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A new instrument for monitoring atmospheric C[O.sub.2] has been developed based on the measurement of the speed of sound in air. The instrument uses a selective scrubber to yield highly precise and accurate measurements of C[O.sub.2] mixing ratios at ambient concentrations. The instrument has a precision of 0.3 ppmv (1[sigma]) with a signal that is independent of pressure and requires a flow rate of only 30 mL/min. Laboratory measurements of atmospheric C[O.sub.2] showed excellent agreement with values obtained by nondispersive infrared absorption. The instrument has the advantage of collecting continuous, high-precision data every 25 s and can be modified for vertical profiling studies using kites, balloons, or light aircraft for the purpose of measuring landscape-scale fluxes. 10.1021/ac101365p

A new portable instrument has been developed that offers rapid detection of ozone at the parts per billion (ppb) level for personal exposure monitoring. The personal ozone monitor is based on the EPA Federal Reference Method of UV absorbance and has the advantage of being small (10 cm x 7.6 cm x 3.8 cm), lightweight (0.3 kg), low power (2.9 W), and battery-operated. The instrument can be worn by an individual during normal daily activities because it is unaffected by humidity, physical orientation, temperature, and vibration. In order to eliminate any significant interference from water vapor, Nation tubing was installed before the detection cell, and the optical path was lined with quartz. A precision of 1.5 parts per billion by volume (ppbv) and limit of detection of 4.5 ppbv (S/N = 3) was demonstrated with the instrument making measurements every 10 s. 10.1021/ac1013578

A highly portable calibration source of nitric oxide (NO) based on photolysis of nitrous oxide (N2O) supplied by 8- or 16-g disposable cartridges is demonstrated to serve as an accurate and reliable transfer standard for the calibration of NO monitors in the field. The instrument provides output mixing ratios in the range 0-1,000 ppb with a precision and accuracy of better than the greater of 3 ppb or 3% of the target NO mixing ratio over a wide range of environmental conditions of ambient temperature (8.5-35.0 °C), pressure (745-1,015 mbar corresponding to 2.7-0.0 km elevation) and relative humidity (0-100% RH). Combination of the NO calibration source with a previously described ozone calibration source based on photolysis of oxygen in air provides a new instrument capable of outputting calibrated mixing ratios of NO, ozone (O3) and nitrogen dioxide (NO2), where the NO2 is produced by the stoichiometric gas-phase reaction of NO with O3. The portable NO2/NO/O3 calibration source requires no external gas cylinders and can be used for calibrations of NO, NO2 and O3 instruments for mixing ratios up to 1,000, 500, and 1,000 ppb, respectively. This portable calibrator may serve as a convenient transfer standard for field calibrations of ozone and NOx air pollution monitors. [ABSTRACT FROM AUTHOR]

It was observed that silver colloids exhibit blinking, independent of the nature of the adsorbate in the presence or absence of surface enhanced Raman scattering (SERS). It is believed that further research of the relationship between optical behavior and SERS and the continuum will lead to better understanding of the entire process.

Understanding nitrogen oxides (NOx = NO + NO2) measurement techniques is important as air-quality standards become more stringent, important sources change, and instrumentation develops. NOx observations are compared in two environments: source testing from the combustion of Southwestern biomass fuels, and urban, ambient NOx. The latter occurred in the urban core of Albuquerque, NM, at an EPA NCORE site during February-March 2017, a relatively clean photochemical environment with ozone (O3) <60 ppb for all but 6 hr. We compare two techniques used to measure NOx in biomass smoke during biomass burning source testing: light absorption at 405 nm and a traditional chemiluminescence monitor. Two additional oxides of nitrogen techniques were added in urban measurements: a cavity attenuated phase shift instrument for direct NO2, and the NOy chemiluminescence instrument (conversion of NOy to NO by molybdenum catalyst). We find agreement similar to laboratory standards for NOx, NO2, and NO comparing all four instruments (R2 > 0.97, slopes between 0.95 and 1.01, intercepts < 2 ppb for 1-hr averages) in the slowly varying ambient setting. Little evidence for significant interferences in NO2 measurements was observed in comparing techniques in late-winter urban Albuquerque. This was also confirmed by negligible NOz contributions as measured with an NOy instrument. For the rapidly varying (1-min) higher NOx concentrations in biomass smoke source testing, larger variability characterized chemiluminescence and absorption instruments. Differences between the two instruments were both positive and negative and occurred for total NOx, NO, and NO2. Nonetheless, integrating the NOx signals over an entire burn experiment and comparing 95 combustion experiments, showed little evidence for large systematic influences of possible interfering species biasing the methods. For concentrations of <2 ppm, a comparison of burn integrated NOx, NO2, and NO yielded slopes of 0.94 to 0.96, R2 of 0.83 to 0.93, and intercepts of 8 to 25 ppb. We attribute the latter, at least in part, to significant noise particularly at low NOx concentrations, resulting from short averaging times during highly dynamic lab burns. Discrepancies between instruments as indicated by the intercepts urge caution with oxides of nitrogen measurements at concentrations <50 ppb for rapidly changing conditions. Implications: Multiple NOx measurement methods were employed to measure NOx concentrations at an EPA NCORE site in Albuquerque, NM, and in smoke produced by the combustion of Southwestern biomass fuels. Agreement shown during intercomparison of these NOx techniques indicated little evidence of significant interfering species biasing the methods in these two environments. Instrument agreement is important to understand for accurately characterizing ambient NOx conditions in a range of environments. [ABSTRACT FROM AUTHOR]

