Biochemical properties of pomegranate (Punica granatum L.) juice as influenced by severe water stress
Introduction
The Mediterranean basin is among the most vulnerable regions to water scarcity, both currently and in future years as predicted by climate change scenarios (Senatore et al., 2011). Furthermore, it is extremely probable that agriculture in these regions will face more severe water stress conditions due to the increase in potential evapotranspiration due to increase in mean temperature (Giannakopoulos et al., 2005). In Morocco, as one of the Mediterranean countries most vulnerable to climate change, water has become scarce and is a limiting factor for agricultural sector. Linked to the population growth, water resources were already under extensive pressure of industrialization and agricultural extension (El Jaouhari et al., 2018). Several rapports (Agoumi, 2003; Balaghi, 2017) warn of significant impacts on both mean rainfall and variability of hydrological processes, some researches predicting a reduction of 15% in precipitation in 2050 associated with an additional increase in the temperature of 1.5 °C according to the same scenarios.
In addition, all Moroccan agrosystems must cope with the water deficit; only 18% of Moroccan total cropped land is irrigated, using about 69% of water resources (Schilling et al., 2020). In this sense, the Moroccan agricultural stakeholders must be directed towards the use of sustainable strategies to save water, especially for the most water-demanding species, such as fruit trees. The research on this topic mainly focused on two strategies. The first one is based on the use of plant materials less water demanding or able to withstand water deficit with minimum impact on marketable yield and fruit properties. However, the second strategy use innovative practices to improve deficit irrigation management with the aim to minimize water stress impact on production and quality levels (Galindo et al., 2017; Gratacós and Cortés, 2007).
In this sense, pomegranate (Punica granatum L.) could an interesting crop to promote in semi-arid regions due to its drought resilience plasticity (Intrigliolo et al., 2011). There is a growing interest in pomegranate not only because of its pleasant taste but also for its huge demand for industrial processing to obtain pomegranate juice, oil, and jams and their use in medicine by many traditional cultures due to its beneficial properties in the human diet such as the reduction of the risk of chronic disorders like atherosclerosis, cancer, diabetes, and other diseases. Because of market demand, it has become increasingly important to characterize its different genotypes to obtain a high-quality product with economic interests (Çam et al., 2009; Martínez et al., 2012).
In this sense, pomegranate has been known as one of the drought-tolerant crops, with its high leaf relative apoplastic water content and the ability to confront water deficit by developing complementary water stress tolerance mechanisms. However, pomegranate requires deficit irrigation throughout the season for commercial production, especially when it is cultivated in arid and semiarid geographic regions, to reach optimal vegetative growth, yield, and fruit quality (Mena et al., 2013; Intrigliolo et al., 2013).
In Morocco, during the last years, the cultivation of pomegranate has known a great expansion and produced in different geographical regions, from North to Southwest, with an overall production of 117.000 tons for an area around 14.121 Ha in the 2019 season (MAPMDREF, 2019). Two groups of cultivars are grown in Morocco: (i) local ecotypes with red and yellow colored and soft seeds, consumed fresh, and (ii) exotic varieties with acid juice and hard seeds, which are intended for juice extraction processing (Haddioui, 2012).
Scientific reports regarding water stress tolerance of pomegranate under the Moroccan environmental conditions remain very limited and to the best of our knowledge, there has been no scientific assessment of irrigation deficit effect on juice biochemical properties of the imported varieties and local germplasm of pomegranate under the Moroccan climate. This work was a contribution to this topic, carried out on local cultivars and exotic varieties that are widely cultivated in Moroccan regions. The objective was to evaluate the effects of sustained deficit irrigation (SDI) applied during the whole fruit growth period on eleven pomegranate juice attributes.
Section snippets
Plant material, experimental conditions and treatments
The experiment was carried out during two successive seasons of 2019 and 2020 at the experimental field station of Ain Taoujdate, National Agricultural Research Institute (INRA) of Meknes, Morocco (33°56′E, 5°13′N; 499 m). The soil of the orchard is sandy-clay textured (46.8% sand, 10.2% silt, and 43.0% clay). Analytical data showed low available potassium and phosphorus levels, a concentration of lime of 3%, and 2.51% of organic matter, with an electrical conductivity of soil saturation
Juice chemical properties
Water stress effects on chemical properties of juice, TSS, pH, and TA of the eleven pomegranate cultivars are shown in Table 2. Significant differences were detected among the pomegranate cultivars tested for total soluble solids, pH, and titratable acidity. The decreases in TSS were significant in a single year in some cultivars, as observed in ‘Grenade Rouge’ in the first year by an average of 7%, as well as in ‘Gordo de Jativa’ in the second year by the same average (7%), compared to control
Chemical traits
Data analyses were presented clearly differences between pomegranate cultivars tested regarding chemicals juice traits under SDI. Indeed, no significant effect was detected on all juice chemical traits in ‘Bzou’, ‘Djebali’, and ‘Mollar Osin Hueso’ cultivars, while the others were differently affected by SDI treatment. The decrease of total soluble solids in response to water deficit as observed in ‘Grenade Jaune’, ‘Ounk Hmam’, ‘Sefri’, ‘Gordo de Jativa’ and ‘Grenade Rouge’ cultivars were often
Conclusion
Large differences were observed in the behavior of the studied pomegranate cultivars in response to SDI treatment. Globally, significant reduction in chemical and biochemical traits of pomegranate juice was observed under SDI regime during the two consecutive years. The effects of water stress were more pronounced in the second year of the experiment. Based on the stability indexes of measured juice traits, total soluble solids and total amino acids were shown to be the most discriminating
CRediT authorship contribution statement
Atman Adiba: Funding acquisition, Formal analysis, Data curation, Writing – original draft. Lahcen Hssaini: Funding acquisition, Formal analysis, Data curation, Writing – review & editing. Abdelmajid Haddioui: Conceptualization, Visualization. Anas Hamdani: Funding acquisition. Rachid Razouk: Conceptualization, Visualization, Funding acquisition, Formal analysis, Data curation, Writing – original draft, Writing – review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors are grateful to M. Lahlou, M. Alghoum and C.D Khalfi for their help in experimental orchard management and laboratory work.
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