The long‐term survival of Phytophthora cinnamomi in mature Banksia grandis killed by the pathogen

The ability of Phytophthora cinnamomi to survive long dry periods is the key to its persistence in the south-west of Western Australia. It has been proposed that dead Banksia grandis are a significant long-term reservoir for P.cinnamomi inoculum. To test this, 36 healthy B.grandis trees were inoculated in April 1999, and the presence of viable propagules in planta was determined between 2 and 34 months after tree death. By 10 months after inoculation, 75% of the trees had died, with the remaining seven trees dying by 22 months. The pathogen was more commonly recovered from bark than from wood, except from those trees that died at 22 months, and more commonly from above-ground trunks than below-ground trunks and roots until 8 months after plant death. In trees that died 12 months after inoculation, P.cinnamomi was recovered from 60% of trunk and root core samples at 3 months, declining to 33% at 10 months, 5.5% at 12 months and 0.1% at 34 months after tree death. In trees that died at 22 months, P.cinnamomi was recovered from 87% of trunk and root samples 2 months after tree death, decreasing to 0.5% by 33 months. This study suggests that the pathogen does not have a saprotrophic phase within dead B.grandis tissue, and B.grandis is unlikely to be a long-term reservoir for P.cinnamomi. However, the manipulation of the density of B.grandis and the use of fire to facilitate the breakdown of dead Banksia trunks in the Eucalyptus marginata (jarrah) forest may reduce the spread and impact of P. cinnamomi.