Fruit-set Success Research Articles

The selective advantage of mast flowering in Veratrum album subsp. oxysepalum: Implications of the predator satiation hypothesis.

Synchronous, highly variable flower or seed production among years within a population (i.e., masting) has been reported in numerous perennial plants. Although masting provides ecological advantages such as enhancing pollination efficiency and/or escape from predator attack, little is known about the degree of these advantages and variations in masting behavior among populations of conspecific plants. We determined flowering ramet density and reproductive success (fruit-set success and herbivorous damage) of a perennial herb, Veratrum album subsp. oxysepalum, across six lowland and six alpine populations in northern Japan during 2-3 years. We then analyzed the relationship between floral density and reproductive success to assess the ecological significance of mast flowering. Flowering intervals of individual plants were estimated by counting annual scars on rhizomes. Most populations had mast flowering, but the intervals between flowering for individual plants were shorter in the alpine populations than in the lowland populations. Floral damage by stem borers (dipteran larvae) and seed predation by lepidopteran larvae were intense in the lowland populations. Seed production of individual ramets increased with higher floral density owing to the effective avoidance of floral-stem damage and seed predation. Although stem borers were absent in the alpine habitat, seed predation decreased with higher floral density also in the alpine populations. Pollination success was independent of floral density in both of the alpine and lowland populations. These results strongly support the predator satiation hypothesis for mast flowering by this species.

Sexual compatibility in cacao clones drives arrangements in the field leading to high yield

Sexual self-incompatibility is a very salient trait of woody plants, including cacao (Theobroma cacao L.). In this species, most commercial clones are self-incompatible and, therefore, productivity depends on pollen flow for fruit formation due to the combinatorial ability of each clone to accept or reject pollen tubes in the embryo sac. To determine the combinatorial ability of commercial cacao clones, artificial (manual) pollinations were performed between cacao clones of the same and between groups for three years. In total, 46 cacao clones of five geographical groups were evaluated: ‘FHIA’ from Honduras, ‘ICS’ from Trinidad and Tobago, ‘UF’ from Costa Rica, ‘CAUCASIA’ from Colombia, and ‘EET’ from Ecuador. The results showed that, except for ‘CAUCASIA’, there is a high level of inter-compatibility between groups. Cacao clones exceed the established threshold of 30% in Fruit Set Success when used as a female or a male donor. As expected, low self-compatibility rates were found among the clones studied. We propose the use of sexual inter-compatibility information for the design of planting arrangements to maximize cacao yields.

Is increased male flower production a strategy for avoidance of predispersal seed predation in andromonoecious plants?

Floral gender in angiosperms often varies within and among populations. We conducted a field survey to test how predispersal seed predation affects sex allocation in an andromonoecious alpine herb Peucedanum multivittatum. We compared plant size, male and perfect flower production, fruit set, and seed predation rate over three years among nine populations inhabiting diverse snowmelt conditions in alpine meadows. Flowering period of individual populations varied from mid‐July to late August reflecting the snowmelt time. Although perfect flower and fruit productions increased with plant size, size dependency of male flower production was less clear. The number of male flowers was larger in the early‐flowering populations, while the number of perfect flowers increased in the late‐flowering populations. Thus, male‐biased sex allocation was common in the early‐flowering populations. Fruit‐set rates varied among populations and between years, irrespective of flowering period. Fruit‐set success of individual plants increased with perfect flower number, but independent of male flower number. Seed predation by lepidopteran larvae was intense in the early‐flowering populations, whereas predation damage was absent in the late‐flowering populations, reflecting the extent of phenological matching between flowering time of host plants and oviposition period of predator moths. Seed predation rate was independent of male and perfect flower numbers of individual plants. Thus, seed predation is a stochastic event in each population. There was a clear correlation between the proportion of male flowers and the intensity of seed predation among populations. These results suggest that male‐biased sex allocation could be a strategy to reduce seed predation damage but maintain the effort as a pollen donor under intensive seed predation.

Seasonal variation in air temperature drives reproductive phenology of entomophilous plants in a cool-temperate mire community

Phenological responses of plants to temperature dynamics are receiving attention due to the ongoing challenge with climate change. Most previous phenological studies have focused on flowering phenology rather than fruiting phenology. However, at mid-latitudes, the air temperature periodically changes during the growing period of plants. Hence, cool temperatures early and late in the growing period may affect reproductive success through pollination and fruit-development processes. To evaluate the linkages between reproductive phenology and success, we compared the phenologies, photosynthetic capacities, and fruit-set rates among 25 species within a cool-temperate community in northern Japan. The ambient temperature during the flowering periods of individual species increased with delays in flowering-onset time, whereas the ambient temperature during fruit-development periods was highest for species which bloomed in July. Fruit-set success among species was positively correlated with the ambient temperatures during the reproductive periods and with the photosynthetic capacity. Fruit production of early blooming species was limited by cool temperatures during the flowering period, presumably because of low pollinator activity, whereas that of late-blooming species was limited by cool temperatures during the fruit-development period because of slow fruit-development (i.e., sink limitation). Thus, limiting factors of fruit production varied depending on the flowering phenology of individual species within a community.

