Evaluation of Fire Blight Resistance in some Quince (Cydonia oblonga Mill.) Genotypes. II. Resistance of Genotypes to the Disease

Fire blight (Erwinia amylovora) is an important and catastrophic disease of pome fruits in Iran. Among various host plants, the quinces (Cydonia oblonga Mill.) trees usually suffer more damages than other hosts. Resistance of indo- and exogenous germplasm of pear and apple of Iran to the disease has been evaluated previously both in the greenhouse and orchard conditions. This study was carried out to evaluate fire blight resistance in some Iranian quince genotypes, respecting to the high susceptibility and genetic variation of quince in Iran. After isolation and appropriate tests of bacteria, thirteen quince genotypes of central region of Iran, as well as cultivar Isfahan (encoded as KVD3) as control, were propagated on quince seedlings and screened for fire blight resistance during a three years period (2004-2007) in the greenhouse condition, using K2, Z1 and Z2 isolates of bacteria. Resistance was evaluated by survey of necrosis progress rate at 4, 8, 17 and 22 days after inoculation, and index of varietal susceptibility (I.V.S.) in the shoots. The cultivar Isfahan with 50% and genotype SHA1 with 90% final disease progress showed the lowest and the highest susceptibility to the disease, respectively. Correlation analysis between different characteristics demonstrated the highest relation of fire blight resistance with vigor of lateral bud growth, especially at the beginning of disease establishment (first 4-8 days) in the shoots.