Phosphorus fertilization for rice and control of environmental pollution problems.

Aim of this study to review information on various aspects of P fertilization in rice i.e., P nutrition of rice, P response of rice plant, P availability in rice soils and P adsorption in rice soils for better understanding of P fertilization in rice culture. A substantial portion of the applied P along with the soil P is lost from rice fields to water bodies causing environmental pollution problems through eutrophication. These pollution problems can be minimized by using proper source of P as fertilizer, proper timing and methods of P fertilizer application, soil P management, transport management, use of plant growth promoting microorganisms which helps in efficient use of P by crops and use of green manure crops which improves soil fertility as well as helps in efficient use of P by crops.

Biodegradation of endosulfan by a soil bacterium.

A bacterium capable of metabolizing endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepine3-oxide) was isolated from cotton-growing soil and effectively shown to degrade endosulfan into endosulfan sulfate. The bacterium degraded 50% of the compound within 3 days of incubation. Endosulfan sulfate was the only terminal product and no other metabolites were formed during the incubation. Endosulfan and its metabolites were analyzed by gas chromatography. The metabolites formed indicated that the organism follows an oxidative pathway for metabolism of this pesticide. Therefore, the present study, microbial degradation of endosulfan by a soil bacterium, may provide a basis for the development of bioremediation strategies to remediate the pollutants in the environment.

The fate of endosulfan in water.

Although the use of endosulfan to control cotton pests has declined, this insecticide still has widespread application in agriculture and can contaminate riverine systems as runoff from soil or by aerial deposition. The degradation of endosulfan in pure water at different pH values of 5, 7 and 9 and in river water from the Namoi and the Hawkesbury rivers of New South Wales (NSW), Australia, was studied in the laboratory. Endosulfan transformation into endosulfan sulfate in river water using artificial mesocosms was also investigated. The results show endosulfan is stable at pH 5, with increasing rates of disappearance at pH 7 and pH 9 by chemical hydrolysis. Incubation of endosulfan with river water at pH 8.3 resulted in the disappearance of endosulfan and the formation of endosulfan diol due to the alkaline pH as well as formation of endosulfan sulfate. Although the degradation of endosulfan by Anabaena, a blue-green alga, did not result in the transformation of endosulfan to endosulfan sulfate, we conclude that other microorganisms catalyzed the formation of the sulfate. Significant conversions of endosulfan into endosulfan sulfate were also reported from associated field studies using artificial mesocoms containing irrigation water from rivers inhabitated by micro-macro fauna. From these results, we conclude that the presence of endosulfan sulfate in river water cannot be used to distinguish contamination by runoff from soil from contamination by aerial drift or redeposition.

Environmental monitoring of pesticides by immunoanalytical techniques: validation, current status, and future perspectives.

Reliable monitoring technology is an essential component of effective regulation and risk management of environmental contaminants such as pesticides. Most environmental monitoring and analysis is currently conducted using instrumental techniques such as gas-liquid chromatography (GLC) and liquid chromatography (LC). Immunoanalysis provides powerful monitoring techniques that have emerged in the last 3 decades. This paper shows they can deliver rapid, accurate, and relatively inexpensive analysis with high throughput and that have the capability to be field oriented. The technique is versatile in application and can be formatted to suit different purposes such as quantitative analysis or simple "yes/no" tests that are field-portable. While there is a range of opinion on the merits of immunoassays as an analytical tool for pesticides, we suggest that this technology is best considered as complementary to GLC and LC, extending the range of capability for field monitoring. Supporting this view, an increasing number of successful applications of immunoassays to monitoring have been reported in recent years. We also report here the implications of recent developments in the field of immunodiagnostics and their application to monitoring of environmental contaminants. We emphasise that, together with adequate validation by instrumental techniques, immunoassays provide monitoring services yielding realistic and comprehensive data for risk management, allowing decisions on appropriate action by various authorities to be made.

Stability of chlorpyrifos for termiticidal control in six Australian soils.

Chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate] is the most widely used soil-applied termiticide in Australia. It is relatively stable, has low water solubility, is absorbed by organic matter, and has a high affinity for soil with low partitioning potential from soil matter to soil water. The purpose of this degradation study is to determine the effect of soil alkalinity on the longevity of termite protection when chlorpyrifos is applied as a termiticide in a range of Australian soils, particularly high-pH substrates. The study also examines the effects of initial soil concentration on the degradation of chlorpyrifos in the range of soils. At an initial soil concentration of 1000 mg kg(-)(1) for termite control, the degradation rate of chlorpyrifos is very strongly retarded in soils tested when compared with lower soil concentrations of 100 and 10 mg kg(-)(1) in the same soils. The degradation data correlated with a logarithmic model of decay, and it was thus possible to produce half-lives and predict likely periods of termite control. Average half-lives for all soils for the three concentrations were 385, 155, and 41 days, respectively. Soil pH had no effect on the rate of degradation at all concentrations tested.

Off-site movement of endosulfan from irrigated cotton in New South Wales.

The fate and transport of endosulfan (6,7,8,9,10,10-hexachloro-1,5, 5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin 3-oxide) applied to cotton (Gossypium hirsutum L.) fields were studied throughout three consecutive years on two selected locations in New South Wales (Australia). Rates of dissipation from foliage and soil, volatilization from the field, and transport of residues in irrigation and/or storm runoff waters were measured in order to estimate a total field balance. Dissipation of endosulfan from both foliage and soil is best explained by a two-phase process rather than by a first-order decay. Half-lives of total endosulfan toxic residues (alpha- and beta-endosulfan and the sulfate product) in the first phase were 1.6 d in foliage and 7.1 d in soil, and could be explained by the rapid volatilization of the parent isomers in the first 5 d (up to 70% of endosulfan volatilizes). In the second phase, half-lives were 9.5 d in foliage and 82 d in soil, mostly due to the persistence of the sulfate product. Concentration of endosulfan residues in runoff water varied from 45 to 2.5 microg L(-1) depending on the residue levels present on field soil at the time of the irrigation or storm events. These in turn are related to the total amounts applied, the cotton canopy cover at application, and the time since last spraying. Most of the endosulfan in runoff was found in the water phase (80%), suggesting it was bound to colloidal matter. Total endosulfan residues in runoff for a whole season accounted for no more than 2% of the pesticide applied on-field.

Simulating endosulfan transport in runoff from cotton fields in Australia with the GLEAMS model.

Endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9methano-2,4,3-benzodioxathiepin 3-oxide), a pesticide that is highly toxic to aquatic organisms, is widely used in the cotton (Gossypium hirsutum L.) industry in Australia and is a risk to the downstream riverine environment. We used the GLEAMS model to evaluate the effectiveness of a range of management scenarios aimed at minimizing endosulfan transport in runoff at the field scale. The field management scenarios simulated were (i) Conventional, bare soil at the beginning of the cotton season and seven irrigations per season; (ii) Improved Irrigation, irrigation amounts reduced and frequency increased to reduce runoff from excess irrigation; (iii) Dryland, no irrigation; (iv) Stubble Retained, increased soil cover created by retaining residue from the previous crop or a specially planted winter cover crop; and (v) Reduced Sprays, a fewer number of sprays. Stubble Retained was the most effective scenario for minimizing endosulfan transport because infiltration was increased and erosion reduced, and the stubble intercepted and neutralized a proportion of the applied endosulfan. Reducing excess irrigation reduced annual export rates by 80 to 90%, but transport in larger storm events was still high. Reducing the number of pesticide applications only reduced transport when three or fewer sprays were applied. We conclude that endosulfan transport from cotton farms can be minimized with a combination of field management practices that reduce excess irrigation and concentration of pesticide on the soil at any point in time; however, discharges, probably with endosulfan concentrations exceeding guideline values, will still occur in storm events.

Mutants with enhanced nitrogenase activity in hydroponic Azospirillum brasilense-wheat associations.

