study of effects topping on qualitative and quantitative of silymarin in native populations of milk thistle (silybum marianum, l.)

milk thistle is used traditionally as a hepaprotective agent and supportive treatment of liver disorders. the most problems in milk thistle harvest are tall height, seed shedding and being spinous. in this trial, effects of 3 native populations (p1: isfahan violet flower, p 2: ahvaz white flower and p3: ahvaz violet flower) and 3 topping levels (t1:control, t2: topping in 7 leaves stage and t3: cutting back in first capitulum appearance stage) on qualitative and quantitative properties of silymarin, silybin, isosilybin, silychristin, silydianin, taxifolin , seed, tall height and days until blooming was studied. experimental design was factorial and conducted as a randomized complete block design with 3 replications in experimental field of ramin agricultural and natural resources university (2006-2007). the results indicated that, seed yield in topping and native populations had not significant difference. effect of topping on decrease of tall height was significant but populations was't. topping moreover creation stress caused delay in blooming and synchrony seed filling with high heat, thereupon, thermal stress increased medicinal active substances. amount of medicinal active substances among popoulations were very difference. in p1 amount of silymarin was 2.81 and 2.09, silychristin 2.30 and 4.64 and isosilybin 3.63 and 4.90 fold p2 and p3 respectively. p2 had not silydianin. amount of silybin in p 3 was 2 and 6.09 fold of p1 and p2 respectively. the results showed that effects of populations on medicinal active substances were much more than topping. p1 was 26 days more serotine than p2 and p3.