Guttation Droplets Research Articles

Auxin- and pH-induced guttation in Phycomyces sporangiophores: relation between guttation and diminished elongation growth.

Guttation, the formation of exudation water, is widespread among plants and fungi, yet the underlying mechanisms remain largely unknown. We describe the conditions for inducing guttation in sporangiophores of the mucoracean fungus, Phycomyces blakesleeanus. Cultivation on peptone-enriched potato dextrose agar elicits vigorous guttation mainly below the apical growing zone, while sporangiophores raised on a glucose-mineral medium manifest only moderate guttation. Mycelia do not guttate irrespective of the employed media. The topology of guttation droplets allows identifying the non-growing part of the sporangiophore as a guttation zone, which responds to humidity and medium composition in ways that become relevant for turgor homeostasis and thus the sensor physiology of the growing zone. Apparently, the entire sporangiophore, rather than exclusively the growing zone, participates in signal reception and integration to generate a common growth output. Exogenous auxin applied to the growing zones elicits two correlated responses: (i) formation of guttation droplets in the growing and transition zones below the sporangium and (ii) a diminution of the growth rate. In sporangiophore populations, guttation-induction by exogenous control buffer occurs at low frequencies; the bias for guttation increases with increasing auxin concentration. Synthetic auxins and the transport inhibitor NPA suppress guttation completely, but leave growth rates largely unaffected. Mutants C2 carA and C148 carA madC display higher sensitivities for auxin-induced guttation compared to wild type. A working model for guttation includes aquaporins and mechanosensitive ion channels that we identified in Phycomyces by sequence domain searches.

New insights into transmission pathways and possible off-target effects of insecticidal dsRNA released by treated plants

RNAi has shown great potential in controlling pests and pathogens, and dsRNA-based pesticides have been used in different ways. Due to off-target effects, the transmission pathways and possible impacts of dsRNA on non-target organisms after release should be researched. Here, we tested pathways of dsRNA transmission through the rice-hopper-spider food chain and their efficiency for triggering RNAi.The results revealed five new pathways by which plants transfer dsRNA into the environment through the food chain. We found that ingestion of the tissues or guttation droplets of treated plant could trigger both targeted and off-target RNAi both in consumers and predators. Ingestion of consumer hoppers could also result in localized RNAi in the midguts of the predator spiders. Trace amounts of dsRNA were detected in plant root excretions and in hopper honeydew. Cutting the root tips dramatically increased the levels of dsRNA in root excretions. Host shifting experiments proved that hoppers could transfer a trace amount of dsRNA via vomit. With specially designed dsRNAs, we showed that dsRNA sharing matching sequences of 29 bp or 32 bp in length with non-target genes could trigger off-target RNAi, but that dsRNA sharing 13 bp matching sequences could not.We conclude that field-released pesticidal dsRNA could be transmitted via the hydrophilic transport system in plants, and that this may pose a safety risk to non-target animal consumers that are closely related to target pests. Rational use of pesticidal dsRNAs should involve careful consideration of dsRNA design to manage the biosafety risk.

Salt and Metal Tolerance Involves Formation of Guttation Droplets in Species of the Aspergillus versicolor Complex.

Three strains of the Aspergillus versicolor complex were isolated from a salty marsh at a former uranium mining site in Thuringia, Germany. The strains from a metal-rich environment were not only highly salt tolerant (up to 20% NaCl), but at the same time could sustain elevated Cs and Sr (both up to 100 mM) concentrations as well as other (heavy) metals present in the environment. During growth experiments when screening for differential cell morphology, the occurrence of guttation droplets was observed, specifically when elevated Sr concentrations of 25 mM were present in the media. To analyze the potential of metal tolerance being promoted by these excretions, proteomics and metabolomics of guttation droplets were performed. Indeed, proteins involved in up-regulated metabolic activities as well as in stress responses were identified. The metabolome verified the presence of amino sugars, glucose homeostasis-regulating substances, abscisic acid and bioactive alkaloids, flavones and quinones.

