JWSS - Journal of Water and Soil Science

A glasshouse study was conducted to measure the effects of salinity and drought stresses on growth and chemical and biochemical composition of 4 onion cultivars. The cultivars were Dessex, Texas Early Grano (Texas), Dehydrator, and PX492. Salinity treatments included control, 45mM NaCl, 45mM NaCl + 5mM CaCl2 and drought treatments were control (maintaining soil moisture at field capacity) and irrigation when 50% of available water was used. Four weeks after the treatments, the plants were harvested and root and shoot dry weights (RDW, SDW), Na⁺, K⁺, Ca²⁺, total protein, reduced sugars, as well as free proline contents were measured in both roots and shoots.

 Results showed that NaCl and drought treatments significantly reduced SDW and RDW. The Texas cultivar and the Dessex cultivar produced the highest and the lowest amounts of SDW, respectively. NaCl significantly increased Na⁺ uptake but reduced K⁺ uptake in shoots and roots and also reduced Ca²⁺ uptake in roots. NaCl+CaCl₂ significantly alleviated the deleterious effects of NaCl such that SDW significantly increased in two cultivars and increased RDW and the K⁺ contents while causing decreased Na⁺ and sugar contents in shoots and roots of all cultivars. All stresses increased total protein contents of shoots in Texas only but decreased or had no effect on others. Root total protein increased under salinity stress, while drought had no effect. Changes in proline and sugars in both shoots and roots did not follow any particular pattern. Out of the biochemical compositions measured, shoot total protein in plants under the stresses showed a positive significant correlation with SDW, which may be used to screen onion cultivars for drought and salinity stresses.