Organic amendments affecting sorption, leaching and dissipation of fungicides in soils

Metalaxyl and tricyclazole are two fungicides widely used in Spain in vineyard and rice crops respectively. In this study an investigation has been made of the effect of three organic amendments [two commercial amendments, solid fertiormont (SF) and liquid fertiormont (LF), and a residue from the olive oil production industry, alperujo (OW)] on fungicide fate in soils. Changes in soil porosity on amendment were studied by mercury intrusion porosimetry, sorption-desorption studies were performed by the batch equilibration method, dissipation of metalaxyl and tricyclazole in the soil was studied at - 33 kPa moisture content and 20 degrees C and leaching was studied in hand-packed soil columns. Amendments with SF and LF reduced soil porosity, while OW increased porosity through an increase in pore volume in the highest range studied. Tricyclazole sorbed to soils to a much higher extent than metalaxyl. With some exceptions, sorption of both fungicides increased on amendment, especially in the case of SF-amended soils, which rendered the highest K(oc) values. In soils amended with the liquid amendment LF, sorption either remained unaffected or decreased, and this decrease was much higher in the case of metalaxyl and a soil with 70% clay. In this clay soil, amendment with OW, of very high soluble organic matter content, also decreased metalaxyl sorption. Tricyclazole is more persistent in soil than metalaxyl, and both fungicides were found to be more persistent in amended soils than in unamended soils. Leaching of metalaxyl and tricyclazole in soil columns was inversely related to sorption capacity. The low recoveries of tricyclazole in leachates and in soil columns when compared with metalaxyl, a less persistent fungicide, were attributed to diffusion into micropores and to increase in sorption with residence time in the soil, both processes favoured by the low mobility of tricyclazole.     

Efficacy and effects on yield of different fungicides for control of wet bubble disease of mushroom caused by the mycoparasite Mycogone perniciosa

Carbendazim, iprodione, prochloraz-Mn, thiabendazole and thiophanate-methyl were tested in vitro and in vivo for their effect on Mycogone perniciosa, the mycoparasite that causes wet bubble disease of white button mushroom. In vitro experiments showed that prochloraz-Mn (ED₅₀ = 0.006–0.064 μg ml⁻¹) and carbendazim (ED₅₀ = 0.031–0.097 μg ml⁻¹) were the most effective fungicides for inhibiting the mycelial growth of M. perniciosa, while iprodione (ED₅₀ = 1.90–3.80 μg ml⁻¹) was the least effective. The resistance factors calculated for the five fungicides were between 1.4 and 2. The results obtained suggest that there is very little risk that M. perniciosa will develop resistance to the fungicides assayed. The in vivo efficacy of fungicides for control of wet bubble was studied in two mushroom cropping experiments, which were artificially infected with two doses of M. perniciosa, 10⁶ and 10⁷ spores m⁻², respectively. There was, in the low dose inoculum experiment, a very high degree of effectiveness (96.5–100.0%) with all the fungicides assayed. However, iprodione performed poorly (20.5–24.4%) compared with the other fungicides (88.7–100.0%) in the high concentration inoculum experiment. The most effective treatments for controlling wet bubble did not improve the biological efficiency of Agaricus bisporus.     

Release of doxycycline through cellulose acetate symmetric and asymmetric membranes produced from recycled agroindustrial residue: Sugarcane bagasse

Cellulose acetate is one of the components employed in drug controlled-release systems in the form of membranes. The aim of this study was to examine the controlled-release of doxycycline employing cellulose acetate symmetric and asymmetric membranes as matrices. The cellulose triacetate was produced from sugarcane bagasse through a homogeneous acetylation reaction, using acetic acid as the solvent, acetic anhydride as the acetylating agent and sulfuric acid as the catalyst. The viscosity average molecular weight of the cellulose acetate produced was 39,000 g mol⁻¹. The symmetric membranes were produced using a system solvent of dichloromethane/ethanol (9:1, v/v) and the asymmetric membranes were produced from the same solvent system and 10% of water. For the formulation of both, 5% of doxycycline was used. The membranes were characterized by thermal analysis (DSC and TGA) and scanning electron microscopy SEM. The release of doxycycline through cellulose triacetate matrices was examined using spectrophotometric analysis in the ultraviolet-visible region, at 275 nm. The results revealed that asymmetric membranes release 80% of the drug in 100 min, while symmetric membranes release 14% of the drug during the same time interval.     

Development of an appropriate breeding scheme for tolerance to Empoasca kraemeri in common bean

Summary Significant advances in increasing tolerance to the leafhopper Empoasca kraemeri Ross & Moore in common bean have been obtained using a new breeding scheme where yield under leafhopper attack is the principal selection criterion in the evaluation of progenies. However, to further refine this breeding scheme, a study was conducted to determine whether selection for nonprotected yield would be more effective in early versus late generations. Two selection strategies were compared. In Strategy I, early generation selections in the F₂ and F₃ were compared to Strategy II where late generation selections were made in the F₄ and F₅, with the F₂ and F₃ generations advanced using single pod descent and bulk practices, respectively. Yield trials of the F₆ lines from both selection strategies were conducted under nonprotected and insecticide protected treatments. No significant differences were detected between the two selection strategies. However, Strategy II did produce advanced lines with greater nonprotected yields than did Strategy I, with the best F₆ line, in three out of four crosses, coming out of Strategy II. Late generation selection is recommended over early generation selection. Results of the new leafhopper breeding scheme, based on yield, are compared to the old breeding scheme where selections were made using visual selection practices in early generations.     