A highly portable ozone (O3) calibration source that can serve as a U.S. EPA level 4 transfer standard for the calibration of ozone analyzers is described and evaluated with respect to analytical figures of merit and effects of ambient pressure and humidity. Reproducible mixing ratios of ozone are produced by the photolysis of oxygen in O3- scrubbed ambient air by UV light at 184.9 nm light from a low-pressure mercury lamp. By maintaining a constant volumetric flow rate (thus constant residence time within the photolysis chamber), the mixing ratio produced is independent of both pressure and temperature and can be varied by varying the lamp intensity. Pulse width modulation of the lamp with feedback from a photodiode monitoring the 253.7 nm emission line is used to maintain target ozone mixing ratios in the range 30-1000 ppb. In order to provide a constant ratio of intensities at 253.7 and 184.9 nm, the photolysis chamber containing the lamp is regulated at a temperature of 40 °C. The resulting O3 calibrator has a response time for step changes in output ozone mixing ratio of < 30 s and precision (σp) of 0.4% of the output mixing ratio for 10 s measurements (e.g.,σp D ±0:4 ppb for 100 ppb of O3). Ambient humidity was found to affect the output mixing ratio of ozone primarily by dilution of the oxygen precursor. This potential humidity interference could be up to a few percent in extreme cases but is effectively removed by varying the lamp intensity to compensate for the reduced oxygen concentration based on feedback from a humidity sensor. [ABSTRACT FROM AUTHOR]

We describe and characterize a modular folded tubular photometer for making direct measurements of the concentrations of nitrogen dioxide (NO2) and specify how this method could be extended to measure other pollutants such as sulfur dioxide (SO2), ozone (O3), and black carbon particulate matter. Direct absorbance measurements using this photometer can be made across the spectral range from the ultraviolet (UV) to the near infrared. The absorbance cell makes use of modular components (tubular detection cells and mirror cubes) that allow construction of path lengths of up to 2m or more while maintaining low cell volumes. The long path lengths and low cell volumes enable sensitive detection of ambient air pollutants down to low part-perbillion levels for gas species and aerosol extinctions down to 1Mm-1, corresponding to ~0.1 μgm-3 for black carbon particulates. Pressure equalization throughout the stages of the absorbance measurement is shown to be critical to accurate measurements of analyte concentrations. The present paper describes the application of this photometer to direct measurements of nitrogen dioxide (NO2) and the incorporation of design features that also enable measurement of nitric oxide (NO) in the same instrument. Excellent agreement for ambient measurements along an urban roadside was found for both NO2 and NO measured by the folded tubular photometer compared to existing standard techniques. Compared to commonly used methods for measurements of NOx species, the advantages of this approach include (1) an absolute quantification for NO2 based on the Beer-Lambert law, thereby greatly reducing the frequency at which calibrations are required; (2) the direct measurement of NO2 concentration without prior conversion to NO as is required for the commonly used chemiluminescence method; (3) the use of modular components that allow construction of absorbance detection cells of varying lengths for extending the dynamic range of concentrations that can be measured; (4) a more economical instrument than other currently available direct measurement techniques for NO2; and (5) the potential for simultaneous detection of additional species such as SO2, O3, and black carbon in the same instrument. In contrast to other commercially available direct NO2 measurements, such as cavity-attenuated phase-shift spectroscopy (CAPS), the folded tubular photometer also measures NO simultaneously in the same apparatus by quantitatively converting NO to NO2 with ozone, which is then detected by direct absorbance. [ABSTRACT FROM AUTHOR]

The 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. [ABSTRACT FROM AUTHOR]

