Flower Position Research Articles

Factors affecting haploid induction through in vitro gynogenesis in summer squash ( Cucurbita pepo L.)

Haploid production using in vitro ovule cultures has long been recognized as an important tool to produce haploid and homozygous double-haploid plants for genetic studies and plant breeding programs. In the present study, four experiments were carried out to study the influence of genotype, position of female flowers on plant stem, temperature and sucrose concentration on the in vitro gynogenesis induction of squash. (1) Ovules of 12 genotypes were excised from female flowers, 1 day before anthesis, and cultured onto MS medium containing 3% sucrose and 1 mg l −1 from each of kinetin and 2,4-D (2,4- dichlorophenoxy acetic acid). Differences in response among genotypes were demonstrated. Raad F 1 showed the highest percentage of responding ovules and number of plantlets per dish with 48.8% and 15 plants, respectively. The results revealed that genotype is a key factor influencing the in vitro gynogenesis in squash. (2) Ovules were excised from first, second and third female flower of two hybrids (Giad and Raad) and cultured onto the mentioned above medium. The highest percentage of responding ovules and number of plantlets per dish were obtained from ovules excised from the second female flower on the plant stem. (3) Effect of temperature (4 and 32 °C) for 0, 4, 7 and 12 days on the ovule culture of Queen F 1 was studied. Ovules incubated at 4 or 32 °C for 4 days produced a better embryogenic response. (4) Three sucrose concentrations (30, 60 and 90 g l −1) were tested with the ovule cultures of the local cultivar (Eskandrani). Differences among sucrose concentrations were statistically significant and ovules cultured on the MS medium containing 30 g l −1 produced the best result. MS medium containing 90 g l −1 did not produce gynogenic ovules. Cytological studies reveal that about 65% of the regenerants were haploid (2 n = x = 20 chromosomes) and 35% were double haploid (2 n = 2 x = 40 chromosomes).

Evolution of resupination in Malagasy species of Bulbophyllum (Orchidaceae)

Resupination is the orientation of zygomorphic flowers during development so that the median petal obtains the lowermost position in the mature flower. Despite its evolutionary and ecological significance, resupination has rarely been studied in a phylogenetic context. Ten types of resupination occur among the 210 species of the orchid genus Bulbophyllum on Madagascar. We investigated the evolution of resupination in a representative sample of these species by first reconstructing a combined nrITS and cpDNA phylogeny for a sectional reclassification and then plotting the different types of inflorescence development, which correlated well with main clades. Resupination by apical drooping of the rachis appears to have evolved from apical drooping of the peduncle. Erect inflorescences with resupinate flowers seem to have evolved several times into either erect inflorescences with (partly) non-resupinate flowers or pendulous inflorescences with resupinate flowers.

Manipulation of plant architecture to enhance crop disease control.

Abstract Yield and quality losses due to disease are major factors limiting crop productivity; thus breeding for disease resistance is a primary goal for many plant breeding programmes. Unfortunately, specific sources of resistance are not always available. In cases where sources of genetic resistance are limited or non-existent, manipulating plant architecture to facilitate disease avoidance may be a valuable alternate approach to mitigate disease severity. Modifications of plant architecture can be used to reduce contact with the pathogen, create barriers to pathogen growth and development, or create an unfavourable microclimate for disease development. Architectural variants have long been observed by plant breeders and geneticists, and are frequently utilized to develop new plant types. Key variants that may facilitate disease control include altered plant height, determinacy, branching patterns, branch or leaf angle, flower position, organ coverage or shape, or root structure patterns. Implementing disease avoidance by an architectural approach requires an understanding of both the life cycle of the pathogen and the genetic basis for the desired morphological traits. This review examines examples where modified architecture can be employed to reduce disease. Among the better-documented cases are modified canopy structure to reduce white mould in dry bean and tightly closed ears to reduce Fusarium ear rot of maize. These examples demonstrate that breeding for modified plant architecture can be a valuable component of a broader disease control strategy that also includes genetic resistance and cultural and chemical controls.

