S16 - Session O2 - Apple russeting: the contribution of vascular and transpiration flows in the early fruit growth development stages

Authors: Davide Lambertini, Brunella Morandi, Stefano Tartarini, Luigi Manfrini *

Biophysical fruit growth depends on a balance among the vascular and transpiration flows which enter/exit the fruit via phloem, xylem, and through the epidermis. There is a lack of information about how russet could influence fruit growth in apples by affecting these mechanisms. Two apple cultivars "Renetta Grigia di Torriana" (RGT) and "Golden Delicious" (GD) were monitored in their first stages of development determining phloem, xylem and transpiration flows using highly sensitive, custom-built fruit diameter gauges, which allow determination of minute variations in fruit size. With them also fruit surface conductance, as well as fruit growth parameters as absolute growth rate (AGR) and relative growth rate (RGR) were monitored. The two varieties growth behaviors were then compared to outline if there was a different growth pattern assuming RGT has a more spread russet on its skin while GD has a low russet presence. Within the day the vascular fluxes resulted different between two varieties, even if the daily AGR and RGR trends were very similar. The growth daily pattern showed a lower diameter variation in GD than in RTG where higher shrinkage and recover of the fruit volume was observed. This suggested that there is a cultivar-dependent contribution of the vascular fluxes within the day. This is also supported by the surface conductance measurements which resulted significantly higher in RGT compared to GD, even if fruits had comparable weight and diameter. The fruit growth pattern of the two varieties seem to suggest that russet does not affect fruits quantitative growth but can influence the growth pattern influencing the water and nutrient fluxes into the fruit. This could be an important information that can lead to a daily orchard crop management change shifting from a species-base to a cultivar-base water/environment requirement.