The study evaluated the effect of Ricinus communis aqueous extract on radial growth of Alternaria solani and its most effective concentration. The experiment was laid out using a Completely Randomized Design (CRD) with R. communis extract tested at 3 concentrations of 25, 50 and 100% plus control on Potato Dextrose Agar (PDA) amended medium in 3 replications for 2 separate experiments. Isolation and identification of the early blight pathogen was made by symptoms on tomato plants, macro and microscopic observations in pure culture. Data on radial growth were collected, statistically analysed and percent inhibition (I%) was calculated. Results revealed that, R. communis at 100% concentration recorded the lowest radial growth either at 24, 48 and 72 h post inoculation (hpi) in the first, second, and combined results. The combined results further revealed that, the lowest radial growth 1.43, 2.00, and 2.72 cm were recorded in R. communis treatment at 24, 48 and 72 hpi, respectively. I% varied from 26 to 59%, according to the experimental conditions, and it was then concluded that, R. communis extract used at different concentrations had inhibitory effect on A. solani. It is was then suggested that, R. communis at 100% concentration could be put to field trial to evaluate its effectiveness in the control of the early blight pathogen A. solani.
Key words: Alternaria solani, Ricinus communis, radial growth, concentration.
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