Assessing the effectiveness of oxathiapiprolin towardPhytophthora agathidicida, the causal agent of kauri dieback disease

Abstract

Phytophthora species cause disease and devastation of plants in ecological and horticultural settings worldwide. A recently identified species, P. agathidicida, infects and ultimately kills the treasured kauri trees (Agathis australis) that are endemic to New Zealand. Currently there are few options for managing kauri dieback disease. In this study, we sought to assess the toxicity of the oomycide oxathiapiprolin against several life cycle stages of two geographically distinct P. agathidicida isolates. The effective concentration to inhibit 50% of mycelial growth (EC50) was determined to be approximately 0.1 ng/ml, indicating that P. agathidicida mycelia are more sensitive to oxathiapiprolin than those from most other Phytophthora species that have been studied. Oxathiapiprolin was also highly effective at inhibiting the germination of zoospores (EC50 = 2–9 ng/ml for the two isolates) and oospores (complete inhibition at 100 ng/ml). In addition, oxathiapiprolin delayed the onset of detached kauri leaf infection in a dose-dependent manner. Collectively, the results presented here highlight the significant potential of oxathiapiprolin as a tool to aid in the control of kauri dieback disease.

Sensitivity of the soil-borne pathogen Phytophthora agathidicida, the causal agent of kauri dieback, to the anti-oomycete fungicides ethaboxam, fluopicolide, mandipropamid, and oxathiapiprolin

“…The EC 50 values reported here are consistent with those of other pathogenic Phytophthora species (Gray et al 2018, Belisle et al 2019. Furthermore, the EC 50 value reported for oxathiapiprolin inhibition of P. agathidicida mycelial growth is in agreement with that from a recent study (Lacey et al 2021).…”

“…As has been widely found, Phytophthora pathogens appear to be most sensitive to oxathiapiprolin when compared with ethaboxam, fluopicolide, and mandipropamid (Qu et al 2016, Gray et al 2018, Belisle et al 2019. A recent report of oxathiapiprolin activity against P. agathidicida zoospores and oospores found that this fungicide was also highly toxic to other P. agathidicida life cycle stages (Lacey et al 2021). Thus, it would be pertinent to screen ethaboxam, fluopicolide, and mandipropamid against P. agathidicida spores to characterise differences in fungicide sensitivity across life cycle stages of this pathogen, which could inform potential application methods.…”

Evaluating the potential of environmentally friendly compounds to deactivate different life stages of Phytophthora species

“…Additionally, their thick cell walls help them withstand harsh environmental conditions and remain resistant to chemical treatments such as sterigene (Bellgard et al, 2010; Dick & Kimberley, 2013). To the best of our knowledge, only disinfectants such as Janola (sodium hypochlorite, active ingredient; Bellgard et al, 2010; Dick & Kimberley, 2013), Virkon S (dipotassium peroxodisulphate; Bellgard et al, 2010; Dick & Kimberley, 2013) and the antibiotic oxathiapiprolin (Lacey et al, 2021) have shown any noticeable activity against oospores of P . agathidicida .…”

“…Continuous use also leads to Phytophthora developing resistance to the treatments (Dobrowolski et al, 2008; Hunter, Williams, et al, 2018). Additionally, they are not biodegradable and none of these compounds except oxathiapiprolin (Lacey et al, 2021) are reported to be active against multiple life stages of Phytophthora (Dick & Kimberley, 2013). Resistance to oxathiapiprolin by some Phytophthora has been reported since its approval as a fungicide in 2016 (Miao et al, 2020).…”

A method for quantifyingPhytophthoraoospore viability using fluorescent dyes and automated image analysis

“…P. agathidicida oospores were prepared as described previously (Lacey et al 2021). Briefly, cultures were grown in 4% w/v clarified V8 broth supplemented with 30 µ g/ml β-sitosterol (Sigma-Aldrich, St. Louis, Missouri) and incubated in the dark at 22 °C for 4 to 6 weeks.…”