Geographical variation in seed germination and biochemical response of milk thistle (Silybum marianum) ecotypes exposed to osmotic and salinity stresses

چکیده مقاله

Milk thistle (Silybum marianum) is a valuable medicinal plant and is spread in different habitats over several areas in Iran. However, no information exists about seed germination and its tolerance to osmotic and salinity stresses of Iranian populations. Therefore, seed germination and seedling responses to osmotic and salinity stresses were determined in six Milk thistle populations originated from different native habitats. The populations were collected from six protected areas in Iran. Hence, two laboratory experiments were arranged separately as a completely randomized factorial design to investigate the effect of osmotic and salinity stresses. In the 1 st and 2nd experiment, seeds of six Milk thistle populations were subjected to five osmotic stress levels (0, -0.3, -0.6, -0.9, and -1.2 MPa) and five salinity stress levels (0, 3, 6, 9, and 12 dS m−1), respectively. Ghamsar-Barzak ecotype which, has been harvested from a dry climate with the lowest mean annual precipitation and Golestan National Park ecotype which has been harvested from a Mediterranean climate with the highest mean annual precipitation among the protected areas had the highest and lowest tolerance to osmotic, respectively. Generally, biochemical traits including MDA, Proline, DPPH-Scavenging (%), Soluble carbohydrate, and Total phenol were improved by increasing in osmotic severity in all ecotypes. The response to salinity was higher than osmotic in all ecotypes. However, Ghamsar-Barzak ecotype showed more salinity tolerance compared to other ecotypes. Under salinity conditions, MDA, proline, DPPH-Scavenging (%), soluble carbohydrate, and total phenol increased more compared to the control treatment. The highest tolerance to salinity and osmotic stresses was observed in Ghamsar-Barzak ecotype that obtained its seed was from a dry climate with the lowest mean annual precipitation and soil pH and EC are high. Hence, the results of this study demonstrated that habitat-correlated variation in Milk thistle seed response to osmotic and salinity stresses. It seems that Ghamsar-Barzak ecotype could be a proper genetic source for gene transfer aimed at breeding for higher tolerance cultivars against osmotic and salinity stresses.