Levels Of Fruit Set Research Articles

Pollination and reproductive biology of thirteen species of <i>Begonia</i> in the Serra do Mar State Park, São Paulo, Brazil

The reproductive biology of 13 monoecious species of Begonia that occur in the Serra do Mar State Park, São Paulo, Brazil, was investigated. These species flower annually and present flowers with mostly white tepals, sweet odour, pollen as a reward but no nectar, numerous yellow stamens, and yellow styles. Anthesis is diurnal and floral duration is long (6 - 15 days). The unusual appearance of pistillate flowers of these species supports the view that they are intersexual mimics of the staminate flowers. Despite consistently high levels of fruit-set, none of the 11 species tested proved to be apomictic. In contrast to earlier reports of self-compatibility in Begonia, self-pollinations of B. integerrima and B. itatinensis produced no fruits or seeds, and the complete absence of pollen tubes in the styles of self-pollinated flowers of B. integerrima suggests that the species is self-incompatible. Flowers pollinated under natural conditions showed many pollen tubes that reached ovules, suggesting that adequate numbers of compatible pollen grains had been transported by pollinators. The principal pollinators were bees of the Apidae and Halictidae. Ten species of bees were observed to visit eight species of Begonia, and pollen collection occurred by vibration, except for Trigona spinipes. Visits to rewarding staminate flowers were significantly more frequent than visits to unrewarding pistillate flowers. Duration of visits to pistillate flowers also was significantly shorter than the duration of visits to staminate flowers. We conclude that visits to pistillate flowers occur by mistake but with sufficient frequency to allow for successful reproduction in natural populations of these species.

Phenology, pollination and breeding system of Aegle marmelos (Linn.) correa (Rutaceae) from India

Studies on reproductive biology are difficult but useful in species like Aegle marmelos (Linn.) Correa which is of considerable socio-economic importance and possess morphogenetic variation and qualities of wider adaptability to different soils. Cytology, phenology, pollination, breeding system and natural regeneration of wild and cultivated trees from India revealed the existence of diploid (2n = 18) and tetraploid trees (2n = 36) in Pachmarhi hills and only diploid trees in Punjab plains and Shiwalik hills. The diploid and tetraploid trees showed normal meiosis and high pollen fertility. Phenological events which included leaf fall, leaf emergence, floral bud break, flowering and fruiting are nearly the same in wild and cultivated trees. Natural pollen transfer in the species was highly efficient. Levels of fruit set following open pollination was quite high and is reduced considerably following hand pollination probably due to some injury caused to stigma during experiments. Inspite of synchronous nature of anther dehiscence and stigmatic receptivity, selfing in a flower was avoided due to herkogamy. Some selfing, however, occurred through geitonogamous mode as bagging of panicles yielded 12.21 ± 0.99 to 14.12 ± 0.91% fruit set. High pollen ovule ratio (9,250–10,600) indicated toward the obligate outbreeding nature. The species suited to insect and wind mode of pollination. High amount of air borne pollen grains deposited on glycerine smeared glass microscopic slides suggested towards the wind mode of pollination. Though flowers are dull coloured a variety of insects visited the flowers due to sweet fragrance and stamen/pollen as food reward. Among insect pollinators, honey bee (Apis dorsata) was the major and legitimate pollinator while the rest were either minor pollinators or mere visitors. Inspite of high fruit/seed set, natural regeneration through seeds was poor as fallen fruits were destroyed by fungal pathogens and white ants. The species also propagated vegetatively through coppices and root suckers. It lacks agamospermy as bagging of emasculated flowers yielded no fruit. It is inferred that ‘bael’ which lacks agamospermy reproduced successfully through gamospermy (xenogamy and geitonogamy) and vegetative mode (coppices and root suckers). We also concluded that tetraploid trees growing in the Pachmarhi hills with large sized fruits possessed better potentialities in horticulture if planted through root suckers or coppices.

