Oral Presentation Science Protecting Plant Health 2017

Are multiple Phytophthora species associated with macadamias? (4430)

Olumide OS Jeff-Ego 1 , Andre Drenth 1 , Olufemi OA Akinsanmi 1 , Juliane Henderson 2 , Bruce Topp 1
  1. The University of Queensland, QAAFI, Dutton Park, QUEENSLAND, Australia
  2. Plant Biosecurity, Department of Agriculture and Fisheries, Dutton Park, Queensland, Australia

In Australia, Phytophthora cinnamomi is presumed as the only Phytophthora currently associated with diseases in macadamias trees causing trunk canker, gummosis, dieback, root rot and eventually, tree death. However, the potential of other Phytophthora species as significant pathogens in macadamias has not been established. New macadamia orchards are established in lands previously cultivated to other crops known to be susceptible to multiple Phytophthora species. Report of poor establishment is common, thus, the macadamia trees are prone to ‘replant problems’ due to soilborne pathogens. In order to examine the prevalence and susceptibility of macadamia to multiple species of Phytophthora, a survey of macadamia orchards and native ecosystems commenced in 2016. Fifty macadamia sites representing different cropping histories and habitats in Australia were surveyed. Over 250 soil samples collected from potential sources of Phytophthora into the orchards and root zones of symptomatic and asymptomatic macadamia trees were baited for Phytophthora using blue lupins seedlings (Lupinus angustifolius), umbrella plant leaves (Schefflera arboricola) and Geraldton wax needles (Chamelaucium uncinatum). Isolates of Phytophthora from infected baits were maintained on antibiotics amended V8-juice media at 25oC under 8h/16 h light/dark cycle. Species identification of each isolate was based on DNA sequences of the ITS and cox1 and cox2 genes and morphological characterisation. Preliminary results revealed nine Phytophthora species are associated with macadamia in Australia. P. cinnamomi was predominant, representing 74% of the isolates, followed by P. cryptogea (6%), P. multivora (6%), P. citrophthora (5%), P. nicotianae (4%), P. boehmeriae (2%) and 1 % each of P. nagaii, P. sojae and an unconfirmed Phytophthora taxon. Association between cropping history and the Phytophthora species was evident and pathogenicity tests confirmed infection of these Phytophthora species in macadamia. The study provides a baseline information on the potential of other Phytophthora species as serious pathogens to macadamia.