Pistil Biology of ‘WA 38’ Apple and Effect of Pollen Source on Pollen Tube Growth and Fruit Set

‘WA 38’ (‘Enterprise’ × ‘Honeycrisp’) is an apple variety that is characterized by a peculiar self-thinning trait in which most of the fruitlets naturally shed within the first 8 weeks after bloom, leaving some clusters empty, but most with 1–2 apples. This study aimed to investigate potential causes for the relatively low fruit set observed in ‘WA 38’ by investigating its flower biology. This study comprised three objectives: (1) To characterize the effective pollination period (EPP) of ‘WA 38’ by studying stigmatic receptivity, pollen tube growth, and ovule longevity in ‘WA 38’ flowers, (2) to compare the pollen tube growth of 5 fully compatible pollinizer varieties in ‘WA 38’ pistils, and (3) to evaluate fruit and seed set resulting from controlled pollinations with 5 fully compatible pollinizer varieties. The results showed ‘WA 38’ EPP was approximately 3.2 days in 2019 and 1.4 days in 2020, and that differences in pollen sources did not attribute significant differences in fertility in ‘WA 38’ flowers. The results of this study suggest mechanisms other than pollination and fertilization, such as competition among fruitlets within a cluster or hormone signaling, may have a stronger impact on ‘WA 38’ fruitlet abscission.

Why are flowers ephemeral? Effects of old flower microbes on fruit set in a wild ginger with one-day flowers, Alpinia japonica (Zingiberaceae)

Flowers are colonized by and inhabited by diverse microbes. Plants rapidly replace flowers of short lifespan, and old flowers senesce. This may contribute to avoiding adverse effects of the microbes. In this study, we investigate if the flower microbial community on old flowers impedes fruit and seed production in a wild ginger with one-day flowers. We inoculated newly opened flowers with old flower microbes, and monitored the effects on fruit and seed set. We also assessed prokaryotic communities on the flowers using amplicon sequencing. We found five bacterial amplicon sequence variants (ASVs) whose proportions were increased on the inoculated flowers. These ASVs were also found on flower buds and flowers that were bagged by net or paper during anthesis. Fruit set was negatively associated with the proportions of these ASVs, while seed set was not. The results suggest that old flowers harbor microbial communities different from those at anthesis, and that the microbes abundant on old flowers negatively affect plant reproduction. Though the short lifespan of flowers has gotten little attention, it might be an essential defense mechanism to cope with antagonistic microbes that rapidly proliferate on the flowers.

Inoculation of pear flowers with Metschnikowia reukaufii and Acinetobacter nectaris enhances attraction of honeybees and hoverflies, but does not increase fruit and seed set

Currently, one of the most important challenges is to provide sufficient and affordable food and energy for a fast-growing world population, alongside preserving natural habitats and maintaining biodiversity. About 35% of the global food production depends on animals for pollination. In recent years, an alarming worldwide decline in pollinators has been reported, putting our food production under additional pressure. Therefore, there is an urgent need to find sustainable ways to ensure this crucial ecosystem service. Recent studies have shown that floral nectar is generally colonized by microorganisms, specifically yeasts and bacteria, which may alter nectar chemistry and enhance attraction of pollinators. In this study, we investigated changes in pollinator foraging behavior and pollination success in European pear (Pyrus communis L.) cultivars ‘Regal Red’ and ‘Sweet Sensation’ (red sports of ‘Doyenné de Comice’) after flower inoculation with the typical nectar-inhabiting microorganisms Metschnikowia reukaufii and Acinetobacter nectaris, and a combination of both. Pollination success was monitored by measuring the number of flower visits, fruit set and seed set in two consecutive years, 2019 and 2020. Results revealed that application of a mixture of M. reukaufii and A. nectaris resulted in significantly higher visitation rates of honeybees and hoverflies. By contrast, no effects on flower visits were found when yeasts and bacteria were applied separately. Fruit set and seed set were not significantly affected by any of the inoculation treatments. The only factors affecting fruit set were initial number of flower clusters on the trees and the year. The absence of treatment effects can most likely be attributed to the fact that pollination was not a limiting factor for fruit set in our experiments. Altogether, our results show that inoculation of flowers with nectar microbes can modify pollinator foraging patterns, but did not lead to increased pollination success under the conditions tested.

