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Updated: Oct 2, 2026
Aseptic Laboratory Techniques: Plating Methods
Published on: May 11, 2012
The white-line-in-agar test is not specific for the two cultivated mushroom associated pseudomonads, Pseudomonas
Patricia Munsch1, Tapani Alatossava
1University of Oulu, Department of Physical Sciences/Biophysics, University of Oulu, Finland. patricia.munsch@oulu.fi
Abstract:
A sharply defined white line in vitro forms between the pathogenic form of Pseudomonas tolaasii and another Pseudomonas bacterium, referred to as "reactans". This interaction has been considered as highly specific. However, results presented in this study rise doubt about the strict specificity of this interaction, as some other pseudomonads, associated with the cultivated mushroom Agaricus bisporus, also yielded a white line precipitate when they were streaked towards Pseudomonas tolaasii LMG 2342T. Moreover, some Finnish isolates inducing brown blotch symptoms on mushrooms like P. tolaasii(T), produced a typical white precipitate when streaked towards P. "reactans" LMG5329, even though phenotypical and genotypical features exclude these isolates from the species P. tolaasii. We propose that the white-line-in-agar (WLA) test should no longer be considered as an unequivocal diagnostic trait of P. tolaasii.
Insights
The white-line-in-agar test, used to identify Pseudomonas tolaasii, is not as specific as previously thought. Other Pseudomonas species can also produce the characteristic white line, questioning its diagnostic value.
Area of Science:
- Bacteriology
- Plant Pathology
- Microbial Diagnostics
Background:
- The white-line-in-agar (WLA) test is a diagnostic method used to identify the mushroom pathogen Pseudomonas tolaasii.
- This test relies on the formation of a distinct white precipitate when P. tolaasii is streaked against a specific companion bacterium, P.
Purpose of the Study:
- To re-evaluate the specificity of the white-line-in-agar (WLA) test for identifying Pseudomonas tolaasii.
- To investigate whether other Pseudomonas species associated with Agaricus bisporus exhibit the WLA reaction.
Main Methods:
- In vitro streaking of various Pseudomonas isolates, including P. tolaasii LMG 2342T and P. "reactans" LMG5329, against other pseudomonads.
- Observation and documentation of white line precipitate formation between interacting bacterial streaks.
- Phenotypical and genotypical analysis of bacterial isolates.
Main Results:
- Several pseudomonads associated with Agaricus bisporus produced a white line precipitate when streaked towards P. tolaasii LMG 2342T.
- Finnish isolates, phenotypically and genotypically distinct from P. tolaasii, generated a white precipitate with P. "reactans" LMG5329.
- These findings challenge the presumed high specificity of the WLA interaction.
Conclusions:
- The white-line-in-agar (WLA) test is not an unequivocal diagnostic trait for Pseudomonas tolaasii.
- The specificity of the WLA reaction is broader than previously assumed, encompassing other Pseudomonas species.
- Relying solely on the WLA test for P. tolaasii identification may lead to misdiagnosis.
