Induction of defence-related biochemicals by rhizosphere bacteria against black spot disease of rose

Abstract

Black spot disease caused by Diplocarpon rosae is the most severe and ubiquitous disease of roses. Fungicides used to manage the disease are expensive and generally professed as ‘environmentally unsafe’; therefore, the development of alternative disease management strategies is required. This study was conducted to evaluate the role of rhizosphere bacteria isolated from healthy and infected rose plants to manage black spot disease. A detached leaf assay was performed to select the most virulent pathogenic strain. Then, a greenhouse assay was performed to test the ability of the bacterial strains to manage the disease. Rose plants cv. Gruss an Teplitz were inoculated with bacterial strains in pots followed by pathogen treatment. Strains RB11 and RB4 exhibited the greatest disease management potential, reducing the disease index by more than 60% compared with the control treatment. These strains were identified as Pseudomonas fluorescens and Bacillus subtilis, respectively. Consequential quantitative changes in biochemical markers of plant defence, i.e. phenolics, peroxidase, phenylalanine ammonialyase and polyphenol oxidase activities, and total soluble protein and ascorbic acid concentrations were evaluated in rose plants inoculated with the bacteria. In general, RB11 and RB4 induced higher levels of all these defence-related biochemicals. It was concluded that disease suppression capability of RB11 and RB4 may be due to the potential of these microbes to enhance the production of defence-related biochemicals in plants.