Low-frequency Deficit Irrigation Research Articles

Mild water stress-induced priming enhance tolerance to Rosellinia necatrix in susceptible avocado rootstocks

BackgroundWhite root rot (WRR) disease caused by Rosellinia necatrix is one of the most important threats affecting avocado orchards in temperate regions. The eradication of WRR is a difficult task and environmentally friendly control methods are needed to lessen its impact. Priming plants with a stressor (biotic or abiotic) can be a strategy to enhance plant defense/tolerance against future stress episodes but, despite the known underlying common mechanisms, few studies use abiotic-priming for improving tolerance to forthcoming biotic-stress and vice versa (‘cross-factor priming’). To assess whether cross-factor priming can be a potential method for enhancing avocado tolerance to WRR disease, ‘Dusa’ avocado rootstocks, susceptible to R. necatrix, were subjected to two levels of water stress (mild-WS and severe-WS) and, after drought-recovery, inoculated with R. necatrix. Physiological response and expression of plant defense related genes after drought-priming as well as the disease progression were evaluated.ResultsWater-stressed avocado plants showed lower water potential and stomatal limitations of photosynthesis compared to control plants. In addition, NPQ and qN values increased, indicating the activation of energy dissipating mechanisms closely related to the relief of oxidative stress. This response was proportional to the severity of the water stress and was accompanied by the deregulation of pathogen defense-related genes in the roots. After re-watering, leaf photosynthesis and plant water status recovered rapidly in both treatments, but roots of mild-WS primed plants showed a higher number of overexpressed genes related with plant defense than severe-WS primed plants. Disease progression after inoculating primed plants with R. necatrix was significantly delayed in mild-WS primed plants.ConclusionsThese findings demonstrate that mild-WS can induce a primed state in the WRR susceptible avocado rootstock ‘Dusa’ and reveal that ‘cross-factor priming’ with water stress (abiotic stressor) is effective for increasing avocado tolerance against R. necatrix (biotic stressor), underpinning that plant responses against biotic and abiotic stress rely on common mechanisms. Potential applications of these results may involve an enhancement of WRR tolerance of current avocado groves and optimization of water use via low frequency deficit irrigation strategies.

Fostering sustainable water use in almond (Prunus dulcis Mill.) orchards in a semiarid Mediterranean environment

ABSTRACTThis work examines the long-term effects of deficit-irrigation (DI) practices in almond crop (Prunus dulcis Mill.) in agronomical and physiological terms. The trial was conducted during four-year monitoring period (2014–2017), in an experimental orchard (SW Spain), subjected to three irrigation regimes; i) a full-irrigation treatment (FI), which received 100% of crop evapotranspiration (ETC); ii) a regulated-deficit irrigation (RDI50), which received 50% of ETC during the kernel-filling period; and iii) a low-frequency deficit irrigation (LFDI), that was subjected to continuous periods of irrigation-restriction defined in terms of threshold values of leaf-water potential (Ψleaf) during the kernel-filling period. During the water stress period, there were monitored Ψleaf, stomatal conductance (gs) and canopy temperature (TC). Significant improvements in terms of water-use efficiency were found, as no differences in terms of yield between FI and LFDI were found, leading to the conclusion that significant water savings (between 27 and 40%) can be achieved without compromising the yield. Moreover, threshold values of Ψleaf and thermal indicators were defined which will allow establishing future irrigation scheduling without compromising almond yield, especially when DI strategies are being applied.

Approach to assess infrared thermal imaging of almond trees under water-stress conditions

Approach to assess infrared thermal imaging of almond trees under water-stress conditions. Abstract - Introduction. Optimising agricultural water use implies the combination of physiological, technological and engineering techniques, especially those for continuously monitoring the water status of plants subjected to deficit irrigation. A methodology to estimate water stress of young almond trees from thermal images was developed based on assessing the physiological status of almond crops under limited water-supply conditions. Materials and methods. Two irrigation treatments were tested during the maximum evapotranspirative demand period (214th to the 243rd day of the year) in an experimental almond (Prunus dulcis (Mill) D.A. Webb, cv. Guara) orchard: a low-frequency deficit irrigation (LFDI) treatment, irrigated according to the plant-water status, and a fully irrigated treatment (C100) at 100% of crop evapotranspiration. Daily canopy temperature at midday (TC) was measured with an infrared camera, together with standard measurements of stem-water potential (ΨStem) and stomatal conductance (gS). The time course of these parameters and their relationships were analysed. Results and discus- sion. The time course of the parameters studied showed highly significant correlations among the diffe- rentials of canopy-air temperature (ΔT), ΨStem and gS. The methodological protocol for analysing thermal images allowed a time saving in processing information and additionally offered the possibility of estima- ting the ΨStem and gS values. Conclusion. Our results confirm that infrared thermography is a suitable technique for assessing the crop-water status and can be used as an important step towards automated plant-water stress management in almond orchards.

