Abstract
The aim of this research was the evaluation of whether the application of 5-ALA, which has potential as a plant growth stimulating agent with indirect anti-stress activity, can limit the damage caused by low temperatures in winter. The research was conducted on frost-sensitive apple cultivars for three years in an orchard and in a laboratory. During the vegetative seasons of each year, the trees of three apple cultivars (‘Golden Delicious’, ‘Gala’ and ‘Šampion’) were subject to 5-ALA foliar application. Three times during each winter following the field application, apple shoots were taken to the laboratory and frozen at −20°C, −25°C and −30°C. After incubation, the damage to the sensitive parts of the shoots was evaluated. The application had a positive effect on the frost resistance of all cultivars, most often at the end of dormancy, which is especially noteworthy because frost damage occurs most frequently during this period. Positive effects of the application were found in most of the experiment combinations of cultivar, year, freezing date and shoot part. Additionally, the positive influence of 5-ALA application on frost resistance was found to increase with each year of the research.