In vitro evaluation of plant extracts, bioagents and fungicides against Alternaria porri (Ellis) Cif., causing purple blotch disease of onion

Purple blotch of onion caused by Alternaria porri (Ellis) Cif. is an economically important disease posing threat to onion cultivation in warm and humid regions. Bioefficacy of six plant products (Clerodendron, cinnamon, garlic, neem oil, pongamia oil and turmeric), five biocontrol agents (Trichoderma harzianum, Chaetomium sp. Beauveria bassiana, Verticillium lecanii and Metarhizium anisopliae) was evaluated under in vitro conditions and compared with commonly used fungicides viz., mancozeb, chlorothalonil, propineb and copper oxy chloride. Among plant products evaluated, fresh aqueous extract of garlic (20%) was effective in causing 100 per cent inhibition of mycelial growth. Neem oil and pongamia oil (20%) caused 76.94 and 69.94 per cent inhibition. Among the biocontrol agents evaluated, maximum inhibition (79.5%) was recordedin T. harzianum. Among the fungicides, mancozeb and propineb (0.3%) caused 100 per cent inhibition of mycelial growth. The present study indicated that plant products and biocontrol agents have shown significant inhibition of A. porri and were comparable with fungicides.