Evaluation of Resistance of Stone Fruit Rootstocks to Phytophthora Crown Rot*

The pathogenicity of Phytophthora citrophthora\ Phy! tophthora cactorum and Phytophthora me`asperma strains was con_rmed on 1!year!old stone fruit rootstocks arti_cially inoculated in the _eld[ Phytophthora me`a! sperma was not virulent or less virulent than P[ cactorum or P[ citrophthora[ The rootstocks Damas and AN 0:6 were resistant whereas the rootstocks J0\ Titan Nemaguard 4:0\ GF 566\ Myrandier 502\ Italian Nemaguard 0 and Myrandier 506 were susceptible to P[ citrophthora[ The rootstocks Tsukuba 8\ Tit! an Nemaguard 3:6\ AN 0:1\ AN 0:2\ St[ Julien 544:1 and B0 showed medium susceptibility to this species[ The isolates of P[ cactorum induced more extensive necrosis in Myrandier 506 and Italian Nemaguard than in Myr! andier 502\ GF 566\ J0 "ADAFUEL#\ Tsukuba 8 and St[ Julien 544:1[ Among seven rootstocks\ Tsukuba 4 and St[ Julien 544:1 were more resistant than Myrandier 502Myrandier 506\ J0 "ADAFUEL#\ Tsukuba 8 and St[ Julien 544:1[