Prem Dureja

Isolation, characterization and antifungal activity of major constituents of the Himalayan lichen Parmelia reticulata Tayl.

Antifungal activity of hexane, ethyl acetate and methanol extracts of Parmelia reticulata was evaluated against soilborne pathogenic fungi, namely, Sclerotium rolfsii, Rhizoctonia solani, R. bataticola, Fusarium udum, Pythium aphanidermatum and P. debaryanum by poisoned food technique. Maximum antifungal activity was exhibited by hexane and ethyl acetate extracts against most of the test pathogens. Secondary metabolites, namely, (±)-isousnic acid, (±)-protolichesterinic acid, atranorin, evernyl, ethyl hematommate, ethyl orsellinate, methyl hematommate (3-formyl-2,4-dihydroxy-6-methylbenzoic acid methyl ester), 2-hydroxy-4-methoxy-3,6-dimethylbenzoic acid, 1-hydroxy-3,6-dimethoxy-8-methyl-xanthen-9-one, baeomycesic acid and salazinic acid, were isolated from the above extracts and identified by 1H NMR, 13C NMR and mass spectroscopic methods. When these metabolites were tested for antifungal activity against test pathogens, maximum antifungal activity was exhibited by (±)-protolichesterinic acid against R. solani (ED50=23.09 μg mL(-1)) and P. debaryanum (ED50=16.07 μg mL(-1)) and by atranorin against S. rolfsii (ED50=39.70 μg mL(-1)). The antifungal activity of protolichesterinic acid was found to be comparable to that of hexaconazole, a commercial fungicide.

Synthesis, antimicrobial evaluation and QSAR analysis of novel nalidixic acid based 1,2,4-triazole derivatives

Novel nalidixic acid based 1,2,4-triazole derivatives were synthesized and characterized using spectral techniques like (1)H NMR, (13)C NMR, IR and mass spectrometry. All these compounds were screened for antimicrobial activity against five bacteria and two pathogenic fungi. Most of these compounds showed better antimicrobial activity than the parent compound, 4-amino-5-mercapto-1,2,4-triazole. Among all the screened compounds, 3-{6-(2-chlorophenyl)-1,2,4-triazolo [3,4-b] [1,3,4]thiadiazol-3-yl}-1-ethyl-7-methyl-1,8-naphthyridin-4(1H)-one (23) was emerged as promising antimicrobial agent (MIC = 16 μg/mL). Quantitative structure activity relationship (QSAR) analysis was carried out using various distance-based topological indices, steric and hydrophobic parameters. Based on the QSAR analysis it is indicative that lipophilic and steric parameters are the pre-requisites for these molecules to act as potent antimicrobial agents.

Schiff bases as potential fungicides and nitrification inhibitors.

A number of substituted Schiff bases were synthesized and characterized by (1)H NMR and mass spectrometry. These compounds were screened for antifungal activity in vitro against pathogenic fungi, namely, Sclerotium rolfsii and Rhizoctonia bataticola, and for their effect on nitrification inhibition under laboratory conditions. Maximum antifungal activity was exhibited by (2,4-dichlorobenzylidene)-(2,4,5-trichlorophenyl)-amine and (3-nitrobenzylidene)-(2,4,5-trichlorophenyl)-amine against both fungi (ED(50) with range from 3 to 24 microg/mL). Maximum nitrification inhibition (NI) was exhibited by (2,4-dichlorobenzylidene)-(2-fluorophenyl)-amine, (4-fluorophenyl)-(3-nitrobenzylidene)-amine, (2,6-dichlorobenzylidene)-(4-fluorophenyl)-amine, and (2,6-dichlorobenzylidene)-(3 fluorophenyl)-amine (NI in the range 91-96%).

