Onkar D. Dhingra

Composition and Antifungal Activity of the Essential Oil of the Brazilian Chenopodium ambrosioides L.

The antifungal activity of essential oil (EO) from the Brazilian epazote (Chenopodium ambrosioides L.) was evaluated by the poison food assay at concentrations of 0.3%, 0.1%, and 0.05% with eight postharvest deteriorating fungi (Aspergillus flavus, Aspergillus glaucus, Aspergillus niger, Aspergillus ochraceous, Colletotrichum gloesporioides, Colletotrichum musae, Fusarium oxysporum, and Fusarium semitectum). EO components were tentatively identified by Kováts retention indices (RIs) using gas chromatography and gas chromatography combined with mass spectrometry (GC-MS). Growth of all fungi was completely inhibited at 0.3% concentration, and by 90% to 100% at 0.1% concentration. The following 13 tentatively identified compounds (relative percent) accounted for 90.4% of the total volatile oil: α-terpinene (0.9), p-cymene (2.0), benzyl alcohol (0.3), p-cresol (0.3), p-mentha-1,3,8-triene (0.2), p-cimen-8-ol (0.6), α-terpineol (0.5), (Z)-ascaridole (61.4), piperitone (0.9), carvacrol (3.9), (E)-ascaridole (18.6), (E)-piperitol acetate (0.5), and (Z)-carvyl acetate (0.3). Autobiographic thin layer chromatography of the EO to separate the principal fungitoxic fraction yielded only one fraction that completely inhibited the growth of all test fungi at a concentration of 0.1%. This fraction was characterized by RIs and GC-MS presenting a composition (%) of p-cymene (25.4), (Z)-ascaridole (44.4), and (E)-ascaridole (30.2). The results suggest ascaridoles were the principal fungitoxic components of the EO.

Identification of the major fungitoxic component of cinnamon bark oil

The study was done to identify the most active fungitoxic component of cinnamon bark (Cinnamomum zeylanicum) oil that can be used as a marker for standardization of cinnamon extract or oil based natural preservative of stored seeds. Aspergillus flavus and A. ruber were used as test fungi. The hexane extracted crude oil and the hydro-distilled essential oil from cinnamon bark had complete growth inhibition concentration (CGIC) of 300 and 100 µl/l, respectively. Both oils produced three fractions on preparative thin layer silica-gel chromatography plates. The fraction-2 of either oil was the largest and most active, with CGIC of 200 µl/l, but the fungitoxicity was also retained in the other two fractions. The fraction-1 and 3 of the crude oil reduced growth of both the fungal species by 65%, and those of distilled oil by 45% at 200 µl/l. The CGIC of these fractions from both the sources was above 500 µl/l. The gas chromatography and mass spectrometry (GC-MS) of the fraction-2 of the hexane extract revealed that it contained 61% cinnamaldehyde, 29% cinnamic acid, and two minor unidentified compounds in the proportion of 4% and 6%. The GC-MS of the fraction-2 of the distilled oil revealed that it contained 99.1% cinnamaldehyde and 0.9% of an unidentified compound. The CGIC of synthetic cinnamaldehyde was 300 µl/l and that of cinnamic acid above 500 µl/l. The 1:1 mixture of cinnamaldehyde and cinnamic acid had CGIC of 500 µl/l. The data revealed that cinnamaldehyde was the major fungitoxic component of hexane extract and the distilled essential oil of cinnamon bark, while other components have additive or synergistic effects on total fungitoxicity. It is suggested that the natural seed preservative based on cinnamon oil can be standardized against cinnamaldehyde.

Avaliação de produtos alternativos para controle da requeima do tomateiro

The efficacy of alternative products to manage tomato (Lycopersicon esculentum) late blight, caused by Phytophthora infestans, was evaluated in three field trials (E) that compared: E1- [chili pepper (Capsicum chinense) + black pepper (Piper nigrum) + clove (Syzygium aromaticum) + turmeric (Curcuma longa) + garlic (Allium sativum) extracts]; (black pepper + clove + garlic extracts); and (clove + turmeric + garlic extracts); E2 - neem (Azadirachta indica) oil (0.5%), crude cow milk diluted in water (20% v/v), and Bordeaux mixture; E3 - homeopathic preparation (from tomato tissue infected with P. infestans - C30), the water-ethanol mixture, and Bordeaux mixture. All experiments had two controls: no sprays and metalaxyl. Severity at halfway through the epidemic (Y50); at the end of the epidemic (Ymax); area under disease progress curve (AUDPC); and disease progress rate (r) were estimated. None of the extracts reduced Y50, Ymax, AUDPC, or r values. Neem oil and Bordeaux mixture resulted in similar Y50 values (3% and 1%, respectively). Ymax (44%) in plots treated with neem was higher than in those treated with Bordeaux mixture (14%). Milk at 20% did not reduce Ymax. Values of r (0.161) and AUDPC (533) were lower with neem oil than in control (r = 0.211 and AUDPC = 1186) and similar to the Bordeaux mixture plots (r = 0.156 and AUDPC = 130). Values of r and AUDPC on plots treated with milk were similar to those in the control plots. There was no significant reduction of Y50, Ymax, AUDPC, or r values when plants were treated with homeopathic product. Bordeaux mixture was the most efficient treatment in controlling late blight. Neem oil is potentially useful. Integrated management must be implemented to keep late blight at acceptable levels on alternative tomato production systems.

