Foliar Application of Glycine Betaine Affects Morpho-physiological, Biochemical and Fruit Quality Traits of Thomson Navel Orange Under Deficit Irrigation

Given the scarcity of water resources, optimal irrigation management is needed to reduce water while realizing maximal crop productivity. Deficit irrigation (DI) is one of the main agricultural practices known to save irrigation water under water scarcity conditions. On the other hand, glycine betaine (GlyBet) is recognized to alleviate drought injury in many fruit species. Therefore, this study was performed to evaluate the alleviative effects of GlyBet (0, 100 and 200 mu M) under different DI conditions [100% field capacity (FC, fully irrigated), 75% FC (moderate DI; MDI), and 50% FC (severe DI; SDI)] on Thomson Navel orange during two growing seasons (2018 and 2019). The DI significantly reduced relative water content (RWC), water potential, leaf area index (LAI), stomatal conductance, and total chlorophyll content, whereas soluble sugars, proline, electrolyte leakage, malondialdehyde, and antioxidant enzymes activity significantly enhanced in leaf samples. In fruit samples, fruit length, diameter, weight, and fruit yield significantly decreased in response to MDI and SDI. Fruit quality improved under DI conditions by an increment of total soluble solids (TSS), vitamin C content, total phenolic content, total flavonoid content, and total antioxidant capacity. Moreover, it was found that foliar application of GlyBet significantly alleviates the adverse effects of water scarcity, as plants treated with 200 mu M of GlyBet had the highest RWC, water potential, stomatal conductance, total chlorophyll content, soluble sugars, proline, and antioxidant enzymes activity, fruit length, diameter, weight and fruit yield, TSS, vitamin C content, total phenolic content, total flavonoid content, and total antioxidant capacity, as well as the minimum level of electrolyte leakage and malondialdehyde. Overall, foliar application of GlyBet at 200 mu M concentration could be recommended in Thomson Navel orange cultivation areas under water scarcity conditions.

Automated summary

Deficit irrigation is an important agricultural practice to save water, while glycine betaine can alleviate drought injury in fruit species. This study found that glycine betaine application under deficit irrigation conditions can improve fruit quality and have positive effects on certain growth indicators.