Halo Tolerance of Biocontrol Agents against Root Rot of Mung Bean (Vigna radiata (L.) Wilczek var. radiata) Caused by Macrophomina phaseolina (Tassi) Goid in Salt Affected Soils

Root rot of mung bean [Vigna radiata (L.) Wilczek var. radiata] is major disease and claims huge yield loss if they occur in the field. The pathogen is basically soil borne and survivability may vary depends on soil condition. The fungicide chemicals are available to manage the disease; however, the biocontrol agents are nowadays available for the disease management and the microbial activity of the biocontrol agents is influenced by existing soil condition including soil pH. Hence, a study was conducted to find out the halo tolerance capacity of the biocontrol agents against root rot disease in salt affected soils under in vitro, in vivo and field condition. The root rot pathogen Macrophomina phaseolina was isolated from infected root. Efficacy of biocontrol agents against growth of M. phaseolina was assessed in vitro. The results revealed that TNAU strain of Bacillus subtilis reduced the mycelial growth of the M. phaseolina significantly when media supplemented with NaCl at 5% (1.4 cm), 7.5% (1.5 cm), 10% (1.6cm) and 12.5% (1.6 cm) and without NaCl (1.2 cm) and similar trend of reduction also expressed by BCA1 strain of B. subtilis, Pseudomonas fluorescens and Trichoderma viride under in vitro. The performance of the biocontrol agents against the pathogen is slightly reduced when media supplemented with NaCl. The reduction of mycelia weight of M.phaeolina was more in media added with TNAU strain of B.subtilis and the performance of TNAU strain of B.subtilis on reduction of mycelial weight of M.phaseolina is reduced when the broth added with NaCl at 5% (3.15g), 7.5% (3.25g), 10% (3.32g) and 12.5%(3.65g) level and which is followed by P. fluorescens, BCA 1 strain of B. subtilis and Trichoderma viride. Under pot culture conditions, the effect of talc formulated biocontrol agents and challenge inoculation with pathogen was assessed against root rot incidence. It was found that the soil application of TNAU strain of B.subtilis performed better in reducing the root rot incidence at pH of 7.0 (2.37%), 7.5 (4.50%), 8.0 (5.53%) and 8.7 (6.57%) and followed by BCA 1 of B.subtilis in all pH level. Among the biocontrol agents, TNAU strain of B.subtilis applied as seed as well as soil application expressed more population in the rhizosphere in all pH level. The biocontrol agents applied as soil application had more populations of the agents in the soil when compared to seed treatment. The halo tolerance performance of the biocontrol agents was also assessed under field condition in pH of 7.5 and 8.7 during 2019-20 and 2020-21. It was found that the minimum root rot incidence and maximum yield was observed from soil application of TNAU strain of B subtilis at 2.5 kg/ha but the effect is on par with soil application of BCA1 strain of B.subtilis at 2.5 kg/ha.