Breeding systems and pollination inVigna minima (Leguminosae,Papilionoideae)

Four types of floral breeding systems—(i) chasmogamy, (ii) aerial pseudocleistogamy, (iii) subterranean pseudocleistogamy and (iv) obligate subterranean true cleistogamy—are observed in the populations ofVigna minima inhabiting the Western Ghats (India). Five categories of phenotypes are recognized based on the number and kinds of floral breeding systems found in a given individual. The frequencies of different categories of phenotypes not only show intra- and interpopulation variation, but also fluctuate from generation to generation suggesting differences in the genetic structure of populations. This polymorphism in the breeding system of a single species is unique and may be adaptive. Obligate subterranean true cleistogamy and amphicarpy appear to be adaptations to jungle fires and soil erosion.—The flowers are of the flag-blossom type and insect visitors act as tripping agents. The tripping mechanism together with the polymorphic floral breeding system result in a balanced mixture of selfing and outcrossing. Such a recombination system may enhance the fitness ofV. minima which is essentially a colonizing species.     

Mating System in a Low-density Natural Population of the Dioecious Wind-pollinated Patagonian Cypress

The mating system of a species is an essential factor that determines the genotypic frequencies of its populations in each generation. Thus, knowledge in this regard is important in the application of practical measures in conservation and forest tree breeding. Austrocedrus chilensis (D.DON) PIC. SER. ET BIZZARRI is a member of the Cupressaceae native to the Andean–Patagonian Forest of Argentina and Chile with regional economic importance. It is a dioecious tree with pollen and seeds distributed by wind. Isozyme markers were utilized to study the mating system of this species through the survey of individual effective pollen clouds in a natural low-density population. If random mating occurs, effective pollen clouds that pollinate single seed trees are expected to be genetically homogeneous. The classical HardyWeinberg test of panmixia was also performed. Although it failed to reject random mating, the analysis of the pollen clouds showed that this mating pattern does not occur. Evidence of locally distributed heterogeneous pollen clouds is presented. The two methods are critically compared.     

Genetic variation within and between populations of Potamogeton pusillus agg.

Patterns of isozyme variation were examined in 17 populations of P. pusillus and P. berchtoldii, together with one population of P. trichoides taken for comparison. Both P. pusillus and P. berchtoldii displayed low levels of variation within populations associated with high levels of interpopulation differentiation. This pattern of partitioning of genetic variation within and between populations is attributed to the founder effect, frequent vegetative propagation by turions, dominant self-fertilization and limited seedling recruitment. The mechanism of pollen transfer was investigated in cultivation. Effective pollination takes place in air above the water surface (autogamy, geitonogamy, anemogamy), on the water surface (epihydrogamy) or below water surface (hydroautogamy). The species are self-compatible. The low level of infra-population variation together with rare occurrence of heterozygotes suggest that selfing is the most frequent mode of pollination, although the protogynous flowers may occasionally permit some cross-pollination. Unique enzyme markers were found for P. pusillus and P. berchtoldii, and also for the single population of P. trichoides. All multienzyme phenotypes were species-specific. Isozyme data support the separate position of P. pusillus and P. berchtoldii. UPGMA dendogram based on enzyme data of 133 plant samples revealed three distinct main enzymatic entities perfectly corresponding to the three morphologically defined species.     

Reproductive biology ofFrangula alnus (Rhamnaceae) in southern Spain

Various aspects of the reproductive biology of the perennial hermaphroditeFrangula alnus Mill. were studied in two populations located in the province of Cádiz, southern Spain. Flowering extends from the second week of May to early July. The small, whitegreenish, entomophilous flowers are incompletely protandrous and last 8–10 days, but pollen transfer takes place only on days 1–3. A very weak, pleasant odour along with nectar and pollen attract over 45 insect species, of which 21 are probable pollinators. These are mainlyDiptera but also includeHymenoptera and the unusual (as flower visitors)Mecoptera. Reproduction is exclusively sexual and strictly xenogamous, with pollen transfer depending solely on insect vectors. Although flower morphology and individual flower phenology do not fully prevent self-pollination, and geitonogamy can easily take place, the level of autogamy was negligible. Therefore, some self-incompatibility mechanism is operative in this species. Only 2.8% of open-pollinated flowers set fruit. At the flower level, fruit initiation was apparently limited by availability of cross-pollen, which in turn seemed influenced by the structure of the population. The seed/ovule ratio in ripe fruits was ca. 50%. Predispersal (maternal) reproductive success (percent ovules becoming filled seeds) was 1.42%. For mature individuals this corresponded to ca. 430 to 1560 potential offspring per year.     

