In three separate experiments, the influence of temperature, irrigation and irradiance on the physiological response of different organs (bud, leaf, fruit) of sweet cherry (Prunus avium L.) was investigated. In the first series of experiments, sweet cherry trees of cultivars 'Grace Star' and 'Schneiders' on rootstock Gisela 5 were exposed to low temperatures in cold storage at 4.7 °C and 2.2 °C, and under natural conditions at 3.6 °C for up to three consecutive nights during the post-flowering period. No differences in response were found between cultivars, while exposure at 2.2 °C and 3.6 °C resulted in significantly lower values of maximum and effective quantum yield of the photosystem II, net photosynthesis, stomatal conductance and transpiration, higher contents of zeaxanthin, antheraxanthin, lower contents of violaxanthin, neoxanthin, higher contents of sugars, total flavonoids, neochlorogenic acid and epicatechin in leaves and lower fruit set. Multiple consecutive exposures to lower temperatures caused greater stress than a single exposure, prolonged plant recovery time, and additionally reduced fruit set. In the second experiment, trees of the cultivar 'Regina' on the rootstocks Weiroot 72 and Gisela 5 were either irrigated or not irrigated in two growing seasons. The results show that irrigated trees had higher content of total sugars in buds and leaves, total organic acids in fruits, lower contents of total hydroxycinnamic acids, total flavonols and flavanols in leaves and fruits, higher growth, fruit weight and lower yield efficiency. Rootstock significantly affected sugar content and phenolic content in different organs, yield efficiency and fruit quality. The influence of irradiance in canopy of cultivar 'Grace Star' on rootstock Gisela 5 on sugar content in buds, leaves and fruits was studied in the third experiment. Higher values of photosyntetic radiation intensity in the canopy resulted in significantly higher contents of glucose, fructose, sorbitol, and sucrose in buds, higher contents of glucose and fructose in leaves, and lower contents of fructose, sorbitol, and SSL in fruits. The lowest light intensity values were measured in the inner part of the canopy, as well as the lowest contents of fructose and sorbitol in buds and glucose, fructose, sorbitol and total sugars in leaves. Our results showed that that suboptimal growing conditions cause stress in sweet cherry. The type of stress affected leaf sugar content differently. Physiological limitations, accumulation of antioxidants, changes in growth, yield and fruit quality was also observed.
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