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Rhizobacteria associated with crops constitute an important source of potentially beneficial microorganisms with plant growth promoting activity or antagonistic effects against phytopathogens. In this study, we evaluated the plant growth promoting activity of 11 bacterial isolates that were obtained from the rhizosphere of healthy avocado trees and from that of avocado trees having survived root rot infestations. Seven bacterial isolates, belonging to the genera Bacillus, Pseudomonas and Arthrobacter, promoted in vitro growth of Arabidopsis thaliana. These isolates were then tested for antagonistic activity against Phytophthora cinnamomi, in direct dual culture assays. Two of those rhizobacterial isolates, obtained from symptomatic-declining trees, displayed antagonistic activity. Isolate A8a, which is closely related to Bacillus acidiceler, was also able to inhibit P. cinnamomi growth in vitro by 76% through the production of volatile compounds. Solid phase microextraction (SPME) and analysis by gas chromatography coupled with mass spectrometry (GC-MS) allowed to tentatively identify the main volatiles emitted by isolate A8a as 2,3,5-trimethylpyrazine, 6,10-dimethyl-5,9-undecadien-2-one and 3-amino-1,3-oxazolidin-2-one. These volatile compounds have been reported to show antifungal activity when produced by other bacterial isolates. These results confirm the significance of rhizobacteria and suggest that these bacteria could be used for biocontrol of soil borne oomycetes through their volatiles emissions.

Northern Labrador tea, Rhododendron tomentosum ssp. subarcticum, is one of the most commonly used medicinal plants by Inuit and other First Nations peoples of Canada. The phenolic profile and seasonal variation of this commonly used medicinal plant remains largely unknown. To assess optimal harvesting time, R. tomentosum was collected in accordance with traditional knowledge practices bimonthly throughout the snow-free summer in Iqaluit, Nunavut. The antioxidant potency was measured in a DPPH radical scavenging assay, and the anti-inflammatory activity was determined with a TNF-α production assay. The seasonal variation of phenolic content was assessed with HPLC-DAD for fifteen of the most abundant phenolic compounds; (+)-catechin, chlorogenic acid, PARA-coumaric acid, quercetin 3-O-galactoside (hyperoside), quercetin 3-O-glucoside (isoquercitrin), quercetin 3-O-rhamnoside (quercitrin), quercetin pentoside, myricetin, quercetin, 3 procyanidins, and 3 caffeic acid derivatives. The most abundant constituent was (+)-catechin, which made up 19 % of the total weight of characterized phenolics. There was significant seasonal variation in the quantity of all fifteen constituents assessed, whereas there was no seasonal variation of their total sum. The antioxidant activity was positively correlated with phenolic content and negatively correlated with daylight hours. The anti-inflammatory activity was negatively correlated with caffeic acid derivative 1 and daylight hours. Together these results demonstrate that the timing of harvest of R. tomentosum impacts the plant's phenolic content and its antioxidant and anti-inflammatory activities.