Hand Pollination Research Articles

Community-wide assessment of pollen limitation in hummingbird-pollinated plants of a tropical montane rain forest

Although pollen limitation of reproduction (PL) has been widely studied, our understanding of its occurrence in tropical communities, especially for bird-pollinated plants, is underdeveloped. In addition, inclusion of both quantity and quality aspects in studies of PL are generally lacking. Within hummingbird-pollinated plants, a prediction was made for higher PL for the quality than quantity aspects and a minor effect of temporal variation because hummingbirds are constant and efficient pollen vectors but they may transfer low quality pollen. Field hand and open pollination experiments were conducted on 21 species in a tropical montane rain forest over 2 years. The quantity (fruit set and seeds per fruit) and quality (seed weight and germination) aspects of reproduction were assessed as the response to open pollination relative to outcross hand pollination. The relationships between the effect size of quantity and quality aspects of reproduction and predictive plant features (self-incompatibility, autogamy, density and pollinator specialization level) were assessed with phylogenetic generalized linear models. Just over half of all the species expressed PL for one or more response variables. On average, the severity of PL was strong for one quality variable (seed germination; 0·83), but insignificant for another (seed weight; -0·03), and low to moderate for quantity variables (0·31 for seeds per fruit and 0·39 for fruit set). There was only a minor contribution of temporal variation to PL within the studied species. Common predictors of PL, i.e. phylogenetic relatedness, self-incompatibility, autogamy, plant density and pollinator specialization level, did not adequately explain variation in PL within this community. Despite the measurable degree of PL within these hummingbird-pollinated plants, the causes of pollen quality and quantity insufficiency are not clear. Variables other than those tested may contribute to PL or causes of PL may vary among species and cannot adequately be accounted for when assessed from the within-community perspective.

Vertebrate pollination of the endemic Trochetia granulata (Malvaceae) on Réunion

Abstract:The pollination ecology and breeding system of Trochetia granulata (Malvaceae), an endemic tree species from Réunion were studied. In 2010–2011, compatibility studies were conducted on a total of 154 flowers from 35 different individuals using three different hand pollination treatments: (a) autofertility, (b) self-pollination and (c) cross-pollination. During the period, we also studied the pollination ecology of T. granulata. During 48 h of video recordings, we tracked flower visits to T. granulata in six different sites and studied the behaviour of the visitors. The results from the hand-cross experiments show that T. granulata is self-compatible (60.8% fruit set) but cannot produce fruit (5.4% fruit set) without the visit of a pollen vector. During surveys, four different visitors were reported: the introduced honey bee (Apis mellifera), two endemic species of white-eye (Zosterops borbonicus borbonicus and Z. olivaceus) and the endemic Réunion day gecko (Phelsuma borbonica). This study documented a new case of vertebrate-pollination by lizard and birds in an insular context. These interactions might be linked to several uncommon floral traits of Trochetia species.

Melittophily and ornithochory in Tilesia baccata (L.f.) Pruski: An Asteraceae of the Atlantic Forest understory with fleshy fruits

Many Asteraceae species inhabit open vegetation areas and, as a rule, members of this family have dry, wind-dispersed fruits. Tilesia baccata, on the other hand, occurs in forested areas and, differently from all neotropical Asteraceae, has fleshy fruits with ornithochorous characteristics. However, no studies have confirmed the dispersion by birds or any other aspect of the reproductive biology of this unique Asteraceae. The present study aims to investigate the reproductive phenology, floral biology and breeding system and to identify the pollinators and seed dispersers of T. baccata. The study was carried out in a natural population located in a semideciduous forest (Viçosa, Minas Gerais State), southeastern Brazil. The reproductive cycle of T. baccata is annual and seasonal, related to precipitation, temperature and day length. The longevity of flowers and capitula depends on the performance of pollinators and dispersers. Hand pollination tests showed that the species is self-incompatible and therefore dependent on synchronous flowering and pollinator availability. Pollination occurred in the morning, in the period of pollen availability, and social bees were the major pollinator group. Seeds are dispersed by frugivorous birds, that swallow the ripe fruits and defecate viable seeds later. Our study confirmed the bird dispersal of Tilesia baccata seeds and also demonstrates that pollinator activity and fruit removal by birds influence the magnitude of activity and the intensity of flowering and fruiting.

