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UBC Theses and Dissertations

Non-fumigant alternative soil management practices for mitigating replant disease of fruit trees : mechanisms contributing to Pratylenchus penetrans suppression Watson, Tristan Tanner


Replant disease presents a significant barrier to the reestablishment of orchards. In the Okanagan Valley, Canada, the root-lesion nematode, Pratylenchus penetrans, is widely distributed and implicated in poor growth of newly planted fruit trees. Restrictions on soil fumigants have generated interest in alternative management strategies for disease control. Using a combination of greenhouse and field experiments, this dissertation evaluated the effects of composts, bark chip mulch, biocontrol inoculation, and two different irrigation systems (drip emitter and microsprinkler) on the establishment of apple and sweet cherry trees in old orchard soil, P. penetrans population dynamics, as well as biotic and abiotic factors that may have contributed to enhanced plant growth and nematode suppression. In the first greenhouse experiment, compost amendments, but not biocontrol inoculation, improved growth of apple and sweet cherry seedlings in old orchard soil, suppressed P. penetrans, enhanced soil populations of total bacteria, 2,4-diacetylphloroglucinol-producing (DAPG+) bacteria, pyrrolnitrin-producing (PRN+) bacteria, and altered the composition of the soil microbial community. In the field experiment, compost amendment and surface application of bark chip mulch increased trunk diameters of sweet cherry trees planted at an old orchard site as well as suppressed P. penetrans populations. Compost enhanced rhizosphere populations of total bacteria, DAPG+ bacteria, and PRN+ bacteria, soil microbial activity, soil biological suppressiveness, and root colonization by arbuscular mycorrhizal fungi (AMF). Bark chip mulch enhanced rhizosphere populations of total fungi, soil microbial activity, and soil biological suppressiveness. Drip irrigation promoted greater trunk diameters and fruit yield, suppressed P. penetrans populations, and trees had greater root colonization by AMF relative to microsprinkler irrigation. In the second greenhouse experiment, compost amendments increased plant growth relative to that of untreated soil in six out of twelve of the orchard soil x compost type combinations evaluated, and suppressed P. penetrans in four out of twelve treatment combinations. Inoculation with antagonistic Pseudomonas isolates provided minor plant growth promotion and P. penetrans suppression in orchard soil. Overall, preplant incorporation of composts and surface application of bark chip mulch, alongside the use of drip irrigation resulted in the best establishment of sweet cherry trees in old orchard soil.

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