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Globally, agricultural crops are often dependent on insect pollination. Blueberries are an example of such a crop and owing to their proposed health benefits they are grown around the world, including locations where their native bumble bee pollinators do not occur. In the absence of bumble bees, blueberry pollination in South Africa and many other parts of the non-native, commercial range is performed primarily by honey bees. Despite this, the effectiveness of honey bee pollination on blueberries remains understudied. This study determined the effect of honey bee pollination on components of fruit yield (fruit set and mass) of five blueberry varieties that are extensively planted in South Africa. For each variety, two metrics were calculated: 1) the benefit of bees — a comparison of fruit yields after exposure to honey bees and fruit yields after honey bee exclusion, 2) the pollination deficit — the difference in yield between hand pollination (maximum yield potential) and yields after exposure to honey bee pollinators. Honey bee pollination consistently resulted in improved yields, although the magnitude of this improvement (i.e., the benefit of bees) was dependent on the variety considered. Similarly, the pollination deficit also varied considerably across varieties and while some varieties appeared to perform close to maximum potential (small pollination deficit), others yielded well below their maximum potential under honey bee pollination. This study demonstrates that honey bees are functional pollinators of blueberries in areas where native blueberry pollinators are absent. However, in such areas, it is important that special focus be given to selecting blueberry varieties that perform well with honey bees as their sole pollinator. Further research is necessary to determine how the pollination deficit of blueberry varieties can be decreased as well as how to increase the effectiveness of honey bee pollination.

Global pollinator declines and land-use change can lead to pollination limitation with implications for agricultural productivity. Hand pollination is used in agricultural production as a technique to manually pollinate crops. But the prevalence of hand pollination, as well as benefits and costs, remain unknown. We systematically reviewed the literature for examples, methods, drivers, and economic motivations of hand pollination. Furthermore, we discuss the risks, constraints, and opportunities of hand pollination. We found evidence for 20 hand-pollinated crops, including minor but also economically important crops (e.g. apple, oil palm, cacao). The lack of pollinators was the most important reason for the application of hand pollination (50% of crops), while insufficient proportion or proximity of pollinizers (8% of crops) and skewed sex ratio or dichogamy (8% of crops) were second most important. The main economic motivations for practicing or recommending hand pollination were to increase fruit set, and/or fruit quality (78% of crops). Hand pollination is practiced in large- and small-scale farming, home gardens, and greenhouses. Opportunities of hand pollination are the control of pollen origin and quantity, pollination timing and frequency as well as independence from environmental fluctuations. Farmers can increase yields, improve fruit quality, avoid fruit abortion, increase employment, and secure subsistence food. The main constraints of hand pollination are high labor inputs, high material costs, and required skills. Major risks of hand pollination include management ignoring pollinator conservation, high food prices, over-pollination, labor accidents, and unfair labor. We conclude that in the face of global change, hand pollination allows improved control of pollination and is likely to increase in importance. The benefits of hand pollination need to outweigh the costs and fair labor is essential. Altogether, hand pollination can be a valuable tool for crop systems where pollinators are absent or are not reliable for sustaining high-quality crop production.

Animal-mediated pollination is an essential ecosystem service on which over a third of the world's agricultural crops depend. Blueberry fruit production is highly dependent on animal pollination and although visited by a range of bee species in their native range and agricultural settings, bumble bees are thought to be their primary native pollinators. Demand for blueberries has increased in recent years due to their perceived health benefits. Consequently, blueberry cultivation has expanded well beyond their native and original agricultural range, including several regions where bumble bees are not present. In South Africa, like many areas in the world, honey bees are the only commercially available pollinators for blueberries because many countries ban the importation of bumble bees. This study aimed to determine the benefits of honey bee pollination on blueberry fruit yield for the variety Ventura by comparing yields of honey bee-pollinated flowers to flowers where pollinators were excluded. Our results show that honey bees significantly increased berry mass and diameter. We conclude that Ventura in South Africa can be pollinated by honey bees, and that honey bee pollination can be an effective substitute for bumble bees in areas where bumble bees are unavailable. We also determined the extent to which blueberry yields could be improved by comparing fruit yield under honey bee pollination to fruit yield achieved through hand pollination. We found that honey bee pollinated blueberry yields were lower than yields achieved through hand pollination, suggesting that there is potentially room to improve honey bee pollination. Furthermore, we offer a conceptual figure to demonstrate how yield obtained through pollinator exclusion, open pollination, and hand pollination relate to each other. Additional research is required to study how beneficial honey bees are to fruit yield on other blueberry varieties as the benefits of honey bees are likely to vary depending on the variety.

Insect pollination plays a vital role for the yield of many crops, such as apples, strawberries and coffee, which are economically significant commodities on the global market. Yet, knowledge about the role of insect pollination is lacking for many cash crops that support the livelihoods of small-scale farmers in developing countries. To assess if yields of watermelon are pollen limited, we conducted a supplemental hand-pollinated experiment (using a pollen mixture of cross and self-pollen) in 13 small-scale farms in an agricultural landscape in the Kilimanjaro and Arusha regions in northern Tanzania. We assessed fruit set, fruit abortion and weight of the mature fruits stemming from hand pollinated and control flowers. To check if differences in yield responses between hand-pollinated and control treatments depended on resource availability, we also accounted for local soil conditions. We found that hand pollination (i) increased the probability of fruit initiation by 30%, (ii) reduced the probability of fruit abortion by 13%, (iii) increased the probability of flowers developing into mature fruits by 42% and (iv) increased average fruit weight by 1.3 kg (±0.15 SE). Our results indicate that our system is pollen limited, due to insufficient visitor frequency and/or inefficient pollinator species. Fruit initiation and fruit weight were positively related to soil carbon, irrespective of treatment. The influence of soil moisture was not consistent across the measured responses, and differed between hand-pollinated and the control treatments. We suggest that farmers in our focal area should focus on improving the quality of the landscape to sustain and enhance healthy pollinator communities ultimately improving yields. We also suggest that farmers should continue current practices with respect to fertilization. The role of soil moisture on fruit initiation and maturation should be investigated to ensure that the positive effects of pollen is not hindered by soil moisture conditions.

