Xylem Fluid Research Articles

Lack of host phylogenetic structure in the gut bacterial communities of New Zealand cicadas and their interspecific hybrids

Host-microbe interactions are intimately linked to eukaryotic evolution, particularly in sap-sucking insects that often rely on obligate microbial symbionts for nutrient provisioning. Cicadas (Cicadidae: Auchenorrhyncha) specialize on xylem fluid and derive many essential amino acids and vitamins from intracellular bacteria or fungi (Hodgkinia, Sulcia, and Ophiocordyceps) that are propagated via transmission from mothers to offspring. Despite the beneficial role of these non-gut symbionts in nutrient provisioning, the role of beneficial microbiota within the gut remains unclear. Here, we investigate the relative abundance and impact of host phylogeny and ecology on gut microbial diversity in cicadas using 16S ribosomal RNA gene amplicon sequencing data from 197 wild-collected cicadas and new mitochondrial genomes across 38 New Zealand cicada species, including natural hybrids between one pair of two species. We find low abundance and a lack of phylogenetic structure and hybrid effects but a significant role of elevation in explaining variation in gut microbiota.

First Report of Bacterial Leaf Scald of Plum Caused by Xylella fastidiosa in Texas.

Xylella fastidiosa is the etiological agent of Plum Leaf Scald (Greco et al. 2021). The disease was first reported in Argentina (Fernandez-Valiela et al. 1954) and then Brazil and Paraguay (French et al. 1978). In the USA, Plum Leaf Scald has been reported in the Southeastern United States (Wells et al. 1981a) and California (Hernandez-Martinez et al. 2009). In August 2021, during the Stone Fruit Survey of FY2020, plum trees (Mexican variety, Prunus mexicana) with symptoms of leaf scald, were observed in a Central Texas orchard with approximately 7% of trees exhibiting symptoms. Leaf margins were asymmetrically scorched, with necrotic areas that transitioned into chlorotic and healthy green tissues. To detect the presence of the pathogen, leaf sample petioles were tested using a double-antibody sandwich (DAS) ELISA® with X. fastidiosa specific antiserum (Agdia Inc., Elkhart, IN) according to manufacturer's guidelines. X. fastidiosa was detected in 20 of the 35 symptomatic samples. To confirm ELISA results, total DNA was extracted from the plant samples using the Plant DNeasy® kit (Qiagen Co. Hilden, Germany) following the manufacturer's protocol. All 20 ELISA-positive samples tested positive in a X. fastidiosa-specific real time PCR assay, using the primers XF1F and XF1R and probe XF1p (Schaad et al. 2002). Moreover, the ELISA-negative samples were also negative for PCR assay. Symptomatic samples were used to isolate the pathogen. Samples were debarked, surface-sterilized and xylem fluid collected. The fluid was gently imprinted on buffered charcoal yeast extract (BCYE) (Wells et al. 1981b) or periwinkle wilt modified (PWM) agar plates (Summer et al. 2010). After 10 days of incubation, individual colonies were observed. The colonies were slightly convex, white, opalescent, mucoid, circular with entire margins and with smooth surfaces on both media plates. Isolated colonies were triple-streak single colony purified and archived. Genomic DNA was extracted from four purified isolates using the DNeasy Blood and Tissue Qiagen® Kit, to conduct conventional PCR using HL5/HL6 (Francis et al. 2006), which identified the isolates as X. fastidiosa. Using the 16S rRNA primer pair U3/U4 (James 2010), amplicons were sequenced and compared against the NCBI database using the BLASTn algorithm. Comparative sequence analysis of amplicons from the four isolates were identical and indicated that the isolates were 100% identical to X. fastidiosa subsp. multiplex RIV5 (CP064326.1) from cherry plum, and IVIA5901 (CP047134.1) from almond. The sequences of all four isolates were deposited into NCBI GenBank, with the accession numbers OM617940 (467), OM617941 (470), OM617942 (471) and OM617943 (468). To our knowledge, this is the first report of X. fastidiosa associated with plum leaf scald in Texas, extending the geographical range of this important bacterial disease, in the Southern United States. This study highlights the importance of routine scouting of agricultural settings with a view to assessing and detecting early threats from either pests or disease and implementing relevant management strategies.