The Effect of Guttation on the Growth of Bamboo Shoots

Guttation is the process of exudating droplets from the tips, edges, and adaxial and abaxial surfaces of the undamaged leaves. Guttation is a natural and spontaneous biological phenomenon that occurs in a wide variety of plants. Despite its generally positive effect on plant growth, many aspects of this cryptic process are unknown. In this study, the guttation phenomenon characteristic of bamboo shoots and the anatomical feature of these and culm sheaths were systematically observed. In addition, the water transport pathway and the compounds in guttation droplets of bamboo shoots were analyzed, and the effect of bamboo sheaths’ guttation on the growth of bamboo shoots was assessed. The results revealed that bamboo shoots began to exudate liquid in the evening through to the next morning, during which period the volume of guttation liquid gradually increases and then decreases before sunrise. Many vascular bundles are in bamboo shoots and culm sheaths to facilitate this water transport. The exudate liquid contains organic acids, sugars, and hormones, among other compounds. Our findings suggest that the regular guttation of the sheath blade is crucial to maintain the normal growth of bamboo shoots.

Guttation Fluids Containing Pseudomonas amygdali pv. lachrymans Are a Potential Source of Secondary Infection in Cucumber.

Guttation is a common feature of cucumber leaves under high relative humidity conditions; however, little is known about the role of guttation in the transmission of Pseudomonas amygdali pv. lachrymans, which is the pathogen of cucumber angular leaf spot disease. In this study, experimental evidence for the transmission of P. amygdali pv. lachrymans inside cucumber plants and through guttation was provided, and the results proved that P. amygdali pv. lachrymans can be transmitted from the bottom leaf to the upper leaves inside the plant and excreted from the upper leaves through guttation. After that, the third leaf of cucumber was inoculated with P. amygdali pv. lachrymans bacterial suspension, P. amygdali pv. lachrymans was detected on the fifth leaf, the petiole, and the stem and in guttation drops. Healthy cucumber seedlings were infected by P. amygdali pv. lachrymans in the guttation droplets, indicating that guttation fluids containing P. amygdali pv. lachrymans could become a potential source of secondary infection. The results from this study verified the hypothesis that guttation is a potential route for P. amygdali pv. lachrymans excretion from cucumber plants and may be a source of secondary transmission under high relative humidity.

Guttation droplets of sugarcane red rot pathogen Colletotrichum falcatum: Formation, toxigenic properties, and composition

ABSTRACT Production of guttation droplets in the cultures of Colletotrichum falcatum was often noticed. Hence, formation of guttation droplets, exudation of toxin in guttation, and guttation droplet chemical composition were assessed to find the ecological importance of guttation. Among the tested culture media, more guttation was noticed in oat meal agar medium and host extracts broth medium. Assessing the effect of five different carbon sources on guttation of C. falcatum showed that among solid media, sparse guttation droplets were noticed in glucose-, fructose-, and starch-amended media, whereas in broth cultures except fructose-amended media no other carbon sources induced guttation in mycelium. The guttation phenomenon was noticed only in sporulating mycelia, and it also followed a specific pattern in connection with sporulation. Bioassay of guttation exudates on sugarcane leaves produced pronounced necrotic lesions with large, yellow halo similar to positive control, thus confirming the presence of toxin. The guttation fluid initiated browning symptom on sugarcane leaves at a concentration of 1000 ppm and produced pronounced necrotic lesions of 3.7 cm at 10 000 ppm. The toxicity of crude fraction was thermostable up to 60 C. The gas chromatography–mass spectrometry (GC-MS) analysis of crude guttation droplets identified the presence of 24 compounds belonging to fatty acids, derivatives of fatty acids, flavonoids, flavonoid glycosides, sterols, quinone derivatives, amides, and glycol ethers, and among them fatty acids were dominant. The two compounds, viz., hexadecanoic acid methyl ester and 9-octadecenoic acid (Z) methyl ester, were abundant (18.14% and 17.98%, respectively) and identified as probable toxic compounds.

Colonization and Movement of Green Fluorescent Protein-Labeled Clavibacter nebraskensis in Maize.