Phloem-Feeding Herbivores Affect Floral Development and Reproduction in the Etruscan Honeysuckle (Lonicera etrusca Santi)

Floral development depends on multifactor processes related to genetic, physiological, and ecological pathways. Plants respond to herbivores by activating mechanisms aimed at tolerating, compensating, or avoiding loss of biomass and nutrients, and thereby survive in a complex landscape of interactions. Thus, plants need to overcome trade-offs between development, growth, and reproduction vs. the initiation of anti-herbivore defences. This study aims to assess the frequency of phloem-feeding herbivores in wild populations of the Etruscan honeysuckle (Lonicera etrusca Santi) and study their effects on floral development and reproduction. The incidence of herbivory by the honeysuckle aphid (Hyadaphis passerinii del Guercio) was assessed in three wild populations of the Iberian Peninsula. The effect of herbivory on floral morphology, micromorphology of stigmas and pollen, floral rewards, pollination, and fruit and seed set were studied. The herbivory by aphids reduces the size of flowers and pollen. Additionally, it stops nectar synthesis and causes malformation in pollen and microstructures of stigmas, affecting pollination. As a consequence, fruit set and seed weight are reduced. This work provides evidence of the changes induced by phloem-feeding herbivores in floral development and functioning that affect the ecological processes necessary to maintain the reproductive success of plants.

Impact of Pollinator Insects Associated with Cucumber Fruit Set

Background: Cucumber is one of the popular vegetables of the cultivated cucurbits. Different insect species harbored with cucumber plant and they influence on its production, but little have been studied in Bangladesh. This study investigated the abundance of the insect species and the impact of insect pollinators on cucumber yield. Methods: Investigation was conducted in summer and rainy seasons at Gazipur, Bangladesh. Insects were collected and categorized as pest, predator, pollinator and casual visitor. Occurrence of the insects at different hours of the day and impact of supplemented insect pollinators on fruit and seed set compared to natural and hand pollination were studied. Result: In total thirty species of insects were found with cucumber plants and their relative abundances ranged from 0.4 to 13.7%. We found ten species of insects as pest, ten species as predator, four species as pollinator and six species as casual visitor. The red pumpkin beetle, epilachna beetle and fruit fly were found as the major pests. The red pumpkin beetle revealed the top ranks among the insects and the highest abundance of the insects occurred at 09:00 h of the day. Supplemented insect pollinators revealed higher yield, which indicated the significant for conserving insect pollinators.

Floral Biology and Pollination Efficiency in Yam (Dioscorea spp.)

Yam (Dioscorea spp.) is a monocotyledonous herbaceous vine cultivated for its starchy underground or aerial tubers in the tropics and subtropics. It is an allogamous and polyploid species that reproduces by both sexual and asexual mechanisms. However, many of the landrace cultivars, including most of the popular varieties, reproduce exclusively by vegetative propagation (planting the tubers). These varieties are either sterile or produce sparse and irregular flowering with high flower abortion rate, low fruit and seed set. Production of crossbreed seeds for genetic improvement and for maintaining genetic diversity in yams is, therefore, mainly achieved through natural or managed pollination. Flowering in yam is mostly dioecious and, in some instances, monoecious. Flowering asynchrony, sticky nature of the pollen grains, and cross incompatibility are among the challenges in making genetic progress in yam breeding. There are many limitations in basic and applied knowledge of yam flower biology and pollination. This paper, therefore, reviews the flowering biology, pollination, and methods of improving pollination efficiency in yam breeding programs.

