AUTHOR=Takishita Yoko , Charron Jean-Benoit , Smith Donald L. 

TITLE=Biocontrol Rhizobacterium Pseudomonas sp. 23S Induces Systemic Resistance in Tomato (Solanum lycopersicum L.) Against Bacterial Canker Clavibacter michiganensis subsp. michiganensis

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.02119

DOI=10.3389/fmicb.2018.02119

ISSN=1664-302X

ABSTRACT=<p>Tomato bacterial canker disease, caused by <italic>Clavibacter michiganensis</italic> subsp. <italic>michiganensis</italic> (<italic>Cmm</italic>) is a destructive disease and has been a serious concern for tomato industries worldwide. Previously, a rhizosphere isolated strain of <italic>Pseudomonas sp.</italic> 23S showed antagonistic activity toward <italic>Cmm in vitro</italic>. This <italic>Pseudomonas sp</italic>. 23S was characterized to explore the potential of this bacterium for its use in agriculture. <italic>Pseudomonas sp</italic>. 23S possesses ability to solubilize inorganic phosphorus, and to produce siderophores, indole acetic acid, and hydrogen cyanide. The strain also showed antagonistic activity against <italic>Pseudomonas syringae</italic> pv. <italic>tomato</italic> DC 3000. A plant assay indicated that <italic>Pseudomonas sp</italic>. 23S could promote growth of tomato seedlings. The potential of treating tomato plants with <italic>Pseudomonas sp.</italic> 23S to reduce the severity of tomato bacterial canker by inducing systemic resistance (ISR) was investigated using well characterized marker genes such as <italic>PR1a</italic> [salicylic acid (SA)], <italic>PI2</italic> [jasmonic acid (JA)], and <italic>ACO</italic> [ethylene (ET)]. Two-week-old tomato plants were treated with <italic>Pseudomonas sp.</italic> 23S by soil drench, and <italic>Cmm</italic> was inoculated into the stem by needle injection on 3, 5, or 7 days post drench. The results indicated that plants treated with <italic>Pseudomonas sp</italic>. 23S, 5 days prior to <italic>Cmm</italic> inoculation significantly delayed the progression of the disease. These plants, after 3 weeks from the date of <italic>Cmm</italic> inoculation, had significantly higher dry shoot and root weight, higher levels of carbon, nitrogen, phosphorus, and potassium in the leaf tissue, and the number of <italic>Cmm</italic> population in the stem was significantly lower for the plants treated with <italic>Pseudomonas sp.</italic> 23S. From the real-time quantitative PCR (qRT-PCR) analysis, the treatment with <italic>Pseudomonas sp.</italic> 23S alone was found to trigger a significant increase in the level of <italic>PR1a</italic> transcripts in tomato plants. When the plants were treated with <italic>Pseudomonas sp.</italic> 23S and inoculated with <italic>Cmm</italic>, the level of <italic>PR1a</italic> and <italic>ACO</italic> transcripts were increased, and this response was faster and greater as compared to plants inoculated with <italic>Cmm</italic> but not treated with <italic>Pseudomonas sp.</italic> 23S. Overall, the results suggested the involvement of SA signaling pathways for ISR induced by <italic>Pseudomonas sp.</italic> 23S.</p>