Cultivar placement affects pollination efficiency and fruit production in European pear (Pyrus communis) orchards

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 ‘Conférence’ (21% vs. 30.7%) and ‘Doyenné 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.     

Is bigger better? Apidae (Xylocopinae), megachilidae and cowpea (Vigna unguiculata) pollination

Cowpea is an important grain legume crop in Africa. Cowpea flowers are capable of self-fertilization, which might be the most frequent type of reproduction. Nevertheless, the rate of cross-pollination could vary between 1% and 10%, depending on the populations of bumblebees or domestic bees that are present, the climate and the cultivar. The aim of this study was to identify and assess the efficiency rate of the pollinators of the wild cowpea, Vigna unguiculata subsp. unguiculata var. spontanea, the progenitor of the domesticated cowpea Vigna unguiculata subsp. unguiculata. Pollination study was conducted by observing patches of flowers (average 10–20/m²) from dawn to midday, approximately 05:00–12:30 hr for three years. All insects visiting the flowers were noted and identified to species level, where possible, and their foraging behaviour was monitored. Pollen grain deposit and pod set were estimated using single bee visits on plants with strictly outcrossing flowers. Major flower visitors were large bees of the family Megachilidae and the genus Xylocopa (Apidae, Xylocopinae). Xylocopa caffra (Linnaeus) was the most abundant bee species, accounting for 59% of total bees observed and 58% of total flower visited. Pod set was higher in visits by megachilid bees compared to Xylocopa bees. Within Xylocopa, there is a good correlation between size and efficiency (r = .95, p = .0477), the larger insects being more efficient. Honeybees, small bees (Ceratina and Nomia species) and Lepidopterans also visited flowers but without any effect on pollination. Cowpea pollination system is specialized, and pollinators are restricted to Megachilidae and Xylocopa species. Variation in pollen load deposit and pod set reveals that pollination success depends on the insect species involved and their size. Megachilids are the most efficient pollinators, especially since they are able to promote outcrossing more efficiently than Xylocopa species.     

Do floral resources influence pollination rates and subsequent fruit set in pear (Pyrus communis L.) and apple (Malus x domestica Borkh) cultivars?

Pear and apple are among the main fruit crops worldwide. These species can be planted in mixed orchards, and they both depend on insect pollination for fruit set. As pollinating insects are attracted by the floral resources, we investigated nectar and pollen production and chemical composition in four pear (‘Concorde’, ‘Conférence’, ‘Doyenné du Comice’, ‘Triomphe de Vienne’) and five apple (‘Braeburn’, ‘Golden Reinders’, ‘Jonagored’, ‘Pinova’, ‘Wellant’) cultivars commonly grown in Belgium. We also investigated whether insect flower visitation rate and pollination efficiency are linked to floral resource quantity and quality. The pear cultivars flowered one week before the apple cultivars in early spring, and their flowers were about six times less visited by insects. The visitors foraged more on the pollen of the pear trees and the nectar of the apple trees. Pear flowers produced higher volumes of nectar than apple flowers (1.3–3.2 μl vs. 0.4-0.6 μl), but with lower sugar concentration (9.6%-10.8% vs. 28.3%-36.4%). Pear flowers also produced fewer pollen grains per anther than apple flowers (2425–4937 vs. 3284–7919), but these had higher polypeptide (346–362 μg/mg vs. 216–303 μg/mg), amino-acid (40–77 μg/mg vs. 12–18 μg/mg) and phytosterol (21–47 μg/mg vs. 15–43 μg/mg) concentrations. The foraging behavior of the insects is thus better explained by nectar and pollen quality rather than quantity. Despite the differences in flower visitation rates, pollination of both species resulted in valuable fruit production.     

Inheritance of flower and pod colour in cowpea (Vigna unguiculata L. Walp.)

