Relative leaf water content as an efficient method for evaluating rice cultivars for tolerance to salt stress

Efficient and reliable screening criteria are a prerequisite for an effective breeding program to incorporate tolerance to abiotic stress in crop plants. In this study we presented preliminary results demonstrating the effective use of one physiological trait (relative water content, RWC) to incorporate salinity tolerance in rice. Sixteen rice genotypes were used in this case study and subjected to salinity stress of 6 dS m -1 for 2 weeks. RWC was determined on fully expanded youngest leaves, and shoot tissues were sampled for the measurements of sodium and potassium concentration and hence calculation of the Na + /K + ratio. Rice plants with low salt injury scoring were found to have high RWC and maintain a low Na + /K + ratio, and thus considered as a salt tolerant group. Cultivars with medium RWC also have medium salt injury scores and a moderate Na + /K + ratio and considered as moderately tolerant, while the susceptible group has high salt injury scores and a high Na + /K + ratio. The correlation between salt injury scoring and the Na + /K + ratio was strongly positive, while the relationship between RWC and the Na + /K + ratio was strongly negative. The data of RWC in the tolerant group was clearly distinguishable from the moderately tolerant group and the susceptible group. We therefore conclude that RWC determination could be used as an effective screening technique for salt tolerance in rice. The method is simple and cheap, and allows evaluation of a large number of breeding lines in relatively shorter period of time. The method is also more quantitative compared to visual scoring, and eliminates the need of equipments and expense needed when the Na + /K + ratio is used as