to seed maturity. Prior to pollen tube entry, a significantly greater number of ovules ceased to develop following self- vs. cross-pollination. These results indicate that self-sterility in N. triandrus operates prezygotically but does not involve differential pollen tube growth typical of many self-incompatibility (SI) systems. Instead, low seed set following self-pollination is caused by a reduction in ovule availability resulting from embryo sac degeneration. We hypothesize that this is due to the absence of a required stimulus for normal ovule development. If this is correct, current concepts of SI may need to be broadened to include a wider range of pollen–pistil interactions.     

The cross-fertilization mechanism and reproductive interference of self-pollen of Medicago varia ‘Xinmu No. 1’

Some control tests and a technique employing the fluorescent properties of pollen and pollen tube stained with aniline blue dye were utilized to study the stigma receptivity, the optimum pollination period, the self-pollen clogging effect, pollen germination and the pollen tube growth state in alfalfa. The results can be summarized as follows: (1) The stigma receptivity and flower longevity barely overlap. On the first day after pollination, the pollination efficiency was the highest, with a pod-seting rate per raceme of 65.17%±2.01% (P<0.01). The period of the highest pollination efficiency was the same as the peak of stigma receptivity. When pollination was on the fourth day after flowering, the pod-setting percentage per raceme was still 34.25%±6.73%. (2) Self-pollination led to a lower pollen germination frequency and a lower pollen tube growth rate than cross-pollination. When artificial cross-pollination was applied after self-pollen grains on the stigma was re-moved, the pod-setting percentage per raceme was 72.31%±6.24%, and the number of seed per pod was 3.46±0.25, In contrast, these two values were 51.76%±5.37% (P<0.01) and 2.11%±0.18 respectively (P<0.01) when the self-pollen grains were not removbed in the artificial cross-pollination experiements. Hence, the clog-ging effect of self-pollen to stigma was significant. (3) In the breeding system of alfalfa, there are two mecha-nisms that help the plants to avoid self-fertilization: dichogamy and self-incompatibility. However, due to the structure of flowers, they were not effective enough to improve cross-fertilization rate, even if the stamen matured earlier than the stigma. The typical self-incompatibility system guaranteed the lower self-fertilization rate, but cannot avoid the reproductive interference of self-pollen.     

Developmental and environmental factors affecting level of self-incompatibility response in <Emphasis Type="Italic">Brassica rapa</Emphasis> L.

We performed artificial self-pollination throughout the period of sexual reproduction in six inbred lines of Brassica rapa, a plant with sporophytic self-incompatibility (SI). The level of SI changed between each pollination date in all lines, suggesting the effects of both internal and external factors. To further investigate the potential factors affecting the changes in the level of SI, multiple regression was performed, with plant line, seeding date, and temperature and humidity on the day of pollination (external factors) and plant age (internal factor) as explanatory variables. The factors affecting the change in the level of SI differed between the lines, and temperature and plant age had especially large effects. The level of SI was reduced by maximum temperatures >24°C on the pollination day, but this effect was no longer significant at maximum temperatures >28°C. High temperatures before flowering also influenced the reduction of SI. The level of SI was particularly reduced at plant age 0.75 (i.e., the last quarter of the flowering period), and a significant positive interaction between average temperature and plant age was found. This is the first study to quantify the change in the level of SI in plants across the entire period of sexual reproduction and to analyze the relationship between the change in rate of seed set and various external and internal factors.     

Self-pollen interference is absent in wild radish (Raphanus raphanistrum, Brassicaceae), a species with sporophytic self-incompatibility

Explaining the diversity of mating systems and floral forms in flowering plants is a long-standing concern of evolutionary biologists. One topic of interest is the conditions under which self-pollination can interfere with seed set for flowering plants with a self-incompatibility system. We investigated the effect of self-pollen interference for wild radish, Raphanus raphanistrum, which has sporophytic self-incompatibility. We performed pollinations and determined seed set for plants grown in the greenhouse, using pollen mixtures representing either self- with outcross-pollen or outcross-pollen alone. Stigmas were collected for a subset of pollinated flowers to determine the number of pollen grains applied. Average seed set for the self/cross (5.13 seeds/pollination) and cross treatments (5.09 seeds/pollination) did not differ significantly. Stigmatic pollen loads averaged around 700 grains, an amount close to observed natural pollen loads on R. raphanistrum. We concluded that for R. raphanistrum in natural populations, self-pollen is unlikely to interfere with outcross-pollen success. This study is the first to investigate effects of self-pollen interference on seed set for a homomorphic species with sporophytic self-incompatibility where rejection occurs at the stigmatic surface.     

恶性入侵植物豚草的繁育系统特性

豚草(Ambrosia artemisiifolia L.)是原产于北美的一年生恶性入侵植物,目前已广泛分布在我国东北、华北、华中和华东等地,威胁农业、生态和民众健康。该种雌、雄头状花序同株,以种子繁殖,因而其有性繁殖特性对其扩散和爆发具有重要影响。运用套袋授粉和联苯胺-过氧化氢法等实验方法,对入侵江苏常熟的豚草种群的繁育系统特性进行了研究。结果表明,豚草花粉活力在开花后第4天开始出现,第8天到第10天花粉活力比较高;柱头可授性在开花第2天开始出现,第5天到第8天柱头可授性较高;同植株上同一时期开花的雌花的柱头可授性和雄花的花粉活力有5d左右的重叠期。不套袋处理(自然条件)和异株授粉处理下,豚草的结实率都比较高,分别达48.4%和44.4%,两者间无显著差异(P0.05);而同株授粉处理的结实率较低,仅3.4%,极显著低于不套袋处理和异株授粉的结实率(P0.01)但显著大于0(P0.05)。分析表明,豚草属于自交不亲和种,但又可部分自交亲和,不具有无融合生殖特性。因此,对在新分布区的零星豚草植株进行及时防除,将取得事半功倍的效果。     

