Evening primrose (Oenothera biennis L.) is native to North America, belongs to Onagraceae family, and is a biennial plant. This experiment was performed as factorial based on a completely randomized design in three replications. The main purpose of the study was to evaluate the effect of moist-chilling and GA3 on seed germination and flower induction of evening primrose. The seeds were soaked in distilled water for 30 min, and treated with seven levels of moist-chilling period (0,10, 20, 30, 40, 50, and 60 days) and were kept in 2-4 °C in refrigerator conditions. At the end of day 60 half of the seeds were treated with 500 ppm GA3 solution for 24 hours. After that, both groups were planted in pots with three replications to see the plant reproductive responses. Simultaneously, the same seeds were planted in Petri dishes with three replications for seed germination. Germination was controlled every three days and seed germination test was done for 15 days. Seedling characteristics were measured at the end of germination test. Results showed that moist-chilling and GA3 significantly influenced the seed germination percentage. The highest germination percentage was observed in a combination of 20 days moist-chilling conditions and 500 ppm GA3. Rootlet length increased while moist-chilling was increased from 10 to 30 days. By increasing moist-chilling to 40 - 60 days, rootlet length decreased unexpectedly. Combination of moist-chilling and GA3 did not influence flower stem production and seed yield significantly. On the other hand, the earliest flower stem production was observed in seeds treated with moist chilling for 40 and 60 days. To guaranty flower stem production of spring sowing evening primrose in the areas with warm winter, seeds are strongly recommended to be treated with moist chilling for 40 days at 4 °C. تفاصيل المقالة

Evening primrose is one of the herbal biennial medicinal and oilseed plants. Its seed oil is one of the important sources of omega-6 as well as gamma-linolenic acid. Encouraging the plant to flower without winter conditions is important in biennial plants. This experiment aimed to investigate the phenology of evening primrose as affected by vernalization and gibberellic acid. At the beginning of the experiment, the seeds samples were kept in refrigerator conditions (2 to 4 °C) at ‎different periods of 0 to 60 days. To study the influence of GA3 at the end of 60 days, half ‎ of the vernalized seeds were treated with 500 ppm GA3 solution for 24 hours and then were ‎planted. The time of seedling emergence; 4, 6, 8, and 10 leave stages of seedling; stem ‎formation time, flowering time, capsule formation, capsule filling time, side stem production, ‎the time of physiological ripening of the seed, the time capsule browning, and harvest time was ‎recorded. Results showed that, while control plants did not flower, ‎vernalization significantly influenced all of the phenological stages of experimental ‎plants. A combination of vernalization and GA3 significantly affected stem formation ‎time, side stems production time, and capsule filling time. Finally, according to the ‎results, seed priming with 2 to 4 °C moist-chilling for at least 10 days and GA3 in a minimum concentration of 500 ppm guarantee ‎flower formation of seeds of evening primrose with late sowing time in spring. تفاصيل المقالة