Background: The dieback disease of tea caused by Fusarium solani is one of the major constraints in determining its production and quality. Genus Trichoderma is a promising biocontrol agent to control the dieback without any residual effect and is the most suitable option for integrated disease management approach. A few local Trichoderma spp were isolated from tea rhizosphere of the Dooars zone and preliminary identified. Based on dual culture bioassay, the most efficient isolate got re-identified from well reputed national institutes and its liquid formulation (2% Aqueous Suspension) was prepared. Different concentrations of this formulation, T. harzianum and Hexaconazole were evaluated for the control of dieback disease and other parameters for two seasons in three zones under field conditions.
Results: The fungal antagonist (KBN-29) was identified as T. asperellum based on characteristics such as regular mycelial branching, typically paired conidiophores with straight phialides and globose to sub-globose shaped conidia. It had the maximum control of dieback pathogen in lab experiment. Spray of T. asperellum formulation at 1200 and 1000 ml/ha concentration conferred comparatively better disease control and enhanced the yield of green tea leaves. The formulation was safe to non-target beneficial insects in all three zones without any phytotoxicity to tea leaves at 4, 8, and 16ml/L concentrations.
The present study confirms that T. asperellum 2% AS formulation was significantly superior in managing the dieback disease of tea plantations in Darjeeling, Dooars, and Assam zones at concentration of 1200 followed by 1000 ml / ha during both seasons. The maximum made tea yield was achieved in plots treated with T. asperellum at 1200 followed 1000 ml/ha. This formulation was safe to beneficial insects viz., C. carnea, O. javanus, and S. gilvifrons, furthermore it was not phytotoxic to tea leaves at 4 to 16ml/L concentrations.