Root Absorption and Xylem Movement of Ethephon in Tomato

Although ethephon is commonly used as a plant growth regulator during commercial production of horticultural crops, information on its movement within plants is limited. In this study, we developed a method to detect ethephon in plant tissues, and determined ethephon localization and movement using tomato (Solanum lycopersicum L.) as a model system. Tissues were ground in an acidic buffer that preserved ethephon intact. Ethylene was released from the extracts by adding sodium hydroxide and was determined subsequently by gas chromatography. Ethephon was detected in leaves within 1 hour of application to peat-based root zones and within 10 minutes in hydroponics. In a pulse–chase experiment, ethephon levels increased initially, then decreased after the plants were returned to ethephon-free solutions. Ethephon was present in directly collected xylem fluid; fluid collected from petiole stumps (after leaf blade excision) had similar ethephon levels between the different petioles. Stem girdling had no effect on ethephon accumulation in leaves. Together, these data indicate ethephon is readily mobile in the xylem stream and provides insight into the commercial use of ethephon as a root zone-applied growth regulator.

Why cicadas (Hemiptera: Cicadidae) develop so slowly

Abstract Cicadas have amongst the longest development times and are also amongst the largest insects. Cicadas feed exclusively on xylem fluid, which is nutritionally dilute and difficult to obtain. One possible explanation for their slow development is that poor nutrition limits their growth rate. An analysis of 30 cicada species with known development times is consistent with this hypothesis as species with more equatorial distributions grew more rapidly than those at higher latitudes. A second possible explanation is that prolonged development maximizes net reproductive rate because there is little risk of mortality once early instar cicada nymphs establish feeding sites. Extended development probably allows nymphs to store resources and produce more offspring. Spittlebugs also feed obligately on xylem fluid and grow at similarly slow rates although they attain small adult sizes. Unlike cicadas, spittlebugs do not have steep survivorship curves and have shorter development times. The life histories of cicadas and spittlebugs are therefore consistent with both hypotheses. Cicada development times may be limited if (1) the risk of nymphal mortality equals increased fecundity associated with prolonging development, (2) fluctuating conditions sometimes favour rapid development times, or (3) host plant quality changes over time and penalizes nymphs that cannot relocate feeding sites.

Exploring Environmental Factors That Drive Diel Variations in Tree Water Storage Using Wavelet Analysis

Internal water storage within trees can be a critical reservoir that helps trees overcome both short- and long-duration environmental stresses. We monitored changes in internal tree water storage in a ponderosa pine on daily and seasonal scales using moisture probes, a dendrometer, and time-lapse electrical resistivity imaging (ERI). These data were used to investigate how patterns of in-tree water storage are affected by changes in sapflow rates, soil moisture, and meteorologic factors such as vapor pressure deficit. Measurements of xylem fluid electrical conductivity were constant in the early growing season while inverted sapwood electrical conductivity steadily increased, suggesting that increases in sapwood electrical conductivity did not result from an increase in xylem fluid electrical conductivity. Seasonal increases in stem electrical conductivity corresponded with seasonal increases in trunk diameter, suggesting that increased electrical conductivity may result from new growth. On the daily scale, changes in inverted sapwood electrical conductivity correspond to changes in sapwood moisture. Wavelet analyses indicated that lag times between inverted electrical conductivity and sapflow increased after storm events, suggesting that as soils wetted, reliance on internal water storage decreased, as did the time required to refill daily deficits in internal water storage. We found short time lags between sapflow and inverted electrical conductivity with dry conditions, when ponderosa pine are known to reduce stomatal conductance to avoid xylem cavitation. A decrease in diel amplitudes of inverted sapwood electrical conductivity during dry periods suggest that the ponderosa pine relied on internal water storage to supplement transpiration demands, but as drought conditions progressed, tree water storage contributions to transpiration decreased. Time-lapse ERI- and wavelet-analysis results highlight the important role internal tree water storage plays in supporting transpiration throughout a day and during periods of declining subsurface moisture.

Biomolecular corona formation on CuO nanoparticles in plant xylem fluid

CuO nanoparticles selectively remove proteins from Cucurbita pepo (pumpkin) xylem to form a nanoparticle corona.

