Suresh Walia

Comparing impacts of plant extracts and pure allelochemicals and implications for pest control

Many plant extracts or allelochemicals show a broad spectrum of activity against pests and such products have long been touted as attractive alternatives to synthetic chemical pesticides for pest management because they pose little threat to the environment or to human health. The studies available suggest that plant-based materials do affect arthropod pests, vectors and other pathogens, yet only a handful of botanicals are currently used in agriculture in the industrialized world, and there are few prospects for commercial development of new botanical products. Secondary allelochemicals from plants are usually commercialized as single, concentrated compounds, despite research showing that compound mixtures reduce pest resistance better than single compounds. Several factors appear to limit the success of botanicals, most notably regulatory barriers and the availability of competing products of microbial origin and fermentation products that are costeffective and relatively safe compared with their predecessors. In the context of agricultural pest management, botanical pesticides are best suited for use in organic food production in industrialized countries but can play a much greater role in the production and post-harvest protection of food in developing countries. It is in developing countries that are rich in endemic plant biodiversity where these pesticides may ultimately have their greatest impact in future integrated pest management (IPM) programmes, given their safety to non-target organisms and the environment. However, there is a need to organize natural sources, develop quality control, adopt standardization strategies and modify regulatory mechanisms.

Development of controlled release formulations of imidacloprid employing novel nano-ranged amphiphilic polymers

Amphiphilic copolymers, synthesized from poly (ethylene glycols) and various aliphatic diacids, which self assemble into nano-micellar aggregates in aqueous media, were used to develop controlled release (CR) formulations of imidacloprid [1-(6 chloro-3-pyridinyl methyl)-N- nitro imidazolidin-2- ylideneamine] using encapsulation technique. High solubilisation power and low critical micelle concentration (CMC) of these amphiphilic polymers may increase the efficacy of formulations. Formulations were characterised by Infrared (IR) spectroscopy, Dynamic Light Scattering (DLS) and Transmission Electron Microscope (TEM). Encapsulation efficiency, loading capacity and stability after accelerated storage test of the developed formulations were checked. The kinetics of imidacloprid release in water from the different formulations was studied. Release from the commercial formulation was faster than the CR formulations. The diffusion exponent (n value) of imidacloprid, in water ranged from 0.22 to 0.37 in the tested formulations. While the time taken for release of 50 % of imidacloprid ranged from 2.32 to 9.31 days for the CR formulations. The developed CR formulations can be used for efficient pest management in different crops.

Isolation, characterization and insect growth inhibitory activity of major turmeric constituents and their derivatives against Schistocerca gregaria (Forsk) and Dysdercus koenigii (Walk)

Curcuminoids, the major colouring constituents of Curcuma longa (turmeric) rhizome powder, comprise mainly three closely related curcumins (I, II and III). A simple method has been devised for their efficient extraction and separation. Their structures have been confirmed by 1H NMR spectroscopy and unique mass fragmentation pattern. Curcumin-I, the major constituent has been converted to five alkyl ether derivatives, which have been tested along with the parent compounds and other extractives for insect growth inhibitory activity against Schistocerca gregaria and Dysdercus koenigii nymphs. At 20 µg per nymph, benzene extract and dibutyl curcumin-I were the most active (60% inhibition) against S gregaria, whereas at 50 µg per nymph these substances exhibited moderate growth-inhibitory activity (45%) against D koenigii nymphs. At these concentrations, turmeric oil caused 50–60% nymphal mortality in both test insects. The insect control activity of most of the turmeric products was comparable to or better than that of a commercial neem formulation. © 2000 Society of Chemical Industry

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.