Precision of the daily pollen count. Identifying sources of variation using variance component models

Summary During the pollen season, a daily account of airborne pollen is reported by radio and newpapers in Denmark as «Today's pollen count». The Aerobiological Group under the Danish Asthma and Allergy association is responsible for the daily identification and counting of pollen. In 1984 the Group set up a trial to investigate the reproducibility of the pollen count.Three trained pollen counters independently examined the same specimens from two Burkard pollen traps. The traps were located on the roof of the Meterological Institute in Copenhagen 15 meters above ground level in the northern outskirts of central Copenhagen. This is the usual sampling site. Specimens from each trap from 20 days during the grass pollen season were selected. Four species groups were identified in sufficient numbers for statistical analysis. These were, in order of occurrence, spruce/pine (Picea/Pinus), grass (Poaceae), nettle (Urtica) and mugwort (Artemisia).Identification of sources of variation and assessment of their relative importance were carried out using variance components models. A detailed account of the method is given.Qualitatively equivalent conclusions were reached for each group: i) The expected seasonal variation was identified; ii) The counters contributed significantly to the variation of pollen counts; iii) The traps did not contribute to the variance, but a day-trap interaction was identified. This interaction was interpreted. as a problem of instrumental variation over time of traps of variation in meteorological conditions; iv) The total variance was larger than originally expected. The relative uncertainty was greater than 50 per cent.The variance of the daily pollen count cannot be reduced much by reducing counter variation or day-trap interaction. The variation among pollen counters is small, and the day-trap interaction is difficult to fully comprehend. The basic measurement error can be reduced by examining a larger area of each specimen. Although this implies a greater cost, it is probably the most effective method of reducing the uncertainty of «Today's pollen count».     

Reproductive ecology of a perennial outcrosser with a naturally dissected distribution

We surveyed four populations of contrasting size (two isolated and two large stands) of a woody outcrossing species, Discaria trinervis (Rhamnaceae), which has a naturally dissected distribution. Our main goal was to investigate the floral biology, breeding system and pollination mechanism of the species, which in turn may help to explain the mechanisms underlying the survival of the isolated populations. Discaria trinervis is both wind- and insect-pollinated, showing interactions with a large fraction of the available flower visitors at both stand sizes. In the larger populations, stigmatic loads were larger, more pollen tubes reached the ovules, and fruit and seed set were higher; however, the reproductive output in the smaller populations (over 2000 seeds per plant per year) seemed adequate for population persistence. Human disturbance (e.g. destruction of trees for wood extraction) may put these smaller populations at risk through loss of incompatibility alleles. The results suggest that plant species with naturally dissected distributions may provide clues about which reproductive mechanisms ensure survival under fragmentation.     

A long-term study of winter and early spring tree pollen in the Tulsa, Oklahoma atmosphere

Since 1986 the atmosphere in Tulsa, Oklahoma has been monitored for airborne pollen and spores with a Burkard 7-day spore trap situated on the roof of a building at The University of Tulsa. The present study specifically examined the early spring tree pollen season for several local taxa and the occurrence of pre-season pollen during December and January. Knowledge of the local pollen season will help identify the presence of out-of-season pollen and possible long distance transport (LDT) events. Average daily concentrations of airborne pollen for species ofBetula, Quercus, Ulmus, and Cupressaceae were determined for each year from 1987 to 1996. The data showed that during the early spring the precise pollination periods for these allergenic tree species are highly variable. There were considerable variations in start date, season length, peak concentration, date of peak, and cumulative season total. The start dates forUlmus, Betula, andQuercus varied by 30 days or more, while the early spring Cupressaceae pollen showed the least variation in start date (only 23 days). More research is needed to understand the mechanisms which govern the onset and magnitude of pollen release. Although several reports have documented episodes of long distance transport (LDT) of pollen, the actual contribution of out-of-season or out-of-region pollen to local air spora is poorly known. The current study also re-examined the LDT ofJuniperus ashei pollen in Oklahoma.Juniperus pollen appeared in the Tulsa atmosphere on 40% of the days in December and January with concentrations as high as 2400 pollen grains/m³ of air; however, no local populations ofJuniperus pollinate at this time of the year. High concentrations occurred on days with southerly winds suggesting thatJuniperus ashei populations in southern Oklahoma and Texas were the pollen source. Since no local pollen is present in the Tulsa atmosphere in December and January, this example of LDT has been easy to document.     