INSECTICIDE RESIDUES IN COTTON CROP SOIL

Dimethoate, monocrotophos, triazophos, deltamethrin, cypermethrin and endosulfan were applied to a cotton crop soil located at Nurpur village, Punjab, India. The insecticides were applied sequentially at recommended dosages in cotton fields by foliar application in 1995, 1996 and 1998. Soil samples were collected from the cotton crop farms and extracted with acetone. The extracted material was analysed by a gas liquid chromatograph (GLC) equipped with an 63Ni electron-capture detector (ECD-63Ni). Recovery data was obtained by fortifying soil with insecticide. The average recoveries from the fortified soil samples were 76–92% for organophosphorous compounds and 90 –98% for synthetic pyrethroids and organochlorines. The results showed that the insecticide residues under study were present in the range of 1.16 to 41.97 ng g 1 d.wt.soil. The pattern of dissipation of the insecticides used was similar for the duration of the crop. Half lives of the insecticides ranged from 7 to 22 days. Except endosulfan none of the other insecticides used were leached below 15 cm. Endosulfan was found to be rapidly degraded in the soil and formed a sulfate metabolite. Persistence and dissipation pattern in soils with history of exposure to the insecticide compared to non-history soils were similar.

Photostabilizers for azadirachtin-A (a neem-based pesticide).

Photostability of azadirachtin‐A (a neem based pesticide) has been studied without and with adding stabilizers such as ter. butyl‐p‐cresol, 8‐hydroxy quinoline and ter. butyl hydroquinone as thin film on glass surface and on leaf surface under sunlight and UV light. Half‐life of azadirachtin has been found to be 48 min and 3.98 days as thin film under UV light and sunlight and 2.47 days on leaf surface, respectively. 8‐Hydroxy quinoline and ter. butyl hydroquinone have been found effective in controlling degradation of azadirachtin under both sunlight and UV light with half‐life of 44.42 and 35.90 days under sunlight, and 55.80 and 48.50 h under UV light, respectively. Whereas ter. butyl‐p‐cresol has been found effective A only under sunlight. Significant decreases in antifeedant and insect growth regulatory activity against third instar larvae of Spodoptera litura has been observed with azadirachtin when exposed to sunlight and UV light. However, by the addition of above stabilizers, the biological activity of azadirachtin‐A has been retained even after 24 h of irradiation under UV light and up to 30 days of exposure to sunlight.

Effect of organic amendments on microbial activity in chlorpyrifos contaminated soil.

The aim of this research was to study the inhibitory effect of chlorpyrifos (CPF) on soil microbial activity and to evaluate the efficacy of different organic amendments as a biostimulation agent for sustaining the microbial activity and thereby assisting in the remediation of CPF (10 ppm) contaminated soil. Experiments were carried out under controlled conditions (37 °C) up to 74 days; CPF was analyzed by GC-ECD while dehydrogenase activity (DHA) was measured as one of the indices of soil microbial activity. Throughout the experiment, there was higher microbial activity in uncontaminated soil (S) as compared to CPF contaminated soil (SP) and overall a considerably high reduction (63.51%) in average DHA was noticed in CPF contaminated soil. Organic amendments enhanced the microbial activity over unamended CPF contaminated soil. The trend of DHA on 24th day was MS (SP + 1% Mushroom Spent) >VC (SP + 1% Vermicompost) >BS (SP + 1% Biogas Slurry) >SP (Soil spiked with 10 ppm CPF) >FM (SP + 1% Farmyard Manure). The enhancement in pesticide dissipation over the unamended soil showed the following trend VC (37%)>MS (24%) >FM (1.9%). In spite of sufficient DHA, BS could not enhance pesticide dissipation over the unamended soil (SP). These results indicate the potential of vermicompost and mushroom spent compost as suitable biostimulation agents to sustain the microbial activity in CPF contaminated soil.

