Relationship between aggressiveness and zoosporangia viability inPlasmopara halstedii(sunflower downy mildew)

Abstract

Relationship between aggressiveness and zoosporangia viability was studied in seven Plasmopara halstedii (sunflower downy mildew) isolates of races 100, 300, 304, 314, 710, 704 and 714. Aggressiveness criteria including latent period and sporulation density were analysed on sunflower inbred line showing a high level of quantitative resistance. There were significant differences between pathogen isolates for the two aggressiveness criteria. Viability analyses were performed on oval and spheric zoosporangia. The number of zoospores released from oval zoosporangia was significantly higher than those released from spheric ones. The oval zoosporangia for more aggressive isolates of races 100 and 3xx produced more zoospores than the oval ones for less aggressive isolates of races 7xx. There was a significant correlation between aggressiveness criteria and the number of zoospores released from oval zoosporangia and vice versa for zoospores released from spheric ones. It is concluded that the relationship between aggressiveness and oval zoosporangia viability may be established in P. halstedii.

Can Pl Resistance Gene in Sunflower Line D4 be Used to Differentiate the Pathogenicity in Four Plasmopara halstedii (Sunflower Downy Mildew) Races 304, 314, 704 and 714?

“…However, for another Oomycete Plasmopara viticola, Delmotte et al (2014) found evidence for a trade-off between the size and the number of sporangia produced within P. viticola. In the same pathosystem, Sakr (2011c) found a relationship between a life-history trait (viability of zoosporangia) and aggressiveness in P. halstedii. Table 4 showed that there were significant morphological differences for 20 pathogen single zoosporangium isolates in two groups including four isolates DU1943 and DU1767, DU1915 and DU1734.…”

“…The interactions between sunflower plants and P. halstedii on the level of pathogenicity have been the object of several studies: virulence and aggressiveness (Tourvieille de Labrouhe et al, 2000, 2010Delmotte et al, 2008;Sakr, 2011aSakr, , 2011bSakr, , 2011cSakr, , 2012Sakr, , 2014aSakr, , 2014bSakr, , 2014cSakr, , 2015aSakr, , 2015bAhmed et al, 2012). Virulence has been defined as specific disease-causing abilities and aggressiveness as non-specific disease-causing abilities ( Van der Plank, 1968).…”

“…Moreover, pathogenic reaction of Pl PMI3 gene to avirulence Avr gene in P. halstedii races has not been studied. However, in sunflower downy mildew populations, the life-history traits: zoosporangia and sporangiophores size can be modified due to Avr gene in P. halstedii races that correspond to Pl genes (Sakr, 2011c(Sakr, , 2014a. In order to determine the importance of Pl PMI3 (Pl gene has still not been mapped) resistance gene in D4, phenotypic analyses (morphological and pathogenic) and genetic characteristics were carried out in two groups including four pathotypes which have never been documented outside of France: two isolates of 3xx races in which pathotype 304 do not overcome Pl PMI3 gene and 314 one can overcome, and two isolates of 7xx races in which pathotype 704 do not overcome Pl PMI3 gene and 714 one can overcome.…”

Pathogenic, morphological and genetic diversity in Plasmopara halstedii, the causal agent of sunflower downy mildew

“…The index of aggressiveness of P. halstedii isolates was calculated as the ration of sporulation density / latent period. The index of aggressiveness of the P. halstedii isolate was used to summarize all values for two criteria on sunflower inbred lines `FU` in one value to facilitate the comparison between the different P. halstedii isolates (SAKR, 2011b). Latent period was defined as the number of days of incubation necessary to obtain the sporulating pathogen on 80% of the plants.…”

“…Concerning that P. halstedii is characterized by a high level of evolutionary potential (SAKR, 2011b(SAKR, , 2012VIRANYI;, there have been several studies on virulence (DELMOTTE et al, 2008;SAKR, 2011bSAKR, , 2012TOURVIEILLE DE LABROUHE et al, 2000 and more recently on aggressiveness (SAKR, 2011a, b andc, 2012;SAKR et al, 2011). Virulence has been defined as specific disease-causing abilities and aggressiveness as nonspecific disease-causing abilities ( VAN DER PLANK, 1968).…”