Comparative evaluation of composts and dried powdered biomass of botanicals for organic management of downy mildew of sorghum

Abstract

The biomass of 10 selected botanicals was evaluated as soil amendments, in the form of composts and dry powder biomass, to compare their potential to suppress downy mildew disease caused by oosporic inoculum of Perenosclerospora sorghi. Eight botanicals (Allium cepa, Lantana camara, Polyalthia longifolia, Hyptis suaveolens, Azadirachta indica, Nerium oleander Eucalyptus globulus and Tamarindus indica) proved effectively in the form of dry biomass powder at 4% (w/w) rate to control infection by oospores, while two (Croton sparsiflorus and Tagetes erecta) promoted it. In the form of composts (2% rate), the efficacy of botanicals was generally found reduced with the appearance of more disease than negative control in case of all botanicals except one (A. cepa). At the 4% compost rate, only four botanicals namely, A. cepa, P. longifolia, H. suaveolens and L. camara were found to suppress the disease. At higher amendment rates of 6, 8 and 10%, six botanicals suppressed the disease. Dry powders are not only superior in disease suppression but confer additional benefits like reduced bulk, increased shelf life, consistent composition and results.

Keywords:

• downy mildew
• sorghum
• organic management
• Peronosclerospora
• compost
• shelf-life

Acknowledgements

The authors are thankful to the University Grants Commission for financial support to carry out this work. The authors also thank Dr H. Shekar Shetty, Emeritus Professor, Department of Biotechnology, University of Mysore, Mysore, for his valuable suggestions. The authors acknowledge Dr M.Y. Kamatar, Professor, Department of Genetics and Plant Breeding, University of Agricultural Sciences (U.A.S.), Dharwad, Karnataka, India and Dr Y.D. Narayana, Principal Scientist (Pathology), All India Co-ordinated Sorghum Improvement Project, U.A.S., Dharwad, Karnataka, India, for providing sorghum seeds.