Inheritance of flower colour and pod colour in cowpea (Vigna unguiculata L. Walp.) has followed a qualitative pattern. Purple flower colour is dominant over white flower colour, whereas black pod colour is partially dominant over white pod colour. A segregation ratio of 3 purple:1 white flowers in F₂ generations of two crosses indicated that white flower colour is controlled by a single recessive. Segregation ratio of F₂ 1 white:2 light black:1 black indicated that black pod colour is partially dominant over white pod colour and is governed by one gene. These results were further confirmed by backcross generations. White flower and pod colour are controlled by single recessive genes on separate chromosome. Gene symbols were assigned. This revised version was published online in July 2006 with corrections to the Cover Date.     

The use of insects for pollinating brassica crops in small isolation cages

1. 1.
   Research was carried out on the suitability of honey bees, bumble bees and flies for pollinating cabbage crops.     
   
   

Influence of the apetalous character in rape (Brassica napus) on the foraging behaviour of honeybees (Apis mellifera)

In order to establish whether commercial hybrid seed production between apetalous and apetalous rapeseed lines could be developed through insect cross-pollination, observations were made to compare the foraging behaviour of honeybees on both flower types with regard to their attractiveness. Number of flowers/m² and nectar volumes, considered as important attractive factors, did not differ between the two lines but nectar sugar composition was slightly different. Honeybee density was significantly higher on the apetalous line when their foraging activity was rather high. Honeybees showed a considerable constancy to each flower type. Passages between both types were not very frequent. Nectar foraging behaviour, observed under cages, differed with the floral morphology. On the apetalous flowers, honeybees visited the two inner nectaries by crawling over the anthers and the stigma, while on the apetalous ones they often inserted their tongues between the sepals, thus having less contact with the reproductive organs. From these results, the honeybee efficiency in cross-pollination between petalous and apetalous lines appears to be reduced.     

Cajanus platycarpus (Benth.) Maesen as the donor of new pigeonpea cytoplasmic male sterile (CMS) system

Cajanus platycarpus, a distantly related wild species, was successfully crossed with cultivated pigeonpea using embryo rescue and tissue culture techniques. Advance generation lines showed a range of desirable characters including cytoplasmic male sterility. A range of pigeonpea cultivars restored fertility and was maintained by a few lines including cultivar ICPL 85010. Clasmogamous flowers were observed in the male sterile lines. In such flowers anthers did not form di-adlephous bundle. Cytological analysis revealed that meiosis proceeded normally till the tetrad stage in those anthers with pollen grains. After which many of the pollen grains turned sterile. In the anthers with pollen grains, dehiscence was not observed, thus creating functional sterility. In many other anthers, pollen mother cells (PMCs) were not formed at all, giving rise to sepalous anthers. In conclusion two mechanisms of male sterility existed, one was premeiotic, where PMCs did not form and in the second, although PMCs gave rise to pollen grains, they were either partially or totally sterile accompanied by non-dehiscence of anther wall.     

酸枣花器官结构、花粉形态及生活力比较研究

为了给酸枣花器官研究、花粉生活力的快速测定提供理论依据,笔者测定了不同的酸枣类型花器官结构、花粉形态及花粉萌发率和生活力的差异。结果表明：（1）不同的酸枣类型花序花朵数、花冠直径、蜜盘直径、雄蕊长度等方面都有不同程度的差异。花序花朵数一般在2~9个;单花雄蕊个数为5个;蜜盘颜色一般有淡黄色和黄绿色2种。（2）酸枣花粉比较小,通常在18.86~26.19 μm,以近球形为主,萌发孔以三孔沟居多。（3）不同的酸枣类型花粉的萌发率存在显著差异,其中酸枣4的萌发率最高,为32.54%;TTC法和I-KI法测定的花粉生活力显著高于离体培养法,测定值误差较大,故离体培养法更适合酸枣花粉生活力的测定。     

Confirmation and characterization of interspecific hybrids of <Emphasis Type="Italic">Passiflora</Emphasis> L. (Passifloraceae) for ornamental use

