Effect of temperature and flooding duration on phosphate sorption in an acid sulphate soil from Vietnam

Phosphate sorption in soil is controlled largely by Fe-oxihydroxides, and so important changes in P dynamics are expected when the redox potential is modified. Such changes in P sorption when acid soil is flooded, as for rice cultivation, have been evaluated. Samples from an acid sulphate soil in the Mekong Delta of Vietnam were flooded for up to 56 d at 20°C and 30°C. Some of the samples incubated at 30°C were dried in open air for 30 d after flooding. Small redox potential (Eh<0) and pH>6 were rapidly reached in soil flooded at 30°C; less drastic reducing conditions (Eh ?0.2 V) and pH 4–5 occurred at 20°C. Phosphate sorption increased during flooding. The increase was twofold at 20°C, and 10-fold at 30°C. Phosphate sorption index decreased in the soil that was air dried after flooding at 30°C, but still remained two to three times greater than before flooding. These results were compared to the changes in oxalate-extractable Fe, i.e. poorly crystalline or amorphous Fe-oxihydroxides. The increase of P sorption per unit increase of oxalate-Fe was seven to eight fold larger at 30°C than at 20°C.     

Evaluation of Likelihood of Co-Occurrence of Erwinia amylovora with Mature Fruit of Winter Pear

ABSTRACT Phytosanitary concerns about fire blight prohibit export of U.S.-grown pears to some countries without this disease. To examine these concerns, we evaluated the potential for co-occurrence of Erwinia amylovora with mature, symptomless winter pear fruit by inoculation experiments and by survey of commercial orchards. Immature pear and apple fruit were inoculated in orchards with E. amylovora strain 153N as resuspended lyophilized cells or as ooze from diseased tissues. Regardless of inoculum source, population size of Ea153N on fruit declined by an order of magnitude every 3 to 4 days during the first 2 weeks after inoculation; at 56 days after inoculation, Ea153N was not detected, except on 1 of 450 fruit with 4 colony forming units (CFU). After inoculation of flowers, calyx-end survival of Ea153N on pear and apple fruit declined from high populations at petal fall to a few cells at harvest, with no detection of the pathogen after a 7-week cold storage. Migration of Ea153N into symptomless pear fruit from diseased branches was evaluated by enrichment assay and nested polymerase chain reaction of internal fruit core tissues; these assays failed to detect the pathogen in healthy fruit from diseased trees. At harvest, E. amylovora could not be detected on 5,599 of 5,600 fruit of d'Anjou pear sampled from commercial orchards in major production areas of the Pacific Northwest; one fruit yielded 32 CFU of the pathogen. Postharvest, mature pear fruit contaminated with Ea153N and subsequently wounded required a dose of >10,000 cells at the wound site to allow for persistence of the pathogen through a 7-week-cold storage. We conclude that epiphytic E. amylovora shows similar survival characteristics on both pear and apple fruit, this pathogen is not an endophyte within mature symptomless pear fruit, its presence is exceptionally rare on commercially produced fruit, and that epiphytic survival of E. amylovora through a postharvest chilling period is unlikely given the unrealistically high population size required for persistence.     

Bioavailability of Iron to Pseudomonas fluorescens Strain A506 on Flowers of Pear and Apple

ABSTRACT The addition of 0.1 mM FeCl(3) to a defined culture medium induces the bacterial epiphyte Pseudomonas fluorescens strain A506 (A506) to produce an antibiotic toxic to the fire blight pathogen, Erwinia amylovora. Consequently, because A506 is registered and applied as a commercial product to suppress E. amylovora before floral infection of pear and apple, the relative availability of iron to A506 on surfaces of pear and apple flowers is of potential significance. An 'iron biosensor' construct of A506 was developed by transformation with an iron-regulated promoter (pvd) fused to a promoterless ice nucleation reporter gene (inaZ). This construct, A506 (pvd-inaZ), established high populations on pear and apple flowers, ranging from 10(4) to 10(6) CFU/flower. In seven trials on pear and apple trees, A506 (pvd-inaZ) expressed high ice nucleation activity (INA) on flowers, indicating limited iron bioavailability or a low-iron environment unlikely to induce antibiotic production by A506. A506 (pvd-inaZ) also colonized flowers when mixed with chemicals containing iron: FeSO(4) or the iron chelates ferric ethylenediaminedi-(o-hydroxyphenyl-acetic) acid (FeEDDHA) and ferric diethylenetriamine pentaacetate (FeDTPA). These compounds represent an array of commercial iron formulations applied to foliage to avert iron chlorosis. Treatment of flowers with a mixture of A506 (pvd-inaZ) and 3 mM FeEDDHA or FeDTPA significantly decreased INA compared with flowers treated with A506 (pvd-inaZ) in water. Lower concentrations (0.3 mM) of FeEDDHA, however, did not consistently suppress INA. These results indicate that apple and pear flowers represent an iron-limited environment to A506 and that treatment with 3 mM FeEDDHA is needed to increase significantly the level of iron available to this bacterium.     

