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Kauri dieback
Kauri dieback is a forest dieback disease of the native kauri trees (Agathis australis) of New Zealand that is suspected to be caused by the oomycete Phytophthora agathidicida. Symptoms can include root rot and associated rot in a collar around the base of the tree, bleeding resin, yellowing and chlorosis of the leaves followed by extensive defoliation, and finally, death.
Phytophthora (from Greek φυτόν (phytón), "plant" and φθορά (phthorá), "destruction"; "the plant-destroyer") is a genus of plant-damaging oomycetes (water moulds), whose member species are capable of causing enormous economic losses on crops worldwide, as well as environmental damage in natural ecosystems.
The species name agathidicida means "kauri killer", from the genitive noun agathid- (meaning "of the kauri genus Agathis") and the Latin suffix -cide (from the verb cadere, to kill).
Symptoms of kauri dieback include root rot of both fine-feeder and larger structural roots; a collar rot lesion causing resin production ("gummosis") at the collar and lower trunk region; severe chlorosis and defoliation of the canopy; and overall crown decline. Infection by kauri dieback can rapidly kill seedlings and trees of all ages. Trees of all size classes are killed in natural forest remnants, amenity garden and park trees, and kauri plantations.
Phytophthora agathidicida was first discovered on Great Barrier Island in 1972 by Peter Gadgil, and was initially identified from slides as a different organism, P. heveae. Phytophthora in mainland New Zealand kauri trees was also identified causing dieback in the Waitākere Ranges linked to Phytophthora cinnamomi.
In March 2006, entomologist Peter Maddison noticed a distinctly different infection in mature kauri in the Waitākere Ranges. Plant pathologists Ross Beever and Nick Waipara recognised this as a distinct Phytophthora species and it was named Phytophthora 'taxon Agathis' (abbreviated PTA). It was formally named Phytophthora agathidicida in 2015.
Phytophthora agathidicida is a species in the group of Phytophthora called ‘Clade 5’ which is defined by ITS DNA sequences. Within Clade 5 P. agathidicida can be distinguished from the other species by DNA sequence differences and oospores that have a moderately bumpy surface. In pure agar culture the optimum growth temperature is 21.5 °C.
It is not known when the microorganism arrived in New Zealand nor the source, but the centre of diversity of Phytophthora Clade 5 is believed to be in the East Asia / Pacific region. A media report of an unpublished study based on mitochondrial genomes of 17 isolates suggested that it may have existed in New Zealand for centuries and has only recently become a danger to kauri. However, the 100% mortality rate and speed with which the disease has spread since 2016 suggests that it is a more recent arrival.
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Kauri dieback
Kauri dieback is a forest dieback disease of the native kauri trees (Agathis australis) of New Zealand that is suspected to be caused by the oomycete Phytophthora agathidicida. Symptoms can include root rot and associated rot in a collar around the base of the tree, bleeding resin, yellowing and chlorosis of the leaves followed by extensive defoliation, and finally, death.
Phytophthora (from Greek φυτόν (phytón), "plant" and φθορά (phthorá), "destruction"; "the plant-destroyer") is a genus of plant-damaging oomycetes (water moulds), whose member species are capable of causing enormous economic losses on crops worldwide, as well as environmental damage in natural ecosystems.
The species name agathidicida means "kauri killer", from the genitive noun agathid- (meaning "of the kauri genus Agathis") and the Latin suffix -cide (from the verb cadere, to kill).
Symptoms of kauri dieback include root rot of both fine-feeder and larger structural roots; a collar rot lesion causing resin production ("gummosis") at the collar and lower trunk region; severe chlorosis and defoliation of the canopy; and overall crown decline. Infection by kauri dieback can rapidly kill seedlings and trees of all ages. Trees of all size classes are killed in natural forest remnants, amenity garden and park trees, and kauri plantations.
Phytophthora agathidicida was first discovered on Great Barrier Island in 1972 by Peter Gadgil, and was initially identified from slides as a different organism, P. heveae. Phytophthora in mainland New Zealand kauri trees was also identified causing dieback in the Waitākere Ranges linked to Phytophthora cinnamomi.
In March 2006, entomologist Peter Maddison noticed a distinctly different infection in mature kauri in the Waitākere Ranges. Plant pathologists Ross Beever and Nick Waipara recognised this as a distinct Phytophthora species and it was named Phytophthora 'taxon Agathis' (abbreviated PTA). It was formally named Phytophthora agathidicida in 2015.
Phytophthora agathidicida is a species in the group of Phytophthora called ‘Clade 5’ which is defined by ITS DNA sequences. Within Clade 5 P. agathidicida can be distinguished from the other species by DNA sequence differences and oospores that have a moderately bumpy surface. In pure agar culture the optimum growth temperature is 21.5 °C.
It is not known when the microorganism arrived in New Zealand nor the source, but the centre of diversity of Phytophthora Clade 5 is believed to be in the East Asia / Pacific region. A media report of an unpublished study based on mitochondrial genomes of 17 isolates suggested that it may have existed in New Zealand for centuries and has only recently become a danger to kauri. However, the 100% mortality rate and speed with which the disease has spread since 2016 suggests that it is a more recent arrival.