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Authors: Bohra, Yogita
Advisor: Kumar, J.
Title: Elucidating Cu-Trichoderma interaction and Trichoderma-chitosan interaction in “Cu-Chi-Tri”, a novel consortium for potato late blight management
Publisher: G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Language: en
Type: Thesis
Pages: 213
Agrotags: null
Keywords: elucidation, copper, Trichoderma, Trichoderma, chitosan, consortium, potatoes, blight
Abstract: Threat of emerging pesticide resistant races and excessive usage of pesticides calls for an effective and ecofriendly management strategy. A triple combination “Cu-Chi-Tri” consisting of reduced dosage of Cu(OH)2, an antimicrobial and defence inducing biopolymer chitosan and a Trichoderma TCMS 36 exhibiting copper-chitosan tolerance, was found effective against late blight in earlier researches. Therefore, this study was conducted to decipher the underlying operative mechanism for disease control by the ‘triple combination’. The cultural, morphological and molecular characterization established the identity of TCMS 36 to be Trichoderma asperellum. SEM studies on interaction of Cu(OH)2 and tolerant and sensitive Trichoderma isolates, TCMS 36 and TCMS 25 revealed mycelial shrinkage and collapse in the sensitive isolate. Elemental analysis through EDX-mapping revealed presence and uniform distribution of Cu in the mycelial matrix of TCMS 36. Moreover, dual combination containing 500 ppm Cu(OH)2 and 1 percent Trichoderma and the triple combination containing 500 ppm Cu(OH)2 along with 500 ppm chitosan in oligomeric form and Trichoderma TCMS 36 (1%) was found to support the maximum build-up of Trichoderma population in soil as evident from 58.21 fold and 46.88 fold increase in population under sterilized soil condition. TLC and UPLC-qTOF-MS studies determined the production of chitosan oligomers by T.asperellum TCMS 36 machinery as was evident from development of dimer and trimer spots in TLC plate that were absent in control and moreover by increased relative intensities of m/z ~162, ~180, ~323 in MS spectrum corresponding to monomer, dimer and trimer units. The expression profile of chitosanase gene of TCMS 36 revealed the maximum expression accounting to 50.56 fold relative increase on 3rd day by combination of both Cu(OH)2 and chitosan. The expression of chitosanase gene was found to reduce gradually from 3rd to 10th day thus indicating the need of repeating sprays at 10 days interval. The in-vitro and microscopic observations revealed anti-Phytophthora activity of chitosan in terms of extensive mycelial inhibition and morphological alterations, the larger oligomers (pentamers to heptamers) being more effective. The polymeric chitosan was found to form a chemical barrier between host and pathogen leading to reduced sporangial germination and sporangiophore production on leaf surface. However, Trichoderma depolymerized smaller oligomers (monomers to tetramers) were found to enhance the defense activities mediated by lipoxygenase and catalase higher than those activated by polymers and larger oligomers (greater than hexamers), hence, leading to a switch-over of defense mechanism from being antimicrobial to a defense inducer. The lipoxygenase and catalase were activated earliest by smaller oligomers (DP<5) and were most prolonged (high activity upto 96 hpi) by the ‘triple combination’ containing chitosan monomers to hexamers. The totality of different mechanisms was summed up with reference to disease severity that was found to be minimum for Cymoxanil+Mancozeb (14.82 %) followed by Metalaxyl M+Mancozeb (20.37 %) which was followed by triple combination containing Trichoderma depolymerized chitosan CS661 as chitosan (25.93 %) 91 DAS, that was much effective than dual combinations (50-59.26 %) and the defense inducer BABA (48.15 %) thus establishing a resilient synergy for sustainable management of late blight disease. Moreover, no residual Cu was found in soil 130 DAS with treatments containing 500 ppm Cu(OH)2 whereas, Cu residue corresponding to 0.79 percent weight of soil was found 130 DAS with treatments containing 1000 ppm Cu(OH)2, thus establishing environment resilience of the triple combination. The efficacy of triple combination Cu-Chi-Tri with both polymeric and oligomeric chitosan variant needs to be validated in larger scale at farmer’s field in different potato growing regions. Moreover, future study needs to focus on large scale validation and development of product for the farmers and also on understanding the role of copper in enhancing the expression of chitosanase gene in T.asperellum TCMS 36.
Subject: Plant Pathology
Theme: Fungal Diseases
Research Problem: Potatoes
These Type: Ph.D
Issue Date: 2019-08
Appears in Collections:Theses

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