Toward a holistic view of orchard ecosystem dynamics: A comprehensive review of the multiple factors governing development or suppression of apple replant disease

Authors: Somera, Tracey; MAZZOLA, MARK - Retired ARS Employee

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/4/2022
Publication Date: 7/5/2022
Citation: Somera, T.S., Mazzola, M. 2022. Toward a holistic view of orchard ecosystem dynamics: A comprehensive review of the multiple factors governing development or suppression of apple replant disease. Frontiers in Microbiology. 13. Article 949404. https://doi.org/10.3389/fmicb.2022.949404.
DOI: https://doi.org/10.3389/fmicb.2022.949404

Interpretive Summary: This study aims to provide clarification regarding long-standing confusion surrounding the causes of Apple Replant Disease. This will include a discussion of how various biotic elements contribute to disease etiology depending on geographic location. The study will also include new scientific findings/data on the role of specific root exudates in disease progression. Finally, we will propose a model for the transition of orchard soil from a healthy state to a replant disease conducive state. The manuscript is designed to enable change within the research community towards reliable identification of causative agents and to provide new research insights into apple replant disease.

Technical Abstract: Replant diseases are a common occurrence in perennial cropping systems, and a similar suppression of growth and yield often emerges from the monoculture of annual cropping systems. In apple, progress towards the development of a universally effective disease management strategy, beyond the use of broad-spectrum soil fumigants, is impeded by inconsistencies in defining replant disease etiology. A preponderance of evidence attributes apple replant disease to plant-induced changes in the soil microbiome including the proliferation of soil-borne plant pathogens. Findings from alternative studies suggest that the contribution of abiotic factors, such as the accumulation of phenolic detritus from previous orchard plantings, may play a part as well. Recent research on engineering of the resident soil microbiome using resource-based strategies is demonstrating the potential to limit activity of replant pathogens and improve productivity in newly established orchards. In addition to understanding resource-based microbial recruitment factors instrumental to facilitating pathogen suppression, developing a more holistic view of orchard ecosystem dynamics also requires consideration of host factors that confer disease tolerance or resistance. Here, we review the literature concerning the transition of orchard soil from a healthy state to a replant disease conducive state. Included in the scope of this review are studies on the influence of soil type and geography on the apple replant pathogen complex. Furthermore, several tolerance and innate resistance mechanisms that have been described in apple to date, including the role of root chemistry/exudates are discussed. Finally, the interplay between apple rootstock genotype and key resource-based strategies which have been shown to “reshape” the plant holobiont in favor of a more prophylactic or disease-suppressive state is highlighted. A comprehensive understanding of the multiple factors and mechanisms leading to the evolution or suppression of apple replant disease is essential to the optimal integration of amendment-based management approaches with disease-tolerant or resistant apple rootstocks.