Effect of Light and Temperature on Seed Germination of Plant Glycine max (soybean)

Abstract

Soybean (Glycine max) germination and early seedling establishment are strongly influenced by environmental conditions, particularly temperature and light, yet the combined effects of these factors on fresh and aged seeds remain insufficiently understood. Therefore, this study investigated the influence of light, darkness, constant and alternating temperatures, photoperiod, seed age, and exposure duration on soybean germination and early seedling growth. Fresh and old soybean seeds were evaluated under control, light, dark, and temperature treatments using seven replicates. Germination number, radicle length, and leaf number were recorded after three days. Additional experiments assessed initial germination following exposure to 5°C and 25°C for 1, 2, 5, 10, and 20 hours, constant temperatures of 15°C, 30°C, and 45°C, alternating temperature combinations of 45–15°C, 45–30°C, and 30–15°C, and different temperature–photoperiod regimes. The results showed that germination, radicle elongation, and leaf development generally increased across successive observations. Temperature treatment produced the highest final germination in both fresh and old seeds, reaching 10 ± 9.9, whereas dark conditions produced the greatest final radicle length of 2.2 ± 2.0 mm. Old seeds frequently demonstrated stronger germination and leaf development than fresh seeds. During initial germination, no germination occurred at 5°C, while germination at 25°C increased progressively to 2.2% after 20 hours. Among constant temperatures, 30°C produced the highest germination, whereas no germination occurred at 15°C. Alternating temperature treatments promoted greater germination in old seeds, while the highest overall germination percentage of 90.4% was recorded under the 6 h (30°C)–18 h (45°C) photoperiod treatment. In conclusion, temperature, light regime, seed age, and exposure duration substantially influenced soybean germination and early growth. Moderate temperatures and suitable temperature–photoperiod combinations were most effective in improving germination, while dark conditions favored radicle elongation and early vegetative development.