Components of fecundity and abortion in a tropical tree, Dahlstedtia pentaphylla (Leguminosae)

Studies were conducted on pollination and patterns of fruit and seed production to assess the potential factors causing high fruit and seed abortion in Dahlstedtia pentaphylla (Leguminosae) through analyses of relationships between flower position in the inflorescence and ovules and seeds within ovaries and fruits, and flower, fruit and seed abortion. No differences were found in pollination and fruit set as a function of inflorescence position. There was no relationship, neither between degenerating ovules and their position within the ovary, nor between developing seed and fruit position. Maternal resource limitation related to fruits and embryos, due to the high cost of fruit production and seed maturation, was one of the factors that led to a high abortion rate in D. pentaphylla.

Floral meristem indeterminacy depends on flower position and is facilitated by acarpellate gynoecium development in Impatiens balsamina

* Floral meristems are generally determinate. Termination of their activity varies with species, occurring after carpel or ovule development, depending on the placentation type. In terminal flowering Impatiens balsamina (cv. Dwarf Bush Flowered) some flowers exhibit meristem indeterminacy; they produce organs from the placenta after ovule development. * Here we provide a detailed description of gynoecium development in this line and explore the basis of the indeterminate nature of some of its floral meristems. * We find that the placenta is sometimes established without complete carpel fusion. Proliferative growth derives from meristematic remnants of the placenta and is more common in the terminal inflorescence. RNA in situ hybridization reveals that IbLFY (Impatiens LFY homologue) is expressed in all meristem states, even in proliferating meristems. Expression of IbAG in axillary flowers is as expected in the meristem, stamens and carpels but absent from the proliferating meristem. * We conclude that I. balsamina has cauline placentation. Incomplete suppression of inflorescence identity in flowers of the terminal inflorescence leads to floral meristem proliferation after ovule development in this species.

Role of sink–source relationships in chrysanthemum flower size and total biomass production

The present work was aimed at understanding and quantifying the effect of sink–source relationships on flower size, using chrysanthemum as a model system. Sink/source ratio was manipulated by flower bud removal (leaving one, two or four flowers, and a control), axillary shoot removal, and varying daily light integral. Furthermore, the influence of flower position within the stem on the flower size was investigated. All means applied to reduce sink/source ratio resulted in a significantly higher individual flower dry mass and area in plants with a fixed number of flowers. Nevertheless, control plants responded to supplementary assimilation light with an increased number of flowers rather than producing larger flowers. Flower position had a negligible effect on flower size in both disbudded and control plants, except that the second‐order lateral flowers were significantly smaller than the first‐order ones. Singly flowered plants without side shoots represented the greatest potential flower size; they had flowers up to 2.4 times heavier than the control plants. Total aerial plant dry mass was only reduced at very low sink strength treatments, whereas flower mass ratio showed a saturating response to the number of flowers per plant. The results indicate that individual flower size is very sensitive to total plant sink strength, but it does not change with plant source strength when the number of flowers is not manipulated.

The effect of flower position on male and female reproductive success in a deceptively pollinated tropical orchid

In many plants, including orchids, differential fruit set along the inflorescence has been attributed to pollinator behaviour. For instance, the pollinator, moving up the inflorescence, becomes satiated with the resources and leaves before visiting the upper flowers. Consequently, the pollinators do not visit flowers as frequently higher up the inflorescence. Alternatively, flower size may vary along the inflorescence, making pollination ineffective as flowers decrease in size. I tested for the presence of differential pollination along the inflorescence in a pollinator-limited tropical epiphyte, Lepanthes rupestris Stimson, and determined the likely cause of the observed pattern. As this species has inflorescences with sequential flowering, pollinator behaviour, moving up the inflorescence as in synchronous multiflowering inflorescences, can be discounted as an explanation for differential fruit set. Fruit set is shown to be more frequent at the base of the inflorescence, but male reproductive success through pollinarium removal is basically independent of flower position. Moreover, cross-pollination by hand at variable flower positions along the inflorescence results in equal fruit set, suggesting that resources are not limiting and cannot explain the cause of differential fruit production along the inflorescence in natural populations. Furthermore, flower size is shown to diminish along the inflorescence, suggesting that the pollinator(s) may be ineffective at depositing the pollinarium in the smaller higher flowers. Consequently, pollinator behaviour and its interaction with flower size, and not resource limitation, is likely to be the main cause of differential fruit set along the inflorescence in L. rupestris.

