Control of root-knot disease of brinjal (Solanum melongena L.) by the application of leaf extracts of certain medicinal plants

Microscopic plant parasitic nematodes are round worms that feed on plants and damage them. The most common and serious amongst the nematodes is the root-knot nematode found throughout the country with a very wide host range of cultivated crops. Brinjal (Solanum melongena) crop yield is considerably reduced by root-knot nematodes particularly Meloidogyne incognita. Root-galls of brinjal caused by Meloidogyne incognita can be controlled effectively by using the bio-agents and botanicals which in turn increases the yield and plant growth. Present study explored the effect of leaf extracts of certain plants on the root-knot development, plant growth and nematode multiplication in pot experiments. Extract treated and nematode inoculated plants showed improvement on growth over untreated inoculated plants and reduced the disease development. Five (viz., margosa, marigold, datura, hemp and tobacco) leaf extracts, irrespective of concentration, apparently induced tolerance in inoculated plants as evidenced by better plant growth in comparison to control and suppressed the multiplication of nematode which resulted in low root-knot index. Margosa (Azadirachta indica) leaf extract suppressed the nematode multiplication, reduced root galling and improved the plant growth of inoculated plants. Margosa and marigold (Tagetes erecta) leaf extracts were found more effective in controlling the root-knot development than the leaf extracts of hemp (Cannabis sativa), datura (Datura metel) and tobacco (Nicotiana tabacum). Higher concentrations (20 ml/plant) of leaf extracts were found to be more effective in controlling the root knot development. Based on our observations, it may be concluded that margosa or marigold extract treatment of brinjal seedlings prior to transplantation can avoid severe damage by suppressing the nematode multiplication and inducing the tolerance in treated inoculated plants.