Management of foliar blight of amaranthus (Amaranthus tricolor L.) caused by rhizoctonia solani kuhn using microbial antagonists

Abstract

The possibility of biological control of foliar blight pathogen of amaranthus Rhizoctonia solani with microbial antagonists was studied. Trichoderma longibrachiatum and a fluorescent Pseudomonas sp., Pl were found to be most effective in inhibiting R. solani in vitro. After mass multiplication the selected antagonists were formulated in an insert carrier material, viz., talc and were tested separately by different methods of application under greenhouse conditions. Soil application followed by foliar spray with one per cent suspension of the formulated product of the microbial antagonists was selected as the best method of delivering the biocontrol agent in checking the disease in vivo. Green house studies conducted indicated that soil application followed by foliar spray with T. longibrachiatum was more effective in suppressing the disease than by either combining the fungal and bacterial antagonists or by applying the bacterial antagonist Pl alone. Further, it was revealed that the abiotic elicitor salicylic acid had no synergistic influence on biocontrol properties of the antagonists. Application of T.longibrachiatum in the soil followed by foliar spray at 15 days interval starting from 25 days after sowing was very effective in controlling the disease in field conditions. There was no appreciable difference in the yield of plants. There was an earlier induction of the enzymes PAL and PO in plants treated with Trichoderma longibrachiatum compared to plants sprayed with mancozeb. Level activity of PO was high in R. solani inoculated plants in the presence of trichoderma longibrachiatum. The content of total phenols in plants treated with T. longibrachiatum was found to be low.