Flower Anthesis Research Articles

Effects of relative humidity and temperature stress on pollen viability of Cistus incanus and Myrtus communis

Cistus incanus and Myrtus communis are two species commonly found in Mediterranean shrublands, flowering respectively in spring and summer. Pollen of single flowers of C. incanus is available for dispersal for 8-10 hours, during which time viability decreases from 91% to 61%. Field measurements of the variation in the percent pollen viability during the anthesis of single flowers of M. communis shows that, immediately after anthesis, pollen viability is very high; by the end of the first day it significantly declines and 36 hours after anthesis almost all grains are unviable. Experiments carried out under controlled environment showed that, in C. incanus, the greatest loss of viability occurs at 100% humidity and high temperatures, while under dry conditions pollen viability remains high throughout a wide temperature range. Similarly, pollen viability of M. communis remains high for several hours at high temperature and dry conditions, while it rapidly decreases at high humidity. In conclusion, the temperature experiments indicate that in C. incanus and M. communis, pollen viability does not appear to be drastically reduced if the relative humidity of the environment is low. Therefore, humidity is a far more important factor determining pollen viability loss in both species.

Fruit‐Set Induced Changes in the Sex of Flowers in Caesalpinia calycina (Leguminosae)

Abstract: The proportions of hermaphrodite to staminate flowers in inflorescences of the andromonoecious species Caesalpinb calycina vary. Analysis of fruit position along the flowering rhachis, and also of the sex of floral buds in inflorescences with fruits set in different positions, indicate that fruiting success influences the sex of flowers in distal positions along the rhachis. Other reports of andromonoecy in caesalpinoid species are examined with reference to floral sex lability and the influence of fruit set.

Pollination requirements of West Indian cherry (Malpighia emarginata) and its putative pollinators, Centris bees, in NE Brazil

The pollination requirements of West Indian cherry (Malpighia emarginata DC) were investigated in NE Brazil through observations of flower morphology, floral rewards, anthesis, anther dehiscence, stigma receptivity, pollen cross and self-compatibility and proportion of fruit set. Potential insect pollinators and their foraging behaviour were also studied, and the pollination efficiency of the most frequent flower visitor, the bee Centris tarsata Smith (Anthophoridae), was assessed using single visits to flowers. It was shown that the West Indian cherry flower has a short lifespan, thus requiring pollination on the day of anthesis, when both cross- and self-pollen grains set fruit. The flower can potentially be pollinated by an array of insect visitors, but only oil-collecting bees of the genus Centris find it very attractive. Centris tarsata appeared as the main pollinator of West Indian cherry in the area studied, and farmers are advised to encourage its presence in orchards. Despite high levels of natural pollination, only 30% of flowers set fruits. It is suggested that a high proportion of abnormal ovule development may be responsible for low fruit set where pollination is satisfactory, and that West Indian cherry varieties showing a lower percentage of such abnormalities should be selected for.

029 Performance of Short-vined Tropical Pumpkins Derived from Temperate × Tropical Crosses

A joint breeding effort of the Universities of Puerto Rico and Florida involves the development of short-vined tropical pumpkin (Cucurbita moschata) genotypes that are able to reach maturity earlier than traditional long-vined types. Sixteen promising hybrids and inbreds were planted in Lajas, Puerto Rico, in June 1998. Pedigrees of this material included traditional tropical genotypes crossed with bush or compact temperate genotypes. Anthesis in both pistillate and staminate flowers occurred on average 49 days after planting. However, the variability of flowering dates among genotypes was far greater for pistillate (40 to 60 days) than staminate (46 to 54 days) flowers. Hybrids flowered earlier than inbred lines. Female flowers opened before male flowers in many genotypes. It seems likely that an inadequate source of pollen contributed to the low yields of some of the earliest genotypes. The five highest-yielding genotypes had pistillate flowers that opened after their male counterparts. All plots were once-over harvested 86 days after planting. Average yield per plant varied from 1.4 to 6.0 kg. Average fruit weight varied from 0.8 to 3.1 kg. High-yielding genotypes tended to have the highest fruit weight, a factor that should be considered when breeding for the next generation of short-vined genotypes. Yields were less than what could be expected from a long-vined tropical pumpkin. However, this yield could be obtained with a once-over harvest at about 90 days, compared to multiple harvests beginning at 120 days, saving costs of additional field practices, and allowing the land to be used for other purposes.

