Efficacy of different combinations of microbial biocontrol agents against sheath blight of rice caused by Rhizoctonia solani

Abstract

Background: Sheath blight of rice caused by Rhizoctonia solani is one of the most important diseases worldwide, causing considerable yield losses. The estimation of losses due to sheath blight of rice in India has been reported to be up to 54.30%. As a consequence of this fact, eco-friendly approaches were explored in this investigation. Results: The pathogen R. solani was isolated from the infected sheath of rice plant, which was identified and characterized on the basis of morphology and through molecular Sequencing. The sequences of ITS were submitted to NCBI GenBank and the accession number allotted is SUB11543577. In dual culture best two potential isolates of biocontrol agents were selected Pseudomonas fluorescens (Pf27) and Trichoderma harzianum (Th47). Their different combinations with Herbal Kunapajala (HKJ) were tested in glasshouse, experimental field and farmers’ fields against sheath blight pathogen R. solani. The maximum plant vigor index was found in treatment combination P. fluorescens (27) + T. harzanium (47) + Herbal Kunapajala, seed treatment, soil drenching and three foliar applications. Minimum disease severity and incidence at 30 days after sowing (DAS) and 60DAS, maximum Phenylalanine Ammonia Lyase Activity (PAL), Polyphenol Oxidase Activity (PPO) and Peroxidase Activity (PO) were also recorded in the same treatment. In field experiment the maximum population of biocontrol agents after 60 days of transplanting cfu/g soil for Trichoderma spp. (32.33 × 104) and Pseudomonas spp. (36.33 × 104) in rhizosphere and in rhizoplane. Maximum cfu/g soil for Trichoderma spp. (24.67 × 104) and Pseudomonas spp. (24.0 × 104) was observed in treatment Th + Pf + HKJ [seed treatment + soil drenching + foliar spray]. At experimental and farmers field minimum disease severity, disease incidence at 60 DAT was recorded in treatment Th + Pf + HKJ [seed treatment + soil drenching + foliar spray] and was at par with the chemical treatment Carbendazim, but the maximum yield was obtained in the treatment Th + PF + HKJ [seed treatment + soil drenching + foliar spray] due to the maximum growth promotion activity. Conclusions: Among various treatment seed treatment, soil drenching and three foliar sprays with combination T. harzianum (47), P. fluorescens (27) and Herbal Kunapajala was found very effective in reducing the disease incidence, disease severity and increasing growth promotion activity at all conditions. Therefore, the recommendation of this investigation could be exploited under bio-intensive disease management program for sustainable cultivation of rice.