Disease suppression by the cyclic lipopeptides iturin A and surfactin from Bacillus spp. against Fusarium wilt of lettuce

Iturin A and surfactin are antimicrobial cyclic lipopeptides secreted by antagonistic Bacillus strains, and both elicit defence gene expression in host plants. We previously showed that a soil amendment with either of the purified lipopeptides confers suppression against Fusarium yellows of tatsoi (Brassica rapa) caused by the soil-borne pathogen Fusarium oxysporum and that excess amounts of iturin A or surfactin do not confer suppression. Here, we evaluated the impacts of purified iturin A or surfactin against Fusarium wilt of lettuce (Lactuca sativa). As a soil amendment, iturin A and surfactin each conferred suppression of Fusarium wilt of lettuce on diverse lettuce cultivars similar to the results for tatsoi. However, higher concentrations of iturin A (1.88mg/l of soil or higher) but not of surfactin (up to 7.5mg/l of soil) negated the suppression. Growth of Fusarium in liquid cultures was suppressed by iturin A but not surfactin.