Study of the mechanisms underlying synergy in triple combination of copper-chitosan-Trichoderma based novel fungicide against late blight disease of potato (Solanum tuberosum L.)
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Date
2018-08
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
A ‘triple combination’ comprising of low dose of fungicide (CuOH), plant defence activator compound (Chitosan) and copper tolerant biocontrol agent (Trichoderma asperellum TCMS 36 (MH593785) wasdeveloped at Biocontrol laboratory, GBPUA&T, Pantnagar and field tested over years. In the present study, the copper tolerance mechanism of Trichoderma TCMS 36 was investigated and was found that Trichoderma TCMS 36 showed Copper tolerance mechanism by modulating fatty acid composition of its membrnane in copper containing environment. Specifically, derivatives of linoleic acid, oleic acid, palmitic acid and phosphate ester, which determine the membrane stability of Trichoderma in copper toxic environment. Simultaneously, in ‘Triple combination’ chitotsan may chelate the copper ions making Cu-Chitosan chelated complex, which was not absorbed/adsorbed by the T.asperellum. Hence, high modulation in membrane fatty acid composition was recorded in dual combination of Trichoderma+copper while in Triple combination as Chitosan interfere copper adsorption by Trichoderma not much modulation in fatty acid composition was required. Four important beneficial secondary metabolites with high concentration were produced in case of ‘Triple combination’ (Diphenyle sulphone 12.36%; 6-Pentyl alpha pyrone 61.12%; Tetracontane 6.01% and Pentacosane 3.36%) while in dual combination of Copper + Trichoderma three metabolites (Diphenyle sulphone 10.39%, 6-Pentyl alpha pyrone 69.96%, and Tetracontane 2.98%) were observed. Resistance inducing marker enzymes (APX, GR, CAT and LOX) and non enzymatic antioxidants (Ascorbate, reduced Glutathione and total Flavanoids) were significantly high in triple combination and BTH as compared to single and dual combination within 24-72 hrs post inoculation. Hypersensitive reaction through ROS (H2O2) production was observed in triple combination and BABA treated leaves while excessive oxidative stress damage was found in control. Meanwhile, PR-2 (β1,3-Glucanase) protein and antimicrobial secondary metabolites including phytoalexins production were also significantly higher in Triple combination (1.433 μmol/mim/mg and 12.58 peak area% ) as compared to control ( 0.723 μmol/mim/mg and 2.5 peak area%). Disease severity (91.66%) and pathogen invasion were maximum in control and minimum in ‘Triple combination’ treated leaves (4.53%) in detached leaf assay at 72 hr. post inoculation. Field trial at Pantnagar (plain) and at village Gaja (hills) revealed that triple combination containing ready to use Chitosan-661-500ppm gave better results (4.8% to 8.33%) that were at par with commercially available standard fungicides Mancozeb (5% to 7%) as compared to control (95% to 98.99%). Resistance inducer BTH and BABA managed the disease severity up to a certain limit (25% to 33.33%) under field condition. Synergestic action of all theses mechanisms made the ‘Triple combination’ more effective than single or dual combination. The results revealed that ‘triple combination’ so designed could be a viable alternative to chemical fungicides for late blight disease management as well as for increasing the tuber yield of potato.
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