Page 317 - PC2019 Program & Proceedings

PLANT CANADA 2019

P207. Cucurbit seed biogels antagonize major plant pathogens
Khalaf, E.; M. Raizada
University of Guelph

The amniotic fluid that surrounds the human embryo possesses compounds with antimicrobial activity
needed to maintain healthy pregnancy and prevent premature delivery. Here we hypothesized that the
mucilaginous tissue (biogel) that naturally coats cucurbit seeds may exhibit antimicrobial protection by
hosting beneficial microbes with antagonistic activity against pathogens. We isolated 34 unique strains
from the wash of aseptically isolated fresh seeds, including the mucilage, belonging to 3 domesticated
cucurbit species (Cucumis sativus, Cucumis melo, Cucurbita pepo) and a wild non-edible cucumber
species (Echinocystis lobata) native to North America.16S rRNA sequences of biogel microbes
(endophytes) assigned them to 12 bacterial genera within three phyla (Firmicutes, Proteobacteria and
Actinobacteria). Bacillus was the most dominant bacterial genus constituting 32% of the identified
endophytes. Interestingly, 62% of the biogel endophytic library showed in vitro antagonism against 4
major soil-borne phytopathogens (Fusarium graminearum, Rhizoctonia solani, Phytophthora capsici,
Pythium aphanidermatum). We conclude that cucurbit seed biogels host potential disease-suppressive
microbiota dominated by Bacilli. We speculate that the biogel microbiomes protect germinating seeds and
seedlings against soil borne pathogens.

Eman Khalaf (ekhalaf@uoguelph.ca)

P208. Evaluating the ability of endophytic bacteria to support boreal forest tree growth
*
Puri, A. ; K. Padda; C. Chanway
University of British Columbia

In natural ecosystems like boreal forests, nitrogen-fixing bacteria could be a potent nitrogen source for
trees growing on nutrient-poor soils. West Chilcotin region in British Columbia is located in the Sub-
Boreal zone where cold climate and low annual precipitation have resulted in dry and weakly-developed
soils lacking essential plant nutrients, particularly nitrogen. Lodgepole pine is the most common tree
species growing in this region. The ability of pine to grow on such nitrogen-limited soils raises a crucial
question regarding its nitrogen sources. We found that pine trees growing in this region harbour several
nitrogen-fixing bacteria in their internal tissues. But, can these bacteria sustain tree growth on nitrogen-
limited soils of this region? To answer this question, we selected six of these bacteria based on their in
vitro nitrogen-fixing ability and tested them in a yearlong greenhouse study with their original host
(lodgepole pine) and another host native to this region (hybrid white spruce). Each bacterium fixed
significant amounts of nitrogen from the atmosphere and considerably enhanced pine and spruce seedling
length and biomass. Particularly, two bacterial strains, Caballeronia sordidicola HP-S1r
and Caballeronia udeis LP-R2r, fulfilled about 50% of nitrogen-requirements of pine and spruce, and
enhanced seedling length and biomass by nearly 1.5-fold and 4-fold, respectively. Therefore, such
bacteria could potentially be used as biofertilizers for trees native to this region, since they represent a
low-cost, environment-friendly alternative to chemical fertilizers.

Akshit Puri (akshit.puri@alumni.ubc.ca)

Page 315 of 339