Breeding systems have been associated with polyploidization and genomic change, which have a central role in the diversification of Angiosperms. Polyploidy commonly leads to isolated populations and species, and sometimes to apomixis, as observed for some woody plants of Cerrado, the Neotropical savannas in Central Brazil. Eriotheca gracilipes and E. pubescens are common trees in this region, and present both sexual and sporophytic apomictic individuals. We studied here how morphological features and breeding systems are linked to ploidy and genome size differences, and how these features may help to understand cytotypes distribution. We confirmed breeding systems by hand pollination experiments and complemented histological analyses to describe the apomixis and sexual process for individuals with previously defined ploidy levels. We used flow cytometry and morphometry data to verify the relationships among cytotypes. Fruit and seed features were also measured for extensive samples of both species to observe environmental correlates such as altitude of occurrence and distribution of each embryony pattern and cytotypes. In both species, agamic complexes included individuals with nucellar polyembryony associated to putatively neopolyploid, hexaploid cytotypes, while lower ploidy individuals were sexual and self-sterile. Higher genome sizes were also associated with larger pollen grains and stomata, besides other more complex morphological trends. Embryonic patterns were consistent for each site, individuals, and along years, although the percentage of polyembryonic seeds and number of embryos per seed varied. Monoembryonic sexual individuals were associated with higher elevation, allegedly last glacial maximum Cerrado refuges, while polyembryonic sporophytic apomicts appeared in lower areas.

Fresh market demands high quality fruit and, therefore, citrus growers and researchers are constantly looking for solutions to avoid seed presence. Current horticultural techniques have low effectiveness or high cost. The objective of this study is to evaluate the inhibition effect of seven products on the in vivo pollen tube growth in Nadorcott mandarin, which is a high-value seedy variety. To achieve this main objective, three inorganic fertilizers (ammonium nitrate, potassium nitrate, sulfur), and four saccharides (saccharose, methyl cellulose, callose, chitosan) were applied to Nadorcott stigmas 24 h before and after hand pollination. Pollen tubes were counted 1, 3, and 5 days after treatment in longitudinal blue violet autofluorescence-stained sections. Of the seven evaluated products, only sulfur had a strong inhibitory effect. Elemental sulfur (S8) inhibited pollen tube growth by 94-100%. This strong effect was observed regardless of sulfur being applied 24 h before or after pollination, and on fixed flowers 1, 3 or 5 days after applications. Saccharose treatment seemed to have the opposite effect: stimulated pollen tube growth, but the difference with the positive control was small and non-significant. The sulfur effect could be useful for designing agronomic applications capable of preventing seed presence in Nadorcott mandarin.

Field observations suggest high air temperatures during bloom decrease fruit set of many sweet cherry (Prunus avium L.) cultivars. We investigated the role of temperature on stigma receptivity and ovule viability in four sweet cherry cultivars that exhibit variability in productivity and fertility: ‘Sweetheart’ (self-fertile, high productivity), ‘Benton’ (self-fertile, low productivity), ‘Rainier’ (self-sterile, high productivity), and ‘Tieton’ (self-sterile, low productivity). The development of the stigmatic surface, and pollen hydration, germination and tube growth in vivo, were evaluated by hand pollination and used as proxies for stigma receptivity. In addition, the senescence of primary and secondary ovules was analyzed with fluorescence microscopy. The stigmatic papillae began deteriorating by the second day after anthesis and had collapsed by the sixth day post-anthesis across cultivars. Pollen hydration exhibited 5 stages related to the length-width ratios of 2.5:1, 2:1, 1.75:1, 1.5:1 to 1:1. Maximum pollen hydration and pollen germination occurred on the stigmas within 2 days of bloom, depending on cultivar and air temperature. Pollen hydration and germination, and ovule senescence accelerated under warmer temperatures. At 7 days post-anthesis and under 24 °C approximately 80% of ‘Rainier’ ovules were viable compared to 30% in the three other cultivars. Under moderate temperature (18 °C) which mimicked the field average flowering temperature, ovule of the two high productivity cherry cultivars, ‘Rainier’ and ‘Sweetheart’, kept full viabilities for 3–4 days post-anthesis while only 1 day for the two low productivity cultivars ‘Benton’ and ‘Tieton’. These results reveal that low commercial productivity of sweet cherry cultivars in the Pacific Northwest (PNW) of U.S. is likely due to rapid ovule senescence, a condition exacerbated in warm conditions.

In a previous work, it was found that ‘Spadona’ the main European pear cultivar grown in Israel, is semi-compatible with each of its three pollinators ‘Gentile’,‘Coscia’ and ‘Spadochina’. Thus, the full yield potential of these cultivars is not being realized. The Japanese pear (Pyrus pyrifolia) can fertilize European pears. In Israel, the environmental conditions for growing pears are sub-optimal for most pear cultivars. However, the Japanese pear ‘Hosui’ is well adapted to these conditions; moreover, it is fully compatible and flowers simultaneously with the cultivated European pears. In this work, we report on a 10-year evaluation of pollination of ‘Spadona’ and ‘Coscia’ pollinated by ‘Hosui’. The experiments were conducted in three stages: hand pollination; ‘bouquet insertion’; and a combined European-Asian pear orchard. The results indicate that this is a beneficial means for significantly improving fruit quality and quantity.

Seed production is the key factor for maintaining plant population renewal and development. Because of pollination limitations and other factors, orchids, especially rewardless ones, generally have low fruit set rates. In Rhomboda tokioi, however, the natural fruit setting rate is very high, more than 90%. Common reasons for such a high natural fruit setting rate include high pollinator efficiency, autonomous selfing, seed formation through apomixis and so on. To test these possibilities, we carried out field observations, morphological examinations, and breeding system experiments. The results showed no migration of pollinia into or out of flowers and suggested that the structure of the floral organs hinder autonomous selfing. Interestingly, the fruit setting rate of this orchid was still higher than 90% when the gynostemium was removed prior to flowering. Additionally, after hand pollination, the pollen tube stopped growing at a late stage and could not enter the ovule, indicating the seeds were produced by obligate apomixis. Morphological experiments showed that a megasporocyte first forms a chain tetrad and then develops into a mature embryo sac, while the embryo of the offspring developed from unfertilized egg cells. More interestingly, the offspring had the same number of chromosomes as the female parent. According to the existing theory of apomixis, we can infer that the reproductive model of R. tokioi is Allium-type apomixis.

Faba bean (Vicia faba minor L.) is partially dependent on insects for pollination, but the degree of pollinator-dependency and whether crop productivity is limited by insufficient insect pollination remain unknown. We monitored insect pollinators and their foraging behaviors (i. e., legitimate flower visitation, nectar robbing and extra-floral nectary visitation) in a total of 20 faba bean fields of a single cultivar (Tiffany) 2018–2019. Focal fields were situated along a gradient of landscape complexity. In each field, a pollination experiment was established, where plants were either bagged to exclude pollination by insects or remained open for pollinator visits. In addition, all flowers on half of the bagged and open-pollinated plants were pollinated by hand to measure the degree of pollen limitation. We found that bumble bee abundance was higher, and legitimate flower visitor abundance tended to be higher, in complex landscapes with more semi-natural habitat, indicating that the faba bean pollination potential is higher in complex landscapes. The pollination experiment showed that the number of beans per pod was lower in bagged plants compared with other treatments in one of the years, but the lower number of beans per pod was compensated for by a higher individual bean weight, such that there was no pollinator-dependency or effect of hand pollination on total bean mass per plant. We conclude that to be able to characterize the value of insect pollination services in faba bean we need an improved understanding of how pollinator-dependency varies across modern cultivars, and how environmental conditions can increase or, as in our case, cancel this pollinator-dependency.

