EVIDENCE OF DISEASE RESISTANCE INDUCED BY RHIZOSPHERE PSEUDOMONAD AGAINST PSEUDOMONAS SYRINGAE pv. PHASEOLICOLA

Abstract

Promotion of plant growth with plant growth-promoting rhizobacteria (PGPR) is sometimes related to disease suppression and induction of general defense responses in plants inoculated with such bacteria. Induced disease suppression was observed after seed bacterization in a bean (Phaseolus vulgaris) challenged with Pseudomonas syringae pv. phaseolicola in greenhouse conditions, both in terms of symptom expression and bacterial viable counts in the leaves and in the intercellular washing fluids (IWF) from the leaves. Comparison of in vitro growth of the pathogenic strain in IWF from protected and unprotected plants suggested that the inhibitory activity against pathogen establishment lies partly in the IWF of bacterized plants 10 days after challenge inoculation. SDS-polyacrylamide gel electrophoresis revealed that the relative levels of proteins had increased in the leaf extracts of protected plants. A correlation was thus found between the reduction in symptom expression and a lower bacterial population in the leaves and a general rise in protein content in the IWF. Poor establishment of the test pathogen in the bean inoculated with PGPR strain Pseudomonas fluorescens, S97 may also involve accumulation of certain phenolic compounds.