Evaluation of Thermal-Based Physiological Indicators for Determining Water Stress Thresholds in Drip- Irrigated 'Regina' Cherry Trees

Abstract

Abstract This work aimed to assess the performance of different thermal-infrared (TIR)-based physiological indicators (PI) as an alternative to the stem water potential (Ψs) and stomatal conductance (gs) for monitor the water status of grafted drip-irrigated 'Regina' cherry trees. In addition, we evaluated the usefulness of piecewise linear regression for finding PI thresholds that are important for post-harvest regulated deficit irrigation (RDI) management. With this purpose, an irrigation experiment was carried out in the post-harvest period. Trees were submitted to three Ψs-based water stress treatments: T0 (fruit grower management treatment, or control) (Ψs > -1.0 MPa, without-to-low water stress); T1 (low to mild water stress treatment = -1.0 > Ψs > -1.5 MPa); and T2 (mild-to-severe water stress treatment = -1.5 > Ψs > -2.0 MPa). The results indicated that the trees were more stressed in T2 than in T0. In the former, averages of Ψs and gs were -1.75 MPa and 372 mmol m-2 s-1, whereas they were -1.56 MPa and 427 mmol m-2 s-1 in T0. The piecewise model allowed determining the water stress thresholds of almost all studied PI. The breakpoints yielded by this analysis indicated that trees at Ψs lower than -1.5 MPa had a gs lower than 484 mmol m-2 s-1. These results also showed that TIR-based PI, whose equations incorporate a temperature normalization, are a better indicator of cherry tree water status than those without normalization. The derived TIR-based PI threshold values could be used as a reference for managing drip-irrigated 'Regina' cherry trees.