Genetic diversity of Phytophthora pluvialis, a pathogen of conifers, in New Zealand and the west coast of the United States of America

Authors: BRAR, S - Massey University; TABIMA, JAVIER - Oregon State University; MCDOUGAL, R - New Zealand Forest Research Institute; DUPONT, P - Massey University; FEAU, N - University Of British Columbia; HAMELIN, R - University Of British Columbia; PANDA, P - University Of British Columbia; LEBOLDUS, J - Oregon State University; Grunwald, Niklaus - Nik; HANSEN, E - Oregon State University; BRADSHAW, R - Massey University; WILLIAMS, N - Massey University

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2017
Publication Date: 1/30/2018
Citation: Brar, S., Tabima, J.F., Mcdougal, R.L., Dupont, P.Y., Feau, N., Hamelin, R.C., Panda, P., Leboldus, J.M., Grunwald, N.J., Hansen, E.M., Bradshaw, R.E., Williams, N.M. 2018. Genetic diversity of Phytophthora pluvialis, a pathogen of conifers, in New Zealand and the west coast of the United States of America. Plant Pathology. 67:1131–1139. https://doi.org/10.1111/ppa.12812.
DOI: https://doi.org/10.1111/ppa.12812

Interpretive Summary: The plant pathogen Phytophthora pluvialis is the causal agent of red needle cast on radiata pine in New Zealand. It was first discovered in 2005 but had previously been recovered from tanoak and Douglas-fir trees in Oregon, USA in 2002. Phytophthora pluvialis was subsequently described as a new species in 2013. The aim of this project was to gain a better understanding of the genetic diversity, population structure and origin of this pathogen. A total of 360 pathogen isolates were collected from the USA and New Zealand. The genome sequences of two P. pluvialis strains were used to identify 27 single nucleotide polymorphism (SNP) markers, that were then used to genotype the two populations. The US population of the pathogen has higher genetic diversity compared to the New Zealand population. Genetic analysis suggests two potential introductions of P. pluvialis into New Zealand from the USA. This study provides novel insight into the genetic structure of P. pluvialis in New Zealand and the USA.

Technical Abstract: Phytophthora pluvialis is the causal agent of red needle cast on Pinus radiata in New Zealand. It was first discovered in 2005 but had previously been recovered from tanoak (Lithocarpus densiflorus) and Douglas-fir (Pseudotsuga menziesii) trees in Oregon, USA in 2002. Phytophthora pluvialis was subsequently described as a new species in 2013 and classified as a clade III Phytophthora species. The aim of this project was to gain a better understanding of the genetic diversity, population structure and origin of this pathogen. A total of 360 P. pluvialis isolates were collected from the USA and New Zealand. The genome sequences of two P. pluvialis strains were used to identify 27 single nucleotide polymorphism (SNP) markers, that were then used to genotype the two populations. The genotypic data showed that the USA population of P. pluvialis had twice the genetic diversity and a greater number of multi locus genotypes (MLG) compared to the New Zealand population with 126 and 24 MLGs respectively. The majority of the sub-populations within the USA and New Zealand showed linkage disequilibrium. All sub-populations had a negative fixation index, indicating that clonal reproduction is prevalent in both countries. A minimum spanning network (MSN) showed two unique clusters of isolates in the New Zealand population, suggesting two potential introductions of P. pluvialis into New Zealand from the USA. There was no significant structure within the New Zealand or USA populations. This study provides novel insight into the genetic structure of P. pluvialis in New Zealand and the USA.