Soil moisture deficiency limits eggplant growth and affects the yield and quality. Identifying an appropriate deficit irrigation strategy to enhance irrigation water productivity is an urgent task. Additionally, the dynamic response of eggplants to water stress at various phenological stages needs further clarification. In this study, eggplants were used as experimental materials, with field capacity (FC) (Senyigit et al.) serving as the irrigation standard. Two levels of deficit irrigation treatments (60 % FC and 50 % FC) were applied at three key phenological stages of eggplant (seedling stage, flowering and fruiting, and prime fruit stage). A randomized block design was used with non-deficit irrigation (80 % FC) during the phenological stages as the control (W1), resulting in seven treatments, each with three replicates. The results showed that at the same phenological stage, plant height, stem diameter, leaf area index (LAI), dry matter accumulation, total fresh root weight, total root length, total root surface area, and total root volume decreased as the irrigation threshold was lowered. The content of vitamin C, soluble sugars, souble proteins, and crude fiber increased as the irrigation threshold decreased. Leaf photosynthetic parameters (photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), and intercellular CO2 concentration (Ci)) were positively correlated with the irrigation threshold. The W1 treatment had the highest yield (89.1 t·ha−1 in 2018; 88.8 t·ha−1 in 2019), followed by the W2 treatment (86.1 t·ha−1 in 2018; 85.6 t·ha−1 in 2019). Water deficit during the prime fruit stage (W6, W7) had the most significant impact on yield. W1 had the highest water productivity (19.4 kg·m−3 in 2018; 19.2 kg·m−3 in 2019), with no significant difference from W2 (19.4 kg·m−3 in 2018; 19.0 kg·m−3 in 2019). Using the Jensen function, the water sensitivity of eggplants at different phenological stages was ranked as follows:prime fruit stage > flowering and fruiting stage > seedling stage. Path analysis indicated that dry matter accumulation, single fruit weight, and single plant yield were important indicators affecting yield. Considering irrigation amount, eggplant growth, fruit yield and quality, and water productivity, the optimal deficit irrigation thresholds for eggplants in arid regions are determined to be 60 % FC during the seedling stage, 60 % FC during the flowering and fruiting stage, and 80 % FC during the prime fruit stage. The findings of this study offer valuable insights for precision agricultural irrigation practices.
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