Do annual and perennial populations of an insect-pollinated plant species differ in mating system?

Background and Aims Theory predicts that outcrossing should be more prevalent among perennials than annuals, a pattern confirmed by comparative evidence from diverse angiosperm families. However, intraspecific comparisons between annual and perennial populations are few because such variation is uncommon among flowering plants. Here, we test the hypothesis that perennial populations outcross more than annual populations by investigating Incarvillea sinensis, a wide-ranging insect-pollinated herb native to China. The occurrence of both allopatric and sympatric populations allows us to examine the stability of mating system differences between life histories under varying ecological conditions. Methods We estimated outcrossing rates and biparental inbreeding in 16 allopatric and five sympatric populations in which both life histories coexisted using 20 microsatellite loci. In each population we measured height, branch number, corolla size, tube length and herkogamy for ~30 individuals. In a sympatric population, we recorded daily flower number, pollinator visitation and the fruit and seed set of annual and perennial plants. Key Results As predicted, outcrossing rates (t) were considerably higher in perennial (mean = 0.76) than annual (mean = 0.09) populations. This difference in mating system was also maintained at sympatric sites where plants grew intermixed. In both allopatric and sympatric populations the degree of herkogamy was consistently larger in outcrossing than selfing plants. Perennials were more branched, with more and larger flowers than in annuals. In a sympatric population, annuals had a significantly higher fruit and seed set than perennials. Conclusions Genetically based differences in herkogamy between annuals and perennials appear to play a key role in governing outcrossing rates in populations, regardless of variation in local ecological conditions. The maintenance of mating system and life history trait differentiation between perennial and annual populations of I. sinensis probably results from correlated evolution in response to local environmental conditions.

Floral biology and reproductive effort of andromonoecious Aesculus indica Wall. ex Camb. Hook (Hippocastanaceae)

Background Andromonoecious is an unusual sex-expression in trees; in which an individual plant bears both functionally staminate and hermaphrodite flowers on the inflorescences. The significant effects of crown layers on reproductive success have not been studied so far. This study aims to investigate the effect of crown layers on floral biology and reproductive effort of Aesculus indica. Results The results revealed that the peak period of peak period of anthesis was between 06:00-08:00 h of the day. Male flower production was predominantly higher as compared to the perfect flower on the inflorescence. There was no significant variation between total pollen production in staminate and perfect flowers. The features like protogyny and inter-level asynchrony promote xenogamy, however, the intra-level asynchrony resulted geitonogamy. Controlled pollination treatment revealed the existence of self-incompatibility in flowers. Pollination syndromes of flowers are supporting ambophily. A trend of consistent improvement in reproductive success from lower canopy layers to upper canopy layers in trees was recorded. The crown layers have a significant impact on flower production, fruit, and seed set. Conclusions Increment in male flower production due to the increment in crown is a mechanism of reproductive assurance as a pollen donor and pollinator recipient and also due to the differential cost of expenditure of reproduction in crown layers.

Reciprocal Heterospecific Pollen Interference among Alien and Native Species

1. Heterospecific pollen interference has recently been proposed as a mechanism contributing to the success of alien invaders, as heterospecific pollen of alien plants interferes with the reproduction of natives by reducing fruit and seed set. However, no study has looked at the opposite interaction. Moreover, few studies have considered the roles of phylogenetic and trait distances between pollen donors and recipients. 2. We did a large multi-species experiment in which we used alien and native species both as pollen recipients and as pollen donors, and included phylogenetic as well as trait distance as explanatory variables. 3. We found that both alien and native recipients suffered from heterospecific pollen from donors of the opposite status in terms of seed and fruit set. Phylogenetic distance and trait distance both affected heterospecific pollen interference, but the effect depended on recipient and donor statuses. 4. We conclude that heterospecific pollen interference affects both native and alien recipients, thus indirectly altering community composition and increasing biotic resistance against invaders.