INDUCED SYSTEMIC RESISTANCE IN RADISH IS NOT ASSOCIATED WITH ACCUMULATION OF PATHOGENESIS-RELATED PROTEINS

The non-pathogenic Pseudomonas,fluorescens strain WCS417r has been sho wn to induce systemic resistance in radish against Fusarium oxysporum f.sp. raphani. In this paper we investigate the involvement of pathoge nesis-related (PR) proteins in this Pseudomonas induced resistance. Fo r comparison, salicylic acid (SA) and isonicotinic acid (INA) were use d as inducers. It appeared that in our rock wool artificial soil syste m both strain WCS417r and SA could induce resistance, whereas strain W CS4 17r-B4, a lipopolysaccharide-mutant, and INA could nor. The induce d resistance was expressed as a reduction in the percentage of disease d planes, but not in the disease severity. Western blot analyses revea led that in the control plants PR-2 is constitutively present in the i ntercellular fluid of leaves and PR-3 in the roots. Treatment with eit her of the inducing agents, with or without. pathogen-inoculation, ind uced no further accumulation of cross-reacting homologues of PR-1-5. W e concluded that in our system induction of systemic resistance by str ain WCS417r and SA is not associated with accumulation of PRs proteins . This demonstrates that accumulation of PR proteins is not a prerequi site for the expression of induced systemic resistance.