The effect of temperature on the duration of the effective pollination period in ‘Oblica’ olive (Olea europaea) cultivar

The effective pollination period (EPP) was determined for ‘Oblica’ olive trees in response to sequential pollinations at anthesis and at increasing days after. The role played by each of three components of the EPP, namely the stigmatic receptivity, pollen tube growth and ovule longevity was examined and the duration of the EPP under different environmental conditions was calculated. An increase in temperature in the field was caused by enclosing bearing trees within polyethylene cages. The duration of the EPP varied between years and environmental conditions. Initial fruit set (IFS) declined gradually in response to sequential cross‐pollination. The significant decrease with respect to the maximum levels of IFS occurred 5 days after anthesis (DAA) in 2007 and between 4 and 5 DAA in 2010 at both environmental conditions. However, the fruit set decrease with sequential pollinations was sharper for the trees inside the cages than for trees growing at the open air, suggesting that high temperatures induce earlier and more pronounced decrease in flower fertility. The stigma receptivity was quite extended decreasing slowly with time. In 2010, the stigma receptivity was prolonged beyond sampling date (7 DAA) in both environmental conditions. Stigmas first lost the capacity to support pollen germination and later their capacity to adhere pollen grains. Pollen tube growth occurred rapidly and fertilization took place 1 or 2 days after pollination. Cross‐pollination resulted with higher fertilization levels, whereas fertilization was reduced and delayed under self‐pollination. Enclosing the trees within the cages had small effect on cross‐pollination but impaired the self‐pollination which resulted with reduced levels of fertilization. The ovule longevity was prolonged beyond the end of sampling in both years and conditions (beyond 9 DAA in 2009 or 7 DAA in 2010). Discrepancy between the estimates of the duration of the EPP based on analyses of its components and those indicated by the declines in fruit set from delayed pollination suggests that a different component of the pistil, the style, could have the critical role in determining the duration of the EPP.     

The self-incompatibility mating system of the olive (Olea europaea L.) functions with dominance between S-alleles

The self-incompatibility type is of key importance to understanding pollination in orchards, because most olive cultivars are partially self-incompatible and thus require pollinizers to ensure fruit set. The gametophytic model has been advocated to function in the olive, but no allele pair has been attributed to any variety. The GSI model failed in most combinations to explain fruit set. Olive growers must screen experimentally and empirically to look for inter-compatible pair-wise combinations of varieties for optimum pollination. The sporophytic model, with given dominance relationships for six S-alleles matches 98 % of the experimental data of the two sets investigated. We propose a method to analyze data from controlled crosses between olive cultivars applied to two experiments for varieties crossed in a diallel design. Furthermore, the dominance between the S-allele pair allows rational prediction of olive variety self-incompatibility levels. The S-allele pairs were unraveled for more than 60 cultivars. To go further, crosses between reference varieties—those in which the S-allele pair was unraveled—and varieties under experimentation (VarE) with an unknown S-allele pair will enable an increase in knowledge and the choice of the best pollinizers in silico. Nevertheless, we pose outstanding questions in orchards where open-pollination efficiency with varieties harboring the R2R3, R1R3, R1R5, or R3R5 pairs. These S-allele pairs require pollen grains without R2 or R3 , R1 or R3, and R3 or R5 determinants. Such pollinizer varieties are not abundant in France and Italy, and this questions whether their spread is sufficient for optimal pollination of main varieties.     

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

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

     

Effect of pollination intensity on fruit and seed set in cacao (Theobroma cacao L.)

