BARC Biostimulant 1, a novel Streptomyces rochei C3-based formulation for disease biocontrol and plant growth promotion

Pythium aphanidermatum is a very destructive plant pathogen causing damping-off disease of vegetable seedlings in nurseries. In addition, this plant pathogenic oomycete causes seed, stem and rhizome rot, as well as post-harvest diseases. Currently, the disease management relies heavily on high dosages of chemicals like metalaxyl and copper oxychloride biocides, which are not only expensive, but are hazardous to the ecosystem. In our quest for developing a disease management strategy that is economical and safe, we isolated a strain of an actinobacterium that is highly inhibitory to P. aphanidermatum, the major cause of damping-off disease. Based on morphology and 16S rRNA sequence analysis, we identified this isolate as Streptomyces rochei. Using an LC-MS/MS analysis, the inhibitory principle has been tentatively identified as (4 S)-4,5-dihydro-4-hydroxygeldanamycin.We developed a novel formulation “BARC Biostimulant 1” using split tamarind seeds as a substrate and talcum powder as a carrier and S. rochei as the active ingredient. In P. aphanidermatum-infested soil, seed treatment and drenching resulted in about 50 % improvement in germination in greenhouse assay and protected field experiments. Under open field conditions, the germination improved to the extent of 20 %. In addition to suppression of the disease, the formulation also improved plant growth parameters like weight and height of seedlings, and induced defense responses. We further undertook multi-location replicated field trials to evaluate this purely organic formulation as a biostimulant across four states of India. Seed treatment with BARC Biostimulant 1 at the rate of 5 g/ kg seeds enhanced germination of seedlings by 80 % and enhanced fresh weight by 105 % (average of four locations), indicating a good commercial potential of this formulation.