Abstract
Six Trichoderma strains (collected from IARI, New Delhi and MTCC, Chandigarh) were tested for their ability to inhibit soil-borne pathogen of groundnut mainly Sclerotium rolfsii (causing stem rot on groundnut). In vitro percent growth inhibition of S. rolfsii by various Trichoderma strains were recorded at 5th day after inoculation (DAI). Results obtained from the antagonism study indicated that Trichoderma viride (NBAII Tv 23) inhibited 61% growth of phytopathogenic fungi S. rolfsii followed by Trichoderma harzianum (NBAII Th1) (55% growth inhibition of pathogen). The specific activities of cell wall degrading enzymes chitinase, β-1,3 glucanase, protease and cellulase were tested during different incubation period (48, 72 and 96 h) when Trichoderma spp. grew in the presence of pathogen cell wall in synthetic media. The antagonist T. viride (NBAII Tv 23) induced higher chitinase and protease activity. The growth inhibition of pathogen during antagonism were positively correlated with coiling pattern of antagonists at 14th day after inoculation (DAI) as well as with the induction of chitinase, β-1,3 glucanase and total phenol content. However, the amount of cellulase and polygalacturonase recorded was least in these antagonists treatment. A significant positive correlation (p = 0.01) between percentage growth inhibition of test fungus and lytic enzymes (chitinase, β-1,3-glucanase and protease) in the culture medium of antagonist treatment established a relationship to inhibit growth of fungal pathogen by increasing the levels of these enzymes. Among all the tested Trichoderma strains, T. viride (NBAII Tv 23) was found to be the best strain to be used in biological control of plant pathogen S. rolfsii. Key words: Antagonism, soil-borne pathogens, lytic enzyme, Trichoderma, biocontrol agent.
Highlights
Groundnut (Arachis hypogaea L.) is the most important oil seed crop of India
Among Trichoderma species, Trichoderma harzianum, Trichoderma viride and Trichoderma reesei are known as producers of these extracellular hydrolytic enzymes
T. harzianum is a known producer of the extracellular hydrolytic enzyme, chitinase, which is one of the biocontrol mechanisms exerted by Trichoderma towards fungal pathogens, besides antibiosis and competition, which degrades the chitin polymers of the fungal cell wall
Summary
The distribution of several phytopathogenic fungi such as Sclerotium rolfsii, Pythium, Phytophthora, Rizoctonia and Fusarium has spread during last few years due to changes introduced in farming, with detrimental effects on crops of economic importance. Chemical compounds such as Topsin-M, Rhizolex, Benlite and Vitavax have been used to control plant diseases but it has adverse effect that creates health hazards for humans and other non-target organisms (Graham-Bryce, 1981). Trichoderma strains are free-living fungi that are common in soil and root ecosystems. T. harzianum is a known producer of the extracellular hydrolytic enzyme, chitinase, which is one of the biocontrol mechanisms exerted by Trichoderma towards fungal pathogens, besides antibiosis and competition, which degrades the chitin polymers of the fungal cell wall
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