Role of plant growth substances in MS33‐controlled stamen filament growth in Arabidopsis

The rapid growth of stamen filaments just before flower anthesis in Arabidopsis thaliana does not occur in the male sterile33 (ms33, formerly known as msZ) mutant. ms33 filaments were approximately 40% shorter than the wild type (WT), and there was corresponding reduction in the epidermal cell length of filaments. This suggests that MS33 controls the final cell‐elongation phase of filament growth. Both low temperatures and gibberellic acid (GA3) restored filament and cell growth in intact ms33 flowers, but these treatments only had a small promotive effect on WT filaments. Decapitation experiments involving the removal of the anther had the opposite effect on WT and ms33 filaments; growth was inhibited in WT, but was increased in ms33 filaments. In young stamen primordia cultured in vitro, filament growth was less in WT, but more in ms33, than in respective in vivo produced filaments. Plant growth substances (PGSs), GA3 and indole‐3‐acetic acid (IAA) were promotive, zeatin had no effect, and abscisic acid (ABA) and ethrel inhibited filament growth in both intact and decapitated WT and ms33 filaments. Together these observations suggest that MS33 is activated immediately before anthesis and that the MS33 product either regulates temporal biosynthesis of gibberellins (GAs) and/or IAA or makes the filament tissue sensitive to these PGSs, which in turn trigger cell elongation and filament growth. The data also suggest that ms33 mutant anthers contain a relatively high ratio of growth inhibitors to promoters, which inhibits epidermal cell elongation and filament growth.

Observations on the Reproductive Biology of Miconia calvescens DC (Melastomataceae), an Alien Invasive Tree on the Island of Tahiti (South Pacific Ocean)1

ABSTRACT Miconia calvescens DC (Melastomataceae) is a dominant invasive species in the tropical oceanic island of Tahiti (French Polynesia, South Pacific Ocean), where it was introduced as an ornamental plant. Whereas this small tree is sparse in its native range of Central America, it has spread in Tahiti into a wide variety of habitats including native wet forests. The remarkable success of this invasion is due in great part to prolific reproduction: a mature tree can bear up to 220 inflorescences with an average of 1330 flowers/inflorescence, 208 fruits/infructescence and 195 seeds/fruit. Two and a half years of phenological observations in a highly invaded site indicated that three major peaks of flowering occur/year over brief periods: flower anthesis lasted a few days and pollen grain germination suggested a short stigmatic receptivity of only a few hours; no pollinators were observed foraging on flowers during our survey; the production of fruits containing viable seeds in bagged inflorescences showed that self‐fertilization can occur; pollen‐ovule ratio (log P/O = 2.68) suggested facultative xenogamy; bagged isolated flowers to test for autogamy and style cutting to learn whether apomixis occured or not were not conclusive. The flowering phenology and the breeding system of M. calvescens enable this plant to build up rapidly successful populations from even a single propagule on the island of Tahiti and on other sites of introduction. The vegetation structure of Polynesian native forests compared to Neotropical rain forests probably plays an important role in determining the reproductive success of M. calvescens and could provide a complementary explanation of the biological invasion processes in tropical oceanic islands.