Clavibacter nebraskensis causes Goss's bacterial wilt and leaf blight, a major disease of maize. Infected crop residue is the primary inoculum source and infection can occur via wounds or natural openings, such as stomata or hydathodes. The use of resistant hybrids is the primary control method for Goss's wilt. In this study, colonization and movement patterns of C. nebraskensis during infection were examined using green fluorescent protein (GFP)-labeled bacterial strains. We successfully introduced a plasmid to C. nebraskensis via electroporation, which resulted in GFP accumulation. Fluorescence microscopy revealed that in the absence of wounding, bacteria colonize leaf tissue via entry through the hydathodes when guttation droplets are present. Stomatal penetration was not observed under natural conditions. Bacteria initially colonize the xylem and subsequently the mesophyll, which creates the freckles that are characteristic of the disease. Bacteria infiltrated into the mesophyll did not cause disease symptoms, could not enter the vasculature, and did not spread from the initial inoculation point. Bacteria were observed exuding through stomata onto the leaf surface, resulting in the characteristic sheen of diseased leaves. Resistant maize lines exhibited decreased bacterial spread in the vasculature and the mesophyll. These tools to examine C. nebraskensis movement offer opportunities and new insights into the pathogenesis process and can form the basis for improved Goss's wilt management through host resistance.

Bioreactivity, Guttation and Agents Influencing Surface Tension of Water Emitted by Actively Growing Indoor Mould Isolates.

The secretion of metabolites in guttation droplets by indoor moulds is not well documented. This study demonstrates the guttation of metabolites by actively growing common indoor moulds. Old and fresh biomasses of indoor isolates of Aspergillus versicolor, Chaetomium globosum, Penicillium expansum, Trichoderma atroviride, T. trixiae, Rhizopus sp. and Stachybotrys sp. were compared. Metabolic activity indicated by viability staining and guttation of liquid droplets detected in young (<3 weeks old) biomass were absent in old (>6 months old) cultures consisting of dehydrated hyphae and dormant conidia. Fresh (<3 weeks old) biomasses were toxic more than 10 times towards mammalian cell lines (PK-15 and MNA) compared to the old dormant, dry biomasses, when calculated per biomass wet weight and per conidial particle. Surfactant activity was emitted in exudates from fresh biomass of T. atroviride, Rhizopus sp. and Stachybotrys sp. Surfactant activity was also provoked by fresh conidia from T. atroviride and Stachybotrys sp. strains. Water repealing substances were emitted by cultures of P. expansum, T. atroviride and C. globosum strains. The metabolic state of the indoor fungal growth may influence emission of liquid soluble bioreactive metabolites into the indoor air.

Plant guttation provides nutrient-rich food for insects.

Plant guttation is a fluid from xylem and phloem sap secreted at the margins of leaves from many plant species. All previous studies have considered guttation as a water source for insects. Here, we hypothesized that plant guttation serves as a reliable and nutrient-rich food source for insects with effects on their communities. Using highbush blueberries as a study system, we demonstrate that guttation droplets contain carbohydrates and proteins. Insects from three feeding lifestyles, a herbivore, a parasitic wasp and a predator, increased their longevity and fecundity when fed on these guttation droplets compared to those fed on control water. Our results also show that guttation droplets, unlike nectar, are present on leaves during the entire growing season and are visited by numerous insects of different orders. In exclusion-field experiments, the presence of guttation modified the insect community by increasing the number of predators and parasitic wasps that visited the plants. Overall, our results demonstrate that plant guttation is highly reliable, compared to other plant-derived food sources such as nectar, and that it increases the communities and fitness of insects. Therefore, guttation represents an important plant trait with profound implications on multi-trophic insect–plant interactions.

Explosive morning growth phenomena of NH3 on the North China Plain: Causes and potential impacts on aerosol formation

