Synergetic role of melatonin and salicylic acid on growth, ion homeostasis and yield of sunflower (Helianthus annuus) under salinity

Context Salinity is an important factor affecting plant growth and development. The combined application of melatonin (MT) and salicylic acid (SA) plays a key role in enhancing salt tolerance. Aims This study aimed to evaluate the effect of individual and combined seed priming with melatonin and salicylic acid on the growth, ions homeostasis, osmolyte accumulation and yield performance of sunflower hybrids under saline conditions. Methods The experiment included three salinity levels (0, 75, 150 mM NaCl), four seed priming treatments (priming with water, 100 μM MT, 100 μM SA and 100 μM MT + SA) and two sunflower hybrids (AGUARA-4 and ORISUN-741). Key results At 150 mM NaCl, shoot and root biomass declined in AGUARA-4 (37.0% and 30.6%) and ORISUN-741 (44.7% and 45.1%), whereas MT + SA increased shoot and root biomass by 36.7% and 38.9%, and 54.9% and 36.8% respectively. Root Na+ increased by 117.7% (AGUARA-4) and 105% (ORISUN-741), whereas MT + SA treatment enhanced the root K+ and Ca2+ by 70.2% and 54.8% in AGUARA-4 and 62.5% and 38% in ORISUN-741 respectively, at 150 mM NaCl. Saline treatment at 150 mM caused a higher reduction in 100-achene weight in AGUARA-4 (73.4%) than in ORISUN-741 (40.2%), whereas MT + SA increased 100-achene weight by 69.5% (AGUARA-4) and by 6.7% (ORISUN-741). Conclusion These findings have shown that MT + SA treatment mitigates salinity stress and enhances sunflower growth and yield under controlled experimental conditions. AGUARA-4 was shown to be more resilient to salt stress than was ORISUN-741. Implications This approach may serve as a promising strategy to improve salinity tolerance in sunflower; however, field evaluation is required before large-scale agricultural use.