Investigation of winter hardiness and cold hardiness in apple progenies

Diallel crosses of 8 apple cultivars ('Orlik', 'Noris', 'Auksis', 'Katja', 'Kaunis', 'Tellissaare', 'Prima', 'Idared') were carried out according to Griffing's method 4. In the spring of 1991 seedlings of 28 progenies were planted in the orchardin a randomised complete-block design. Tt was established that apple seedlings could resist -30 40 degreesC during different periods of wintering. Most hardy seedlings were found in crosses of local cultivars 'Kaunis','Auksis', 'Noris' and 'Tellissaare'. The highest percentage (65,7%) of winter hardy plants was established after the mild winter of 1997-98, the winter 1996-97 16.3%, 1993-94 - 13.8%, 1995-96 - 6.8%. Progenies of crosses involving local cultivars were more winter hardy than progenies from other crosses. Similar results of seedling evaluation for cold and winter hardiness were obtained by using the freezing method. Therefore, the freezing method can be suitable for screening of hardy seedlings. Inheritance of winter hardiness was estimated as well. General and specific combining abilities were highly significant for winter hardiness. But the mean square for the general combining ability was several times larger than the one for the specific combining ability. It indicates that winter hardiness is mainly controlled by additive genes. Selection of parents based on their own winter hardiness or general combining ability effects should be effective to increase winter hardiness of breeding populations.