Evaluation of physiological markers for assessing drought tolerance and yield potential in bread wheat

Carbon isotope discrimination (Δ) has been recognized as a valuable phenotyping tool in wheat breeding. However, technical expertise and analysis cost restrict its large-scale use. We examined the associations of ash content (AC), minerals content (Ca, K, Mg, Fe and Mn) and leaf chlorophyll content (Chl) with grain Δ and grain yield (GY) to assess their potential as substitute to grain Δ. We evaluated 49 wheat genotypes under two water deficit regimes (W₁₂₀ and W₂₀₀) in a rain-out shelter. Leaf chlorophyll content (Chl) was strongly correlated with grain Δ and GY under moderate water deficit regime (W₂₀₀). Significant and negative correlations (P < 0.01) of AC and potassium concentration (K) with grain Δ, and between AC and GY was observed under both water regimes, while manganese concentration (Mn) was negatively correlated with grain Δ under W₁₂₀ regime only and magnesium concentration (Mg) correlated negatively under the W₂₀₀ regime only. Grain Δ was correlated (P < 0.01) positively with photosynthesis rate (A), stomatal conductance (g_s) and GY, while correlated negatively (P < 0.01) with intrinsic water use efficiency (iWUE) under both water regimes. Results confirm the role of grain Δ as an indirect selection criterion for drought tolerance under a wide range of drought conditions. Additionally, Chl is the most suitable trait to predict yield under moderate water deficit conditions. AC and K concentration in grain proved potentially useful and economical alternative criterion to grain Δ in the evaluation of differences in yield potential and drought tolerance in wheat under drought.