Induced systemic resistance (ISR) in bean (Phaseolus vulgaris L.) mediated by rhizobacteria against bean rust caused by Uromyces appendiculatus under greenhouse and field conditions

Abstract

Bean rust caused by Uromyces appendiculatus Pers., is one of the major foliar diseases in bean (Phaseolus vulgaris L.) worldwide, which leads to considerable crop loss. Selected fluorescent rhizobacteria were screened for their ability to trigger induced systemic resistance (ISR) against rust in beans under greenhouse and field conditions. Rhizobacteria, applied as seed treatments, were compared to untreated seeds (control) for the suppression of rust. Because of rhizobacteria and the pathogen were spatially separated the phenomenon has to be attributed to ISR. Only three isolates out of four root colonizers namely Pseudomonas fluorescens WM35, Pseudomonas aureofaciens WM09 and Pseudomonas putida WM06 significantly protected bean leaves in detached leaf assays, indicating that apart from the root colonization some other criteria may play a role in triggering ISR by rhizobacteria. Moreover, Pseudomonas aeruginosa 7NSK2 and SA44, soil application of salicylic acid, previously reported ISR inducers in bean, also significantly reduced disease development in greenhouse pot experiments. Under field conditions, WM35, WM09 and WM06 significantly induced ISR against bean rust up to 30 days after seeding (DAS). However, only P. fluorescens WM35 and P. putida WM06 were able to protect bean plants from rust infection throughout the experiment. Therefore, this study clearly demonstrated the ability of rhizobacteria to suppress bean rust under field conditions.