The effect of a mutation affecting flocculation, differentiation into cyst-like forms, and root colonization on nitrogenase expression by Azospirillum brasilense is described. The gene flcA of strain Sp7 restored these phenotypes in spontaneous mutants of both strains Sp7 and Sp245. Employing both constitutive pLA-lacZ and nifH-lacZ reporter fusions expressed in situ, the colony morphology, colonization pattern, and potential for nitrogenase activity of spontaneous mutants and flcA Tn5-induced mutants were established. The results of this study show that the ability of Sp7 and Sp245 mutant strains to remain in a vegetative form improved their ability to express nitrogenase activity in association with wheat in a hydroponic system. Restoring the cyst formation and colonization pattern to the spontaneous mutant Sp7-S reduced nitrogenase activity rates in association with plants to that of the wild-type Sp7. Although Tn5-induced flcA mutants showed higher potentials for nitrogenase expression than Sp7, their potentials were lower than that of Sp7-S, indicating that other factors in this strain contribute to its exceptional nitrogenase activity rates on plants. The lack of lateral flagella is not one of these factors, as Sp7-PM23, a spontaneous mutant impaired in swarming and lateral-flagellum production but not in flocculation, showed wild-type nitrogenase activity and expression. The results also suggest factors of importance in evolving an effective symbiosis between Azospirillum and wheat, such as increasing the availability of microaerobic niches along the root, increased supply of carbon sources by the plant, and the retention of the bacterial cells in vegetative form for faster metabolism.

Development of a compound-specific ELISA for flufenoxuron and an improved class-specific assay for benzoylphenylurea insect growth regulators.

This study describes immunochemical approaches for the compound-specific detection of flufenoxuron and class-specific detection of benzoylphenylurea (BPU) insecticides. With the aim of developing a highly specific immunoassay for flufenoxuron, a hapten was synthesized by introducing a spacer arm at the 2,6-difluoro substituent aromatic ring of a flufenoxuron derivative. An IC(50) value of 2.4 ppb was obtained for flufenoxuron, with detection of the other four BPUs being more than 4000-fold less sensitive. For the development of class-specific ELISA for five BPUs, a new approach was used for the hapten preparation in which a butanoic acid linkage was introduced into the 3,5-dichloro-substituted aniline ring of chlorfluazuron analogue. Although the resultant ELISA still exhibited slightly differing cross-reactions for these five BPUs, this method had broader specificity than the previously reported polyclonal antibody-based ELISA. Spike and recovery studies for five BPUs in soil and water indicated that both the compound- and class-specific ELISAs were able to quantitatively detect BPU residues in soil and water. This study also provided additional insights into the influence of the immunizing hapten structure on the specificities of the antibodies obtained.

Sorption and desorption kinetics of diuron, fluometuron, prometryn and pyrithiobac sodium in soils.

The sorption and desorption characteristics of four herbicides (diuron, fluometuron, prometryn and pyrithiobac-sodium) in three different cotton growing soils of Australia was investigated. Kinetics and equilibrium sorption and desorption isotherms were determined using the batch equilibrium technique. Sorption was rapid (> 80% in 2 h) and sorption equilibrium was achieved within a short period of time (ca 4 h) for all herbicides. Sorption isotherms of the four herbicides were described by Freundlich equation with an r2 value > 0.98. The herbicide sorption as measured by the distribution coefficient (Kd) values ranged from 3.24 to 5.71 L/kg for diuron, 0.44 to 1.13 L/kg for fluometuron, 1.78 to 6.04 L/kg for prometryn and 0.22 to 0.59 L/kg for pyrithiobac-sodium. Sorption of herbicides was higher in the Moree soil than in Narrabri and Wee Waa soils. When the Kd values were normalised to organic carbon content of the soils (Koc), it suggested that the affinity of the herbicides to the organic carbon increased in the order: pyrithiobac-sodium < fluometuron < prometryn < or = diuron. The desorption isotherms were also adequately described by the Freundlich equation. For desorption, all herbicides exhibited hysteresis and the hysteresis was stronger for highly sorbed herbicides (diuron and prometryn) than the weakly sorbed herbicides (fluometuron and pyrithiobac-sodium). Hysteresis was also quantified as the percentage of sorbed herbicides which is not released during the desorption step (omega = [nad/nde - 1] x 100). Soil type and initial concentration had significant effect on omega. The effect of sorption and desorption properties of these four herbicides on the off-site transport to contaminate surface and groundwater are also discussed in this paper.