Stakeholders’ Perception of Xylella Fastidiosa (Xf) Disease Risk Assessment: First Results from Puglia (IT), Chania (GR), Valencia and Andalucia (ES)

Xylella fastidiosa (Xf) is an aerobic, Gram-negative bacterium of the monotypic genus Xylella. It is transmitted exclusively by xylem fluid feeding sap insects. Xf is one of the most dangerous plant bacteria worldwide, causing a variety of diseases, with huge impact for agriculture, and affecting cultivated plants of high economic value (e.g., olive trees, stone fruits—plums, almonds, cherries) or wide-spread ornamental plants (e.g., myrtle-leaf milkwort, oleander). In the frame of H2020 Project XF-ACTORS, analysis of the environmental, socio-economic and governance impact and vulnerability to Xf have been carried out in selected case study areas. To reach this goal, an extensive survey was conducted with the support of a comprehensive questionnaire in Puglia (Italy), Crete (Greece), Valencia and Andalusia (Spain). Questionnaires were completed through face-to-face interviews with local farmers, decision makers, extension experts and practitioners. The survey aimed to: 1) collect the point of view and perception of people about Xf disease and the containment plans; 2) identify possible gaps in communication, understand possible weak points in the communication strategy that could hamper the application and the effectiveness of containment measures; 3) understand the network of relationships existing among stakeholders in territorial contexts; and 4) collect suggestions from local people with a view to improving the management of information related to the disease. Questions were grouped under different main criteria: Knowledge, Perception, Practices, Involvement, Effectiveness, Responsibility. A scoring procedure assigned to each question a value to assess the corresponding indexes: DKI-Disease Knowledge Index, DPI-Disease Perception Index, FPI-Farm Practices Index, INV-Involvement Index, EFF-Effectiveness Index, RES-Responsibility Index. The overall values of RISK (DKI/DPI/FPI) and GOVERNANCE (INV/EFF/RES) were then obtained. To investigate linkages (correlation and causation) between Governance and Risk (perception and management) domains as well as among their indices, Structural Equation Modelling (SEM) technique was adopted. The proposed methodology proves to be useful to describe attitudes of respondents when facing the epidemic, as well as how they appreciate and tackle disease management. The work allows practical suggestions to be made to improve the knowledge-perception relationship that directly influences willingness to adopt preventive/control measures against the pathogen, and consequently will increase the efficiency of Xf disease management. The result of the whole analyses confirmed that the engagement of stakeholders, the involvement of expert groups (enlarged to experts in economy and social science) and an appropriate communication strategy are essential for a successful implementation of phytosanitary measures.

Methiocarb metabolites are systemically distributed throughout corn plants grown from coated seeds

Systemic insecticides such as neonicotinoids are widely used in seed coating practices for pest control in many crops, e.g., corn. Their success is due to their ability to protect the whole plant, from the roots to the upper leaves, but their use at high amounts is causing possible adverse effects on non-target animals exposed to contaminated pollen, nectar, leaves, and dust emitted during sowing. In 2018, the European Union banned some neonicotinoids and fipronil as seed coating insecticides in open fields. Consequently, the methylcarbamate methiocarb and less-toxic neonicotinoids, e.g., thiacloprid, have been authorized and largely used as alternative pesticides for corn seed coating. Here, an analytical protocol based on QuEChERS extraction/purification procedure and analysis by liquid chromatography-mass spectrometry has been optimized for the identification and the quantification of methiocarb, thiamethoxam, thiacloprid, and their metabolites in guttation drops, the xylem fluid excreted at leaf margins, and in leaves of corn plants grown from coated seeds. Although methiocarb is a non-systemic pesticide, we unexpectedly found high concentrations of its metabolites in both guttations and leaves, whereas methiocarb itself was below detection limits in most of the samples. The methiocarb main metabolite, methiocarb sulfoxide, was found at a mean concentration of 0.61 ± 1.12 µg mL−1 in guttation drops and 4.4 ± 2.1 µg g−1 in leaves. Conversely, parent compounds of neonicotinoids (thiamethoxam, thiacloprid) are systemically distributed in corn seedlings. This result raises safety concerns given that methiocarb sulfoxide is more toxic than the parent compound for some non-target species.