Flowering Phenology, Floral Display and Reproductive Success in the GenusSirindhornia(Orchidaceae): A Comparative Study of Three Pollinator-Rewarding Species

Numbers of flowers and their arrangement in time and space greatly influence levels of pollination and fruit set in natural populations of flowering plants. We examined relations between flowering phenology, floral display and reproductive success in the nectar-producing orchids Sirindhornia mirabilis, S. monophylla and S. pulchella in Thailand. We found each species to be self-compatible and dependent on insects for pollination. Sirindhornia mirabilis exhibited prolonged longevity of individual flowers and produced more flowers per inflorescence — features that may have evolved in response to low visitation rates. Patterns of reproductive success in relation to floral display suggest selection for increased inflorescence size in S. mirabilis and S. monophylla, but this may be counterbalanced by selection for a sustainable annual fruit set. In all three species, the female (and in S. mirabilis also the male) reproductive success decreased from the basal to the apical part of the inflorescence. Against this background, we propose a hypothesis for explaining differential fruit set in polinator-rewarding orchid species.

Biological Flora of the British Isles:Spiranthes spiralis(L.) Chevall.

Summary1. This account presents information on all aspects of the biology ofSpiranthes spiralis(L.) Chevall. that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the framework of theBiological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characteristics, herbivores and disease, history and conservation.2. Spiranthes spiralisis a long‐lived orchid species that is widely distributed in the southern part of the British Isles, southern Europe and the Mediterranean. It is native to Britain. Its most characteristic habitats are unimproved, well‐grazed grasslands on dry calcareous soils, particularly chalk and limestone, cliff‐tops and grassy coastal dunes. It can also be found in garden lawns and, less frequently, in slightly acidic heathland habitat. It occurs on both dry and wet soils, but it does not tolerate heavy shading.3. Spiranthes spiralisis a non‐bulbous geophyte regenerating by sexual reproduction and by vegetative spread, although the latter is limited. Vegetative reproduction involves the growth of a lateral bud on the underground stem. The new plant forms its own tubers, and eventually the connection between the mother plant and the vegetatively produced daughter plant withers away.4. The main perennating organ is a tuberous root. In most years, the tuber generates a rosette of expanded leaves, and at the end of every year of the plant’s life, the tuber is completely replaced. In some cases, however, only part of the reserves is exhausted in flowering and, when this happens, a tuber may survive for several years. Vegetative adult dormancy – the failure of above‐ground parts to appear in a growing season, followed by reappearance of full‐sized photosynthetic plants in subsequent seasons – has been observed. It most commonly lasts for only 1 year, but sometimes plants can remain dormant for several years.5. The species is not autogamous and pollinators – mainly bumblebees and bees – are necessary for successful pollination and fruit set. Natural levels of fruit set are usually <50%. Hand‐pollination increases fruit set toc. 75%, indicating that reproduction is to some extent pollen‐limited. Sexual reproduction comes at a cost, and few individuals flower for two or more consecutive years. Within fruits many very small seeds are produced, but most are dispersed to a distance of less than a few dm from maternal plants, leading to strongly aggregated distribution patterns and significant spatial genetic structuring within natural populations.6. Spiranthes spiralishas suffered significant declines in distribution in Britain and other European countries. In Britain, populations were lost from many sites before 1930, when many pastures were re‐sown or converted to arable land. Losses of populations due to agricultural intensification (ploughing of old fields and fertilization) still occur and are the major causes of the decline of the species. Conservation of remnant populations primarily requires the maintenance of a short turf by grazing, most often by sheep. Ideally, grazing should be suspended during flowering and seed set, allowing new recruits to become established and adult plants to flower profusely and to produce seeds.