Essential oil of mustard to control Rhizoctonia solani causing seedling damping off and seedling blight in nursery

The essential oil extracted from mustard (Brassica rapa) seeds was evaluated for its effect on suppression of Rhizoctonia solani growth in vitro, and in field soils, for reducing saprophytic substrate colonization and seedling damping off and blight using snap beans as indicator plant, the in vitro growth was completely inhibited at a concentration of 50 ml/l. The saprophytic substrate colonization in soils 24 h after treatment was drastically reduced to 45% at 150 ml/kg soil concentration, in contrast to 100% colonization at concentrations of 0, 50, or 75 ml/kg. This recovery rate gradually declined to 6% and 60%, respectively, in nine days. A control of pre and post-emergence seedling damping off and blight in common beans (Phaseolus vulgaris), without any apparent phytotoxic effect was achieved by irrigating R. solani infested soils with water containing the emulsified essential oil to provide 150 ml/l soil volume ten days prior to planting, gave over 95%. The effect of the mustard essential oil was not influenced by the physical soil texture, and it appears to be a good substitute for methyl bromide fumigation in nurseries for seedling production.

Isolation and Identification of the Principal Fungitoxic Component of Turmeric Essential Oil

Abstract The essential oil of turmeric (Curcuma longa L.) rhizomes showed toxicity to seven fungi involved in deterioration of stored agricultural commodities. Depending upon the fungus, in vitro growth inhibition varied from 36%-77% at 0.1%. Aspergillus flavus, Fusarium semitectum, Colletotrichum gloeosporioides and C. musae were most sensitive with growth inhibition of over 70%. The bioautography of the oil produced only one antifungal band representing 40% of the total oil. The fractionation of this band by reverse phase preparative HPLC (high performance liquid chromatography) yielded two peaks, in the proportion of 57.9% and 42.1%. The larger peak had only one compound, which was identified as ar-turmerone by MS (mass spectrometry) and NMR (nuclear magnetic resonance) spectra. The smaller peak contained two compounds, in the proportion of 31% and 69%, which were identified as β-turmer-one and ar-turmerone, respectively. Thus ar-turmerone constituted 87% of the fungitoxic component of the oil. The purified ar-turmerone showed antifungal activity similar to the crude oil.

Ergosterol accumulation and oil quality changes in stored soybean invaded by Aspergillus ruber (A. glaucus group)

Soybean seed samples inoculated with spores of Aspergillus ruber were stored for 20 to 140 days at 25 ± 1 °C with moisture content varying from 11.3% to 17.7%. Seeds were colonised by the fungus within 20 days at all moisture levels. Ergosterol concentration in seeds increased with time of storage, being slow in samples with moisture content of 11.3% to 13.1% and more rapidly in those with higher moisture content. Free fatty acid (FFA) content also increased following the pattern of ergosterol. Equations were used to predict minimum safe storage period of the seeds at 25 °C. The rise in FFA is due to increase of A. ruber mass within the seed. Fungal growth did not affect fatty acids profiles or iodine index of the extracted oil. The results suggest revision of the present recommendations regarding seed moisture during storage. The FFA concentration of a seed lot can be used as a sensitive indicator of seed deterioration due to storage fungi.