Pollen tube growth and self-incompatibility in three Ziziphus species (Rhamnaceae)

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.

Andromonoecy and developmental plasticity in Chaerophyllum bulbosum (Apiaceae-Apioideae).

Andromonoecy, the presence of hermaphrodite and male flowers in the same individual, is genetically fixed or induced, e.g. by fruit set. Little is known about the forces triggering andromonoecy in the Apiaceae. In the present study, a natural population of the protandrous Chaerophyllum bulbosum was investigated to elucidate architectural constraints and effects of resource reallocation. Three sets of plants (each n = 15) were treated by hand pollination, pollinator exclusion and removal of low-order inflorescences. Fifteen untreated plants were left as controls. Untreated plants produce umbels up to the third branch order, with increasing proportions of male flowers from 15 % (terminal umbel) to 100 % (third-order umbels). Fruit set correspondingly decreases from 70% (terminal umbel) to <10 % (second-order umbels). Insignificant differences from hand-pollinated plants do not reveal any sign of pollinator limitation at the study site. Bagged individuals show the same increase in male flowers with age as untreated plants, indicating that the presence of andromonoecy is not induced by fruit set. After umbel removal, individuals tend to present a higher number of hermaphrodite flowers and fruits in the umbels of second and third order. Three plants (25 %) produced an additional branch order composed of 100 % male umbels. Inherited andromonoecy and the plastic response to environmental conditions are interpreted as a self-regulating system saving investment costs and optimizing fruit set at the same time.

Stingless bees, Melipona fasciculata, as efficient pollinators of eggplant (Solanum melongena) in greenhouses

Detailed studies of the behavior of pollinators allow insights into pollination mechanisms and may indicate which pollinators are more efficient for a particular plant species. Our aim was to evaluate if Melipona fasciculata is an efficient pollinator of eggplant (Solanum melongena L., Solanaceae) in greenhouses. We analyzed (1) the colony foraging pattern of M. fasciculata in greenhouses, (2) the behavior of bees during the visits to flowers, and (3) fruit set and fruit quality after different pollination treatments (hand pollination: autogamy, geitonogamy, xenogamy; bee pollination). Our results show that M. fasciculata is an efficient pollinator of eggplants and, consequently, may be a viable alternative to bumblebees in Brazil.

Effect of Different Light on Pollen Germination, Tube Growth, Fruit Set and Fruit size in Alkaloid Yielding Plant Solanum Torvum Sw.

The present study showed the improvement of S. torvum plant through the effect of different light on pollen germination, pollen tube growth, fruit set, fruit size and fresh weight of ripened fruits. The pollen grains of S. torvum were germinated on a basal medium and study the effect of blue, green, white, yellow and red light under in–vitro condition. Percent of pollen germination and tube growth were lesser in the dark condition than the white light but maximum by the red light in 4 and 5 hrs incubation. Based on pollen germination and tube growth variability in-vitro from different light. Hundred long-styled flowers (before anthesis) were chosen randomly for each colour and after hand pollination obtained the per cent of fruit set, size and weight of ripened fruit was lesser in the dark as compared to other lights and aforementioned these values were maximum under the red light. Thus, the present work emphasised that the red light should be used for the improvement of fruit size in S. torvum.