A transcriptional regulator of the LuxR-UhpA family, FlcA, controls flocculation and wheat root surface colonization by Azospirillum brasilense Sp7.

Genetic complementation of a spontaneous mutant, impaired in flocculation, Congo red binding, and colonization of root surface, led to the identification of a new regulatory gene in Azospirillum brasilense Sp7, designated flcA. The deduced amino acid sequence of flcA shared high similarity with a family of transcriptional activators of the LuxR-UphA family. The most significant match was with the AgmR protein, an activator for glycerol metabolism in Pseudomonas aeruginosa. Derivatives of Sp7 resulting from site-directed Tn5 mutagenesis in the flcA coding sequence were constructed by marker exchange. Characterization of the resulting mutant strains showed that flcA controls the production of capsular polysaccharides, the flocculation process in culture, and the colonization of the root surface of wheat. This study provides new information on the genetic control of the mechanism of plant root colonization by Azospirillum.

Biodegradation and plant protection from the herbicide 2,4-D by plant-microbial associations in cotton production systems.

A significant "biosafening" protection of plants from the effect of 2,4-D in plant-microbial associations has been demonstrated in this study. The 2,4-D-degrading plasmid, pJP4 was transferred into Rhizobium sp. CB1024, which nodulates Dolichos lablab, and Azospirillum brasilense Sp7 carrying a nifA-lacZ gene marker, which can colonize cotton roots. Both transconjugants degraded 2,4-D in pure culture via cometabolism up to 50 microg mL(-1). When the transconjugants were inoculated onto Dolichos lablab and cotton, respectively, such plants were resistant to this herbicide when the nutrient solution was treated with 2,4-D up to 10 microg mL(-1) for Dolichos lablab and 0.5 microg mL(-1) for cotton. Plants inoculated with wild-type strains were dead (Dolichos lablab) or dying (cotton). Because cotton is more sensitive to herbicides, only incomplete protection of plants was achieved with the transconjugant. Improving the effect of colonization of Azospirillum on cotton roots may be critical for a complete degradation and plant protection. The transconjugant of Rhizobium sp. CB1024 was still able to nodulate Dolichos lablab, N(2)-fixing activity was only slightly affected. Other pesticide-degrading capacities may also be inserted into those plant-associated bacterial strains for the degradation of these chemicals by plant-microbial associations. Whether such systems will be successful when applied in the field with competition from other bacteria is being examined. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 513-519, 1997.

A mutant of Azospirillum brasilense Sp7 impaired in flocculation with a modified colonization pattern and superior nitrogen fixation in association with wheat.

We report here significant phenotypic and genetic differences between Azospirillum brasilense Sp7 and spontaneous mutant Sp7-S and their related properties in association with wheat. In contrast to the wild-type strain of Sp7, colonies of Sp7-S stained weakly with Congo red when grown on agar media containing the dye and did not flocculate in the presence of fructose and nitrate. Scanning and transmission electron micrographs showed clearly that the Sp7-S strain lacked surface materials present as a thick layer on the surface of the wild-type Sp7 strain. Different patterns of colonization on wheat roots between Sp7 and Sp7-S, revealed by in situ studies using nifA-lacZ as a reporter gene, were related to a large increase in nitrogenase activity (acetylene reduction) with Sp7-S in association with normal and 2,4-dichlorophenoxyacetic acid-treated wheat for assays conducted under conditions in which the nitrogenase activity of free-living Azospirillum organisms was inhibited by an excess of oxygen. Randomly amplified polymorphic DNA analysis indicated the close genetic relationship of Sp7-S to several other sources of Sp7, by comparison to other recognized strains of A. brasilense. Genetic complementation of Sp7-S was achieved with a 9.4-kb fragment of DNA cloned from wild-type Sp7, restoring Congo red staining and flocculation.

