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Doctoral thesis2024Open access

Forest Phytophthora – Ecology, Diversity and Management

López-García, Noelia

Abstract

Invasive Phytophthora species significantly threaten the health and productivity of forest ecosystems. This thesis aims to explore the diversity and distribution of pathogenic forest Phytophthora species, as well as their interactions with microbial communities and human activities. We explore existing regulations and management strategies to prevent and control the spread of Phytophthora species across different production settings and ecosystems worldwide. Phytophthora species were isolated from different forest settings in southern-mid Sweden through both direct isolations and a Sanger sequencing approach. To understand the role of the soil microbiome in oak decline, we studied the fungal and bacterial communities in the rhizospheres of both declining and healthy pedunculate oak trees. We used metabarcoding to analyse microbial diversity and composition. We found that current regulations have largely been ineffective in controlling the issues caused by oomycete pathogens. The adaptability of these pathogens and their spread through human activities and international trade highlight the urgent need for exhaustive management approaches and robust legislative measures. Enhancements in testing, detection methods, and phytosanitary infrastructure, along with raised awareness among stakeholders and consumers, are key. Our study identified significant gaps in the practical implementation of existing research, which are attributed to the limited holistic understanding by practitioners of these processes over time and space. Furthermore, there are few or no field experiments, which are essential for validating new treatments and optimizing application methods. Advancements in technology and a better understanding of epidemiology and host resistance are crucial for enhancing surveillance and management tools, enabling more effective control measures. Metabarcoding analysis revealed significant differences in bacterial and fungal diversity between healthy and declining trees, suggesting a bidirectional dependence between tree health and microbial community composition. We isolated eight Phytophthora species, including some newly-identified species and first-time host associations, underscoring the intricate interactions among this pathogen, microbial communities, host trees, and human activities on Phytophthora distribution. Overall, our findings emphasise the need to integrate advanced detection methods, public engagement, and robust legislative measures to develop effective management strategies against Phytophthora diseases, ultimately aiming to protect forest ecosystems from this escalating threat.

Keywords

EU legislation and policie; oomycete dispersal pathways; management practices; biocontrol mechanisms; pesticides; metabarcoding; microbial community; Phytophthora damage; forest decline

Published in

Acta Universitatis Agriculturae Sueciae
2024, number: 2024:67ISBN: 978-91-8046-358-4, eISBN: 978-91-8046-394-2Publisher: Swedish University of Agricultural Sciences