Evaluating Physiological, Biochemical, and Yield-Related Responses of Borage Exposed to Varying Levels of Salinity and Silicon

Salinity stress is a major constraint to crop productivity, particularly in arid and semi-arid regions. This study evaluated the effects of silicon (Si) application on the physiological, biochemical, and yield-related responses of borage (Borago officinalis L.) under varying salinity levels. Increasing salinity disrupted ionic balance by elevating Na+ and Cl– accumulation while reducing Ca2+ and $${\text{NO}}_{3}^{ - }$$ contents, and caused significant declines in plant dry weight, seed yield, and leaf area index, with reductions exceeding 50% at high salinity levels. Salinity also induced the accumulation of proline, phenolic compounds, and flavonoids, whereas anthocyanin content plateaued under moderate stress. Antioxidant responses revealed a decline in DPPH scavenging activity but an increase in superoxide radical scavenging, indicating a limited capacity to counteract oxidative stress under severe salinity. Silicon application, particularly the combined seed priming and foliar treatment, effectively mitigated the adverse effects of salinity by improving ionic balance, enhancing antioxidant activity, and increasing nitrate reductase activity and relative water content. These improvements translated into significant increases in plant dry weight (42%), seed yield (26%), and seed oil content (7%) compared with untreated plants. Notably, salinity reduced total fatty acid concentrations by up to 80%, while total oil content declined to a lesser extent, highlighting a greater sensitivity of lipid composition than oil quantity. Overall, Si application enhanced stress tolerance and productivity in borage, with combined treatments providing the greatest benefit. These findings suggest that Si is a promising strategy for improving the resilience of oilseed crops under saline conditions.