Atypical distyly in Psychotria goyazensis Mull. Arg. (Rubiaceae), an intramorph self-compatible species

Distyly is a genetically controlled floral dimorphism, characterized by the reciprocal positioning of pin and thrum morphs, a heteromorphic incompatibility system and a balanced morph ratio (isoplethy). This study aimed to investigate the phenology, features of distyly, reproductive biology, and floral visitors of Psychotria goyazensis Mull. Arg. (Rubiaceae), an intramorph self-compatible species, in a tropical semideciduous forest in the municipality of Catalao, located in the state of Goias, Brazil. The phenology was recorded for a sample of individuals, the floral morphology being described using fresh and fixed material. The incompatibility system was tested using controlled hand pollinations. Floral visitors were collected and identified. Blooming began in November 2009 and ended in April 2010. Fruits developed from December 2009 to March 2010. The population presented atypical distyly, because only plants with pin flowers were found. The intramorph and open pollinations set more fruits than did spontaneous self-pollinations. The main flower visitors were Systropus sp. (Diptera), as well as Hymenoptera and Lepidoptera species. Morphological variations in distyly can occur by breakdown/permutation of the gene that controls the polymorphism. However, some authors argue that, in Rubiaceae, genetic control of the incompatibility system can operate independently of the morphological factor, and species might respond in different ways to the same selective pressures.

Pollination of invasive Eichhornia crassipes (Pontederiaceae) by the introduced honeybee (Apis mellifera L.) in South China

Heterostyly functions as an outcrossing mechanism facilitating accurate pollen transfer from anthers to stigmas of particular heights as a result of the behavior of specialist pollinators. However, heterostylous plants are also visited by generalist pollinators, which may affect the plant–pollinator mutualism. Eichhornia crassipes is a tristylous invasive species, with only the mid- and long-styled morphs (M and L) found in China. We recorded flower-visiting insects in Zhuhai, Zhongshan and Nanning in South China. We hand-pollinated the two morphs to determine their compatibility. In addition, by allowing controlled insect pollination in artificial isoplethically monomorphic and bimorphic populations, we undertook a detailed analysis of pollen deposition between the floral morphs, and fruit and seed set. Ranked by relative abundance, the flower-visiting insects were: Apis mellifera, A. cerana, Lasioglossum sp. and Eristalis arvorum. Hand pollination showed that both the M and L morphs were self-compatible, but the former was probably more so than the latter. Intra-morph pollen transfer by A. mellifera within a population was significantly greater than legitimate pollen transfer between populations, suggesting that the pollen exchange between populations was limited. Seed set of the L morph was significantly greater than that of the M morph in monomorphic populations, indicating intra-morph pollen deposition in the former was higher than in the latter. The results showed that A. mellifera was the major pollinator in South China and able to pollinate E. crassipes legitimately and to promote its fruit and seed set, even though high levels of intra-morph pollination occurred.

FLOWERING PATTERN AND FRUITFUL CAPACITY OF 'FINO DE JETE' CHERIMOYA SHOOTS

Cherimoya is a subtropical fruit tree indigenous to the inter-Andean valleys between Peru and Ecuador. Cherimoya dichogamy and the lack of efficient pollinators in Spain hinder natural fruit set, making hand pollination unavoidable. Cherimoya flowers are formed on current season growth and on 1-year-old shoots of different vigour. Hand-pollination allows selection of the more convenient flowers to be pollinated in order to obtain high quality fruits. Here, we have determined the frequency, fertility and flowering dates and patterns of the different kinds of shoots (high, medium and low vigour) found in cherimoya trees as the first step to modifying current pruning procedures. The results show that adult vase-trained trees traditionally-pruned have an equilibrated proportion of vigorous, semi-vigorous, and weak shoots. However, the number of flowers formed and the distribution of flowers along the wood were significantly different among the different kinds of shoots. Vigorous shoots formed an average of 65 flowers; semi-vigorous shoots produced an average of 36 flowers, while weak wood formed only 17 flowers per shoot. Flowering pattern was also different. Basal nodes of vigorous shoots formed a high proportion of flowers, while apical nodes did so in weak shoots. The flowering season extended from May to August with peak flowering occurring in mid-June with no differences in flowering dates among shoots. Based on these results, we recommend pruning to focus on encouraging the production of vigorous and semi-vigorous shoots able to sustain a crop load of 400 fruits per tree and to develop sufficient pollen-donor flowers. Hand-pollination is advised for flowers formed in the basal-central nodes of these shoots. A higher number of flowers per node did not diminish their size.

