Phenology of evening primrose (Oenothera biennis L.) as affected by vernalization and gibberellic acid (GA3)

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.