The Effects of Inflorescence Size and Flower Position on Biomass and Temporal Sex Allocation in Lobelia sessiliflora

To test the prediction of sex allocation theory that plants or flowers high in resource status emphasize the female function, we explored the variation in both biomass (the number of pollen grains and ovules) and temporal (male and female durations) sex allocation among and within plants of protandrous Lobelia sessilifolia in relation to plant size and flower position within plants. Among plants, the mean number of pollen grains and ovules per flower of a plant increased with plant size, whereas the mean P/O ratio (number of pollen grains/number of ovules ratio) decreased with plant size. The mean male duration, the mean female duration, and the mean ratio of male duration/flower longevity per flower of a plant were not correlated with plant size. Thus, large plants emphasized female function in terms of biomass sex allocation, which is consistent with the prediction of size-dependent sex allocation theory. The results for temporal sex allocation, however were inconsistent with the theory. Within plants, the mean number of pollen grains and ovules per flower at each position decreased from lower to upper flowers (early to late blooming flowers) and that of the P/O ratio increased from lower to upper flowers. The mean male duration and the mean female duration per flower decreased from lower to upper flowers, whereas the mean ratio of male duration/flower longevity increased from lower to upper flowers. The population sex ratio changed from male-biased to female-biased. Thus, later blooming flowers emphasized the male function in terms of both biomass and temporal sex allocation, consistent with the sex allocation theory, regarding the change in the population sex ratio.

Phenotypic gender variation within inflorescences of the protogynous species Helleborus foetidus L. (Ranunculaceae)

In the protogynous species H. foetidus, I investigated if investment in sexual structures and seed set shows any trend with position in the flower-opening sequence. In four-flower inflorescences, stamen number decreased with flower position i.e. was highest for the earliest flower and lowest for the latest flower. Ovule number was significantly higher in the latest flower. Stamen and ovule number did not covary, indicating that there is no structural gender trade-off in this species. Seed set (i.e. percentage of ovules producing seed) did not differ between control plants and pollen-supplemented plants and the effect of pollen supplementation did not vary among positions. Seed set showed marginally significant differences between control plants and simulated-herbivory plants, but the effects of this treatment varied significantly among positions. Significant among-position variation in seed set was observed in the control plants but not the simulated-herbivory plants. Seed set of latest-opening flowers of simulated-herbivory plants was significantly higher than that of latest-opening flowers of control plants. H. foetidus support Brunet and Charlesworth's (1995) prediction that in plants with protogynous flowers, later-opening flowers should specialize as female flowers, at least under conditions of high resource availability.

Variáveis multicategóricas na determinação da divergência genética entre acessos de pimenta e pimentão

A manutencao de acessos de Capsicum em bancos de germoplasma tem crescido em importância para preservacao da diversidade e uso em programas de melhoramento genetico. Este trabalho visou avaliar a divergencia genetica entre acessos de Capsicum spp. e verificar a eficiencia da utilizacao de medidas de dissimilaridade e da discriminacao de genotipos em especies, baseando-se em 13 variaveis multicategoricas. O experimento foi realizado em Campos dos Goytacazes, RJ, em blocos ao acaso com tres repeticoes utilizando 59 acessos com dez plantas por parcela, entre novembro/2001 e julho/2002. Os descritores considerados foram: cor do caule, da antera e da corola; numero de flores por axila; posicao da flor; habito de crescimento; cor do fruto imaturo e maduro; forma e epiderme do fruto; cor da semente e da folha cotiledonar; numero de loculos; constricao anular do calice e do fruto. Os dados foram obtidos pela moda de cada descritor seguindo-se os criterios do IPGRI. As analises realizadas foram: agrupamento pelo metodo de Tocher e Hierarquico do Vizinho Mais Proximo; Projecao das Distâncias no Plano e Analise Discriminante de Anderson. O metodo de Tocher diferenciou as especies de C. annuum var. annuum, C. annuum var. glabriusculum, C. chinense e C. pubescens, confirmando que os descritores qualitativos essenciais para a caracterizacao de Capsicum spp. devem ser utilizados no manejo de bancos de germoplasma. Os metodos de Tocher, Hierarquico do Vizinho Mais Proximo e Projecao das Distâncias no Plano foram concordantes e eficazes em agrupar acessos com pequena distância genetica entre si. As funcoes discriminantes de Anderson identificaram 100% das especies e variedades botânicas estudadas.