Pollination techniques could affect fruit size, whereas optimal maturity stage during harvest could affect postharvest life and the eating quality of fruit. Therefore, the right pollination technique and timing to harvest fruit is an important factor in reducing postharvest losses. The objective of this study was to determine the physico-chemical changes of jackfruit harvested at four different maturity stages and produced from natural and assisted pollination. This study was conducted at a jackfruit commercial farm in Bukit Beruntung, Selangor, Malaysisa. For assisted pollination, the selected female inflorescences were covered with bags before anthesis. Hand pollination was performed by gently rubbing mature male inflorescences over the surface of receptive female inflorescences. For natural pollination, female inflorescences were left to develop into syncarps by themselves. Syncarps at the age of 12, 13, 14 and 15 weeks after anthesis (WAA) were used in this study. For each maturity stage, four syncarps were harvested and allowed to ripen naturally at 27±2 °C and 70−80% relative humidity until a sweet aroma was detected. Physico-chemical characteristics such as colour, firmness, pH, titratable acidity, β-carotene, lycopene content, sugars, organic acid content and antioxidant activity were evaluated. In this study, the pollination technique did not affect the eating quality of jackfruit flesh. However, the physico-chemical quality of jackfruit flesh was affected by ripening level and WAA. The initial stages of syncarp maturity, the L*, C* and ho values, remained unaffected. However, the L*, C* and ho decreased significantly from 14 WAA onwards when the syncarp rind turned fully yellow. This indicated that the rind and bulb colour became lighter and less intense with a green colour changing to yellow during ripening. Rind and flesh firmness decreased as ripening progressed due to cell wall modification and starch hydrolysis when ripening occurred. The β-carotene content of fleshy syncarps harvested at 14 and 15 WAA was higher than those harvested at 12 and 13 WAA. Sugar content such as glucose, fructose and sucrose increased as syncarps ripened. Total phenolic, flavonoid and antioxidant content were higher after syncarps ripened compared to before ripening. The ripe edible parts of jackfruit contain high levels of antioxidant and thereby signify the nutritional value of jackfruit for human health. In conclusion, harvesting stages affect the nutritional quality of jackfruit cv. Tekam Yellow, and it is recommended that the optimal harvesting stage of jackfruit is 14 WAA for local markets and 12 WAA for long-distance markets.

European pear ( Pyrus communis ) requires insect pollination among compatible cultivars for fruit production. However, most commercial orchards have a limited number of cultivars arranged in monotypic blocks or rows. This can result in insufficient inter-cultivar pollination. We hypothesise that limitations in pollen transfer among cultivars could be explained by both insect behaviour and orchard design. We compared insect activity and pollination efficiency in two European pear cultivars, in orchards with different designs: (i) cultivars alternated in the same row or (ii) cultivars in separate rows. To assess limitations in pollen transfer, we also compared hand pollination with compatible pollen versus open pollination by insects. Insect visitors mainly foraged on neighbouring trees within a row, with few movements across rows (1%). Honey bees ( Apis mellifera ) and bumble bees ( Bombus terrestris ) visited significantly more flowers per tree (8.5 vs. 3) and more trees (2.1 vs. 1.3) than solitary bees ( Andrena spp.) and hoverflies. Insect visitors deposited large amounts of pollen (∼500 pollen grains) on flower stigmas regardless of the insect type. Cultivar placement affected inter-cultivar pollination; less incompatibility signs were observed when cultivars alternated in the same row (5%) than when cultivars were in separate rows (38%). We observed limitations in pollen transfer as open pollination resulted in significant reduced fruit set, compared with hand pollination, in ‘Conference’ (21% vs. 30.7%) and ‘Doyenne du Comice’ (7.2% vs. 16.8%). The foraging behaviour of the insects limited thus inter-cultivar pollen transfer in the orchards with cultivars in separate rows. Cultivars used for pollination (pollinizers) should be planted in the same rows as the main cultivar to increase inter-cultivar pollination.

Variations in floral traits and floral structures influence plant mating systems. Hibiscus trionum produces large, showy flowers typical of an outcrossing species, yet flowers are autonomously self-pollinated. In this study, we measured floral morphology, breeding system and outcrossing rate estimated by ISSR markers. Results indicate that two types of flowers were observed in H. trionum , and the type I with bigger petals appears to be much more visible to pollinators, demonstrated by than type II flowers with smaller petals. The flowers with hand pollination were closed 1 h earlier than intact flowers, whether they were type I or II. The relationship between the amount of pollen deposited on the stigma and the number of seeds per capsule was highly significant, and 80 or more pollens per flower can make the mean number of seeds (mean = 37) in H. trionum . Delayed selfing in H. trionum did not provide a large contribution to seed production, since reproductive assurance were only 0.025. However, successful reproduction of 72.5% flowers in the absence of pollinators suggested that selfing provides reproductive assurance during seasons, in which pollinators were limiting. The multilocus outcrossing rates in different populations varied from 0.982 to 1.200, with a mean of 1.116. Our data provide an empirical demonstration of a predominantly outcrossing species with potential delayed selfing when pollinators are absent or scarce.

Oxalis corymbosa , a tristylous species, lacks seed-set in Taiwan. In a previous survey, six floral types (3 floral morphs in combination with two types of anthers) of 23 populations in Taiwan were assigned based on qualitative visual observation. In this study, we conducted experiments on one of the populations to pursue following objectives: to analyze the floral types of the population based on quantitative measurement and to test the hypothesis that the lack of seed-set is partially attributed to pollination limitation. The heights of anthers and stigmata were measured and analyzed. The number of viable pollen grains per anther was estimated. Pollen germination and seed-production after hand-pollination treatments were examined. Variations in anther and stigma heights were found in each type of previously assigned flowers. Unequal heights of reciprocal sexual organs between floral types were also found. Each level of anthers of MS-Y (mid-styled bearing yellow anthers) and SHS-Y (semi-homostylous bearing yellow anthers) flowers contained about 60 and 25 viable pollen grains, respectively; while anthers of SHS-W (semi-homostylous bearing white anthers) flowers had no pollen. Among hand-pollination treatments of inter-morph, cross-intra-morph and self-intra-morph crossings, only in one inter-morph crossing, i.e. SHS-Y (pollen receiver) × l/MS-Y [pollen donor, pollen from lower (l)-level anthers of MS-Y], pollen tubes were found entering micropyles of the ovules, and seeds were built. Thus, this species can produce seeds by hand-pollination. The result supports that limitation of pollen transfer at least partially contributes to the absence of seed-production in field populations of O. corymbosa in Taiwan.

