Study of adaptive forms of clonal apple tree rootstocks in extreme conditions of the South Ural

Abstract

Background. In the context of horticultural intensification, rootstocks play a key role in ensuring plantation resilience to extreme environmental factors. The Southern Urals region is characterized by a sharply continental climate with moisture deficiency, high summer and low winter temperatures, necessitating the use of specialized adaptive rootstocks. Traditional dwarf forms (e.g., M9) are losing relevance due to advancements in tree growth regulation technologies and mechanization for tall plantations. Domestic studies confirm the promise of semi-dwarf rootstocks (54-118, MM106, MM111) and regional forms (Volga 3, Ural 5), which exhibit drought and frost resistance. Of particular interest are new OB-series lines selected in the Southern Urals and undergoing trials at the Orenburg State University (OSU) Botanical Garden. Their comprehensive evaluation based on biometric, physiological, and productivity traits will identify optimal genotypes for developing resilient scion-rootstock combinations, aligning with the principles of adaptive horticulture established by I.V. Michurin. The findings will contribute to competitive horticulture under Russia’s extreme conditions.

Purpose. To conduct a comparative study of the resistance of selected apple clonal rootstock forms to biotic and abiotic stressors, assessing their rhizogenic capacity and productivity in a mother plantation established by the vertical layering method.

Materials and methods. The study was conducted in the Southern Urals (OSU Botanical Garden) on southern calcareous chernozems under a sharply continental climate (winter temperatures down to –48 °C, summer up to +42 °C, precipitation 363 mm/year). The subjects were 37 promising OB-series apple clonal rootstocks selected in 2008 from second-generation seedlings obtained through open pollination of rootstocks and apple cultivars from various geographic zones (Kuibyshev, Donetsk, Crimean stations, etc.). Seed sowing (2007) and seedling evaluation followed fruit crop (1999) and clonal rootstock (1980) study methodologies. Field germination, standard rootstock yield, and morphological traits (fibrous roots, brachyblasts) were recorded. Selected forms were propagated in a mother plantation by vertical layering, analyzing survival, preservation, and productivity (standard layer yield, rooting capacity) compared to the control (Ural 5 rootstock). Statistical analysis was performed using Statistica 9.0 and Microsoft Excel (ANOVA, Student’s t-test).

Results. The features of replication and adaptation to biotic and abiotic stress of promising forms of clonal apple tree rootstocks obtained by the free pollination method and by selection among apple seedlings, which had increased drought and frost resistance of the root system, and which were unpretentious to soil conditions, were studied in the South Ural climatic and soil conditions. Plants were characterized by better adaptability to biotic and abiotic stressors and a high reproduction rate compared to the control (Ural 5). The OB 2-4, OB 3-4, OB 3-14, OB 2-12, OB 2-15 forms and some other hybrids were distinguished by vegetative productivity. A slight relative sampling error (less than 25%) indicates a high reliability of the obtained results. The exception was the OB 2-1 and OB 2-8 forms, which require additional study, since the annual yield of vertical branches of these forms per unit area and the average over the years exceeded the control.