Effect of Drought Stress on Alfalfa Cultivars (Medicago sativa L.) in Germination Stage

Drought is one of the most important natural phenomenon which affects on plant growth. Alfalfa (Medicago sativa L.) is an essential fodder product which has extensive and depth roots system, this advantage enables the plant to tolerate long term drought without any damage to its regrowth process. In order to measure germination percentage and rate, root and shoot growth of 6 alfalfa cultivars (each cultivar has few years old) under various osmotic potential, an experimental design was carried out complete randomized in vitro condition in four replications. To expose drought stress over plant polyethylene glycol (PEG6000) with 0 (control), -3, -6, -9 bar was used. Those cultivars under experiment include Yazdi, Hamedani, Qareh Yonjeh, Maupa, Simmer Chenskaya and CUF101. The results indicated that by reducing osmotic potential of culture environment higher drought stress, a significant decrease in germination percentage and rate, radicle and plumule length and seed vigority index were observed, while the ratio of radicle to plumule was increased. Correlation coefficients of studied plant traits also showed that germination percentage and rate have significant and positive correlations with plumule length, but significant and negative correlation with the ratio of radicle to plumule. Among cultivars, Yazdi and Maupa had higher germination percentage and rate under sever stresses, therefore their tolerance against drought stress during germination stage is more than other cultivars.