Pollination services provided to small and large highbush blueberry fields by wild and managed bees

Summary 1. Plantings of pollinator‐dependent crops vary from large, intensively managed fields to small fields that are managed less intensively, yet there is relatively little information on how pollinator populations and their contribution to crop productivity vary across this gradient. 2. We determined the relative importance of wild bees and managed honey bees Apis mellifera L. for crop pollination in the blueberry Vaccinium corymbosum L. system of Michigan, USA, by comparing bee communities in small, isolated blueberry fields with those in large blueberry fields (stocked with managed honey bee hives) and measuring the difference in yields of open‐pollinated and pollinator‐excluded clusters of flowers. We combined these assessments to calculate the contribution of bees to crop production in this system. 3. Wild bees were the dominant pollinators in small fields, comprising 58% of flower‐visiting bees, whereas 97% of bees in large fields were honey bees. Large fields had four times as many bees visiting flowers than small fields, but only one‐tenth as many bumble bees as small fields. 4. Levels of fruit set exceeded 85% in all fields and were similar between field sizes. Berry weight increased with flower exposure to pollinators and was positively correlated with bee abundance. Berry weights from open‐pollinated flowers were twice as high in large fields compared with small fields. 5. By combining berry weight increases attributable to honey bees and wild bees in blueberry fields with measurements of the bee community adjusted for pollinator efficiency, we calculated the relative contributions of honey bees and wild bees to pollination of Michigan blueberries. We estimate that wild bees provide 82% of the pollination in small fields but only 12% of the total pollination services across this system, mostly through their secondary role in large fields. 6. Synthesis and applications. Wild bees are the primary pollinators of small blueberry fields, but these insects are at low abundance in large fields, perhaps due to a lack of nesting resources or competition for resources with honey bees. Our findings highlight the dependence of commercial fruit producers on honey bees and suggest that increasing the pollination contribution of other bees, particularly bumble bees, in large fields will require that growers adopt wild bee conservation strategies or stock their fields with managed colonies. Quantifying the contributions of managed and wild pollinating bees across the range of crop production scenarios will help to direct development of integrated crop pollination strategies to minimize the risk of pollination deficits affecting food production.

Pollinator limitation and the effect of breeding systems on plant reproduction in forest fragments

Reproduction of plants in fragmented habitats may be limited because of lower diversity or abundance of pollinators, and/or variation in local plant density. We assessed natural fruit set and pollinator limitation in ten species of woody plants in natural and restored fragments in the Pondicherry region of southern India, to see whether breeding system of plants (self-compatible and self-incompatible) affected fruit set. We tested whether the number of flowering individuals in the fragments affected the fruit set and further examined the adult and sapling densities of self-compatible (SC) and self-incompatible (SI) species. We measured the natural level of fruit set and pollinator limitation (calculated as the difference in fruit set between hand cross-pollinated and naturally pollinated flowers). Our results demonstrate that there was a higher level of pollinator limitation and hence lower levels of natural fruit set in self-incompatible species as compared to self-compatible species. However, the hand cross-pollinated flowers in SC and SI species produced similar levels of fruit set, further indicating that lower fruit set was due to pollinator limitation and not due to lack of cross-compatible individuals in the fragments. There was no significant relation between number of flowering individuals and the levels of natural fruit set, except for two species Derris ovalifolia, Ixora pavetta. In these species the natural fruit set decreased with increasing population size, again indicating pollinator limitation. The adult and sapling densities in self-compatible species were significantly higher than in self-incompatible species. These findings indicate that the low reproductive output in self-incompatible species may eventually lead to lower population sizes. Restoration of pollinator services along with plant species in fragmented habitats is important for the long-term conservation of biodiversity.

