Effect of plant extracts on growth of Alternaria porri (Ellis) Cif. and other fungal pathogens of onion

Abstract

This study was undertaken to establish the potential of crude plant extracts of Warburgia ugandensis Sprague, Solanum nigrum L., Cleome gynandra L. and Acocanthera schimperi (ADC) Schweinf for the control of Alternaria porri the causal agent of onion purple blotch and other onion fungal pathogens. The effect of three concentrations of the test plants' extracts on the radial mycelial growth of A. porri was determined using onion leaf decoction agar (OLDA) amended with the extracts. A crude extract of Solanum nigrum L. at concentration levels 0.1, 0.05, 0.025 g ^-l water, inhibited the growth of A. porri completely while extracts of Warburgia ugandensis Sprague (0. 1 g ^–l water) and Cleome gynandra L. (0.1 g ^–l water) inhibited the growth by 56.7 and 44.8 %. The survival of all onion pathogens after culturing in extracts for 6 hours indicates that the time is not adequate to kill the spores of A. porri , A. niger, A. alternate and Stemphylium vesicarium. However, after 24 hours, the fungi survival was nil except for A. niger that was not affected by these crude extracts. In vitro studies indicated that S. nigrum L. extract was fungitoxic while that of C. gynandra L. was fungistatic and had potential for managing purple blotch.

Keywords: Purple blotch, Alternaria porii, Crude plant extracts, Solanum nigrum L., Warburgia ugandensis Sprague, Cleome gynandra L., Acocanthera schimperi (ADC) Schweinf.

> Journal of Tropical Microbiology and Biotechnology Vol. 3(1) 2007: pp. 7-11