Bees provide important pollination services for crops, but pollination limitation is a common problem in agricultural landscapes worldwide. To promote ecological intensification in fruit production, more knowledge is needed concerning the interacting effects of insect pollination services and soil fertility on crop quality and quantity. We investigated the effects of three pollination treatments (open, self and hand pollination) on apple quantity and quality parameters. We also analyzed the effects of bee abundance (wild bees and managed honeybees (Apis mellifera)) and soil nitrogen on fruit quantity and quality, and the responses of bee abundance and species richness to landscape metrics. Apple fruit set and yield of open pollinated flowers increased by 57 % and 25 t/ha (compared to bagged controls), respectively. Hand pollination further enhanced yields by 7 t/ha (compared to open pollination; i.e. to 39 t/ha), indicating pollination limitation in the orchards. Seed number was highest in open pollinated fruits, and increased with bee abundance if soil nitrogen was low, but decreased with bee abundance at high nitrogen levels, possibly due to higher flower density resulting in pollinator dilution effects. Higher seed numbers reduced the proportion of deformed apples and thus increased fruit quality. The percent of surrounding semi-natural habitats positively affected species richness of wild bees in apple orchards. We conclude that yield and quality of apples may benefit from ecological intensification comprising the augmentation of wild bees by semi-natural habitat and lowering of fertilizer inputs.

Avocado trees ( Persea americana Mill.) invest heavily in flowering but fruit set percentage is unusually low, even after hand pollination. Our hypothesis was that the carbohydrate and boron content of avocado flowers at anthesis affected the potential of these flowers to set fruit. We hand pollinated ‘Hass’ avocado flowers in orchards in New Zealand and Spain, then 24 h later, after pollen tube growth had occurred, collected the styles from these flowers leaving the ovary intact. The excised styles were then analysed for starch, total and individual sugars and boron content. These data were later compared with the fate of the flower from which the style had been collected. Starch and all individual sugars were higher in the styles from flowers that went on to successful fruit set. Boron content was significantly higher in the styles from flowers that successfully set fruit in New Zealand but no significant difference was observed in the boron content of styles from Spain. These data support previous findings that suggest sink strength of flowers is predetermined at anthesis and influences the probability of fruit set for that flower.

Increasing demand for cocoa and climate-related yield declines have sparked a multi-stakeholder debate on cocoa production strategies. Agrochemical inputs and pollination enhancement through hand pollination are two strategies to increase yields. Here, we test both strategies with field experiments in Indonesia. We show that even partial hand pollination (13% of easily accessible flowers/tree), and not fertilizers or insecticides, increases yield/tree by 51%. The more laborious 100% hand pollination of the entire tree increases yield/tree by 161%, and farmer’s annual net income from 994 USD/ha up to 1,677 USD/ha, or 69% in the study area, after accounting for farm operational, hand pollination labor, and opportunity costs. Thus, intensifying cocoa pollination appears to be a potential solution for closing cocoa yield gaps and should be considered in the current industry-led discussion of designing farms for mitigation of climate change.

Yield and quality of grapes are markedly enhanced by cross-pollination although self-pollination ensures some level of berry set. Cross pollination is also employed to breed a new fruitful genotype to sustain the food to feed the increasing world population on the face of climate change. The present investigations were performed to reveal the effects of diploid and tetraploid pollinizers on the agronomy of ‘Michele Palieri’ table grape cultivar. For cross pollinations, the flower buds of the maternal cultivar were emasculated 5–6 d before bloom, while the clusters belonging to self- or free pollination groups were not emasculated. All the clusters including the pollinizers, except for free pollination, were covered with cheesecloth bags to exclude random pollination. Hand pollination was carried out for each cross-combination with hairbrushes when the stigma attains peak receptivity. Pollination was carried out two times (morning in the following day), while the flowers of self-pollination group were allowed to bloom and self-pollinate in the bags. The clusters of free pollination were left after labeling without isolation. The pollinizers had remarkably different impacts on the agronomy of maternal cultivar. The highest values on berry set (20.22 %), seed size (7.18 mm) and soluble solid content (15.5°Brix) were achieved when ‘Crimson Seedless’ was used as pollinizer. The clusters set berries poorly when the pollen of interploid tetraploid ‘Kyoho’ (13.46 %) was used. However, berry color was markedly improved by ‘Kyoho’ pollens with darker and more intense skin color. Cluster mass was significantly improved by external pollens of diploid cultivars resulting from better berry set and berry development in comparison with self-pollination. Berry mass values of free pollination and ‘Michele Palieri’ x ‘Italia’ treatments were 26.6 % and 22.8 % higher than that of self-pollination. The highest values on berry detachment and skin rupture forces were detected in ‘Michele Palieri’ x ‘Italia’ combination, while the lowest measures were on both parameters were found in self-pollination berries. Finally, the use of pollinizer cultivars, instead of monovarietal vineyard establishment, could be recommended to improve berry set and quality under vineyard or protected cultivation conditions. Tetraploid ‘Kyoho’ could be used in an interspecific and interploid breeding study as donor for unique characters.

Macadamia nuts are a valuable culinary resource, but yields can vary substantially between varieties, orchards and seasons. The nuts are harvested from commercial varieties derived from two endemic Australian tree species; Macadamia integrifolia Maiden & Betche and Macadamia tetraphylla L.A.S. Johnson. While some aspects of crop management for this relatively new crop are well known and generally well applied—including variety selection, irrigation and pesticide application—progress towards increasing quantity and reliability of yield has proven elusive. Hand pollination studies indicate that inadequate cross pollination contributes to low nut set and thus low yield. Typically just 0.3% of flowers develop into harvestable nuts. Lack of nut development after flowering and early abscission are indicators of poor fertilisation of the ovule. Honey bees ( Apis mellifera Linnaeus, 1758) are routinely reported as the most common insect visitor to macadamia flowers, and are widely regarded as the most important agent for transferring pollen between flowers. Stingless bees, beetles, flies and birds also visit flowers and have been considered as pollinators. In this review, we aim to collate what is currently known about the pollination of macadamia varieties, assess the factors that may hinder effective pollination and subsequent yield, and identify opportunities to improve both pollination and yield in commercial macadamia orchards.

