Modulation in Morphological and Biochemical Attributes of Sunflower (Helianthus annuus L.) Under Saline Conditions Through Co-Application of Melatonin and Salicylic Acid as Seed Priming

Sunflower (Helianthus annuus L.) is an important oilseed crop worldwide and threatened by salt stress due to climate change. The current study was devised to examine the impact of melatonin and salicylic acid (water soaked, 100 μM melatonin, 100 μM salicylic acid and 100 μM melatonin + salicylic acid) on growth and physiological traits of two sunflower hybrids, that is, AGUARA-4 and ORISUN-741 under three different salt levels (control, 75 and 150 mM NaCl). A pot experiment was carried out twice (two consecutive years) to check the combined effect of melatonin and salicylic acid on two sunflower hybrids. Melatonin and salicylic acid were applied as pre-sowing seed treatment on sunflower hybrid seeds. Results showed that electrolyte leakage (%) was increased in salt stress (150 mM NaCl) by 169.4% (AGUARA-4) and 194.8% (ORISUN-741) in both hybrids. In comparison with control, the combination of melatonin and salicylic acid improved the morphological attributes root and shoot fresh weight (45.2% and 41.9%) in AGUARA-4, whereas 81.5% and 46.1% in ORISUN-741 reduced the reactive oxygen species such as hydrogen peroxide and malondialdehyde content (35% and 27.2%) in AGUARA-4 and 33.8% and 25.1% in ORISUN-741 under salinity stress (150 mM NaCl). In conclusion, under salinity stress, ORISUN-74 showed a notable reduction in morphological attributes and enhancement in reactive oxygen species compared to AGUARA-4, whereas the combination of melatonin and salicylic acid improved the growth by decreasing reactive oxygen species and increasing the anti-oxidants. These results collectively suggested that the melatonin and salicylic acid, particularly their combination, were more effective in enhancing crop growth and production under saline conditions.