Fruit set and the diurnal pollinators of the invasive Lantana camara and the endemic Lantana peduncularis in the Galapagos Islands

Fruit set is highly relevant to a plant's reproductive success. Fruit set can vary due to predation on flowers, pollinator services and/or resource availability. Reproductive success, measured as the fruit set of the invasive Lantana camara and the endemic Lantana peduncularis in the cool–dry season and the warm–wet season of the Galapagos Islands, was studied. Also, autonomous self‐pollination ability and seed viability were probed for both species. Furthermore, flower visitors and their activity were registered for both species during the warm–wet season. Lantana peduncularis produced fewer flowers per inflorescence, but had a higher fruit set in the cool–dry season, compared to the warm–wet season. In contrast, the fruit set in L. camara did not change seasonally. The fruit set in L. camara was higher than in L. peduncularis in the warm–wet season. Moreover, ～18% of the bagged flowers of the invasive Lantana produced fruits by autonomous self‐pollination, while for the endemic Lantana, the rate of autonomous self‐pollination was very low. More than 80% of the fruits for both species had at least one viable seed per fruit. The number of pollinators and their frequency, inflorescence‐ and flower‐visiting rates and the duration of the visit per flower were higher in the invasive Lantana than in the endemic one. The endemic Lepidoptera Urbanus galapagensis (the main pollinator of both Lantana species) and the introduced Hymenia perspectalis were observed pollinating both Lantana species. These results indicate that the alien L. camara is more attractive to pollinators and it has reproductive advantages regarding fruit set in comparison with L. peduncularis, factors that contribute to the colonization pattern of this invasive species.     

Bacterial inflorescence rot of grapevine caused by Pseudomonas syringae pv. syringae

Molecular sequencing (rpoB) and standard pathological and microbiological methods identified Pseudomonas syringae pv. syringae (Pss) as the causal agent of bacterial inflorescence rot of grapevines (Vitis vinifera) in three vineyards in Tumbarumba, NSW, Australia in 2006 and 2007. Pss strains from shrivelled berries and necrotic inflorescences of diseased grapevines were used to inoculate leaves and inflorescences of potted cv. Semillon grapevines. Pss caused disease symptoms similar to those experienced in the field, including angular leaf lesions, longitudinal lesions in shoot tissues and rotting of inflorescences from before flowering until shortly after fruit set. High humidity promoted symptom severity. The necrotic bunch stem and leaf lesions were susceptible to the development of Botrytis cinerea infections. Cryo‐scanning electron microscopy (cryoSEM) indicated that Pss entered leaves and inflorescence tissues via distorted, open, raised stomata surrounded by folds of tissue that appeared as ‘star‐shaped’ callose‐rich complexes when viewed by UV light microscopy. In necrotic tissues, cryoSEM revealed Pss within petiole parenchyma cells and air‐filled rachis xylem vessels. This is the first report of inflorescence and hence fruit loss caused by Pss in grapevines. The disease is described as ‘bacterial inflorescence rot’ and regarded as one that expands the previously reported pathology of grapevines caused by P. syringae. This study also indicated that infection by Pss might promote destructive B. cinerea infections when the fungus is already present but latent, although further experimentation is needed to prove such an interaction.     

Self-incompatibility in Mikania micrantha in South China

Mikania micrantha is a successful invasive weed in many parts of the world, but we do not know how its mating system may have contributed to this. Therefore, its mating system was studied in an open M. micrantha population during the flowering seasons of 2004 and 2005. Pollen/ovule ratio was determined and pollination treatments were applied on entire inflorescences to estimate the seed/ovule ratio. The pollen/ovule ratio of M. micrantha was 4008, and seed/ovule ratio was 0.56 for open pollination and 0.0034 and 0.0038 for wind pollination and selfing respectively. These data indicate that the weed is self‐incompatible and needs insect pollination.     

