Management of Kauri dieback and Phytophthora taxon Agathis'

摘要

A soilborne pathogen,, Phytophthora taxon Agathis (PTA), has been identified as a causal agent of declining health and tree death of kauri (Agathis australis) across much of the natural range of kauri in New Zealand (Beever et al. in press). Kauri illthrift, commonly referred to as kauri dieback, has been identified as an increasing problem across the Auckland region, particularly within the Waitakere Ranges Regional Park. PTA was first reported, as Phytophthora heveae, from Great Barrier Island (Gadgil 1974), and has now also been found in Northland. It is associated with a collar rot causing large bleeding lesions at the base of the trunk. These lesions bleed copious amounts of resin (kauri gum) and may encircle the stem. Other symptoms include yellowing foliage, severe defoliation, canopy thinning and tree death. Pathogenicity tests confirm PTA is highly pathogenic to kauri (Beever et al 2008, Gadgil 1974). Typically, affected stands are relatively small in size with size class distributions indicating trees of many ages are affected. Beever et al. (in press) proposed that collar rot caused by PTA is an emerging disease caused by an introduced pathogen that is spreading from widespread disease foci. They conclude PTA poses a threat to kauri, both at the individual iconic tree level and at the population level.