Leaf hydration status under drought is predominantly linked to stomatal regulation and leaf roll but not osmotic adjustment in Canadian hard red spring wheat (Triticum aestivum) cultivars

ABSTRACT For wheat ( Triticum aestivum ), sustained crop yield at limited soil water has been linked to osmotic adjustment (OA) as one of the main drivers to minimize drought-induced reductions in leaf hydration status and growth. Canada Western Red Spring (CWRS) cultivars are typically grown in rainfed areas in northern regions with milder climates, but ongoing climate change has increased the frequency and intensity of drought event questioning how successful they are in tolerating drought. The extent of OA and its relation to stomatal behavior, leaf roll, and kernel development under periods of drought remain elusive for CWRS. For several commercially used Canada Western Red Spring (CWRS) wheat cultivars (‘Superb’, ‘Stettler’, ‘AAC Viewfield’), OA was not found to be a mechanism contributing to drought tolerance. In contrast, we 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 roll (i.e., reductions in flag leaf width). Moreover, leaf hydration status (Θ RWC ) marked the onset of drought-induced losses in kernel weight in all three cultivars. In conclusion, CWRS wheat lacks OA but leaf stomatal behavior and leaf rolling aid in securing leaf hydration status and kernel weight under drought. One-sentence summary Select wheat cultivars maintain leaf hydration status and yield by early leaf roll and rapid stomatal closure in the absence of osmotic adjustment and isohydric behavior.