Page 204 - PC2019 Program & Proceedings

PLANT CANADA 2019

S193. Isolation and characterization of endophytic microbes in poplar trees antagonistic to stem
canker causative pathogenic fungus Sphaerulina musiva
*1
1
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1
S. Naik ; S. Palys ; A. Tsang ; P. Perinet ; R. UmaShaanker ; D. Dayanandan
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1 Concordia University; Ministère des Forêts, de la Faune et des Parcs; University of Agricultural
2
Sciences
Species of the genus Populus commonly known as poplars are one of the most widely used groups of
forest trees in North America and Europe, and play a significant ecological role as pioneer species in
boreal forests, and as a dominant species in the riparian forests that serve as rich wildlife habitats and
watersheds. Numerous natural and artificial hybrids of poplars with superior qualities are being widely
used in commercial plantations. However, many hybrid poplars are susceptible to Sphaerulina musiva, the
leaf spot and stem canker causative pathogenic fungal species and limits the utility hybrid poplar as a
plantation tree. Endophytic microbes living inside host plant tissues without causing visible symptoms are
known to produce antimicrobial compounds and emerging as important players in biocontrol of plant
diseases. We isolated endophytic microbes from Populus deltoides, P. balsamifera and their hybrid, P. x
jackii in Quebec and tested against Sphaerulina musiva cultured on Potato Dextrose Agar plates, and
discovered one bacterial and several fungal species antagonistic to S. musiva. The whole genome
sequencing and biochemical characterization of the bacterial species revealed it as a strain of Bacillus
amyloliquefaciens, contains secondary metabolite production gene clusters and produces at least seven
compounds with antifungal activities. Five of these compounds were identified as Iturins, and the
remaining two compounds remain unidentified.

Sachin Naik (me.sach71@gmail.com)

S194. A biosensor assay (GlnLux) for visualizing symbiotic nitrogen fixation output in root systems
involved in the legume–rhizobia symbiosis
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Thilakarathna, M. ; M. Raizada
University of Guelph

+
Inside legume root nodules, atmospheric nitrogen (N2) is fixed into usable nitrogen (NH4 ) by rhizobia
bacteria which is then assimilated into amino acids including glutamine (Gln) for export to shoots. There
is a need for new tools to image in planta nitrogen fixation, assimilation and transport across plant
genotypes and rhizobia strain combinations. Here, we demonstrate the use of companion biosensor cells
called GlnLux (Escherichia coli auxotrophic for Gln and constitutively expressing lux) to image Gln
accumulation in nodulated root systems across a diversity of legume/rhizobia
species. Companion GlnLux cells are embedded into agar (GlnLux-agar) upon which legume root systems
are placed following freeze-thawing to cause Gln leakage. Photons released from nearby activated
biosensor cells are captured using a photon capture camera. Using split root systems, we demonstrate that
in diverse amide-exporting legumes (alfalfa, lentil, and green pea) that GlnLux-agar imaging is
sufficiently sensitive to detect Gln release from individual nodules and can differentiate root systems with
active nif+ from inactive nif− nodules. Using this technology, we show that defoliation of forage legumes
leads to release of Gln as root exudates, but unexpectedly, this release is rapid (starting within 2 hours)
and it originates from not only root tips but also nodules. GlnLux-agar-based imaging is thus a new
research tool to localize the accumulation and transfer of a critical amino acid required for rhizobia
symbionts.

Malinda Thilakarathna (mthilaka@uoguelph.ca)

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