Avocado has a singular synchronous protogynous dichogamy breeding system that promotes outcrossing. In this work different steps have been optimized to improve controlled pollinations in avocado in order to perform basic studies of reproductive biology and directed crosses in breeding programs. The results show that, in order to achieve successful fruit set, male flowers should be collected when all the anthers have dehisced and the pollen transferred by direct contact of the anthers with the stigma during the female stage using preferentially determinate inflorescences and pollinating at least 11 flowers per inflorescence. To perform crosses between cultivars of complementary floral groups, the flowers should be stored under high relative humidity during the hand pollination process. When the crosses involved cultivars of the same floral group, the male flowers should be collected just before anther dehiscence and could be stored for several days at 4 °C. Pollen application should be performed preferentially on flowers within determinate inflorescences or within indeterminate inflorescences where vegetative growth has been removed. The results obtained are useful to optimize controlled pollinations in avocado and can help to increase fruit set in breeding programs and avoid the incorrect interpretation from pollination experiments in studies of reproductive biology.

The fruit set of commercial Annonaceae pollinated by natural pollinators is generally insufficient to produce commercially acceptable yields. In addition, several studies have reported that both the pollen source and age affect the potential percent fruit set of sugar apple and atemoya. Annona flowers are hermaphrodite; however, the female part mature before the male, which is known as dichogamy of the protogynous type. The objectives of the present study were to determine the effect of pollen storage duration on pollen viability; the percent fruit set by hand pollination of ‘Red’ sugar apple, ‘Lessard Thai’ green sugar apple and ‘Gefner’ atemoya; and resulting fruit characteristics as a result of pollen source in South Florida. Hand pollination and in vitro pollen germination tests were arranged in a 3 × 5 factorial design, with three cultivars, five treatments, and five replicates per treatment. The percentage of in vitro pollen germination was the highest for ‘Red’ sugar apple pollen (26.5%) collected from male stage flowers and for pollen collected from female stage flowers collected late afternoon and germinated 18 h later (23%). Percent pollen germination was higher for ‘Lessard Thai’ (∼33%) than for ‘Red’ sugar apple and pollen storage for up to 24 h was not significantly different than male stage pollen used immediately and pollen collected from female stage flowers and used 18 h later. ‘Gefner’ atemoya pollen did not germinate when pollen grains were collected from male stage flowers and when using female stage flowers collected late afternoon and stored for 72 h. Fruit set and fruit quality varied significantly as a result of pollen storage treatments. Hand pollination promoted high percentages of fruit set, greater than 80% when female stage flowers were collected late afternoon and hand pollination performed 18 h after collection. Fruit harvested as a result of the various pollen storage treatments varied significantly in weight, diameter, and the number of seeds per fruit. The pollen from ‘Lessard Thai’ sugar apple and ‘Gefner’ atemoya may be stored up to 24 and 48 h, respectively.

Self-incompatibility and synchronous protandrous dichogamy have previously been reported in Ziziphus species. In this work, we conducted a comparative analysis of fluorescence microscopy observations of pollen tube growth following controlled cross pollinations of emasculated flowers and self-pollinations of non-emasculated flowers in three Ziziphus species, Z. jujuba , Z. mauritiana and Z. spina-christi , with the aim to determine the type of the self-incompatibility system of each species. In addition, to test whether autonomous self-pollination, parthenocarpy or agamospermy occurs, flowers were emasculated (or not) and covered. Fruit set and seed viability were monitored. The presence of binucleate pollen grains and the cessation of pollen tube growth in the style suggest that the self-incompatibility system operating in the studied Ziziphus species is gametophytically controlled. Controlled self-pollination in Z . mauritiana resulted in fruits that dropped off before maturation, whereas in Z. spina-christi the flowers dropped off one or two days after pollination. Following controlled self-pollination, small fruits lacking viable seeds were obtained in Z. jujuba , probably due to the stimulus provided by pollination (stimulative parthenocarpy). In the cultivar Tamar of Z. jujuba , the relatively high percentage of seedless fruits obtained in emasculated bagged flowers without hand pollination suggests that this cultivar can set seedless fruits without any pollination stimulus.

Plants in small populations may receive fewer visits, smaller pollen loads or pollen of poorer quality and suffer from reduced reproductive success compared to plants in larger populations. Consequently, pollen limitation of plants in small populations has been suggested to result in the evolution of reduced reliance on pollinators or the enhancement of traits that attract pollinators. The main aim of this study was to experimentally quantify the strength of pollinator-mediated selection on floral display size and flowering phenology in populations of varying size, using the self-incompatible, perennial herb Phyteuma spicatum as study species. We conducted supplementary hand pollinations in six populations (ranging in size between ca. 20–3000 flowering individuals) over two consecutive years and assessed selection gradients (i.e., trait–fitness relationships) in open- and hand-pollinated plants. Our results show that some populations are pollen limited in some years, but, contrary to our expectation, the degree of pollen limitation was not significantly related to population size. We found phenotypic selection for increased inflorescence size (in most populations and in both years), but we obtained no or no strong evidence that selection was pollinator-mediated or that the strength of selection was related to population size. This may have been the result of low statistical power, an inherent problem of studies examining effects of population size that require the inclusion of populations with only few individuals. In addition, given that selection appeared to be spatially and temporally variable, abiotic or biotic factors other than pollinators may have contributed to selection on inflorescence size.

Occurrence of secondary pollen presentation (SPP) is evidenced for Duperrea pavettifolia. For this, self-pollen was presented on the stigma and reduced fertilization was observed in this case. The receptive area located in the furrow of the stigma becomes receptive from the third day of elongation growth. Fruit set upon hand pollination with pollen from other individuals was significantly higher than the results of selfed, bagged, emasculated and control treatments. However there was no difference in pollen tube growth rate between selfed and crossed pollen on a receptive stigma. Hawkmoths and butterflies were effective pollinators for D. pavettifolia, but the visiting frequencies were very low. Stingless bees removed pollen from the unreceptive stigma which had no contribution to reproductive success. High level of outcrossing in D. pavettifolia was demonstrated by molecular analyses using the simple sequence repeats (SSR) method. Although the wild populations of D. pavettifolia are small and with fragmented distribution, the genetic diversity of seedlings was high, with fluctuations among years. Our results indicated that protandry and the visitation of stingless bees reduced the amount of self-pollen on the still unreceptive stigma and self-incompatibility prevented fertilization by un-removed self-pollen.

Despite highly specialized pollination strategies, hybridization is a common phenomenon among Mediterranean deceptive orchids. Food-deceptive species sire a progeny of F 1 unfertile plants, which work as a late post-zygotic barrier. Conversely, when pre-zygotic barriers of sexually deceptive ( Ophrys ) species are absent, the hybrids are fertile and an extensive introgression may occur. Here, we have performed molecular analysis and hand pollination treatments to characterize a hybrid zone of two food-deceptive species, O. mascula and O pauciflora . Hybrids (called O. × colemanii ) have shown different amounts of parental nrDNA, strongly supporting that they are F 2 and/or successive hybrid generations. Comparable high levels of reproductive success have been detected in natural conditions and in experimental crosses suggesting the absence of effective reproductive barriers either between hybrids, either between hybrids and parental species. In light of ecological and distributional features of O. × colemanii across its distribution range, we hypothesize that these populations have originated by secondary contact in the periglacial belt of Apennines. Moreover, the rare and localized O. pauciflora could benefit a genetic enrichment by hybridizing with a widespread related species. O. × colemanii is not a dead end population, but may have a role as potential reserve of adaptive variability and is an unusual stage along the speciation process.

