|YANG, M - Northwest A&f University|
|MAVRODI, D. - University Of Southern Mississippi|
|MAVRODI, O. - University Of Southern Mississippi|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2019
Publication Date: 10/11/2019
Citation: Yang, M., Mavrodi, D.V., Mavrodi, O.V., Thomashow, L.S., Weller, D.M. 2019. Exploring the phytotoxic effect of Pseudomonas brassicacearum Q8r1-96 on tomato. Plant Disease. 104(4):1026-1031. https://doi.org/10.1094/PDIS-09-19-1989-RE.
Interpretive Summary: The bacterium Pseudomonas brassicacearum produces the antibiotic 2,4-diacetylphloroglucinol, a key factor in the ability of the strain to control the wheat disease take-all in the Pacific Northwest of the USA. We determined whether the strain also can induce disease in assays using unripe fruits of tomato. A minimum of a million bacteria per milliliter was required to cause visible tissue damage when injected into tomato fruits, and at least ten-fold more of a type III secretion mutant was required to cause symptoms under the same conditions. However, mutants that did not produce the antibiotic were consistently reduced in virulence as compared to the parental strain. Another mutant engineered to overexpress the biocontrol enzyme ACC deaminase, caused a similar amount of tissue damage as the parent strain. We suggest that DAPG plays a significant role in the ability of Q8r1-96 to cause damage to tomato tissue, but other factors also are involved.
Technical Abstract: Pseudomonas brassicacearum has been reported to be a biocontrol and growth-promoting rhizobacterium and a quasi-pathogen. We determined whether P. brassicacearum Q8r1-96, which is typical of the 2,4-diacetylphloroglucinol (DAPG)-producing fluorescent pseudomonads responsible for take-all decline in the Pacific Northwest, can also have pathogenic characteristics. The strain caused visible necrosis when injected into immature tomato fruits but lesion development was dose dependent, with a minimum of 106 CFU/per ml required to cause tissue damage. Type III secretion system (T3SS) mutants of Q8r1-96 injected at a concentration of 107 CFU/ml were significantly reduced in virulence, but not consistently, as compared to the wild-type strain. However, DAPG-deficient (phlD-) mutants of Q8r1-96 were significantly and consistently reduced in virulence as compared to the wild type. Strain Q8r1-96acc, engineered to overexpress ACC deaminase, caused a similar amount of necrosis as the wild type. We suggest that DAPG plays a significant role in the ability of Q8r1-96 to cause necrosis of tomato tissue but other factors are also involved.