Genetic structure and pathogenicity of populations ofPhytophthora infestansfrom organic potato crops in France, Norway, Switzerland and the United Kingdom

Abstract

Genetic variation and pathogenicity of Phytophthora infestans isolates collected from organic potato crops of the susceptible cv. Bintje and the moderately resistant cv. Santé were assessed in France, Norway, and the United Kingdom in 2001 and in Switzerland in 2001 and 2002. Population structures differed considerably between the four P. infestans populations. Those from France, Switzerland and the UK were mainly clonal populations showing restricted levels of genetic diversity, whilst those from Norway were mixed A1 and A2 mating type populations with high levels of genetic diversity, suggesting periodical sexual reproduction. Isolates collected from cv. Bintje were on average more aggressive than or comparable to isolates from cv. Santé. Race complexity varied considerably between the regional P. infestans populations, with isolates from France and Switzerland showing the highest number of virulence factors. In all pathogen samples but the French, isolates collected from cv. Santé were more complex than isolates collected from cv. Bintje. No directional selection towards increased aggressiveness towards the more resistant cultivar Santé was observed. This suggests that there is no shift towards increased levels of pathogenicity in P. infestans populations following the large-scale introduction of more resistant potato varieties in organic production systems in Europe.

Characterization of Phytophthora infestans Isolates from Jersey, Channel Islands

“…There is a common perception in Western Europe that since these introductions, late blight of potato has become more difficult to control. Studies using molecular markers have shown increased diversity of the populations in Great Britain (Cooke et al 2003;Day et al 2004) and France Flier et al 2007).…”

Genetic variation and host specificity of Phytophthora citrophthora isolates causing branch cankers in Clementine trees in Spain

“…These new strains were more aggressive to scion cultivars than the predominant population, which was conversely more aggressive to rootstocks (Cohen et al 2003;Vernière et al 2004). Evidence of genetic differentiation and host specialization has been described for other Phytophthora species such as P. cactorum (Hantula et al 1997;Eikemo et al 2004;Bhat et al 2006), P. capsici (Lamour and Hausbeck 2000;Lamour and Hausbeck 2001), P. cinnamomi (Linde et al 1997), P. infestans (Abu-El Samen et al 2003;Flier et al 2007) and P. megasperma (Hamm and Hansen 1981).…”

“…Among them, InterSimple Sequence Repeat (ISSR), also known as microsatellites, has been used for identifying intraspecific patterns within Oomycetes (Zietkiewicz et al 1994;Hantula et al 1996Hantula et al , 1997Knapova and Gisi 2002;Cohen et al 2003). Studies on the population structure of some Phytophthora species using molecular tools have also found phenotypic variability and host specificity associated to intraspecific genetic differentiation (Day et al 2004;Flier et al 2007). However, in other cases, this intraspecific genetic differentiation has not been correlated with differences in phenotypic characters and aggressiveness to the host.…”

Analyzing the Influence of Qualitative Resistance Selection Pressure on Variation of Aggressiveness in Plasmopara Halstedii

“…nicotianae. Also, Flier et al (2007) showed that, following large-scale introduction of more resistant potato varieties in organic production systems in Europe, there was no shift towards increased levels of aggressiveness of Phytophthora infestans populations.…”