IMPROVEMENT OF SYSTEM FOR TESTING OF POME FRUIT RESISTANCE TO ERWINIA AMYLOVORA USING IN VITRO ARTIFICIAL INOCULATION

Fire blight is a destructive bacterial disease that presents potential threat to apple and pear industries throughout Europe. Specific, safe and reliable methods for identifying the pathogen Erwinia amylovora and a consistent system for cultivar resistance testing can be very important factors in the management of the disease. Therefore a screening system for testing of pome fruit resistance to E. amylovora was developed based on in vitro artificial inoculation. Selected pome fruit genotypes were successfully established in vitro using mercuric chloride in a concentration of 0.15% as a sterilization solution. MS medium according to Murashige and Skoog (1962) with addition of cytokinins 6-benzylaminopurine (BAP, 2 and 4 mg/L) or thidiazuron (TDZ, 0.5 and 1 mg/L) proved to be suitable for in vitro proliferation. We obtained multiplication coefficients higher than 2.0 for all tested pome fruit genotypes. The application of TDZ in both concentrations induced hyperhydricity in the case of 90% shoots of apple cultivar (‘Kaiser Alexander’). After the multiplication phase, three MS based media were tested for shoot elongation: full MS medium with 1 mg/L indole-3-butyric acid (IBA) and 0.1 mg/L BAP; 50% MS with 1 mg/L IBA and MS medium with macronutrients reduced to 40% and micronutrients reduced to 35% with 2.5 mg/L IBA. The aim in this phase was to obtain actively growing in vitro shoots elongated to at least 2.0 cm for experiments with in vitro artificial inoculation of E. amylovora. Out of the tested media, only full MS medium with 1 mg/L IBA and 0.1 mg/L BAP produced actively growing shoots longer than 2 cm suitable for monitoring of the development of bacterial lesions.