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 (psi(stem)) and the maximum daily shrinkage of the trunk (MDS). Significant relationships were determined for psi(stem) vs. TDG (R-2 = 0.60), and vs. FDG (R-2 = 0.78). In addition, significant relationships were established between TDG vs. FOG (R-2 = 0.60), and between the daily increment of MDS (Delta MDS) and FDG (R-2 = 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 psi(stem), promising automation possibilities for appropriately regulating irrigation under DI programmes, and predicting its effects on fruit size by continuous field measurement. (C) 2011 Elsevier B.V. All rights reserved.