Habitat-specific effects of flowering advance on fruit-set success of alpine plants: a long-term record of flowering phenology and fruit-set success of Rhododendron aureum

Global warming tends to accelerate flowering phenology of alpine plants, and it may cause a decrease in fruit production due to lower pollinator activity and/or higher risk of frost damage earlier in the season. Because flowering period of alpine plants varies highly depending on snowmelt conditions, the effects of phenological variation on fruit-set success may vary among local populations. I observed the relationship between flowering time and fruit-set success in four populations of a bee-pollinated dwarf shrub, Rhododendron aureum, located in fellfield and snowbed habitats in northern Japan, for 12 or 13 years over the 25 years from 1995 to 2019. Flowering of the fellfield populations usually occurred in June, and flowering of the snowbed populations commonly started after mid-July, although there was considerable yearly variation in actual flowering time within individual populations. Generally, the fruit-set rates of the fellfield populations were low, with large yearly fluctuations, whereas those of the snowbed populations were stable and high. There was a clear trend toward a decrease in fruit-set rates with earlier flowering in the fellfield populations due to pollen limitation and occasional frost damage. The risk of frost damage increased with earlier flowering in the fellfield habitat. These results indicate that the effects of climate change on fruit-set success of alpine plants are strongly site-specific and are greatest early in the growing season.

Ecological factors affecting the fitness of the threatened orchid Anacamptis robusta (Orchidaceae): Habitat disturbance, interactions with a co-flowering rewarding orchid and hybridization events.

The food-deceptive species Anacamptis robusta is threatened in the Balearic Islands, and its habitat has recently been transformed through human disturbance. This study investigated how human disturbance affects the reproductive output of A. robusta and how its fitness is affected by competition with rewarding relatives, fungal infections and hybridization processes. To evaluate the impact of habitat loss on plant fitness, data on reproductive measures were obtained in two well-conserved subpopulations and the unique disturbed subpopulation. Photo-trapping cameras were installed to determine the floral visitation rate. All flowering individuals in 2019 were georeferenced using differential GPS to examine the influence of geospatial patterns on the reproductive success of A. robusta. In addition, hand-pollination treatments were performed to evaluate the hybridization between A. coriophora and A. robusta and the origin of A.×albuferensis. The human-disturbed subpopulation of A. robusta had a lower fruit set success than the subpopulations in well-conserved areas. The presence of A. coriophora is negatively affecting the reproductive output of A. robusta. Moreover, A. robusta can only act as the pollen donor during hybridization. The complexity of the ecological system, which is enhanced by the strong pollinator dependence of the threatened species, must be considered when making conservation decisions. Although human disturbance directly affects plant population stability, other ecological issues must be considered, such as pollinator interaction, interspecific competition for pollinators, fungal infection and hybridization events.

Genetic Resources of Olea europaea L. in the Garda Trentino Olive Groves Revealed by Ancient Trees Genotyping and Parentage Analysis of Drupe Embryos

The area of the Garda Lake within the Trentino province (north of Italy) is the northernmost part of Europe where the Mediterranean species Olea europaea L. is traditionally cultivated. ‘Casaliva’ is claimed as the main variety traditionally grown in the Garda Trentino area (GT) from which a world renowned niche extra virgin olive oil is produced. Since a dominant presence of ‘Casaliva’ would link the fruit set success and yield to a self-pollination compatibility system, a deep genetic survey of the olive tree population in the GT has been performed with the aim of establishing the actual varietal composition and of understanding from which pollen donor the ‘Casaliva’ olives originate. Forty-four different genetic profiles were observed among the 205 leaf samples collected from 106 ancient trees through the analysis of 20 nuclear microsatellite markers. The varietal composition in modern orchards was also explored and the vast majority of the additional 151 trees analyzed showed the same genotype as the ancient accessions of ‘Casaliva’. The results support the long historical link of ‘Casaliva’ with the GT and, besides a high varietal homogeneity, they also revealed the presence of olive genetic resources essential to fruit production. In fact, the parentage analysis of 550 embryos from drupes of ‘Casaliva’ evidenced that a cross-fertilization system is favored and a list of candidate cultivars most suitable as local pollinizers of ‘Casaliva’ was identified.