Hormone Sprays and Supplemental Light Prevent Cold-storage-induced Postharvest Leaf Chlorosis and Abscission in `Stargazer' Hybrid Lilies

Rapid leaf chlorosis and abscission limits the use of cold storage for post-production short-term holding of potted lilies. We investigated the effects of storage temperature, storage irradiance and pre-storage foliar sprays of gibberellin and/or cytokinin on postharvest leaf and flower quality of Lilium sp. `Stargazer' hybrid lilies. Storage of “puffy bud” stage plants at 4, 7, or 10 °C in dark for 2 weeks induced leaf chlorosis within 4 days in a simulated consumer environment, and resulted in 60% leaf chlorosis and 40% leaf abscission by 20 days. Cold-storage also reduced the duration of flower bud opening, inflorescence and flower longevity, and increased flower bud abortion. Providing light up to 40 μmol·m–2·s–1 during cold-storage at 4 °C significantly delayed leaf chlorosis and abscission and increased the duration of flower bud opening, inflorescence and flower longevity. Foliar sprays of ProVide (100 mg·L–1 GA4+7) and Promalin [100 mg·L–1 GA4+7 and 100 mg·L–1 benzyladenine (BA)] effectively prevented leaf chlorosis and abscission at 4 °C, while ProGibb (100 mg·L–1 GA3) and ABG-3062 (100 mg·L–1BA) were not effective. Accel (10 mg·L–1 GA4+7 and 100 mg·L–1 BA) showed intermediate effects on leaf chlorosis. Flower longevity was increased and bud abortion was prevented by all hormone formulations except ProGibb. The combination of light (40 μmol·m–2·s–1) and Promalin (100 mg·L–1 GA4+7 and 100 mg·L–1 BA) completely prevented cold-storage induced leaf chlorosis and abscission and significantly improved flower opening and overall plant quality.

Status of self-pollen in bee pollination efficiency of white clover (Trifolium repens L.).

Flowers of white clover (Trifolium repens L.) are hermaphrodite and self-incompatible; their cross-pollination depends entirely on insect visitors, mainly bees (Apoidea). Because self-pollination of white clover occurs before flower anthesis, we determined whether selfing affected the pollination efficiency of a honeybee visit. We compared pollen deposition in emasculated and intact flowers following (1) a single honeybee visit, (2) open-pollination for a day and (3) enclosure in a cloth bag to prevent insect visits. In emasculated flowers, open-pollination resulted in more pollen deposited than after one visit (+30%) which is consistent with flowers being visited more than once by pollinators during the course of a day. On intact flowers, saturation of the stigma was achieved after the first visit of a honeybee (near 280 grains) because of self-pollination. Additional visits did not increase pollen deposits, but they improved pollen efficiency in terms of numbers of pollen tubes reaching the ovules. In such a context of easily saturated stigmas, self-pollen does not inhibit cross-pollen activity, but represents a constraint for pollination which demands multiple bee visits to each flower to achieve maximum fertilization.

Predicting Yield and Time to Maturity of Muskmelons from Weather and Crop Observations

A simple method to predict time from anthesis of perfect flowers to fruit maturity (full slip) and yield is presented here for muskmelon (Cucumis melo L.) grown in a northern climate. Developmental time for individual muskmelons from anthesis to full slip could be predicted from several heat unit formulas, depending on the temperature data set used. When temperature at 7.5 cm above soil level was used, the heat unit formula resulting in the lowest coefficient of variation (cv=6.9%) accumulated daily average temperatures with a base temperature of 11 °C and an upper threshold of 25 °C. With temperatures recorded at a meteorological station located 2 km from the experimental field, the method showing the lowest cv (8.9%) accumulated daily maximum temperatures with a base temperature of 15 °C. This latter method was improved by including a 60-degree-day lag for second cycle fruit. The proportion of fruit volume at full slip of 22 fruit from the first cycle could be described by a common Richards function (R2=0.99). Although 65% of the plants produced two fruit cycles, fruit from the first cycle represented 72% of total yield in terms of number and mass. The blooming period of productive flowers lasted 34 days, each cycle overlapping and covering an equal period of 19 days. Counting the number of developing fruit >4 cm after 225 degree days from the start of anthesis (when 90% of the plants have at least one blooming perfect flower) could rapidly estimate the number of fruit that will reach maturity.

