A Method to Measure Aggressiveness of Plasmopara halstedii (Sunflower Downy Mildew)

Abstract

For the first time, a method was used to measure aggressiveness of two Plasmopara halstedii races (100 and 710), the parasite causing sunflower downy mildew. Two sunflower lines showing different levels of quantitative resistance were used to measure two aggressiveness criteria: latent period and sporulation density. A strain of race 100 had a shorter latent period and greater sporulation density than a strain of race 710. The sunflower inbred line BT, rather susceptible in the field, presented a greater sporulation density and a shorter latent period than another inbred line FU, which shows greater resistance in the field. These results indicated that race 100 was more aggressive than race 710. The behaviour in the field of the two inbred lines was confirmed in the laboratory observations.

Can percentage infection and dwarfing be used to differentiate aggressiveness inPlasmopara halstedii?

“…Our results showed that the high level of quantitative resistance in the inbred line FU made it possible to detect significant differences between single zoosporangium isolates and parental isolates (Tables 2 and 3). These results are in accordance with our previous analysis on the comportment of sunflower inbred line 'FU' in the growth chamber Sakr 2009a,b;Sakr et al 2009). Similarly, for Phytophthora infestans, Carlisle et al (2002) reported that the differences in aggressiveness of the different isolates of the pathogen were most easily measured on a potato variety with a high level of quantitative resistance.…”

“…Year isolated soaking sub-samples of the seeds for 3 h in a suspension of 1 6 10 5 zoosporangia ml 71 (counted with a Malassez cell) for single zoosporangium isolates (Sakr et al 2009). The seedlings were grown in soil-less horticultural compost.…”

“…In this patho-system, there have been several studies on virulence (Tourvieille de Labrouhe et al 2000;Gulya 2007;Delmotte et al 2008) and more recently on aggressiveness Sakr 2009b;Sakr et al 2009;Tourvieille de Labrouhe et al 2010). Virulence has been defined as specific disease-causing ability and aggressiveness as non-specific disease-causing ability according to Van der Plank (1968).…”

“…Virulence has been defined as specific disease-causing ability and aggressiveness as non-specific disease-causing ability according to Van der Plank (1968). Sakr et al (2009) used two aggressiveness criteria, latent period and sporulation density, to differentiate between two field isolates of races 100 and 710. Moreover, evolution of aggressiveness in P. halstedii populations was measured under different strategies of Pl gene management Tourvieille de Labrouhe et al 2010).…”

Pathogenicity and its alternation with both morphological and genetic variation inPlasmopara halstedii(sunflower downy mildew)

“…Several studies have revealed the components of pathogenicity in P. halstedii: virulence , 2010Gulya 2007;Sakr 2011Sakr , 2012 and aggressiveness (Sakr et al 2009Tourvieille de Labrouhe et al 2010;Sakr 2011Sakr , 2012. Virulence has been defined as specific disease-causing abilities and aggressiveness as non-specific disease-causing abilities (Van der Plank 1968).…”