Flowering and fruit set in cherimoya (Annona cherimola Mill.) as affected by the tree-training system

SummaryManagement of flowering and fruit set are of prime importance in order to obtain high yields in cherimoya (Annona cherimola Mill.) due to floral dichogamy. This phenomenon is largely dependent on environmental conditions such as temperature, relative humidity, and light intensity, which usually make hand-pollination of flowers necessary in order to achieve acceptable levels of fruit set and yield. Nevertheless, these factors can be modified by means of the growing system. In this work, we studied the effects of two tree-training systems on the environment inside the canopy, on flowering, on pollination, and on fruit set in mature ‘Concha Lisa’ cherimoya trees. The open-centre vase training system (6 m 4 m) and the high-density slender-spindle (tunnel) training system (4 m 1 m) were used. The high-density tunnel training system increased the relative humidity, as well as reducing the temperature and the level of photosynthetically active radiation, inside the canopy, which resulted in an earlier onset of the male floral stage and in an extended maintenance of the highly-receptive female stages. This resulted in an overlap of the sexuallycompatible floral stages, thus increasing the incidence of natural cross-pollination and maintaining the viable, receptive sexual stages and pollen, over time, to improve hand-pollination.

Autonomous self-pollination and pseudo-fruit set in South African species of Eulophia (Orchidaceae)

Autonomous self-pollination is surprisingly common among orchids and is thought to provide reproductive assurance when pollinators are scarce. During investigations of the reproductive biology of the orchid genus Eulophia, consistently high rates of capsule set were observed in Eulophia clavicornis var. clavicornis, E. c. var. inaequalis, E. c. var. nutans and E. tenella. A breeding system experiment showed that E. c. var. nutans is capable of autonomous self-pollination. Emasculated flowers of this taxon did not set fruit, suggesting that agamospermy is unlikely. The likely mechanism of autonomous self-pollination in these taxa was identified as the partial or complete absence of rostellum tissue, allowing contact between pollinia and stigmatic fluid, and thus for pollen tubes to grow from in situ pollinia to the ovules. In some individuals, basal flowers on an inflorescence possess intact rostellae and functional pollinaria, whereas distal flowers lack pollinia. Neither of these two flower classes set capsules. A few individuals of the otherwise outcrossing E. zeyheriana, which normally have well-developed rostellae, show evidence of autonomous self-pollination resulting from interrupted rostellae in these plants. Other outcrossing Eulophia species ( E. speciosa and E. streptopetala) sometimes show high levels of fruit set, seemingly without insect visitation. However, investigations showed that these are pseudo-fruits lacking seeds and are a result of insect parasitism. Therefore, high levels of fruit set alone should not be used to infer autonomous self-pollination in orchids.

Temporal and spatial variation in flower and fruit production in a food-deceptive orchid: a five-year study

Deceptive orchids are generally characterized by low levels of fruit set; however, there may be substantial variations in fruit set between sites and years. Within a single population, individual plants may also differ greatly in their reproductive output as a result of differences in inflorescence size or local density. In this study, we determined flower and fruit production over 5 years in two populations of the food-deceptive orchid, Orchis purpurea. All plants were monitored annually for survival and flowering at each site to determine whether flowering and fruiting induced costs. The number of flowers per inflorescence varied considerably from year to year (min: 36.6, max: 49.5). Average fruit set was low (7%) and varied considerably among years and populations. A considerable proportion of plants also failed to set any fruit. However, the probability of producing at least one fruit was not affected by inflorescence size or local density. The number of fruits was significantly related to inflorescence size, but proportional fruit set was not. Local density also did not affect the number of fruits, nor proportional fruit set. There was also no evidence that plants with large inflorescence size or high fruiting success had a larger probability of remaining vegetative the year after flowering than plants with small inflorescence size or low fruiting success. Our results suggest that pollinator-mediated selective forces on inflorescence size through female reproductive success alone are weak, most likely because of the low overall level of visitation and the resulting uncertainty of pollination at the individual level. Our results further demonstrate that investigation of patterns of fruit set over several years is needed to better understand the variability in female reproductive success that is typical of most plant-pollinator interactions.

