Testing of Susceptibility Level of Czech Apple Cultivars to Fire Blight (Erwinia amylovora) in Field Conditions

Ten older apple cultivars and Czech landraces and two commercially-grown cultivars ('Selena', 'Golden Delicious') as standards were tested for their relative susceptibility level to fire blight after artificial inoculation in the climatic conditions of the Czech Republic. The experiment was established in a screen-house covered with insect-proof net. The artificial inoculation was carried out by cutting the apical part of one year old shoot tips with scissors dipped in a bacterial suspension of mix isolates of Erwinia amylovora (concentration 106 CFU/ml) in climatic conditions conducive for infection (temperature > 15 degrees C, relative humidity > 75%). Evaluation of susceptibility level was performed 40 days after inoculation according to the percentage of necrotic lesion development. Calculated intensity of infection was consequently transferred to a six-point evaluation scale. From the tested genotypes, only 'Selena' was evaluated as resistant (11.2% infection intensity). The remaining genotypes were categorized as medium susceptible, susceptible or highly susceptible.