NEW MANGO HYBRIDS FROM AUSTRALIA

The Australian National Mango Breeding Program has been breeding mangoes since 1994. In recent years, evaluation of the elite selection have identified three high performing hybrids, NMBP1243, NMBP1201 and NMBP4069, which are in the process of commercial release. These hybrids all have 'Kensington Pride' as their paternal parent and are characterised by improved fruit colour and tree productivity over 'Kensington Pride'. NMBP1243 is noted for its early season production, and NMBP1201 and NMBP4046 for their firm fruit. The hybrids were produced using hand pollination breeding and selection techniques. The breeding program is ongoing with the current hybridisation program being supported by a multidiscipline approach, that includes marker assisted screening, disease screening, postharvest evaluation and a genomics gene discovery program.

Reproductive strategy of the invasive Oxalis pes-caprae: distribution patterns of floral morphs, ploidy levels and sexual reproduction

Oxalis pes-caprae, a tristylous flowering plant native to South Africa, is described in the western Mediterranean basin as an asexual—only 5x short-styled morph (5x S-morph) invasive weed losing all mating partners after introduction. The objective of this study was to reassess the patterns of floral morph and cytotype distribution and the sexual reproduction ability in this invaded range. For that, floral morph and cytotype composition were evaluated in 39 populations of O. pes-caprae in a methodical sampling. The reproductive success of natural populations was assessed as fruit and seed production and seed germination for all floral morphs and cytotypes detected. Self- and morph-incompatibility were also studied with controlled hand pollinations. A remarkable diversity in floral morph and cytotype composition was observed. Furthermore, we observed successful sexual reproduction in several localities across the surveyed area. The S-morph is still dominant in this invaded area, and although it was mostly 5x, an additional cytotype (4x) was also recorded. Records of both a mid-styled morph (M-morph) and an area with trimorphic populations of this species are reported here for the first time in the invasive range of the Mediterranean basin. The long-styled morph appears to occur randomly across the surveyed area, while the M-morph is concentrated mainly in Estremadura province (Portugal), where a breakdown in the incompatibility system was observed. These distribution patterns may result from events of sexual reproduction after incompatibility breakdown and/or from multiple introduction events from the native area. The ability to reproduce sexually, undetected so far, may have important impacts in the population dynamics and major consequences for the adaptation and selection potential of O. pes-caprae in this invaded area.

Population size, pollination and phenotypic trait selection in Phyteuma spicatum

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.

Precautionary hand pollination suggests outbreeding depression between potential seed donor populations for a rare wetland plant1

Pyrrocoma racemosa var. racemosa, is a rare, endemic species found in six remnant Willamette Valley wetland prairie sites in western Oregon, USA. Due to its rarity and association with high-quality wetland habitat, P. r. var. racemosa is a focal species for reintroduction and genetic rescue. However, no genetic studies for this species have been undertaken. I conducted a pollen addition experiment between the two largest P. racemosa populations to determine the effects of selfing, intrapopulation crosses and interpopulation crosses on plant fitness. An ANOVA indicated that the percentage of filled achenes from intrapopulation crosses was significantly greater (≈ 30% more filled achenes) than both interpopulation crossing and selfing, which did not statistically differ from each other. Pollen viability, inferred through flourescein diacetate staining, did not differ statistically over the time span that it took to gather and perform the pollen addition treatments, suggesting that the diminished seed set from the interpopulation crosses was due to genetic incompatibility. Although the two P. r. var. racemosa populations are only about 6 km apart, the established seed transfer zones for other locally rare plants are considerably larger and if applied would not likely provide an effective genetic safeguard.

