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UBC Theses and Dissertations

Actinomycete diversity associated with cherry tree rhizospheres and their potential as microbial inoculants Marin Bruzos, Marieta


Cherry production in British Columbia, has increased dramatically over the past 20 years, representing about 96 % of the total Canadian crop. Increased cherry production, along with climate change, has brought new challenges to the Okanagan valley, such as limited water availability and increased soil-borne pathogens. When young cherry trees are planted to replace old apple or cherry orchards Replant Disease (RD) can arise, negatively affecting the establishment of new trees. In the Okanagan valley, RD has been linked to the presence of high populations of the plant-parasitic nematode Pratylenchus penetrans. Overcoming RD is critical for the successful establishment of high-density orchards; hence, environmentally-friendly methods are needed to manage the soil pathogens. The aim of this dissertation was to isolate multifunctional plant-growth-promoting (PGPR) and nematicidal bacteria from cherry rhizospheres, and to determine their possible mode of action. In addition, the potential of the isolated PGPR strains to induce drought resistance in plants was also assessed. Three Streptomyces and two Pseudomonas strains were isolated with potential to be used as microbial inoculants. The PGPR strains have nematicidal and antifungal activity, produce chitinases, proteases, the phytohormone indoleacetic acid, and the 1-aminocyclopropane-1-carboxylate (ACC) deaminase enzyme. The strains were also found to alleviate drought stress in drought-sensitive pepper plants. A second objective was to study the effect of different land management practices (composting, mulching), land-use history (old, new orchards), and fumigation on the abundance of chitinase chiC gene and the diversity of the actinobacterial communities. Chitinase chiC gene has been implicated as a mechanism of biocontrol through hydrolysis of both, nematode egg-shell and phytopathogenic fungal cell walls. The organic amendments did not increase chiC gene abundance, and there were no significant differences in the chiC gene copy number among old and new orchards. However, a higher chiC gene abundance was found in the adjacent non-cultivated soil indicating the detrimental effects of cherry cropping on bacterial chitinolytic populations. The addition of amendments and land-use history did not affect the actinobacterial diversity, in contrast, fumigation with Basamid, a chemical used to control nematodes, significantly decreased the actinobacterial diversity in the soils.

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