Comparative efficacy of PEG and H2O2 priming in mitigating salt stress during germination and early seedling establishment of cowpea (Vigna unguiculata)

Cowpea (Vigna unguiculata (L.) Walp.) is a vital legume crop commonly cultivated in marginal soils with low nutrient levels and limited water availability. However, salinity stress poses a significant threat to its germination and early seedling growth. Enhancing tolerance at these critical stages through seed priming offers a promising approach to utilize salt-affected lands. Therefore, this study investigated the potential of two exogenous osmopriming agents, Polyethylene Glycol (PEG) and Hydrogen Peroxide (H2O2) alongside hydropriming (water) to enhance germination indices, seedling traits, and salinity tolerance in cowpea. The experiment was conducted under semi-controlled conditions using a Randomized Complete Block Design (RCBD) with three replications. Seeds of cowpea variety 'BARI Felon-2' were primed with distilled water (Hp), 20% PEG (P20), and 10 mM H2O2 (H10) and seedlings were grown for 7 days under control (S0) and 100 mM NaCl (S100) conditions. Salt stress significantly (P < 0.05) inhibited seedling emergence and establishment, reduced biomass accumulation, and triggered oxidative stress and Na+ upregulation. Conversely, seed priming significantly (P < 0.05) improved germination percentage, seed vigor index, total leaf area (TLA), seedling length, and chlorophyll content. While both osmopriming agents were effective, 20% PEG (P20) exhibited the most significant stress mitigation, reducing malondialdehyde (MDA) content by 41% and increasing TLA from 0.07 cm2 to 0.21 cm2 (208% increase) compared to untreated stressed seedlings. In conclusion, osmopriming enhanced cowpea performance under salt stress by promoting early, synchronized emergence and chlorophyll synthesis. These physiological improvements mitigated oxidative damage and Na+ toxicity, resulting in superior seedling growth and biomass production.