Preliminary study of different fruit loads and reflective mulch effects on the phenolic composition in nectarines cv. Stark Red Gold

Aim of this study was to investigate the relationship between fruit phenolic accumulation and different levels of fruit loads. For this purpose, nectarines sampled from trees characterised by different fruit yield at harvest were analysed for their phenolic profile. A reflective mulch was placed in the inter-row space on both sides of the trees on trial with the aim to evaluate its capacity to increase light quantity at canopy level and consequently to modify fruit phenolics accumulation. Fruit loads were settled at the beginning of June on the basis of tree vigor and with the application of selective hand-thinning techniques. Three different fruit loads were achieved at harvest: low (10 kg/tree), medium (12.5 kg/tree) and high (18 kg/tree). Trees on reflective mulch were characterised by a medium-high yield level at harvest (14 kg/tree). Analyses of phenolic compounds were conducted with HPLC and were performed on both fruit skin and pulp tissues. Results showed an inverse relation between the phenolic compounds amount and the fruit load level. In other words, concentrations were higher in nectarines sampled from low yield trees than in high yield ones. This indication was clear for total amount of phenolics detected, but could also be extended to the single different classes of compounds: cinnamic acids, flavanols, flavonols and cyanidins. Pulp tissue was characterised by higher fruit-load related differences. As for the skin tissue, concentrations were higher in comparison to pulp tissue as expected, but apparently less influenced by differences in fruit loads. Carbon-nutrient balance hypothesis is considered and discussed for results interpretation. As for the nectarines on reflective mulch, their phenolic concentrations were in line with the range expected for their fruit load level. The influence of the reflective mulch on phenolic accumulation was then not clear.