Combining Inferential and Deductive Approaches to Estimate the Potential Geographical Range of the Invasive Plant Pathogen, Phytophthora ramorum

Abstract

Phytophthora ramorum, an invasive plant pathogen of unknown origin, causes considerable and widespread damage in plant industries and natural ecosystems of the USA and Europe. Estimating the potential geographical range of P. ramorum has been complicated by a lack of biological and geographical data with which to calibrate climatic models. Previous attempts to do so, using either invaded range data or surrogate species approaches, have delivered varying results. A simulation model was developed using CLIMEX to estimate the global climate suitability patterns for establishment of P. ramorum. Growth requirements and stress response parameters were derived from ecophysiological laboratory observations and site-level transmission and disease factors related to climate data in the field. Geographical distribution data from the USA (California and Oregon) and Norway were reserved from model-fitting and used to validate the models. The model suggests that the invasion of P. ramorum in both North America and Europe is still in its infancy and that it is presently occupying a small fraction of its potential range. Phytophthora ramorum appears to be climatically suited to large areas of Africa, Australasia and South America, where it could cause biodiversity and economic losses in plant industries and natural ecosystems with susceptible hosts if introduced.

Functional traits associated with the establishment of introduced Phytophthora spp. in Swedish forests

“…For instance, we did not find P. ramorum in Swedish forests, even though it is able to create asexual survival structures. Indeed, this species has been found established in parks and private gardens in Norway, a country with similar climatic conditions to those found in Sweden (Herrero, Toppe, & Brurberg, ; Ireland, Hardy, & Kriticos, ), supporting the predictive utility of our findings. The absence of P. ramorum in our survey could indicate that it has been recently introduced to Sweden and and has not yet spread further.…”

Distribution and diversity of Phytophthora across Australia

“…Suitable climatic regions for the persistence of P. ramorum and susceptible native hosts are widespread in Australia and New Zealand (Ireland et al 2013). Phytophthora pluvialis, a common and apparently benign species in western Oregon forests (Reeser et al 2013), has become a major pathogen of Pinus radiata in New Zealand (Dick et al 2014), but it has not been found on P. radiata within its native range in California.…”

Emerging oomycete threats to plants and animals

“…Despite the known reports of P. ramorum in Europe [51] and North America [52][53][54][55], predictive models suggest that the pathogen might be adapted to larger areas in Africa, Australasia and South America. Therefore, potential of invasion and further spread of the pathogen is possible [56]. In addition, given that diagnosis is primarily based on visual inspection, disease symptoms can be masked by agrochemicals, increasing the likelihood of pathogen intrusion into susceptible areas by the ornamental plant trade market [57].…”