A new solid-phase scrubber for use in conventional ozone (O3) photometers was investigated as a means of reducing interferences from other UV-absorbing species and water vapor. It was found that when heated to 100-130 °C, a tubular graphite scrubber efficiently removed up to 500 ppb ozone and ozone monitors using the heated graphite scrubber were found to be less susceptible to interferences from water vapor, mercury vapor, and aromatic volatile organic compounds (VOCs) compared to conventional metal oxide scrubbers. Ambient measurements from a graphite scrubberequipped photometer and a co-located Federal equivalent method (FEM) ozone analyzer showed excellent agreement over 38 days of measurements and indicated no loss in the scrubber's ability to remove ozone when operated at 130 °C. The use of a heated graphite scrubber was found to reduce the interference from mercury vapor to ≤3% of that obtained using a packed-bed Hopcalite scrubber. For a series of substituted aromatic compounds (ranging in volatility and absorption cross section at 253.7 nm), the graphite scrubber was observed to consistently exhibit reduced levels of interference, typically by factors of 2.5 to 20 less than with Hopcalite. Conventional solid-phase scrubbers also exhibited complex VOC adsorption and desorption characteristics that were dependent upon the relative humidity (RH), volatility of the VOC, and the available surface area of the scrubber. This complex behavior involving humidity is avoided by use of a heated graphite scrubber. These results suggest that heated graphite scrubbers could be substituted in most ozone photometers as a means of reducing interferences from other UV-absorbing species found in the atmosphere. This could be particularly important in ozone monitoring for compliance with the United States (U.S.) Clean Air Act or for use in VOC-rich environments such as in smog chambers and monitoring indoor air quality. [ABSTRACT FROM AUTHOR]

Cicadellinae leafhoppers and other Auchenorrhyncha in coffee and citrus farms in Puerto Rico were surveyed five times over 18 mo. We frequently collected four of the seven species of Cicadellinae previously found in Puerto Rico, yet only one species (Caribovia coffeacola Dozier) fed directly on coffee; no species was observed to feed directly on citrus. Populations of C. coffeacola were higher during the rainy season and were more common at higher elevations. Feeding preference and performance experiments established that C. coffeacola preferentially fed, and could survive exclusively, on coffee and the common shade host Inga vera. Within-farm distribution of C. coffeacola was examined at a site with high populations, and abundances were higher with proximity to I. vera. Lastly, sets of novel sites were selected in four municipalities to test hypotheses concerning effects of season, elevation, and host plant assemblages on Cicadellinae populations. These tests confirmed that C. coffeacola was the only species that frequently fed on coffee and no species fed on citrus. Populations of C. coffeacola were higher in the rainy season and at higher elevations. Abundances were also higher when Inga vera was interspersed in coffee plantings compared to when other shade species were present or when coffee was grown as a monoculture (sun coffee). Cicadellinae were our focus, as within this study this subfamily is the predominant potential vector of the bacterium Xylella fastidiosa (Wells). Xylella fastidiosa has yet to be confirmed in Puerto Rico, but both citrus and coffee are susceptible to X. fastidiosa diseases. [ABSTRACT FROM AUTHOR]

There is increasing interest in the culture of satsuma citrus in the states bordering the northern Gulf of Mexico. Yield, tree size, and fruit quality of mature 'Owari' and 'Brown Select' satsuma (Citrus unshiu Marcovitch) on Poncirus trifoliata (L.) Raf. ('Rubidoux' and 'Flying Dragon') were evaluated in north Florida. Canopy area and volume, yield, and fruit quality data were analyzed as a 2 x 2 factorial design with scion and rootstock as the main effects. There were no scion x rootstock interactions. Overall average yield per tree was 16, 88, 91, 143, and 101 kg in 2010, 2011, 2012, 2013, and 2014, respectively. Yield was influenced by scion (higher for 'Brown Select') in three of five years, and by rootstock every year (higher for 'Rubidoux'). Yield per tree was ≈2-fold greater for trees on 'Rubidoux' compared with 'Flying Dragon'; the highest yield was recorded for 'Brown Select' on 'Rubidoux'. Yield per m² canopy area was often similar since canopy area was often ≈2-fold greater for trees on 'Rubidoux'. For three of the five years, fruit weight was greater for 'Brown Select' (average = 157 g) than 'Owari' (average = 146 g), with no rootstock effect. Soluble solids of juice averaged 10.0 °Brix and were higher for trees on 'Flying Dragon' than on 'Rubidoux' in three of five years. Juice pH averaged 3.67 and was unaffected by scion or rootstock. Trees were not subjected to freeze protection and were not damaged by minimum temperatures as low as --9.4 °C, except for 2014/15. A rating of defoliation after a freeze on 19 Nov. 2014 (--5.6 °C) indicated that cold hardiness varied by scion (greater for 'Brown Select') and rootstock (greater for 'Rubidoux'). Differences in cold hardiness did not persist when assessed later in the winter. Successful satsumas production can be achieved in north Florida in the absence of a severe freeze event. [ABSTRACT FROM AUTHOR]

