Adaptability of the Best Domestic and Introduced Apple Rootstocks to Different Soil and Climatic Conditions of Ukraine during the Early Years of Commercial Fruiting

Abstract

Objective. The aim of the research was to identify the most adaptable apple rootstocks for the main apple-growing regions of Ukraine and to evaluate the biological potential of scion–rootstock combinations under the specific environmental conditions of each region. Materials and Methods. Comprehensive studies were established simultaneously in 2013 at five research institutions of the network of the Institute of Horticulture of the National Academy of Agrarian Sciences of Ukraine (NAAS) to investigate the adaptability of clonal apple rootstocks. Four apple cultivars–Amulet, Askolda, Renet Simirenko, and Revena–were studied in combination with 17 new and promising clonal rootstocks. The orchards were established using planting material that met the requirements of DSTU 4938:2008 "Fruit Crop Nursery Trees. Specifications." Observations and measurements were conducted according to the methodologies developed by Kondratenko P.V. and Bublyk M.O., as well as Chyzh O.D. and Bublyk M.O. Economic and energy efficiency were evaluated following the methodology of Shestopal O.M. Statistical analysis was performed according to Dospekhov B.A. using a personal computer and the software recommended by Kondratenko P.V. and Bublyk M.O. Results. In the comprehensive experiment conducted at six research institutions of the NAAS network, the survival rate of apple trees was high, reaching 99–100%. During the first year after planting, the most vigorous tree growth was observed on semi-vigorous and semi-dwarf rootstocks (MM106, D 471, D 1904, and 54-118), whereas growth was more restrained on dwarf and super-dwarf rootstocks. This trend was consistent across all soil and climatic zones included in the study. During the second and third years after planting, trees actively developed vegetative growth. The highest biometric characteristics (tree height, trunk diameter, and shoot length) were recorded on semi-vigorous and semi-dwarf rootstocks, whereas dwarf rootstocks restricted vegetative growth but promoted earlier fruit bearing. Among the cultivars studied, Revena proved to be the most precocious, producing fruit as early as the second year after planting. During the fourth to sixth years, the orchards entered the period of active fruiting. The highest yields were generally obtained from scion–rootstock combinations involving dwarf and semi-dwarf rootstocks (M9, D 1071, D 3038, 54-118, Baturynska, Nadiia, and M26). Trees on semi-vigorous rootstocks exhibited greater vegetative vigor but required more labor for pruning. The yield of individual combinations reached 30–40 t/ha. During the seventh and eighth years, the same trends persisted. The most vigorous tree growth was observed on semi-vigorous rootstocks, whereas the highest productivity was achieved mainly on dwarf and selected semi-dwarf rootstocks. The best yielding combinations were obtained with the cultivars Revena, Amulet, and Askolda grafted on M9, D 1071, D 3038, 54-118, MM106, and D 471. The cultivar Renet Simirenko demonstrated lower productivity than the other cultivars. Conclusions. The earliest fruiting was observed in the cultivar Revena grafted on KD 5 (7.1 t/ha), Sambirska (6.8 t/ha), 54-118 (6.1 t/ha), Baturynska (5.8 t/ha), M9 (5.6 t/ha), and D 1071 (5.2 t/ha), as well as in the cultivar Amulet on KD 5 (6.3 t/ha), which entered commercial fruiting in the third year after planting. In the Eastern Forest-Steppe, the best-performing combinations were Revena on D 1071 and Nadiia (6.7 t/ha), and Amulet on M9 (9.0 t/ha) and D 1161 (4.4 t/ha). In Podillia, the highest early yields were obtained from Revena on M9 (5.7 t/ha) and 54-118 (6.2 t/ha). During the early fruiting period, the most adaptable rootstocks providing the highest average yields were 54-118, D 471, D 1071, Mariia, and Baturynska. The highest-yielding orchards were those of Revena on KD 5 (22.2 t/ha), 54-118 (21.4 t/ha), D 1071 (18.6 t/ha), and M9 (15.2 t/ha), and Amulet on D 471 and 54-118 (17.5–17.7 t/ha), D 3038 (14.9 t/ha), Nadiia (14.6 t/ha), and M9 (14.1 t/ha). For Askolda, high productivity was achieved only on the Baturynska and 54-118 rootstocks (13.0–13.5 t/ha). Under these extreme climatic conditions, the cultivar Renet Simirenko exhibited low productivity. Only the rootstocks D 471, 54-118, MM106, and Nadiia ensured average yields of approximately 10.0 t/ha, whereas the remaining rootstocks produced yields two to three times lower.