Limitations on the recruitment of the rare sand shrubby legume Eremosparton songoricum (Fabaceae) in Gurbantunggut Desert, China

Eremosparton songoricum,a rare and endemic sand dune plant,appears to be experiencing recruitment failure.The structure of five populations from the Gurbantunggut Desert,China,was investigated for recruitment patterns,and two of them were examined for flowering,pollination and seed germination limits on regeneration.The results showed that total 150 seedlings only occurred on line transects in riverside Dure population,but they all died half a month later;no seedlings occurred in other four hinterland desert populations indicating recruitment was a failure at all populations although flowers were plentiful.Reproductive success depends on pollinators.Nectar is 'reward' for pollinators,with 0.06 μL-0.12 μL and 0.15 μL-0.35 μL per flower in Dure and Kabu populations,respectively,in continuously two secreting days.Spontaneous self pollination is rare with nearly zero fruit production.Geitonogamous self pollination is predominant with 14.47% fruit set.Seed mass in the riverside Dure population was significantly greater than that in other hinterland desert populations.Consequently,the Dure population exhibited a significantly higher germination rate(about 90%) than those in other populations(about 30%).Results suggested that recruitment failure of E.songoricum is not due to flower shortage,pollination limitation,or poor seed germination but environmental pressure and/or human disturbance.     

Behavior of <Emphasis Type="Italic">Erwinia ananas</Emphasis> transformed with bioluminescence genes on rice plants

Erwinia ananas, the causal agent of bacterial palea browning of rice, was transformed with bioluminescence genes to clarify their behavior on rice plants. Transformant CTB009T2 was used to inoculate rice plants, and the subsequent bioluminescence of CTB009T2 was observed using a two-dimensional luminometer. Luminous spots frequently appeared on anthers after flowering and on dead tissues such as leaf tips, lower leaf sheaths, and leaf blades. In spikelets that developed the disease symptom on the palea, luminous spots appeared 48h after flowering on stigmas, basal parts of ovaries, and lodicules. These results indicate that postflowering anthers and dead tissues on rice plants are important sites for a rapid increase in the pathogen population, and that the multiplication of the pathogen on internal tissues of spikelets after flowering is associated with the appearance of browning.     

Synergistic interactions between an exotic honeybee and an exotic weed: pollination of Lantana camara in Australia

Lantana camara, a woody shrub originating in south and central America, is among the most widespread and troublesome exotic weeds of the old‐world tropics. It invades pasture, crops and native ecosystems, causing substantial economic losses and environmental degradation. In Australia alone, L. camara is currently estimated to cover c. 40 000 km² . In glasshouse studies we demonstrate that L. camara requires cross‐pollination to set fruit, and that honeybee visits result in effective pollination. Field studies carried out in Queensland, Australia, suggest that fruit set is limited by pollinator abundance, and that the main pollinator of L. camara throughout a substantial portion of its Australian range appears to be the honeybee, Apis mellifera. Seed set was strongly correlated with honeybee abundance, and at many sites, particularly in southern Queensland, honeybees were the only recorded flower visitors. Of 63 sites that were visited, seed set was highest at five sites where only honeybees were present. Hives are frequently stationed within and adjacent to areas such as National Parks that are threatened by this noxious weed. Management of honeybee populations may provide a powerful tool for cost‐effective control of L. camara that has previously been overlooked. We suggest that there are probably many other weeds, both in Australia and elsewhere, that benefit from honeybee pollination.     

Virus infection and reproductive losses in faba bean (Vicia faba L.)

The viruses, bean yellow mosaic ( BYMV ), Echtes Ackerbohnenmosaik (EAMV) and bean (pea) leaf roll ( BLRV ) reduced seed yield in faba bean particularly when plants were infected at the pre-and mid-bloom stage. EAMV and BYMV , but not BLRV , delayed senescence and increased branching on glasshouse-grown plants so that more inflorescences were produced on diseased plants; most of the additional flower buds necrosed. All three viruses increased the proportion of flower buds that became necrotic thus reducing the number of mature flowers available for pollination. This, together with enhanced abscission of recently set flowers, diminished pod production. Flower set per se was unaffected by infection. The number of ovule sites per pod and weight of individual mature seeds were also unaffected by these diseases but productivity per pod declined because of increased ovule abortions. Patterns of pod production on the inflorescence and location of mature seeds within the pod were unaffected by virus infection.     

