Effects of salinity on sodium accumulation in interspecific hybrid rice (NERICA) lines grown on different types of soil

Rice yield in Africa is low due to salinity as well as a low fertility. We investigated the effects of soil nutrient conditions on shoot sodium accumulation in 20 interspecific hybrid rice (NERICA) lines, their parents WAB56-104 (Oryza sativa L.) and CG14 (O. glaberrima Steud.), and 8 O. sativa L. cultivars grown on different types of soil. The rice plants were grown in 0.5 L pots filled with paddy soil or Masa soil which is less fertile, and subjected to saline irrigation (100 mM NaCl) for one week on Masa soil or two weeks on paddy soil from 18 days after sowing. This was because the visible injury by salinization appeared earlier on Masa soil. Leaf age at the beginning of salinization did not vary with the soil type. The average sodium content of shoot in all cultivars on Masa soil was significantly higher than that on paddy soil. In both types of soil, sodium content of shoot was highest in CG14 and lowest in Pokkali (30-40% of CG14). There were large differences in sodium content of shoot among NERICA lines. The highest was close to the value in CG14 and the lowest was lower than that in WAB56-104 (55-65% of CG14). Sodium content of shoot on paddy soil was positively correlated with that on Masa soil. However, the ratio of sodium content of shoot on Masa soil to that on paddy soil significantly varied with the cultivar. These results indicated that there was a large variation in the sodium content of shoot, i.e., salinity tolerance, among NERICA lines. Sodium accumulation in the shoot was increased by salinity more easily on the soil poor in nutrients than on the fertile soil.