Atmospheric ammonia (NH3) as the most important alkaline gas in the atmosphere has attracted much attention in recent years due to its critical role in haze formation, especially on the North China Plain (NCP). Comprehensive studies are needed for investigating diurnal variations of NH3 and underlying mechanisms in different seasons and their potential impacts on atmospheric chemistry. In this study, continuous long-term observation (Mar. 2016 to May 2017) of NH3 at a rural site in the NCP was used to characterize the diurnal variation of NH3 in different seasons and to unveil its causes and potential impacts on atmospheric chemistry. NH3 concentrations displayed rapid increases during the morning, reaching very prominent peaks mostly between 8:00 to 11:00 LT. Such frequent (55%) morning peaks were mainly caused by the evaporation of dew and guttation water droplets. Average dew and guttation water volume concentrations of 750 mL m−2 was estimated for spring, which resulted in approximate NH3 emissions of 800 ng m−2 s− 1. Such high emission fluxes from dew and guttation water evaporation have never been reported before, suggesting dew and guttation droplets to be significant night-time reservoirs and strong morning sources for NH3. In light of recent studies putting forward that NH3 can promote the heterogeneous formation of HONO and nitrate under high humidity conditions, we investigated the differences in HONO and aerosol chemical composition diurnal variations between days with and without NH3 morning spikes during November. HONO, nitrate and sulfate concentrations were significantly higher for days with NH3 morning spikes, with HONO displaying a morning peak near that of NH3. These results demonstrate that the prevailing NH3 morning spikes on the NCP have significant influences on aerosol formation and atmospheric chemistry. NH3 emission mitigation strategies and regulations are urgently needed.

Penicillium expansum strain isolated from indoor building material was able to grow on gypsum board and emitted guttation droplets containing chaetoglobosins and communesins A, B and D.

AimsEmission of toxic metabolites in guttation droplets of common indoor fungi is not well documented. The aims of this study were (i) to compare mycotoxins in biomass and guttation droplets from indoor fungi from a building following health complaints among occupants, (ii) to identify the most toxic strain and to test if mycotoxins in guttation liquids migrated trough air and (iii) to test if toxigenic Penicillium expansum strains grew on gypsum board.Methods and ResultsBiomass suspensions and guttation droplets from individual fungal colonies representing Aspergillus, Chaetomium, Penicillium, Stachybotrys and Paecilomyces were screened toxic to mammalian cells. The most toxic strain, RcP61 (CBS 145620), was identified as Pen. expansum Link by sequence analysis of the ITS region and a calmodulin gene fragment, and confirmed by the Westerdijk Institute based on ITS and beta‐tubulin sequences. The strain was isolated from a cork liner, was able to grow on gypsum board and to produce toxic substances in biomass extracts and guttation droplets inhibiting proliferation of somatic cells (PK‐15, MNA, FL) in up to 20 000‐fold dilutions. Toxic compounds in biomass extracts and/or guttation droplets were determined by HPLC and LC‐MS. Strain RcP61 produced communesins A, B and D, and chaetoglobosins in guttation droplets (the liquid emitted from them) and biomass extracts. The toxins of the guttation droplets migrated c. 1 cm through air and condensed on a cool surface.ConclusionsThe mycotoxin‐containing guttation liquids emitted by Pen. expansum grown on laboratory medium exhibited airborne migration and were >100 times more toxic in bioassays than guttation droplets produced by indoor isolates of the genera Aspergillus, Chaetomium, Stachybotrys and Paecilomyces. Significance and Impact of the StudyToxic exudates produced by Pen. expansum containing communesins A, B and D, and chaetoglobosins were transferable by air. This may represent a novel mechanism of mycotoxin dispersal in indoor environment.

Guttation capsules containing hydrogen peroxide: an evolutionarily conserved NADPH oxidase gains a role in wars between related fungi.

SummaryWhen resources are limited, the hypocrealean fungus Trichoderma guizhouense can overgrow another hypocrealean fungus Fusarium oxysporum, cause sporadic cell death and arrest growth. A transcriptomic analysis of this interaction shows that T. guizhouense undergoes a succession of metabolic stresses while F. oxysporum responded relatively neutrally but used the constitutive expression of several toxin‐encoding genes as a protective strategy. Because of these toxins, T. guizhouense cannot approach it is potential host on the substrate surface and attacks F. oxysporum from above. The success of T. guizhouense is secured by the excessive production of hydrogen peroxide (H2O2), which is stored in microscopic bag‐like guttation droplets hanging on the contacting hyphae. The deletion of NADPH oxidase nox1 and its regulator, nor1 in T. guizhouense led to a substantial decrease in H2O2 formation with concomitant loss of antagonistic activity. We envision the role of NOX proteins in the antagonism of T. guizhouense as an example of metabolic exaptation evolved in this fungus because the primary function of these ancient proteins was probably not linked to interfungal relationships. In support of this, F. oxysporum showed almost no transcriptional response to T. guizhouense Δnox1 strain indicating the role of NOX/H2O2 in signalling and fungal communication.