蛛网萼开花物候、花部特征及繁育系统研究

为探讨蛛网萼(Platycrater arguta)传粉生物学特性,该研究以江西上饶广丰铜钹山国家级自然保护区、江西阳际峰国家级自然保护区蛛网萼为材料,采用野外观察和人工授粉等方法,对蛛网萼开花物候、花部形态及繁育系统进行了研究。结果表明:(1)蛛网萼为伞形花序,种群花期一般在6月中下旬至8月中旬,单花花期为2~3 d,花序花期持续10 d。两个保护区由于年均温度与光照的不同,花期进程有显著不同。(2)蛛网萼可孕花与不孕花从绿色变为白色时对访花昆虫有吸引作用,不孕花能够增加昆虫的访花频率。(3)蛛网萼花粉胚珠比(P/O)为2 520~3 100,杂交指数即是3或4。(4)繁育体系属于以异交为主,部分自交亲和,需要传粉者;熊蜂(Bombus sp.)、四条蜂(Apis florea)和油茶地蜂(Andrena cammelia)是蛛网萼的有效传粉昆虫。(5)套袋和人工授粉结果显示,蛛网萼为兼性自交和异交授粉,异株异花授粉能显著提高坐果率及结籽率,这主要与生境中有效传粉昆虫种类、数量少,花粉传递效率低,种群间基因流交流降低以及柱头自花及同株异花传粉等有关,从而表明在蛛网萼现有生境中植株的早期生殖成功受到影响。蛛网萼种群分布范围扩张以有性繁殖为主,无性繁殖作为重要补充及繁殖保障。     

SLR1 function is dispensable for both self-incompatible rejection and self-compatible pollination processes inBrassica

TheSLR1 gene inBrassica is related both in DNA sequence and in pattern of expression to theS-locus glycoprotein (SLG) gene involved in the self-incompatibility mechanism which recognises and arrests the germination of self pollen. However,SLR1 shows minimal allelic variation and is expressed in both self-incompatible and compatibleBrassica lines and in related, self-compatible cruciferous plants. The function of the SLR1 protein is unknown. TheSLR1 gene was specifically ablated in self-incompatible and self-compatibleBrassica plants byAgrobacterium-mediated transformation with an antisense construct. Primary transformants and homozygous T2 progeny of both self-incompatibleB. oleracea and self-compatibleB. napus recipients were found to exhibit normal pollination responses despite having no detectable SLR1 glycoprotein. This shows that the high, wild-type level of SLR1 protein is not required to sustain the self-incompatibility reaction, nor is it necessary for successful intra-specific cross-pollination between compatible lines.     

紫花含笑传粉生物学初探

紫花含笑(Michelia crassipes)花色艳丽、花香浓郁,为解释其在自然条件下结实率低的原因和判断最佳杂交时期,该研究从传粉生物学入手,通过观察紫花含笑开花动态,运用异交指数(OCI)、花粉胚珠比(P/O)、花粉和柱头活性、人工授粉试验等方法对其繁育系统进行了检测,并记录访花昆虫的种类和行为。结果表明:(1)紫花含笑花期在4—5月,持续50 d左右,单花花期4~5 d。(2)雌雄同花,雌蕊先成熟,雄蕊空间位置高于雌蕊。(3)OCI等于4,P/O为2671±123。(4)套袋实验表明紫花含笑能进行少量的自花传粉,人工异花授粉结实率和种子质量显著高于人工自花授粉和自然条件下,且不存在无融合生殖。(5)开花后36 h雌蕊群弯曲分泌粘液时,与含笑(M.figo)杂交结实率最高达85.7%,为最佳授粉时期。(6)有效访花者主要有东方蜜蜂、黑纹食蚜蝇和独角仙,访花频率易受天气影响。综上说明,紫花含笑繁育系统以异交为主,部分自交亲和需要传粉者,存在一定近交衰退,自然条件下结实率低,主要受传粉昆虫和雌雄异熟限制,最佳授粉期的确定能够提高其杂交成功率。该研究结果为紫花含笑资源保护和杂交育种奠定了基础。     

Variation in style length and anther–stigma distance in Ixiolirion songaricum (Amaryllidaceae)

Variation in style length and anther–stigma distance (ASD) was investigated in 18 populations of Ixiolirion songaricum, an early-spring ephemeral perennial herb in northern Xinjiang. The effect of ASD on autonomous self-pollen deposition and seed set was assessed using bagging experiments. Seed production under autonomous self-pollination, cross-pollination and natural pollination was determined by manual pollination experiments. Stigmas of multiple flowers within an individual were sandwiched between two separate anther levels, and no individuals possessed approach or reverse herkogamy. Style length varied continuously among flowers, resulting in a wide range of variation in ASD. There were fewer flowers with a small ASD than with a large ASD in populations. ASD was negatively correlated with autonomous self-pollen deposition and seed set, but it was positively correlated with natural pollination seed set. Seed production under natural pollination was higher than that under autonomous self-pollination, but it was smaller than that under cross-pollination. Variation in style length and ASD among flowers was not caused by style or stamen elongation in I. songaricum, which differ from other species reported in literature that have continuous variation in style length and ASD.