Responses of Three Contrasting Rice Cultivars to Salt Stress and Water Deficit.

Understanding salinity tolerance of different rice cultivars is an important step in devising management strategies to utilize millions of hectares of arable saline areas otherwise suitable for rice cultivation. This study compared the responses of three contrasting rice cultivars: 1) salt tolerant FL478, 2) medium tolerant IR64, and 3) salt sensitive IR29, to osmotic stress of 0.32 MPa imposed at the root level. To establish the importance of the osmotic (water stress) and ionic effects of salinity, stress was imposed using PEG6000 and NaCl in two separate experiments: 1) stress at vegetative stage, and 2) stress at reproductive stage. Crop growth and tissue ion concentration were monitored throughout each experiment. Regardless of the timing of stress, more tolerant cultivars consistently performed better than the less tolerant ones implying that cultivar selection is a crucial step. Grains and aboveground biomass at physiological maturity were apparently less sensitive to stress imposed at vegetative stage, but were significantly affected by stress at reproductive stage. Ion (Na, K, Ca, Mg, and P) concentrations in plant tissues during and immediately after stress were significantly affected by cultivar, type of stress, and their interaction but the differences seem to diminish with time (>60 after stress imposition).  The difference between the types of stress varied depending on the cultivar. Findings imply that either responses of the cultivars to salinity stress were mainly attributed to osmotic components or the more sensitive cultivars have better osmotic adjustment to reduce the effect of water stress and balance out the overall salinity effects.  Further assessment of the osmotic pressure in the plant tissues is needed to understand the responses of different cultivars, nonetheless, rice should be protected from salt stress at reproductive stage. - Findings from PN10: Coastal Resource Management for Improving Livelihoods under CGIAR Challenge Program on Water and Food