Assessment of the degree of frost resistance of blueberry varieties (Vaccinium corymbosum L.) of early ripening

Goal. To determine the degree of frost resistance of introduced varieties of blueberries (Vaccinium corymbosum L.) of early ripening. Methods. The degree of damage by low temperatures to the vegetative and generative organs of blueberries during wintering was determined using a laboratory method using an MBS-10 microscope. One-year shoots of blueberries were examined by the direct freezing method [10]. Mathematical and statistical data processing was performed using the analysis of variance method and Microsoft Office Excel. Results. Objects of research were the varieties of early ripening Shantekler, Diuk, Erlibliu, Fiolent, Reka, Spartan. It was proven that growing 6 early ripening varieties of blueberries in the Polissia zone of Ukraine (2023–2024) caused damage during wintering due to low temperatures. Based on the analysis of the tissues of shoots (bark, cambium, wood, core) and their parts (tops, internodes, buds), the degree of damage to shoots in natural and artificially created conditions was determined. Under natural conditions of growth in varieties Diuk and Spartan, the total score of freezing tissues and organs of one-year growth was, respectively, 1.0 and 1.5 points. The average winter hardiness was fixed for the Shantekler variety with a total score of 3.2; the lowest winter hardiness was possessed by the varieties Fiolent, Erlibliu, Reka with total points, respectively, 6.0, 6.2, and 7.3. In the laboratory, blueberry shoots were frozen in a freezer CRO/400/40 at temperatures of–25 and–30°C. The highest frost resistance for freezing to –25°C was noted in the varieties Diuk and Spartan, with a total score of 6.4. Average frost resistance at–25°C was fixed for the varieties Shantekler and Erlibliu with a total score of 9.1 and 9.5, respectively. The least frost-resistant were Fiolent and Reka — 11.7 and 16.0 points, respectively. At a freezing temperature of–30°C, the most frost-resistant varieties were Shantekler, Diuk, and Spartan with total points, respectively, 13.4; 14.8, and 19.0; the lowest frost resistance were varieties Reka, Erlibliu, and Fiolent with a freezing point, respectively, 20.5; 21.7; and 27.1. It was proved that temperatures of–25 and–30°C were critical for individual parts of shoots. The most sensitive to the action of low negative temperatures among all early ripening varieties were tissues of the bark and cambium, and the greatest frost endurance was distinguished by tissues of wood and the core. Conclusions. Of the studied varieties, Shantekler, Diuk, Spartan had the highest winter hardiness. In conditions of freezing at temperatures of–25 and–30°C, the highest frost resistance was noted in the varieties Shantekler, Spartan, and Diuk. Tissues of the varieties Reka and Fiolent at freezing temperatures of–25 and–30°C were the most damaged. The average winter hardiness was characterized by the Erlibliu variety. Laboratory and field studies confirmed that the tissues of bark, cambium, and the tops of shoots of blueberry plants had the least winter and frost resistance. Significant damage to generative buds in early ripening varieties was observed exclusively at a freezing temperature of –30°C; the exception was the Erlibliu variety, the generative formations of which were least damaged at low temperatures.