Abstract
Dry root rot caused by Macrophomina phaseolina is an emerging and highly destructive disease responsible for significant yield losses in groundnut production, particularly in semi-arid tropics regions of the world. The present study aimed to isolate, characterize and evaluate the antagonistic efficacy of bioagents against M. phaseolina via in vitro methods (dual culture, inverted plate and culture filtrate assays) and talc-based formulations of potential Trichoderma and Bacillus isolates under in vivo conditions. A total of sixteen isolates of each fungal and bacterial bioagents were isolated and screened for their inhibitory effects against M. phaseolina. Among these, five Trichoderma isolates (PNT01, PNT05, PNT08, PNT11 and PNT16) and five Bacillus isolates (PNB01, PNB05, PNB10, PNB13, and PNB16) exhibited the highest level of mycelial growth inhibition under in vitro conditions. Molecular characterization revealed that four Trichoderma isolates (PNT01, PNT05, PNT10, and PNT16) were closely related to Trichoderma harzianum species complex, and PNT14 was identical to T. virens. Similarly, the Bacillus isolates PNB05 and PNB10 have similarities with Bacillus subtilis, PNB03 (B. oceanisediminis), PNB13 (B. pacificus), and PNB16 (B. cereus). In the culture filtrate assay, PNT05 (T. harzianum species complex) and PNB10 (B. subtilis) exhibited highest mycelium growth inhibition of M. phaseolina. Field results revealed that the seed treatment combined with soil application of T. harzianum species complex resulted in the maximum reduction in disease inhibition and significant improvement in plant-growth and yield parameters such as germination percentage, shoot length, root length, number of root nodules per plant, number of pods per plant and pod yield followed by seed treatment combined with soil application of B. subtilis. These findings indicate that T. harzianum species complex and B. subtilis may be used as potential biocontrol agents against M. phaseolina, which favours the eco-friendly management of groundnut dry root rot disease.