Evaluation of Relative Resistance in Five Stone Fruit Rootstocks to Phytophthora cactorum and P. drechsleri

Tree decline induced by pathogenic soil fungi is one the most important problems in the orchards of stone fruit trees in Iran. Phytophthora spp. are the most principal fungi that particularly prevent the root and crown growth of stone fruit trees. This study aimed to assess the relative resistance of five new stone fruit trees rootstocks Penta، Cadaman، Tetra، Mr. S2/5 and GF677، to Phytophthora cactorum and P. drechsleri. The experiment was conduced in laboratory by active and dormant cutting shoot method and also the pot soils artificially inoculated with the fungus. The inoculum grown on vermiculite containing cannabis extract was placed next to the crown and root and the necrosis length was measured four months after inoculation. Results showed that trees exhibited different sensitivity to two Phytophthora species. P. drechsleri was less virulent than P. cactorum. The results of the laboratory and glasshouse assessments showed that Cadaman and GF677 rootstocks had the maximum necrosis length، while Penta and Tetra indicated the minimum value. Hence، Penta and Tetra rootstocks seem to have high relative resistance to crown rot.