Assessment of plum genotypes for resistance to Phytophthora root rot

Early decline of stone fruit is one of the challenges of stone fruit cultivation in Iran. Multiple reasons are believed to cause this problem including soilborn fungi such as Phytophthora species. In order to screen some of promising genotypes of plum to Phytophthora, the causal agent was isolated from infected plant tissues collected from Meshkin Abad and Kamal shahr Horticultural Research Stations in Karaj and then was cultured on semi selective media containing Pimaricin, Carbendazim and Rifampicin each 10 mg per liter concentration that three isolates of Phytophthora were recovered. All three isolates were identified as P. cactorum using morphological and physiological characters. Other fungi including Pythium, Fusarium and Rossellinia were also recovered. Using green unripe pear fruits, pathogenicity test was conductedfor two strains. For assessment of disease resistance, 22 plum genotypes reproduced with cutting stem in the greenhouse condition on perlite layered on warm pipes. Plum cuttings were inoculated with mixture of three P. cactorum isolates. The inocula was prepared in suspension and applied on the crown area of two year cutting stems in greenhouse condition. Disease severity was recorded using a four degree scale and the data was analysed with non parametric test. The result showed that most genotypes were resistant to the disease and the most disease severity was recorded for 3543 genotype. Key words: Phytophthora cactorum, plum genotypes, disease resistance