The susceptibility of some Swedish pear cultivars to fire blight: an experimental test.

Fire blight, caused by Erwinia amylovora, is a serious disease, which attacks plants within the family of Rosaceae. This bacterial disease causes major problems in the cultivation of pears (Pyrus communis) around the world. The occurrence of the disease is still geographically limited to certain areas in Sweden and neighbouring countries. However, increasing temperatures due to climate change and the relative unawareness of the public, augment the risk of its spread. Within the EU, there are no approved antibiotics for use in pear orchards. Within the species of P. communis, cultivars vary in their susceptibility to fire blight. Many scientists believe that new, resistant cultivars and rootstocks are important tools to enable pome fruit cultivation in the future.In this study,the susceptibility of some Swedish pear heirloom cultivars to E. amylovora was investigated by using immature pear fruit. The bacteria were introduced into immature pear fruit by using defined concentrations of inoculum. The fruit were incubated at 25°C, and disease severity was recorded over time. Disease was measured and recorded as the extent of lateral lesion size on the surfaces of the pear fruit. No definite differences in disease development were recorded across the concentrations tested. The cultivars were compared to one another, and ranked according to susceptibility. The most susceptible to the least susceptible were: `Sollerö´ > `Unknown Gävle´ = `Esperens herre´ = `Aspa´ > `Höstbergamott´ > `Göteborgs Diamant´ > `Conference´ = `Lilla dalpilen´ = `Carola´ > `Alexander Lukas´ = `Blodpäron´ = `Bonne Louise´. The results could have become clearer if immature fruit of younger physiological age had been used. Nevertheless, the ranking of some cultivars agrees with the published results of others