Pathogenicity of four Phytophthora species on wild cherry and Italian alder seedlings

Inoculation tests were carried out in the greenhouse on wild cherry (Prunus avium) and Italian alder (Alnus cordata) seedlings, to determine their susceptibility to certain Phytophthora species (P. citrophthora, P. alni, P. megasperma and P. cinnamomi) that are commonly present in the soil. Host susceptibility was evaluated in accordance with a disease index, with the lesion length after stem inoculation, and with a root system disease index. Wild cherry was found to be highly susceptible to P. citrophthora, and was also found to be susceptible to P. alni, although to a lesser extent. Italian alder was very susceptible to P. alni, but had only low susceptibility to P. citrophthora. The other Phytophthora species caused only modest symptoms. The danger to alder and wild cherry is all the greater because these trees not only share the same pathogens, but also commonly planted together in mixed stands. The results will now have to be confirmed by using a more natural inoculation method.