Habitat suitability of soils from a topographic gradient across the Fitzgerald River National Park for invasion by Phytophthora cinnamomi

Habitat suitability for P. cinnamomi was compared between soils from the major soil groups of the Fitzgerald River National Park. Because of the mainly disease-free status of the National Park, only ex-situ testing was possible by Gradsect sampling of soils on a topographic gradient and determining the influence on disease expression in a shadehouse environment and stimulation of sporangium production in a controlled environment. The upper asymptote (Kmax), lag time (t½K) and intrinsic rate of increase (r) of the logistic model were calculated from disease progress curves of Banksia baxteri plants following soil inoculation with P. cinnamomi and sporulation curves. The Qualinup Sands and the Dry Phase of the Nyerilup Sand had the greatest % mortality Kmax values and the Perkins and Red Loams had the least. For B. baxteri mortality, delay significantly increased and rate decreased along a fertility gradient from relatively infertile sands to fertile loams. Kmax of total number of sporangia/mm2 of mycelium for winter collected soils was significantly linearly positively correlated with Kmax of germinating spores/disc and negatively correlated with rate of mortality of B. baxteri. The loams with the slowest rate of mortality of B. baxteri stimulated the most sporulation. Habitat suitability of the major soil groups of the landscape matrix of the Fitzgerald River National Park for P. cinnamomi can be used to predict risk of invasion and hazard in healthy areas and prioritise areas of greatest risk of invasion and conservation consequences from hazard.