Open-pollination Provides Sufficient Levels of Cross-pollen in Spanish Monovarietal Olive Orchards

Most Spanish olive orchards are monovarietal as a result of the farmer's belief that the species does not require cross-pollination. Paradoxically, accumulated evidence from controlled experiments demonstrates that olive is partially self-incompatible and that cross-pollination increases yield and fruit quality in this wind-pollinated crop. With the aim of assessing cross-pollination deficit in large plots of the most widespread olive oil cultivar in Spain, fruit set was compared in two solid orchards of ‘Picual’ in response to self-, open-, and artificial cross-pollination. In both orchards, ‘Picual’ behaved as a self-incompatible cultivar with reduced fruit set under self-pollination (index of self-incompatibility = 0.21). However, cross-pollination rarely increased fruit set in comparison with open-pollination. Bagging experiments demonstrated that open-pollination provided enough cross-pollen to induce high levels of fruit set. The increase in fruit set in response to mechanical application of cross-pollen was limited to the trees directly receiving the pollen flow and only in one orchard. Consistently, airborne pollen concentration after a single terrestrial application significantly fits a decay curve with a short dispersal. In contrast with the limited dispersal of single mechanical applications, open-pollination results suggest that trees from plantations at least 250 to 500 m away are acting as unsuspected pollenizers. This is probably taking place to some extent in most traditional olive districts in Spain, and it explains why farmers have never demanded pollination designs in this crop. Modern homogeneous plantations can, however, change this situation dramatically and give rise to pollination deficits.

Specialities of the vegetation start and level of primary fruit set affect fruit quality

Thinning is a h ighly crucial point of the apple production technology. According to results of numerous studies the earliest thinning is deemed to have the best amending effects. There can be considerable difference between trees of the same cul tivar and age in a plantation in respect to their flowering, in the numbers of fruits set and also in their canopy volume. Thus it can be crucial -just l ike in the case of pruning- to establish a fruit thinni ng su i ted for specif ic characteristics of actual trees. This experiment was established to examine how does primary fruit set (fruit load before thinning) and further on specific (fruit/TCS cm2) and absolute (fruit/tree) fruit-load of the trees affect quality attri butes at harvest. Our experiment was establ ished in a plantation on medium-tight loamy soil in north-east of Hungary. Harvest date was determined w ith the joint observation of the calendar date, starch-index, flesh firmness, background colour and fruit weight. Three fruit-load levels were established based on local experience and on data of several years, I Ot/ha lower and higher besides the advised optimum yield in the same orchard with slender-spindle shaped 'Gala must' cultivar standing on M9 rootstock in 1m x 3,8 m spacing. In the establishment of the 15, 25 and 35t/ha fruit-load levels on 20-20 apple trees total number of fruits set was counted at each tree. After this number of apples due to be removed was defined using an objective index on the basis of trunk cross sections (fruit/TCScm2) (Lafer, 1999). The following attributes were measured: weight (g), flesh firmness (lb/cm2) total soluble solid content (Brix %) and total titrate-able acid content (g/J).From the data on sugar and acid content quality index (Pomona value) was determined (Thialult, 1970). We could ascertain, that in an orchard, of the same aged but in concern to trunk cross sections somewhat different trees besides the specific index (apple/TCS cm2 the absolute fruit load (fruit/tree) can also be an important data, that has considerable effect on the internal quality. Secondly we could observe, that higher level of fruit load before thinning (primary fruit set) negatively affects quality index of the apples irrespective of the specific fruit load level (fruit/cm2 TCS) set later. Results underlines necessity of the earliest chemical thinn ing.

Biological Flora of the British Isles:Orchis mascula(L.) L.

