Adaptation ofPhytophthora infestansto Partial Resistance in Potato: Evidence from French and Moroccan Populations

Abstract

The use of partially resistant cultivars should become an essential component of a sustainable management strategy of potato late blight, caused by Phytophthora infestans. It is therefore important to determine to what extent P. infestans populations can be selected for increased aggressiveness by potato cultivars with different levels of partial resistance. To this end, we sampled P. infestans populations from France and Morocco, chosen as locations where late blight occurs regularly but which differ in the distribution of potato cultivars. Cross-inoculation experiments were used to determine the aggressiveness of all populations to potato cvs. Bintje (prevalent in France but not grown in Morocco) and Désirée (popular in Morocco but cultivated to a very small extent in France). French populations were more aggressive on cv. Bintje than on cv. Désirée, irrespective of the site they were sampled from. Their aggressiveness increased between early and late samplings, suggesting that both cultivars selected for increased aggressiveness during epidemics. By contrast, Moroccan populations were more aggressive on Désirée, regarded as partially resistant in Europe, than on Bintje, highly susceptible under European conditions. These data indicate that P. infestans populations adapt to locally dominant cultivars, irrespective of their resistance levels, and can therefore overcome polygenic, partial resistance. This adaptive pattern may render partial resistance nondurable if not properly managed.

Seasonal Changes Drive Short-Term Selection for Fitness Traits in the Wheat Pathogen Zymoseptoria tritici

“…This was consistent with the increase in disease intensity recorded in different fungal pathogens after only a few asexual cycles (29)(30)(31)(32). Isolates of the final population (Pf) showed greater sporulation intensity under winter conditions, and a shorter latency period under spring conditions, than isolates of the initial population (Pi).…”

“…Directional selection for increased aggressiveness during the epidemic period was established experimentally for Phytophthora infestans, but no evidence of any trade-off between aggressiveness and overwinter survival was found (31,46). Further experimental investigations taking into account the pathogenic and saprophytic phases of the disease cycle (40,41), guided by theory (43,47), would be appropriate for characterizing the effect of seasonality on year-to-year disease transmission.…”

Resistance to Phytophthora infestans in Solanum tuberosum landraces in Southern Chile

“…On the other hand, Huarte & Capezio (2003) reported that genotype vs. environment (GxE) interactions in resistance to late blight have not yet been clearly determined. The absence of genotype vs. environment interactions has also been noted by Andrivon et al (2007) for different varieties in different locations in Morocco. In general terms, the significance of the interaction does not appear to be greater than the variation due to genotype and location.…”

Genetic Structure and Aggressiveness of Erysiphe necator Populations during Grapevine Powdery Mildew Epidemics

“…This result contrasts with those obtained previously for other fungal plant pathogens. Villareal and Lannou (38) and Andrivon et al (2) showed that directional selection for increased aggressiveness takes place in Erysiphe graminis and Phytophthora infestans populations, respectively, during the epidemic stage. Some fungal plant pathogens alternate between highly aggressive life stages and life stages in which highly aggressive strains are selected against, whereas the aggressiveness of other fungal plant pathogens, such as Mycosphaerella graminicola (9) and E. necator, remains stable.…”