In vitro evaluation of botanicals against the brown leaf spot causing fungus, Alternaria alternata (Fr.) Kiessler in tobacco.
Plant based pesticides which are relatively cheaper, safe and non-hazardous can be used successfully against the plant pathogenic fungi. The present investigation was aimed to study the antifungal activity of six botanicals like NSKE (Azadirachta indica A. Juss), Neem leaf extract (Azadirachta indica A. Juss), Clerodendron leaf extract (Clerodendron inerme (L.) Gaerth.), Congress grass leaf extract (Parthenium hysterophorus L.), Prosopis (Prosopis juliflora (Sw) Dc.) and Tridex (Tridex procumbens L.) against the fungus Alternaria alternata (Fr.) Kiessler causing brown leaf spot of tobacco. The botanicals were studied in vitro at two concentrations (5% and 10%) for their efficacy against A. alternata, by poison food technique. All the six botanicals evaluated against A. alternata were found to be significant. Prosopis (49.05 per cent inhibition of mycelia growth) was significantly superior over all other plant extracts evaluated. The next best treatment was parthenium (22.53 per cent inhibition of mycelia growth), which was on par with NSKE (20.83 per cent inhibition of mycelia growth). Least inhibition was noticed in case of clerodendron (11.05 per cent inhibition of mycelia growth). Irrespective of the plant species, botanicals were found to be the most effective at 10 per cent (24.79%). Interactions between botanicals and concentrations were significant. All the plant extracts reduced the mycelial growth with increase in concentrations. Maximum reduction of mycelial growth (53.26%) was noticed in case of prosopis followed by parthenium (25.06%) at 10 per cent and prosopis (44.83%) at 5 per cent concentration. Least reduction of mycelial growth was noticed in case of Clerodendron (9.84%) at 5 per cent concentration.