We studied the functional relationship between pollination intensity and fruit survival as well as the number of seeds per pod in the tropical tree Theobroma cacao L. on a Forastero Upper-Amazon clone (UPA 409) in Ivory Coast. Cutting the style 24 h after pollination allowed for counting the number of pollen grains deposited on a stigma without affecting fruit set and seed development. Forty-three pollen grains were necessary to reach 50% of maximum fruit set 28 days after pollination. Above 115 pollen grains, the proportion of developing ovaries reached a maximum of 88% 28 days after pollination and 75% at maturity. With fewer than 238 pollen grains per stigma, there was a close relationship between pollination intensity and number of seeds per pod; the pollenseed ratio increased from 1.61 to 3.81 for PI increasing from 30 to 238 pollen grains. For higher pollination intensities, the average number of seeds per pod reached a maximum of 58. The relationship between pollination intensity and seed content was modelled. Results are consistent with the hypothesis that ovules attracted pollen tubes in a similar way regardless of whether or not they had already been reached by another pollen tube.     

The breeding system of Lycium cestroides: a Solanaceae with ovarian self-incompatibility

To determine the breeding system of Lycium cestroides,several treatments were performed: self-, cross-, and geitonogamous pollinations, autonomous self-pollination, and a control (flowers exposed to natural pollinators). Production and quality of fruits and seeds as well as pollen tube growth were evaluated for each treatment. Experimental pollinations indicate that L. cestroides is self-incompatible since fruits were obtained only under cross-, and open-pollination treatments. However, in self- and geitonogamous hand pollinations, as well as in autonomous self-pollination, pollen tubes developed successfully and reached the ovules. The speed of pollen tube growth did not differ significantly among the different hand-pollinated flowers (cross-, self-, and geitonogamous). These facts indicate the presence of an ovarian self-incompatibility system. Significant differences were observed in fruit set, fruit size, and seed number per fruit between cross-pollinated flowers and open pollination (control). These results could be explained in terms of quantity and quality of pollination in each case. Received: 2 November 2000 / Revision accepted: 26 January 2001     

Test-tube fertilization inNicotiana tabacum by means of an artificial pollen tube culture

Three techniques of the test-tube fertilization by means of an artificial pollen tube culture are described. The essentials for each individual method are:

1. Transfer of pollen tubes from the sugar solution onto the placentae in the test tube.
2. Placing the placentae with ovules onto pollen tube culture.
3. Precultivation of pollen tubes on small cellophane squares placed on the surface of a semi-liquid medium and transfer of cellophane squares along with the pollen culture to the solid medium, over which finally the placentae with ovules are placed.

By means of all the three techniques viable seeds were obtained in vitro. In an artificial medium pollen tubes are able to maintain their fertilizing ability even after the 24 hours cultivation, i.e. at the time after the formation of the gametes.     

Asymmetrical conspecific seed-siring advantage between Silene latifolia and S. dioica

Background and Aims

Silene dioica and S. latifolia experience only limited introgression despite overlapping flowering phenologies, geographical distributions, and some pollinator sharing. Conspecific pollen precedence and other reproductive barriers operating between pollination and seed germination may limit hybridization. This study investigates whether barriers at this stage contribute to reproductive isolation between these species and, if so, which mechanisms are responsible.

Methods

Pollen-tube lengths for pollen of both species in styles of both species were compared. Additionally, both species were pollinated with majority S. latifolia and majority S. dioica pollen mixes; then seed set, seed germination rates and hybridity of the resulting seedlings were determined using species-specific molecular markers.

Key Results

The longest pollen tubes were significantly longer for conspecific than heterospecific pollen in both species, indicating conspecific pollen precedence. Seed set but not seed germination was lower for flowers pollinated with pure heterospecific versus pure conspecific pollen. Mixed-species pollinations resulted in disproportionately high representation of nonhybrid offspring for pollinations of S. latifolia but not S. dioica flowers.

Conclusions

The finding of conspecific pollen precedence for pollen-tube growth but not seed siring in S. dioica flowers may be explained by variation in pollen-tube growth rates, either at different locations in the style or between leading and trailing pollen tubes. Additionally, this study finds a barrier to hybridization operating between pollination and seed germination against S. dioica but not S. latifolia pollen. The results are consistent with the underlying cause of this barrier being attrition of S. dioica pollen tubes or reduced success of heterospecifically fertilized ovules, rather than time-variant mechanisms. Post-pollination, pre-germination barriers to hybridization thus play a partial role in limiting introgression between these species.     

