Managing groundnut dry root rot with organic amendments and rhizosphere antagonists

Groundnut (Arachis hypogaea L.) is an important oilseed crop which is primarily grown in tropical and subtropical regions. Dry root rot caused by soil borne fungus Macrophomina phaseolina is the most destructive and widespread disease worldwide. For better management of this disease, rhizosphere antagonists and organic amendments were employed both in vitro and in vivo studies. Seven rhizosphere antagonists (Trichoderma sp. - Tsp 1, Tsp 2, Tsp 3, Tsp 4, Bacillus sp. - Bsp 1, Bsp 2 and Pseudomonas sp.) were isolated from rhizosphere regions of healthy groundnut plants and tested in vitro against M. phaseolina by dual culture method. Among the antagonists tested, Tsp1 recorded maximum mycelial inhibition of 67.81 %. The best performing antagonists Tsp1 was molecularly characterised and confirmed as Trichoderma virens. Among the seven different organic amendments tested, neem cake showed maximum mycelial inhibition of 52.21 % and 52.50 % at 10 % and 15 % concentrations respectively. The effective rhizosphere antagonists and organic amendments were tested against M. phaseolina under pot culture and field condition. In pot culture experiment, soil application of T. virens (5 g/pot) + neem cake (5 g/pot) was effective in managing the dry root rot disease with lowest disease incidence (22.21 %) against inoculated control (88.88 %). In field experiment, soil application of T. virens (2.5 kg/ha) + neem cake (150 kg/ha) recorded lowest disease incidence of 10.32 % and highest yield of 3200 kg/ha against untreated control (58.57 %, 900 kg/ha respectively).