From shade to sun: rapid phenotypic recovery but persistent metabolic legacy in apple fruit after summer pruning

Apple fruit can acclimate to changes in light availability, but whether fruit developing under shade can rapidly recover when suddenly exposed to full sun late in development remains unclear. Several agronomical practices aim to regulate light incidence on the fruit, thereby influencing their growth and development. Summer pruning is a good model to analyze this regulation as it includes a transition between shade and full-sun conditions. In this study, we used summer pruning as a field-scale light perturbation and analyzed the impact of summer pruning on apple fruit at both morphological and metabolic levels by comparing fruit grown under full-sun conditions, fruit grown in the shade, and fruit exposed to full-sun conditions after summer pruning. In the analysis, we included continued measurements of growth, temperature, color, and chlorophyll content before and after performing summer pruning over the last 5 weeks before harvest. Additionally, fruit and leaf dynamics of phenolic compounds was characterized in detail using HPLC/MS. Following pruning, shaded fruit rapidly converged toward sun-exposed fruit in surface temperature, color and anthocyanin accumulation, with anthocyanins reaching sun-exposed levels within six days. However, convergence was incomplete: fruit growth, total soluble solids and several phenolic traits remained intermediate. These results demonstrate that apple fruit exhibits rapid phenotypic acclimation to increased light exposure, whereas metabolic acclimation is slower and constrained by developmental history.