Pollination of Echinodorus grandiflorus (Alismataceae)

Studies on the pollination and breeding system of Echinodorus grandiflorus (Chamisso and Schlechtendal) Micheli were carried out on two natural populations in Viçosa, Minas Gerais State, southeastern Brazil. One population was formed by individuals of ssp. grandiflorus and the other by individuals of ssp. aureus (Fassett) Haynes and Holm-Nielsen. The flowering periods were within the rainy season. Flower anthesis occurred during the morning hours and flowers lasted ca. 8 h. E. grandiflorus ssp. grandiflorus is self-incompatible; few fruits, but many adventitious plantlets are produced at the inflorescences. E. grandiflorus ssp. aureus is self-compatible; many fruits and few adventitious plantlets are formed. Bees are the main flower visitors. The bee Protodiscelis echinodori (Colletidae) presents oligolectic foraging behavior, i.e., collects pollen from a single plant species or a group of related plant species.

The plant homologue of the defender against apoptotic death gene is down-regulated during senescence of flower petals

Petal senescence is an example of a highly reproducible cell death programme. In this programme, DNA is fragmented internucleosomally and cells with condensed nuclei containing an increased number of 5′ ends can be detected with the TUNEL technique. The pea homologue of defender against apoptotic death ( dad), a gene described to suppress endogenous programmed cell death in Caenorhabditis elegans and mammals was isolated. Expression studies show that dad declines dramatically upon flower anthesis disappearing in senescent petals, and is down-regulated by the plant hormone ethylene. © 1997 Federation of European Biochemical Societies.

Ｚｅｐｈｙｒａｎｔｈｅｓ ｃａｎｄｉｄａ Ｈｅｒｂ．の生育開花に及ぼす温度の影響

The growth periodicity of Zephyranthes candida grown outdoors and the effect of temperature on the initiation and development of flower buds were investigated.A bulb has a sympodial branching system; each unit of the sympodial branch is com-.posed of 2 foliage leaves with a circular base and 1 foliage leaf with semi-circular base in 1/2 alternate arrangement from the base upwards and terminates in an inflorescence with 1 floret. During the growing period, extending from spring to autumn, repeated sympodial branching results in 3-4 inflorescences.In October, after the flowering season, 2 inflorescence primordia remain in each bulb. The first inflorescence is at carpel initiation stage and the pollen mother cell is at the tetrad stage; the pollen grains mature and become functional between June and August of the following year. Anthesis occurs from July to September.When plants with inflorescences at carpel differention stage were moved to a growth chamber kept at 10°, 15°, 23° or 30 °C, plants transferred to 23 °C chamber developed flower buds most rapidly and reached the pollen formation stage 4 months later and bloomed after 20 days. Plants kept at the other temperature regimes had fewer inflorescences and flowered later.In plants kept continuously at 23 °C from October, the first inflorescence flowered in March of the following year. During the growing period for about 13 months, these plants produced 4.7 flowering inflorescences and initiated 5.1 inflorescences by repeated sympodial branching.In a commercial forcing trial, plants kept at a min. 20 °C from early March flowered in May, 2 months earlier than the natural flowering time.

THE PREDICTION OF PHENOLOGICAL STAGES IN FOUR NAMAQUALAND EPHEMERAL SPECIES USING THERMAL UNIT INDICES

Flowering time of ephemeral plant species in Namaqualand (South Africa) generally ranges from mid-July through September, depending on the timing of the first substantial winter rains. The precise timing of the flowering of species is determined by the individual's life history and the integrated effects of a complex of environmental factors. Phenological and climatic data were recorded and used to determine the number of thermal units required by four Namaqualand ephemeral species to reach a certain phenological stage. Twenty-three thermal unit indices were used to calculate the number of thermal units needed to reach a specific phenological stage. The index combining cold units from sowing until flower initiation, with Growing Degree Days (heat units) from flower initiation until anthesis flowering or display/peak flowering, gave the most accurate predictive values. Flowering time of Namaqualand ephemerals can therefore be predicted at the beginning of the growing season after the first substantial rainfall, and refinements made throughout the season by the use of actual temperature data.