Seed germination patterns of Salvia mellifera in fire-prone environments

Summary I examined the effects of pollen loads containing pollen from one, three and five donors on fruit production and fruit quality in Campsis radicans. Number of pollen donors had no significant effect on % fruit production, seed number, seed weight or seed germination. In singledonor pollinations the identity of the donor did have a strong effect on the above parameters. Furthermore, the best single donor sired fruits with more seeds and heavier seeds than any mixture containing this donor. This pattern indicates interference of pollens or preemption of some ovules by the inferior pollen. In Campsis, therefore, the number of pollen donors contributing to a pollen load is less important than the identity of these donors in determining fruit production and fruit quality. Seeds from fruits resulting from mixed pollination were slightly more variable than seeds from fruits resulting from single-donor pollinations.     

l-Ascorbic acid metabolism in parthenocarpic and seeded cherry tomatoes

The auxin treatment in tomato plants during anthesis has been extensively used for setting fruits in adverse climatic conditions (e.g., low temperatures and inadequate light), which is well known that reduces pollen availability and fertility. Since auxin application may affect fruit composition and quality, we examined l-ascorbic acid metabolism in seeded fruit (set by natural pollination) and parthenocarpic fruit (set by auxin) in cherry tomato cv. Conchita. Specifically, we studied the oxidized and total ascorbic acid contents, the expression of all characterized genes of l-ascorbic acid metabolism, the activity of ascorbate peroxidase and dehydroascorbate reductase and the immunolocalization of ascorbate peroxidase. Differences were detected between seeded and parthenocarpic fruits, in the expression of some of the genes of ascorbic acid metabolism. However, strong presence of l-ascorbic acid peroxidase protein was detected on the developing seeds. Our data indicate that induced parthenocarpy in auxin treated plants has a significant influence in ascorbic acid metabolism comparing to seeded tomato fruits.     

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

Background and Aims

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

Methods

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

Key Results

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

Conclusions

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

Ant pollination of <Emphasis Type="Italic">Syzygium occidentale</Emphasis>, an endemic tree species of tropical rain forests of the Western Ghats,India

Although mutualism between ants and flowering plants is wide spread, ant pollination has not evolved as a major pollination syndrome. So far ant pollination has been reported largely in herbaceous species, growing in warm and dry habitats. While studying pollination ecology of Syzygium species (Myrtaceae), growing in tropical forests of the Western Ghats, India, we observed one of the ant species, Technomyrmex albipes, to be the dominant floral visitor in S. occidentale (Bourd.) Chithra among a range of other insect (species of Xylocopa and Trigona, and Apis cerana) and bird visitors. We studied the role of ant species in pollination when compared to other floral visitors. The fruit set in flowers exclusively visited by T. albipes was significantly higher than those visited by any other visitor. The day and night exclusive pollination experiments allowing only T. albipes indicated diel pollination by T. albipes, which was the only active flower visitor during the night. The breeding system of the species was studied through controlled pollinations. The species is partially self-compatible and exhibits considerable autogamy.     

Hanging by a coastal strand: breeding system of a federally endangered morning-glory of the south-eastern Florida coast, Jacquemontia reclinata

Background and Aims

Coastal development has led to extensive habitat destruction and the near extinction of the beach clustervine, Jacquemontia reclinata (Convolvulaceae), an endangered, perennial vine endemic to dune and coastal strand communities in south-eastern Florida. We examined the breeding system of this rare species, and observed visitors to its flowers, as part of a larger effort to document its status and facilitate its recovery.

Methods

Reproductively mature experimental plants were grown from seed collected from wild plants in two of the largest remaining populations. Controlled hand pollinations on potted plants were conducted to determine the level of compatibility of the species and to investigate compatibility within and between populations. Seeds from the hand pollinations were planted in soil, and they were monitored individually, recording time to seed germination (cotyledon emergence). Wild plants were observed in several of the remaining populations to determine which species visited the flowers.