Failure of reproductive assurance in the chasmogamous flowers of Polygala lewtonii (Polygalaceae), an endangered sandhill herb

Hypothetically, a species with both cleistogamous (CL) flowers and delayed selfing chasmogamous (CH) flowers should display high levels of reproductive assurance because, over time, obligate selfing by CL flowers should reduce inbreeding depression and delayed selfing in CH flowers should compensate for the absence of outcross pollen. We used pollinator-exclusion experiments to investigate reproductive assurance in the CH flowers of Polygala lewtonii, an herb with a mixed mating system. We followed CH flowers from bud-break to flower/fruit abscission to quantify fruit initiation and maturation and rates of floral development. We also evaluated the efficacy of the selfing mechanism, conducted pollinator watches to assess the likelihood of pollinator limitation, and performed regression analysis to determine the effect of flower position on fruit production. Pollinator exclusion significantly reduced fruit initiation and maturation. Investigation of floral development demonstrated that the selfing mechanism is largely dysfunctional in CH flowers, indicating the failure of reproductive assurance. Low observed rates of insect visitation appear to contradict high rates of CH fruit production in open-pollinated plants, particularly given the rarity of delayed selfing. In both treatments, flower position significantly affected fruit initiation, suggesting a role for resource limitation in both pollinator-excluded and open-pollinated flowers.

The Mating System of Verbascum thapsus (Scrophulariaceae): The Effect of Plant Height

Several factors attract pollinators to individual plants. Among them, plant height is one of the least studied. Previous studies have demonstrated that taller plants often receive larger pollen loads, indicating that they may experience higher rates of outcrossing and have more diverse pollen donor arrays. In this study we sampled three populations consisting of at least 50 flowering individuals to estimate the mating system of the biennial weed Verbascum thapsus. Six tall and six short plants in each population were chosen for study. Mating system estimates were based on progeny arrays from three zones within the infructescence of each plant. Estimates of the mating system imply that plant height and flower position within the inflorescence affect outcrossing rates. Taller individuals in all three populations experienced higher rates of outcrossing than shorter individuals during both years of the study. The top infructescence section of short plants during the second year had significantly higher outcrossing than the middle or lower sections. However, in taller plants the middle section of the infructescence had higher outcrossing than the top and lower sections. The effective number of outcrossed pollen donors per maternal plant was also higher for taller plants. Our results indicate that tall plants receive larger and more genetically diverse pollen loads while shorter individuals may experience some pollen limitation leading to increased selfing.

<I>Brasiliocroton</I>, a New Crotonoid Genus of Euphorbiaceae s.s. from Eastern Brazil

A new genus and species of Euphorbiaceae s.s., Brasiliocroton mamoninha, is described from two disjunct areas of lowland forest remnants in eastern and northeastern Brazil. It is a member of tribe Crotoneae and was previously confused with Croton and Micrandra. The resemblance to Micrandra is based on the branched inflorescences and terminal position of the pistillate flowers, trigonous capsules, and ovate leaves with basal glands, but the stamens are more numerous and the pollen is inaperturate (like Croton). Brasiliocroton has a stellate-rosulate indumentum like some Croton species, but its anthers are erect in bud, and the position of the pistillate flowers is anomalous in Croton. Molecular data place Brasiliocroton as the closest sister group to Croton, once Astraea has been removed from Croton and placed sister to Acidocroton and Ophellantha. Wood anatomical features support the generic status of Brasiliocroton.

