Exogenous neoagaro-oligosaccharides accelerate seed germination and alleviate the impact of growth retardants on germination and seedling growth of garden cosmos (Cosmos bipinnatus Cav.)

Neoagaro-oligosaccharides (NAOS) are degraded seaweed polysaccharides of low molecular weight and high water solubility. Currently, little information is available on the utility of NAOS for seed germination. Here, we investigated seed germination of garden cosmos under NAOS concentrations of 0, 0.01, 0.1, 1, 5, and 10 g/L and monitored the role of 1 g/L NAOS in physiology of germinating seeds and recovery from plant growth inhibitor stress. The results showed that 1 g/L NAOS maximized germination potential of seeds and hypocotyl length, along with increasing α-amylase and β-amylase activities and soluble starch and soluble sugar contents of seedlings. Radicle length and hypocotyl fresh weight showed progressive decrease with the increase in NAOS concentration. The optimal dose of NAOS (1 g/L) decreased abscisic acid level but increased the levels of auxins, gibberellins and strigolactones in germinating seeds. Addition of 1 g/L NAOS to germination medium alleviated the impact of different growth retardants on seed germination and seedling growth, particularly radicle dry weight. This study shows that exogenous NAOS can improve seed germination and alleviate the stress induced by growth retardants on garden cosmos.