Distribution of Phytophthora cinnamomi at different spatial scales: When can a negative result be considered positively?

Abstract

In October 1999, patches of dead and dying trees were identified in rainforest vegetation throughout the Tully Falls area in north Queensland, Australia. Previous incidents of patch death in the region had been attributed to Phytophthora cinnamomi . The distribution of P. cinnamomi was assessed by testing for its presence in seven sites displaying signs of dieback and seven sites that appeared healthy. Each site was a circular quadrat, 20-m radius (total area = 1256.6 m 2 ). Within each quadrat, two perpendicular line transects were constructed. A single soil sample (250 g) was taken at the centre point and at 1-m intervals along each transect. All soil samples were tested for the presence of P. cinnamomi using a combination of lupin baiting, subsequent culturing and microscopic identification. Of the 1134 samples, 783 recorded positive responses. The mean number of positive responses was not significantly greater in patch death sites than in control sites, suggesting that at this scale of resolution the distribution of P. cinnamomi was uniform. However, at spatial scales of 1-m intervals across transects the distribution of P. cinnamomi was random.

Defining Plant Resistance to Phytophthora cinnamomi: A Standardized Approach to Assessment

“…It is one of the most widely distributed Phytophthora species with a large and diverse host range of >3500 species (Hardham and Blackman 2010). The pathogen causes serious disease in horticultural crops such as avocado, macadamia and pineapple, in ornamentals such as camellia and azalea, and in Australia, disease has resulted in a devastating loss of biodiversity (Pryce et al 2002;Cahill et al 2008).There is widespread infestation of native Australian forests (Environment Australia 2001), and some recent estimates put the extent of the disease in Western Australia alone at one million ha (J. Tippett, personal communication). In the ecosystems of south-western Australia, especially those with Mediterranean affinities, P. cinnamomi contributes to placing them among the most vulnerable to tipping points in the country (Laurance et al 2011).…”