Interaction between sunflower plants and five isolates ofPlasmopara halstediion the level of pathogenicity

Abstract

The interaction between sunflower plants showing a high level of quantitative resistance and five Plasmopara halstedii (the causal agent of downy mildew) isolates of several races were studied using five single zoosporangium isolates per pathogen isolate. Aggressiveness criteria were analyzed for 25 P. halstedii single zoosporangium isolates. Based on the reaction for the P. halstedii isolates to four sunflower hybrids H1ÁH4 varying only in their downy mildew resistance genes, there were differences in virulence spectrum in pathogen isolates. Analysis of five single zoosporangium isolates for P. halstedii isolates showed significant variability within pathogen isolate for all aggressiveness criteria but not for all pathogen isolates. The hypothesis explaining the interaction between P. halstedii and its host plant was discussed on the level of pathogenicity.

Aggressiveness variation inPlasmopara halstediiand its alternation with non-race-specific resistance in sunflower

“…Our results (Table 3) involving the correlation between aggressiveness criteria on two sunflower inbred lines FU and BT were not in accordance with our analyses on FU (Sakr 2009(Sakr , 2011b concerning latent period and sporulation density. Only latent period was correlated with both sporulation density and percentage infection.…”

“…Knowledge of the interaction between P. halstedii and H. annuus would help to understand the co-evolution of pathogen populations that use their aggressiveness to better improve adaptation to their host (Sakr 2011a(Sakr , 2011bViranyi and Spring 2011). With this in mind, aggressiveness variability was studied in 19 P. halstedii isolates belonging to several races, and the non-race-specific criteria under controlled conditions were determined.…”

“…For reduction of hypocotyl length, data were presented as percentage of length for diseased plants as compared with healthy plants. The index of aggressiveness of the P. halstedii isolate was used to summarise all values for criteria on the two sunflower inbred lines in one value to facilitate the comparison between the different P. halstedii isolates (Sakr 2011a(Sakr , 2011b. It was calculated as the ratio of (percentage infection6sporulation density6percentage of length for diseased plants of healthy plants)/latent period.…”

“…Several studies have revealed the interactions between sunflower plants and P. halstedii on the level of pathogenicity: virulence , 2010Gulya 2007) and aggressiveness (Sakr et al 2008(Sakr et al , 2011Sakr 2009Sakr , 2011aSakr , 2011bTourvieille de Labrouhe et al 2010). Virulence has been defined as specific disease-causing abilities and aggressiveness as non-specific disease-causing abilities (Van der Plank 1968).…”

Variation in two components of pathogenicity and its relationship with genetic diversity inPlasmopara halstedii(sunflower downy mildew)

“…Variability of virulence in P. halstedii has been the object of several studies (Tourvieille de Labrouhe et al 2000;Gulya 2007;Sakr 2011bSakr , 2011cSakr , 2011dSakr , 2012aSakr , 2012b because major monogenic resistances have been overcome rapidly by the parasite. Downy mildew races have been observed by Sakr (2009Sakr ( , 2011aSakr ( , 2011bSakr ( , 2011dSakr ( , 2012aSakr ( , 2012bSakr ( , 2012c to show considerable differences in aggressiveness and this affects host response; these are the most aggressive races often producing symptoms which cannot be compared with those produced by those that are less aggressive.…”