Three new varieties of Passiflora hybrids were developed from crosses between P. sublanceolata J. M. MacDougal (ex P. palmeri var. sublanceolata Killip) versus P. foetida var. foetida L. Twenty putative hybrids were analyzed. Hybridizations were confirmed by RAPD and SSR markers. The RAPD primer UBC11 (5′-CCGGCCTTAC-3′) generated informative bands. The SSR primer A08FP1 amplified species-specific fragments and heterozygote status was observed with the two parent bands 240 and 280 bp. The molecular markers generated by primers were analyzed in terms of the presence or absence of specific informative bands. The morphological characterization of the hybrids enabled their differentiation into three groups, identified as: (1) Passiflora ‘Alva’, composed of five hybrid plants with white flowers, large corona, light purple filaments at base, white and purple/white banding to apex; (2) P. ‘Aninha’, composed of six hybrid plants with pale pink flowers, corona filaments reddish/purple at base, white, purple/white banding to apex; (3) P. ‘Priscilla’, composed of nine hybrid plants with white flowers, small corona, filaments dark purple at base, white and purple to apex. The genomic homology of parent plants was verified by cytogenetic analysis. Both parents were 2n = 22. Meiosis was regular in genitors and hybrids. Aneuploidy was observed at hybrid groups P. ‘Alva’ and P. ‘Priscilla’ (2n = 20). Other authors had already observed the same number of chromosomes for some P. foetida genotypes. Obtaining valuable interspecific hybrids opens up new perspectives to offer opportunities in agribusiness for producers and to arouse the interest of consumers into using passion flowers in the Brazilian ornamental plant market.     

Distribution,stability and fate of phenolic compounds in white and purple eggplants (Solanum melongena L.)

Eggplants rank among the vegetables richest in antioxidants, but little is known about the allocation, stability, and turnover of these metabolites. The distribution, accumulation and degradation of phenolic antioxidants in the inner and outer pulp of two commercially important eggplant types (white and dark purple), at harvest and after 14 and 30 d of refrigerated storage under non-chilling conditions (10 °C and 90% RH) were determined in this study. Chlorogenic acid (ChA) was histolocalized by fluorescence with 2-aminoethyl-diphenylborinate and the activity of phenolic compounds oxidizing enzymes (polyphenoloxidase, PPO and peroxidase, POD) as well as H₂O₂ concentration in both fruit regions was determined. During storage, dark purple fruit were more susceptible to dehydration and showed greater deterioration than white eggplants. Both genotypes accumulated higher sugar content in the inner pulp as opposed to acids, which were more concentrated in the outer region. At harvest, pulp antioxidant capacity was similar in both eggplant types. TEAC and DPPH assays and in situ localization, showed greater total antioxidants and ChA content in the core than in the outer pulp in both white and dark purple fruit. The stability of ChA was markedly different between genotypes. In white fruit, antioxidants increased during the first two weeks of storage, remaining stable afterwards. In contrast, in dark purple eggplants, phenolic compounds declined after an initial stage at which they accumulated. PPO and POD in vitro activities, associated mainly with fruit seeds, fibers, and vascular bundles did not correlate with pulp browning or loss of phenolic antioxidants. Instead, the reduction of ChA in the core of dark purple fruit was associated with increased production of H₂O₂. Results indicate that antioxidants are predominantly located in the inner pulp of eggplants regardless of the genotype, but are more stable in white fruit. Rather than being the result of browning reactions, substantial losses of phenolic antioxidants in whole eggplants under the recommended storage conditions likely result from seed coat development and vascular lignification in the immature fruit.     

Pollination requirements for seed set in ulluco (Ullucus tuberosus)

Summary Pollination experiments were carried out on ulluco (Ullucus tuberosus), known as a very poor seed producer. All the clones used were diploids. The effect of self-vs. cross-pollination was studied in Experiment 1. Caged selfpollinated flowers produced no seeds. Different clones produced seeds in 0–8% of caged cross-pollinated flowers and in 5–19% of cross-pollinated non-caged flowers. Ulluco is thus basically an outbreeder.Experiment 2 studied whether seed set is limited by pollen availability. Total seed number per inflorescence number did not differ between plants treated with supplemental pollen and control plants; pollen availability thus did not limit seed set. The treated plants, however, produced more seeds in cross-pollinated than in other flowers on the plant, and the control flowers on treated plants produced fewer seeds than those on the control plants. In the treated plants, resources may have been allocated to artificially cross-pollinated flowers at the expense of other flowers. In some clones, seed set after artificial cross-pollination was at a level practicable for breeding work.     

