Mitochondrial phylogeny reveals intraspecific variation in Peronospora effusa, the spinach downy mildew pathogen

Abstract

Since about two hundred years, downy mildew caused by Peronospora effusa is probably the most economically important disease of spinach (Spinacia oleracea). However, there is no information on the global phylogeographic structure of the pathogen and thus it is unclear whether a single genotype occurs worldwide or whether some local genetic variation exists. To investigate the genetic variability of this pathogen, a sequence analysis of two partial mitochondrial DNA genes, cox2 and nad1, was carried out. Thirty-three specimens of Peronospora effusa from four continents were analyzed, including samples from Australia, China, Japan, Korea, Mexico, Russia, Sweden, and the USA. Despite the potential anthropogenic admixture of genotypes, a phylogeographic pattern was observed, which corresponds to two major groups, an Asian/Oceanian clade and another group, which includes American/European specimens. Notably, two of six Japanese specimens investigated did not belong to the Asian/Oceanian clade, but were identical to three of the specimens from the USA, suggestive of a recent introduction from the USA to Japan. As similar introduction events may be occurring as a result of the globalised trade with plant and seed material, a better knowledge of the phylogeographic distribution of pathogens is highly warranted for food security purposes.

Population Structure of Peronospora effusa in the Southwestern United States

“…Because P . effusa is an obligate pathogen, the disease is postulated to have spread with the crop and is thought to have originated in a small geographic area [ 17 ]. However, the limited amount of genomic resources for P .…”

Population structure and migration of the Tobacco Blue Mold Pathogen, Peronospora tabacina, into North America and Europe

“…High levels of genetic diversity have been reported in other oomycete pathogens such as Peronospora effusa (Choi et al., ), Peronospora farinosa (Danielsen & Lubeck, ) and Phytophthora spp. (Chamnanpunt, Shan, & Tyler, ; Judelson, ), and this diversity has been attributed to factors such as genetic instability, transposable elements, gene conversion, mitotic recombination and/or dispensable chromosomes (Haas et al., ; Kamoun, ).…”

“…We analysed the genetic structure of populations of Peronospora tabacina from a global collection of isolates from 11 countries in T A B L E 2 (Continued) High levels of genetic variation were found among populations of P. tabacina when DNA from allelic regions of several loci was cloned and sequenced in our work. Other downy mildews such as cucurbit downy mildew also exhibit high levels of genetic diversity in the United States in Florida and North Carolina (Choi, Thines, Han, & Shin, 2011;Ojiambo, Gent, Quesada-Ocampo, Hausbeck, & Holmes, 2015). Several possible mechanisms could explain the high genetic variation observed in the blue mold pathogen.…”

Characterisation and risk assessment of the emerging Peronospora disease on Aquilegia

“…It has now been accepted that Gäumann's (1923) narrow species hypothesis is more appropriate than the broader species concept of Yerkes and Shaw (1959), as phylogenetic studies have generally revealed phylogenetically distinct lineages specifically present only on a particular host species (Riethmüller et al 2002;Voglmayr 2003;Göker et al 2004Göker et al , 2009Voglmayr et al 2004Voglmayr et al , 2009Choi et al 2007Choi et al , 2008aChoi et al , b, 2009Choi et al , 2011Choi et al , 2015Thines et al 2009Thines et al , 2011Constantinescu and Thines 2010).…”