Trichoderma harzianum (Th-3) a Potential Strain to Manage the Purple Blotch of Onion (Allium cepa L.) Caused by Alternaria porri under North Indian Plains

Purple blotch of onion by Alternaria porri (Ellis) Neerg. causes heavy yield loss in both bulb and seed crops. Using biocontrol agent to manage the disease is one of the most important approaches for successful disease management and sustainable onion production. For the development of bioagents based strategy seventeen isolates of fungal and six isolates of bacterial bioagents obtained from different sources were tested for their bioefficacy against A. porri. Effective isolates (Th-3, Th-30, Tv-12, Tv-15, Pf-3 and Bs-2) were selected and tested for volatile and non-volatile metabolites production and vigour induction under in vitro. Trichoderma harzianum isolate (Th-3) expressed high level of disease reduction and growth promotion in susceptible onion (cv. Pusa Red) when different methods viz., seed treatment, seedling dip and three foliar sprays were evaluated on onion bulb crop under glass house and field conditions. Field experiments (2008-2010) on onion seed crop also confirmed the potential of Th-3 isolate on disease suppression and growth promotion.