Geographical distribution, genetic diversity, and reproductive traits of mixed polyploid populations in Parasenecio kamtschaticus (Senecioneae; Asteraceae)

In order to clarify the genetic differentiation and reproductive traits of mixed polyploid populations in Parasenecio kamtschaticus complex, geographical distribution, genetic diversity, and reproductive performance were compared among three intraspecific types composed of two cytotypes and two varieties in Japan. Diploid P. kamtschaticus var. kamtschaticus (2×-kamtschaticus) was distributed at the center of the distribution range, tetraploid P. kamtschaticus var. kamtschaticus (4×-kamtschaticus) existed widely throughout the entire range, and tetraploid P. kamtschaticus var. bulbifera (4×-bulbifera), producing bulbils, was restricted to higher elevations. Genetic structure was analyzed using allozyme markers. The genetic diversity of 4×-kamtschaticus was higher than that of 2×-kamtschaticus, with that of 4×-bulbifera being intermediate. Populations of 4×-bulbifera and 2×-kamtschaticus were genetically discriminable from each other in principle coordinate analysis, and the genetic structure of 4×-kamtschaticus populations largely overlapped with those of the other types. Flower and achene production levels were highest in the 4×-kamtschaticus populations and lowest in the 4×-bulbifera populations. Germination activity of achenes was highest in the 2×-kamtschaticus populations and lowest in the 4×-bulbifera populations. Fruit-set success of 4×-bulbifera decreased with elevation because of a shorter growing season, indicating the importance of vegetative reproduction by bulbils at higher elevations. Unexpectedly, the inbreeding coefficients of the 4×-bulbifera populations were the lowest among the three types. Occasional achene production by outcrossing might maintain the high genetic diversity of the 4×-bulbifera populations. The evolution of polyploidy and subsequent bulbil production might enable P. kamtschaticus to disperse a wider range of environmental conditions.

A linkage between flowering phenology and fruit-set success of alpine plant communities with reference to the seasonality and pollination effectiveness of bees and flies.

To clarify the linkage between flowering phenology and pollination success in alpine plant communities, we quantified the seasonality of flower visitors, the temporal transition of floral resources, and the variation in pollination success of alpine plants in northern Japan. Bumble bees, syrphid flies, and non-syrphid flies were the predominant flower visitors. Foraging activity of bumble bees increased toward the late flowering period reflecting the life cycle of colony development. The activity of syrphid flies was sensitive to ambient temperature, while that of non-syrphid flies remained high throughout the season. Flower production of bee-pollinated plants fluctuated significantly between years with a bimodal pattern peaking in the early and late periods, while flower production of fly-pollinated plants was less variable between years. Fruit-set success of bee-pollinated plants increased considerably from the early to the late flowering period, while the trend for fly-pollinated plants was less marked. Three times more visits of dipteran insects are necessary for fly-pollinated plants to achieve fruiting success comparable to bee-pollinated plants. Bumble bees are potentially excellent pollinators, but the visitation frequency is low early in the season. Lower pollination ability of dipteran insects may be compensated for by abundant flower visits. The relationships between flowering phenology and fruit-set success of alpine plant communities highly depend on the type of pollinators.

LINKAGES BETWEEN PHENOLOGY, POLLINATION, PHOTOSYNTHESIS, AND REPRODUCTION IN DECIDUOUS FOREST UNDERSTORY PLANTS

Light availability in the understory of deciduous forests changes drastically within the growing season due to the foliage dynamics of canopy trees. Because flowering phenology, photosynthetic characteristics, and fruiting success respond to such strong seasonality in light availability, we hypothesized that understory plants in such ecosystems should describe distinct phenological groups or syndromes where "syndrome" is defined only as a set of characteristics that co-occur. To identify these phenological syndromes, we studied the flowering phenology, fruit or seed set, and photosynthetic characteristics for 18 perennial understory herbaceous species that differed in reproductive strategy over eight years in a deciduous forest in northern Japan. Three phenological groups emerged from this study: (1) spring bloomers, flowering and fruiting before the completion of canopy closure; (2) early-summer bloomers, flowering during the progress of canopy closure and fruiting after canopy closure; and (3) late-summer bloomers, flowering and fruiting after canopy closure. The spring bloomers had high photosynthetic rates and high fruiting abilities, but the flowering time varied considerably among years due to yearly fluctuations of snowmelt date. Bumble bee-pollinated species of spring bloomers showed variable seed-set success, while fly-pollinated species showed relatively stable seed sets over the years. The early-summer bloomers showed low fruiting abilities irrespective of pollination success, reflecting severe resource limitation with decelerating light availability during fruit development. Although the late-summer bloomers showed low photosynthetic rates under low-light conditions, high fruit-set success was attained if pollination was sufficient. These results support our hypothesis that phenological syndromes may be found in deciduous forest understory plants. Given that reproductive success of bee-pollinated spring bloomers is highly susceptible to seasonal fluctuation, climate change may have its strongest impacts on this group.