Microgametophytes in flowers with and without fruits ofPhlox drummondii (Polemoniaceae)

Relationships between microgametophyte numbers per flower and fruit-set were sought inPhlox drummondii Hook. This was accomplished by counting fluorescentstained pollen tubes in flowers with and without fruits in 21 populations, and in flowers subject to either supplemental or sparse pollination, and then determining whether the flowers initiate fruits. There was a conspicuous variation in mean pollen tubes per flower (3–38) and in percent fruit-set (17%–92%) among populations. Neighboring populations often differed strikingly in these respects. Flowers with fruits had an average of 15.2 pollen tubes per stigma whereas those without had an average of 3 7 tubes. Over all flowers, there was a mean of 3.7 tubes per ovule. There was a strong correlation between mean tube number within populations and their percent fruit-set (r = 0.86). Supplemental pollination significantly enhanced fruit-set, thereby supporting the notion that fruit-set was pollen-limited in most populations. In both natural and artificial pollinations a portion of flowers without fruits still had several pollen tubes. The occurrence of fruitless flowers containing tubes is explained by attrition factors, like late-acting pollen-pistil incompatibility, and resource limitation. Fruit-set could be initiated with one pollen tube, but this rarely occurred in nature. Higher pollen loads were accompanied by higher percents of fruit-set and number of seeds per flower.     

Variation in the genetic structure and reproductive biology of holm oak populations

Five polymorphic enzymatic loci were studied in 30 populations of Quercus ilex distributed from Crete to North Africa. A high within-population genetic diversity was found for each locus studied. Most of the alleles were common to all the populations, indicating that the holm oak corresponds to a single genetic entity. Observation of breeding system characteristics showed that the holm oak is monoecious, wind-pollinated, and likely to possess genetic autoincompatibility. Furthermore, studies of flowering phenology in a single population showed that the period of flowering varied notably among trees. An average of 29% of the trees showed inter-annual variation in flowering time. The male, female or vegetative investment also varied widely among trees from one year to another. This results in a diversification of pollen source received by a given tree each year, and also from one year to another.     

Pollen gene expression analysed by micro-isoelectric focusing of proteins from isolated pollen grains in Cucurbita pepo L.

Summary Isoelectric focusing of proteins from single pollen grains of Cucurbita pepo L. has been developed for large scale study of pollen grain populations' heterogeneity. Forty to forty-five protein bands from one pollen grain are revealed after silver staining. Applications of this technique to pollen grain populations from different genotypes are described in this paper. Possible applications and limits of this technique are discussed with respect to plant breeding especially for the measure of gene frequencies in pollen grain populations.The work was partly supported by a grant from LIMAGRAIN and AGPM     

Effects of pollen donors on seed formation inEspeletia schultzii (Compositae) populations at different altitudes

The influence of different pollen donors on seed formation was investigated in three populations ofEspeletia schultzii that differ in environmental conditions and life history characteristics. Self pollen and pollen from different donors (< 15m apart) within each population was used in a diallel design in order to test the genetic base of seed set variation. Three measures of seed formation were used: (1) achene number; (2) proportion of filled achenes (fruits) that distinguishes between achenes with seeds and empty achenes; (3) proportion of aborted seeds that distinguishes between viable and aborted seeds. Self-pollinations resulted in empty achenes. Achene number did not vary between the different pollen donors. A bimodal pattern of filled achenes was found in two populations in two consecutive years. On the other hand, a unimodal pattern was found in crosses between more distant donors (> 30m). These patterns seems to be the results of a sporophytic incompatibility system. Seed abortion was highest at the higher elevations and seems to be correlated with elevation rather than with any genetic effect.     

Interspecific pollen transfer as a mechanism of competition: Consequences of foreign pollen contamination for seed set in the alpine wildflower,Polemonium viscosum

Summary Earlier studies showed that under natural conditions foreign pollen receipt is correlated with loss of seed set in populations of P. viscosum. Here, we report on experimental pollinations using foreign pollen from two co-flowering species that share pollinators with P. viscosum. Experiments were designed to ascertain whether improper pollen transfer causes reduced seed set under controlled conditions and, if so, to determine the stage at which interference occurs. In flowers pre-treated by pollination with either Mertensia or Castilleja pollen, adherence of subsequently deposited conspecific pollen grains was unaffected. However, conspecific grains had significantly lower germination and ovule fertilization success in flowers receiving foreign pollen than in controls. These results suggest that pollinator infidelity in high alpine plant communities can reduce female reproductive success of P. viscosum by inhibiting the performance of conspecific pollen grains. Negative effects of Mertensia and Castilleja pollen were comparable despite large interspecific differences in pollen grain morphology. Accordingly, susceptibility to foreign pollen interference appears to be an intrinsic property of P. viscosum that is not dependent on the unique structural properties of pollen produced by competitive species.     