Cadinene sesquiterpenes from Eupatorium adenophorum and their antifungal activity

Bioactive constituents of Eupatorium adenophorum were investigated for antifungal activity. A structure-antifungal activity relationship of cadinene sesquiterpenes was predicted by evaluating individual derivatives. Cadinene derivatives were extracted from leaves of Eupatorium adenophorum using ethyl acetate. Five cadinene sesquiterpenes were isolated by column chromatography and Preparative Thin Layer Chromatography. Bioactivity of these cadinene sesquiterpenes were evaluated in vitro against four phytopathogenic fungi using poison food technique. Purified sesquiterpenes were spectroscopically elucidated as cadinan-3-ene-2,7-dione (1), 7-hydroxycadinan-3-ene-2-one (2), 5,6-dihydroxycadinan-3-ene-2,7-dione (3), cadinan-3,6-diene-2,7-dione (4) and 2-acetyl-cadinan-3,6-diene-7-one (5). Antifungal evaluation of these compounds against pathogenic fungi was found to be selective. Compound 1 was highly inhibitory towards S. rolfsii (ED50 181.60 ± 0.58 μgmL−1) and R. solani (ED50 189.74 ± 1.03 μgmL−1). Availability of plant material and significant antifungal activity makes the plant a potential source of antifungal agent and that can be exploited for the development of a natural fungicide.

Release kinetics of controlled release formulations of thiamethoxam employing nano-ranged amphiphilic PEG and diacid based block polymers in soil

Amphiphilic copolymers, synthesized from poly(ethylene glycols) and various aliphatic and aromatic diacids, which self-assemble into nanomicellar aggregates in aqueous media, were used to develop controlled release (CR) formulations of thiamethoxam (3-(2-chloro-1,3-thiazol-5-ylmethyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene(nitro)amine) using encapsulation technique Formulations were characterised by Infrared (IR) spectroscopy, Dynamic Light Scattering (DLS) and Transmission Electron Microscope (TEM). Encapsulation efficiency, loading capacity and stability after accelerated storage test of the developed formulations were checked. The kinetics of thiamethoxam, released in sandy loam soil from the different formulations was studied. Release from the commercial formulation was faster than the CR formulations. The time taken for release of 50 % of thiamethoxam ranged from 3.56 to 6.07 days for the CR formulations. Although the diffusion exponent (n value) of thiamethoxam in soil ranged from 0.532 to 0.881 in the tested formulations showing non-Fickian transport. These CR formulations may be used in safer, effective and economic crop protection.

Structure–biological activity relationships in triterpenic saponins: the relative activity of protobassic acid and its derivatives against plant pathogenic fungi

BACKGROUND Triterpenic saponins from Sapindus mukorossi Gaertn. and Diploknema butyracea JF Gmelin were evaluated for in vitro antifungal activity against four phytopathogenic fungi. The study of the structure-antifungal activity relationships of protobassic acid saponins was widened by including semi-synthetic derivatives. RESULTS Diploknema butyracea saponins exhibited significant antifungal activity against three fungi (ED(50) 230-455 microg mL(-1)), whereas S. mukorossi saponin was effective against two fungi (ED(50) 181-407 microg mL(-1)). The n-butanol extract after preparative HPLC separation provided two saponins from D. butyracea saponin mixture: 3-O-[beta-D-glucopyarnosyl-beta-D-glucopyranosyl]-16-alpha-hydroxyprotobassic acid-28-O-[arabinopyranosyl-glucopyranosyl-xylopyranosyl]-arabinopyranoside (MI-I), and 3-O-beta-D-glucopyranosyl-glucopyranosyl-glucopyranosyl-16-alpha-hydroxyprotobassic acid-28-O-[arabinopyranosyl-xylopyranosyl-arabinopyranosyl]-apiofuranoside (MI-III). The single saponin extracted from S. mukorossi saponin mixture was identified as 3-O-[O-acetyl-beta-D-xylopyranosyl-beta-D-arabinopyranosyl-beta-D-rhamnopyranosyl] hederagenin-28-O[beta-D-glucopyranosyl-beta-D-glucopyranosyl-beta-D-rhamnopyranosyl] ester (SM-I). Monodesmosides resulting from the partial degradation of hederagenin and hydroxyprotobassic acid bisdesmosides exhibited significant reduction in antifungal effect. Further removal of sugar moiety yielded complete loss in activity. The antifungal activity of the triterpenic saponins was associated with their aglycone moieties, and esterification of the hydroxyl group led to change in antifungal activity. CONCLUSION Sapindus mukorossi saponin, which is effective against Rhizoctonia bataticola (Taub.) Briton Jones and Sclerotium rolfsii Sacc., can be exploited for the development of a natural fungicide. A sugar moiety is a prerequisite for the antifungal activity of triterpenic saponin.