Antibiosis Contributes to Biological Control of Fire Blight by Pantoea agglomerans Strain Eh252 in Orchards

ABSTRACT Fire blight, caused by Erwinia amylovora, is the most serious bacterial disease of pear and apple trees. Biological control with strains of Pantoea agglomerans (syn. Erwinia herbicola) may provide an effective disease management strategy for fire blight. Most strains of P. agglomerans evaluated for suppression of fire blight produce compounds that inhibit the growth of E. amylovora in culture. The role of these inhibitory compounds in fire blight suppression in orchard environments has not been studied. In seven field trials in Oregon, we compared the population dynamics and disease suppression with P. agglomerans Eh252, a strain that produces a single antibiotic, with its near-isogenic antibiotic-deficient derivative, strain 10:12. Water or suspensions of Eh252 or 10:12 (1 x 10(8) CFU/ml) were applied at 30 and 70% bloom to pear or apple trees. Aqueous suspensions of freeze-dried cells of E. amylovora (3 x 10(5) CFU/ml) were applied at full bloom. Additional trees were treated with streptomycin or oxytetracycline at 30 and 70% bloom and in some experiments, 1 day after application of the pathogen. Population sizes of Eh252 or 10:12 on pear blossoms were estimated by spreading dilutions of blossom washes on culture media. Average population sizes of Eh252 and 10:12 on blossoms ranged from 10(5) to 10(7) CFU, and in five of six trials, the relative area under the population curve of Eh252 was not significantly different than that of its derivative 10:12. Both Eh252 and 10:12 reduced the growth of the pathogen on blossoms compared with inoculated water-treated controls. Eh252 significantly decreased the incidence of fire blight in six of seven field trials compared with the incidence on water-treated trees, and 10:12 similarly reduced the incidence of fire blight in four of seven trials. In three of seven field trials, trees treated with Eh252 had a significantly lower incidence of fire blight compared with trees treated 3 with 10:12. Overall,3 Eh252 reduced the incidence of fire blight by 55 +/- 8%, 10:12 by 30 +/- 6%, streptomycin by 75 +/- 4%, and oxytetracycline by 16 +/- 14%. The effectiveness of strain 10:12 compared with water treatment indicates that other mechanisms (e.g., competitive exclusion or habitat modification) also contribute to disease suppression by P. agglomerans. The increased suppression of fire blight by the parental strain Eh252 compared with the antibiotic-deficient mutant 10:12 indicates that antibiosis is an important mechanism of biological control of fire blight.     

Automated mercury determination in waters

A rapid technique for dissolved Hg determination in water at ultra-trace level is described. It consists of the automatisation of the cold-vapor/gold amalgamation/atomic fluorescence technique, which allows the determination of 8 samples per hour with an analytical precision of 5 % and a 0.1 ng.l^?1 detection limit for a 45 ml sample. It is suitable for Hg determination in most of the natural waters.     