A Heat Unit Model to Predict Growth and Development of Muskmelon to Anthesis of Perfect Flowers

Growth of `Earligold' muskmelon (Cucumis melo L.), expressed as plant dry weight from transplanting to anthesis, could be predicted using a multiple linear regression based on air and soil temperatures for 11 mulch and rowcover combinations. The two independent variables of the regression model consisted of a heat unit formula for air temperatures, with a base temperature of 14C and a maximum reduced threshold of 40C, and a standard growing-degree day formula for soil temperatures with a base temperature of 12C. Based on 2 years of data, 86.5% of the variation in the dry weight (on a log scale) could be predicted with this model. The base temperature for predicting developmental time to anthesis of perfect flowers was established at 6.8C and the thermal time ranged between 335 and 391 degree days in the 2 years of the experiment.

Unidirectionality of floral colour changes

Many angiosperms have arranged their flowers in inflorescences forming a distinct signalling unit to flower visitors. In some species, the flowers of inflorescences undergo a temporal colour change corresponding exactly to a change in the reward status. Based on information obtained from the spectral reflection curves of pre-change and postchage colours of flower corollas and/or floral guides, it was possible to demonstrate that the colour phase associated with reward closely corresponds to the visual stimuli which trigger behavioural responses of inexperienced flower visitors, and that the colour phase associated with less reward corresponds to visual stimuli less attractive to naive flower visitors. Reciprocal colour changes were not observed. It is to be assumed that the unidirectionality of floral colour changes is an adaptation of angiosperms aimed at the guidance of first-time flower visitors. Signalling reward to inexperienced flower visitors is an additional function of floral colour changes. The main function of floral colour changes, however, is to provide cues with which the flower visitors can learn to associate one colour phase with reward.

EFFECT OF FLORAL BUD REDUCTION ON INDIVIDUAL FLOWER LONGEVITY IN ASIATIC HYBRID LILIES

Floral bud abortion was found to be an undesirable source of non-genetic variation in breeding trials directed on the improvement of individual flower longevity in Asiatic hybrid lilies. It increased the longevity of the remaining flowers of the inflorescence. A similar response was found after elimination of developing terminal flower buds by hand, which significantly increased the longevity of the remaining flowers in inflorescences of eight of the eleven Asiatic hybrid lilies studied. The response to bud reduction was independent of the original flower longevity, so ranking of the cultivars based on longevity values will change due to bud abortion and selection results will be disturbed. Preharvest and postharvest influences of bud removal on flower longevity were distinguished by comparing longevities of undetached and detached flowers within four cultivars. Our data suggest that the increase in flower longevity of the remaining flowers after bud removal was mainly attributed to a decrease in sink strength within the harvested inflorescence. In two of the four cultivars tested the increase in flower longevity was partly caused during cultivation and was accompanied by an increase in methanol soluble sugar content in the flower petals at harvest. Bud opening and flower longevity were not significantly influenced by defoliation after harvest, indicating that within lily inflorescences translocation of metabolites mainly takes place between developing flower buds. Flower longevity and carbohydrate content in open flowers at harvest did not correspond between the two cultivars studied probably due to differences in developmental stage of the other flower buds of the inflorescence and, therefore, sink strength.

