Short note on the effects of ethanolic extracts of selected South African seaweeds on the growth of commercially important plant pathogens, Rhizoctonia solani Kühn and Verticillium sp.

Abstract

This paper describes the biological activity of ethanolic extracts from some commonly abundant seaweeds from KwaZulu-Natal, South Africa. The pour-plate method was used to determine the effects of selected seaweed extracts on the growth of two phytopathogens; Verticillium sp. and Rhizoctonia solani . Extracts from Caulerpa filiformis and Ulva rigida (Chlorophyta); Zonaria tournefortii (Phaeophyta); and Hypnea spicifera , Gelidium abottiorum and Osmundaria serrata (Rhodophyta) inhibited fungal growth by more than 50%. The extracts from the rhodophytes, Spyridia cupressina and Beckerella pinnatifida showed the weakest antifungal activity of the seaweeds tested. The pour plate method demonstrated both fungal growth promotion and inhibition, due to the seaweed extracts. At low concentrations (1:16 and 1:32 dilutions) the H spicifera extract promoted the growth of R . solani .