Water Status Measurements of Excised Wheat Leaves: Position and Age Effects

The ability of excised leaves to retain water has been implicated as an indicator of drought resistance, and considerable genetic diversity exists for this characteristic; however, genotypic differences are often not consistent throughout the growing season and are confounded by maturity differences. The objectives of this study were to determine the specific effects of leaf position and age on water status measurements of excised leaves and assess the potential relevance to sampling in a large‐scale breeding program. Initial water content (IWC) (kg H 2 O kg ‐1 dry wt.) at the time of excision and rate of water loss (RWL) ( g H 2 O kg ‐1 dry wt. min ‐1 ) following stomatal closure were measured on leaves of four tetraploid wheat ( Triticum turgidum L.) genotypes grown in two controlled‐environment experiments. Genotypic differences in RWL were more pronounced at early growth stages and were more consistent between experiments than were differences in IWC. The RWL of leaves 3, 4, and 5 of ‘Hercules’ and ICD1385 underwent considerable fluctuations during aging; the RWL for ‘Pelissier’ and ICD 2627 leaves were low and much more constant during leaf maturation. The flag leaves did not display the same fluctuations in RWL as were evident in the earlier leaves. Higher specific leaf weights (SLW) of flag leaves were responsible for lower RWL values of flag leaves compared to earlier leaves. Genotypic differences and fluctuations of RWL associated with leaf aging could not be attributed to differences in SLW. Decreasing RWL associated with higher leaf insertion levels and changes in RWL associated with leaf aging may lead to misclassification of genotypes unless considerable care is exercised during sample selection. It is suggested that RWL may be influenced by reversible changes in the leaf surface associated with aging.