Seed treatment combined with foliar application of oligosaccharides enhances seed germination and seedling growth in pepper and tomato under low-temperature stress

Low-temperature stress during early spring critically limits seed germination and seedling establishment in solanaceous crops. This study investigated the effects of seed treatment (ST) combined with foliar spraying of oligosaccharides (FSO) on improving seed germination and early seedling growth of pepper and tomato under constant 15°C conditions. The seed treatment (ST) involved soaking seeds in a tri-component oligosaccharides solution (0.11 g/L of a 1:1:1 ratio of chitosan oligosaccharide, D-cellobiose, xylo-oligosaccharide) for 24 h at 20°C, followed by solid matrix priming (SMP) with vermiculite (seed:vermiculite:water, 1:2:1.8, w/w/w) for 72 h at 20°C and subsequent air-drying. The treated and control seeds were germinated at 25°C for 3 days prior to being transferred to 15°C. Seedlings from treated seeds received two foliar sprays of the same oligosaccharides solution (0.11 g/L) at 14 and 18 days after sowing. The results showed that seed treatment (ST) significantly enhanced all emergence parameters and reduced the mean emergence time in both species compared to the untreated control. Statistical analysis indicated a significant species × treatment interaction for most emergence parameters, with a more pronounced promotive effect in pepper. The integrated ST + FSO treatment significantly improved seedling growth parameters. Significant species × treatment interactions were observed for stem diameter and fresh weight, with tomato exhibiting a greater relative increase in fresh weight. ST + FSO enhanced the activities of superoxide dismutase (SOD) and glutathione peroxidase (GPX), and increased soluble sugar content in both species. However, a significant increase in glutathione reductase (GR) activity and soluble protein content occurred specifically in pepper, highlighting a species-specific physiological response. In conclusion, the combination of seed treatment and foliar spraying of oligosaccharides (ST + FSO) is an effective strategy for enhancing low-temperature tolerance in solanaceous crops, although its efficacy and underlying physiological mechanisms exhibit significant species-specific variation.