Pollination of chasmogamous flowers and the effects of light and emergence time on chasmogamy and cleistogamy in Monochoria vaginalis

Monochoria vaginalis is one of the most serious weeds of rice fields in Asia. The species has both chasmogamous (CH) and cleistogamous (CL) flowers on individual plants. The objective of this study is to clarify the reproductive characteristics that affect the selfing rate of M. vaginalis. An emasculation experiment revealed that the CH flowers emasculated just after flower opening produced seeds. The seed production in the flowers emasculated just after flower opening was less than that of the flowers emasculated and hand‐pollinated with pollen from another plant. These results indicate that, although self‐pollination before anthesis occurs, cross‐pollination also can produce seeds. An experimental manipulation of light and the emergence time of the plants revealed that more than half of the flowers produced were CL flowers and the CH/CL ratio decreased with reduced light availability. The plants that emerged later produced as many CH flowers as those that emerged earlier. There was no significant difference between the CH and CL flowers in the seed number per fruit and the seed mass. These results suggest that M. vaginalis has reproductive characteristics that make the selfing rate high; however, outcrossing also can occur. Under favorable light intensity conditions, such as on the edges of paddy fields or in fallow fields, M. vaginalis will produce more CH flowers and will have a higher outcrossing rate than in shaded conditions.     

Overcompensation of seed production caused by clipping of Bidens pilosa var. radiata (Compositae): Implications for weed control on Iriomote‐Jima Island,Japan

The invasion of natural ecosystems by exotic species is a major threat to biodiversity on a local, regional, and global scale. Endemic island flora are particularly vulnerable to invasive species. Bidens pilosa var. radiata is a common invasive weed of roadsides, which are subject to clipping, on Japanese subtropical islands. To assess compensation by the weed to damage by clipping, a pot experiment was conducted under common garden conditions. The above‐ground parts were clipped with pruning shears at various frequencies, ranging from no clipping (the control) to clipping at 4–16 week intervals for 32 weeks in summer. The clipped individuals regenerated new branches from the axillary buds and flowered for ≤12 weeks after the clipping. The regeneration after the clipping gave rise to secondary reproduction, whereas minimal regeneration occurred in the unclipped individuals after the maturation of the fruit. Consequently, the total flower head mass, represented by the dry weight of the inflorescences throughout the experiment, was higher on the individuals that were clipped at 12 and 16 week intervals than on the unclipped individuals, suggesting overcompensation in fecundity. At the higher frequencies of above‐ground clipping, the flower head mass was suppressed at 8 week clipping intervals, while both the flower head mass and the productive biomass were suppressed at 4 week clipping intervals. This indicates that clipping at intervals of ≤8 weeks is required to prevent the reproduction of this weed.     

How can natural hybridisation between self‐compatible and self‐incompatible species be bidirectional?

Self‐compatible (SC) plants often deposit pollen on their own stigmas before flowers open. Thus, if we find natural hybrids between a SC species and a closely related self‐incompatible (SI) species, the pollen donor is usually expected to be the SC species. However, in previous studies of naturally occurring mixed populations of invasive Cakile maritima (SI) and Cakile edentula (SC) in Australia, hybridisation was found to have been bidirectional. Here, we explored the floral development of these species in order to test the hypothesis that there might be a short opportunity for pollinators to visit open SC flowers before the self‐pollen is released. Results indicated that both species showed reverse herkogamy during early development, though by the time pollen was ripe the four long anthers always overtopped the stigma; in C. maritima, most of the short anthers remained below the stigma. In both species, ripe, compatible pollen was able to germinate on the stigmatic surface at all stages of floral development. Anther dehiscence commenced earlier in C. edentula and well before flowers opened, in contrast to C. maritima, but the timing of pollen release varied between individual flowers, with a small proportion of uncontaminated stigmas after flowering; therefore, C. edentula can be either pollen recipient or pollen donor when interspecific outcrossing occurs. In summary, our results suggest that the variation between individual flowers of C. edentula contributed to the bidirectional hybridisation despite being a predominant selfer, providing new insights into plant colonisation.     

