Coincidence of virulence shifts and population genetic changes of Pseudoperonospora cubensis in the Czech Republic

Abstract

Pseudoperonospora cubensis is an oomycete pathogen causing downy mildew disease on a variety of Cucurbitaceae, and has recently re‐emerged as a destructive disease on crops in this family, mainly on cucumber and squash. Multilocus sequence analysis (MLSA) of four mitochondrial and two nuclear DNA regions was used to detect changes in the genetic structure of P. cubensis populations occurring in the Czech Republic that might be associated with recently reported shifts in virulence. The analysed sample set contains 67 P. cubensis isolates collected from 1995 to 2012 in the Czech Republic and some other European countries. Sequence analyses revealed differences and changes in the genetic backgrounds of P. cubensis isolates. While all isolates sampled before 2009 exhibited the genotype of the subspecies of Clade II and were collected from cucumber, all samples collected from other hosts belonged to Clade I (P. cubensis sensu stricto) or were sampled from 2009 onwards. In addition, 67·16% of all post‐2009 isolates from Clade II had two heterozygous positions in their nrITS sequence, which suggests sexual reproduction and/or a mutational origin. Thus, the results indicate that, apart from the rise in prevalence of Clade I, the change in the genetic structure of P. cubensis populations may be linked with a hybridization or, less likely, a mutation event that rendered strains able to infect a broader spectrum of host species.

Resurgence of cucurbit downy mildew in the United States: Insights from comparative genomic analysis of Pseudoperonospora cubensis

“…Previous studies using multilocus phylogenetic analyses of variation in cox2 , ypt1, and nrITS in several similar strains also provided evidence of two clades within P. cubensis (Kitner et al., ; Runge et al., ). Evolutionary lineages I and II identified in the current study were found to be congruent with clades 1 and 2 (Runge et al., ), respectively, based on a phylogenetic analysis of sequence data obtained from NCBI (Figure ).…”

“…The evolutionary origin of P. cubensis and the relatedness to its sister species, P. humuli that infects hop, have been widely investigated (Choi, Hong, & Shin, ; Göker, Voglmayr, Riethmüller, & Oberwinkler, ; Kitner et al., ; Mitchell, Ocamb, Grünwald, Mancino, & Gent, ; Runge & Thines, ; Runge et al., ). Choi et al.…”

“…In that study (Mitchell et al., ), one P. humuli isolate from Korea clustered with P. cubensis isolates from Asia, whereas P. humuli isolates from Europe and the United States formed a separate cluster ancestral to P. cubensis . Some cohesion between the two species was observed in the cox 2 region of two isolates obtained from Cucurbita pepo in North Carolina and a P. humuli isolate from South Korea (Mitchell et al., ), and between P. humuli and P. cubensis isolates from non‐cucumber host types (Kitner et al., ). Generally, these studies indicate that although P. cubensis and P. humuli are morphologically and physiologically similar, they exhibit quantifiable physiological and genetic differences that support their retention as two separate species.…”

Genetic structure and phylogeny of Italian and Czech populations of the cucurbit powdery mildew fungus Golovinomyces orontii inferred by multilocus sequence typing

“…(), and also affects population genetics of cucurbit downy mildew, Pseudoperonospora cubensis (Lebeda & Cohen, ; Kitner et al ., ). The majority of the borders of the Czech Republic are natural mountain barriers, except for the southeastern region, which is relatively open to air currents from southern Europe, thus representing the main potential source of genetic material at the beginning of the cucurbit growing season (May–June) (Kitner et al ., ). During the main growing season (July–August), infection by propagules from all neighbouring European countries could also occur.…”

Characterisation and risk assessment of the emerging Peronospora disease on Aquilegia

“…& M.A. Curtis) Rostovzev, even various genera of a host family ( Wa t e r h o u s e a n d B r o t h e r s 1 9 8 1 ; L e b e d a a n d Widrlechner 2003; Runge and Thines 2009, 2012Kitner et al 2015). Thus, it is necessary that new occurrences of Peronospora are investigated not only by the recording of new hosts but also by morphological and phylogenetic characteristics.…”