INDUCTION OF DISEASE RESISTANCE IN COMMON BEAN SUSCEPTIBLE TO HALO BLIGHT BACTERIAL PATHOGEN AFTER SEED BACTERIZATION WITH RHIZOSPHERE PSEUDOMONADS

Abstract

With the aim of elucidating the immunizing ability of plant-growth-affecting rhizosphere pseudomonads, seeds of a susceptible bean (Phaseolus vulgaris L) cv. Bonita, were subjected to bacterization before challenging with the halo blight bacterial pathogen Pseudomonas syringae pv. phaseolicola. In the greenhouse, induced systemic resistance to halo blight was found in bean plants treated with a plant growth stimulatory strain of P. fluorescens (S 97), whereas deleterious pseudomonads MA 250 and VS 50 were found to induce susceptibility towards the disease. Immunization ability of S 97 was reduced at low inoculum densities (<10⁷ live cells per ml) or eliminated when the suspension was autoclaved. The maximum disease protection, measured in terms of number of halo blight lesions in trifoliate leaves, was obtained at the highest inoculum concentration (10⁸ live cells per ml). Agar diffusion assay in vitro revealed that S 97 exhibits bacteriostatic activity against the bean pathogen. It is suggested that S 97 might evolve substances already during seed germination that are translocated to the foliage; there they might accumulate around the site of bacterial multiplication and contribute to their restricted growth.