Improving Almond Productivity under Deficit Irrigation in Semiarid Zones

Sustainable water use is one of the greatest challenges of irrigated agricultural systems. This study presents the results related to the agronomic and physiological response to the deficit irrigation of almond trees (Prunus dulcis DA Webb Mill cv. Guara) under semiarid Mediterranean conditions in the Guadalquivir river basin (SW Spain). Two deficitirrigation strategies were tested: i) regulated deficit irrigation (RDI), which was irrigated at 100% of crop evapotranspiration (ETC) throughout the irrigation period, except during the kernel-filling stage, when these trees where irrigated at 30% ETC, and ii) low-frequency deficit irrigation (LFDI), in which trees were subjected to different irrigationrestriction periods, defined in terms of stem water potential at midday (ΨStem). As control, a fully irrigated treatment (C-100) was used, which received irrigation covering the 100% of ETC. The stem water potential (ΨStem), the stomatal conductance (gS), the photosynthesis rate (Pn) and canopy temperature (TC) were monitored, revealing significant differences mainly in LFDI in comparison with C-100. Also, highly significant relationships were found among plant physiological parameters, showing that the water status is strongly related to the crop water availability. On other hand, in terms of nut yield, there was a notable improvement under LFDI compared with RDI, with increases of 16% in relation to C-100, and with water savings of close to 170 mm. Thus, these findings demonstrate that the LFDI is a sustainable strategy to improve almond productivity as well as water-use efficiency under limited water resources.

Production and oil quality in ‘Arbequina’ olive (Olea europaea, L.) trees under two deficit irrigation strategies

The effect of two deficit irrigation (DI) strategies on fruit and oil production and quality in a 12-year-old ‘Arbequina’ olive orchard with 238 trees ha−1 was evaluated. The T1 treatment was a sustained DI regime (65% ETc, 2–3 irrigation events per week). The T2 treatment was a low-frequency DI (increasing stress/rewatering cycles, which consisted in withholding irrigation until fruit shrivelling and then applying a recovery irrigation providing the same amount of water that supplied in T1 for that period). As compared to full irrigation, both strategies reduced fruit production and increased the variability of fruit ripening, but favoured oil extraction. Free acidity, peroxide value, K232, K270 and sensory quality of oil were not affected by DI. Furthermore, carotenoid, chlorophyll, phenol, and oleic contents increased. The greatest phenol content and bitterness index were found in oil from T2 trees. Later harvesting caused sensory quality and tocopherol losses, although the oil synthesized in DI olives increased.

YIELD RESPONSE OF CITRUS TREES TO DIFFERENT IRRIGATION STRATEGIES IN GUADALQUIVIR RIVER BASIN (SW SPAIN)

Three different deficit-irrigation strategies were studied: sustained deficit irrigation (SDI), regulated deficit irrigation (RDI), and low-frequency deficit irrigation (LFDI) in different commercial citrus orchards located in the Guadalquivir river basin SW Spain. Each irrigation treatment was based on different water-stress ratio (WSR), which is the ratio of water supplied to deficit-irrigation treatment with respect to the control treatment (100% ETC). Midday stem-water potential (psistem) was measured during the irrigation periods and was used to characterize plant-water status. Also, integrated stem-water potential (psiInt) was calculated for all treatments and used as a timing water-stress indicator for the crop. Yield and fruit quality were evaluated at harvest in each treatment taking into account the temporal and spatial variability, associated mainly with local weather conditions, and agronomic orchard management. Relationships among water applied, psiInt and yield response were performed to quantify the effects of deficit irrigation on yield and fruit-quality parameters. Analysis of data showed that, in all cases, the irrigation-water restriction significantly affected yield and some fruit-quality parameters (total soluble solids, titratable acidity, and maturity index). The results confirmed that the water productivity (WP) was positively related to water amount and irrigation strategy applied. Consequently, when WSR of 0.70 was applied (moderate deficit irrigation) RDI strategy showed better results than the SDI. However, with WSR of 0.60 (severe water reduction), LFDI strategy provided the best crop response. Under Mediterranean climate and water scarcity conditions, the application of DI strategies allowed water savings up to 1000 m3 ha-1 yr-1. In DI treatments, the total water applied was better correlated with WP than with yield, indicating that this parameter should be used when trying to improve irrigation management.

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% ET C on average, and low-frequency deficit irrigation, applied according to plant–water status, establishing different irrigation–restriction cycles. Additionally, a control treatment at 100% ET C 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 ( Ψ stem) and the maximum daily shrinkage of the trunk (MDS). Significant relationships were determined for Ψ stem vs. TDG ( R 2 = 0.60), and vs. FDG ( R 2 = 0.78). In addition, significant relationships were established between TDG vs. FDG ( R 2 = 0.60), and between the daily increment of MDS (ΔMDS) 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 Ψ stem, promising automation possibilities for appropriately regulating irrigation under DI programmes, and predicting its effects on fruit size by continuous field measurement.

