From Salt Tolerance Threshold Analysis to Optimized Cultivation: An Integrated Variety–Technology Pathway for the Forage Mulberry Variety ‘Fengyuan No. 1’

This study aimed to establish an integrated variety–technology cultivation pathway for the new forage mulberry variety ‘Fengyuan No. 1’, linking salt tolerance mechanisms with practical application. A systematic investigation was conducted via a pot experiment with a 0–5‰ NaCl gradient and a field trial comparing three cultivation modes: Ridge Planting (RP), Furrow Planting (FP), and Flat-Bed Planting (FBP). Key findings are as follows. (1) The salt tolerance threshold was clearly defined: a 100% survival rate at salinity ≤ 4‰ (with no injury symptoms at ≤3‰), and 5‰ identified as the lethal threshold (33.33% survival). Salt stress triggered a resource reallocation strategy, increasing the leaf-to-stem fresh weight ratio from 1.53 (0‰) to 2.78 (5‰) to prioritize leaf photosynthetic function. Stable leaf circularity (0.83–0.87) indicated morphological stress resistance. (2) Optimized cultivation pathways were identified: FBP was the core pathway for maximizing biomass accumulation (root, stem, and leaf fresh weights were 5.0, 2.3, and 1.5 times those of RP, respectively) and resulted in the lowest leaf Na+ accumulation (124 mg/kg), making it suitable for lightly to moderately saline–alkali land (≤4‰). FP served as an effective pathway for salt avoidance and height promotion (plant height: 113.18 cm). RP constituted a specialized pathway for high-quality forage, yielding the highest crude protein content (23.3 g/100 g). (3) Cultivation modes significantly affected functional components; FBP activated alkaloid DNJ synthesis (215.16 mg/kg), whereas RP and FP increased osmolyte GABA accumulation (~586 mg/kg). In conclusion, this study integrates a complete technical pathway from salt tolerance mechanism analysis to diversified cultivation options, providing a systematic variety–technology solution for the industrial development of forage mulberry on coastal saline–alkali land.