Abstract: Botryosphaeria spp. are ligninolytic ascomyceteous fungi that incite many diseases in economically important woody plant species. Four Botryosphaeria isolates, Botryosphaeria rhodina (Lasiodiplodia theobromae), Botryosphaeria obtusa, Botryosphaeria dothidea and Botryosphaeria ribis (Neofusicoccum ribis) were used in this study. Ten naturally occurring phenolic compounds from plants were tested to evaluate their effect on mycelium growth and the production of ligninolytic and pectinolytic enzymes. The effect of phenolic compounds in vitro varied with the Botryosphaeria isolates. Inhibition of mycelium growth was dose-dependent, and varied from 2 to 100% inhibition in the ten phenolic compounds tested except syringic acid, which has no toxic effect on mycelium of Botryosphaeria isolates. A significant decrease in laccase production occurred when Botryosphaeria isolates were grown on phenolic compounds. Benzoic acid significantly inhibited pectinase activity in all isolates. The percent inhibition of pectinase activity in B. dothidea and B. obtusa was significantly increased in the presence of salicylic acid and syringic acid, respectively. [Copyright &y& Elsevier]

Homalodisca vitripennis (Germar) and related species have caused millions of dollars in damage to southern California vineyards in recent years through the vectoring of Pierce's disease. However, the effects of surrounding vegetation on the dispersal and distribution of H. vitripennis are poorly understood. Therefore, the relationship between dispersal rates and patch quality was tested, as well as the basic predictions of the marginal value theorem. Additional experiments were conducted to compare the H. vitripennis distribution in an isolated crape myrtle (Lagerstroemia indica) patch and a L. indica patch bordering two alternative host patches. In mark-release-recapture tests, H. vitripennis dispersed farther from the release point in a patch of low-quality host plants (Prunus persica) than in patches of high-quality host plants (L. indica). In addition, H. vitripennis remained in L. indica patches longer than in P. persica patches and adjusted patch residence times in P. persica in correlation with known changes in plant physiology. These data suggest that H. vitripennis follows the basic predictions of marginal value theorem. In distribution tests, H. vitripennis were more abundant in the patch center than patch edges in the isolated L. indica patch, but in a patch bordering cottonwood (Populus sp.) and peach (P. persica), H. vitripennis numbers were generally higher along the edges of the patch. These data suggest that alternate hosts bordering cropping systems may be important to the spatial dynamics of H. vitripennis. Implications of these spatial observations on the biology of H. vitripennis and potential control methods are discussed. [ABSTRACT FROM AUTHOR]

Insect species exhibiting a weak linkage between adult preference and immature performance have frequently been shown to be prone to outbreaks. We used choice and no-choice tests to examine the preference-performance linkage of the xylem fluid-feeding leafhopper, Homalodisca vitripennrs Germar. Leafhoppers were offered a choice of hosts common to their native range and also a choice from hosts where they have been recently introduced. Behavior (residence preference, oviposition preference, and consumption rates) was quantified in choice tests. Performance (development of immature leafhoppers, fecundity, body weights, and survivorship) was quantified in no-choice tests. Virtually all aspects of leafhopper behavior and performance varied with host species, yet there were no linkages between adult preference and immature performance. Lagerstroemia indica and Citrus sinenris were the preferred hosts, but both species supported <30% of neonate development until the second stadia Glycine max was the superior developmental host with development to the adult stage exceeding 40%, but this host was seldom used by adult leafhoppers. Adult preference reflected aspects of adult performance including increases in fecundity, body weights, and survivorship. These preference-performance linkages were impacted by environmental context, insect reproductive status, and insect feeding history. Essential amino acids were consistently correlated with performance of both adult and developing insects; relationships between nutrients and preference were less consistent. The weak linkage of adult preference and immature leafhopper performance are discussed in terms of outbreaks of H. vitripennis. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa is the causal agent of Pierce's disease in grapevines. The mechanisms of pathogenicity are largely due to occlusion of xylem vessels by aggregation of X. fastidiosa and biofilm formation. Xylella fastidiosa was subjected to xylem fluids with varying chemistries to examine the effects of nutritional components on bacterial growth in vitro. The exposure of X. fastidiosa to xylem fluids collected from different Vitis genotypes resulted in highly significant differences in both planktonic growth and biofilm formation. Planktonic growth of X. fastidiosa in Vitis xylem fluid was correlated to the concentration of citric acid, amino acids (glutamic acid, glutamine, histidine, valine, methionine, isoleucine and phenylalanine) and inorganic ions (copper, magnesium, phosphorus and zinc). Biofilm formation was correlated to many amino acids at 1 h of incubation. Xylem fluid from Vitis rotundifolia cv. Noble (fluid that supported low planktonic growth) was supplemented with the compounds that were correlated above to levels found in Vitis champinii cv. Ramsey (fluid that supported high planktonic growth) to determine the direct impact of xylem constituents on the growth characteristics of X. fastidiosa. Augmentation of fluid from Noble with the amino acids listed above, citric acid, calcium and magnesium resulted in increased planktonic growth and aggregation. [ABSTRACT FROM AUTHOR]

