Leaching of Alachlor from Alginate-Encapsulated Controlled-Release Formulations

The mobility of alachlor from alginate-encapsulated controlled-release (CR) formulations was investigated in two contrasting soil profiles. Two CR formulations of alachlor were prepared with the following components (1) base—sodium alginate+kaolin+‘Tween’ 20 (1+10+0·5 by mass) and (2) base+40 g kg⁻¹ linseed oil. These were compared to technical grade alachlor and to a commercial alachlor EC formulation (‘Lasso’ 4EC). All herbicide treatments were labeled with [¹⁴C]alachlor and were applied to duplicate soil columns that were composed of a surface and a subsoil horizon. Each horizon was packed to a depth of 12·5 cm, giving a total column length of 25 cm. The columns were leached with 21 cm (420 ml) to 30 cm (600 ml) of 0·01M calcium chloride for a period of 7 to 10 days. Alachlor leaching from the EC formulations was the same as that from the technical material in both soils: 33% in the Evesboro and 10% in the Conover soil. The CR-Oil formulation leached 4 and 2% of the applied [¹⁴C]alachlor, compared to 12 and 3% for the CR-N formulation for the Evesboro and Conover soils, respectively. The CR-Oil formulation also increased the amount of [¹⁴C]alachlor retained in the soil surface horizon (105–114%), compared to CR-N (39–45%), technical material (14–23%) and EC (12–17%).     

Spatial and temporal distribution of geminiviruses in leafhoppers of the genus cicadulina monitored by conventional and quantitative polymerase chain reaction

ABSTRACT Spatial and temporal distribution of Maize streak virus (MSV, family Geminiviridae, genus Mastrevirus) was monitored in the vector species Cicadulina mbila and the nonvector species C. china? using conventional and real-time quantitative polymerase chain reaction. Sustained feeding on MSV-infected plants showed that virus accumulation reaches a maximum in C. china?, but not in C. mbila. After a 3-day acquisition access feeding period (AAP), MSV was detected in the gut, the hemolymph, and the head of C. mbila, but only in the gut of C. china?. Similarly, Digitaria streak virus (genus Mastrevirus), which is not transmitted by either of the two species, was only detected in the gut. MSV was detected in the hemolymph of C. mbila 3 h after the beginning of the AAP. Although viral DNA progressively decreases in the vector and nonvector species after a 3-day AAP, MSV DNA remained stable in the salivary glands of C. mbila.     

Incidence of competitors and landscape structure as predictors of woodland-dependent birds

Globally, modification of landscapes for agriculture has had a strong influence on the distribution and abundance of biota. In particular, woodland-dependent birds are under threat across agricultural landscapes in Britain, North America and Australia, with their decline and extirpation attributed to the loss and fragmentation of habitat. Other native species have become over-abundant in response to anthropogenic landscape change and have strong interactive effects on avian assemblage structure. In eastern Australia, the hyper-aggressive noisy miner (Manorina melanocephala) often dominates woodlands in agricultural landscapes through interspecific competition, resulting in declines of species richness of woodland-dependent birds. We aimed to determine the relative influence and importance of interspecific competition, in situ habitat structure and landscape structure for woodland-dependent bird species at the landscape level. We recorded species-specific landscape incidence of woodland-dependent birds in 24 agricultural-woodland mosaics (25 km²) in southern Queensland, Australia. We selected extensively cleared landscapes (10–23 % woodland cover) where fragmentation effects are expected to be greatest. We applied generalised linear models and hierarchical partitioning to quantify the relative importance of the landscape-level incidence of the noisy miner, mistletoe abundance, shrub cover, woodland extent, woodland subdivision and land-use intensity for the incidence of 46 species of woodland birds at the landscape-scale. The landscape-level incidence of the noisy miner was the most important explanatory variable across the assemblage. Both in situ habitat structure and landscape structure were of secondary importance to interspecific aggression, although previous research suggests that the increasing incidence of the noisy miner in fragmented agricultural landscapes is itself a consequence of anthropogenic changes to landscape structure. Species’ responses to fragmentation varied from positive to negative, but complex habitat structure had a consistently positive effect, suggesting in situ restoration of degraded habitats could be a conservation priority. Landscape wide conservation of woodland-dependent bird populations in agricultural landscapes may be more effective if direct management of noisy miner populations is employed, given the strong negative influence of this species on the incidence of woodland-dependent birds among landscapes.     

Further Contributions to the Development of a Differential Set of Pea Cultivars (Pisum sativum) to Investigate the Virulence of Isolates of Aphanomyces euteiches

Common root rot (Aphanomyces euteiches Drechs.) has become a very destructive disease in the French pea crops since 1993. For an accurate investigation of the virulence variability among French A. euteiches populations and between French and foreign populations, a new set of differential pea genotypes was developed. Thirty-three American and European pea lines, displaying different levels of resistance, were screened in a growth chamber against two French isolates. Symptoms (disease severity from 0 to 5, evaluating symptom surface on roots and epicotyl) and percentage of top fresh weight (inoculated/uninoculated top fresh weight ratio) were measured. From this screening 12 relatively resistant lines, from various genetic backgrounds, were identified along with a highly susceptible control. This set of 13 genotypes was inoculated under controlled conditions with 14 isolates from France, Sweden, USA, Canada and New Zealand, to investigate genotype–isolate interactions. Root symptoms were rated (disease severity), and a susceptibility/resistance threshold was established at disease severity = 1. Significant quantitative interactions were observed, and five 'resistance patterns' were identified, leading to a set of six pea genotypes: Baccara (susceptible), Capella, MN313, 902131, 552 and PI180693. Fields trials of this set in 1999 and 2000 gave the same resistance rankings than in growth chamber conditions. This set will allow more accurate assessments of the variability in virulence/aggressiveness of A. euteiches isolates from France and foreign countries, and further investigations of the epidemiological and genetic basis of pea–A. euteiches interactions.     