Genetic diversity and phylogenetic relationships in alder,Alnus firma, revealed by AFLP

Molecular markers for alder,Alnus firma Sieb. et Zucc, have not been studied extensively. Here, we used amplified fragment length polymorphism (AFLP) to investigate genetic relationships among 15 natural populations. EcoRI-ACG + Msel-CTG combinations revealed the highest polymorphism (62.2%). A total of 171 DNA fragments were identified. On average, 58.1% of the AFLP markers that were generated using four primer pairs were polymorphic. Diversity was insignificant among the populations. The combination of a wind-pollinated, outcrossing breeding system along with large population sizes, and the ability to regenerate by stump sprouting may explain the high level of genetic diversity within this species. The majority (98%) of the genetic variance resided within populations. The average number of individuals that were exchanged between populations per generation was very high (N _em = 12.3). Gene dispersal in alder is apparently by seed dispersalvia water and human activity as well as through pollen. Five individuals per population were claded in the same cluster.     

Breeding system and spatial variation in the pollination biology of the heterocarpic Thymelaea velutina (Thymelaeaceae)

Thymelaea velutina (Thymelaeaceae) is a unique dioecious and heterocarpic shrub, each female producing both dry and fleshy fruits. It is endemic to the Balearic Islands (western Mediterranean) and has suffered an important regression in recent decades, especially due to habitat loss. It lives in coastal areas, mainly in dunes, but a few populations occur up to 1300 m in the mountains of Mallorca. In the present study, we examined its breeding system and pollen vectors, determined whether seed production is pollen-limited, and quantified the relative importance of different insect visitors at coastal and mountain sites. Selective exclusions showed no differences between populations in the relative importance of insects and wind as pollen vectors. Pollen was limiting at both populations, though not consistently in time. Flowers of T. velutina were visited mostly by generalist insects, and species composition and abundance of flower visitors varied both in space and time. The flowering period is about a month later in the mountain than in the dune, and this results in a higher frequency of insect visits to plants in the mountain due to the higher insect abundance; insects were also more diverse in the mountain, although they visited a proportionally lower number of flowers than in the dune. Despite this spatio-temporal variation in the frequency of insect visits and in the importance of a particular insect group, the ambophilous system in this species (previously described as anemophilous) ensures a relatively high fruit set at the two different sites.     

三倍体丹参杂交种的花粉形态研究

三倍体丹参是以二倍体丹参为父本、人工染色体加倍的四倍体白花丹参为母本杂交选育的杂交种。为深入了解三倍体丹参花粉的特性,以及为三倍体种质利用提供孢粉学依据,该文以二倍体丹参为对照,研究了三倍体丹参杂交种花粉的形态变异规律。利用光学显微镜和扫描电镜对二倍体和三倍体丹参的花粉萌发沟、外壁纹饰、花粉粒形状等特征进行了显微和超微形态观察,综合进行了花粉形态差异比较,并对花粉大小和形状数据进行了差异显著性分析和正态检验。结果表明:(1)二倍体丹参为6沟花粉,三倍体花粉萌发沟有6沟和8沟两种类型,沟内疣状颗粒分布不匀,出现畸形萌发沟。(2)二倍体和三倍体花粉外壁均为网状雕纹。二倍体花粉网眼内具多个多边形穿孔,穿孔大; 6沟和8沟两种类型的三倍体花粉网眼无穿孔或仅有几个小穿孔,6沟和8沟花粉的外壁雕纹相同。(3)三倍体花粉的极轴长(P)和赤道宽(E)均值显著小于二倍体花粉,花粉大小呈偏正态分布,P*E的差异系数大于二倍体花粉,且有极值存在。三倍体和二倍体丹参的萌发沟和雕纹存在差异,而花粉形状差异不显著。综上结果表明三倍体丹参花粉在倍性效应和杂合性的双重影响下发生了形态变异,且有多种形态变化。     

Cryptic dioecy in Mammea (Clusiaceae)

