Kauri dieback

Phytophthora (from Greek (), "plant" and (), "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 , to kill). == Disease ==

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. == Identification ==

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. 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. == History of spread ==

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. In the Waitākeres 58% of large areas of kauri ecosystem over 5 hectares have some state of infection. An independent review of the epidemiology of the Kauri study found that "the Auckland data is of limited use if we want to conduct an analysis to identify factors associated with PTA being present". Current pathogen distribution knowledge is based on soil sampling, ground-truthing, and aerial surveillance, but that has usually been limited to stands of kauri showing symptoms, at a coarse scale. Aerial surveillance has not used multi- or hyperspectral imagery or change detection. It is unclear to what extent the disease spread is caused by distribution of the pathogen or whether unknown factors such as kauri resistance or how P. agathidicida living on alternative hosts has influenced the spread of the disease. ==Transmission==

The disease is solely soil-borne and mostly spread in infected soil carried from tree to tree. P. agathidicida spores can be carried in soil the size of a pinhead. The consensus among experts is that the predominant vector for spread of the disease is human activity. While only kauri trees develop the characteristic dieback disease following infection, it appears that seven other native New Zealand forest plants can act as hosts for the pathogen without showing symptoms themselves. These include Dracophyllum, tanekaha (Phyllocladus trichomanoides), tall mingimingi (Leucopogon fasciculatus), rewarewa (Knightia excelsa) and Astelia trinervia. It is thought that the community of symbiotic mycorrhizal fungi living on the roots of healthy kauri trees may help protect them from Phytophthora infection. https://www.scionresearch.com/__data/assets/pdf_file/0003/15663/FHNews-199_Oct.pdf''''' --> ==Disease management==

Auckland Regional Council (ARC) began disease surveys and information workshops in October 2006. A Joint Agency was formed in November 2008 comprising the ARC, Northland Regional Council (NRC), the Department of Conservation (DOC) and Ministry of Agriculture and Fisheries Biosecurity New Zealand (MAFBNZ), to develop joint communications and share information. This was replaced in November 2009 by the National Kauri Dieback Management Programme, sponsored and funded by MAFBNZ, DOC, ARC, NRC, Environment Waikato (EW), Environment Bay of Plenty (EBoP), and tangata whenua. This began a five-year national programme of research and science oversight, surveillance, education and outreach. In 2014 this was renewed for a further 10 years. This experimental approach aims to supplement existing treatments such as phosphite, though it remains at an early, experimental stage. ==See also==