In broad bean ( Vicia faba L.), an apoplastic phloem loader, the sucrose concentration increases up to ∼ 2 mM in the leaf apoplast and up to ∼ 150 mM in the guard-cell apoplast during the photoperiod. This high concentration in the guard-cell apoplast results from transpiration and is sufficient osmotically to reduce stomatal aperture size by up to 3 µm or ∼ 25% of the maximum aperture size. In this paper, we investigated a parallel and required role for high bulk-leaf apoplastic sucrose concentration, which correlates with high photosynthesis rate. An empirically determined combination of lowered light intensity and lowered CO2 concentration reduced the photosynthesis rate to nominally one-fifth of the control value without a significant change in transpiration. This reduction in photosynthesis caused the sucrose concentration in the leaf apoplast – the immediate source pool for guard cells – to decrease by 70% (to 0.4 mM). In turn, sucrose concentration in the guard-cell apoplast decreased by ∼ 80% (to ∼ 40 mM). These results complete the required evidence for a non-exclusive, transpiration-linked, photosynthesis-dependent passive mechanism for the modulation of stomatal aperture size. In an ancillary investigation, hexoses in the bulk-leaf apoplast decreased when photosynthesis was lowered, but their concentrations in the guard-cell apoplast of control plants indicated that their osmotic contribution was negligible. [ABSTRACT FROM AUTHOR]

The abundance of Homalodisca coagulata (Say) (Hemiptera: Cicadellidae) was examined in north Florida from 2001 to 2003 on the following Vitis genotypes: V. rotundifolia Michx. (cultivars ‘Carlos’, ‘Early Fry’, ‘Regale’, and ‘Noble’), V. rupestris Scheele. (cultivars ‘St. George’ and ‘Constaneia’), V. simpsoni Munson (cultivar ‘Pixiola’), V. champini Planch. (cultivars ‘Dogridge’ and ‘Ramsey’), and V. vinifera L. (cultivars ‘Chardonnay’, ‘Chenin blanc’, and ‘Exotic’). The mean number of adult H. coagulata was less than two per vine per day during 2001 and was lowest on V. rotundifolia cultivars. During June/July 2002, the number of leafhoppers varied between 2 per vine per day on V. rotundifolia cultivars and 10–20 per vine per day on the other Vitis genotypes. The distribution of H. coagulata was examined from June to September 2002 and during August 2003 in relation to the primary organic nutrients (19 amino acids, 7 organic acids, and 3 sugars) in xylem fluid. The concentrations of most amino acids varied with Vitis genotype. Glutamine represented between 58 and 89% of all amino acids. Leafhopper abundance was positively correlated with total amino acids and percentage glutamine and inversely correlated with many of the remaining amino acids. The percentage of proline in xylem fluid was the best inverse correlate to leafhopper abundance during 2002 and 2003. Consumption rates of H. coagulata were positively correlated to insect abundances. The adult to nymph ratio was over 10:1, mad egg masses were only occasionally found on Vitis. These data suggest that adult H. coagulata used Vitis primarily as a feeding host. The ratio of glutamine to proline (GlnPro) was the most consistent chemical correlate to H. coagulata abundance and feeding. Glutamine and proline may play a behavioral role in determining H. coagulata host selection and consumption rates. [ABSTRACT FROM AUTHOR]

Manufacturers, consumers, and regulators use various water test methods to test the integrity of the barrier offered by natural rubber latex condoms. The purpose of this study is to analyze three alternative water test methods and determine which is the best method for detecting holes in condoms. Three types of holes (laser, acupuncture, and 28 gage insulin needles), approximating defects that occur in condoms, were placed in condoms and then into equal size test sets for testing by six laboratories for the purpose of evaluating the three alternative methods: the ASTM method, the ISO/FDA method, and the CSI/FHI method. Each method shares a hang portion for 1 min, and then uses a different form of manipulation; either elevate (ASTM), roll (ISO/FDA), or squeeze (CSI/FHI). The interlaboratory study data indicate the CSI/FHI is the most sensitive method for locating holes in condoms, becoming more sensitive as the defect approaches the closed end. [ABSTRACT FROM AUTHOR]