Stomatal Functioning and Its Influence on Fruit Calcium Accumulation in Northern Highbush Blueberry

Accumulation of calcium (Ca) in fruit is largely caused by transpiration and varies depending on the concentration of Ca in the xylem fluid. The objective of the present study was to evaluate the relationship between fruit stomatal functioning and Ca accumulation during different stages of development in northern highbush blueberry (Vaccinium corymbosum L.). Stomata were scarce on the berries and were concentrated primarily on the distal end near the calyx. The density of the stomata was greatest at petal fall, averaging 5 to 108 stomata/mm2 from the proximal end (pedicel end) to the distal end of the berries. Stomata were wide-open at the early green stage of berry development and had a slight deposit of wax along the guard cells. As the berries expanded during the initial period of rapid growth (stage I), most of the stomata remained near the distal segment of the berries; by the late green stage, almost none was found in the middle and proximal segments. The majority of these stomata were completely covered with wax when the berries began to change color and ripen (stage II and stage III). Stomatal conductance (gS) of the berries averaged 45 mmol·m−2·s−1 at petal fall and rapidly declined as the fruit developed. By the fruit coloring stage, conductance was low and remained less than 15 mmol·m−2·s−1 throughout the ripening period. In four cultivars, including Duke, Bluecrop, Aurora, and Elliott, Ca uptake in the berries increased rapidly during the early green stage; however, it slowed considerably between the late green and fruit coloring stages and stopped completely during fruit ripening. The results of this study strongly suggested that practices used to increase the Ca content of blueberries, such as the application of foliar fertilizers, should be performed early in the season during the first few weeks after flowering.

Activation of Ralfuranone/Ralstonin Production by Plant Sugars Functions in the Virulence of Ralstonia solanacearum.

Plant pathogenic bacteria possess sophisticated mechanisms to detect the presence of host plants by sensing host-derived compounds. Ralstonia solanacearum, the causative agent of bacterial wilt on solanaceous plants, employs quorum sensing to control the production of the secondary metabolite ralfuranones/ralstonins, which have been suggested to be involved in virulence. Here, we report that d-galactose and d-glucose, plant sugars, activate the production of ralfuranones/ralstonins in R. solanacearum. As a result, two new derivatives, ralfuranone M (1) and ralstonin C (2), were found in the culture extracts, and their structures were elucidated by spectroscopic and chemical methods. Ralstonin C (2) is a cyclic lipopeptide containing a unique fatty acid, (2S,3S,Z)-3-amino-2-hydroxyicos-13-enoic acid, whereas ralfuranone M (1) has a common aryl-furanone structure with other ralfuranones. d-Galactose and d-glucose activated the expression of the biosynthetic ralfuranone/ralstonin genes and in part became the biosynthetic source of ralfuranones/ralstonins. Ralfuranones and ralstonins were detected from the xylem fluid of the infected tomato plants, and their production-deficient mutants exhibited reduced virulence on tomato and tobacco plants. Taken together, these results suggest that activation of ralfuranone/ralstonin production by host sugars functions in R. solanacearum virulence.

Influence of phosphorus limitations on the growth, nutrient partitioning and physiology of mahogany (Swietenia macrophylla King) seedlings

ABSTRACTThe effects of four rates of phosphorus (P) fertilization (0, 0.56, 5.6 and 56.0 mg l−1) in soilless medium on the growth and physiology of mahogany seedlings were examined. The greatest response occurred at the 56 mg l−1 rate, with relatively small differences between other treatments. Biometric parameters increased at the 56 mg l−1 compared to 0 mg l−1 rate except root dry mass. Both the concentration and the total content of P and Kjeldahl nitrogen (N) increased in leaves, stems and roots with P application rate. Foliar concentrations of potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn) and sulfur (S) declined, and boron (B) and copper (Cu) increased with P limitations; zinc (Zn) and iron (Fe) were unaffected. Physiological adaptations of mahogany to P limitations include the preferential allocation of carbon (C) to plant roots, and increases in P utilization efficiency, P acquisition efficiency and the concentration of organic acids in xylem fluid. Root phosphatase activity was not influenced by P fertilization.

Bacterial diversity of bacteriomes and organs of reproductive, digestive and excretory systems in two cicada species (Hemiptera: Cicadidae).

