Frost hardiness of flower buds of three plum (Prunus domestica L.) cultivars

- Frost hardiness profiles of flower buds of three plum (Prunus domestica L.) cultivars have been established across 8 years.
- LT50 values were determined based on results of artificial freezing tests.
- Frost hardiness reached its maximum in the middle of winter, when genotypic differences was the largest variance component.
- During dehardening the year effect as variance component became most pronounced.

Frost hardiness of flower buds of three plum (Prunus domestica L.) cultivars ('Cacanska lepotica', 'Stanley', 'Besztercei') was characterised by the LT50 values calculated from artificial freezing experiments conducted during eight dormancy periods between 2004 and 2016. Of the two variance components, the year effect was the strongest at the beginning of dormancy explaining around 60% of the phenotypic variation in LT50 values, while the effect of genotype started to increase from November and reached its maximum in the middle of January, when 81.2% of the variance in LT50 was due to the genotype. During the first part of winter the frost hardiness of the overwintering organs developed gradually in parallel to the decreasing ambient temperature. Flower buds were the most frost tolerant in the first half of January, when the maximum LT50 of 'Cacanska lepotica' was −22.8 °C, for 'Stanley' −24.8 °C and for 'Besztercei' it was −26.5 °C, averaged over the 8 dormancy periods. From the end of dormancy the effect of year became much stronger over the genotypic differences from the second half of January. Milder days during this period resulted in faster flower bud development paralleled by a steeper and quicker decline in frost tolerance, which may significantly increase the probability of frost damages in flowers caused by late winter and spring frosts.