Directing the apple rhizobiome toward resiliency post-fumigation

Authors: Somera, Tracey; COOK, CHRIS - Washington State University Extension Service; MAZZOLA, MARK - Stellenbosch University

Submitted to: Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2023
Publication Date: 11/6/2023
Citation: Somera, T.S., Cook, C., Mazzola, M. 2023. Directing the apple rhizobiome toward resiliency post-fumigation. Agriculture. 13(11). Article 2104. https://doi.org/10.3390/agriculture13112104.
DOI: https://doi.org/10.3390/agriculture13112104

Interpretive Summary: As an apple replant disease control strategy, pre-plant soil fumigation is the industry standard. Although fumigation significantly reduces pathogen activity and improves tree growth, this benefit is limited to approximately 1 year. Post-fumigation, orchard soil rapidly re-establishes a microbial community that is indistinguishable from that found in the corresponding non-fumigated replant soil (i.e., a chronic disease state). Mechanical incorporation of pre-plant soil amendments to tree rows following fumigation should fit easily into an orchard management program. Therefore, the application of soil amendments following fumigation is an opportune and crucial time to improve the ability of soil to defend against pathogen re-invasion and improve orchard productivity for an extended period. To that end, our work assessed the potential of a variety of easily attainable, cost-effective amendments to improve biotic and abiotic soil health characteristics following fumigation. Results from this study ground support for the use of soil amendments as an intervention strategy for “steering” the soil and rhizosphere microbiome in more beneficial and/or prophylactic directions following fumigation. Many of the soil amendments used here evidenced compositional changes that encouraged desired outcomes (i.e., an increase in taxa with the potential to suppress disease progression). Although stimulatory towards Pythium, the results of these experiments suggest that insect frass is a promising treatment for boosting the growth of young trees as well as multiple aspects of soil health post-fumigation. Logical next steps include a more comprehensive evaluation of how the amendment affects additional components of the ARD disease complex, optimization of amendment rates, and/or determination of which rootstocks and soil types respond best to the amendment.

Technical Abstract: Currently, there are no standard management practices to counteract the adverse effects of fumigation on the soil microbiome. In this study, a variety of pre-plant soil amendments were examined for their ability to recruit and maintain apple rhizosphere microbiomes that are suppressive to pathogen re-infestation of fumigated orchard soils. The capacity of these amendments to improve other characteristics of soil productivity was also evaluated. Results suggest that composted chicken manure and liquid chitin are likely to be detrimental to plant and soil health when used as a post-fumigation soil amendment. In comparison, insect frass (IF) resulted in a significant increase in tree trunk diameter relative to the fumigated control. Following pathogen re-infestation of fumigated soil, however, IF induced a significant increase in Pythium ultimum in the rhizosphere. Therefore, IF can benefit the growth of young apple trees in fumigated soil but may stimulate pathogen activity upon re-infestation. To date, the possibility of using soil amendments to suppress pathogen re-infestation of fumigated soils has not been tested. Results from this study ground support the use of soil amendments as an intervention strategy for “steering” the soil and rhizosphere microbiome in more beneficial and/or prophylactic directions following fumigation.