Pathogenic variability of Plasmopara halstedii infecting sunflower in the Czech Republic

Abstract

Plasmopara halstedii was isolated from diseased sunflowers collected from eight locations in the Czech Republic from 2007 to 2014. Races of the pathogen were determined based on 84 isolates collected during the study. In total, eight races of P. halstedii were detected using a set of nine sunflower differential lines. Races 700, 704, 705, 710, 714 and 715 were proven by soil drench inoculation, and two additional races (730 and 770) proposed by the previously applied leaf disc inoculation method. Race 700 was the most dominant in the Czech P. halstedii populations, with race 710 being the second most frequent. Races 704 and 714 were found over three seasons, while other races were recorded only in one growing season (race 730 in 2010, and the new races 705 and 715 in 2014). A comprehensive study was further conducted for isolates collected in 2013-14 using an extended differential set consisting of 15 sunflower lines. According to the latter methodology which marks races with five-digit virulence codes, races 70060, 70471, 70571, 71060, 71461 and 71571 were recorded. The growing complexity of P. halstedii pathogenicity exhibited by the ability to infect higher numbers of differential genotypes and resulting in determination of the new pathogen races (virulence profiles) 70571, 71461 and 71571 is alarming. Although the limited number of isolates studied cannot characterize the entire pathogen diversity in the Czech Republic, the trend towards more diverse virulence in P. halstedii populations is clearly demonstrated by the new records of races 704, 705, 714 and 715, all capable of overcoming the resistance gene Pl 6 .

Spatial Genetic Structure and Pathogenic Race Composition at the Field Scale in the Sunflower Downy Mildew Pathogen, Plasmopara halstedii

“…However, the interesting pattern found here is that these genetically differentiated races are coexisting at a very fine scale, allowing potential recombination of individuals. The large number of races detected in our study is in agreement with the regular discovery of new races in other countries in Europe and in North America [ 13 , 15 , 18 , 21 , 23 , 71 , 72 , 73 , 74 ].…”

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.…”

“…Interestingly, in our analysis of the concatenated cox2 and SSR data, the CZE samples were distributed across the NJ tree and DAPC scatterplot. The CZE samples, located in Group B together with samples from Russia, were collected from agricultural areas in South Moravia (Hustopeče u Brna, Lednice, Podivín, Kroměříž), and probably represent genotypes from chronically infested soil (Drábková Trojanová et al, 2018). It is interesting that, in the first half of the 1950s, the first reports of P. halstedii in former Czechoslovakia were also from this region (Bojňanský, 1957).…”

“…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.…”

Preliminary Investigation of Effect of Neem-Derived Pesticides on Plasmopara halstedii Pathotype 704 in Sunflower under In Vitro and In Vivo Conditions

“…This pathogen affects sunflower yield losses, more than 85%, as well as the cost of sunflower crop protection and resistance breeding [1][2][3]. From an economic and scientific point of view, the community of oomycete molecular geneticists ranked P. halstedii as the 16th most important oomycete [4,5]. The distribution and genetic variability of P. halstedii have been studied extensively, especially in North America and Europe.…”