SummaryThis account presents information on all aspects of the biology ofOrchis mascula(L.) L. (early purple orchid) relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characteristics, herbivores and disease, history and conservation.Orchis masculais a native herb of the British flora. It is mostly found in woodland, copses, grasslands and open pastures, mostly on neutral or base‐rich soils. It can also occur in hedgerows, scrub, on roadsides and railway banks, in grikes on limestone pavement and on moist cliff ledges. It is absent from very acid or very wet sites. It tolerates a sparse to moderately dense canopy, but it does not flower in deep shade.Orchis masculais a non‐bulbous geophyte with little or no capacity for vegetative spread. The main perennating organ is a tuber (strictly a rootstem tuber). In most years the tuber generates a rosette of expanded leaves, and, at the end of every year of the plant's life, the tuber is replaced by at least one new tuber. Dormancy, the failure of above‐ground parts to appear in a growing season, and the subsequent reappearance of full‐sized photosynthetic plants in subsequent seasons, has been observed, but does not last longer than 1 year. The species is long‐lived: it takes at least 4 years from first appearance above‐ground to achieve flowering for the first time. The maximum recorded lifetime after first appearance is 13 years.Orchis masculais not autogamous and pollinators are necessary for successful pollination and fruit set. Flowers are nectarless, and pollinated by deceit, mainly by bumblebees and solitary bees. Natural levels of fruit set are usually < 20%. Hand‐pollination can increase fruit set to approximately 80%, indicating that seed production is strongly pollen‐limited. The lowest four flowers are more likely to be pollinated than the upper flowers, probably because pollinators learn to avoid the species after discovering that it offers no reward.As in most other European countries,Orchis masculahas declined in the British Isles, although it is not at threat of extinction at a national level. Most sites from which it has been lost are in central England and Scotland. Most losses have been caused by woodland clearance and coniferization, intensification of grassland management and ploughing. The cessation of traditional coppicing practises has also led to a decline in the abundance ofO. mascula. Since the species is slow to colonize new forest stands or grasslands, management should focus mainly on conservation of ancient forest habitats and grasslands in which fertility is moderate to low and grazing is absent or low in intensity. Restoration of traditional coppicing practices could also lead to higher chances of the species flowering and surviving in the long‐term.

Limited mate availability decreases reproductive success of fragmented populations of Linnaea borealis, a rare, clonal self-incompatible plant.

Small populations of rare plant species are increasingly reported to have high levels of reproductive failure. The objective of this study was to understand the principal constraints on sexual reproduction in small fragmented populations of a rare clonal self-incompatible plant. The pollinator spectrum, diversity of flower colour, natural pollination and fruit-set levels of L. borealis were examined in Scotland. Artificially crossed seed production was compared within and between different flower colour types and patches. Linnaea borealis was pollinated by a diverse spectrum of insect species and the principal pollinators were muscid, syrphid and empid flies which mostly moved only small distances (<0.25 m) between flowers when foraging. Natural pollination levels were high, indicating high pollinator effectiveness, but fruit set was very low in most patches. Flower colour diversity was low in most patches and only those with a diversity of flower colour types had high fruiting success. Pollination experiments showed L. borealis to be highly self-incompatible and artificial crosses within and between patches and flower colour types confirmed that low fruit success was the result of a lack of compatible mates and limited pollen movement between them. Evidence of isolation from pollen exchange was apparent at as little as 6 m and severe at 30 m and beyond. Limited mate availability and isolation from pollen exchange compromise the reproductive success of fragmented populations of L. borealis in Scotland. A diversity of compatible mates situated within close proximity (<6 m) is the key requirement to ensure high natural fruiting success. This study emphasizes that an understanding of the breeding system, pollinator spectrum and potential for interconnectivity via pollinator movement are fundamental to identify isolation distances and to establish when conservation intervention is necessary for rare species.

Effective pollination period for ‘Manzanillo’ and ‘Picual’ olive trees

SummaryThe effective pollination periods (EPP) for ‘Manzanillo’ and ‘Picual’ olive trees have been determined in two consecutive years in irrigated orchards in California and Spain. The duration of the EPP was variable between year and cultivar. Fruit set declined gradually in response to sequential cross-pollination. Consistent differences with respect to the maximum levels of initial fruit set occurred between 4 – 6 d after anthesis (DAA) in ‘Manzanillo’, and between 8 – 14 DAA in ‘Picual’. Fertilisation was first observed on day-2 after cross-pollination in both cultivars. Ovule longevity, determined by fluorescence microscopy, appeared to last > 14 d in both cultivars. The stigmas remained receptive for > 8 d. Estimates of the duration of the EPP, based on analyses of its components, were longer than those indicated by the declines observed in fruit set, suggesting that other factors such as the suitability of the style to support pollen tube growth may limit the duration of the EPP. These results suggest that self-incompatibility may be a more important factor than a short EPP in limiting fruit set in ‘Picual’, as well as in ‘Manzanillo’ olive trees.

