Pathogenicity and relative virulence of 11 Greek Phytophthora species on apple and pear rootstocks

The pathogenicity and virulence of 11 Phytophthora spp. isolated from various host plants were examined on an apple (Malus domestica Borkh.) (MM106) and a pear (Pyrus communis L.) (O.H.F. 333) rootstock. Only P. cactorum and P. citricola isolates were pathogenic to these rootstocks. The isolates of P. cactorum were the most aggressive. The severe crown rot caused by isolates of P. cactorum and P. citricola suggests that these pathogens pose a potential threat to apple and pear orchards. P. citrophthora, P. boehmeriae, P. erythroseptica, P. capsici, P. cryptogea, P. drechsleri, P. cambivora, P. palmivora, and P. parasitica, isolated from various hosts, were not pathogenic to MM 106 and O.H.F. rootstocks, suggesting that these pathogens may not be a serious threat to apple and pear trees grafted on these rootstocks.