Page 299 - PC2019 Program & Proceedings

PLANT CANADA 2019

P171. Validation of antagonistic activity against fungal pathogens and the presence of antifungal
genes in Pseudomonas chlororaphis strain S1Bt23
Xu, R.; J. Tambong; V. Plante
Agriculture and Agri-Food Canada

Fungal pathogens cause significant yield losses annually to agricultural crops. The use of chemical
pesticides is faced with fungal resistance as well as reported risks to the environment and public health.
Bacterial pesticides are emerging as reliable alternatives. Strains of Pseudomonas chlororaphis are
reported to be excellent candidates due to their ability to produce antifungal compounds. In 2015, a new
strain, S1Bt23, was isolated and classified as Pseudomonas chlororaphis by multilocus sequence analysis
(16S rRNA, recA, gyrB, rpoB and rpoD). The objectives of this project were (1) to confirm the
antagonistic activity of strain S1Bt23; (2) to detect, by PCR, the presence of phenazine and pyrrolnitrin
antifungal gene clusters; and (3) to visualize the antifungal metabolites using thin layer chromatography
(TLC). In in vitro dual-cultures, strain S1Bt23 significantly inhibited the mycelial growth of the six fungi
Rhizoctonia solani, Fusarium graminearum, Alternaria solani, Pythium ultimum, Pythium arrhenomanes
and Sclerotinia sclerotinium. Pyrrolnitrin (4 genes, prnA-D; 5.8 kb) and phenazine (7 genes, phzA-G;
10.2 kb) operons were PCR amplified from the genomic DNA of strain S1Bt23, confirming the presence
of complete clusters. TLC analysis validated the hypothesis that S1Bt23 secretes phenazine-1-carboxylic
acid (PCA) and the extracts inhibited the growth of Pythium arrhenomanes. TLC results were confirmed
by high pressure liquid chromatography. In conclusion, strain S1Bt23 embodies the desired characteristics
for greenhouse and field studies as a potent biopesticide.

Renlin Xu (renlin.xu@canada.ca)

P172. Growth inhibition of the plant pathogen, Streptomyces scabies, using plant tinctures
*
Bakke, A. ; M. Vatta; R. Merrill
University of Guelph

Streptomyces scabies is a species of pathogenic bacteria that infects tuber crops through a specific
pathway, causing the common scab disease. When this bacterium is in a germinating spore state, it infects
tubers in various crops through natural openings and lesions. S. scabies uses a virulence factor called
thaxtomin A in its infectious pathway once the crop has been contaminated. This poster outlines multiple
methods used to measure S. scabies growth and for discovery of plant tinctures as natural antimicrobials
towards this pathogen. It was determined that the Methylene Blue Assay (MBA) is an effective method
for monitoring bacterial growth. A growth curve for S. scabies constructed using the MBA gave a
doubling time of 6 hours. The MBA, in tandem with agar diffusion, was used to test a library of plant
tinctures as S. scabies growth inhibitors. These experiments demonstrate the potential role of plant
tinctures as antimicrobials and their utility for bacterial disease management.

Amanda Bakke (abakke@uoguelph.ca)

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