Relationships between trunk- and fruit-diameter growths under deficit-irrigation programmes in orange trees

This study examines the suitability of trunk dendrometers for assessing fruit growth under deficit irrigation (DI) for two consecutive years in a mature citrus orchard. Two DI programmes were applied during the maximum evapotranspirative demand period: sustained-deficit irrigation, applied at 50% ETC on average, and low-frequency deficit irrigation, applied according to plant–water status, establishing different irrigation–restriction cycles. Additionally, a control treatment at 100% ETC was monitored for the entire irrigation season. Trunk daily growth (TDG) and fruit daily growth (FDG) were estimated together with stem-water potential at midday (Ψstem) and the maximum daily shrinkage of the trunk (MDS). Significant relationships were determined for Ψstem vs. TDG (R2 = 0.60), and vs. FDG (R2 = 0.78). In addition, significant relationships were established between TDG vs. FDG (R2 = 0.60), and between the daily increment of MDS (ΔMDS) and FDG (R2 = 0.50), revealing the strong connection between trunk and fruit variations caused by water stress. According to these findings, the DI effects on fruit growth can be monitored by means of TDF or temporal evolution of Ψstem, promising automation possibilities for appropriately regulating irrigation under DI programmes, and predicting its effects on fruit size by continuous field measurement.

► Deficit irrigation can be controlled by means of trunk diameter fluctuations or Ψstem.
► Deficit irrigation was manifested in dynamics of fruit and trunk diameter values.
► Maximum daily shrinkage allow characterizing the fruit growth.
► Trunk diameter fluctuations improves our knowledge of fruit growth.