Long-term salinity irrigation alters nutritional composition in date palm fruits: implications for variety selection in hyper-arid agriculture

Numerous studies have examined the effects of salinity on the growth of date palms, yet few have addressed the changes in fruit quality. This study investigates the impact of long-term saline water irrigation, applied over two decades, on the nutritional quality of date palm fruits. Ten varieties were irrigated with three levels of salinity (5, 10, and 15 dS.m ^− 1 ), and their fruits were analyzed for protein, phenolic compounds, sugars, and mineral content. Results showed that protein, total polyphenols (TPH), and minerals were significantly affected by variety, salinity, and their interactions. Sugar content was only influenced by variety (P < 0.001). The study found a strong positive correlation between protein content and total polyphenol levels (r² = 0.8), which remained stable with increasing salinity. Additionally, the correlation between protein and iron increased from r² = 0.3 at low salinity to r² = 0.7 at higher salinity, due to the mineral content of saline water affecting mineral levels in dates and the trees' defense mechanisms. Principal component analysis and clustered heat maps revealed five distinct groups. One group, including Ajwat-Al-Madinah irrigated with three salinity levels, Abu-Maan irrigated with 10 dS.m-1, and Rhothan and Sukkari irrigated with 15 dS.m-1, showed the highest levels of TPH, protein, iron, and potassium, along with medium sugars and low sodium. Ajwat-Al-Madinah maintained high fruit quality despite increasing salinity levels. These varieties exhibited favorable nutritional characteristics for human consumption and dietary considerations, making them suitable for cultivation in hyper-arid saline environments.