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Drought-induced soil water limitations are a limiting factor in wheat yield; therefore, the expected increased frequency in drought events make it a vital topic of research. For wheat, sustained crop yield at limited soil water availability (i.e., drought tolerance) has been linked to osmotic adjustment (OA) as the main driver to minimize drought-induced reductions in leaf hydration status and growth. Hard red spring wheat (HRSW) cultivars are typically grown in rainfed areas of western Canada with milder climates, but ongoing climate change has increased the frequency and intensity of drought events during the summer months, which raises questions about how successful HRSW cultivars are in tolerating drought. The extent of OA and its relation to stomatal behavior, leaf rolling, and kernel development under periods of drought remains unknown for HRSW. For several commercially used cultivars (‘Superb’, ‘Stettler’, ‘AAC Viewfield’), data indicates that OA does not contribute to drought tolerance. In contrast, I found that sustained kernel weight during periods of relatively low soil water content was linked to ‘tight’ stomatal behavior (i.e., efficient transition from onset to full stomatal closure) and ‘early’ leaf rolling (i.e., reductions in flag leaf width). Among cultivars, ‘Superb’ was most successful in employing these strategies which also prolonged the onset of severe leaf dehydration under drought to a soil relative water content (i.e., % of field capacity) as low as 36% (defined as threshold ΘRWC); ‘Stettler’ at a ΘRWC of 48%, and ‘AAC Viewfield’ at a ΘRWC of 51%. Moreover, ΘRWC marked the onset of drought-induced losses in kernel weight in all three cultivars. Leaf epicuticular waxes exhibited differences in chemical composition between cultivars, which is discussed in the context of leaf water loss beyond stomatal regulation under drought. In conclusion, hard red spring wheat lacks OA but both leaf stomatal behavior and leaf rolling aid in securing leaf hydration status and kernel weight under drought.
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