Five flavonoids, namely (-)-epicatechin-3-O-β-glucopyranoside (1), 5-hydroxy-3-(4-hydroxylphenyl)pyrano[3,2-g]chromene-4(8H)-one (2), 6-(p-hydroxybenzyl)taxifolin-7-O-β-D-glucoside (tricuspid) (3), quercetin-3-O-α-glucopyranosyl-(1 → 2)-β-D-glucopyranoside (4) and (-)-epicatechin(2-(3,4-dihydroxyphenyl)-3,4-dihydro-2H-chromene-3,5,7-triol (5), were isolated from the leaves of mango (Mangifera indica L.). Antifungal activity of these compounds was evaluated against five fungal species, namely Alternaria alternata (Fr.) Keissler, Aspergillus fumigatus Fresenius, Aspergillus niger van Tieghem, Macrophomina phaseolina (Tassi) Goid. and Penicillium citrii. Six concentrations, namely 100, 300, 500, 700, 900 and 1000 ppm of each of the five flavonoids were employed by means of the poisoned medium technique. All concentrations of the five test flavonoids significantly suppressed fungal growth. However, the specificity of different test compounds was evident against different fungal species. In general, antifungal activity of the flavonoids was gradually increased by increasing their concentrations. The highest concentration (of 1000 ppm) of compounds 1-5 reduced the growth of different target fungal species by 63-97%, 56-96%, 76-99%, 76-98% and 82-96%, respectively.
The antifungal activity of Melia azedarach L. leaves was investigated against Ascochyta rabiei (Pass.) Lab., the cause of destructive blight disease of chickpea (Cicer arietinum L.). Bioassay guided fractionation revealed that the chloroform fraction of the methanolic extract of M. azedarach leaves was highly effective against A. rabiei. Six compounds, namely β-sitosterol (1), β-amyrin (2), ursolic acid (3), benzoic acid (4), 3,5 dimethoxybenzoic acid (5) and maesol (6) were isolated from the chloroform fraction through column chromatography. The in vitro antifungal activity of compounds 2-5 was evaluated against A. rabiei. A commercial fungicide, mancozeb, was used as a positive control. Different concentrations of mancozeb and the isolated compounds, ranging from 0.0039 to 4 mg mL(-1), were used in the antifungal bioassay, and data regarding minimum inhibitory concentration (MIC) was recorded 24, 48 and 72 h after incubation. All concentrations of mancozeb inhibited the fungal spore germination at all three incubation periods. The tested compounds exhibited variable antifungal activity against the target fungal pathogens. All compounds showed their highest antifungal activity after 24 h of incubation. Compound 2 was found to be the most effective, with an MIC of 0.0156 mg mL(-1), followed by compounds 3, 4 and 5, with MIC values of 0.0312, 0.25 and 0.125 mg mL(-1), respectively.
In the present study, herbicidal activity of culture filtrates of nine phytopathogenic fungi, namely, Alternaria alternata (Fr.) Keissl., Drechslera australiensis (Bugnicourt) Subramanian & Jain, Drechslera hawaiiensis (Curtis and Cooke) Shoemaker, Drechslera biseptata (Saccardo & Roumeguere) Richardson & Fraser., Drechslera rostrata (Drechsler) Ricardson & Fraser, Fusarium oxysporum (Massey) Synd. & Hans., Fusarium solani (Martius) Saccardo., Monilia stophila (Montagne) and Cladosporium sp. (Grey) de Hoff, was evaluated against parthenium weed (Parthenium hysterophorus L.). In laboratory bioassays, the effect of original (100%) as well as lower concentrations (75, 50 and 25%) of these cultural filtrates was studied on germination and early seedling growth of parthenium. Cultural filtrates of different concentrations of A. alternata, Cladosporium sp. and D. rostrata significantly suppressed the germination of parthenium seeds by 70-90, 13-73 and 27-50%, respectively. Cultural filtrates of these fungi also exhibited pronounced adverse effects on the seedling root and shoot growth. Among other fungal species, cultural filtrates of D. australiensis, D. hawaiiensis, F. oxysprium and F. solani significantly reduced the root and shoot length of parthenium seedlings. Foliar spray bioassay was performed using cultural filtrates of three fungal species, namely A. alternata, F. solani and D. rostrata. In this bioassay, three sprays of fungal cultural filtrates, with 4 day intervals each, were carried out on 1 and 2 week-old pot-grown seedlings of parthenium. Cultural filtrates of all the three fungal species markedly suppressed root and shoot growth of parthenium weed.
Sclerotium rolfsii is a soil-borne plant pathogen that causes root diseases in hundreds of plant species. It also causes collar rot disease in chickpea (Cicer arietinum L.). The present pot study was carried out to investigate the effect of soil amendment with dry biomass of a weed Chenopodium album L. and two antagonistic fungi, namely Trichoderma harzianum and T. viride, on growth and yield of chickpea variety Noor 2009 in soil infected with S. rolfsii. The pathogen-contaminated soil was amended either with 1, 2, or 3% C. album dry biomass, T. harzianum, and T. viride alone, or combinations of either of the two Trichoderma species and plant dry biomass. The lowest shoot and root dry biomass and grain yield of chickpea were recorded in S. rolfsii inoculation alone without any soil amendment (positive control). Plant growth and yield were significantly and gradually increased over positive control with an increase in C. album dry biomass application in the soil. Likewise, soil application of either of the two Trichoderma species significantly enhanced plant growth and yield over positive control under biotic stress of S. rolfsii. Combined application of either T. harzianum or T. viride with 3% dry biomass of C. album also proved highly effective in alleviating biotic stress of S. rolfsii on growth and yield of chickpea.
Sclerotium rolfsii is a soil-borne fungal pathogen causing diseases in more than 500 plant species. It causes southern blight disease in chili. Chemical fungicides are used to control this disease, which also pollute the environment. The present study was designed to assess the potential of two species of plant-growth-promoting rhizobacteria (PGPR) viz. Bacillus megaterium and Pseudomonas fluorescence, and an allelopathic weed, Anagallis arvensis L., for the control of southern blight disease of chili.
Initially, three PGPR strains, viz. B. megaterium OSR3, B. megaterium ZMR6, and P. fluorescence PF-097, were selected for their in vitro antagonistic assessment against S. rolfsii by dual culture technique on potato dextrose agar medium. OSR3 showed the highest antagonistic potential (68%), followed by PF-097 (54%) and ZMR6 (33%). In a pot experiment, the two best strains of PGPR, namely OSR3 and PF-097, and dried biomass of A. arvensis (DBA) in different concentrations (1, 2 and 3%) were used to manage southern blight disease of chili. In positive control treatment (S. rolfsii only), plant survival was low (73%) than the negative control (100%). OSR3, PF-097, OSR3 + 2% DBA, and PF-097 + 2% DBA significantly enhanced plant survival over positive control. The highest increase in chili growth over positive control was recorded due to OSR3, followed by PF-097 inoculations. Contents of carotenoid and chlorophyll were significantly decreased due to the fungal pathogen and improved due to PGPR strains. Application of the two PGPR strains and different concentrations of A. arvensis distinctly increased the catalase (CAT), peroxidase (POX), and polyphenol peroxidase (PPO) activities over positive control.
The present study concluded that PGPR strains B. megaterium OSR3 and P. fluorescence PF-097 can control southern blight disease effectively and increase growth and yield of chili.
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