Spray pollination as a labor-saving pollination system in Japanese pear ( Pyrus pyrifolia (Burm.f.) Nakai): Development of the suspension medium

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.

POLLINATION, BREEDING AND SELECTION OF NEW VARIETIES OF CUSTARD APPLE (ANNONA SPP. HYBRIDS) IN AUSTRALIA

Progress has been made in understanding the mechanism of pollination in custard apple (Annona spp. hybrids) in subtropical Australia. ‘KJ Pinks’, a bud sport of the custard apple ‘Pink’s Mammoth’ exhibited natural fruit set in excess of 40% compared with its parent which set <3%. The very high fruit set levels of the ‘KJ Pinks’ will revolutionise the production of custard apple in Australia as it offers major commercial advantages over older cultivars which required expensive hand pollination. Some 30,000 breeding lines have been field planted at the Maroochy Research Station, Nambour, Queensland since 1998 including interspecific crosses between Annona cherimola, Annona squamosa, Annona reticultata and Annona diversifolia and intergeneric crosses with Rollinia deliciosa. Phylogenetic relationships have been established between the different species and varieties in the breeding program using 15 polymorphic SSR markers.

Floral development and breeding systems of Dryandra sessilis and Grevillea wilsonii (Proteaceae)

Dryandra sessilis (Knight) Domin. and Grevillea wilsonii A.Cunn. co-occur on lateritic soils in the jarrah forest of Western Australia, with their flowering seasons overlapping for several months during winter and spring. Both species are protandrous, with pollen presentation occurring 1–2 days before the stigmas of individual flowers become receptive. Peak receptivity, as indicated by maximum peroxidase secretion, coincides with the maximum opening of stigmatic grooves for D. sessilis or maximum elevation of the stigmatic papillae in G. wilsonii. Pollinators such as western wattlebirds, New Holland honeyeaters and western spinebills almost exclusively visit flowers or inflorescences at times when large amounts of nectar are present, and when self-pollen is available for transfer or stigmas are receptive to the deposition of pollen. By foraging in this manner, yet still moving frequently between plants and inflorescences, honeyeaters that visit D. sessilis should guarantee an effective spread of pollen. The overall level of fruiting success achieved by this species is considerably higher than that for G. wilsonii, a species whose flowers are visited much less often than those of D. sessilis. Allozyme analysis, artificial pollination experiments and the calculation of pollen : ovule ratios indicate that D. sessilis is essentially an obligate outcrosser, at least in locations where plant densities are high, whereas G. wilsonii has a mixed mating system that allows it to set fruits as a consequence of either selfing or outcrossing. Potential fruit-set is low for both species, with post-zygotic incompatibility mechanisms mediated by the availability of nutritional resources thought to be at least partly responsible for the even lower levels of final fruit-set. Total fruit and seed production by individual plants is much greater for D. sessilis than for G. wilsonii, and possibly a reflection of differences in the regeneration requirements of the two species after environmental disturbance such as fire.

Impact of floral traits on the reproductive success of epiphytic and terrestrial tropical orchids

We investigated the relationship between habit, population size, floral traits and natural fruit set levels of 23 tropical orchid species of south-east Bangladesh. We showed that epiphytic orchids had lower fruit set levels than terrestrial species and that habit explained much of the variation in floral traits among the orchids. We compared our results with data from 76 other species occurring in the study area and hypothesize that a suite of floral and population characteristics present in tropical orchids combine in epiphytes to reduce their reproductive success. Characteristics which, in addition to their habit, are associated with low reproductive success are small population size, small inflorescences, non-sectile pollinia and self-incompatibility. Several of these characteristics were phylogenetically conserved and we predict that epiphytes might therefore generally have lower fruit set levels than recorded in terrestrial species. Nectar rewards are uncommon in tropical orchids and nectarless species have displays of larger flowers, which may represent an adaptation to increase pollinator attraction, although other rewards such as oils, waxes and pseudo pollen may replace nectar. We suggest that, like many temperate orchids, a high proportion of tropical orchids may lack floral rewards and be pollinated by deceit.