A previously unknown maltose transporter essential for starch degradation in leaves

A previously unknown maltose transporter is essential for the conversion of starch to sucrose in Arabidopsis leaves at night. The transporter was identified by isolating two allelic mutants with high starch levels and very high maltose, an intermediate of starch breakdown. The mutations affect a gene of previously unknown function, MEX1. We show that MEX1is a maltose transporter that is unrelated to other sugar transporters. The severe mex1 phenotype demonstrates that MEX1is the predominant route of carbohydrate export from chloroplasts at night. Homologous genes in plants including rice and potato indicate that maltose export is of widespread significance.     

Pressurized liquid extraction and HPLC quantification of folic Acid in fortified wheat flours

A pressurized liquid extraction (PLE) method using phosphate buffer as solvent was applied for folic acid (FA) extraction from fortified wheat flours and was compared to a standard solid-liquid extraction (SLE) method. Extracted FA was quantified by reverse phase high-performance liquid chromatography (RP-HPLC) hyphenated with a phenyl column and an absorption photometric detector (λ = 280 nm). Detection and quantification limits were 0.12 and 0.4 ng, respectively, corresponding to 0.06 and 0.2 μg g(-1) of analyzed wheat flour. Equivalent FA contents were found by both extraction methods, but a single PLE allowed a total recovery of FA content, whereas at least three successive SLEs were needed to achieve a total recovery of FA. The obtained results indicated that PLE is a rapid and efficient technique for FA extraction from fortified wheat flour.     

Impact of artificial root exudates on the bacterial community structure in bulk soil and maize rhizosphere

Bacterial densities, metabolic signatures and genetic structures were evaluated to measure the impact of soil enrichment of soluble organic carbon on the bacterial community structures. The exudates chosen were detected in natural maize exudates (glucose, fructose, saccharose, citric acid, lactic acid, succinic acid, alanine, serine and glutamic acid) and were used at a rate of 100 μg C g⁻¹ day⁻¹ for 14 days. Moreover two synthetic solutions with distinct carbon/nitrogen ratios (20.5 and 40.1), obtained by varying carboxylic and amino acids concentrations, were compared in order to evaluate the potential role of organic N availability. The in vitro experiment consisted of applying exudate solutions to bulk soil. In the case of the control, only distilled water was added. Both solutions significantly increased bacterial densities and modified the oxidation pattern of Biolog® GN2 plates with no effect of the C/N ratio on these two parameters. Genetic structure, measured by means of ribosomal intergenic spacer analysis (RISA), was also consistently modified by the organic amendments. N availability levels led to distinct genetic structures. In a second experiment, one of the previous exudate solutions (C/N 20.5) was applied to 15-day-old maize plants to determine the structural influence of exudates on the rhizosphere microbial community (in situ experiment). Bacterial densities were significantly increased, but to a lesser extent than had been found in the in vitro experiment. Metabolic potentials and RISA profiles were also significantly modified by the organic enrichment.     

Immobilized-S, microbial biomass-S and soil arylsulfatase activity in the rhizosphere soil of rape and barley as affected by labile substrate C and N additions

Bulk and rhizosphere soil of rape and barley grown in a calcareous soil were pre-incubated for 7 days at 20 °C with Na₂³⁵SO₄ to partially label soil organic S. The soils were then incubated for 7 days more with increasing levels of two C sources as organic acids (succinic and malic acids) and as glucose (from 0 to 640 mg C kg⁻¹ soil) with or without increasing levels of N (from 0 to 15 mg N kg⁻¹ soil) in the form of ammonium nitrate, in order to mimic rhizodeposition inputs into soil. A second incubation experiment with a single highest dose of the used substrates was undertaken and two destructive soil samplings on days 17 and 35 were carried out. Both incubation experiments showed the intensities of S immobilization in the order: barley rhizosphere>rape rhizosphere>bulk soil. Glucose addition generated positive S priming effects in all studied soils after one week of incubation. Significant correlation coefficients were observed between immobilized-S and microbial biomass-S (r=0.95,p<0.001), arylsulfatase activity (ARS) and microbial biomass-S (r=0.65,p<0.05) on day 17 but not on day 35, whereas significant correlation coefficients were found between arylsulfatase activity and immobilized-S at both days 17 (r=0.79,p<0.01) and 35 (r=0.75,p<0.01). A marked decline of biomass-S noted in substrate-amended treatments at day 35 suggests a quick turnover of this compartment followed by its incorporation into the organic S. Finally, with organic acids high values of ARS per unit of biomass-S were recorded over the two studied dates in the rhizosphere soil of rape. It is concluded that the rhizosphere microbial biomass under rape exhibited more efficient arylsulfatase activity and hence greater turnover of organic S than that under the barley rhizosphere soil.