SUMMARYDrought strongly affects cereal yield in several regions of the world. Plant growth and plant water status in response to soil water deficit play an important role in tolerance to drought and in yield stability. In order to investigate the relationship between plant growth and w^ater relations, 187 barley {Hordeum vulgare L.) recombinant inbred lines from a cross between two Mediterranean varieties, Tadmor and Fr/Apm, were studied in a growth chamber for RWC , number of leaves on the main tiller (NL), number of tillers (NT) and total shoot fresh and dry biomass (TSFM and TSDM). Measurements were made at the beginning of tillering on well watered plants and at a soil moisture content of 14% of field capacity. A negative phenotypic correlation between RWC and growth parameters was obtained in both treatments. Under water stress, a negative genetic correlation was also found between the same characters. QTLs involved in RWC, NL and TSFM variation were positioned on a RFLP-RAPD genetic map. Different DNA regions involved in constitutive and water stress responses were detected. In the stress treatment, one region on chromosome 1 was involved in RWC and NL variation giving a genetic basis to the phenotypic correlations found. Separated map positions were also found for RWC and NL. Epistatic interactions between several QTLs and between QTLs and other markers were detected only in the water stress treatment, suggesting that some chromosomal regions might be involved in the regulation of the expression of the traits under water stress. This work suggested that even if some parameters are strongly correlated, finding QTLs for only one trait is not sufficient to detect all the candidate regions which might be involved in the control of the correlated traits. The results of localization and co-localization of QTLs are physiologically interpreted.

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Summary• Dry mass per unit of leaf area (LDM) and ash content were evaluated as alternative criteria for carbon isotope discrimination ( ∆ ) in durum wheat ( Triticum durum ) flag leaves and grains.• Using correlation analysis the relationships between the three parameters (LDM, ∆ , ash content) and productivity were determined over three consecutive years in 37 field-grown durum wheat genotypes under contrasting drought conditions.• Highly significant differences were found between years and among genotypes for all measured traits. Grain ∆ and ash content, and LDM and flag leaf ∆ were negatively correlated under nondroughted conditions. Positive correlations were found between grain yield, harvest index and both ∆ and ash content of the flag leaf under drought. No significant correlations were found between LDM and both ∆ and grain yield.• Differences in LDM do not predict variations in ∆ , whereas ash content of grain and flag leaf (under droughted conditions) might be useful in predicting ∆ and grain yield. Ash content might provide an alternative screening method in the improvement of drought tolerance and yield stability in durum wheat.