Gynoecism has been used on a large scale in heterosis breeding of cucumber. Production of hybrid seeds in bitter gourd is highly expensive because it is done mainly through hand pollination. But utilization of a gynoecious line would be more economical and easier method. Since gynoecious parent has only female flowers, the open pollinated seeds it produces will be F 1 hybrid. It will reduce the cost of male flower pinching and hand pollination. Two gynoecious lines, DBGY-201 and DBGY-202 were crossed with two monoecious cultivars, “Pusa Do Mausami” and “Pusa Vishesh” and their F 2 populations were observed to determine the inheritance pattern of gynoecious sex form. Another experiment was conducted to determine magnitude of heterosis by utilizing nine inbred lines including one gynoecious line, DBGY-201 in diallel (without reciprocal) mating system. All the gynoecious hybrids showed significant heterosis in a desirable direction for traits like sex ratio (male:female), days to first picking, number of fruits per plant, yield per plant, and vine length. The segregation pattern in F 2 suggested that gynoecious sex form in bitter gourd was governed by single recessive gene. The gynoecious hybrids DBGY-201 × “Pusa Vishesh” and DBGY-201 × “Pusa Do Mausami” were important for early harvest (∼50 days after sowing) whereas DBGY-201 × “Priya” and DBGY-201 × “Arka Harit” were promising for higher yield.

Effects of suspension media used for spray pollination on pollen grain viability were investigated in Japanese pear (Pyrus pyrifolia (Burm.f.) Nakai ‘Kosui’). The suspension media tested in this study consisted of pectin methylesterase (PME) and polygalacturonase (PG) combined with either 0.1% agar or 0.04% xanthangum (XG). We also evaluated the influences of spray pollination on fruit set and fruit quality. Pollen grain viability, as measured by germination and pollen tube growth rates, was maintained in media supplemented with 0.1 mg L−1 PME or 0.1 mg L−1 PG. The level of fruit set after spray pollination using media containing PME or PG in combination with either 0.1% agar or 0.04% XG was almost the same as the level after artificial pollination by hand (hand pollination). The media containing XG combined with either PME or PG seemed to show better results for pollen grain viability and fruit set, although the results were variable from year to year. With regard to fruit size, shape and other parameters for fruit quality, spray pollination and hand pollination gave comparable results, irrespective of the medium composition. The time required for spray pollination was less than half of that required for hand pollination, and the amount of pollen grain required for spray pollination was one-third or less than the amount required for hand pollination. Thus, spray pollination may be a time- and labor-saving pollination system for the cultivation of Japanese pear.

Michelia coriacea (Magnoliacae) is a critically endangered tree, endemic to Southeast Yunnan province, China. Most of the individuals in the extant populations normally bear flowers, but fruit set and fertile seed production rates were only 6.7% and 0.2%, respectively. To identify possible causes of reproductive barriers, the following studies were carried out: examination of stamen and pistil development; experiments using controlled pollination; observations of behavior and frequency of floral visitors in both cultivated and natural populations. The results revealed that about 60% of pollen was abnormal and approx. 70% of ovules had delayed development. Hand pollination could effectively enhance the fruit set (F(4.25) = 35.139, P < 0.0001) and seed set per fruit (F(4.25) = 85.022, P < 0.0001). Both cultivated and wild M. coriacea had an extremely low frequency of floral visitors. Some beetles, a few species of Andremdae and some Bombus sp. are likely to be the effective pollinators. The fruit set and seed set per fruit from controlled self-pollination and cross-pollination were significantly different (P < 0.05), and thus it is inferred, that inbreeding depression may be a contributing factor in the very low seed production. It appears that low seed set in M. coriacea is due to a combination of factors: abnormalities in pollen and ovules, low number of effective pollinators, and inbreeding depression. (C) 2009 Elsevier GmbH. All rights reserved.

Dichogamy and the lack of efficient pollinators in most producing countries make hand pollination of cherimoya unavoidable. In contrast to its high-cost, this technique allows growers to fix crop load levels and fruit location within the tree canopy. Over three consecutive years we have studied the optimal fruit load for the cultivar ‘Fino de Jete’ and checked the effects of the vigor of the fruit-bearing shoots and of the fruit position along the shoot on the resulting fruit set and quality. Our results show that yield in well-managed orchards fitted a logarithmic curve with a maximum close to 30 t ha −1 achieved by setting about 400 fruits per adult tree. No significant effects of crop load were detected on fruit size during the first 2 years; in the third year, however, trees with a lower yield produced heavier fruits. An upper limit of 0.22 kg (fresh fruit weight) cm −2 of trunk cross-sectional area is proposed if fruit quality is to be preserved. High yield during three consecutive years did not diminish tree growth. We found no consistent effects of shoot vigor on fruit set and quality. However, a gradient for heavier fruits was observed from the base to the apex of the bearing shoots.

Knowledge on reproductive phenology and pollination biology are basic elements that should be considered in the management and exploitation of plant species that offer non-timber products. The tropical tree Manilkara zapota is a species from which non-timber products have been obtained for centuries by Mayan communities in Mexico. Nevertheless, there are no quantitative reports on its reproductive biology and the factors that limit fruit production. The present study describes the reproductive phenology, breeding system and pollination of this species in two contrasting environments: medium-height, subdeciduous forest, and homegardens (“solares”) in a Mayan community in the state of Yucatan. Significant differences were found between environments both in the temporal distribution of flower and mature fruit production, as well as in the proportion of mature fruits. Homegarden trees showed the greatest fruit production, although flower production did not differ between environments. Mature fruits were of better quality ( i.e. , greater fresh weight) in homegardens. Hand pollination experiments showed that M. zapota is self-compatible, and that there is pollinator limitation for fruit production in trees that grow in homegardens. We propose that water and soil nutrients are the main factors limiting M. zapota fruit production in forests, while in homegardens the main factor appears to be pollinator availability.

