Endospore-forming bacterial endophytes from Amaranthus spp. improve plant growth and suppress leaf blight (Rhizoctonia solani Kühn) disease of Amaranthus tricolor L

Abstract

Amaranthus (Amaranthus tricolor L.) is a popular vegetable crop grown in South India. Leaves being the main economic part, foliar blight disease caused by Rhizoctonia solani Kühn greatly reduces marketability of the produce. Isolation and characterization of endospore-forming endophytic bacteria (EEB) from endorhizosphere of Amaranthus spp., and their effects on plant growth promotion and suppression of leaf blight disease in a susceptible amaranthus variety are reported here. Eight EEB strains were isolated from roots of healthy Amaranthus spp. through a novel “two-step” enrichment process. They were identified as Bacillus spp. by morphological, biochemical and molecular characterization. In vitro screening tests were performed for plant growth promotion and antagonism against R. solani, and greenhouse experiments were conducted with selected superior isolates. Inoculation with EEB isolate Bacillus amyloliquefaciens GR1, obtained from the leaf blight resistant green amaranthus variety CO-1, significantly improved growth of red amaranthus variety Arun. Fresh weight of shoot portions, the economical part of the crop, recorded 35% increment over that in the uninoculated control. Bacillus sp. WR1, isolated from the leaf blight resistant wild species Amaranthus viridis, suppressed the blight disease in the susceptible red variety Arun to a tune of 41% compared to the pathogen inoculated control. Spray application of the recommended contact fungicide, mancozeb (0.2%), was less efficient in suppressing the disease compared to bacterization of plants with three of the EEB from amaranthus.