Determining the origin of the emerging pathogen, Phytophthora multivora

Phytophthora multivora is widespread in Western Australia (WA); it has a wide host range and considerably variability in the sequence of the mitochondrial gene cox1 led to the hypothesis that it may be endemic to the region. To test this hypothesis, four nuclear (ITS, enolase, HSP90 and ras) and three mitochondrial (coxI, coxIGS and nadh1) loci were sequenced for 80 isolates of P. multivora isolated from Australia, South Africa (RSA), North America, Canary Islands, New Zealand and Europe and the data were subjected to phylogenetic, coalescent-based and population genetic analyses. Isolates from RSA possess greater nucleotide diversity and a greater number of alleles at three of the nuclear loci and at all three mitochondrial loci than those from WA. In addition, the RSA population had more unique multilocus genotypes than the WA population. While P. multivora is widely distributed in natural ecosystems in WA and RSA, it is usually isolated from nurseries or horticulture elsewhere in the world. Additionally, P. multivora is consistently isolated from cankers and dead and dying plants of numerous endemic hosts in WA, but is predominantly isolated from soil associated with asymptomatic plants in RSA. Based on this evidence it is proposed that P. multivora is endemic to RSA and has been introduced to Western Australia.