Investigations on Resistance of In Vitro Regenerants of Apple (Malus domestica Borkh.) 'Cadel'® to Major Diseases

Decreasing the application of agrochemicals, especially pesticides, in fruit growing practices is one of the most important problems placed by the European Commission of Agriculture with the aim of preserving human health and protecting the environment. The problem is a matter of urgency in the apple crop, which occupies a leading position by the number of pesticide treatments. Solving the problem necessitates the establishment of cultivars resistant or tolerant to the major diseases and pests. The aim of the present study is to test the resistance of in vitro obtained apple regenerants 'Cadel'(R), to the most widely distributed phytopathogens in apple - scab (Venturia inaequalis), powdery mildew (Podosphaera leucotricha) and fire blight (Erwinia amylovora). Varying concentrations of monospore cultures of the respective fungal pathogens isolated from naturally infected leaves and most aggressive bacterial strain from Bulgaria are used in the investigation. The acclimatized in vitro somaclones, 8-10 cm in height or at the 4th-5th true leaf development stage, are inoculated with the respective phytopathogens following standard or improved methods. It is established that 3 out of the studied clones demonstrated a complex resistance to scab and powdery mildew diseases and low susceptibility/tolerance to the dangerous bacterial disease fire blight.