Plasticity and stability of quantitative productivity traits of apple cultivars under the conditions of Podillia

Apple was one of the leading fruit crops worldwide, ranking third in production volumes after bananas and watermelons, and the continuously increasing demand for apples determined the need to improve cultivars with high productivity and adaptability. The aim of the study was to evaluate apple cultivars in terms of ecological plasticity in order to identify promising genotypes for breeding programmes. The results of cultivar testing of apple of Ukrainian and foreign breeding (orchard established in 2017, planting scheme 2.5 × 4.5 m, rootstock MM106) were presented based on yield and average fruit weight. Five apple cultivars (‘Free Gold’, ‘Juliet’, ‘Luna’, ‘Red Topaz’, ‘Rosela’) selected from 27 introduced genotypes tested during 2021-2024 were evaluated. The highest values of environmental indices, both for apple yield and fruit weight, were recorded in 2023 and amounted to 1.80 and 6.15, respectively. The lowest environmental indices were observed in 2022 and 2024, when the average yields were 0.28 and 1.3 t ha⁻¹, respectively. This analysis demonstrated the strong influence of annual climatic fluctuations on cultivar productivity and emphasised the need to consider genotype adaptability in breeding programmes. Based on mathematical processing of yield and average fruit weight data, regression equations and ecological plasticity indices were derived. It was established that, in terms of fruit yield, the cultivars ‘Rosela’ and ‘Juliet’ belonged to the intensive type and were characterised by high sensitivity to changes in environmental conditions, with regression coefficients of 2.743 and 0.921, respectively. For average fruit weight, a high level of ecological plasticity was demonstrated by the cultivars ‘Rosela’, ‘Luna’, and ‘Free Gold’, whereas ‘Juliet’ belonged to the neutral type. Assessment of ecological stability showed that, for yield, ‘Free Gold’, ‘Luna’, and ‘Red Topaz’ were the most stable cultivars. The cultivar ‘Juliet’ was relatively stable, although it did not exhibit a high yield level. The highest average yield over the years was recorded for ‘Rosela’, which was simultaneously the least stable. For average fruit weight, ‘Free Gold’ and ‘Luna’ proved to be stable cultivars