Suppressive effect of bacteriophage on bacterial palea browning of rice caused by Pantoea ananatis

Bacterial palea browning of rice, caused by Pantoea ananatis from infection during flowering, occurs widely in Japan and degrades the quality of rice. In a search for environmentally friendly control measures, effects of bacteriophages on the incidence of the disease were examined. Phages lytic to both pathogenic and nonpathogenic P. ananatis were isolated from an inflorescence of eulalia (Miscanthus sinensis), a gramineous weed, and one of the phages was sprayed with and without a nonpathogenic isolate of P. ananatis on rice plants at the flowering stage. Coapplication of the phage and nonpathogenic P. ananatis suppressed the disease in sunlight. Surprisingly, application of the light-labile phage by itself was suppressive. The phage retarded the growth of the pathogen on rice plants and on LB medium. Because nonpathogenic Pantoea strains are abundant on rice panicles at the flowering stage and could be hosts of the phage and the optimum infection period of rice with P. ananatis is during the flowering stage, disease suppression by the phage is thought to be due to the combined effects of the phage, naturally inhabiting nonpathogenic bacteria, and the limited susceptible period.     

Potential gene flow from transgenic rice (Oryza sativa L.) to different weedy rice (Oryza sativa f. spontanea) accessions based on reproductive compatibility

BACKGROUND: The possibility of gene flow from transgenic crops to wild relatives may be affected by reproductive capacity between them. The potential gene flow from two transgenic rice lines containing the bar gene to five accessions of weedy rice (WR1–WR5) was determined through examination of reproductive compatibility under controlled pollination. RESULTS: The pollen grain germination of two transgenic rice lines on the stigma of all weedy rice, rice pollen tube growth down the style and entry into the weedy rice ovary were similar to self‐pollination in weedy rice. However, delayed double fertilisation and embryo abortion in crosses between WR2 and Y0003 were observed. Seed sets between transgenic rice lines and weedy rice varied from 8 to 76%. Although repeated pollination increased seed set significantly, the rank of the seed set between the weedy rice accessions and rice lines was not changed. The germination rates of F₁ hybrids were similar or greater compared with respective females. All F₁ plants expressed glufosinate resistance in the presence of glufosinate selection pressure. CONCLUSIONS: The frequency of gene flow between different weedy rice accessions and transgenic herbicide‐resistant rice may differ owing to different reproductive compatibility. This result suggests that, when wild relatives are selected as experimental materials for assessing the gene flow of transgenic rice, it is necessary to address the compatibility between transgenic rice and wild relatives. Copyright © 2009 Society of Chemical Industry     

Efficacy of Artocarpus altilis (Parkinson) Fosberg extracts on contact mortality,repellency, oviposition deterrency and fumigant toxicity of Callosobruchus maculatus (F.) (Coleoptera:Bruchidae)

Callosobruchus maculatus (F.), a major pest of grain legumes, causes considerable losses worldwide. C. maculatus management relies on synthetic insecticides with their adverse environmental and health concerns. The current study investigated the use of Artocarpus altilis (breadfruit) extracts on contact and fumigant toxicity, repellency and oviposition deterrency of C. maculatus as a management strategy. Fumigant mortality (LC₅₀) of the dry inflorescence extract of A. altilis was 126.65 µL L^?1 air at 53.4 h. Fruit extract gave 73.3% repellency at 1000 ppm after 24 h. Percent repellency was dose and time dependent. Green inflorescence extract of A. altilis reduced egg laying with 50% oviposition occurring after 37.78 h at 1000 ppm. We conclude that extracts of leaf, fruit, green and dried inflorescence of A. altilis displayed contact mortality, repellency, deterred oviposition and had fumigant activity toward C. maculatus.     

