Integrated strategies for the management of root rot disease of medicinal coleus (Coleus forskohlii Briq.) incited by Macrophomina phaseolina (Tassi.) Goid

Abstract

Medicinal coleus (Coleus forskohlii) is a member of mint family Lamiaceae. The crop is affected by many diseases. Among them, the most challenging disease is dry root rot which is caused by Macrophomina phaseolina. The growing use of chemical fertilizers has been witnessing the grave consequence of global economic imbalance as well as environmental pollution. In this context of increased awareness, biocontrol agents and organic amendments can play a significant role in the future agro-economic scenario, as a partial substitute to chemical fertilizers. A survey was conducted in different coleus growing areas of Tamil Nadu and the pathogen associated with root rot infected plants was isolated and identified as M. phaseolina (Tassi.) Goid. Among the different native fungal and bacterial antagonists evaluated, Trichoderma viride (Tv-Ve1), Pseudomonas fluorescens (Pf-K3), Bacillus subtilis (Bs-K3) effectively inhibited the mycelial growth of M. phaseolina under in vitro conditions. Among the different oil cake extracts tested, neem cake (10%) and mahua cake (10%) effectively reduced the mycelial growth of M. phaseolina. The effective antagonists screened under in vitro conditions were further tested in pot culture experiments during the year 2014-15. The results of the pot culture experiment showed that soil application of T. viride (Tv-Ve1) at 5 g pot(-1) recorded the minimum disease incidence followed by T. viride (Tv-Si7) at 5 g pot(-1). The most effective antagonist and oil cake extracts screened both in laboratory and pot culture experiment, were further tested against the root rot disease under artificially inoculated condition. The results revealed that soil application of T. viride Tv-Ve1 (5 g pot(-1)) plus neem cake (20 g pot(-1)) recorded the lowest disease incidence (5.09%) which indicated 93.53% disease reduction over control. It can be concluded from the studies that biocontrol agents and organic amendments have potential to inhibit M. phaseolina when supplied as an organic amendment, thereby, supporting sustainable agriculture.