Cicadas form intimate symbioses with bacteria to obtain nutrients that are scarce in the xylem fluid they feed on. The obligate symbionts in cicadas are purportedly confined to specialized bacteriomes, but knowledge of bacterial communities associated with cicadas is limited. Bacterial communities in the bacteriomes and organs of reproductive, digestive and excretory systems of two cicada species (Platypleura kaempferi and Meimuna mongolica) were investigated using different methods, and the bacterial diversity and distribution patterns of dominant bacteria in different tissues were compared. Within each species, the bacterial communities of testes are significantly different from those of bacteriomes and ovaries. The dominant endosymbiont Candidatus Sulcia muelleri is found not only in the bacteriomes and reproductive organs, but also in the “filter chamber + conical segment” of both species. The transmission mode of this endosymbiont in the alimentary canal and its effect on physiological processes merits further study. A novel bacterium of Rhizobiales, showing ~80% similarity to Candidatus Hodgkinia cicadicola, is dominant in the bacteriomes and ovaries of P. kaempferi. Given that the genome of H. cicadicola exhibits rapid sequence evolution, it is possible that this novel bacterium is a related endosymbiont with beneficial trophic functions similar to that of H. cicadicola in some other cicadas. Failure to detect H. cicadicola in M. mongolica suggests that it has been subsequently replaced by another bacterium, a yeast or gut microbiota which compensates for the loss of H. cicadicola. The distribution of this novel Rhizobiales species in other cicadas and its identification require further investigation to help establish the definition of the bacterial genus Candidatus Hodgkinia and to provide more information on sequence divergence of related endosymbionts of cicadas. Our results highlight the complex bacterial communities of cicadas, and are informative for further studies of the interactions and co-evolution of insect-microbial symbioses in Cicadoidea.

First finding of a dual-meaning X wave for phloem and xylem fluid ingestion: Characterization of Scaphoideus titanus (Hemiptera: Cicadellidae) EPG waveforms

The leafhopper Scaphoideus titanus (Hemiptera: Cicadomorpha: Cicadellidae), an invasive deltocephaline species introduced into Europe from North America, is the vector of the most important phytoplasma disease in European viticulture, flavescence dorée. In this first electropenetrography (EPG) study of S. titanus, we characterized its feeding waveforms and defined their biological meanings. Four typical waveform phases (pathway, X wave, sustained ingestion, and interruption) and four families within those phases (A, B, C, and N) were characterized using DC EPG technology. We proposed biological meanings for these waveforms based on excreta pH-ingestion correlations, presence of X waves, and comparison with previous AC, DC, and AC-DC EPG waveforms conducted on Cicadomorpha. We observed that sustained (i.e., >10min) ingestion by a deltocephaline leafhopper can occur from both xylem and phloem vascular cells. Waveform C2x represented ingestion of xylem fluid, and two waveforms represented behaviors when stylets were inserted into phloem sieve elements: C2p variant 1 (C2p-1), which may represent salivation (perhaps simultaneous with ingestion), and C2p variant 2 (C2p-2), which represented active ingestion. Furthermore, we found that the EPG-recorded X wave has a dual meaning by occurring prior to sustained ingestion from either phloem or xylem. This X wave was very similar in appearance to the model X wave of sharpshooters, an entirely different leafhopper subfamily, Cicadellinae. All cicadellines are obligate xylem-ingesters. Such a “dual-meaning X wave” will provide insights into how the feeding tactics of S. titanus relate to other sheath-feeding hemipterans, and will provide support for future research to clarify the role of this leafhopper as a vector of plant pathogens.

The vascular plant-pathogenic bacterium Ralstonia solanacearum produces biofilms required for its virulence on the surfaces of tomato cells adjacent to intercellular spaces.

The mechanism of colonization of intercellular spaces by the soil-borne and vascular plant-pathogenic bacterium Ralstonia solanacearum strain OE1-1 after invasion into host plants remains unclear. To analyse the behaviour of OE1-1 cells in intercellular spaces, tomato leaves with the lower epidermis layers excised after infiltration with OE1-1 were observed under a scanning electron microscope. OE1-1 cells formed microcolonies on the surfaces of tomato cells adjacent to intercellular spaces, and then aggregated surrounded by an extracellular matrix, forming mature biofilm structures. Furthermore, OE1-1 cells produced mushroom-type biofilms when incubated in fluids of apoplasts including intercellular spaces, but not xylem fluids from tomato plants. This is the first report of biofilm formation by R. solanacearum on host plant cells after invasion into intercellular spaces and mushroom-type biofilms produced by R. solanacearum in vitro. Sugar application led to enhanced biofilm formation by OE1-1. Mutation of lecM encoding a lectin, RS-IIL, which reportedly exhibits affinity for these sugars, led to a significant decrease in biofilm formation. Colonization in intercellular spaces was significantly decreased in the lecM mutant, leading to a loss of virulence on tomato plants. Complementation of the lecM mutant with native lecM resulted in the recovery of mushroom-type biofilms and virulence on tomato plants. Together, our findings indicate that OE1-1 produces mature biofilms on the surfaces of tomato cells after invasion into intercellular spaces. RS-IIL may contribute to biofilm formation by OE1-1, which is required for OE1-1 virulence.