Fusarium mangiferae localization in planta during initiation and development of mango malformation disease

Mango malformation disease (MMD), caused by Fusarium mangiferae, is a major constraint to mango production, causing significant yield reduction resulting in severe economic impact. The present study characterizes fungal localization in planta during initiation and development of vegetative and floral malformation. Young mango trees were artificially inoculated with a green fluorescent protein (GFP)‐expressing strain of F. mangiferae. Shoots and buds were sampled periodically over a period of more than a year and localization of the GFP‐expressing fungi was determined using confocal microscopy. Fungal localization appears to be epiphytic: mycelia remained in close contact with the plant surface but did not penetrate the tissue. In vegetative malformation and in young inflorescences, the fungus was confined to protected regions between scales, young leaf bases and buds. Fungal colonization was only very rarely detected on open leaves or on exposed shoot sections. In developed flowers, mycelia were localized mainly to protected regions at the base of the flower organs. Upon development of the inner flower organs, specific mycelial growth occurred around the anthers and the style. Mycelial penetration through the stylar tract into aborting carpels was observed. For several months, mycelia were confined to the surface of the organs and were not detected within plant tissues. Only at later stages, transient saprophytic growth of the fungus was detected causing the malformed inflorescences to senesce and collapse, concurrent with dispersion of conidia. Implications of the present study on MMD in natural field infections are discussed.     

Grapevine inflorescences are susceptible to the bunch rot pathogens, Greeneria uvicola (bitter rot) and Colletotrichum acutatum (ripe rot)

Grapevine inflorescences (cv. Chardonnay) were found to be susceptible to infection by the berry rotting pathogens Colletotrichum acutatum and Greeneria uvicola responsible for ripe rot and bitter rot of grapes respectively. Infection of inflorescences on field-grown grapevines at mid-flowering led to subsequent berry rot at veraison. An application of the strobilurin fungicide Cabrio (active ingredient pyraclostrobin) at flowering reduced the incidence of ripe rot and bitter rot at veraison from 88% to 0% and from 86% to 2%, respectively. The infection of detached inflorescences was influenced by temperature and was greatest at 25–30°C for C. acutatum and 30°C for G. uvicola. Our results demonstrate for the first time that grapevine flowers are susceptible to C. acutatum and G. uvicola and that flower infections have the potential to lead to subsequent rotting of the grape berries. The findings have implications for the management of ripe rot and bitter rot of grapes.     

Notes on the biology and ecology of Ptecticus testaceus (Diptera: Stratiomyidae) a soldier fly associated with mango fruit (m. indica) in Costa Rica

Abstract

The association between Ptecticus testaceus Fabr. (Dipt.: Stratiomyidae) and mango fruits attached to the tree is reported, with some observations on the ecology and behaviour on the soldier fly. P.testaceus apparently synchronized its biological cycle to mango fruit set in Costa Rica, and its adults feed on nectar of sunflower inflorescences. More detailed studies to determine the status of this dipteran, and its association with mango fruits, are suggested.     

Colonization of red raspberry flowers and fruit by Botrytis cinerea under commercial production conditions in northwestern Washington,USA

