Increase in the water stress sensitivity at early panicle-development stage in rice under saline soil conditions

Rice yield in the north regions of China remains low due to saline soil subjected to drought. This study was conducted to analyze the changes in yield of rice due to water stress under the saline soil conditions. Four-litter pots were filled with the paddy soil and various amounts of salt (NaCl) (0, 5, 10 and 15 g / pot) were incorporated into the soil. Seedlings of rice cultivar Akihikari were transplanted at a rate of one plant per pot and grown under the submerged soil conditions in a rain shelter. Plants were subjected to various degrees of soil-water deficits at panicle formation stage. During the soil drying, pre-dawn leaf water potential was measured and cumulative water stress (CWS), which is an integrated scale of duration and degree of water stress, was estimated. At maturity, plant dry weight and Na contents of leaf and stem were determined. Heading was delayed and panicle dry weight per plant was decreased by the soil salinity under the submerged soil conditions. Further, heading was delayed and panicle dry weight was decreased by additional water stress on each saline soil, the days of delay and decrease of the dry weight being proportional to CWS. Water stress susceptibility estimated from the relationship between CWS and panicle dry weight was increased with higher concentration of soil salinity. Plant Na content increased with soil salinity, while water stress changed plant Na content little. Water stress susceptibility became larger with increase of plant Na content. Therefore, it was concluded that panicle dry weight decreases and water stress susceptibility becomes larger with increase of plant Na concentration under the saline soil conditions in rice.