Evaluation of the effect of drouth stress on growth, esential oil and some physiological traits of four Basil (Ocimum basilicum L.) cultivars

Water availability is one of the most important environmental factors affects the distribution, growth and successful production of crops. Drought stress, as the main non-biological limiting factor of plant growth and yield, can caused or intensify other stresses in the plant, especially the stress of nutrient deficiency.On the other hand, plants produce similar amounts of primary metabolites under water deficit stress conditions compared The to non-stress conditions. Scince plant reduces its biomass under stress conditions, so higher portion of primary metabolites allocate to the production of secondary metabolites.The present study was conducted to evaluate the growth, esential oil and some physiological traits of four Basil cultivars under water deficit stress condition.

The experiment was conducted as a factorial based on a completely randomized design in greenhous in 2017. Four commercial Basil cultivars (including Iranian green, Iranian violet, Genovese and Amethyst) were used as the first factor and water deficit stress at four levels (including irrigation at 100%, 85%, 70% and 55% FC) was used as second factor. Traits such as fresh and dry weight of the plant, fresh and dry weight of the root, essential oil content, essential oil yield, chlorophyll, malondialdehyde, proline, catalase, peroxidase, ascorbate peroxidase, photosynthesis, stomatal conductance and stomatal strength were measured. The data obtained from the experiment were analyzed using Minitab software and means comparidion were done by LSD test.

The results showed that water deficit stress decreased fresh and dry weights of the plant and photosynthesis in all cultivars. In addition, fresh and dry weights of root and stomatal conductance were reduced under drought stress. While, proline, malondialdehyde, chlorophyll and antioxidant enzymes activity were increased in respons to drought stress. However, the amount of change in traits was different among the cultivars. The reduction of different traits in respone to drought was mostly lower in the genoves cultivar than the others. Iranian green and genoves cultivars had the highest fresh and dry weight of the plant. In addition, the highest percentage of essential oil belonged to the genoves cultivar.

Genoves cultivar had the highest fresh and dry weight of shoot, had the highest percentage of essential oil and the highest stomatal conductance and recommended as a resistant cultivar in order to essential oil production under drought condition. Keywords : Physiological parameters, water deficit stress, essential, photosynthesis parameters