Features of the development of apple budded trees on clonal rootstocks bred by Michurinsk State Agrarian University in the second nursery field

Clonal apple rootstocks play a fundamental role in the intensification of contemporary horticulture. The study examined the main biometric parameters of apple budded trees in the second nursery field and performed ranking of new rootstock forms based on their growth vigor. Records of plant biometric parameters were taken in 2024–2025 after the end of the active growth period (in the first ten days of September) at the fruit nursery of Michurinsk State Agrarian University, located in Michurinsk, Tambov oblast. In the second nursery field, for apple budded trees of the Berkutovskoe, Lobo, and Sinap Orlovskiy cultivars on 5 regionalized and 7 promising clonal rootstock forms, variation in the average values of the main morphological parameters was noted depending on the rootstock vigour. This variation was as follows: plant height by 1.2–1.4 times (C_v=6.4 to 8.2 %); trunk diameter by 1.4 times (C_v=10.2 to 11.1 %); leaf blade area by 1.5–1.7 times (C_v=12.6 to 15.6%); number of leaves by 1.2–1.4 times (C_v=7.3 to 9.4 %); and total leaf area by 1.9–2.4 times (C_v=18.4 to 23.0 %). All minimum values of these characteristics were identified in seedlings on the Malysh Budagovskogo super-dwarf rootstock, while the maximum values were on the semi-vigorous rootstock 70-20-20. High positive correlations (r=0.74 to 0.96) between the main biometric parameters of one-year-old apple seedlings were noted. For an early preliminary assessment of the growth vigour of new clonal rootstock forms, a quantitative indicator was calculated – the plant growth vigour coefficient for the studied scion-rootstock combination in the second nursery field. This coefficient is defined as the product of plant height and trunk diameter. For plants of the three apple cultivars on semi-vigorous rootstocks, its values exceeded 200–230 units; for semi-dwarfing rootstocks, values were within 170–200; and for dwarfing rootstocks, less than 180. Based on the evaluation of the budded tree development from various scion-rootstock combinations in the second nursery field, the new clonal apple rootstock forms were grouped according to their growth vigor as follows: dwarf – 9-1-1; semi-dwarfing – 5-28-11, 9-1-2, 9-1-3, 9-1-9; semi-vigorous – 9-1-4, 9-1-5.

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