Key Results

Hand pollination and seed planting experiments indicate that J. reclinata has a mixed mating system: flowers are able to set fruit with viable seeds with self-pollen, but outcross pollen produces significantly greater fruit and seed set than self-pollen (≥50 % for crosses vs. <25 % for self-pollinations). Visitors included a wide array of insect species, primarily of the orders Diptera, Hymenoptera and Lepidoptera. All visitors captured and examined carried J. reclinata pollen, and usually several other types of pollen.

Conclusions

Remnant populations of beach clustervine will have greater reproductive success not only if floral visitor populations are maintained, but also if movement of either pollen or seed takes place between populations. Restoration efforts should include provisions for the establishment and maintenance of pollinator populations.Key words: Breeding system, conservation, beach clustervine, Jacquemontia reclinata, Convolvulaceae, endangered species, floral visitors, coastal dunes, pollination, reproductive biology, Florida, Caribbean, bees, butterflies     

Effect of parthenocarpy on ovule development in cucumber (Cucumis sativus L.) after pollination with normal and irradiated pollen

In nonparthenocarpic cucumber, analysis of the interaction between season and female receptivity demonstrated two different modes of fruit development and seed set. Spring climatic conditions induced significantly longer ovaries at anthesis with an autonomous fruit set as in natural parthenocarpy. Autumn climatic conditions induced smaller ovaries with fruit set influenced by the pollination stage of the female flower. These differences involve, during fruit development, a regulation of the empty seed number especially at both ends of female receptivity period. Indeed, seasons have no effect on ovule receptivity and fertility measured by full seed number. It is supposed that priority is given to seeds with an embryo in the competition for limited maternal resources in spring as well as in autumn. In spring, the use of irradiated pollen during the whole female receptivity period did not modify the seed set profile. Moreover, a cytological study of 6-day-old ovules pollinated by irradiated pollen has revealed a similar precocious embryogenesis compared to the control. In cucumber, pollination with irradiated pollen involves stenospermocarpy rather than induced parthenocarpy. However, we have not been able to determine whether the early abortive embryogenesis induced by irradiated pollen is gynogenetic or abnormal zygotic.     

Pollen Viability and Pollen-tube Growth Following Controlled Pollination and their Relation to Low Fruit Production in Teak (Tectona grandisLinn. f.)

Pollen released at 1100 h has the highest viability (92.2%)but is no longer viable 3 d (84 h) after anthesis.In vitropollen-tubegrowth is fast (140 µm h^-1) and increases significantlywithin the first 8 h.In vivopollen tubes also grow quickly andreach the base of the style within 2 h after pollination andenter the micropyle 8 h after pollination. There is no significantdifference between self- and cross-pollination in either therate and the number of pollen tubes in the pistil and the numberof ovules penetrated by a pollen tube. Teak has late-actinggametophytic self-incompatibility; the majority of pollen tubesgrow through the style but some do not continue to grow fromthe style towards the embryo sacs. Pollen-tube abnormalitiesinclude swollen, reversed, forked and tapered tips and irregularand spiralling tubes. These are most prevalent in self-pollination(20.4%). The index of self-incompatibility of 0.17 and low fruitset following self-pollination (2.49%) indicates that teak ismostly self-incompatible. Drastic fruit abortion occurs withinthe first week following controlled pollination. Within 14 d,fruit size and fruit set from cross-pollination is generallymuch greater than from self-pollination. Tectona grandis; pollen viability; pollen-tube growth; pollination; controlled pollinations; incompatibility.     