Reproductive biology and pollinator limitation in a deceptive orchid, Serapias vomeracea (Orchidaceae)

AbstractDeceptive orchid species that offer no floral rewards to pollinators often experience pollinator limitation. Serapias vomeracea is considered a particular example of terrestrial orchids using deceptive strategies because its sepals, petals and the lateral lobes of the hypochile form a small tube imitating a little hole that the insects use to rest. The pollination biology and breeding system were investigated in two populations of S. vomeracea in order to examine the extent of pollinator limitation. Visiting insects were immobile in the Serapias flowers during the early morning and late evening. The main pollinators were Oedemeridae and Lymexylidae (Coleoptera), but Hymenoptera (Ceratina, Eucera, Osmia) were also observed. Fruit set did not vary in response to floral display size, suggesting that variations in flower number per inflorescence and plant height were not responsible for attracting pollinators and thus reproductive success. Although S. vomeracea is self‐compatible, bagged inflorescences produced no fruits. Artificial pollination resulted in 95–100% fruit set by induced autogamy, 95–100% by geitonogamous pollination and 90–95% by xenogamous pollination. Fruit set in the open‐pollinated control was 13–18%. Fruit production was not related to the size, number or position of flowers. Pollinator observation and supplemented hand‐pollination indicated a positive relationship between fruit set and pollinator visitations in this species.

Effects of local density and flower colour polymorphism on pollination and reproduction in the rewardless orchid Dactylorhiza sambucina (L.) So�

The rewardless orchid Dactylorhiza sambucina shows a stable flower colour polymorphism, with both yellow- and red-flowered morphs growing sympatrically. Pollination biology and breeding system were investigated to examine the effects of density of plants, colour polymorphism, inflorescence dimension, and flower position within inflorescence on male and female reproductive success in three natural populations of D. sambucina. There were significant differences among sites in the number of pollinia removed and in fruit set per inflorescence. Number of removed pollinia and capsule production in D. sambucina were independent from flower and inflorescence size or flower position. As a whole, the red morphs showed the highest number of capsules produced, while the yellow morphs had the greatest male success. The relative male and female reproductive success were independent from plant density but were significantly correlated with the yellow morph frequency at the population level. Overall, our findings show that the contribution to the total reproductive success deriving from the two colour morphs does not conform with the predictions of negative frequency-dependent selection.

Temperature affects Chrysanthemum flower characteristics differently during three phases of the cultivation period

SummaryThe sensitivity to temperature of the number of flowers per plant including flower buds (NFPP), flower size, position and colour was investigated in cut chrysanthemum (Chrysanthemum morifolium cv. ‘Reagan Improved’). Plants were grown either in a glasshouse at constant 24 h mean temperatures throughout cultivation (17°C or 21°C), or in growth chambers at 32 different temperature combinations (from 15°C to 24°C). The latter temperature combinations were applied by dividing the cultivation period into three sequential phases: long-day period (phase I), start of short-day period to visible terminal flower bud (phase II), and end of phase II to harvest stage (phase III). All flower characteristics were affected significantly by temperature, except for flower position within the plant. Higher temperatures increased NFPP, mainly by increasing the number of flower buds, but decreased individual flower size. The temperature effect was also dependent on the phase of the cultivation period. In general, flower characteristics were less sensitive to temperature applied during the long-day period. NFPP was affected positively by temperature, mainly during phase III, whereas individual flower size increased with temperature during phase II, but decreased with temperature during phase III. Lower temperatures during phase III significantly enhanced flower colour intensity. Interest in using a more dynamic heating strategy is discussed.

