Abstract
In agriculture, biocontrol agents have been emerged as safe alternative to chemical pesticides where Streptomyces spp. and their metabolites constitute a great potential for their exploration as potent agents for controlling various fungal phytopathogens. The present study reports an antifungal compound purified from Streptomyces hydrogenans strain DH16, a soil isolate, using silica gel chromatography and semi preparative HPLC. The compound was characterized using various spectroscopic techniques (IR, 1H and 13C NMR) and named 10-(2,2-dimethyl-cyclohexyl)-6,9-dihydroxy-4,9-dimethyl-dec-2-enoic acid methyl ester (SH2). Compound (SH2) showed significant inhibitory activity against fungal phytopathogens and resulted in severe morphological aberrations in their structure. Minimal inhibitory and minimal fungicidal concentrations of the compound ranged from 6.25 to 25 μg/ml and 25 to 50 μg/ml, respectively. In vivo evaluation of the compound showed strong control efficacy against Alternaria brassicicola, a seed borne pathogen, on radish seeds. In comparison to mancozeb and carbendazim, the compound was more effective in controlling damping off disease. Additionally, it promoted plant growth with increased rate of seed germination, and displayed no phytotoxicity. The compound retained its antifungal activity after its exposure to temperature of 100°C and sunlight for 1 h. Furthermore, the compound (SH2) when tested for its biosafety was found to be non-cytotoxic, and non-mutagenic against Salmonella typhimurium TA98 and TA100 strains. This compound from S. hydrogenans strain DH16 has not been reported earlier, so this new compound can be developed as an ideal safe and superior biofungicide for the control of various fungal plant diseases.
Highlights
Plant pathogens, especially fungi are one of the major threats to agricultural productivity of economically important crops worldwide (Cornelissen and Melchers, 1993)
Their indiscriminate and repeated use has triggered the emergence of resistance in phytopathogens, due to which several important chemical fungicides have lost their efficacy against the resistant pathogens in the field (Yang et al, 2008)
Many attempts were made to explore various antibiotics from microorganisms for control of plant diseases and some viz. blasticidin S, polyoxin, kasugamycin, validamycin, gopalamycin, dorrigocins, geldanamycin, nigericin, fistupyrone, jiggangmycin, phenyl acetic acid, azalomycin have been developed as fungicides for agricultural use (Hochlowski et al, 1996; Kim and Hwang, 2007)
Summary
Especially fungi are one of the major threats to agricultural productivity of economically important crops worldwide (Cornelissen and Melchers, 1993). Long term application of these chemicals has resulted in severe negative impacts on environment and human health Their indiscriminate and repeated use has triggered the emergence of resistance in phytopathogens, due to which several important chemical fungicides have lost their efficacy against the resistant pathogens in the field (Yang et al, 2008). These limitations of chemical fungicides and increased public concern for pesticide free food highlight the discovery and development of new safer fungicides (Coloretti et al, 2007). Many attempts were made to explore various antibiotics from microorganisms for control of plant diseases and some viz. blasticidin S, polyoxin, kasugamycin, validamycin, gopalamycin, dorrigocins, geldanamycin, nigericin, fistupyrone, jiggangmycin, phenyl acetic acid, azalomycin have been developed as fungicides for agricultural use (Hochlowski et al, 1996; Kim and Hwang, 2007)
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