Annual Variation in Flowering Phenology, Pollination, Mating System, and Pollen Yield in Two Natural Populations of Schima wallichii (DC.) Korth

Background. Schima wallichii is a highly valuable tree of tropical forest in north-east Himalaya region that grows naturally in a wide range of altitudes between 750 and 2400 m asl with varying environments. Flowering phenology of tropical tree species at population level is generally ignored and therefore a detailed knowledge of flowering and fruiting patterns of important multipurpose tree species is critical to the successful management of forest genetic resources. Materials and Methods. The study was conducted at two different altitudes (i.e., 750 m and 900 m asl) in the tropical semideciduous forest of north-east Himalaya. The floral phenology including flowering synchrony in the populations, anthesis, anther dehiscence, stigma receptivity, pollinators visitation frequency, and mating system including index of self-incompatibility were worked out in Schima wallichii according to the ear-marked standard methods given by various scientists for each parameter. Results. The flowering period in Schima wallichii varied from 33 to 42 days with mean synchrony of 0.54 to 0.68 between the populations. The stigma was receptive up to 2.5 days only and showed slightly protandrous type of dichogamy. Average pollen production ranged between 6.90 × 107 pollen per tree in 2007 and 15.49 × 108 pollen per tree in 2011. A three-year masting cycle was noticed in this species. The frequency of visitation of honey bees was fairly high (5.2 ± 1.12 visits/flower/hour) as compared to other pollinators. The hand pollination revealed maximum fruit (74.2 ± 5.72%) and seed (70.8 ± 7.46%) settings. Conclusions. The variation in flowering phenology and pollen yield individually and annually along with temporal separation in anther dehiscence and pollinator's visitation cause pollen limited reproduction, which ultimately influences the reproductive success in Schima wallichii.

Erratum to: Unexpectedly high outcrossing rate in both dense and sparse patches in self-compatible Pedicularis rex (Orobanchaceae)

Pedicularis rex, a self-compatible alpine herb, depends exclusively on pollinators for reproduction. Previous study has revealed that 74.7 % of genetic variability occurs among populations in Yunnan, indicating a mixed mating system for the species. The large floral display also indicates high potential geitonogamy. Therefore, plant density and display size may be important factors influencing the realized mating system of P. rex. In the study reported here we explored the effects of plant density and floral display size on pollinator movements and thus outcrossing rate in two patches of in P. rex at low and high plant densities. We examined foraging behavior of bumblebees, measured reproductive outputs under hand and natural pollination, and estimated the outcrossing rates using RAPD markers. Floral display size was significantly larger and bumblebees visited significantly more flowers in sequence on individual plants in the sparse patch than in the dense patch. We found a significant positive correlation between floral display size and successive visits in the sparse patch, but not in the dense patch. Regression analysis revealed a significant inverse correlation between fruit production and flower production per plant with a theoretical maximum of 63 fruits per plant, but no relationship between seed production and flower production per plant. Contrary to previous studies on genetic structure, however, we found an unexpectedly high outcrossing rate in both the sparse and the dense patch (tm = 1.151 and 0.924, respectively). Resource limitation may intensify seed competition and result in selected seed abortion, which may largely explain the unexpectedly high outcrossing rate.

Self-interference is reduced in a secondary pollen presentation species, Duperrea pavettifolia (Rubiaceae)

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.

Creating patches of native flowers facilitates crop pollination in large agricultural fields: mango as a case study