Infection Assay for Xanthomonas campestris pv. campestris in Arabidopsis thaliana Mimicking Natural Entry via Hydathodes.

Xanthomonas campestris pv. campestris (Xcc) causes the devastating disease Black rot in Brassicaceae. Typically Xcc enters the plant through specialized organs on the leaf margin, called hydathodes, and spreads from there through the vasculature. In order to mimic natural entry as closely as possible, we here describe a "hydathode guttation"-based entry assay for Xcc in Arabidopsis. This disease assay combines spray inoculation with the induction of guttation and allows reabsorption of guttation droplets by the plant. Moreover, our assay relies on a bioluminescent reporter strain of Xcc to allow direct visualization of both entry and subsequent spreading of Xcc in its host. The assay allows the routine infection from one to two hydathodes per Arabidopsis leaf. Infections are scored 14days postinoculation, just before the infection goes systemic.

Indoor Trichoderma strains emitting peptaibols in guttation droplets.

The production of peptaibols, toxic secondary metabolites of Trichoderma, in the indoor environment is not well-documented. Here, we investigated the toxicity of peptaibols in the guttation droplets and biomass of Trichoderma strains isolated from problematic buildings. Seven indoor-isolated strains of T. atroviride, T. trixiae, T. paraviridescens and T. citrinoviride were cultivated on malt extract agar, gypsum boards and paperboards. Their biomass extracts and guttation droplets were highly cytotoxic in resting and motile boar sperm cell assays and in inhibition of somatic cell proliferation assays. The toxins were identified with HPLC/ESI-MS/MS as trichorzianines, trilongins, trichostrigocins and trichostrigocin-like peptaibols. They exhibited toxicity profiles similar to the reference peptaibols alamethicin, trilongins, and trichorzianine TA IIIc purified from T. atroviride H1/226. Particular Trichoderma strains emitted the same peptaibols in both their biomasses and exudate droplets. The trilongin-producing T. citrinoviride SJ40 strain grew at 37°C. To our knowledge, this is the first report of indoor-isolated Trichoderma strains producing toxic peptaibols in their guttation droplets. This report proves that indoor isolates of Trichoderma release peptaibols in their guttation droplets. The presence of toxins in these types of exudates may serve as a mechanism of aerosol formation for nonvolatile toxins in the indoor air.

Fate and transport of furrow-applied granular tefluthrin and seed-coated clothianidin insecticides: Comparison of field-scale observations and model estimates.

The transport of agricultural insecticides to water bodies may create risk of exposure to non-target organisms. Similarly, widespread use of furrow-applied and seed-coated insecticides may increase risk of exposure, yet accessible exposure models are not easily adapted for furrow application, and only a few examples of model validation of furrow-applied insecticides exist using actual field data. The goal of the current project was to apply an exposure model, the Pesticide in Water Calculator (PWC), to estimate the concentrations of two in-furrow insecticides applied to maize: the granular pyrethroid, tefluthrin, and the seed-coated neonicotinoid, clothianidin. The concentrations of tefluthrin and clothianidin in surface runoff water, sampled from a field in central Illinois (USA), were compared to the PWC modeled pesticide concentrations in surface runoff. The tefluthrin concentrations were used to optimize the application method in the PWC, and the addition of particulate matter and guttation droplets improved the models prediction of clothianidin concentrations. Next, the tefluthrin and clothianidin concentrations were calculated for a standard farm pond using both the optimized application method and the application methods provided in PWC. Estimated concentrations in a standard farm pond varied by a factor of 100 for tefluthrin and 50 for clothianidin depending on the application method used. The addition of guttation droplets and particulate matter to the model increased the annual clothianidin concentration in a standard farm pond by a factor of 1.5, which suggested that these transport routes should also be considered when assessing neonicotinoid exposure.

