Phytophthora agathidicida: research progress, cultural perspectives and knowledge gaps in the control and management of kauri dieback in New Zealand

Abstract

Kauri (Agathis australis), which is one of the world's largest and longest‐living conifer species, is under threat from a root and collar dieback disease caused by the oomycete pathogen Phytophthora agathidicida. The noted incidence of kauri dieback has increased in the past decade, and even trees >1000 years old are not immune. This disease has profound effects on both forest ecosystems and human society, particularly indigenous Māori, for whom kauri is a taonga or treasure of immense significance. This review brings together existing scientific knowledge about the pathogen and the devastating disease it causes, as well as highlighting important knowledge gaps and potential approaches for disease management. The life cycle of P. agathidicida is similar to those of other soilborne Phytophthora pathogens, with roles for vegetative hyphae, zoospores and oospores in the disease. However, there is comparatively little known about many aspects of the biology of P. agathidicida, such as its host range and disease latency, or about the impact on the disease of abiotic and biotic factors such as soil health and co‐occurring Phytophthora species. This review discusses current and emerging tools and strategies for surveillance, diagnostics and management, including a consideration of genomic resources, and the role these play in understanding the pathogen and how it causes this deadly disease. Key aspects of indigenous Māori knowledge, which include rich ecological and historical knowledge of kauri forests and a holistic approach to forest health, are highlighted.

Kauri dieback

“…1 in Bradshaw et al, 2020). As noted in their review, this interpretation is the basis of present disease management, including actions such as track closures and the provision of disinfectant shoe cleaning stations, intended to stop further dispersal (Bradshaw et al, 2020). Under a “precautionary principle” this is a reasonable and sensible approach while it is not fully known how the pathogen is behaving.…”

“…Kauri dieback, as it is known, is caused by the root‐ and butt‐infecting oomycete, Phytophthora agathidicida . Research into the nature and control of the disease has been extensive and ongoing, and was reviewed by Bradshaw et al (2020) in a paper published in Plant Pathology . The review was thorough and wide ranging and the authors were appropriately cautious regarding the status of the pathogen.…”

Screening a Natural Product-Inspired Library for Anti-Phytophthora Activities

“…At present, one of the most effective treatments for both Phytophthora species is potassium phosphite [12][13][14][15], which functions both as an antimicrobial and as an inducer of host defence mechanisms [16][17][18]. While phosphite is relatively effective and has low environmental toxicity, it does not eradicate the pathogens, meaning ongoing treatment is required [14].…”

“…Phytophthora agathidicida is the causative agent of kauri dieback, a disease afflicting the kauri ( Agathis australis ) forests of northern New Zealand. Kauri are one of the largest and longest-living tree species in the world, and these trees are both culturally and ecologically significant to New Zealand [ 12 ].…”

Early infection by Phytophthora agathidicida up‐regulates photosynthetic activity in Agathis australis seedlings

“…The pathogen infects the living tissue consuming available sugars and nutrients, undermining the tree's physiological resilience and eventually killing the tree Bellgard et al (2019)The infection progresses to the root collar of the tree forming a canker that exudes resin, causing vascular dysfunction inhibiting water and nutrient uptake (Bellgard et al, 2016;Shilton, 2017). These symptoms represent the chronic phases of the disease but P. agathidicida probably infects the fine roots many years before above-ground symptoms become visible (Bradshaw et al, 2020).…”