gopals@student.ubc.ca; tknipfer@ubc.ca; gurcharn.brar@ualberta.ca

For wheat (Triticum aestivum), in previously published literature, 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 plains region 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 (ΘRWC) marked the onset of drought-induced losses in kernel weight in all three cultivars. 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 RWC); ‘Stettler’ at a RWC of 48%, and ‘AAC Viewfield’ at a RWC of 51%.

Moreover, RWC 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 will be discussed in the context of leaf water loss beyond stomatal regulation under drought.

In conclusion, Canadian 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.