Microsatellite markers reveal two admixed genetic groups and an ongoing displacement within the French population of the invasive plant pathogen Phytophthora infestans

Potato late blight is an example of a re‐emerging disease of plants. Phytophthora infestans was first introduced into Europe during the 19th century, where it caused the Irish potato famine. During the 20th century several additional introduction events have been suspected, especially in the mid‐70s due to the import of large quantities of potato needed after the shortage caused by drought in 1976. Here, we investigate the genetic population structure of Phytophthora infestans, at the first stages of a recent invasion process in France. A total of 220 isolates was collected from 20 commercial fields of the potato susceptible cultivar Bintje, during two consecutive years (2004 and 2005). Clustering analyses based on eight recently developed microsatellite markers reveal that French P. infestans populations are made of two differentiated genetic clusters of isolates (F_ST = 0.19). This result suggests multiple introductions of P. infestans into France, either through the introduction of a composite population of isolates or through the successive introduction of isolates having differentiated genetic backgrounds. Both clusters identified have a strong clonal structure and are similar regarding genetic diversity and mating type composition. The maintenance of differentiation between the two genetic clusters should result from the low or non‐existent contribution of sexual reproduction in French P. infestans populations.     

Presumed Behavior: Comments on Cara E. Richards' Brief Communication

Cara E. Richards recently pointed out that instead of the well-established dichotomy between ideal and real behavior, one should consider a trichotomy, with presumed behavior as a third term. The present note agrees with this, but (a) briefly examines some previous publications specifically dealing with this trichotomy, (b) suggests some points of view complementary to those of the Richards communication, and (c) attempts to place studies of presumed behavior in the context of anthropological theory.