Metabolic signatures of the true physiological impact of canopy light environment on peach fruit quality

Fruit developing in different canopy positions are exposed to distinct light environments that can influence their maturation process and internal quality development. Maturation, a highly regulated process at the molecular level, significantly impacts fruit quality. Our understanding of the true effect of various pre-harvest factors on fruit quality is limited due to poor control of maturity among comparisons in previous studies. Here, an experiment was conducted to assess the true impact of canopy vigor and position (bottom: 0.3-1.2 m and top: 2.1-3.0 m) on 'Sierra Rich' (low vigor, LV) and 'Cresthaven' (high vigor, HV) peach fruit internal quality. Given the lower vigor of 'Sierra Rich,' it was recorded that light was more evenly distributed throughout the canopy thus, hypothesized that this could be leading to fruit of uniform quality across the different positions. Fruit from the different canopy positions were assessed at the commercial harvest stage for size, dry matter content (DMC) and physiological maturity (index of absorbance difference, IAD), using non-destructive visible (Vis) to nearinfrared spectroscopy (NIRS). Fruit maturity and DMC advanced/increased with the elevated height of canopy in both cultivars. However, when controlling for equal maturity, only fruit coming from the vigorous 'Cresthaven' trees showed a significant (P <= 0.05) Delta DMC of 2.1 % between extreme canopy positions. Non-targeted metabolite profiling was carried out using gas chromatography mass spectrometry (GC-MS) on the mesocarp and exocarp of equally mature peach fruit samples. Mesocarp metabolite profiling of equally mature fruit coming from the different canopy positions demonstrated minimal metabolic variation. However, significant metabolite variation across canopy positions was observed in the exocarp of the HV cultivar. In general, sucrose, sorbitol and catechin were more abundant in higher quality, exposed to high-light environment fruit, while increased aspartic acid, asparagine, threonine, citric acid, monosaccharides (sorbose and fructose), butanoic acid and shikimic acid were associated with inferior quality, exposed to low-light environment fruit. Overall, this combined physiological and metabolomic analysis provides insight into the true impact of canopy position and underscores the light environment-related metabolic regulations that facilitate peach fruit quality development.