The role of some quince stock (Cydonia oblonga) genotypes in susceptibility to fire blight disease

Fire blight caused by Erwinia amylovora (Burrill) Winslow et al. is one of the most catastrophic bacterial diseases of pome fruits. Among the various host plants, the quince (Cydonia oblonga) tree is one of the most susceptible hosts to the disease. Using the tolerant cultivars is the most economic method for disease control. This research was carried out in order to study the rootstock role on susceptibility of budded quince genotypes to the disease. 13 quince genotypes from central region of Iran, as well as cultivar "Isfahan" as control, were budded on quince and crataegus rootstocks and were evaluated for fire blight resistance in the greenhouse condition by using Ea273, S1 and Z1 isolates of bacteria in spring, 2007. Resistances were evaluated by necrosis progress rate and index of varietal susceptibility (I.V.S) in the shoots. On quince rootstock, the cultivar "Isfahan" and genotype SHA1 with 57.9 and 90.4% final disease progress, showed the lowest and highest symptoms respectively, while on crataegus rootstock, PH2 and NB3 genotypes with 71.5 and 100% final disease progress showed the lowest and highest symptoms, respectively. Results showed crataegus rootstock increased damage severity in 11 genotypes and decreased in other 3, compared with quince rootstock. Effect of rootstock type on the susceptibility changes in KVD3 and NB3 were the highest and in NB4 and PH2 were the lowest. According to the results in most quince genotypes, the crataegus rootstock can not be effective to increase resistance to disease.