Ralstonia solanacearum uses inorganic nitrogen metabolism for virulence, ATP production, and detoxification in the oxygen-limited host xylem environment.

ABSTRACTGenomic data predict that, in addition to oxygen, the bacterial plant pathogen Ralstonia solanacearum can use nitrate (NO3−), nitrite (NO2−), nitric oxide (NO), and nitrous oxide (N2O) as terminal electron acceptors (TEAs). Genes encoding inorganic nitrogen reduction were highly expressed during tomato bacterial wilt disease, when the pathogen grows in xylem vessels. Direct measurements found that tomato xylem fluid was low in oxygen, especially in plants infected by R. solanacearum. Xylem fluid contained ~25 mM NO3−, corresponding to R. solanacearum’s optimal NO3− concentration for anaerobic growth in vitro. We tested the hypothesis that R. solanacearum uses inorganic nitrogen species to respire and grow during pathogenesis by making deletion mutants that each lacked a step in nitrate respiration (ΔnarG), denitrification (ΔaniA, ΔnorB, and ΔnosZ), or NO detoxification (ΔhmpX). The ΔnarG, ΔaniA, and ΔnorB mutants grew poorly on NO3− compared to the wild type, and they had reduced adenylate energy charge levels under anaerobiosis. While NarG-dependent NO3− respiration directly enhanced growth, AniA-dependent NO2− reduction did not. NO2− and NO inhibited growth in culture, and their removal depended on denitrification and NO detoxification. Thus, NO3− acts as a TEA, but the resulting NO2− and NO likely do not. None of the mutants grew as well as the wild type in planta, and strains lacking AniA (NO2− reductase) or HmpX (NO detoxification) had reduced virulence on tomato. Thus, R. solanacearum exploits host NO3− to respire, grow, and cause disease. Degradation of NO2− and NO is also important for successful infection and depends on denitrification and NO detoxification systems.

ASSESSMENT OF THE BIOLOGICAL CHARACTERISTICS OF XYLELLA FASTIDIOSA IN XYLEM FLUID FROM A PIERCE'S DISEASE (PD) RESISTANT GRAPEVINE

The biological characteristics of Xylella fastidiosa (Xf) were investigated in vitro by examining the effect of pure xylem fluid from Pierce?s disease (PD)-resistant Vitis smalliana grapevines on Xf cell multiplication, aggregation, biofilm formation, and motility in microfluidic flow chambers. The aggregations of large clumps were formed in artificial medium, whereas small clumps were observed in V. smalliana xylem fluid. Xylem fluid from V. smalliana negatively affected twitching motility and repressed biofilm formation of Xf, whereas artificial medium enhanced twitching motility and supported robust biofilm development. The results indicate that chemical components of V. smalliana xylem fluid may affect the function of type IV pili of Xf, leading to reduced twitching motility and aggregation as compared to artificial medium.

Plant Water Stress Effects on Stylet Probing Behaviors of <I>Homalodisca vitripennis</I> (Hemiptera: Cicadellidae) Associated With Acquisition and Inoculation of the Bacterium <I>Xylella fastidiosa</I>

ABSTRACT The glassy-winged sharpshooter, Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), is a xylem fluid-ingesting leafhopper that transmits Xylella fastidiosa Wells et al., a plant-infecting bacterium that causes several plant diseases in the Americas. Although the role of plant water stress on the population density and dispersal ofH. vitripennis has been studied, nothing is known about the effects of plant water stress on the transmission of X. fastidiosa by H. vitripennis. A laboratory study was conducted to determine the influence of plant water stress on the sharpshooter stylet probing behaviors associated with the acquisition and inoculation of X. fastidiosa. Electrical penetration graph was used to monitor H. vitripennis feeding behaviors for 20-h periods on citrus [Citrus sinensis (L.) Osbeck] and almond [Prunus dulcis (Miller) D.A. Webb] plants subjected to levels of water stress. Adult H. vitripennis successfully located xylem vessels, then performed behaviors related to the evaluation of the xylem cell and fluid, and finally ingested xylem fluid from citrus and almond plants under the tested fluid tensions ranging from -5.5 to -33.0 bars and -6.0 to -24.5 bars, respectively. In general, long and frequent feeding events associated with the acquisition and inoculation of X. fastidiosa were observed only in fully irrigated plants (i.e., >-10 bars), which suggests that even low levels of plant water stress may reduce the spread of X. fastidiosa. Results provided insights to disease epidemiology and support the hypothesis that application of regulated deficit irrigation has the potential to reduce the incidence of diseases caused by X.fastidiosa by reducing the number of vectors and by decreasing pathogen transmission efficiency.

