Determination of seed dormancy of Silybum marianum L. Gaertn. seeds : Effects of afterripening and gibberellic acid treatments at different temperatures

Medicinal plants are one of the important economic plants that are used raw or processed in traditional or modern industrial medicine. Nowadays, this increasing demand has caused the extraordinary and inappropriate harvesting of these plants, which is due to the destruction of the natural habitat of these plants and the presence of a number of them at risk of extinction and destruction. Therefore, in order to prevent the extraction of these plants in the natural habitats, it is necessary to cultivate and domesticate these plants. One of the primary problems in the domestication of medicinal plants is the presence of dormancy in the seeds of these plants. Milk thistlel is a medicinal herb from the Asteraceae family, whose seeds contain valuable medicinal compounds. Primary problems in the domestication of this plant are the presence of a dormancy in its seeds, which leads to the non-uniformity of germination and its emergence in the field. Hence, the first step in the domestication of wild plants is to identify the type of dormancy with the aim of choosing the most effective method to solve it. Therefore, the study was conducted with the aim of: 1) determining the type of dormancy; 2) studying the germination reaction of milk thistle seeds to different levels of gibberellic acid and after ripening under different temperature conditions.

This research was carried out in two separate experiments on fresh and after- ripe milk thistle seeds, with the aim of investigating the effects of various concentrations of gibberellic acid on dormancy removal and germination of this plant at different temperatures. In each experiment, the germination test was carried out at 5, 10, 15, 20, 25, 30 and 35 ° C temperatures on fresh and after-ripe milk thistle seeds with different levels of gibberellic at five levels 0, 500, 1000, 1500 and 2000 ppm. In each experiment, traits such as percentage, rate and uniformity of germination, along with time to germination, were determined in different treatments. The response of these traits toafter-ripening, temperature and gibberellic acid was investigated.

The results showed that fresh and after ripe seeds of milk thistle could not germinate at any temperature, and using gibberellic acid, seeds could germinate at different temperatures. But the response of the fresh and after ripe seeds to gibberellic acid was different. In fresh seeds, percentage, rate, and uniformity of germination were less than the after ripe seeds. Also, the time to start germination in after ripe seeds was less than fresh seeds. In other words, it can be said that although the after-ripening did not remove the seeds dormancy of milk thistle, but increased the susceptibility to gibberellic acid, so that the percentage after ripe seeds and germination rate at lower concentrations of gibberellic acid (500 ppm) was observed. It also after ripening increased the optimum temperature and seed germination ceiling of this plant compared to fresh seeds. The optimum temperature for fresh and after ripe seeds was 10 ° C and 25 ° C, respectively, and the temperature was 30 ° C and 35 ° C, respectively. However, there was no significant difference between the fresh and after ripe seeds at the base temperature In other words, it can be said that the after ripening increases the germination temperature of the milk thistle seeds with gibberellic acid.