ABSTRACT
Plants and soil microorganisms interact at every stage of growth. Pseudomonas spp. are highly regarded for their ability to increase crop production and protection from diseases. The aim of this study is to understand the mechanisms of the rhizobacterial colonization of tomato roots via chemotaxis assay and the activation of tomato resistance against the pathogenic bacterium, Pseudomonas syringae pv. tomato DC3000 (Pst). The capillary assay was used to evaluate the chemotaxis response of PGPRs (plant growth-promoting rhizobacteria). The activities of defense enzymes and the expressions of PR (pathogenesis-related) genes were measured using real-time qPCR. Chemotactic responses to malic and citric acids (the most important root exudates found in different plant species) at low concentrations varied substantially among the rhizobacterial isolates (63 species). Beneficial isolates including Pseudomonas resinovorans A5, P. vranovensis A30, P. resinovorans A28, P. umsongensis O26, P. stutzeri N42, and P. putida T15 reacted well to different concentrations of root exudates. P. putida T15 demonstrated the most potent anti-Pst activity. At three and six days after inoculation, the greatest levels of polyphenol oxidase and peroxidase activity were reported in the A5 and T15 groups. In tomato, transcript levels of four PR (pathogenesis-related) genes were elevated by rhizobacterial treatments. PGPR isolates alone or in combination with BABA (ß-amino butyric acid) up-regulated the transcriptions of PR1, PR2, LOX, and PAL genes. Treatments with N42 and T15 resulted in the greatest improvements in tomato growth and yield traits. In conclusion, the results explain the mechanisms of rhizobacterial colonization for the improved management of Pst. Rhizobacterial isolates play a role in tomato's resistance to Pst via salicylic acid and jasmonic acid pathways.
ABSTRACT
BACKGROUND: Induced resistance against several plant pathogens was reported using different beneficial plant growth-promoting microorganisms. The potential of five fungal isolates, Trichoderma harzianum GT 3-2, Fusarium equiseti GF 18-3, F. equiseti GF 19-1, Phoma sp. GS 10-1 and Phoma sp. GS 14-1, to stimulate tomato growth and resistance against bacterial speck disease caused by Pseudomonas syringae pathovar (pv.) tomato DC3000 was evaluated. RESULTS: Based on the results of disease severity and growth promotion experiments, GF 18-3 exhibited the best results among all fungal isolates. Treatment with barley grain inocula (BGI) and culture filtrate (CF) of the isolates promoted tomato growth and suppressed the pathogen in pot trials. Furthermore, expressions of the pathogenesis-related genes (PR-1, ß-1,3-glucanase A, ß-1,3-glucanase B and LOX) were relatively higher than the control in the leaves of tomato plants treated with both BGI and CF. The transcription levels remained consistently higher than the control plants for 6 days post-inoculation with pathogen. CONCLUSION: Taken together, the results indicate that the tested fungal isolates have the potential to promote tomato growth and induce systemic resistance against the bacterial speck disease. Analysis of certain PR gene expression revealed significant activation in both BGI and CF treatments, leading to stimulated resistance against the pathogen. © 2021 Society of Chemical Industry.
