New and High Virulent Pathotypes of Sunflower Downy Mildew (Plasmopara halstedii) in Seven Countries in Europe

Abstract

Downy mildew of sunflower, caused by Plasmopara halstedii (Farl.) Berl. et de Toni, is a relevant disease of this crop. High virulent pathotypes have been identified in several countries, while there are few data on the spread of P. halstedii pathotypes in some important sunflower-growing areas of Europe. The goal of this study was to give up-to-date information on the pathotype structure of P. halstedii in Hungary and provide some actual data on the virulence phenotype of the pathogen for six European countries. Infected leaves of different sunflower hybrids and volunteers were collected in seven countries (Hungary, Bulgaria, Serbia, Turkey, Greece, Romania, and Italy) between 2012 and 2019. A universally accepted nomenclature was used with a standardized set of sunflower differential lines for pathotype characterization of isolates. The virulence pattern of the isolates was determined by a three-digit code (coded virulence formula, CVF). A total of 109 P. halstedii isolates were characterized. As a result of our survey, 18 new P. halstedii pathotypes were identified in Europe. Two out of the eighteen pathotypes were detected from the Asian part of Turkey. The detailed distribution of pathotypes in Hungary is also discussed.

Genetic structure of Plasmopara halstedii populations across Europe and South Russia

“…From many previous (Gulya, 2007; Virányi et al, 2015) and recent studies (Bán et al, 2021; Drábková Trojanová et al, 2018; Spring, 2019) it is well known that P. halstedii is highly variable in pathogenicity. More than 50 different pathotypes (physiological races) have been determined so far and new virulence phenotypes are highly likely to occur.…”

“…This scenario is supported by the origin of sunflower varieties cultivated and bred after World War II in Czechoslovakia (Holubec, 2017;Kováčik, 2000;Špaldoň, 1982); for example, the main variety cultivated in 1950-1960 was the Soviet variety VNIIMK-6540 (Špaldoň, 1982). However, the same hypothesis cannot be applied to P. halstedii samples from Hungary, also formerly From many previous (Gulya, 2007;Virányi et al, 2015) and recent studies (Bán et al, 2021;Drábková Trojanová et al, 2018;Spring, 2019) it is well known that P. halstedii is highly variable in were available (File S1) that showed no link to their position on the NJ tree (Figure 4). This is further evidence that P. halstedii virulence is not monogenic (i.e., based on a single gene), and virulence phenotypes have evolved multiple times.…”

“…Nowadays, SDM is one of the major destructive diseases in most sunflower‐growing areas worldwide, except for Australia and Oceania (Constantinescu & Thines, 2010). The pathogen is highly variable in its pathogenicity and succeeded in overcoming efforts for plant protection by evolving new pathotypes or fungicide‐resistant strains (Bán et al, 2021; Molinero‐Ruiz, 2022).…”

“…Nowadays, SDM is one of the major destructive diseases in most sunflower-growing areas worldwide, except for Australia and Oceania (Constantinescu & Thines, 2010). The pathogen is highly variable in its pathogenicity and succeeded in overcoming efforts for plant protection by evolving new pathotypes or fungicide-resistant strains (Bán et al, 2021;Molinero-Ruiz, 2022). P. halstedii is a homothallic (antheridium and oogonium fuse within a single mycelium) pathogen (Spring, 2000), which forms oospores primarily to survive between crop-growing seasons.…”

Efficacy of some plant resistance inducers against several sunflower downy mildew (Plasmopara halstedii (Farl.) Berl. et de Toni) isolates

“…Because of the latter, there is a high risk of spreading different pathotypes (virulence phenotypes or pathotypes) of the pathogen. Approximately 50 pathotypes of P. halstedii have been identified globally (Bán et al 2021). Although sunflower hybrids are cultivated that are resistant to all pathotypes of P. halstedii, the high variability of the pathogen requires continuous and intensive breeding efforts (Vear 2016).…”