Trichoderma species are known globally mostly for the production of industrially useful enzymes as well as their biocontrol ability against plant pathogens. One of the major strategies of biological control is mycoparasitism against fungal pathogens of crop plants. However, till recently the mechanisms of mycoparasitism by biocontrol potential Trichoderma species at molecular level were not clearly understood. The biochemical signaling and the involvement of secondary metabolites that lead to mycoparasitic activities of Trichoderma, in particular, were not very clearly known earlier. Recent findings in this regard revealed that there are a number of signaling cascades activated during the process of mycoparasitism by Trichoderma species against phytopathogenic fungal pathogens. In addition Trichoderma also interacts with beneficial root inhabiting fungi like mycorrhizae. The interaction of Trichoderma species with mycorrhizal fungi is different as during interaction with mycorrhizal fungi different signaling cascades are activated that lead to a synergistic action. In the current review, we gathered updated evidences regarding the signaling cascades that are generated during interactions between Trichoderma species with fungal pathogens resulting mycoparasitism as well as interactions of Trichoderma species with mycorrhizal fungi resulting synergism at molecular level. We also highlighted the role of secondary metabolites that are reported to be associated in the signaling processes.
Trichoderma harzianum is a naturally occurring filamentous fungus which solubilizes mineral nutrients and inorganic fertilizers, increasing availability and uptake of nutrients to the plant. Rhizoctonia solani is a major problem for seedlings, causing damping-off and in mature plants causing foot and root rot in the tomato crop, reducing nutrient uptake. The aim of this study is to evaluate the effect of Trichoderma harzianum (BHU-51), Trichoderma harzianum (BHU-105) and their consortium Trichoderma harzianum (BHU-51+BHU-105) on management of R. solani and nutrient levels in the plants.The application of Trichoderma as a seed treatment significantly decreased the incidence of damping-off and increased the vigour index of the plants. The maximum reduction in disease incidence was recorded for the consortium (BHU-51+BHU-105) treatments. The mineral content in treated plants was also higher than untreated pathogen-inoculated controls. Field trials also showed that the consortium produced better results in terms of shoot length, chlorophyll content and yield than the control.The application of Trichoderma in consortium form increased mineral nutrient uptake, reduced disease incidence and obtained a greater yield with reduced chemical pesticide loads, benefitting farmers and consumers.
Collar rot (Sclerotium rolfsii) of chickpea (Cicer arietinum) is one of the devastating soil-borne diseases of fungal origin, due to which 10-30% yield loss is recorded annually according to severity of the disease. Management of collar rot of chickpea is not feasible in the absence of effective soil fungicides. However, Trichoderma harzianum and plant growth promoting rhizobacteria (PGPR) have shown high efficacy against this disease in vitro as well as in the field. We used T. harzianum (10 4 , 10 6 and 10 8 spore/ml) and two PGPRs (Pseudomonas fluorescens strain 4 and P. aeruginosa) as foliar spray with the fresh and heat inactivated microorganisms. Foliar application of T. harzianum (10 8 spore/ml) and P. fluorescens strain 4 (10 8 cfu/ml) showed maximum efficacy in reducing plant mortality as compared to the control. Foliar application of fresh-and heat-inactivated (121°C for 10 min) P. fluorescens strain 4, and T. harzianum reduced 15-25% plant mortality but P. aeruginosa showed very little disease control of 10-15%. However, regarding plant growth promotion, it was observed that fresh-and heatinactivated P. fluorescens strain 4 showed maximum efficacy followed by fresh and heat inactivated P. aeruginosa and T. harzianum as compared to the control. The disease-controlling efficacy was also associated with the increase in phenolic acid synthesis in chickpea plants. The control of chickpea collar rot by biocontrol agents is safe and ecologically sound and appears to be a healthy approach to the disease control.
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