Microbial biocides - Viable alternatives to chemicals for tea disease management

Abstract

Tea plantations in North east India are mostly rain fed and the cropping season needs moist climate with alternating wet and dry periods that eventually attracts diverse tea pathogens like Fusarium solani, Cephaleuros spp., Corticium spp. Poria hypobrunnea, Ustulina zonata, Fomes lamaoensis etc., known to cause several serious diseases in tea and thereby make enormous losses to crop yield and quality, influencing world tea market, adversely. Tea disease management using chemical fungicides alone is, however, prohibitive since the latter is known for destabilizing soil fertility and thereby directly affects the native microbial populations present in soil. Application of new fungicide molecules at its low doses along with exploitation of biological substances (more especially, microbial biocontrol agents) and adoption of Integrated Disease Management (IDM) schedule has been practiced in the present investigation for controlling certain devastating diseases in tea plantation of North East India. Multilocational field trials has been made throughout the investigations using locally isolated microorganisms such as Azotobacter, Azospirillum, Bacillus, Pseudomonas, Streptomyces, Trichoderma etc. (@ 2%, 5% and 10% spore concentrations), along with crude extracts of botanicals (@ 5% concentration) prepared from Amphineuron opulentum, Cleome gynandra, Ipomea convolvulus, Polygonum hydropiper etc. against dominant tea diseases such as black rot, red rust and Fusarium die back respectively. Maximum emphasis has been made to reduce the load of chemicals and move towards alternative strategies of tea disease management as to promote sustainable tea cultivation. Biological control measures (especially microbial) have potential to reduce the disease severity (up to 78.2% disease reduction) and thereby brought impending perspective for the use of effective biopesticides in tea ecosystem. The potential microbial strains were identified using morphological, biochemical as well as molecular characterization and deposited at NCBI GenBank database with accession numbers. The application technology of microbial biocides has also being popularized among the tea growers throughout the region to accelerate the use of these beneficial microorganisms in tea.