Changes in green cover and chlorophyll and carotenoid contents of milk thistle (Silybum marianum L.) in response to seed hydro-priming and water deficit

In order to investigate the effects of hydro-priming duration on green cover and leaf chlorophyll and carotenoid contents of milk thistle (Silybum marianum L.) under different irrigation treatments, a split plot experiment based on randomized complete block (RCB) design with three replications was conducted in 2015 at the Research Farm of the University of Tabriz. Irrigation treatments (I1, I2, I3, I4: Irrigation after 70, 100, 130 and 160 mm evaporation from class A pan, respectively) were allocated to main plots, and hydro-priming durations (P1, P2, P3: 0, 8 and 16 hours, respectively) were assigned to the sub plots. Germination percentage, mean germination time, number of plants per unit area, percentage of green cover, chlorophyll a, b and total and carotenoid contents were measured. The results showed that hydro-priming especially in 16 hours was reduced the mean germination time. However, had no significant effect on germination percentage. Also, the number of plants per unit area increased with increasing priming duration up to 16 hours. Percentage of green cover was also enhanced with increasing hydro-priming duration under all irrigation treatments. Chlorophyll a, b and total and carotenoid contents considerably decreased as a consequence of water deficit. However, hydro-priming for 8 and especially 16 hours significantly increased these traits. These results clearly indicate that hydro-priming by increasing plant establishment, percentage of green cover and chlorophyll and carotenoid contents has reduced drought effects. This could improve grain production of this medicinal plant under well and limited irrigation conditions.