Evaluation of Neem Seed Extract for the Management of Early Blight (Alternaria solani) Disease of Tomato (Solanum lycopersicum L.)

Abstract

Early bight disease of tomato caused by the fungus, Alternaria solani, accounts for significant yield losses in tomato production annually. This research evaluated the use of aqueous neem seed extract for the management of early blight disease of tomato (Solanum lycopersicon L.)in a screenhouse experiment. Infected samples of tomato leaves and fruits were collected from an experimental plot at the University of Ibadan for isolation of associated fungi. Five kilogrammes of sterilizedsoil were filled into 20cm diameter experimental pots laid out in acompletely randomized design with six treatments and three replications. A susceptible variety of tomato („Cobra‟) was used as the test crop. Three concentrations, 50 g, 100 g, and 200 g per litre of neem seed extract were applied a week before and after inoculation. Synthetic mancozeb fungicide was used as positive control. The inoculum was quantified using the serial dilution method, and a concentration of 106condidia/ml was applied on the plants. Pathogenicity, incidence and severity of isolates were determined following standard procedures. Data were collected on number of leaves, plant height (cm), stem diameter(cm), cumulative fruit weight (g) and total dry matter yield (g) per plant. Plants inoculated and sprayed with aqueous neem seed extract had the lowest disease incidence (40%) and severity score (1) of the early bight disease relative to other treatments. Plants inoculated and sprayed with aqueous neem seed extract also showed significant increase in yield and growth parameters and compared favourably with mancozeb synthetic fungicide. Neem concentrations used in this study reduced the incidence and severity of early blight disease to 33.3-45.1% and 20.7-29.4%,respectively relative to plants treated with mancozeb fungicide (12.8%and 10.6%, respectively). Although aqueous neem seed extract showed potential in the management of early blight disease of tomato, further studies and field investigations should be carried out to explore the possible application of neem seed extract in the integrated management of the disease.