Cold Resistance of Flower Buds of Latvian Plum Cultivars

Cold resistance of fruit tree buds is very important. Climate change brings unstable winters, and the temperature often fluctuates and creates many problems in fruit growing. Research on bud cold damage was conducted during three years (2019–2021) at the Institute of Horticulture. Three Latvian plum cultivars, ‘Ance’, ‘Adelyn’, and ‘Sonora’, were studied, while cultivar ‘Jubileum’ was used as a control. This study aimed to determine the cold resistance of flower buds and vegetative buds of plum cultivars after the deep dormancy period. Evaluation of buds was done on one-year-old shoots and spurs. Evaluation of cold damage on flower buds and vegetative buds was done after the deep dormancy period: in February 2019 and at the end of January 2020 and 2021, after keeping the buds for a limited time in temperatures thresholds of –20 °C, –25 °C, –30 °C, –35 °C in alternating climate chambers. The results showed significant differences among cultivars, years, and between branch types. Vegetative buds for all cultivars were without significant cold damage. Up to –30 °C wood browning was observed near the base of buds. A significant amount of flower bud damage (up to 100%) was observed in 2020, in a temperature threshold until –30 °C for both types of branches. The most durable cultivars were ‘Ance’ and ‘Adelyn’ (up to –25 °C, bud survival was near 100%) all three years. ‘Jubileum’ had the most vulnerable flower buds. The lowest low-temperature damage for all cultivars was in 2021. For one-year-old shoots, bud damage only occurred at –35 °C for all cultivars all years.