Effect of drought and salinity on carbon isotope discrimination in wheat cultivars

Abstract

Plant growth in salt-affected areas is frequently limited by high salt content and lack of moisture. Consequently, improved plant cultivars for use in these areas must have adaptations that confer drought and salt resistance and allow the utilization of limited water. Despite some of the similarities between water and salt stress in their effects on plant growth, few attempts have been made to quantify the combined effect of drought and salinity. The present study was carried out to determine the effect of drought and salinity on carbon isotope discrimination ( Δ) in leaves and other plant parts and to evaluate the relationship between Δ and other agronomic traits, i.e. dry matter (DM), water use efficiency (dry matter/total water applied), harvest index (HI; grains weight/dry matter). Four drought- and salt-tolerant wheat cultivars were grown in pots in a naturally lit glasshouse with two watering regimes (30 and 75% plant available water) and three salinity levels (8, 12 and 16 dS/m), a zero salinity treatment served as control. Carbon isotope discrimination ( Δ) varied significantly ( P < 0.001) among cultivars under well-watered and water-stressed conditions. Soil salinity produced a linear and significant ( P < 0.001) decrease in Δ of all cultivars. Salinity × cultivars interaction for Δ was also significant ( P < 0.05) under both watering regimes. The correlation between Δ of leaves and HI was positive ( r = 0.61, P < 0.05) for salt-tolerant cultivars and negative ( r = −0.63, P < 0.05) for drought-tolerant cultivars under well-watered conditions. Salt-tolerant cultivars showed a significant positive correlation ( r = 0.71, P < 0.05) between HI and Δ of shoots under moisture-deficit conditions. Preliminary data indicated that measurements of Δ may prove to be a useful trait for selecting wheat cultivars with improved harvest index in salt-affected areas.