Plant-based water stress sensing in two olive cultivars with different physiological responses to drought

A large portion of modern olive plantings is dominated by one main cultivar ('Arbequina') planted at super high density (SHD, 1,500 tree ha(-1)), leading to a dangerous reduction in olive biodiversity. Very few cultivars have growth and productive patterns that suit the SHD system requirements. Partial intensification and mechanization with several cultivars may represent the safest and easiest alternative. The efficient use of limited natural resources, such as water, in SHD systems, requires precise management. Continuous plant-based sensing is a promising approach to managing water, mainly tested on the cultivar 'Arbequina'. In this study, we evaluated the sensitivity of two promising indicators of plant water status in two Sicilian olive cultivars differ in their level of drought tolerance: 1) the minimum daily output pressure (Pp(min)) measured with the leaf patch clamp pressure (LPCP) probe and 2) the maximum daily relative growth rate difference (RGR(range)) measured with fruit gauges. Based on the indicators trends, we defined four water status conditions and related them to specific midday stem water potential (Psi(stem)) thresholds. In addition, the relation between Pp(min) and RGR(range) highlighted a greater tendency of the more drought tolerant cultivar to maintain leaf turgor under water deficit. This was accompanied by an increase in daily variations of leaf turgor and fruit shrinkage, not observed in the less drought tolerant cultivar. These results suggest tailoring plant-based water management protocols on cultivar-specific physiological responses to water deficit.