Physiological changes during dormancy onset in apple clonal rootstocks developed at Michurinsk State Agrarian University

This article presents the results of long-term studies on physiological changes during dormancy onset in apple clonal rootstocks developed at Michurinsk State Agrarian University: red-leaved forms 54–118, 62–396, and 70–20–20, and green-leaved rootstock 76–16–11. It was shown that the anthocyanin content in the bark of shoots fluctuated annually in rootstock 54–118, ranging from 77 to 110 units, and in rootstock 62–396, ranging from 58 to 80 units. Sugar accumulation in the bark of these rootstocks was approximately at the same level (3.0–4.5%). Green-leaved rootstock 76–16–11 synthesized 1.5–2 times less anthocyanins than the red-leaved rootstocks by the beginning of dormancy, but accumulated 1.5–2 times more sugars. In field experiments, shoot damage after overwintering was minimal in rootstocks where shoot growth had ceased or did not resume before the onset of frost. Rootstocks 54–118 and 70–20–20 were characterized by long vegetation periods and continued growth processes in September-October during the study. Rootstock 62–396 exhibited an autumn growth wave, forming apex buds in August.Rootstock 76–16–11 showed the least damage from freezing and uprooting during the study. While rootstock 70–20–20 experienced the most frequent winter damage, it had no bush dropouts, indicating its strong regenerative capacity. These differing adaptation strategies to overwintering conditions among the Michurinsk State Agrarian University clonal rootstocks, arising from genotypic diversity, necessitate a comprehensive evaluation of new forms in specific climatic conditions for optimal utilization.