Resurgence of Pseudoperonospora cubensis: The Causal Agent of Cucurbit Downy Mildew

Abstract

The downy mildew pathogen, Pseudoperonospora cubensis, which infects plant species in the family Cucurbitaceae, has undergone major changes during the last decade. Disease severity and epidemics are far more destructive than previously reported, and new genotypes, races, pathotypes, and mating types of the pathogen have been discovered in populations from around the globe as a result of the resurgence of the disease. Consequently, disease control through host plant resistance and fungicide applications has become more complex. This resurgence of P. cubensis offers challenges to scientists in many research areas including pathogen biology, epidemiology and dispersal, population structure and population genetics, host preference, host-pathogen interactions and gene expression, genetic host plant resistance, inheritance of host and fungicide resistance, and chemical disease control. This review serves to summarize the current status of this major pathogen and to guide future management and research efforts within this pathosystem.

Analysis of microsatellites from the transcriptome of downy mildew pathogens and their application for characterization ofPseudoperonosporapopulations

“…Analyses of index of association also showed support for different lifestyles of these species, with indications of P. cubensis undergoing sexual reproduction and P. humuli being clonal. This is also supported by previous findings of the occurrence of mating types within P. cubensis and claims of homothallic lifestyle of P. humuli (Cohen et al, 2015; Cohen & Rubin, 2012). It should be noted that in laboratory settings, Runge & Thines (2012) demonstrated that there is some level of cross-infectivity of P. cubensis on Humulus lupulus and P. humuli on Cucumis sativus .…”

“…The prolific asexual sporulation of the pathogen on the leaf surface and the ease through which it is aerially dispersed from field to field also contribute to the pathogen’s damaging effects. Although the role of sexual reproduction and wild cucurbit hosts as inoculum sources still have not been thoroughly determined, epidemiological studies have helped develop control strategies (Lebeda & Cohen, 2011; Cohen et al, 2015; Holmes et al, 2015; Ojiambo et al, 2015; Wallace et al, 2014; Wallace, Adams & Quesada-Ocampo, 2015). To date, P. cubensis continues to cause major losses as vital fungicides lose efficacy (Ojiambo et al, 2015; Holmes et al, 2015).…”

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

“…Previous studies (Cohen & Rubin, ) have suggested an association between cucurbit host types and mating types of P. cubensis . There have also been reports of both mating types being able to infect the same host species suggesting that mating type and virulence might be genetically unlinked (Cohen et al., ). In the present study, all lineage II isolates were of the A1 mating type, while all lineage I isolates were of the A2 mating type.…”

Pseudoperonospora cubensis virulence and pathotype structure in Kazakhstan

“…Globally, populations of P. cubensis have changed and new virulent pathotypes have emerged (Lebeda et al ., , ; Cohen et al ., ; Kitner et al ., ; Ojiambo et al ., ). New pathotypes not only cause severe epidemics but substantially limit production of commercial cucurbit varieties and hybrids.…”

“…The pathogen is also highly aggressive and has demonstrated a high degree of adaptation that has enabled it to constantly increase its host range by infecting a wide range of cultivated and wild plants of the Cucurbitaceae family (Colucci et al ., ; Lebeda & Urban, ; Lebeda & Cohen, ; Lebeda et al ., ,b). Both mating types of P. cubensis and oospore formation have been reported in several countries (Cohen et al ., ), a characteristic that allows the pathogen to generate high levels of polymorphism within pathogen populations.…”