Cherimoya (Annona cherimola Mill.) is a subtropical fruit crop that exhibits protogyny dichogamy and for which the original pollinators are not present in the main producing countries. Under such circumstances the achievement of profitable yields depends on hand pollination. The present work explores the effects of the amount of pollen applied on pollen–pistil interaction and on fruit set, size, shape and growth. Pollen dilution with Lycopodium spores reduced fruit set and size and favoured the appearance of misshapen fruits, whereas the application of double amount of pollen did not improve fruit size and increased fruit set only the first year. Pollen load did not affect fruit growth model, which always followed a double sigmoid pattern. Nevertheless, the slopes of the curves during the two rapid growth phases were higher when a larger amount of pollen grains was applied. Seed index (seed number per 100 g of fresh fruit weight) rose slightly as pollination level increased.

Native plants in gardens can potentially aid conservation by contributing to genetic diversity and buffering small and otherwise isolated populations from extinction. However, gene flow from such plantings may threaten the genetic integrity of natural populations. We assessed the morphological and genetic diversity of garden plants in an urban population of Grevillea macleayana in south-eastern Australia. There were two main groups of garden plants: some similar to plants in nearby natural populations; others with unusual morphology. Multivariate analysis of morphological characters separated these groupings, which were confirmed by genetic analysis. Both groups produced seeds and flowering phenologies overlapped, indicating a potential for gene flow. Hand pollination showed that plants in each group could fertilize flowers of the other. Thus, these garden plants contributed to genetic variation in an urban/bushland metapopulation but there was potential for gene flow from the unusual plants. Unless carefully managed, garden plants may therefore cause disruption of the genetic integrity of nearby natural populations.

By applying hand pollination, we studied pollen limitation of seed set of female plants in four dioecious plant species with insect-pollination. The effect of hand pollination increased with distance to the nearest male plant. Distances at which seed set was 50% of its maximal value (after hand pollination) were: 2.3 m for Valeriana dioica, 5.3 m for Salix repens, 8.5 m for Asparagus officinale and 10.6 m for Bryonia dioica. We discuss to what extent the reduced seed set was caused by either fewer visits or by visits of a lower quality. We argue that quantifying distance-dependent seed set in dioecious plants may be a good way of studying effects of habitat fragmentation on the breakdown of mutualistic pollination systems.

The effect of diurnal maximum/minimum (20/10 or 25/15 °C) temperatures on seed and fruit development of ‘Irwin’, ‘Kensington’ and ‘Nam Dok Mai’ mangoes ( Mangifera indica L.) was studied in a controlled-environment glasshouse. Exposure to low temperatures (20/10 °C day/night) 3 days after hand pollination significantly increased the percentage of stenospermocarpic fruit (nubbins), in which embryos were aborted at some stage during early fruit development. There were significant differences between cultivars in the percentage of nubbins produced out of the total fruit set following overnight exposure to 10 °C with 21% for ‘Nam Dok Mai’, 11% for ‘Kensington’ and 3% for ‘Irwin’. At 45 days after pollination, nubbin fruits were much smaller in size and weighed ca. 50% less than normal fruits. The lower percentage of nubbin fruits in ‘Irwin’ implies a greater adaptation to cool temperatures by this cultivar during fruit set and early embryo development.

Plants growing in small fragmented populations under stressful environmental conditions may have reduced sexual reproduction. This can cause low gene flow between populations and eventually extinction. Here we report on a pollination experiment with Sorbus torminalis, a rare fleshy-fruited tree with a submediterranean distribution in Europe. At the northern limit of its range in SE-Denmark two relatively small and isolated populations were studied for effects of seven pollination treatments on fruit production and on the timing of fruit abortion. There was evidence that lack of pollination and spontaneous self-pollination caused particularly high fruit abortion, which indicates that apomixis is unlikely and spontaneous self-pollination not efficient. Fruit abortion was delayed after hand pollination, which suggests limitation by pollen quantity. Self-pollination caused earlier abortion than experimental cross-pollination within or between populations indicating inbreeding depression. There was no evidence for outbreeding depression as measured by fruit abortion. We conclude that generative reproduction of S. torminalis is reduced on its northern distribution limit and that it might be negatively affected by pollen limitation and inbreeding effects, which have not been compensated for by increased self-compatibility or apomixis.

Columnar cacti in tropical deserts depend on nectar-feeding bats for their reproduction while species from extra-tropical deserts show a relatively generalized pollination system with both nocturnal and diurnal pollinators. Pachycereus pecten-aboriginum is a columnar cactus with a broad distribution along the Pacific coast of Mexico, from Oaxaca to Sonora. Along its distribution, the nectar-feeding bat, Leptonycteris curasoae, changes from resident within the tropics to migratory in the Sonoran desert. If bat unpredictability has been an important force in the evolution of pollination systems in columnar cacti, P. pecten-aboriginum is expected to show a relatively generalized system in northern populations. We studied the pollination biology of P. pecten-aboriginum in two northern populations in the state of Sonora. Hand pollination experiments showed that this species has a self-incompatible, hermaphroditic breeding system. Although flowers open at night, they remain open and continue secreting nectar during the morning, allowing visitation by both nocturnal and diurnal pollinators. One population showed evidence of strong pollinator limitation while the results from both populations indicated that diurnal pollinators are more important than nocturnal pollinators. These results are discussed in terms of specialization vs. generalization in the pollination biology of columnar cacti in tropical and extra-tropical deserts.

A new method for producing seedless watermelon ( Citrullus lanatus ) in diploid plants using soft-X-irradiated pollen is described. Fruit set at almost the same rate despite soft-X-irradiation. Empty seeds were produced in the watermelon cultivars ‘Benikodama’ and ‘Fujihikari TR’ following hand pollination using soft-X-irradiated pollen. Soft-X-irradiation doses of 800–1000 Gy resulted in small empty seeds in ‘Fujihikari TR’, whereas 400–1000 Gy doses gave the best results for ‘Benikodama’, although empty seeds in the latter were many and conspicuous. Soft-X-ray treatments did not affect fruit weight, shape, rind thickness or days to maturation compared to controls. However, female flowers treated with soft-X-irradiated pollen produced fruits with slightly higher sugar content compared to controls in ‘Benikodama’. Therefore, this new method is an effective technique to produce seedless watermelon.

Cherimoya (Annona cherimola Mill.) is a subtropical fruit tree highly dependent on pollination and in most parts of the world hand pollination is a common agricultural practice. However, erratic results following hand pollination have often been associated with low pollen viability. In spite of this dependence on good pollen viability, a good method to evaluate pollen viability is not yet available. This deficiency may be related to the fact that little is known about pollen germination occurring in vivo. In this work pollen germination is first characterised in vivo and the temperature effect on pollen germination evaluated. Subsequently, a medium for pollen germination has been optimized and the conditions for in vitro pollen germination determined. Mature pollen is trinucleated and is shed from the anther in tetrads. Upon pollen hydration, either on the stigma or in the germination medium, pollen is liberated from the tetrad. While the kinetics of the process are quicker in vitro, both processes occur rapidly and are completed within 2 h in vitro and within 5 h in vivo. Pollen germination is optimum at 20–25°C, that is the same temperature required for good fruit set in the orchard. Pollen requires prehydration prior to in vitro germination and it only germinates when the stamens are also added to the medium, that requires the provision of calcium and boron as well as sucrose at 5–10%. Provided these factors are taken into account, pollen germination can reach levels similar to the ones attained in vivo.