Decay profile and metabolic pathways of quinalphos in water, soil and plants

The widespread occurrence of pesticide residues in different agricultural and food commodities has raised concern among the environmentalists and food chemists. In order to keep a proper track of these materials, studies on their decay profiles in the various segments of ecosystem under varying environmental conditions are needed. In view of this, the metabolites of quinalphos in water and soil under controlled conditions and in plants, namely tomato and radish in field conditions have been analysed and possible pathways suggested. In order to follow the decay of the pesticide, an HPLC procedure has been developed. Studies conducted in water at different temperatures, pH and organic content reveal that the persistence of the pesticide decreases with the increase in all the three variables. In the three different types of soils studied, the effect of pH is more or less apparent on a similar line. On an average a faster decay is observed in the case of plants than in water and soil. The decay profiles in all these cases follow first order kinetics. The metabolites were identified by GC-MS. The investigations reflect that degradation occurs through hydrolysis, S-oxidation, dealkylation and thiono-thiol rearrangement. The pathways seem to be complex and different metabolites were observed with the change in the matrix. Quinalphos oxon, O-ethyl-O-quinoxalin-2-yl phosphoric acid, 2-hydroxy quinoxaline and quinoxaline-2-thiol were observed in all the matrices. Results further indicate that the metabolites, 2-hydroxy quinoxaline and oxon, which are more toxic than parent compound, persist for a longer time.

Biocontrol potential of cyanobacterial metabolites against damping off disease caused by Pythium aphanidermatum in solanaceous vegetables

An investigation was undertaken to explore the biocidal efficacy of fungicidal compound(s) produced by Calothrix elenkenii against damping-off disease in three vegetable crops-tomato, chilli and brinjal. Treatments included application of seeds soaked in water (control), culture filtrate and ethyl acetate extract of Calothrix elenkenii and Metalaxyl in potting mix inoculated with Pythium aphanidermatum in plastic pots. The observations taken after a period of four weeks revealed the superiority of seed treatment with ethyl acetate extracts, in terms of percent mortality and plant parameters. ANOVA revealed that the treatments, crops (tomato, chilli and brinjal) and their interactions exerted a significant influence on the parameters analyzed. Chilli recorded the highest percentage of survivors and responded best to the seed treatment with ethyl acetate extract of Calothrix elenkenii. Future work is being undertaken towards formulation of a biocontrol agent using Calothrix elenkenii and understanding the molecular basis for the biocontrol properties.

New photodegradation products of chlorpyrifos and their detection on glass, soil, and leaf surfaces

The organophosphate insecticide chlorpyrifos was irradiated under different photochemical conditions and the products characterized by gas chromatography, mass spectrometry, and NMR spectroscopy. Irradiation of chlorpyrifos in hexane yielded dechlorinated photoproducts and cleavage products. In methanol, besides these products, chlorpyrifos gave oxons. Several new photoproducts, the formation of which apparently occurs by the displacement of 5-chloro by a methoxy substituent in the pyridyl moiety. The possibility of formation of such products on glass, soil, and leaf surfaces under the influence of UV and solar simulated light have also been explored and many new products presumably formed due to simultaneous photo-dechlorination, oxidation and hydrolytic processes were detected. Photodegradation of chlorpyrifos was rapid on a soil surface but comparatively slow on glass and leaf surfaces.

Metabolism of 14C-azoxystrobin in water at different pH

Metabolism of 14C-azoxystrobin was studied in water at pH 4, 7 and 9. The study suggested that volatilization losses of azoxystrobin were very low (3%) during 130 days of incubation. Only 2.5–4.2% of azoxystrobin was mineralised to CO2 and pH of water did not have much effect on rate of mineralisation. The dissipation of azoxystrobin in water of all the three pHs followed first order kinetic with half-life values ranging from 143 to158 d; degradation was the fastest at pH 9. Azoxystrobin acid, a major metabolite, was detected 4–7 day onwards and its concentration increased up to 130 days. The formation of azoxystrobin acid was more and faster under alkaline (pH 9) condition than neutral (pH 7) or acidic (pH 4) conditions.