Disruption of endosperm development: an inbreeding effect in almond (Prunus dulcis)

A homozygous self-compatible almond, originated from self-fertilization of a self-compatible genotype and producing a reasonable yield following open pollination, exhibited a very high fruit drop rate when self-pollinated. To investigate whether fruit dropping in this individual is related to an abnormal development of the embryo sac following self-fertilization, histological sections of ovaries from self and cross-pollinated flowers were observed by light microscopy. Additionally, the presence of pollen tubes in the ovary and fruit set were determined for both types of pollination. Despite pollen tubes reached the ovary after both pollinations, differences in embryo sac and endosperm development after fertilization were found. Thus, while for cross-fertilized ovules a pro-embryo and an endosperm with abundant nuclei were generally observed, most self-fertilized ovules remained in a previous developmental stage in which the embryo sac was not elongated and endosperm nuclei were absent. Although 30 days after pollination fruit set was similar for both pollination types, at 60 days it was significantly reduced for self-pollination. These results provide evidence that the high fruit drop in this genotype is the consequence of a disrupted development of the endosperm, what could be an expression of its high level of inbreeding.     

Pollination and late-acting self-incompatibility in Cyrtanthus breviflorus (Amaryllidaceae): implications for seed production

Background and Aims

Animal pollination is typically an uncertain process that interacts with self-incompatibility status to determine reproductive success. Seed set is often pollen-limited, but species with late-acting self-incompatibility (SI) may be particularly vulnerable, if self-pollen deposition results in ovule discounting. Pollination is examined and the occurrence of late-acting SI and ovule discounting assessed in Cyrtanthus breviflorus.

Methods

The pollination system was characterized by observing floral visitors and assessing nectar production and spectral reflectance of flowers. To assess late-acting SI and ovule discounting, growth of self- and cross-pollen tubes, and seed set following open pollination or hand pollination with varying proportions of self- and cross-pollen, were examined.

Key Results

Native honeybees Apis mellifera scutellata pollinated flowers as they actively collected pollen. Most flowers (≥70 %) did not contain nectar, while the rest produced minute volumes of dilute nectar. The flowers which are yellow to humans are visually conspicuous to bees with a strong contrast between UV-reflecting tepals and UV-absorbing anthers and pollen. Plants were self-incompatible, but self-rejection was late-acting and both self- and cross-pollen tubes penetrated ovules. Seed set of open-pollinated flowers was pollen-limited, despite pollen deposition exceeding ovule number by 6-fold. Open-pollinated seed set was similar to that of the cross + self-pollen treatment, but was less than that of the cross-pollen-only treatment.

Conclusions

Flowers of C. breviflorus are pollinated primarily by pollen-collecting bees and possess a late-acting SI system, previously unknown in this clade of the Amaryllidaceae. Pollinators of C. breviflorus deposit mixtures of cross- and self-pollen and, because SI is late-acting, self-pollen disables ovules, reducing female fertility. This study thus contributes to growing evidence that seed production in plants with late-acting SI systems is frequently limited by pollen quality, even when pollinators are abundant.     

Influence of environmental variation on the pollination of the ambophilous sedge <Emphasis Type="Italic">Rhynchospora ciliata</Emphasis> (Cyperaceae)

In typically anemophilous families, there are species, such as Rhynchospora ciliata (Cyperaceae), in which both wind and insects have been registered as pollen vectors (ambophily). However, the contribution of each vector to pollination of ambophilous species can change under different environmental conditions. Therefore, this study aimed to determine the primary pollination system, abiotic or biotic, of R. ciliata, comparing wet and dry seasons. We tested the following hypotheses: (1) in dry months, wind is the main pollen vector of R. ciliata; (2) in wet months, insects will contribute more to the reproductive success of R. ciliata and compensate for low fruit formation by the abiotic vector. Our hypothesis was not confirmed. We found that higher wind speed can favor pollination by wind in R. ciliata even in wetter months. Because insects were less susceptible to environmental variation, they contributed more in dry months when wind speed was low, thus compensating for lower fruit set by wind. High rainfall and humidity can result in faster settling of pollen grains suspended in the air; however, rainfall does not prevent pollination by wind. Since individuals of R. ciliata are located near the edge of the forest, grouped quite close together, and as the inflorescence is located at the apex of the floral scape, wind can act as pollen vector and the inhibiting effects of rainfall can be minimized. The contribution of each pollen vector is important to the reproductive success of R. ciliata and the effectiveness of wind varies with local environmental conditions.     