Screening for feeding deterrent and insect growth regulatory activity of triterpenic saponins from Diploknema butyracea and Sapindus mukorossi.

Antifeeding and insect growth regulatory effects of saponins and its hydrolyzed products from Diploknema butyracea and Sapindus mukorossi on the insect pest Spodoptera litura (F.) were investigated in the laboratory. D. butyracea saponins as well as their hydrolyzed prosapogenins were found to be better biologically active in controlling pests. A concentration of 1200 and 3400 mg L(-1) alkaline and acid hydrolyzed D. butyracea saponins exhibited significant antifeeding and toxic effects to third instar larvae when compared to the emulsified water as control. The n-BuOH extract after prep-HPLC separation provided two saponins from the D. butyracea saponin mixture: 3-O-[beta-D-glucopyarnosyl-beta-d-glucopyranosyl]-16-alpha-hydroxyprotobassic acid-28-O-[ara-glc-xyl]-ara (MI-I) and 3-O-beta-D-glucopyranosyl-glucopyranosyl-glucopyranosyl-16-alpha-hydroxyprotobassic acid-28-O-[ara-xyl-ara]-apiose (MI-III). The single saponin extracted from the S. mukorossi saponin mixture was 3-O-[beta-D-xyl(OAc).beta-D-arabinopyranosyl.beta-D-rhamnopyranosyl] hederagenin-28-O-[beta-D-glc.beta-D-glc.beta-D-rhamnopyranosyl] ester (SM-I). Five days after saponin treatment on larvae, the growth index (GI50) was reduced from 0.92% to 1520 ppm in alkaline hydrolyzed D. butyracea saponins. Upon hydrolysis, growth regulatory activity was improved in S. mukorossi saponin, whereas very little difference was found in antifeedant activity. Hydrophile-lipophile balance is important for the proper functioning of saponin/prosapogenin/sapogenin, which could be achieved by manipulating the sugar molecule in the triterpenic skeleton.

Ferrxanthone, a 1,3,5,6-tetraoxygenated xanthone from Mesua ferrea

Abstract A new xanthone was isolated from the heartwood of Mesua ferrea and its structure determined by UV, IR, NMR and mass spectrometry as 1,3-dimethoxy-5,6-dihydroxyxanthone.

Controlled release formulations of metribuzin: Release kinetics in water and soil

Controlled release (CR) formulations of metribuzin in Polyvinyl chloride [(PVC) (emulsion)], carboxy methyl cellulose (CMC), and carboxy methyl cellulose-kaolinite composite (CMC-KAO), are reported. Kinetics of its release in water and soil was studied in comparison with the commercial formulation (75 DF). Metribuzin from the commercial formulation became non-detectable after 35 days whereas it attained maxima between 35–49 days and became non-detectable after 63 days in the developed products. Amongst the CR formulations, the release in both water and soil was the fastest in CMC and slowest in PVC. The CMC-KAO composite reduced the rate of release as compared to CMC alone. The diffusion exponent (n value) of metribuzin in water and soil ranged from 0.515 to 0.745 and 0.662 to 1.296, respectively in the various formulations. The release was diffusion controlled with half release time (t1/2) from different controlled release matrices of 12.98 to 47.63 days in water and 16.90 to 51.79 days in soil. It was 3.25 and 4.66 days, respectively in the commercial formulation. The period of optimum availability of metribuzin in water and soil from controlled released formulations ranged from 15.09 to 31.68 and 17.99 to 34.72 days as against 5.03 and 8.80 days in the commercial formulation.