Chaetomium globosum for reducing primary inoculum of Diaporthe phaseolorum f. sp. meridionalis in soil-surface soybean stubble in field conditions

Abstract The potential of an antibiotic-producing isolate of Chaetomium globosum (CgA-1) to suppress Diaporthe phaseolorum f. sp. meridionalis (Dpm) in soybean stubble was studied in field microplots of no-tillage, minimum-tillage, and shallow plowing. Mature soybean stems colonized in vitro with Dpm were spread on the soil surface and C. globosum ascospore suspension, without nutrient supply, was sprayed over the entire plot prior to any tillage operation. Perithecial formation and survival of Dpm in soybean stems, concomitantly with colonization by C. globosum, were monitored for a 180-day period (mid-autumn through winter and mid-spring), which is the normal interval between soybean harvest and sowing. The proportion of soybean stem segments occupied by Dpm and number of perithecia formed decreased linearly with time and showed a strong negative correlation with increase in the occupation by C. globosum. At the end of the study, which coincided with the soybean sowing season, the soybean stubble was free from viable Dpm and was colonized by C. globosum. The effectiveness of C. globosum in eliminating the pathogen from surface-borne residue or harrowed-in residue was similar but much slower than in the shallow-plowed microplots. C. globosum successfully competed with major interfering fungi such as, Trichoderma, Nigrospora, and Fusarium in colonizing the soybean stems above and under the soil surface. The data provide strong evidence for use of the antibiotic-producing isolate of C. globosum to control soybean stem canker disease.

Effect of herbicides on survival of Macrophomina phaseolina in soil.

The effect of five herbicides, EPTC, dinoseb, alachlor, fluorodifen and fluometuron, on the inoculum density of Macrophomina phaseolina (Tassi) Goid. was tested in two field soils. The herbicides were applied at commercially recommended rates. All herbicides tested incited a significant drop in the population of M. phaseolina. In soils treated with dinoseb, the population of M. phaseolina declined by 96 % in sandy-clay-loam and by 61 % in sandy-loam soil 10 days after treatment. In fluorodifen treated sandy-loam soil, the population dropped gradually by 85 %, whereas in sandy-clay-loam soil, it declined by 50 %, over a fifty day test period. The population of M. phaseolina dropped by 46 % to 63 % in both soils treated either with EPTC, fluometuron or alachlor, over the entire test period. There was a significant interaction between herbicide and soil, as affecting population decline of M. phaseolina in soil.

Effect of soil temperature, moisture, and nitrogen on competitive saprophytic ability of Macrophomina phaseolina

The effect of soil temperature, moisture and nitrogen on saprophytic colonization of bean or wheat stems by Macrophomina phaseolina was studied in two soils. Maximum colonization of the substrate units occurred at 15–20° and decreased with increasing soil temperature. At 15° more wheat than bean stems were colonized whereas at higher temperatures the reverse occurred. Maximum colonization of substrates occurred at 15–25% of moistureholding capacity, and percentage colonization decreased with increasing soil moisture. Addition of nitrogen to soil completely inhibited saprophytic colonization.

Nematicidal activity of extracts of red hot chili pepper, mustard and garlic on Meloidogyne javanica in green house.

Neves, W.S; Freitas, L.G.; Coutinho, M.M.; Giaretta-Dallemole, R.; Fabry, C.F.S.; Dhingra, O.D. & Ferraz, S. Nematicidal activity of extracts of red hot chili pepper, mustard and garlic on Meloidogyne javanica in green house. Summa Phytopathologica, v.35, n.4, p.255-261, 2009 The experiment had the objectives of evaluate the nematicidal activity of botanical extracts of chili pepper fruits (Capsicum frutescens), mustard (Brassica campestris) and garlig (Allium sativum) on the root-knot nematode, Meloidogyne javanica in tomato plants in the greenhouse, and in a second step, to compare the best extracts for the reduction of the number of eggs and root galls with two products containing capsaicin, capsainoids and allyl isothiocyanate. A sieved mixture of soil and sand 1:1 (v:v) was used to fill plastic pots and infested with 4000 eggs of M. javanica. After 4 days, 20 mL of one of the extracts, in the concentration of 1000ppm, were poured over the soil of each pot. Water was poured in the test treatment. Twenty day-old tomato seedlings were planted, one per pot, four days after the aplication of the extracts. Forty five days after planting, the number of galls and eggs per plant was evaluated. The chloroformic and cetonic extracts of chili pepper and the mustard oil presented the highest effect on the nematode population, differing from the control treatment in respect to the number of galls, but only the mustard oil differed from the control in the number of eggs per plant. The chloroformic and cetonic extracts of chili pepper and the mustard oil reduced in 34,5%, 40,4% and 99,9% the number of galls, respectively, and the mustard oil reduced the number of eggs in 99,9%. In the following experiment, the chloroformic extract of chili pepper, the mustard oil, a commercial product (Champon®) and a product in development at the UFV called DS, both containing capsaicin, capsainoids and allyl isothiocyanate, were compared at different concentrations. The Champon®, the DS and the mustard oil reduced the egg and gall numbers in comparison with the control treatment in all the tested concentrations. The pepper extract show the best result at 400 ppm, reducing the number of galls and eggs per root system in relation to the control treatment, however, these numbers were much higher than the observed in the Champon® and the DS treatments.