Intraspecific variability in the Oomycete plant pathogen Phytophthora nicotianae

Phytophthora nicotianae is an Oomycete plant pathogen affecting a broad range of plant species comprising more than 250 genera. It causes several economically relevant diseases and is particularly known as the causal agent of black shank of tobacco and root rot, stem rot and gummosis of citrus. Despite the relevance of this pathogen, information on the field reproductive strategy, population structure and global distribution of genetic variability is not completely known. This is because available studies have been conducted to characterize local populations (mainly from tobacco) or have been based on physiological aspects such as resistance to fungicides and pathogenicity on differential hosts. In the present study, variable mitochondrial and nuclear loci were explored to evaluate genetic intraspecific variability of P. nicotianae on global scale using a collection of isolates from different geographic regions and hosts. A mixed approach of comparative genomics and sequencing of known and anonymous loci was utilised to identify suitable regions for population studies. High mitochondrial and nuclear genetic diversity and a panmictic distribution of haplotypes and genotypes were observed using these markers. This work offers useful tools to analyze the population genetic structure and migrations of P. nicotianae.