From pollination byLepidoptera to selfing: The case ofDianthus glacialis (Caryophyllaceae)

Pollination of the alpine herbDianthus glacialis was studied in a population in the Swiss Alps in 1991 and 1992. Only one insect species,Zygaena exulans (Lepidoptera), was observed to visit the flowers ofD. glacialis. Pollen loads onZ. exulans indicate that it is an effective pollinator ofD. glacialis. In 1991,Z. exulans frequently visited flowers ofD. glacialis. However, in 1992 almost no visits could be observed. Despite the occurrence of pollinators and the conspicuous flowers ofD. glacialis, there are strong indications that this plant is mainly selfing: (1) anthesis of individual flowers is short (c. one and a half days), (2) protandry, although pronounced in otherDianthus spp., is absent, (3) nectar production is low, (4) odour production is weak, (5) seed production by spontaneous selfing is high, (6) seed set in emasculated flowers is extremely low and (7) the seed/ovule ratio is distinctly higher inD. glacialis than in outcrossing plants.—Selfing inD. glacialis could have evolved under a shortage of pollinators during the glaciation periods. Present levels of cross-pollination byZ. exulans have apparently not been sufficient to reverse the pollination mechanism ofD. glacialis from selfing to outcrossing.

Pollination Ecophysiology of Mercurialis annua L. (Euphorbiaceae), an Anemophilous Species Flowering all Year Round

Mercurialis annua L. is a dioecious anemophilous species that flowers all year round in central and southern Italy. The flowers of both sexes are dimorphic: the female flower has a vestigial calyx; the male flower consists only of a calyx that opens at anthesis. The anthers always dehisce after anthesis. The anthesis of male flowers seems to be temperature dependent, whereas anther dehiscence is related to relative humidity. The pollen grains vary in volume according to the season: they are smaller when relative humidity is low and vice versa. They always decrease in volume after anther dehiscence and have the capacity to vary in volume and reach equilibrium with a changing environment. Viability is high, but may drop suddenly during heavy rain or hail that damage the exposed male flowers. The number of pollen grains per stigma varies from 0 to 300. The data is discussed in relation to the type of pollination and environmental characteristics.

Interaction of Bulb Vernalization and Shoot Photoperiod on `Nellie White' Easter Lily

Easter lily (Lilium longiflorum Thunb. `Nellie White') bulbs were exposed to 1, 2, 3, 4, 5, or 6 weeks of cold before shoot emergence; 0, 1, 2, 3, 4, 5, or 6 weeks of long days (LD) upon shoot emergence; or a combination of cold followed by LD: 1/5 (weeks cold/weeks LD), 2/4,3/3,4/2, or 5/1. Experiments were repeated for three consecutive years. LD did not substitute equally for cold; at least 3 weeks of cold were required before LD treatments resulted in anthesis. Depending on the year, 100% of the plants flowered when treated with 3 to 6 weeks of cold alone or in combination with LD. Days to first flower anthesis from planting increased with decreasing weeks of cold in years 1 and 3, but was similar for all treatments in year 2. Decreasing weeks of cold in combination with LD, however, decreased days to anthesis in years 1 and 2, but had no effect in year 3. Regardless of LD, days from emergence to visible bud increased with decreasing weeks of cold in all years, and days to emergence from placement in the greenhouse increased with decreasing cold in years 1 and 3, but not in year 2. Increasing weeks of cold, regardless of LD, decreased leaf count, but had no effect on plant height. Flower count was unaffected by cold when combined with LD, but was significantly reduced by increasing weeks of cold.

Year-to-year variation in the developmental stage of the embryo sac at anthesis in flowers of apricot (Prunus armeniacaL.)

SummaryExamination over several years of the stage of development of ovules at anthesis in eight cultivars of apricot reveals that, in the mild Mediterranean climate of Murcia, ovules are late in developing in comparison with other species. Frequently, ovules were found where there was no sign of the embyro sac. Sacs with two or four nuclei are very scarce and ovules with the egg cell differentiated were hardly found. Although flowers were collected at the same external stage of development, there were substantial differences in the degree of embryo sac development.