Summary As cropland increases, fields become progressively isolated from pollinators, leading to declines in pollinator‐dependent crop productivity. With the rise in demand for pollinator‐dependent foods, such productivity losses may accelerate conversion of natural areas to cropland. Pollination–compensation measures involving managed pollinators or hand pollination are not always optimal or are too costly. Introducing areas of native vegetation within cropland has been proposed as a way to supplement crop pollinators, but this measure is perceived by farmers to carry costs outweighing benefits to agricultural production. Studies quantifying benefits of small patches of native flowers to crop pollination are therefore necessary to encourage such practices. To ascertain whether provision of floral resources within farmlands can facilitate pollination, and hence, crop yields, small experimental patches of perennial native plants (native flower compensation areas, NFCAs) were created in nonproductive areas of large commercial fields of several cultivars of mango Mangifera indica. Pesticide use and isolation from natural habitat were associated with declines in flying visitors and in mango production (kg of marketable fresh fruit), but presence of NFCAs ameliorated these declines, and NFCAs did not harbour any mango pests. In areas far from natural vegetation, orchards near NFCAs had significantly higher diversity and abundance of mango flying visitors, as well as mango production, than orchards far from NFCAs, although these measures were still lower than in orchards close to natural areas. Neither the most abundant flower visitors to mango (ants) nor initial fruit set was significantly affected by distance, pesticides or NFCAs, suggesting that although fertilization is associated with factors unaffected by isolation from natural habitat and pesticide use (i.e. self‐ and ant‐pollination), viable fruit set (and ultimately, production) requires cross‐pollination, for which flying visitors are essential. Synthesis and applications. Our results show that the presence of small patches of native flowers within large farms can increase pollinator‐dependent crop production if combined with preservation of remaining fragments of natural habitat and judicious use of pesticides. Native flower compensation areas represent a profitable management measure for farmers, increasing cost‐effectiveness of cropland while indirectly contributing to preservation of natural habitat.

The importance of plant diversity in maintaining the pollinator bee, Eulaema nigrita (Hymenoptera: Apidae) in sweet passion fruit fields

The euglossine bee Eulaema nigrita plays an important role for the pollination of native and economically important plants, such as the sweet passion-fruit Passiflora alata. E. nigrita uniquely collects the nectar from the flowers of P. alata, nevertheless, it needs to visit other plants to collect pollen, nectar and other resources for its survival. There are two methods to identify the species of plants used by bees in their diet: by direct observation of the bees in the flowers, and through identification of pollen grains present in brood cells, feces, or in the bees' body. In order to identify the other plants that E. nigrita visits, we analyzed samples of pollen grains removed from the bee's body in the course of the flowering period of P. alata. Among our results, the flora visited by E. nigrita comprised 40 species from 32 genera and 19 families, some of them used as a pollen source or just nectar. In spite of being a polyletic species, E. nigrita exhibited preference for some plant species with poricidal anthers. P. alata which has high sugar concentration nectar was the main source of nectar for this bee in the studied area. Nonetheless, the pollinic analysis indicated that others nectariferous plant species are necessary to keep the populations of E. nigrita. Studies such as this one are important since they indicate supplementary pollen-nectar sources which must be used for the conservation of the populations of E. nigrita in crops neighbouring areas. In the absence of pollinators, growers are forced to pay for hand pollination, which increases production costs; keeping pollinators in cultivated areas is still more feasible to ensure sweet passion fruit production.

Effects of biological factors on fruit and seed set in loquat ( Eriobotrya japonica Lindl.)

In this study, the effective pollination period (EPP) was studied using three loquat cultivars with different seed set abilities, ‘Dawuxing’, ‘Longquan No.5’ and ‘Chuannong No.1’, so as to identify the factors determining fruit set and seed set. The EPP was determined by delayed and hand pollination, and the factors affecting the EPP were evaluated through histochemical tests and fluorescence microscopy. The EPP was measured as the capacity to set fruit and seeds after pollination with ‘259’ loquat pollen from anthesis to seven days after anthesis (DAA). The stigmatic receptivity closely fitted the EPP and thus appeared to be the main factor determining fruit set and seed set in ‘Dawuxing’ and ‘Longquan No.5’. In ‘Chuannong No.1’, low rate of style with intense stigma receptivity and early ovule degeneration appeared to be the factor determining seed set. We concluded that loquat flower receptivity is genotype-dependent either on stigmatic receptivity, as in ‘Dawuxing’ and ‘Longquan No.5’, or stigmatic receptivity and ovule degeneration, as in ‘Chuannong No.1’. Key words: Loquat, effective pollination period, stigma receptivity, pollen tube growth, ovule degeneration, seed set.