Inter-accession variation in floral morphology in radish (Raphanus sativus L.)

We investigated variation in floral morphology among 36 accessions of radish (Raphanus sativus L.). We found wide, continuous inter-accession variation in 15 traits related to the size of the floral organs and the stigma position relative to the anthers of long stamens. A principal-component analysis of the 15 floral traits also showed wide variation among accessions. A large proportion of this variation was accounted for by lengths of stamens and the petal tube. In addition, the phenotypic stabilities with respect to the macro-environment (as affected by different sowing dates) and the micro-environment (among the flowers within a plant) differed between traits. Correlation analyses using all traits suggest the existence of genetic linkages or pleiotropies among floral organs. Our results indicate that floral morphologies varied greatly among radish accessions and they could be affected by the macro- and micro-environment. To explore the relationship between floral morphology and pollination efficiency, we compared the number of pollen grains deposited on the stigmas in the presence and absence of insect pollinators using three accessions with very different floral morphology. Because an accession with a higher stigma position than anthers might avoid self-pollination and an accession with a large stigma size received more pollen grains, floral morphology may affect pollination efficiency. Because the effect of pollination efficiency on seed production is well known, our results suggest that radish floral morphology affects seed production through its effect on pollination efficiency.     

The ovular incompatibility system in Gasteria verrucosa (Mill.) H. Duval

Summary The nature and process of ovular incompatibility in Gasteria verrucosa was studied. Using different crossing programs and following the pollen germination and ovule penetration histochemically, an ovular gametophitic incompatibility system based on two or more loci is affirmed. Pollen tubes after self-and cross-pollination penetrate the micropyle. Although the percentage of seed setting reached about 60% after cross pollination no clear differences could be seen between the germination and ovule penetration of cross and self pollen.In the ovules, multiple penetration of micropyles and a preference for the first position ovules was observed. Results of semi-compatible crossings and mixed crossings indicated a gametophytic two or more loci incompatibility system. Ovular incompatibility was manifested by the degeneration of the sporophytic ovular tissues. In Gasteria verrucosa the system of ovular incompatibility does not seem to be restricted to the ovule.     

Bud pollination and hybrid seed production in detergent-induced male sterile plants of Brassica juncea

The efficacy of a synthetic detergent (Surf Excel) as a potential chemical hybridizing agent in Brassica juncea was studied. Foliar sprays with various concentrations of the detergent caused reductions in plant height, number of branches and leaves per plant, size of leaves, anther size, pollen per flower, ovules per flower, pollen fertility, fruits per plant, fruit size, seeds per fruit, total yield per plant and 100 seed weight as compared with those of untreated plants. The style in the floral buds of plants sprayed with different concentrations of Surf Excel elongated and so the receptive stigma protruded from the buds which facilitated cross‐pollination by honey bees. The plants sprayed once with 2% Surf Excel exhibited an elongated style with a raised receptive stigma and 100% pollen sterility without causing a significant reduction in total yield.     

Pollen competition in onion (Allium cepa L.)

Summary Pollen mixtures with two components, one of which carried a dominant marker gene for red or white bulb skin colour, were used to pollinate flowers on onion umbels from several cultivars. Scoring progenies for the marker revealed that pollen components differed in their ability to effect fertilization, suggesting that gametophytic competition can occur in onions. In many cases, self-pollen appeared to have a competitive advantage over cross-pollen. Both of the male components and the female parent played a part in determining the final ratio obtained from a mixed pollination.Crossed seeds were slightly but significantly heavier than selfed seeds in nine out of ten umbels studied.     

Gene flow in common bean (Phaseolus vulgaris L.)

