Management of groundnut root rot with biocontrol agents and organic amendments ∗

Three isolates of Trichoderma viride, and one isolate in each of T. harzianum and Pseudomonas fluorescens were evaluated in vitro, to assess their antagonistic potential against Macrophomina phaseolina (Tassi) Goid. causing root rot of groundnut. T. viride (Tv1) and T. harzianum were the most effective in reducing the mycelial growth and sclerotial formation of M. phaseolina. Culture filtrates of T. viride (Tv1) inhibited the growth of the pathogen as well as sclerotial germination to a greater extent. Due to the antagonistic effect of the biocontrol agents, sclerotial germination of the pathogen was poor when test verified by two methods. The three isolates of Trichoderma were found to release volatiles in vitro, which were fungistatic to M. phaseolina, with maximum effect being observed with Tv1. In greenhouse experiments, the application of T. viride with pungam cake each at 5 g/kg of soil markedly reduced root rot incidence recording 3.12% compared to 43.98% in control. Increased activities of defence-related enzymes viz., peroxidase (PO) and polyphenoloxidase (PPO) were more noticeable in infected plants than in healthy ones. Though inoculation of the pathogen M. phaseolina induced the plants to synthesize PO and PPO an additional increase in activities was observed with P. fluorescens or T. viride treatments.