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.

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 that are endemic to New Zealand. Currently there are few options for controlling or treating P. agathidicida. In this study, we sought to assess the toxicity of the oomycide oxathiapiprolin against several lifecycle stages of two geographically distinct P. agathidicida isolates. Half maximal effective concentration (EC50) values were determined to be approximately 0.1 ng/ml for inhibiting mycelial growth, 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.

<p>Phytophthora are plant pathogens, well known for devastating thousands of ecologically, culturally and economically significant plant crops worldwide. In greek Phytophthora translates directly to ‘plant destroyer’. Though it is ‘fungus-like’, Phytophthora are eukaryotic oomycetes, more closely related to brown algae and diatoms. Phytophthora have three key lifecycle stages: oospores, zoospores, and mycelia. Kauri are ancient conifer species dating back to the Cretaceous period (145 mya) and are now rapidly declining due to Kauri dieback caused by Phytophthora agathidicida. P.agathadicida causes root rot in Kauri trees and was first misidentified as P. hevave on Great Barrier Island in the early 1970s. Its origin is unknown however research argues it may have evolved from P. infestans, the pathogen that caused the Irish potato famine in 1845. For Te Āo Māori, Kauri are highly regarded tīpuna (ancestors) and Kauri Dieback is alarming to many Northern Iwi. Kauri wood and resin are highly sought and economically valuable resources. The Waipoua forest is the largest Kauri forest and the most impacted by Kauri Dieback. Over 25% of Kauri in the Waitākere ranges are either infected with P. agathadicida or are symptomatic, a percentage that is steadily increasing. A rāhui (temporary ban) was placed on the Waitākere ranges by local iwi Te Kawerau a Maki in 2018 as a preventative measure to reduce movement of P. agathadicida in soil. Apart from track closures, scrubbing and spraying equipment - before and after entering the forest - is the only tool of management. Sterigene disinfectant is the only treatment to reduce the spread of Kauri Dieback. Sterigene kills zoospores, mycelia and sporangium but is ineffective against P. agathidicida oospoores. Sexually produced oospores are responsible for the long-term survival of Phytophthora as they have a thick cell wall. The first part of this thesis examines a range of commercially available disinfectants and their efficacy against P. agathidicida oospores. These results confirm that Sterigene and/or Trigene are not effective against P. agathidicida oospores. My results also show that 2% bleach, 1% Virkon, and 70% ethanol all reduce oospore viability. Napisan also reduced oospore viability, but also interacted with the viability stains, therefore further investigations are needed. Napisan is an oxygen bleach, commercially affordable and easily accessible in supermarkets. Unlike sterigene and bleach, Napisan is safe to use on clothes, wool and soft textiles. If effective against oospores and the other lifecycle stages, Napisan could be a promising solution to help reduce the spread of Kauri Dieback.</p>

<p>Phytophthora are plant pathogens, well known for devastating thousands of ecologically, culturally and economically significant plant crops worldwide. In greek Phytophthora translates directly to ‘plant destroyer’. Though it is ‘fungus-like’, Phytophthora are eukaryotic oomycetes, more closely related to brown algae and diatoms. Phytophthora have three key lifecycle stages: oospores, zoospores, and mycelia. Kauri are ancient conifer species dating back to the Cretaceous period (145 mya) and are now rapidly declining due to Kauri dieback caused by Phytophthora agathidicida. P.agathadicida causes root rot in Kauri trees and was first misidentified as P. hevave on Great Barrier Island in the early 1970s. Its origin is unknown however research argues it may have evolved from P. infestans, the pathogen that caused the Irish potato famine in 1845. For Te Āo Māori, Kauri are highly regarded tīpuna (ancestors) and Kauri Dieback is alarming to many Northern Iwi. Kauri wood and resin are highly sought and economically valuable resources. The Waipoua forest is the largest Kauri forest and the most impacted by Kauri Dieback. Over 25% of Kauri in the Waitākere ranges are either infected with P. agathadicida or are symptomatic, a percentage that is steadily increasing. A rāhui (temporary ban) was placed on the Waitākere ranges by local iwi Te Kawerau a Maki in 2018 as a preventative measure to reduce movement of P. agathadicida in soil. Apart from track closures, scrubbing and spraying equipment - before and after entering the forest - is the only tool of management. Sterigene disinfectant is the only treatment to reduce the spread of Kauri Dieback. Sterigene kills zoospores, mycelia and sporangium but is ineffective against P. agathidicida oospoores. Sexually produced oospores are responsible for the long-term survival of Phytophthora as they have a thick cell wall. The first part of this thesis examines a range of commercially available disinfectants and their efficacy against P. agathidicida oospores. These results confirm that Sterigene and/or Trigene are not effective against P. agathidicida oospores. My results also show that 2% bleach, 1% Virkon, and 70% ethanol all reduce oospore viability. Napisan also reduced oospore viability, but also interacted with the viability stains, therefore further investigations are needed. Napisan is an oxygen bleach, commercially affordable and easily accessible in supermarkets. Unlike sterigene and bleach, Napisan is safe to use on clothes, wool and soft textiles. If effective against oospores and the other lifecycle stages, Napisan could be a promising solution to help reduce the spread of Kauri Dieback.</p>