Frost hardiness of apple generative buds during dormancy

The success of apple production is influenced by frost damages. Occurrence of extreme temperatures is increasing worldwide because of global warming, so the risk of frost damages is also increasing in apple orchards during dormancy and blooming time. In our work the frost hardiness of flower buds of eight apple cultivars was observed with artificial freezing tests during four subsequent dormancy periods in Hungary. The studied cultivar assortment contained two standard commercial cultivars (‘Gala’, ‘Idared’), two scab-resistant cultivars from abroad breeding programmes (‘Florina’, ‘Prima’) and four new Hungarian multi-resistant (mainly scab-resistant) cultivars (‘Artemisz’, ‘Cordelia’, ‘Hesztia’, ‘Rosmerta’). There were remarkable differences between cultivars and years from the aspect of frost hardiness of generative overwintering organs. At the end of hardening period, in January, the LT50 values of flower buds were between -22.4 °C and -30.4 °C according to cultivar and year. LT50 means the temperature causing 50 % frost damage in the flower buds of the certain cultivar in the certain time. ‘Gala’ and ‘Florina’ were the most frost hardy, while ‘Prima’, ‘Cordelia’ and ‘Idared’ the most sensitive to frost. Cold hardiness values of flower buds of ‘Artemisz’, ‘Rosmerta’ and ‘Hesztia’ cultivars were regularly between the values of two extreme groups. In winters with inappropriate weather the generative overwintering organs were unable to reach the genetically possible frost hardiness of them.