Benefits of low-frequency irrigation in citrus orchards

Citrus is a crop of major economic importance in Spain, cultivated during the dry season when irrigation is essential to guarantee yields of high quality. As water resources are progressively more insufficient, more effective water management in agriculture is crucial. Deficit irrigation in many agricultural crops has frequently proved to be an efficient tool for improving water-use efficiency. We hypothesise that, despite the effectiveness of deficit irrigation, the most suitable strategy in citrus orchards remains to be defined for Mediterranean environment. In this study, for the period from 2006 to 2008, a 12-year-old orange orchard, Citrus sinensis L. Osb. cv. Navelina, grafted onto Carrizo citrange, C. sinensis L. Osb. × Poncirus trifoliata L. Osb., were subjected under two deficit-irrigation strategies defined as follows: (1) low-frequency deficit irrigation applied according to the plant–water status, and (2) sustained-deficit irrigation with a water-stress ratio of 0.6, defined as the ratio of actual water-limited supply in this treatment related to the water supply of the control treatment. The control treatment was irrigated at 100% of ETC for the entire irrigation season (ETC: crop evapotranspiration). Midday stem–water potential (Ψstem) and stomatal conductance (gS) were used to estimate the water status of the trees. The lowest Ψstem and gS values were registered in the deficit-irrigation treatments with a seasonal pattern consistent with the irrigation dynamics applied in each case. Ψstem and gS values significantly differed from those of the control trees. Although the integrated stress levels were similar in deficit-irrigation treatments, differences in yield and fruit quality were found, having a more positive response to low-frequency deficit irrigation with an increase of 25% in yield in comparison to the sustained-deficit irrigation treatment. Here, we thus demonstrate the significant differences in water productivity. Indeed, water productivity parameter not only depends on the amount of water, but also on the irrigation strategy applied, which promoted substantial water savings without significant impact on yield. The present study highlights that low-frequency deficit irrigation should be adopted as a most appropriate strategy for achieving sustainable water management and attains reasonable yields and improves quality in citrus orchards under Mediterranean semiarid climate.

Improved water-use efficiency by deficit-irrigation programmes: Implications for saving water in citrus orchards

Water efficiency is a key concept to solve water-shortage problems in semiarid areas. Deficit irrigation (DI) in many crops has frequently proved to be an efficient tool to optimise water-use efficiency. Three different DI strategies were studied for commercial orchards of mature sweet orange ( Citrus sinensis L. Osbeck, cv. Salustiana and cv. Navelina) from 2006 to 2008: sustained deficit irrigation (SDI), regulated deficit irrigation (RDI), and low-frequency deficit irrigation (LFDI) all defined physiologically with stem-water potential thresholds. The experimental research plots were located in the Guadalquivir river basin, SW Spain. The effects of DI treatments on the fruit yield and on the crop-water status, by the integrated stem-water potential ( Ψ int) were analysed. Also, the benefits of DI in terms of agricultural water-use efficiency (WUE agr) and financial water-use efficiency (WUE f) were estimated for each irrigation strategy. Different relationships were estimated between these parameters and irrigation and total water applied, in order to establish the best irrigation strategy for different irrigation regimes. Yield and Ψ int showed significant differences consistent with the water amounts applied, although the crop response was influenced by other parameters such as crop variety and irrigation strategy. In this sense, treatments with similar irrigation rates and Ψ int resulted in different yield values, evidencing the importance of these factors. Regarding the crop variety, the results showed that cv. Salustiana responded better than cv. Navelina to DI, from the physiological and agricultural perspectives. In terms of water savings, the RDI and LFDI reduced water use by between 1000 and 1250 m 3 ha −1, respectively, with similar yields in comparison to the fully irrigated treatment, significantly improving the WUE. Consequently, the WUE f, and WUE agr were more strongly affected by deficit-irrigation strategy rather than the total water supplied. Thus, the amount of irrigation water would have a relative importance but other variables such as the irrigation strategy, would decidedly influence prudent water management in semiarid areas.

Linking canopy temperature and trunk diameter fluctuations with other physiological water status tools for water stress management in citrus orchards.

The continuous monitoring of crop water status is key to the sustainable management of water stress situations. Two deficit irrigation (DI) treatments were studied during the maximum evapotranspirative demand period in an orange orchard (Citrus sinensis (L.) Osb. cv. Navelina): sustained deficit irrigation irrigated at 55% crop evapotranspiration (ETC), and low-frequency deficit irrigation treatment, in which the plants were irrigated according to stem water potential at midday (Ψstem). Additionally, a control treatment irrigated at 100% of ETC was established. The daily canopy temperature (TC) was measured with an infrared thermometer camera together with measurements of trunk diameter fluctuations (TDF), Ψstem and stomatal conductance (gS). The time course of all physiological parameters and their relationships were analysed, confirming that canopy air temperature differential (TC - Ta) variations and TDF are suitable approaches for determining the water stress. In addition, the maximum daily shrinkage (MDS) and TC - Ta showed high sensitivity to water stress in comparison to Ψstem and gS. Significant relationships were found among MDS and TC - Ta with Ψstem and gS, for monitoring the crop water status by means of MDS vs Ψstem and TC - Ta vs Ψstem. Thus, the combination of these techniques would be useful for making scheduling decisions on irrigation in orchards with high variability in plant water stress.