Estimation of some salinity-related growth characteristics and evaluation of salinity tolerance threshold of Milk thistle (Silybum marianum L.)

To evaluate the salinity tolerance of Milk thistle, an investigation was conducted in a completely randomized design with 3 replications in a pot in the greenhouse of the National Salinity Research Center. Experimental treatment includes 5 levels 0.44 (control), 3, 6, 9 and 12 dS/m. The results showed that the application of salinity levels significantly reduced all the studied traits. Regarding some growth and yield-related traits, increasing salinity from control to salinity of 12 dS/m reduced plant height by 89%, grain yield by 79%, biological yield by 46%, and harvest index by 59%. Also, with increasing salinity level, relative water content decreased by 9.86% and ion leakage increased by 38.53%. Potassium and sodium elements of plant shoots were also significantly affected by salinity so that increasing salinity from control to 12 dS/m had a significant effect on reducing the ratio of potassium to sodium and caused a 69% decrease in this ratio. The results showed that the salinity tolerance threshold (seed yield) was 0.19 dS/m and a 50% reduction in yield was obtained at a salinity of 7.21 dS/m. In general, according to the results, it seems that Milk thistle does not have a high tolerance to salinity.