Relative Resistance of Four Peach Rootstocks to Phytophthora cactorum and Phytophthora megasperma

Shoot samples of four peach rootstocks that are important to the peach industry in Greece: KID I, GF305, GF677, and PR204, were inoculated with Phytophthora cactorum and Phytophthora megasperma in the ®eld and in the glasshouse and were then evaluated with regard to susceptibility. The pathogen- icity of P. cactorum and P. megasperma to peach rootstocks was con®rmed with an excised twig assay. The peach rootstocks showed di€erential susceptibility to P. cactorum. GF305 was the least susceptible and KID I was the most susceptible, which suggests that the latter rootstock is unsuitable for orchards in which the conditions are favourable for Phytophthora diseases. GF677 and PR204 were moderately susceptible. The plants that were inoculated with P. megasperma in the ®eld and in the glasshouse showed no sign of infection whereas twigs inoculated in vitro with P. megasperma developed necrosis. GF305 was the most resistant, KID I was the most susceptible and PR204 and GF677 were moderately resistant. The present results demonstrate that none of the four peach rootstocks used in this study was completely resistant to P. cactorum, particularly when rootstocks were ¯ooded periodically to enhance disease development. Therefore an integrated approach including host and resistance cultural practices is recommended to manage diseases caused by P. cactorum in peach orchards in Greece