Fishing of Phytophthora: A yearlong investigation into the diversity of Phytophthora species in the Waitakere Ranges, Auckland, NZ

Abstract

Species within the genus Phytophthora are well known as invasive pathogens, linked to high levels of economic or ecological damage when they are present. The most well known example, P. infestans, is the causal agent late blight of potato, which led to the Irish Potato Famine. Their role or even their presence, however, as endemic species within native ecosystems is not well understood or characterised. The purpose of this study was to use stream baiting to profile the Phytophthora community present in the waterways of several natural forest remnants in New Zealand. The stream baiting method was employed in five higher order streams within the Waitakere Ranges, Auckland. Each stream was surveyed in this way seven times over the year-long period. The method was shown to be effective in detecting Phytophthora species within these streams, retrieving isolates of six different species, P. multivora, P. gonapodyides, P. taxon 'pg chlamydo', P. kernoviae, P.aspargi, and a yet to be described species, referred to in this study as P. sp. 'Waitakere'. Three of the species, P. kernoviae, P.aspargi, and P. sp. 'Waitakere' had not previously been detected within the Waitakere Ranges. The species showed variation in the detectability or their relative abundance between seasons, with more species being detectable and abundant in spring and summer. There was also some variation between and catchments on the species detected within them, and their relative abundances. The catchments within the Piha area showed a dominance of the species P. multivora, whereas all other catchments were dominated by P. gonapodyides. This study was the first comprehensive year-long stream baiting investigation into the Phytophthora communities in waterways within bush fragments in New Zealand. As such the study also examined the methods efficacy and possible refinements. A comparison to direct stream filtration showed stream baiting was more able to detect a greater number of species. The study also found a significant difference in the efficacy of baits to detect individual species, and that isolation media containing the amendment hymexazol was significantly better at retrieving Phytophthora spp. from baits than isolation media without this amendment. Being the first study of its kind in New Zealand, this represents an important advance in profiling and understanding the role in natural ecosystems that members of the genus Phytophthora play.