Antibiosis activity of Pantoea agglomerans biocontrol strain E325 against Erwinia amylovora on apple flower stigmas

Pantoea agglomerans E325, the active ingredient in a commercial product for fire blight control, was previously shown in vitro to produce a unique alkaline- and phosphate-sensitive antibiotic specific to Erwinia amylovora. Antibiosis was evaluated as a mode of antagonism on flower stigmas using two antibiosis-deficient mutants. On King's medium B, mutants E325ad1 and E325ad2 have stable smooth-butyrous or hypermucoid colony morphologies, respectively, and the parental strain E325 exhibits phenotypic plasticity with predominantly hypermucoid colonies accompanied by slower-growing, smooth-butyrous colonies. Mutants were tested against E. amylovora on stigmas of detached flowers of crab apple (Malus mandshurica) in growth chambers and apple (Malus domestica) in the orchard. Epiphytic fitness of the antibiosis-negative mutants was similar or greater than the parental strain as determined by relative area under the population curve (RAUPC). In laboratory and orchard trials, both mutants had significantly lower inhibitory activity against the pathogen (i.e., less reduction of E. amylovora RAUPC) compared with the parental strain. E325 and the mutants caused similar decreases in pH in a broth medium, indicating that acidification, which was previously reported as a possible mechanism of pathogen inhibition on stigmas, is not directly related to antibiosis. In this study we provide the first evidence for E325 antibiosis involved in E. amylovora growth suppression on apple flower stigmas.     

Phosphorus sorption in soils of the Mekong Delta (Vietnam) as described by the binary Langmuir equation

Phosphate adsorption isotherms were determined for 20, mostly very acidic, soils from the Mekong Delta. The experimental data were well described by a binary Langmuir equation which considers two groups of sorption sites that differ in their P bonding energies. The maximum P-sorption capacities of these sites were related to the soil properties by simple linear correlation and by stepwise multiple regression. Results suggest that high energy sites are on Al-oxihydroxides or small Al-substituted Fe-oxides and, to a lesser extent, on poorly ordered Fe-oxihydroxides. On the other hand, the P-sorption capacity of low energy sites is mainly related to clay content, and it increases as pH decreases. These sites are also positively correlated with organic carbon and poorly crystalline Fe-oxihydroxides. However, as these two variables are closely correlated with each other, organic matter is likely to be considered as an indirect factor of P fixation through its association with Fe-oxihydroxides and not as an important source of P-sorption sites. The maximum sorption capacity, i.e. the sum of sorption capacities of the two groups of sites, is well described (r²= 0.88) by an equation that takes into account the four variables identified above: Al-bearing oxihydroxides, poorly ordered Fe-oxihydroxides, clay content and pH. Grouping the soils according to the orders of Soil Taxonomy, the P-sorption capacity increases in the following sequence: ultisols < entisols < inceptisols. A P concentration often considered adequate for plant nutrition is 0.2 mg P 1^?1 solution, and only the high energy sites are involved in sorption at that concentration. Thus an equation including only Al- and Fe-oxihydroxides could be used to fix P norms in these soils.     

Evaluation of phenotypic markers in full genome sequences of avian influenza isolates from California

We evaluated phenotypic markers in full-genome sequences of avian influenza isolates to identify avian strains with increased potential for transmission and pathogenicity in mammals. Of 149 markers examined, 67 were positive in the consensus sequences from 206 avian isolates. Analysis of deep sequencing data in a subset of 24 isolates revealed that 344 subpopulations occurred at marker positions. Markers in subpopulations were significantly more likely to be negative (258/344) than positive (86/344), but nearly all of the marker-positive subpopulations (78/86) were associated with marker-negative consensus sequences. Our analysis revealed significant variation in important markers among avian isolates, and showed that consensus sequences do not fully convey an isolate's potential for increased transmissibility and pathogenicity in mammals.     

Insect nicotinic acetylcholine receptor agonists as flea adulticides in small animals

Vo, D. T., Hsu, W. H., Abu‐Basha, E. A., Martin, R. J. Insect nicotinic acetylcholine receptor agonists as flea adulticides in small animals. J. vet. Pharmacol. Therap. doi: 10.1111/j.1365‐2885.2010.01160.x. Fleas are significant ectoparasites of small animals. They can be a severe irritant to animals and serve as a vector for a number of infectious diseases. In this article, we discuss the pharmacological characteristics of four insect nicotinic acetylcholine receptor (nAChR) agonists used as flea adulticides in dogs and cats, which include three neonicotinoids (imidacloprid, nitenpyram, and dinotefuran) and a macrocyclic lactone (spinosad). Insect nAChR agonists are one of the most important classes of insecticides, which are used to control sucking insects on both plants and animals. These novel compounds provide a new approach for practitioners to safely and effectively eliminate adult fleas.