Reproductive biology of Azadirachta indica (Meliaceae), a medicinal tree species from arid zones

Neem or the Margosa tree, Azadirachta indica (Meliaceae), is a versatile tree species common in arid zones. We investigated the reproductive biology of Neem, including phenology, floral biology, pollination ecology and the breeding system, in three natural populations in northern India. Phenological observations established that trees within a population flowered synchronously, but populations varied in the time of onset of flowering; a few trees flowered twice a year. An inflorescence bears ～ 91 bisexual, white and sweet‐scented flowers. The stigma consists of a non‐receptive apical region and a subjacent rim of receptive surface; papillae on the two regions differ in their morphology and function. The occurrence of natural pollination both by wind and insects indicates ambophily. Insect pollinators were predominantly represented by Hymenoptera and Lepidoptera; Apis spp. were the most effective pollinators. Although the occurrence of incomplete dichogamy and a pollen : ovule ratio of ～ 627 indicates the possibility of autogamy, supplemental pollinations clearly established that the trees were 100% self‐incompatible and incompatibility is regulated at the gametophytic level. Natural fruit set was low (～ 5%) and hand cross‐pollinations increased the fruit set to ～ 19%. Our study demonstrated that natural fruit set in Neem is possibly limited by insufficient amounts of xenogamous pollination and resources.     

Effect of three pollination methods on embryo development and seedset in intra- and interspecific crosses between seven Lilium species

Summary Interspecific crosses were made between seven Lilium species, viz. L. candidum, L. concolor, L. dauricum, L. henryi, L. longiflorum, L. nepalense and L. rubellum. A complete diallel cross was carried out between these seven species, including self- and intraspecific pollinations using three pollination methods: normal pollination on the stigma, pollination on the ovary after cutting the style, and pollination on the stigma with the aid of mentor (non-functional, compatible) pollen. Embryo rescue, starting 35 days after pollination, was applied to all interspecific combinations. The percentage of successful crosses was about 2.8% after normal pollination, 5.4% after cut-style pollination and 3.8% with the mentor pollen technique. Crosses with L. nepalense were exceptional in that embryos died during the embryo culture phase. Seventeen cross combinations (including 4 reciprocals) yielded 62 embryo plantlets from 839 interspecific pollinations.     

The relative importance of architecture and resource competition in allocation to pollen and ovule number within inflorescences of Hosta ventricosa varies with the resource pools

Background and Aims

Allocation of resources to floral traits often declines distally within inflorescences in flowering plants. Architecture and resource competition have been proposed as underlying mechanisms. The aim of the present study is to assess the relative importance of resource competition and architectural effects in pollen and ovule production on racemes of Hosta ventricosa, an apomictic perennial herb.

Methods

Combinations of two defoliation treatments (intact and defoliated) and two fruit-set treatments (no-fruit and fruit) were created, and the roles of architecture and resource competition at each resource level were assessed.

Key Results

Pollen and ovule number per flower increased after defoliation, but pollen to ovule ratio per flower did not change. Pollen, ovules and the pollen to ovule ratio per flower declined distally on racemes at each resource level. In the intact treatment, fruit development of early flowers did not affect either pollen or ovule number of late flowers. In the defoliated treatment, fruit development of early flowers reduced both pollen and ovule numbers of late flowers due to over-compensation caused by defoliation. Late flowers on defoliated fruit racemes produced less pollen than intact fruit racemes but the same number of ovules; therefore, the reduction in pollen number was not caused by over-compensation. In addition, the fruit-set rate of early flowers during flowering was higher in intact racemes than in defoliated racemes.

Conclusions

In flowering plants, the relative importance of architecture and resource competition in allocation to pollen and ovules may vary with the resource pools or the overall resource availability of maternal plants.