Specific behaviour of French Aphanomyces euteiches Drechs. populations for virulence and aggressiveness on pea, related to isolates from Europe, America and New Zealand

The pathogenic variability of Aphanomyces euteiches on pea was investigated using a collection of 88 pea-infecting isolates from France and 21 isolates from Denmark, Sweden, Norway, USA, Canada and New Zealand. Aggressiveness and virulence were assessed by scoring the root symptoms on a differential set of six pea genotypes. Eleven virulence types were characterised. The virulence type I, previously described as virulent on the whole set, was predominant and included the most aggressive isolates of all geographical origins. The other types were much less prevalent, existing as one to five isolates. Three virulence types (III, IV and V) contained no French isolates. The type III, avirulent on MN313, was composed of American isolates only, and resembled the ‘major group’ recently described in the USA. A wide range of aggressiveness was found within the virulence type I, and the French isolates appeared globally more aggressive than the foreign isolates. These findings indicate that isolates from the virulence type I should be used as references in breeding programs, and that pea lines PI180693 and 552 may be the most interesting resistance sources to date, despite their only partial resistance.