Colonization of red raspberry flowers and fruit by Botrytis cinerea was determined during 2017–2018 growing seasons under commercial fungicide application programmes used for grey mould management in northwestern Washington, USA. Colonization of flowers and fruit was assessed qualitatively (incidence, %) and quantitatively (abundance, number of colonies) by recovering B. cinerea from surface-disinfested samples. Both incidence and abundance of flower colonization were significantly lower than fruit colonization in both untreated and fungicide-treated plots. Incidence of flower colonization did not differ significantly between untreated and fungicide-treated plots (43% vs. 45%, respectively). In contrast, significantly greater colonization incidence was detected at green fruit stage in untreated compared to fungicide-treated plots (96% vs. 77%, respectively). Ripe fruit had the greatest colonization incidence among the three stages sampled and colonization was not significantly different between untreated and fungicide-treated plots (100% vs. 92%, respectively). Similarly, colonization abundance of flowers did not differ significantly between untreated and fungicide-treated plots (1.0 colonies per colonized flower in both treatments), but colonization abundance of green and ripe fruit was decreased 2.3- and 2.1-fold, respectively, in fungicide-treated plots. DNA fingerprinting analysis of the pathogen revealed that different multilocus genotypes colonized flowers and fruit within the same inflorescence and that genotypic diversity increased through time, suggesting independent infection events. Overall, our results demonstrate that under current environmental conditions, raspberry flowers may not be the exclusive or major route of infection for grey mould of red raspberry in northwestern Washington. Implications of current findings for management and further research are discussed.     

荒漠绿洲交错带苹果园授粉技术研究

在南疆荒漠绿洲交错带的特殊环境条件下,以富士苹果为研究对象,通过开展不同授粉方式、不同授粉时期试验,形成高效节本的辅助授粉技术。结果表明:同一授粉时间的不同授粉方式中坐果率排序依次为人工点粉>器械喷粉>液体授粉。同一授粉方式的不同授粉时间中坐果率排序依次为始花第3/4d>始花第3/5d>始花第4/5d>始花第3d>始花第4d>始花第5d。综合来看在始花第3/4d进行人工点粉坐果率最高,而始花第3d进行液体授粉能在提高坐果率的同时还比点粉和器械喷粉更省工省力,是一种适合大面积推广应用的授粉技术。花前根外营养液喷施较对照可提高0.05的坐果率,配合辅助授粉效果更好。     

Susceptibility of Clematis Varieties and Species to Stem Infection by Phoma Clematidina as an Indicator for Resistance to Wilt

The susceptibility to stem rot and wilt caused by Phoma clematidina was tested for a range of clematis varieties and species widely grown in Europe, and compared with their susceptibility to wilt in practice as judged by amateur and commercial growers in two postal surveys. Most small flowering clematis species did not die back when unwounded stems were inoculated with spores of P. clematidina, and were also reported in the surveys as being very resistant to wilt. In contrast, large flowering hybrids were found to be highly susceptible both to stem infection by P. clematidina and to wilt in practice according to growers. A significant positive linear relationship existed between the susceptibility scores for disease in the stem inoculation test and those for wilt from the surveys. Fungal isolations were made from the stems of naturally wilted clematis plants from British nurseries and private gardens. Unlike the many other fungal species isolated, P. clematidina occurred very frequently, especially in stems of large flowering varieties. Together with the results from the grower surveys and stem inoculation trial, this indicates that this fungus is a regular cause of clematis wilt. The stem inoculation test with P. clematidina described in this study would be useful for European breeders and growers to determine the susceptibility of new clematis varieties to wilt before they are marketed.     

Effect of chemical and cultural methods of weed control on the yield and growth of maize

Abstract

Traditional sorghum cultivars in the tropics are generally photoperiod sensitive, flowering just as or after the rains cease, so that their grains fill and mature during dry weather. Improved cultivars have been developed which flower and mature earlier in the season, when soil moisture levels are generally more favourable for grain filling, which potentially gives higher grain yields. However, the earlier flowering often results in the exposure of developing grain to wet conditions in which it can deteriorate rapidly. Grain moulds are a major component of the sorghum grain deterioration complex, and have become a widespread problem of improved sorghums in temperate and tropical regions. Many fungi have been isolated from mouldy grain, the most commonly occurring genera being Fusarium and Curvularia, and vary from those such as F. moniliforme Sheldon which are pathogenic on young developing inflorescences, to many saprophytic fungi which develop on the mature grains. The review covers terminology, causal agents, time of infection, predisposing factors, effects on yield and quality, control measures, resistance screening procedures and progress and recommendations for further research particularly in resistance.