Effect of mycorrhizal fungi on some morphological & physiological charactristics of Milk thistle (Silybum marianum (L.) Gaertn.) under drought stress

Drought stress, temporally or permanently, is a more limiting factor in growth and distribution of vegetation cover than other environmental factors. In order to study the effects of vesicular arbuscular mycorrhizal and drought stress on growth and yield of Milk thistle (Silybum marianum (L.) Gaertn.), a pot experiment was performed as factorial based on completely randomized design in three replications in the research greenhouse of Chahnimeh at the University of Zabol. Drought stress consisted of two levels including %60 and %30 of field capacity and full irrigation as control treatment. Three mycorrhizal fungi including Glomus mosseae, Glomus versiformis, and Glomus intraradices were investigated. The results showed that after starting of drought stress, vegetative characteristics such as number of capituls, number of seeds in capitul, 1000 seeds weight, leaf number and area, root length, number of minor branches, plant height, and dry weight of leaf, stem and root, significantly decreased with increasing drought stress. RWC of leaf was intensely affected by drought and decreased from 77.3 in control treatment to 57.01 in 30% of field capacity irrigation treatment. In addition, with increasing drought stress, the amount of phosphorus in leaves decreased and the amount of potassium increased. Osmotic adjustment in Milk thistle was increased in response to drought stress and leaf proline content increased (the highest 0.13 mg/g tissue in 30% of field capacity treatment); however, silimarin content decreased from 16.35 in full irrigation to 10.24 in 30% of field capacity treatment. Inoculation with VAM significantly increased vegetative indices, silimarin content (the highest in G. mosseae application and the lowest in control), plant RWC, and leaf content of P and K under drought stress conditions compared to uninoculated plants; however, the leaf proline content was low. In general, application of mycorrhizae fungi increased drought stress resistance in Milk thistle.