Mechanisms involved in fire blight protection of apple with an hrpL mutant of Erwinia amylovora

Abstract

International audiencehrpL and hrpS mutants of Erwinia amylovora have been shown to be significantly more effective than hrp secretory mutants in preventing apple seedlings and apple flowers from developping fire blight symptoms caused by a virulent strain. Mechanisms involved in the protective effect obtained with an hrpL mutant were investigated. Two histochemical techniques (a two-step staining and an immunostaining technique) indicated that when simultaneously inoculated, cells of the two strains localized mainly in separate areas of the leaf tissues. In addition, leaves infiltrated with the hrpL mutant exibited a significant increase in peroxidase activity in contrast to an hrp secretion mutant. Mechanisms of the protective effect obtained with the hrpL mutant are proposed