Sodium and potassium uptake of rice panicles as affected by salinity and season in relation to yield and yield components

Salinity is a major yield-reducing stress in many arid and/or coastal irrig ation systems for rice. Past studies on salt stress have mainly addressed t he vegetative growth stage of rice, and little is known on salt effects on the reproductive organs. Sodium and potassium uptake of panicles was studie d for eight rice cultivars in field trials under irrigation with saline and fresh water in the hot dry season and the wet season 1994 at WARDA in Ndia ye, Senegal. Sodium and potassium content was determined at four different stages of panicle development and related to salt treatment effects on yiel d, yield components and panicle transpiration. Yield and yield components w ere strongly affected by salinity, the effects being stronger in the HDS th an in the WS. The cultivars differed in the amount of salt taken up by the panicle. Tolerant cultivars had lower panicle sodium content at all panicle development stages than susceptible ones. Panicle potassium concentration decreased with panicle development under both treatments in all cultivars, but to a lesser extent in salt treated susceptible cultivars. Grain weight reduction in the early panicle development stages and spikelet sterility in crease in the later PDS were highly correlated (p < 0.01) with an increase in panicle sodium concentration in both seasons, whereas reduction in spike let number was not. The magnitude of salt-induced yield loss could not be e xplained with increases in sodium uptake to the panicle alone. It is argued that the amount of sodium taken up by the panicle may be determined by two different factors. One factor (before flowering) being the overall control mechanism of sodium uptake through root properties and the subsequent dist ribution of sodium in the vegetative plant, whereas the other (from floweri ng onwards) is probably linked to panicle transpiration.