A simplified protocol for rearing the glassy-winged sharpshooter, Homalodisca coagulata (Say) (Homoptera: Cicadellidae), was tested on four genotypes of soybean, Glycine max (L.) Merrill. Growth and development of leafhoppers were examined on three glabrous isolines (D88–5320, D88–5328, and 1390–9216) and one pubescent genotype (Hagood). All three glabrous isolines were adequate hosts producing an average of >100 adults from eight original mating pairs of leafhoppers. Pubescent Hagood produced significantly fewer adults with longer developmental times. Isoline D88–5328 produced 30% more adults than the other glabrous isolines. Genotype also had significant effects on total developmental times, developmental rates within instars, growth rates, and adult masses at eclosion with insect performance being enhanced on isoline D88–5328. All genotypes of G. max had similar xylem chemistry at the initiation of the rearing experiment (6-week-old plants), but as G. max matured (14–18 wk), isoline D88–5328 provided significantly more organic nitrogen. Chemical analyses of xylem fluid and developmental data support the hypothesis that young H. coagulata required balanced profiles of organic nitrogen for development but benefited from increased organic nitrogen as they approached maturation. Poor performance on pubescent Hagood was not related to xylem chemistry and was assumed to result from the inhibitory effect of trichomes. Xylem fluid analysis suggests that some plants may have eventually experienced nitrogen deprivation from high leafhopper loads; this, in turn, resulted in slow development and small body size at maturation for some insects. Although this protocol provides a simplified technique for rearing H. coagulata, it is likely that manipulation of xylem chemistry via fertilization would further maximize growth and developmental rates. [ABSTRACT FROM AUTHOR]

Cecropin B (CB) is a very efficient antimicrobial agent against Xylella fastidiosa. CB activity decreased after incubation with xylem fluid from Vitis vinifera cv. Chardonnay. SDS-PAGE demonstrated the existence of protein(s) in xylem fluid of V. vinifera cv. Chardonnay that interact with CB and inhibit CB activity. The antimicrobial activity of CB was dependent on incubation time and colony size of X. fastidiosa. X. fastidiosa colonies in periwinkle wilt medium plus (PW+), and chemically defined media (3G10-R and CHARD2) showed different patterns in colony size and colony number in these media. After 1h of incubation in 10μM CB, only large-sized colonies were observed in the three media. These results suggested that most of the bacterial cells or small aggregates in suspension were killed by CB. Aggregation of X. fastidiosa cells may serve as a mechanism of protection against CB. [Copyright &y& Elsevier]

Discusses the biology of xylophagous insect vectors of Xylella fastidiosa and the occurrence and epidemiology of leafhopper-vectored Xylella diseases. Importance of xylophagous leafhoppers to the ecosystems; Diseases cause by xylophagous leafhoppers in agricultural crops; Information on the different species of leafhoppers; Transmission efficiency of Xylella fastidiosa.

Abstract Three experiments were performed to assess the effect of the number of the leafhopper Homalodisca coagulata (Say) (Homoptera: Auchenorrhyncha: Cicadellidae) on the plant characteristics of Lagerstroemia indica L. (Lythraceae), Prunus salicina Lindl. (Rosaceae) and Glycine max (L.) Merrill (Leguminoseae) and on subsequent consumption rates and fecundity. Leafhoppers were placed in sleeve cages (L. indica or P. salicina ) or on caged plants (G. max ) for 2–3 weeks at densities of 0–16 per cage. Consumption rates and fecundity were not influenced by leafhopper treatments. Shoot growth and shoot xylem tension were examined on L. indica and G. max , and were not influenced by treatment. For G. max , plant height increased with leafhopper days, however plant dry weight was unaffected. The concentrations of primary organic compounds in xylem fluid were evaluated at the termination of experiments on L. indica (amino acids and organic acids) and G. max (amino acids, ureides, organic acids, and sugars). For L. indica , there was no significant density effect on the concentration of total amino acids or total organic acids. For the smaller legume G. max , concentrations of five primary organic compounds in xylem fluid were moderately reduced (between P = 0.05 and 0.1) with leafhopper days. Consumption rates were inversely related (between P = 0.05 and 0.1) to the concentrations of three organic compounds in xylem fluid. The total quantity of each chemical compound, organic carbon, organic nitrogen, and energy extracted by H. coagulata feeding on G. max was estimated by incorporating consumption rates, leafhopper days, diet composition, and the heat of combustion of each compound quantified. The quantity of water and nutrients (and particularly organic N) depleted by leafhopper feeding at high densities was substantial. Individual H. coagulata extracted 3.9 cm3 water, 57 µmol organic carbon, 21 µmol organic nitrogen, and 2.7 J of... [ABSTRACT FROM AUTHOR]

