Temporal variation of okra fruit traits in coastal saline-alkali soil

The utilization of saline-alkali land is shifting from traditional remediation-based approaches to the adaptive cultivation of salt-tolerant crops. Okra Abelmoschus esculentus L. (Moench), a species with high salt tolerance, offers dual benefits when cultivated in moderately to severely saline-alkali soils, it enhances soil desalination and fertility while providing economic value. However, the temporal variation in okra fruit quality traits in saline-alkali environments — particularly the coordinated response patterns of yield components, color development, and nutritional metabolites across growth stages — remains poorly understood. This knowledge gap limits the development of targeted strategies for quality regulation in high-value agricultural production on marginal land. To address this, a field study was conducted in the saline-alkali region of Nandagang, Cangzhou (total salt content around 4‰), to analyze okra fruit traits at various growth stages. Key parameters included yield traits (transverse and longitudinal diameters, fresh and dry weights), chlorophyll content (chlorophyll a, chlorophyll b, total chlorophyll), and nutritional components flavonoids, soluble sugars, total dietary fiber, and mineral elements (Ca, Fe, Zn). The observed patterns were validated across different harvest months (July–September). Principal component analysis (PCA) and membership function methods were used to compute composite scores for the traits and identify optimal harvest times. The results showed that as okra fruits developed, both fresh and dry weights increased, peaking at 15 days post-anthesis (dry weight: 12.31 ± 0.27 g in July, 11.97 ± 0.24 g in August, and 7.45 ± 0.19 g in September). Fruit size grew rapidly initially and then stabilized at 11 days post-anthesis (transverse: 2.12–2.30 cm; longitudinal: 14.0–17.75 cm). Chlorophyll a content showed a slight upward trend, while chlorophyll b content decreased gradually. Total chlorophyll content remained stable with low variability (coefficient of variation: 3.56% in July, 3.04% in August, 10.07% in September). Soluble sugar and flavonoid contents peaked at 5–7 days post-anthesis (158.92 ± 4.69 mg·g⁻¹ and 33.07 ± 2.74 mg·g⁻¹, respectively), while total dietary fiber accumulated linearly. Mineral elements contents dynamics varied: Ca initially declined before stabilizing, while Fe and Zn showed no significant change. The developmental patterns of fruit size and weight, and chlorophyll b, total chlorophyll, and mineral elelements contents were consistent across the three harvest months. In contrast, trends in chlorophyll a, soluble sugar, flavonoid, and fiber contents exhibited month-specific variability. A trade-off was observed among yield, color, and nutritional components, with the optimal balance point differing by month. The results suggest that in saline-alkali environments, okra exhibits delayed morphological development but enhanced accumulation of osmotic substances. Recommended harvest times are 5 days post-anthesis for July and August and 7 days for September. These findings offer theoretical support for developing saline-alkali-adapted agricultural products, contribute to the implementation of the “planting suitable crops for specific lands” ecological model, and support the sustainable use of saline-alkali lands.