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Laboratory study was conducted to evaluate the effect of leaf extracts of five indigenous plant on conidia germination, growth and sporulation of Pseudoperenospora cubensis causing downy mildew disease of muskmelon. Extracts of five plant; mexican sunflower (Tithonia diversifolia), bush banana (Uvaria chamae), salt and oil tree (Cleistopholis patens), goat weed (Ageratum conyzoides) and African eggplant (Solanum macrocarpon) at Four concentrations (15, 30, 45 and 60%) were tested against the growth, conidial germination and sporulation of Pseudoperenospora cubensis in vitro.
Results show that all the plant extracts significantly inhibited conidia germination and radial growth compared to the control. The extracts had no significant (p≤0.05) effect on sporulation. The rate of inhibition of growth and conidia germination was concentration dependent being highest at 60% for the extracts. The extracts of Solanum macrocarpon was the most effective followed by Ageratum conyzoides, Cleistopholis patens and Uvaria chamea whileTithonia diversifolia caused the least inhibition of growth and conidia germination. At 15, 30, 45 and 60% concentrations growth of Pseudoperenospora cubensis on PDA modified with Solanum macrocqrponwere 3.79, 3.65, 3.33 and 2.87; and 4.25, 4.12, 3.92 and 3.89 for PDA modified with Tithonia diversifolia. Similarly, conidia germination percentages recorded at same concentration of extracts S. macrocarpon were 87, 85, 70 and 62% while that of T. diversifolia were 91, 87, 84 and 72%. The study shows that the plant extracts has the potential for inhibition of the pathogen.