Nitrogenase activity in wheat seedlings bearing para-nodules induced by 2,4-dichlorophenoxyacetic acid (2,4-D) and inoculated with Azospirillum.

Nitrogenase activity (C2H2 reduction) was demonstrated in seedlings of wheat roots bearing para-nodules induced by 2,4-dichlorophenoxyacetic acid (2,4-D) and inoculated with Azospirillum brasilense. Increased nitrogenase activity was observed in inoculated para-nodulated seedlings as compared to inoculated roots not treated by 2,4-D under the conditions of assay used. 2,4-D had no stimulating effect on plant ethylene production in the absence of acetylene. When inoculation was performed with a Nif-mutant of A. brasilense, no ethylene production was detected. It was also shown that the energy source required for nitrogenase activity was supplied by the host plant.

Regional distribution and pH sensitivity ofAzospirillum associated with wheat roots in Eastern Australia.

In a survey ofAzospirillum spp. on the roots and associated soil of wheat grown in eastern Australia, azospirilla were isolated from approximately 40% of samples from areas of soil pH between 5.0 and 6.6. However, azospirilla isolates were rare in soil between pH 4.5 and 5.0 and absent below pH 4.5. Of 25 independent isolates, 17 wereA. brasiliense and eight wereA. lipoferum. No selection forA. brasiliense Nir(-) strains by wheat roots was observed. Only one of six endorhizosphere isolates wereA. brasiliense Nir(-), compared with three of nine from unsterilized roots plus associated soil, and three of eight from soil. With a medium buffered with 0.05 M malate and 0.05 M phosphate, it was found that allAzospirillum isolates had a lower minimum pH for growth when supplied with fixed nitrogen than when grown under nitrogen-fixing conditions. Strains isolated from soils had a minimum pH for growth that was less than the pH of the soil from which they were isolated. However, a significant proportion of strains isolated from roots had a minimum pH for growth that was higher than the pH of the associated soil suggesting that the wheat roots provided an ecological niche protecting against soil acidity.

Preparation of monospecific antiserum to lupin nodule glutamate dehydrogenase.

Immunization of rabbit, using biochemically homogeneous glutamate dehydrogenase, proved to be unsuitable to produce monospecific antiserum. The presence of traces of contaminating immunogen (undetected by physiochemical methods) induced the production of other antibodies. Procedures for rigorously establishing monospecificity of antisera and a technique for preparation of monospecific antiserum, using immunologically impure antigens, are described.

Nitrate reductase from bacteroides of Rhizobium japonicum: enzyme characteristics and possible interaction with nitrogen fixation.

The soluble nitrate reductase of Rhizobium japonicum bacteroids has been purified and its properties compared to those of aerobically grown cells. The enzymes from both sources are similar with molecular weights of about 70 000 suggesting no close relationship with the molybdo-protein component of nitrogenase. Nitrite, the product of nitrate reductase, strongly inhibited the nitrogenase activity from bacteroids, at concentrations less than 100 muM. Thus, an interference in the rate of nitrogen fixation is possible as a result of nitrate reductase activity. A study of the distribution of nitrate reductase in bacteroids indicates that a proportion of the total activity is membrane-bound but that this activity is similar to that in the soluble fraction. Purified nitrate reductase required reduced viologen dyes for activity. Neither NADPH or NADH or FAD could substitute as electron donors. Dithionite is a strong inhibitor and inactivated nitrate reductase from all sources examined. This inactivation is prevented by methyl viologen. Purified nitrate reductase from bacteroids and bacteria Rhizobium japonicum is practically unaffected by exposure to oxygen.