The Effect of Drought Stress and Selenium on some Growth and Physiological Characteristics of Isfahan Yellow Landrace Onions (Allium cepa L.)

Selenium due to its physiological and anti-oxidative properties is considered to be essential micronutrient for humans, animals and plants. The positive effects of selenium on reduction of various environmental stresses in plants is, however, still unclear and need to be explored. In this study, the effect of selenium on increasing drought tolerance of yellow landrace onions in Isfahan was investigated by factorial experiment in a completely randomized design under greenhouse conditions. Treatments were drought stress at three levels (0, 50 and 75% of field capacity) and levels of selenium at three levels (0, 5 and 10 mg.L-1 sodium selenate). Foliar application of selenium was performed in two plant growth stages. The first foliar application at the onset of stress (onion production stage) and the second application was carried out two weeks after the onset of stress (onion development stage). Increasing selenium concentrations, under all levels of drought, traits like plant height (62.66 cm), leaf number (11.66), fresh weight (36.82 g) and dry weight of bulb (4.66 g) were increased. In contrast to drought stress, selenium concentrations increased onion physiological properties (total phenol, flavonoid, total soluble sugar, relative leaf water content and stomatal conductance). Increased onion growth under drought stress is attributed to the antioxidant property of selenium. Because, selenium acts as an oxidant at high concentrations it decreased growth. Selenium at 10 mg.L-1 did not have any detrimental effect on onions. It increased the growth of bulb and seedling onion. These results suggest that selenium application may improve antioxidantal defense system of onions under drought stress conditions. Thus, its use may be recommended under arid and semiarid regions.