Olive plants of broad-leaved 'Minuta' (MN) and 'Nocellara del Belice' (NB) and narrow-leaved 'Passulunara' (PA) and 'Biancolilla Siracusana' (BS) were studied to evaluate their responses to drought. In a greenhouse, two-year-old rooted cuttings were irrigated to field capacity (WW) or with 20% of WW evapotranspiration (DS) for over three months. Subsequently, all pots were rewatered to field capacity for 20 days. Gravimetric soil water content (SWC), leaf relative water content (RWC), stomatal conductance (gs), and leaf carbohydrates, percentage of leaf drop and shoot elongation were determined throughout the trial. In WW, SWC fluctuated between 80 and 100% of field capacity, whereas in DS, SWC decreased sharply reaching a minimum level around 30-35% of field capacity after two months of drought. At this time, drought induced a significant reduction of: (a) RWC in PA and BS, (b) gs in MN, NB, and PA, and (c) shoot elongation (-23%) in PA. Conversely, drought increased leaf drop in all genotypes, especially in MN and NB. RWC and gs levels were mostly restored after rewatering. Initially, drought induced an increase of mannitol and total carbohydrates in MN and a decrease in NB. At more advanced drought stages, mannitol and total carbohydrates decreased in PA and BS. NB exhibited a general increase of the (mannitol + glucose)/sucrose ratio in response to drought. The two broad-leaved genotypes (MN and NB) maintained similar leaf hydration levels in DS and WW plants proving to be generally intolerant to dehydration, whereas the two narrow-leaved genotypes (PA and BS) tolerated a fair degree of dehydration
Sustainable irrigation is crucial to reduce water use and management costs in modern orchard systems. Continuous plant-based sensing is an innovative approach for the continuous monitoring of plant water status. Olive (Olea europaea L.) genotypes can respond to drought using different leaf and fruit physiological and morphological mechanisms. This study aimed to identify whether fruit and leaf water dynamics of two different olive cultivars were differently affected by water deficit and their response to changes of midday stem water potential (stem), the most common indicator of plant water status. Plant water status indicators such as leaf stomatal conductance (g s) and stem were measured in the Sicilian olive cultivars Nocellara del Belice (NB) and Olivo di Mandanici (MN), in stage II and III of fruit development. Fruit gauges and leaf patch clamp pressure probes were mounted on trees and their raw data were converted in relative rates of fruit diameter change (RR fruit) and leaf pressure change (RR leaf), sensitive indicators of tissue water exchanges. The analysis of diel, diurnal and nocturnal fluctuations of RR fruit and RR leaf highlighted differences, often opposite, between the two cultivars under water deficit. A combination of statistical parameters extrapolated from RR fruit and RR leaf diurnal and nocturnal curves were successfully used to obtain significant multiple linear models for the estimation of midday stem. Fruit and leaf water exchanges suggest that olive cultivar can either privilege fruit or leaf water status, with MN likely preserving leaf water status and NB increasing fruit tissue elasticity under severe water deficit. The results highlight the advantages of the integration of fruit and leaf water dynamics to estimate plant water status and the need for genotype-specific models in olive.
Continuous assessment of plant water status indicators provides the most precise information for irrigation management and automation, as plants represent an interface between soil and atmosphere. This study investigated the relationship of plant water status to continuous fruit diameter (FD) and inverse leaf turgor pressure rates ( p p ) in nectarine trees [ Prunus persica (L.) Batsch] throughout fruit development. The influence of deficit irrigation treatments on stem ( Ψ stem ) and leaf water potential, leaf relative water content, leaf stomatal conductance, and fruit growth was studied across the stages of double-sigmoidal fruit development in ‘September Bright’ nectarines. Fruit relative growth rate (RGR) and leaf relative pressure change rate (RPCR) were derived from FD and p p to represent rates of water in- and outflows in the organs, respectively. Continuous RGR and RPCR dynamics were independently and jointly related to plant water status and environmental variables. The independent use of RGR and RPCR yielded significant associations with midday Ψ stem , the most representative index of tree water status in anisohydric species. However, a combination of nocturnal fruit and leaf parameters unveiled an even more significant relationship with Ψ stem , suggesting a changing behavior of fruit and leaf water flows in response to pronounced water deficit. In conclusion, we highlight the suitability of a dual-organ sensing approach for improved prediction of tree water status.
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