The Effect of Arbuscular Mycorrhizal Fungi on Growth and Yield of Rosemary (Rosmarinus officinalis L.) Under Lead and Cadmium Stress

Rosemary (Rosmarinus officinalis L., Lamiaceae) is a perennial medicinal plant used in pharmaceutical, cosmetic, food, and beverage industries. In order to study growth and yield of this plant in symbiosis with arbuscular mycorrhizal fungi under Pb and Cd stress, a twofactored pot experiment was carried out based on a randomized complete block design with 4 replications in greenhouse of Department of Horticultural Sciences, University of Tehran, Karaj, Iran in 2011- 2012. The first factor was arbuscular mycorrhiza (inoculation and noninoculation), and the second factor was heavy metal contamination as listed here per mg/kg of soil: Without contamination, Pb 150, Pb 300, Cd 40, and Cd 80. The parameters plant height, number of lateral branches per plant, length of lateral stem, number of leaves, leaf area, crown diameter, shoot fresh and dry weights, leaf dry weight, leaf dry weight/shoot dry weight ratio, and essential oil content and yield were measured. The results showed that growth and yield of rosemary diminished with increasing concentration of the heavy metals in the medium; however, mycorrhizal inoculation donated a tolerance to the heavy metal stress, thereby improving growth and yield of rosemary in such a stressful situation. The highest fresh and dry weights were observed in mycorrhizal plants grown in non-pollution medium, whereas non-mycorrhizal plants grown under Cd 80 had the worst values, which were decreased respectively by 57.6% and 79.5% as compared to those of mycorrhizal plants grown on non-polluted medium. Moreover, the highest content of essential oil was recorded in non-mycorrhizal plants grown under Pb 300; nevertheless, the highest essential oil yield was found in mycorrhizal plants grown on noncontaminated medium.