We investigated the effects of ultraviolet (UV)-reflective mulch and two rates of nitrogen fertilization on populations of Frankliniella spp. thrips and on the incidence of tomato spotted wilt in field-grown tomato in northern Florida. The higher of the two soil nitrogen fertilizer treatments significantly increased populations of Frankliniella occidentalis (Pergande), whereas mulch reflectance significantly decreased populations of F. occidentalis. Populations of Frankliniella tritici (Fitch) were decreased only by UV-reflective mulch. Decreased thrips populations in UV-reflective mulch plots were probably due to disruptions in host-finding behavior. Increased thrips populations in tomatoes treated with the higher nitrogen fertilization rate were probably due in part to increased nutrients available in flowers. Incidence of tomato spotted wilt was significantly decreased in tomatoes grown on UV-reflective mulch, whereas disease incidence was significantly greater in increased nitrogen-fertilized plots. This research reveals that cultural practices resulted in up to 45% reduction in the numbers of vector and nonvector species of flower thrips and up to 50% reduction in tomato spotted wilt. [ABSTRACT FROM PUBLISHER]

Positive root pressure in Vitis rotundifolia Michx cv. Noble was employed to quantify diurnal and temporal changes in the chemical profile of xylem exudate. Xylem fluid osmolarity (7.2 to 16.8 mM), water flux (8.2 to 18.5 ml h-1) and solute flux (0.7 to 2.2 mmol h-1) from a cut spur exhibited a diurnal pattern with maxima during midday and minima at night. Total osmolarity was similar to the sum of all organic and inorganic entities quantified, indicating that the major solutes have been identified. Total ammo acid and organic acid concentration were about equal (2 to 7 mM). and sugars accounted for a minor fraction of the total profile (<0.2 mM). Glutamine represented ca 80% of the organic N and 70% of the total N transported in the xylem fluid. A circadian rhythm in water flux and net flux of most organic and inorganic entities was observed with maxima during midday and minima at night. The increase in xylem fluid osmolarity occurring during midday was primarily a consequence of increased organic acid (oxalic, citric, tartaric, malic and succinic acids) and ion (NH4+,NO3-, P and Ca) concentration. A diurnal cycle in ammo acid concentration was less clear The concentration of individual organic and inorganic entities varied asynchronously with time. Xylem solute was comprised of 80% organic and 20% inorganic components when collected 5 min to 2 h after the commencement of bleeding, but the ratio of organic to inorganic components fell to about 50% after 7 days. [ABSTRACT FROM AUTHOR]

Almond leaf scorch (ALS) is caused by the pathogenic bacterium Xylella fastidiosa and poses a threat to the California almond industry. Almond cultivars are differentially resistant or susceptible to ALS. X. fastidiosa can infect but does not overwinter in resistant cultivars in sufficient numbers to cause symptoms or be detected by polymerase chain reaction. To better understand the biochemical or morphological factors mediating resistance, we extracted and analyzed almond xylem fluid from four almond cultivars differing in ALS susceptibility, including Butte and Carmel cultivars that are field resistant and Peerless and Sonora that are ALS susceptible. Xylem fluid was collected over winter months in 2007 to 2009, as well as July 2008 and April 2009, and analyzed for the following: pH, osmolarity, concentrations of sugars, calcium, magnesium, organic acids, and total phenolics. For most of these analyses, we found no clear differences in xylem fluid from resistant and susceptible almond cultivars. However, during the winter months, resistant cultivars tended to have higher concentrations of total phenolic compounds compared with susceptible cultivars (P = 0.05). In February 2009, Carmel had the highest total phenolic concentration measured, 233 μg/ml of gallic acid equivalents. The lowest phenolic concentrations occurred in April 2009. The cross-sectional areas of xylem vessels in Butte (resistant) and Peerless (susceptible) trees were not significantly different between cultivars. [ABSTRACT FROM AUTHOR]