This study was conducted in Brazil in order to assess the potential risk posed by gene escape from transgenic into non-transgenic plants and wild populations. A new methodology was applied to evaluate the gene flow between common bean cultivars, by means of a specially delineated experiment in two stages. The first stage consisted of the planting of one cultivar with violet flowers (BB) as pollen source (‘Diamante Negro’), and a receiver (‘Talismã’) with white flowers (bb), at different distances. The source was sown in the center of the area. The pollen receiver cultivar was sown, in concentrical squares around it. At maturity, the rows were sampled at varied distances from the source in the four cardinal directions. In the second stage, the sampled seeds of the previous stage were sown, and the percentage of outcrossing was evaluated during flowering through the presence of violet flowers (Bb). The highest frequency of natural hybrids, 0.136%, occurred at a distance of 0.5 m between the cultivars. The natural outcrossing rate was practically zero beyond a distance of 3.25 m.     

Overexpression of BpMADS4 from silver birch (Betula pendula Roth.) induces early-flowering in apple (Malus × domestica Borkh.)

To shorten the juvenile stage of apple (Malus × domestica Borkh.) the BpMADS4 gene from silver birch (Betula pendula Roth.) was constitutively overexpressed in 25 transgenic apple clones. All clones were characterized by PCR, RT‐PCR and Real Time PCR. Solitary flowers were produced on in vitro shoots of eight transgenic clones and most of them appeared to be morphologically normal. Twenty shoots of each clone were rooted and transferred to a glasshouse. Glasshouse plants of clones T1165, T1187 and T1190 developed flowers. Several plants of T1165 and T1187 started floral initiation within 3–4 months following transfer to the glasshouse. Primary flowers were solitary and in a terminal position on the main shoot. Lateral flower clusters, consisting of three to five individual flowers, were also found. Pollen vitality and tube germination of glasshouse‐grown flowers were investigated, and there were no significant differences compared to pollen of non‐transgenic control plants. Preliminary crosses using flowers of glasshouse plants resulted in small apple fruits. It would seem that this is the first report on in vitro flower induction in transgenic apple.     

Sexual crossing between two genetically female plants and sex genetics of kakrol (Momordica dioica Roxb.)

Summary Application of 200 to 800 mg/l silver nitrate (AgNO₃) to the female kakrol or teasle gourd (Momordica dioica Roxb.) plant was effective for inducing hermaphrodite flowers. Pollen grain viability of the hermaphrodite flowers was as high as that of normal male flowers. Crossing among female genotypes of different fruit morphotypes, taking pollen from the induced hermaphrodite flowers, produced fruits and seeds. Sex of hybrids between female and normal male segregated into male and female in equal proportion, while the hybrids from female homo-sexual crosses produced only female plants. This indicated that sex of kakrol is controlled by a single factor; male being heterozygous and the female is homozygous recessive. The possibility to evaluate both parents for fruit characteristics should facilitate breeding.     

Chromosome location of genes controlling the content of dietary fibre and arabinoxylans in rye

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

Controls over pollination and ovule fertilization in Vicia faba

Summary Variation in the frequencies of pollination and ovule fertilization was generated among faba bean (Vicia faba L.) genotypes in experiments which compared self-and open-pollination, natural and extended photoperiods, presence and absence of honey bees and a range of plant populations.There was a near-1:1 relationship between the frequencies of pollination of stigmas and the fertilization of at least one ovule within the pistil. Pollination was the major barrier to fertilization of the pistil, and ovules, since no mechanism was evident in the style to prevent pistil fertilization. The frequency with which single ovules were fertilized in pollinated pistils fell as their distance from the stigma increased, and averaged 83.5% overall.The frequency of pollination was most influenced by the level of autofertility possessed by the genotype, and the activity of pollinators. Provision of honey bees to plants in caged plots showed that high levels of pollination could be achieved under open-pollinated conditions, but this was also influenced by autofertility. Increasing plant population in the field had only a small effect on pollination, but extending photoperiod caused the levels and timing of self-pollination in three genotypes to vary.Large differences were found among genotypes in their early stigma receptivity, that is, the frequency of stigmas found to be pollinated at the erect standard stage, prior to the flower opening and being visited by bees. The implications of early stigma receptivity for producing new cultivars were discussed.