Page 210 - PC2019 Program & Proceedings

PLANT CANADA 2019

S205. Cucurbit seeds: Reservoirs of functional and antagonistic microbiomes
Khalaf, E.; M. Raizada
University of Guelph

Seeds are potential vectors that transmit beneficial microbiomes across plant generations, to promote
plant growth and antagonize phytopathogens. The Cucurbitaceae family is consumed by humans
globally, however it is relatively overlooked in microbiome research. Here, we explored the cultivated
and non-cultivated microbiomes associated with seeds of economically important cucurbits encompassing
21 varieties belonging to seven species. The cultivated bacterial library was subjected to in vitro
functional and antagonistic tests along with in planta screening against cucumber powdery mildew. In
parallel, seed DNA was sequenced using Illumina 16S miseq to characterize entire microbiomes. In total,
169 unique bacterial strains were cultured that almost entirely belonged to only two phyla
(Firmicutes, Proteobacteria), with Bacillus constituting 50 % of the library and spanning all tested
cucurbit species. Simultaneously, 16S reads from Illumina sequencing emphasized the dominance of
Firmicutes, in particular spore-forming bacteria (e.g., Clostridium, Bacillus and Paenibacillus) followed
by Proteobacteria. The endophytic library exhibited major beneficial functions such as indole-3-acetic
acid (auxin) production and nitrogen fixation/N-scavenging required for nutrient acquisition and growth
promotion. Surprisingly, the majority of the library (70%) exhibited antagonism to five soil-borne
pathogens (Rhizoctonia solani, Fusarium graminearum, Phytophthora capsici, Pythium aphanidermatum)
and a foliar pathogen, Podosphaera fuliginea. These findings highlight the importance of cucurbit seeds
as natural reservoirs of biofertilizers and biocontrol agents and may help to explain the success of Bacilli
as commercial inoculants.

Eman Khalaf (ekhalaf@uoguelph.ca)

S206. Environmental factors and polyketide synthase gene expression in an usnic acid producing
lichen-fungus
2
2
*1
Gunawardana, D. ; N. Sveshnikova ; M.D. Piercey-Normore
1 Memorial University
2 Grenfell Campus, Memorial University
Lichens are slow-growing and exposed to long-term, extreme micro-environmental conditions, which
resulted in the evolution of unique secondary metabolites for adaptation to the environmental conditions.
One of the most commonly produced secondary metabolites in lichens is usnic acid, thought to be
produced by two genes. The objectives of the present study were to compare PKS gene expression and
amount of usnic acid production in Cladonia uncialis, with two environmental factors (soil pH and
moisture) as well as the presence of neighboring species. Lichen samples were collected within three
locations in Newfoundland using a strip transect method (x5 transects x5 quadrats). Soil pH and moisture
were measured in each quadrat. Usnic acid concentration was measured using HPLC and quantitative
PCR was performed using two PKS genes (MPAO and MPAS) for each lichen thallus sample. The results
showed that the percent ground cover of Cladonia uncialis was affected by soil pH level but not soil
moisture; and it correlated with the percent cover of some other species. Usnic acid concentration was
also affected by soil pH level but not soil moisture. MPAS and MPAO genes expression levels were not
significantly affected by either soil pH level or soil moisture. These findings suggest that soil pH and
neighbouring species may be important for the production of usnic acid by C. uncialis but the genes
involved require further study.

Duleeka Gunawardana (dgunawardana@mun.ca)

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