Verticillium dahliae VdTHI4, involved in thiazole biosynthesis, stress response and DNA repair functions, is required for vascular disease induction in tomato

The vascular plant pathogen Verticillium dahliae colonizes the xylem fluid where only low nutrient concentrations are provided. Biosynthesis of the vitamin thiamine is connected to oxidative stress. The highly conserved VdThi4 protein is localized in fungal mitochondria and is required under vitamin B1 limiting conditions. Deletion of the corresponding VdTHI4 gene by Agrobacterium-mediated transformation resulted in strains which were impaired in growth on thiamine-free medium and could be rescued by additional vitamin supply or by complementation with the original gene after protoplastation. Furthermore, we show that VdThi4 increases fungal stress tolerance such as UV-damage or oxidative stress. The orthologous sti35 gene of Fusarium oxysporum, another vascular wilt fungus, was shown to be involved in stress response, however to be dispensable for pathogenicity on tomato. In contrast, VdTHI4 is required for fungal-induced tomato disease demonstrated by infection assays with a V. dahliae ΔVdTHI4 deletion strain which is still able to invade plants through the roots but is asymptomatic. Our results suggest remarkable differences between two vascular tomato pathogens where VdThi4 is required for pathogenicity of V. dahliae, whereas F. oxysporum still causes disease when the corresponding Sti35 protein is absent.

Geochemical behaviour of rare earths in Vitis vinifera grafted onto different rootstocks and growing on several soils

The geochemical behaviour of lanthanides and yttrium (Rare Earth Elements, REEs) has been investigated mainly in geological systems where these elements represent the best proxies of processes involving the occurrence of an interface between different media. This behaviour is assessed according to features recorded in sequences of REE concentrations along the REE series normalised with respect to a reference material. In this study, the geochemical behaviour of REE was investigated in different parts of Vitis vinifera specimens grown off-soil, on soils of different nature and grafted onto several rootstocks in order to evaluate effects induced by these changes.The results indicated that roots are the plant organs where REEs are preferentially concentrated, in particular elements from Sm to Ho (middle REE, MREE) whereas Eu enrichments occur in aerial parts. The geochemical behaviour of REE suggests that MREE enrichments in roots are due to preferential MREE interactions with biological membranes or to surface complexation with newly formed phosphates. Eu-positive anomalies suggest that Eu3+ can form stable organic complexes in place of Ca2+ in several biological processes in xylem fluids. The possibility that Eu mobility in these fluids can be enhanced by its reductive speciation as Eu2+ cannot be ruled out.The assessment of the geochemical behaviour of REE according to the theory of the Tetrad Effect carried out confirms that REEs coming from soil are scavenged onto root tissues or mineral surfaces whereas their behaviour in aerial parts of V. vinifera is driven by dissolved complexation.

Transient habitats limit development time for periodical cicadas

Periodical cicadas (Magicicada spp.) mature in 13 or 17 years, the longest development times for any non-diapausing insects. Selection may favor prolonged development since nymphs experience little mortality and individuals taking 17 years have been shown to have greater fecundity than those taking 13 years. Why don't periodical cicadas take even longer to develop? Nymphs feed on root xylem fluid and move little. Ovipositing females prefer fast-growing trees at forest edges. I hypothesized that (1) adults emerging at edges would be heavier than those from forest interiors and (2) habitat changes could limit development time. I collected newly eclosed females that had neither fed as adults nor moved from their site of development. For M. septendecim, females from edges were 4.9% heavier than those from the interior. I assumed that emergence density indicated habitat quality and measured density at eight sites in 1979, 1996, and 2013. Over three generations, variation in densities was great; densities at two sites crashed, and at one site they exploded to 579/m2 Habitat transience may limit development time because only adults can reassess habitats and reposition offspring. In conclusion, cicadas are affected by habitat characteristics, habitats change over 17 years, and cicadas may emerge, mate, and redistribute their offspring to track habitat dynamics.