Comparing the effects of polyethylene glycol-induced drought stress and paclobutrazol on six cultivars of Medicago sativa

This investigation was carried out with the aim of determining the effect of polyethylene glycol 6000 (PEG; 0, 3%, 6% and 9% w/v) treatment on six cultivars of Medicago sativa. PEG treatment significantly decreased the germination index in cultivars of Isfahani, Hamedani, Bami, Baghdadi, Yazdi and Ghare-Medicago, with the highest reduction in Ghare-Medicago and Hamedani cultivars by about 50% and 44%, respectively. PEG treatment significantly decreased germination percentage and germination rate in two cultivars of Ghare-Medicago (22% and 20%, respectively) and Hamedani (28% and 27%, respectively) while increased mean germination time in them. The seedlings height, fresh weight and water content significantly decreased in all PEG-treated cultivars. The highest reduction in mentioned factors was observed in Ghare-Medicago (43%, 24% and 55%, respectively) and Hamedani (57%, 23% and 53%, respectively), while the lowest reduction was observed in Yazdi, by about 28%, 9% and 17%, respectively. Data showed that PEG treatment reduced seedling dry mass only in Ghare-Medicago and Hamedani cultivars by about 16% in both cultivars. PEG treatment significantly decreased the chlorophyll a, b and total, anthocyanins, phenols and α-tocopherol contents of six Medicago cultivars. The results of greenhouse experiments showed that PEG treatments resulted in a significant reduction in fresh weigh, dry weight and water content of all studied cultivars. In conclusion, the findings of both petri dish and greenhouse experiments suggested that Ghare-Medicago and Hamedani cultivars can be considered as drought sensitive cultivars while Yazdi is a drought tolerant cultivar. It should be noticed that Bami and Baghdadi cultivars were also relatively drought tolerant. Also, our study on paclobutrazol (PBZ) treatment showed that PBZ effectively decreased the negative effect of drought stress on growth of all cultivars of Medicago.