Interactions Between Seasonal Temperature Changes, Activities of Selected Genes and Fruit Quality in Malus domestica Borkh.

Temperature changes strongly affect apple development and quality. In this study, we analyze the relationships between the main factors modulating both of the aforementioned processes in the fruits of four apple cultivars. We assessed three-dimensional data concerning the expression profile (fold change) of eight genes related to fruit ripeness regulation (involved in the cell respiration process and sorbitol metabolism as well as encoding cell kinase receptors) and fruit parameters such as fruit weight, ethylene concentration, concentration of soluble solids and acidity, which are affected by seasonal temperature variations (2018–2020). We observed that low temperatures (before the apple ripening phase) promoted an increase in gene activity and improved the fruit quality of the following cultivars: early-flowering/mid-ripening ‘Pink Braeburn’ and ‘Pinokio’, early-flowering/late-ripening ‘Ligol’ and late-flowering/late-ripening ‘Ligolina’. We confirmed the positive effect of low temperatures on the activity of the AAAA1, AALA1, StG and AAXA genes and on the evaluated fruit quality parameters, and we confirmed their dependence on the genotype of the studied cultivars. The obtained results shed light on the complexity of the variability mechanism in fruit features and fruit harvest dates. This knowledge may improve breeding programs for the production of better-quality apples.