FRUIT SET FAILURE IN TISSUE CULTURE-DERIVED DATE PALM TREES (PHOENIX DACTYLIFERA L.) CV. 'NABT SAIF' AS AFFECTED BY POLLINATOR TYPE AND POLLINATION DENSITY

There is a special interest in date palm plants regenerated by tissue culture. However, one of the major weaknesses of mass tissue culture propagation is the appearance of undesired off-type plants, such as poor fertility and delayed flowering. During the 2004 and 2005 seasons, the effect of five date palm pollinators, namely ‘Ahmar’, ‘Akhdar’, ‘Fard’, ‘Khenizy’ and ‘Maghool’ as well as sugar palm (Phoenix sylvestris), each with five different pollination densities (10, 20, 30, 40 or 50 strands/female spathe), was studied on fruit set, multi-carpel fruit formation, fruit drop, and fruit quality of eight-year tissue culture derived ‘Nabt Saif’ palm trees growing at Al-Ain oasis, United Arab Emirates, The results showed different degrees of compatibility among the pollinators on ‘Nabt Saif’. The pollinator ‘Khenizy’ resulted in the highest (34.3% and 28.7%, for 2004 and 2005, respectively) and ‘Fard’ the lowest (11. 7% and 20 % for 2004 and 2005, respectively) fruit set level. The pollinator ‘Sugar palm’ (Phoenix sylvestris) was as effective as or better than the other pollinators that belong to the species Phoenix dactlifera. There were no significant differences between the different pollination densities on fruit set and fruit quality during both seasons. Generally, neither the pollinators nor the pollination density resulted in a satisfactory level of fruit set. These results may suggest that other endogenous factors are responsible for such abnormality in the tissue culture derived ‘Nabt Saif’ palms. Some metaxenia effects of the different pollinators on fruit quality characteristics were recorded both at Bisir and Tamr stages. In this respect, the ‘Sugar palm’ pollinator significantly increased fruit and flesh weight, fruit length and diameter and seed weight percentages at Bisir stage, but decreased the concentration of total soluble solids, acidity and vitamin C at both Bisir and Tamr stages compared to other pollinators. More research work is needed on tissue culture derived date palms to understand more clearly the nature of abnormalities that appear in some cultivars.

Self-incompatibility and Self-fruitfulness in Pear cv. Agua de Aranjuez

Most pear (Pyrus communis L.) cultivars are impaired to set fruit under self-pollination, because self-fertilization is prevented by a gametophytic self-incompatibility system. However, accumulated information in this species shows that often for a same cultivar, after self-pollination, a variable response in fruit set can be obtained in different years or growing conditions. In this work, we characterize self-incompatibility and self-fruitfulness in ‘Agua de Aranjuez’, the main Spanish pear cultivar, which also shows a variable response to self-pollination. Two years with a different fruit setting response after self-pollination, one with no fruit set and the other with a moderate fruit set, were compared for parthenocarpic fruit development and for pollen tube performance. Results show that in both years, this cultivar behaves as self-incompatible with absence of parthenocarpy. In selfed flowers, most pollen tubes are arrested in the upper half of the style, although in a small proportion of the styles, a pollen tube can reach the base of the style and eventually effect fertilization. Self-fertilization, although occurring at a low level, can explain the fruit set levels obtained under self-pollination given that flowers with just one fertilized ovule are able to set fruit. This behavior could explain confusing results about self-fruitfulness in ‘Agua de Aranjuez’ and other pear cultivars.