Open- and hand pollination, ovule morphology, seed structure and germination of Gloriosa superba L. are discussed as possible factors influencing reproduction. The protogynous flowers in the frondose raceme are psychophilous and ornithophilous with a stigma receptivity period of at least four days. Development of the femaie gametophyte conforms to the Polygonum type, The inner integument acts as an endothelium due to the absence of the nucellus on the lateral sides of the embryo sac, where the nucellus has degenerated. A well-developed funicular obturator directs pollen tubes to a nucellar epistase where a partial self-incompatibility reaction appears to occur. A hypostase on the chalazal side contains transfer cells connecting the vascular tissue with the embryo sac. Seeds are tegmic, surrounded by a sarcotesta showing adaptations for endozoochory. Seed production was slightly better after cross-pollination, and also when 4B hour-old pollen was used, especially when pollination was done in the second flower phase. When the three factors were combined and applied to the proximal flowers in the inflorescence, seed production was significantly improved.

The effects of hand pollination technique, pollen source and the time of pollination were evaluated on the set and development of cherimoya (Annona cherimola) fruit. Up to 5% of flowers on trees of four cultivars (‘Bays’, ‘Reretai’, ‘Spain’ and ‘White’) set naturally but few of these fruit remained on the tree at harvest. Depending on cultivar, 84–96% of flowers that were hand pollinated with pollen from the same cultivar set fruit, compared with 38–69% of flowers pollinated with a mixture of pollen from all cultivars. Fruit resulting from self pollination were more symmetrical and had a higher mean fruit weight than cross pollinated fruit. The cultivars ‘Bays’ and ‘Spain’ showed a higher degree of cross incompatibility than ‘White’ or ‘Reretai’. Pollinating cherimoya flowers in the evening, immediately after pollen collection, was more effective than storing pollen overnight to pollinate newly opened flowers. This suggests that pollen viability, rather than stigma receptivity, is the greatest limitation to successful cherimoya pollination in a humid climate. Flowers pollinated in the evening with diluted pollen via a pollination gun were more likely to set than flowers pollinated with a brush and undiluted pollen; however, the latter produced higher yields. Flowers pollinated in the middle of the flowering period produced larger and more symmetrical fruit than those pollinated at the beginning or end of flowering.

Poor fruit set continues to be a major problem in the avocado industry in South Africa. In the past this was estimated to have caused a loss of income of millions of rands. In this investigation the role of fungi on the pistils of avocado cultivars after pollination was examined. Pollinated pistils of avocado cultivars ‘Pinkerton’, ‘Ryan’, ‘Hass’, ‘Fuerte’ and ‘Nabal’ were removed twenty-four hours after the first anthesis (female stage), for detection and isolation of fungi. Germinating conidia were seen on the surface of stigma adjacent to the germinated pollen grains. A number of dematiaceous fungi were isolated from the pistils and the most important species were identified. When a drop of the spore suspension of the most frequently isolated fungi was inoculated on the stigmas of emasculated flowers after hand pollination, a high rate of abscission was observed. Thus some of these fungi appear to have played a significant role which resulted in greater abscission of flowers.

The fruit production of Japanese persimmons cultivars ‘Fuyu’ and ‘Saijo’ is unstable unless they are pollinated. To ascertain whether gibberellins (GAs) could substitute for hand pollination, fruitlets from flowers which were excluded from pollinators during a flowering period were sprayed with 200 mg l−1 GA3 and a mixture of GA4 and GA7 (GA4+7) about 10 days after full bloom. In both cultivars GA3 was more effective than GA4+7 and GA3 significantly increased seedless fruit set. Further, to determine the lowest concentration of GA3 for practical use without severe inhibition of flowering, effects of GA3 at rates of 0, 25, 50 and 100 mg l−1 on fruit set and development of seedless fruit were examined. All treatments of GA3 at 25, 50 and 100 mg l−1 significantly reduced fruit drop in ‘Saijo’. However, even at 25 mg l−1 the spray of GA3 tended to reduce the flowering potential in the following year. In ‘Fuyu’, GA3 was incapable of inducing sufficient fruit set without reducing flowering. Fruit growth was inhibited in seedless fruits of both cultivars, even if they were treated with GA3.

Spraying N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU, code name KT-30) on unpollinated flowers of kiwifruit, Actinidia chinensis Planch., at or before anthesis, induced parthenocarpic fruit development. Flowers treated 3 days before anthesis developed small and completely seedles fruits. Flowers treated at anthesis developed large fruits with many small seeds which consisted of seed coat only without any indication of the development of embryo or endosperm. Post-bloom application of CPPU strongly stimulated fruit growth, with application about 3 weeks after anthesis being more effective than that just after anthesis. These fruits were larger than untreated open-pollinated control fruit and ripened earlier, as evidenced by softening of the flesh and a decrease in titratable acidity. The possibility of commercial application of CPPU on kiwifruit was discussed in relation to elimination of hand pollination.

Some commercial plantations of gooseberry ( Ribes uva-crispa L. cultivar ‘Careless’) recently carried poor crops of small fruit with few seeds. The flowers appeared normal and there was an effective pollination period of at least 11 days. Hand pollination resulted in a good set of normal fruits. Few pollinating insects were recorded on a typical affected site, but on trouble-free sites insects, particularly honey bees, were plentiful and effective in transferring pollen. On trouble-free sites, excluding pollinating insects by caging bushes resulted in a typical crop failure, but caging had little effect on the problem site. Introducing honey-bee colonies to the affected site increased fruit set and seed number by comparison with caged bushes.

The floral response of the type A avocado cultivars ‘Reed’, ‘Wurtz’, ‘Rincon’ and ‘Jalna’, and the type B cultivars ‘Bacon’, ‘Ryan’, ‘Edranol’, ‘Sharwil’ and ‘Hazzard’ was tested under growth-cabinet conditions of 17° C day, 12° C night, with a 12-h photoperiod and photon flux density of 400 μE m −2 s −1 (400–700 nm). Most of the flowers of all type A cultivars and the type B cultivar ‘Bacon’ had both a female and a male stage. None of the flowers of the other type B cultivars had a female stage but opened in the male stage only. Hand pollination resulted in some ovule penetration in the cultivars with female stage flowers. In those with only male-stage flowers, the pollen tubes grew no further than the style. Maintenance of fertility under low-temperature conditions during flowering appeared to be partly, but not entirely, linked to the type A flowering cycle.