Dew from Warm‐Season Turfgrasses as a Possible Route for Pollinator Exposure to Lawn‐Applied Imidacloprid

Core Ideas This is the first study to report warm‐season turfgrass dew as a potential source for pollinator contact with imidacloprid. Observed imidacloprid concentrations were similar to those reported in creeping bentgrass guttation droplets but less than those typically found in agronomic crops grown from treated seed. Foliar‐treated bermudagrass contained more than 10 times the imidacloprid residue of the isolated soil‐only treatment. Imidacloprid is a neonicotinoid insecticide used for the control of turfgrass insect pests. It can be translocated into guttation fluid, thus potentially creating an exposure avenue for beneficial insects. Our research objectives were to investigate the fate of soil‐ and foliar‐applied imidacloprid in dew forming on bermudagrass (Cynodon spp.) and St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze] turf. Imidacloprid was applied at standard use rates (443 g a.i. ha−1; 6.32 oz a.i. acre−1) to soil only via sub‐irrigation (Years 1 and 2) or by foliar treatment (Year 2), which is representative of standard home lawn application. Dew fluid, which includes guttation, was collected 48 h after treatment and was analyzed for imidacloprid. During Year 1, dew collected from the soil‐only treatment of bermudagrass and St. Augustinegrass contained 15.8 and 9.2 ng imidacloprid mL−1, respectively. During Year 2, foliar treated bermudagrass contained more than 10 times the amount of imidacloprid as found in the soil‐only treatment (59.8 versus 5.2 ng mL−1, respectively). Observed imidacloprid concentrations were similar to those reported in creeping bentgrass guttation droplets but were less than those typically found in agronomic crops grown from treated seed. Levels were less than those reported to be acutely lethal to the European honeybee. However, depending on the amount of contaminated dew or guttation transported into hives, similarly low concentrations could be associated with sublethal effects (reportedly &gt;10 ng mL−1). This is the first study to report warm‐season turfgrass dew as a potential source for pollinator contact with imidacloprid and suggests that post‐application irrigation is perhaps the best way to avoid pollinator exposure.

Effects of Transgenic Bt Rice on Nontarget Rhopalosiphum maidis (Homoptera: Aphididae).

The effects of three transgenic Bacillus thuringiensis (Bt) rice lines, KMD1, KMD2, and G8-7, on biological parameters and population dynamics of nontarget insect, Rhopalosiphum maidis (Fitch) (Homoptera: Aphididae), were investigated in the laboratory and field. No significant differences were found between Bt and non-Bt rice lines for aphid survival. The developmental time of R. maidis that fed on KMD1 and KMD2 did not differ significantly from those of the individuals feeding on the parental variety Xiushui11, but significantly prolonged developmental time was observed on G8-7 as compared with its parental variety Xiushui110. Aphid fecundity was significantly higher on Bt than on parental rice. A 2-yr field survey indicated that Bt rice did not significantly affect the population dynamics of R. maidis in comparison with non-Bt rice. Additionally, guttation droplets of Bt rice and aphids feeding on Bt rice were analyzed for presence of Cry1Ab using ELISA. No Cry1Ab protein was found in aphid adults feeding on Bt rice lines both in the laboratory and field. By using the guttation droplets from the top of rice seedlings, we designed a novel method to collect phloem sap, and found that relatively low concentrations were detected in the guttation droplets from Bt rice lines. In conclusion, although the Bt rice lines tested in this study stimulate the fecundity of R. maidis, the aphid population density did not increase in Bt rice fields.

English

The incidence and severity of leaf and panicle blasts were efficiently reduced in the wind-treated fields. Artificially-generated wind was performed on rice paddy field in order to measure the changes in temperature and humidity during and after the blowing process and to investigate the effects of sending wind on the formation and removal of guttation and dew droplets on rice leaves. A large electric fan was used to send wind with a depression angle of 30° at 4:00 am for 30-40 min. During the blowing process, the humidity percentage was 100% in both treated and control paddy fields, the temperature was 0.8°C higher in the treated than the control field and the dew weight was rapidly decreased from 21 to 8 g in 20 min in the treated field. After the blowing process, the temperature started to rise at 6:28 am (10 min earlier than the control block). It reached 29°C at 6:48 am (30 min earlier than the control block) and remained higher than the control block till 7:20 am (1-7°C higher). The humidity decreased to 95% at 6:30 am (20 min earlier than the control block) and remained 95% till 6:42 am, then rapidly decreased to reach 68% at 6:46 am, and finally reached 60% at 7:20 am. The humidity was 5-30% lower than that in the control block. Moreover, the dew weight increased to the initial level within 10 min and then decreased rapidly in both blocks starting from 6:20 am. Using wind speed of 4.3 m/s or 3.2 m/s for 60 s per rotation at 4:00 am, almost all the guttation droplets except those of less than 0.5 mm were removed from the surfaces of the 1st and 2nd uppermost leaves after two rotations (at velocity 4.3 m/s) or three rotations (at velocity 3.2 m/s) and the dew droplets were mostly removed after five rotations (at velocity 4.3 m/s) or nine rotations (at velocity 3.2 m/s). Sending wind at a speed of 3.2 m/s or faster removed guttation and dew droplets and suppressed the subsequent dew formation. Our data indicates that the removal of dew droplets on rice hills resulted in reduction of the disease development of Pyricularia oryzea. Key words: Generated–wind, rice blast, microclimate, guttation, dew droplets.

