Endospore-forming phyllosphere bacteria from Amaranthus spp. suppress leaf blight (Rhizoctonia solani Kühn) disease of Amaranthus tricolor L.

M. S. Yashaswini, N. S. Nysanth, Pratheesh P. Gopinath, K. N. Anith


Amaranthus (Amaranthus tricolor L.) is the most preferred leafy vegetable of Southern India. Leaf blight incited by Rhizoctonia solani is a devastating disease of amaranthus, especially in the popular red leaf varieties. Many phyllosphere microorganisms have been reported for their antagonism against foliar phytopathogens. Endospore-forming phyllosphere bacteria were isolated from Amaranthus spp. by an efficient “two-step” enrichment process and identified them as Bacillus spp. based on morphological, biochemical and molecular characterization. Their in vitro antagonistic activity against R. solani was tested by dual culture plate assay and detached leaf assay. All the eight isolates showed in vitro antagonism in the plate assay and suppression of development of disease symptom in the leaf assay. Six isolates with better antagonism were selected for further in vivo studies in a greenhouse experiment. Treatments included foliar spray on leaf blight susceptible red amaranthus variety Arun with cell suspension of bacterial isolates and the recommended fungicide Mancozeb (0.2%), pathogen inoculated control and absolute control. Bacillus sp. AL3 obtained from the red amaranthus variety Arun exhibited 44.5 % disease suppression over the pathogen inoculated control. Foliar spray with the recommended fungicide, mancozeb (0.2%), performed poorly in suppressing the disease compared to foliar application of bacterial cell suspension except for a single strain. This forms the first report of exclusive use of endospore-forming phyllosphere bacteria as biocontrol agents against Rhizoctonia solani.


Amaranthus spp.; Bacillus spp.; Endospore-forming bacteria; Leaf blight; Phyllosphere; Rhizoctonia solani

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