Understanding nitrogen oxides (NO x  = NO + NO 2 ) measurement techniques is important as air-quality standards become more stringent, important sources change, and instrumentation develops. NO x observations are compared in two environments: source testing from the combustion of Southwestern biomass fuels, and urban, ambient NO x . The latter occurred in the urban core of Albuquerque, NM, at an EPA NCORE site during February-March 2017, a relatively clean photochemical environment with ozone (O 3 ) <60 ppb for all but 6 hr. We compare two techniques used to measure NO x in biomass smoke during biomass burning source testing: light absorption at 405 nm and a traditional chemiluminescence monitor. Two additional oxides of nitrogen techniques were added in urban measurements: a cavity attenuated phase shift instrument for direct NO 2 , and the NO y chemiluminescence instrument (conversion of NO y to NO by molybdenum catalyst). We find agreement similar to laboratory standards for NO x , NO 2 , and NO comparing all four instruments (R 2  > 0.97, slopes between 0.95 and 1.01, intercepts < 2 ppb for 1-hr averages) in the slowly varying ambient setting. Little evidence for significant interferences in NO 2 measurements was observed in comparing techniques in late-winter urban Albuquerque. This was also confirmed by negligible NO z contributions as measured with an NO y instrument. For the rapidly varying (1-min) higher NO x concentrations in biomass smoke source testing, larger variability characterized chemiluminescence and absorption instruments. Differences between the two instruments were both positive and negative and occurred for total NO x , NO, and NO 2 . Nonetheless, integrating the NO x signals over an entire burn experiment and comparing 95 combustion experiments, showed little evidence for large systematic influences of possible interfering species biasing the methods. For concentrations of <2 ppm, a comparison of burn integrated NOx, NO 2 , and NO yielded slopes of 0.94 to 0.96, R 2 of 0.83 to 0.93, and intercepts of 8 to 25 ppb. We attribute the latter, at least in part, to significant noise particularly at low NO x concentrations, resulting from short averaging times during highly dynamic lab burns. Discrepancies between instruments as indicated by the intercepts urge caution with oxides of nitrogen measurements at concentrations <50 ppb for rapidly changing conditions. Implications: Multiple NO x measurement methods were employed to measure NO x concentrations at an EPA NCORE site in Albuquerque, NM, and in smoke produced by the combustion of Southwestern biomass fuels. Agreement shown during intercomparison of these NO x techniques indicated little evidence of significant interfering species biasing the methods in these two environments. Instrument agreement is important to understand for accurately characterizing ambient NO x conditions in a range of environments.

Almond leaf scorch (ALS) is caused by the pathogenic bacterium Xylella fastidiosa and poses a threat to the California almond industry. Almond cultivars are differentially resistant or susceptible to ALS. X. fastidiosa can infect but does not overwinter in resistant cultivars in sufficient numbers to cause symptoms or be detected by polymerase chain reaction. To better understand the biochemical or morphological factors mediating resistance, we extracted and analyzed almond xylem fluid from four almond cultivars differing in ALS susceptibility, including Butte and Carmel cultivars that are field resistant and Peerless and Sonora that are ALS susceptible. Xylem fluid was collected over winter months in 2007 to 2009, as well as July 2008 and April 2009, and analyzed for the following: pH, osmolarity, concentrations of sugars, calcium, magnesium, organic acids, and total phenolics. For most of these analyses, we found no clear differences in xylem fluid from resistant and susceptible almond cultivars. However, during the winter months, resistant cultivars tended to have higher concentrations of total phenolic compounds compared with susceptible cultivars (P = 0.05). In February 2009, Carmel had the highest total phenolic concentration measured, 233 μg/ml of gallic acid equivalents. The lowest phenolic concentrations occurred in April 2009. The cross-sectional areas of xylem vessels in Butte (resistant) and Peerless (susceptible) trees were not significantly different between cultivars.

In broad bean (Vicia faba L.), an apoplastic phloem loader, the sucrose concentration increases up to approximately 2 mM in the leaf apoplast and up to approximately 150 mM in the guard-cell apoplast during the photoperiod. This high concentration in the guard-cell apoplast results from transpiration and is sufficient osmotically to reduce stomatal aperture size by up to 3 microm or approximately 25% of the maximum aperture size. In this paper, we investigated a parallel and required role for high bulk-leaf apoplastic sucrose concentration, which correlates with high photosynthesis rate. An empirically determined combination of lowered light intensity and lowered CO(2) concentration reduced the photosynthesis rate to nominally one-fifth of the control value without a significant change in transpiration. This reduction in photosynthesis caused the sucrose concentration in the leaf apoplast--the immediate source pool for guard cells--to decrease by 70% (to 0.4 mM). In turn, sucrose concentration in the guard-cell apoplast decreased by approximately 80% (to approximately 40 mM). These results complete the required evidence for a non-exclusive, transpiration-linked, photosynthesis-dependent passive mechanism for the modulation of stomatal aperture size. In an ancillary investigation, hexoses in the bulk-leaf apoplast decreased when photosynthesis was lowered, but their concentrations in the guard-cell apoplast of control plants indicated that their osmotic contribution was negligible.