Keywords: leaf photosynthesis; chlorophyll fluorescence; cultivar; induction coefficient; chlorophyll; adaptability

Abstract Productivity is one of the primary economic and biological characteristics of an apple tree variety; it is this characteristic that determines the value and economic feasibility of the variety. The photosynthetic activity of the leaf surface of plants plays a leading role in forming the potential productivity of the apple tree. By "potential productivity," we mean the productivity of plants under conditions of ideal agroenvironment, optimal nutrition, and absence of diseases. To diagnose the potential productivity of cultivars we used an indicator of chlorophyll fluorescence induction–induction coefficient (Кі). According to our data, the Кі of leaves of columnar cultivars ranged from 0.720 to 0.740, indicating a high level of efficiency of photophysical processes near the photosystem II (PS II) reaction centers. For plants of columnar cultivars, the viability index ranged from 1.78 to 2.19. It has been established that individual age sections of tree trunks form different productivity potentials. Thus, based on the chlorophyll a (Chl a) fluorescence induction index, a higher intensity of photosynthesis was observed in the leaves of the cultivars ‘Valuta’, ‘Favoryt’, and ‘Bilosnizhka’ on seven to nine-year-old trunks. In contrast, for ‘Tantsivnytsia’, the highest intensity was observed on the oldest spur formation (14–19 years old). In traditional apple cultivars, the intensity of photosynthesis, as indicated by Кі, decreased with the age of spur formation; however, such a decline was not observed in columnar cultivars. The leaves of plants from the traditional cultivar ‘Idared’, situated on a homogeneous shoot, exhibited the highest photosynthetic intensity based on the F680γt / F680βt light intensity. Conversely, in the leaves of three-year-old spur formations, a 25.3% decrease in photosynthetic intensity was observed, falling to a 45.7% decrease in six-year-olds. With the optimal combination of agroecological factors for columnar cultivars, stability in the photosynthetic potential across various complex spur formations is observed. In typical apple cultivars, the age of spur formation leads to a suppression of photosynthetic intensity. The cultivar ‘Bilosnizhka’ is characterized by the highest Chl a/ Chl b content, indicating lower adaptability. In the leaves of this cultivar, the amount of Chl a exceeded Chl b by three times; in contrast, in the cultivars ‘Sparta’ and ‘Tantsivnytsia’, the difference was 2.5 times higher. This value (2.5x) correlates with increased adaptability to the conditions in which they were studied. The highest level of leaf net productivity of photosynthesis (NPP) is observed in plants of the ‘Valuta’ cultivar (13.9 g/m² for day); in the cultivars ‘Bilosnizhka’, ‘Favoryt’, ‘Bolero’, ‘Sparta’, ‘Tantsivnytsia’, and ‘Papirovka’, the accumulation of dry matter is lowered by 32.6–40.6%.

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