Effect of Saline Irrigation on Accumulation of Na+, K+, Ca2+, and Mg2+ Ions in Rice Plants

Salinity is an abiotic stress that curtails rice production in many parts of the world. Although Koshihikari and Nikomaru are high-yielding japonica rice cultivars, their salinity-tolerance levels are not well known. This experiment was conducted in Ehime, Japan to assess the effect of salinity on ion accumulation and dry mass production of Koshihikari and Nikomaru compared with a salinity-tolerant indica rice cultivar (Pokkali). Control (0.16 dS/m), 6 dS/m and 12 dS/m irrigation treatments were conducted during the tillering stage (1st phase of experiment), and later only control and 6 dS/m irrigations were applied during the reproductive stage (2nd phase of experiment). Excessive Na+ accumulation in plants hampers the uptake of the macronutrients K+, Ca2+, and Mg2+, which consequently retards growth and yield. Because salinity-tolerant plants can avoid this stress, minimal Na+ was found in Pokkali during the tillering stage (under 6 dS/m salinity). Additionally, Nikomaru showed better growth and dry mass than Koshihikari. Moreover, the Koshihikari leaves contained more Na+ than Nikomaru and Pokkali. The japonica cultivars had higher Na+/K+ in their leaves than Pokkali. In the reproductive stage, the two japonica cultivars accumulated almost the same amount of Na+ under 6 dS/m salinity. However, under 6 dS/m salinity, the grain yield of Nikomaru was higher than control, whereas that of Koshihikari decreased because of salinity. Meanwhile, Pokkali had the lowest Na+/K+ in the whole plant, and most parts of Nikomaru showed lower Na+/K+ than Koshihikari. Koshihikari was relatively less tolerant than Nikomaru under 6 dS/m salinity during both stages, while both failed to withstand 12 dS/m.