Evaluation of Fire Blight Resistance in some Quince (Cydonia oblonga Mill.) Genotypes. I. Isolation, Evaluation and Selection of Causal Bacterial (Erwinia amylovora) Isolates

Fire blight caused by Erwinia amylovora (Burr.) Winslow et al., has the highest importance among different diseases of pome fruits in many countries. Use of resistant or tolerant cultivars has been suggested as the most economic and effective method to control the disease. In this research different isolates of fire blight causal agent bacterium were isolated and evaluated biochemically and pathologically to select the highly virulent isolates for subsequent use in screening of quince (Cydonia oblonga Mill.) genotypes to the disease. Five isolates out of 25 primary isolates successfully passed all biochemical and phytopathological identification tests. Two isolates obtained from Zanjan province (Z1 and Z2) and one isolate from Tehran province (K2) expressed more virulence that shows their appropriateness in the screening of genotypes. Modeling of carbon source utilization by isolates confirmed homology of the isolates and revealed potential of bacterium to metabolize sucrose, glucose and fructose faster than other carbohydrates. Regarding to the dominance of sucrose and glucose in Rosaceae family, it seems that limited host range of bacterium at least in part, is depending on the accessibility of an appropriate carbon source in the members of this family. Test of resistance to the antibiotics revealed existence of an eventual high streptomycin resistance in K1 isolate that is the first report in country