Architectural effects mimic floral sexual dimorphism in Solanum (Solanaceae)

Factors underlying apparent floral sexual dimorphism were examined in six species of andromonoecious Solanum section Lasiocarpa (Solanaceae). Both multivariate and univariate analyses show that hermaphroditic flowers are significantly larger than staminate flowers for all features measured. Thus, flowers could be characterized as sexually size dimorphic. However, when size variation due to flower position (architecture) is controlled experimentally, differences between the floral genders for the nongynoecial characters disappear; there is no difference in corolla or androecium size. Staminate flowers appear to be generally smaller than hermaphroditic flowers, not because of any difference related to primary sexual function, but because they tend to occur in the distal regions of each inflorescence. In contrast, significant differences between hermaphroditic and staminate flowers for primary female traits (ovary, style, and stigma) remain after controlling for position: the two floral types are truly dimorphic for these characters. We show that consideration of architectural effects can direct and refine hypotheses concerning the evolution of andromonoecy. More generally, if architectural effects on flower size are common among taxa with unisexual flowers, then these effects may contribute to the common perception of size dimorphism in taxa with unisexual flowers.

Unraveling the Species Dilemma in Capsicum frutescens and C. chinense (Solanaceae): A Multiple Evidence Approach Using Morphology, Molecular Analysis, and Sexual Compatibility

The species status of two morphologically closely related species, Capsicum frutescens L. and C. chinense Jacq., was investigated using typological, phylogenetic, and biological species concepts. Diagnostic morphological differences, randomly amplified polymorphic DNA (RAPD) marker-based cluster analysis, and hybrid analyses were used to delimit C. frutescens and C. chinense. In many cases two morphological characters, calyx constriction and flower position, can separate accessions of C. frutescens from C. chinense. The RAPD-based analysis clearly separated accessions of C. frutescens and C. chinense into two distinct groups. The average genetic similarity within C. frutescens and C. chinense accessions was 0.85 and 0.8, respectively, whereas the average genetic similarity between C. frutescens and C. chinense accessions was only 0.38. The progenies obtained from C. frutescens and C. chinense hybridization had reduced fertility. Based on these evidences, C. frutescens and C. chinense represent two morphologically diagnosable, phylogenetically distinct, and reproductively isolated species.

Variation in floral sex allocation in Polygonatum odoratum (Liliaceae).

It is well known that resource allocation to male and female functions can be highly variable in hermaphroditic plants. The purpose of this study was to investigate variations in sexual investment at different levels (flower, plant and population) in Polygonatum odoratum, a plant with sequentially opening flowers. Pollen and ovule production in base, middle and top flowers of P. odoratum flowering shoots from two natural populations were quantified. Plant measurements of phenotypic and functional gender were calculated in both populations. Total leaf number was used to investigate the relationship between gender assessments and plant size. Pollen and ovule production varied depending on flower position, although the precise pattern differed between both studied populations; only investment in female floral function decreased markedly from base to top flowers in both populations. The frequency distribution of phenotypic gender and their relationship with plant size differed between populations. Phenotypic and functional gender were correlated in both populations. Sexual investment in P. odoratum has shown a marked variability within plants, among plants, and between populations, which confirms the importance of analysing sex expression in plants of this type. Differences in relative investment in male and female components (phenotypic gender) are reflected in the functional gender and it would be expected that the evolution of sexual specialization in Polygonatum odoratum would be promoted.

Regulation of the mutualism between yuccas and yucca moths: intrinsic and extrinsic patterns of fruit set

In plants that produce many more flowers than fruit, nonrandom patterns of fruit set arise from (1) factors intrinsic to inflorescence architecture, such as flower position or timing in the blooming sequence, and (2) factors extrinsic to the plant, such as pollinator visitation patterns. Here, we address how intrinsic and extrinsic factors drive fruit set in the interaction between Yucca kanabensis McKelvey and its pollinating moths. On inflorescences from which moths were excluded and all flowers were hand pollinated, the flowers most likely to produce fruit were (1) flowers from the first of three waves of flowering, (2) earlier opening flowers but not the earliest, and (3) flowers lower on the inflorescence but not the lowest. However, inflorescences experiencing natural levels of pollination and oviposition showed no effect of flowering wave, and flowers later in the flowering sequence and higher on the inflorescence were the ones most likely to produce fruit. The intrinsic patterns of fruit set were associated with differences among flowers, with the largest flowers being wave 1 flowers and flowers lower on the inflorescence. However, these differences among flowers did not translate into commensurate differences among fruit.Key words: mutualism, abscission, fruit, yucca, yucca moth.