Cold stratification, temperature, light, GA₃, and KNO₃ effects on seed germination of Primula beesiana from Yunnan,...

Primula beesiana Forr. is an attractive wildflower endemically distributed in the wet habitats of subalpine/alpine regions of southwestern China. This study is an attempt to understand how this plant adapts to wet habitats and high altitudes. Specifically, we examined the effects of cold stratification, light, GA₃, KNO₃, and temperature on P. beesiana seed germination. KNO₃ and GA₃ increased germination percentage and germination rate compared to control treatments at 15/5 and 25/15 °C. Untreated seeds germinated well (> 80%) at higher temperatures (20, 25 and 28 °C), whereas at lower (5, 10 and 15 °C) and extremely high temperatures (30 and 32 °C) germination decreased significantly. However, after cold stratification (4-16 weeks), the germination percentage of P. beesiana seeds at low temperatures (5-15 °C) and the germination rate at high temperatures (30 °C) increased significantly, suggesting that P. beesiana has type 3 non-deep physiological dormancy. The base temperature and thermal time for germination decreased in seeds that were cold stratified for 16 weeks. Cold-stratified seeds incubated at fluctuating temperatures (especially at 15/5 °C) had significantly high germination percentages and germination rates in light, but not in dark, compared to the corresponding constant temperature (10 °C). Seeds had a strict light requirement at all temperatures, even after experiencing cold stratification; however, the combinations of cold stratification and fluctuating temperature increased germination when seeds were transferred from dark to light. Such dormancy/germination responses to light and temperature are likely mechanisms that ensure germination occurs only in spring and at/near the soil surface, thus avoiding seedling death by freezing, inundation and/or germination deep in the soil.