In vitro studies of some plant extracts against Rhizoctonia solani Kuhn infecting FCV tobacco in Karnataka Light Soil, Karnataka, India

The antifungal effect of 10 plant extracts viz., Thevetia peruviana, Ocimum basilicum, Piper betel, Murraya koenigii, Chrysanthemum coronarium, Polyalthia longifolia, Catharanthus roseus, Pelargonium graveolens, Moringa officinalis and Lawsonia inermis were evaluated by poisoned food technique against Rhizoctonia solani Kuhn, the causal organism of sore shin disease of tobacco. Among all the plants screened only four plants namely, Lawsonia inermis, Piper betel, Polyalthia longifolia and Pelargonium graveolens have recorded significant antifungal activity against Rhizoctonia solani. The effective concentration inhibiting the growth of mycelium and sclerotia formation of the pathogen by the plant extract of Piper betel was at 50% concentration, Lawsonia inermis inhibited the growth at 75%, and Polyalthia longifolia and Pelargonium graveolens suppressed the growth at 100% concentration. Organic solvents viz., n-hexane, ethyl acetate and methanolic extracts of four plants viz., Lawsonia inermis, Piper betel, Polyalthia longifolia and Pelargonium graveolens were investigated for their antifungal activity against this phytopathogenic fungus. Ethyl acetate extracts showed 100% inhibition of mycelial growth and sclerotia formation of Rhizoctonia solani at 1000 ppm. Methanol extracts moderately inhibited the growth at 1000 ppm and n-hexane extracts were not effective against the test organism. Aqueous extract of Piper betel can be recommended to the farmers for the control of Rhizoctonia solani.