MANAGEMENT OF BACTERIAL CANKER OF TOMATOES: AN ATTAINABLE GOAL

Severe epidemics of bacterial canker and wilt disease (caused by Clavibacter michiganensis subsp. michiganensis; Cmm) occurred in Israel between the years 2005 to 2007, resulting in substantial yield loss in many greenhouses. As there were no effective means to cope with the disease, a national research project named ‘Khosen Clavibacter’ (‘Khosen’ in Hebrew is an acronym for ‘Green Agriculture and Clean Environment’), in which all aspects of disease development were studied, was initiated. It was found that the main source of initial inoculum in commercial greenhouses was asymptomatic seedlings provided by the nurseries. The primary source of inoculum in the nurseries was infested seeds. Means to decrease the secondary spread of the pathogen from the primary infected seedling to the adjacent, healthy seedling in the nursery, were developed. In the commercial greenhouses the disease spread spatially during routine production procedures employed by the farm workers. Cmm-contaminated tools spread the disease for only a limited distance ( 22 plants). Experiments to study the effect of plant age at the time of inoculation on disease development revealed that the period during which inoculations led to wilt and death of tomato plants (designated “window of vulnerability”) ranged from plants bearing 3-4 leaves (transplanting) to those with 17-18 leaves. Plants inoculated after this period expressed less severe disease symptoms and did not wilt or die. These results suggested that implementation of precautionary measures to avoid touching tomato plants bearing guttation droplets during the window of vulnerability would have a season-long effect on plant mortality and minimize, or even prevent, yield losses. This information was distributed to tomato growers in southern Israel. From August 2010 tomato growers received SMS messages twice a week informing them of the likelihood that weather conditions in the coming days would be conducive to guttation formation. Data collected in commercial greenhouses revealed that implementing the new recommendations resulted in a significant decrease in the occurrence of severe bacterial canker epidemics.

Mowing mitigates bioactivity of neonicotinoid insecticides in nectar of flowering lawn weeds and turfgrass guttation.

Systemic neonicotinoid insecticides are used to control turfgrass insect pests. The authors tested their transference into nectar of flowering lawn weeds or grass guttation droplets, which, if high enough, could be hazardous to bees or other insects that feed on such exudates. The authors applied imidacloprid or clothianidin to turf with white clover, followed by irrigation, and used liquid chromatography-tandem mass spectrometry (LC-MS/MS) to analyze residues in clover blooms that were directly sprayed during application or that formed after the first mowing. Imidacloprid residues in guttation fluid from field-grown creeping bentgrass were assessed similarly. The authors used Orius insidiosus, a small anthrocorid bug that is sensitive to dietary neonicotinoids, as a bioindicator of the exudates' toxicity. Nectar from directly sprayed clover blooms contained 5493 ng/g to 6588 ng/g imidacloprid or 2882 ng/g to 2992 ng/g clothianidin and was acutely toxic to Orius. Residues were 99.4% to 99.8% lower in nectar of blooms formed after mowing, and nontoxic to Orius. Imidacloprid residues in turfgrass guttation averaged 88 ng/g at 1 wk after treatment, causing some intoxication of Orius, but declined to 23 ng/g within 3 wk. Systemic transference of neonicotinoids into white clover nectar and creeping bentgrass guttation appears relatively low and transitory. The hazard to nontarget insects via nectar of flowering weeds in treated lawns can be mitigated by adhering to label precautions and mowing to remove blooms if they are inadvertently sprayed.