The flowers of Mammea (Clusiaceae) have been reported to be androdioecious, a rare condition in the angiosperms. Pollen from eight taxa from most of the geographic range of the genus was examined to clarify the type of flowers, and thus the breeding system, of the genus. In six of these taxa pollen from both morphologically perfect and male flowers was examined, while in the other two, only pollen from the perfect flowers was used. In all cases pollen from perfect flowers was inaperturate, while that from the staminate flowers was aperturate. Since the inaperturate pollen probably cannot germinate, it is concluded that the perfect flowers are functionally female. Therefore, Mammea has a cryptic dioecious breeding system.The author would like to thank Peter Endress, Michael Hesse, Toby Kellogg, P. Mick Richardson, and Peter F. Stevens for editorial comments and advice. Andrew Doust, Sara Fuentes and Ken Hiser helped on the SEM. Much thanks goes to Peter F. Stevens for his helpful support throughout this project.     

Pollen size in Hordeum L.: correlation between size,ploidy level,and breeding system

The size of pollen in the genus Hordeum (Poaceae) is correlated with ploidy level and breeding system. Generally, the pollen size increases with the ploidy level, and outbreeding species possess significantly larger pollen than inbreeders. In H. roshevitzii (2x), H. pusilplum (2x), H. murinum subsp. murinum (4x), and H. parodii (6x) pollen, heteromorphisms occur between the central and the lateral florets of the triplet. In all four taxa, pollen from florets in which the anthers are exserted is larger than pollen from florets where the anthers remain inside the floret. The biological consequences of heteromorphic pollen are discussed, and a model for the evolution of breeding strategies in Hordeum is suggested.     

Phylogeography of island canary (Serinus canaria) populations

Island canaries (Serinus canaria) are characterised as a species living exclusively on North Atlantic islands, mainly on the Azores, Madeira and Canary Islands. Although they are very common in their habitats, their behaviour and breeding system has only recently been studied systematically. To advance the understanding of their ecology and to see if the rather isolated archipelagos are already promoting a genetic differentiation, we investigated their phylogeographic relationship as revealed by mtDNA sequences of the cytochrome b gene and investigated whether this measure corresponds to morphological characteristics within the islands. Genetic distances were very low throughout the distribution range of the species. Although the variation of genetic distances within the population of Pico (Azores) was larger than that on Madeira and Canary Islands, the genetic distances between island populations were very low throughout which prevented a clear phylogeographic differentiation. Moreover, morphological measurements did not reveal a consistent pattern to reliably separate the populations, although the measures of beak length and body weight revealed a clear island-specific differentiation. These data lead to the assumption that the colonisation of the Atlantic islands by the canaries occurred very recently, while there is no persisting gene flow between the populations.     

Effect of the breeding system on the genetic structure in threeCephalanthera spp. (Orchidaceae)

The genetic variation of seven enzymes for a total of nine loci was investigated in three species of terrestrial orchids of the genusCephalanthera:C. longifolia, C. rubra, andC. damasonium. These species are characterized by presenting different breeding types: outbreeding , outbreeding with facultative vegetative reproduction, and inbreeding, respectively. Electrophoretic evidence points to a difference in the behaviour of each of the three species which seems strictly related to the breeding type. On the basis of our resultsC. longifolia behaves as a normal outbreeder, whileC. rubra presents the influence of vegetative reproduction in some populations and not in others.C. damasonium shows a total lack of both among and within populations genetic variation, which is most probably due to the autogamic breeding type.     

Influence of arginine,ornithine, DFMO and polyamines on division of the generative nucleus in cultured pollen tubes of <Emphasis Type="Italic">Aechmea fasciata</Emphasis> (Bromeliaceae)

During in vitro pollen tube growth of Aechmea fasciata the second pollen mitosis (PM II) that produces two sperm cells was influenced by exogenous amino acids. Arginine (Arg) as single amino acid was the limiting factor for the second mitosis of the generative nucleus and thus the formation of sperm cells in cultured pollen tubes of A. fasciata. The involvement of Arg was probably related to protein synthesis. The need for Arg was not related to polyamine (PA) biosynthesis, since PA added to the germination medium were unfavourable for sperm cell production. Both ornithine (Orn) and difluoromethylornithine (DFMO) inhibited the second mitosis in cultured pollen tubes of A. fasciata. The addition of Arg during the first 2 h of pollen germination was necessary to establish the division of the generative nucleus 6 h later.