Is productivity of cacao impeded by epiphytes? An experimental approach

The impact of epiphytes on cacao productivity was investigated in agroforests in Central Sulawesi, Indonesia. Effects of epiphyte removal on fruit-set success and eventual yields were studied on 80 trees in an experiment with a balanced full factorial design. The removal treatment had no significant effect on the eventual harvest of the cacao trees. Pollinator availability had the greatest impact on fruit-set success, whereas yields were mainly determined by site-specific factors that mediate fruit-abortion and occurrence of fungal diseases. The results illustrate that epiphytic flora dominated by non-vascular species may have no effects on cacao tree functioning and removal of non-vascular epiphytes is unnecessary for improving the productivity of cacao. Hence, farmers’ labour can be reduced and conservation of the rich biodiversity outside natural forests supported.

FRUIT SET SUCCESS OF THREE MANGO (MANGIFERA INDICA L.) CULTIVARS USING RECIPROCAL CROSSES

'Tommy Atkins' has general characteristics of tall trees, fruit with red blush skin and fair taste. It has reasonable anthracnose resistance, but is highly susceptible to mango malformation. Indian cultivars Amrapali and Mallika are small trees with sweet fruits, but their yellow skin color has low market acceptance. Due to their good characteristics for mango breeding, these cultivars have been used in hybridization studies, but their general combining ability - GCA for fruit set is still unknown. To support future crosses, an experiment was carried out at Embrapa Cerrados, in Brasilia, to study fruit set success or compatibility among these three cultivars. A completely randomized design with six treatments or crosses ('Mallika' x 'Tommy Atkins'; 'Tommy Atkins' 'Mallika'; 'Mallika' x 'Amrapali'; 'Amrapali' x 'Mallika'; 'Tommy Atkins' x 'Amrapali'; 'Amrapali' x 'Tommy Atkins') and five replications (panicles) were used. Opened flowers were discarded from healthy panicles, which were protected by perforated polyethylene bags. In the morning, young and still closed buds were removed, opened flowers were selected, emasculated and hand pollinated using anther of male progenitor. The panicles were bagged and tagged. Fruit set was studied weekly for six weeks. 'Mallika' had the lowest compatibility rate and 'Amrapali' x 'Tommy Atkins' had the best fruit set with 16.1% success.

Pollen Tube growth and fruit-set success in Hevea brasiliensis hand-pollination influenced by the choice of clone and female flower

Differences in fruit-set success reputed to exist between Heveabrasiliensis genetic clones were verified by an analysis of breeding recordsfor the clones PB 5/51, RRIM 600 and PR 107. Although the bestfruit-set success was obtained with PB 5/51 following artificial (hand)pollination, this clonal trait was not reflected in terms of greater numbersof pollen tubes developing it the styles of hand-pollinated PB 5/51 femaleflowers. It was observed, however, that more pollen tubes reached theovules in PB 5/51 than in RRIM 600 or PR 107. Significantly, PB 5/51female flowers required fewer pollen tubes to effect penetration of all threeof its ovules. As fruit formation in Hevea is dependent on all threeovules of the flower being successfully fertilised, PB 5/51 female flowershave hence a greater propensity for successful fruit-set. In all the threeclones studied, the frequency distribution of female flowers with 0, 1, 2 or3 of the ovules penetrated by pollen tubes did not conform to binomialexpectations. Flowers with no ovule penetrated and flowers with all threeovules penetrated were greatly over-represented. One explanation for thisnon-random distribution is the existence of `receptive' female flowers thatfavour successful fertilisation whereas `non-receptive' flowers tend to remainunfertilised even when hand-pollinated.

Distance-independent fruit-set pattern in a dioecious populationof Ceratonia siliqua (Caesalpiniaceae)

Summary Fruit and seed production in relation to the nearest male mate were studied in a dioecious population of Ceratonia siliqua in southern Spain. Results show a general trend towards producing a low and practically constant number of fruits per raceme and so, a low fruit-set. In contrast, the number of seeds was markedly high in the set fruits. Both fruit-set success and seed production per tree did not depend on distance to the nearest pollen source. Results are discussed in relation to flowering phenology, floral biology and fruit production limitation.

Pollination ecology of Aloe divaricata, Berger (Liliaceae): an endemic plant species of south-west Madagascar

The reproductive biology and pollination ecology of an endemic plant species ( Aloe divaricata ) of Madagascar was studied in order to understand the relative significance of various flower visitors to fruit set success. The flowers were hermaphrodite and protandrous, and were primarily visited by souimanga sunbirds ( Nectarinia souimanga ) and stingless bees ( Trigona sp.). Flower development and phenology were examined. Fruit set success of flowers from which sunbirds were excluded was significantly lower than that of flowers visited by both bees and sunbirds. Sunbirds ( Nectarinia souimanga ) appeared to be the most effective pollinators of Aloe divaricata , although numerous stingless bees ( Trigona sp.) also visited the flowers. The latter visitors did not seem to play any role in Aloe divaricata pollination.