Biocontrol of Root Rot in Cotton and Compatibility of Potential Bioagents with Fungicides

Systematic studies were conducted (2006 to 2009) to search for potential biocontrol agent against dry root rot pathogen (Rhizoctonia bataticola) of cotton and consequently compatibility of potential bioagents with fungicides. Among nine local and exotic bioagent isolates evaluated against R. bataticola under dual culture technique, Coimbatore isolate of Trichoderma viride-1 and local isolate of T. harzianum (TG-1) proved most effective inhibited 76.53 and 72.78 per cent growth of R. bataticola respectively. These two bioagents also proved their superiority over rest of the bioagents in controlling root rot disease in pots under cage house conditions. Minimum at par root rot incidence of 35.78 and 38.98 per cent was recorded in pots where seeds and soil was treated with T. viride-1 and T. harzianum (TG-1) respectively. These bioagents exhibited 56.28 and 52.53 per cent disease reduction over untreated control. Metalaxyl, fosetyl-Al, mancozeb, cymoxanil 8% + Mancozeb 64% mixture and copper oxychloride fungicides were found compatible with bioagent T. harzianum (TG-1) and tolerance limits (ED₅₀) of these fungicides were >1000 μg/ml. Metalaxyl proved their compatibility with another potential bioagent T. viride-1 also where even >1000 μg/ml concentration was under safe tolerance limit (ED₅₀). Copper oxychloride, mancozeb, fosetyl-Al and cymoxanil 8% + mancozeb 64% mixture fungicides showed moderate to good compatibility with T. viride1 by exhibiting tolerance limits (ED₅₀) of 848, 710, 578 and 448 μg/ml respectively.