Effect of coupling media on velocity and attenuation of ultrasonic waves in Brazilian wood

Coupling media are necessary to ensure that transducers bond to wood specimens to minimize coupling losses and improve the accuracy of ultrasonic measurements. There are several types of coupling media available, and the optimal choice is not known. In this work, we analyzed the results of ultrasonic wave attenuation for 0.1-MHz longitudinal and transverse transducers with six different materials as coupling media in nine species of Brazilian wood with densities in the range 700–1170 kg/m³. Tests were performed using constant pressure on the transducer and with wave propagation in the longitudinal direction. For transverse transducers, the polarization was in the radial and tangential directions. The results were analyzed statistically and showed that, for attenuation in both longitudinal and transverse waves, the material used for coupling had significant effects, whereas the wood species had no effect. For longitudinal waves, the statistical evaluation showed that the coupling material performance was strongly dependent on the species of wood, but it was not possible to observe any tendency of behavior associated with specific anatomical properties.     

Microsatellite variability in natural populations of the blackspot seabream Pagellus bogaraveo (Brünnick, 1768): a database to access parentage assignment in aquaculture

Eight microsatellite loci previously reported were assessed for their utility in parentage assignment in 96 individuals belonging to natural populations of the blackspot seabream Pagellus bogaraveo (Brünnick, 1768) from the Mediterranean and Northeast Atlantic regions. At the mtDNA level, no differentiation was found between these two regions but based on microsatellite data an overall discrete genetic differentiation is perceivable between the two regions separated by the Strait of Gibraltar. The number of alleles per locus ranged from 8 to 30. A database constructed with allele frequency data from six populations was used in a simulation parentage assignment test using the software cervus . The test showed that the number of markers used is enough to perform parentage assignments with real data. The polymorphic information content for each locus was very high (mean value of 0.849), with a total exclusionary power of 0.9995. In summary, seven of the eight microsatellites analysed proved to be sufficient and powerful tools for parentage assignment in hatcheries and the allele frequency data given here can be used to perform pedigree analysis against which real data may be tested.     

Role of Azospirillum brasilense nitrate reductase in nitrate assimilation by wheat plants

Summary The nitrogen metabolism of wheat plants inoculated with various Azospirillum brasilense strains and nitrate reductase negative (NR^–) mutants was studied in two monoxenic test tube experiments. The spontaneous mutants selected with chlorate under anaerobic conditions with nitrite as terminal electron acceptor fixed N₂ in the presence of 10 mM NO₃ ^– and were stable after the plant passage. One strain (Sp 245) isolated from surface-sterilized wheat roots produced significant increases in plant weight at both NO₃ levels (1 and 10 mM) which were not observed with the NR^– mutants or with the two other strains. Similar effects were observed in a pot experiment with soil on dry weight and total N incorporation but only at the higher N fertilizer level. In the monoxenic test tube experiments plants inoculated with the mutants showed lower nitrogenase activities than NR⁺ strains at the low NO₃ ^– level (1 = mM) but maintained the same level of activity with 10 mM NO₃ ^– where the activity of all NR⁺ strains was completely repressed. The nitrate reductase activity of roots increased with the inoculation of the homologous strains and with the mutants at both NO₃ ^– levels. At the low NO₃ ^– level this also resulted in increased activity in the shoots, but at the high NO₃ ^– level the two homologous strains produced significantly lower nitrate reductase activity in shoots while the mutants more than doubled it. The possible role of the bacterial nitrate reductase in NO₃ ^– assimilation by the wheat plant is discussed.     

Field validation of chlordecone soil sequestration by organic matter addition

Purpose

The use of chlordecone (CLD) has caused pollution of soils, which are now a source of contamination for crops and ecosystems. Because of its long-term impacts on human health, exposure to CLD is a public health concern and contamination of crops by CLD must be limited. To this end, we conducted field trials on chlordecone sequestration in soil with added compost.

Materials and methods

The impact of added compost on chlordecone sequestration was measured in nitisols. After characterization of the soil, the transfer of chlordecone from soil to water was assessed in a leaching experiment and from soil to two crop plants in a nitisol plot. Finally, to understand the underlying processes, changes in CLD content were measured in soil fractions and soil porous properties were assessed after the addition of compost.

Results and discussion

A rapid seven-fold decrease in water extractable CLD was observed in amended soils. Five percent amendment led to a significant reduction in the contamination of crops by CLD; edible radish tubers were 50% more contaminated without added compost and cucumber fruits were 60% more contaminated. After the addition of compost, CLD content increased in the fraction of pre-humified or partially mineralized organic debris. Finally, in contrast to andosols, adding compost to nitisols did not affect the soil microstructure.

Conclusions

Increasing chlordecone sequestration by adding compost could be an alternative solution until soil decontamination techniques become available. This could be a provisional way to control further release of CLD from contaminated soils towards other environmental compartments.