Comparing virulence of phytophthora plurivora and P. pseudosyringae towards fagus sylvatica seedlings using a method ensuring equal growth of both pathogens

Phytophthora plurivora T.Jung & T.I.Burgess and P. pseudosyringae T.Jung & Delatour exhibit different potential to colonise host plants. In order to clarify whether P. plurivora is more aggressive than P. pseudosyringae simply because of its faster growth and sporulation, a method for root infection was developed ensuring equal growth and sporulation for both pathogens during infection of F. sylvatica L. seedlings. Infection with P. plurivora strongly reduced CO2 uptake of seedlings and five out of eight seedlings died by the end of the experiment. In contrast, P. pseudosyringae did not alter physiology of infected plants and no mortality was recorded. The DNA contents of roots infected by either pathogen were similar at the end of the experiment, which indicated that a similar amount of fungal material was present for each species. This indicates that the greater aggressiveness of P. plurivora in comparison to P. pseudosyringae cannot be explained by its faster growth compared to P. pseudosyringae at a given temperature.