Phytophthora root and crown rot is one of the main reasons for stone fruit trees decline that is sometimes called as short life of stonefruits. This study was initiated to establish an accurate and reliable method to inoculate plum genotypes and screening resistant genotypes to the disease. Infected plant tissues were collected from Meshkindasht and Kamalshahr Horticultural Research Stations of Seed and Plant Improvement Institute located in Karaj. Using semi-selective media containing Carbendazim, Pimaricine and Rifampicin, 10 ppm each, two isolates of Phytophthora were obtained from apricot and almond. They were identified as P. cactorum according to physiological and morphological characteristics. Resistance of genotypes to Phytophthora was evaluated using ST107 isolate of P. cactorum isolated from apricot. The plant materials including eight promising genotypes of plum and greengage were propagated on MS tissue culture media amended with Carbendazim successfully, and the pathogen was reproduced on sterilized wheat grains, simultaneously. A single infected grain was located on base of each shoot and the necrosis was recorded after 10 days incubation at 24°C in dark. A four parts scale was used to assess the response of the genotypes. All genotypes were infected with P. cactorum isolate with different severities. Genotypes 3547, 3554, 3553, 3542, 3538, 3528 and 3515 showed more than 70 percent of necrosis extension index. Genotype 3512 showed moderately resistant reaction with less than 50 percent of necrosis extension index.
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