Evaluation of resistance of stone fruit rootstocks to Phytophthora crown rot

The pathogenicity of Phytophthora citrophthora, Phytophthol a cactorum and Phyrophthora megasperma strains was confirmed on 2-year-old stone fruit rootstocks artificially inoculated in the field. Phytophthora megasperma was not virulent or less virulent than P. cactorum or P. citrophthora. The rootstocks Damas and AN 1/7 were resistant whereas the rootstocks J1, Titan x Nemaguard 5/1, GF 677, Myrandier 613, Italian x Nemaguard 1 and Myrandier 617 were susceptible to P. citrophthora. The rootstocks Tsukuba 9, Titan x Nemaguard 4/7, AN 1/2, AN 1/3, St. Julien 655/2 and B1 showed medium susceptibility to this species. The isolates of P. cactorum induced more extensive necrosis in Myrandier 617 and Italian x Nemaguard than in Myrandier 613, GF 677, J1 (ADAFUEL), Tsukuba 9 and St. Julien 655/2. Among seven rootstocks, Tsukuba 5 and St. Julien 655/2 were more resistant than Myrandier 613, Myrandier 617, J1 (ADAFUEL), Tsukuba 9 and St. Julien 655/2.