Prominent winter wheat varieties response to post-flowering heat stress under controlled chambers and field based heat tents

Post-flowering heat stress shortens grain filling duration and limits resource allocation to grains leading to lower productivity in wheat. Wheat grown in Kansas and US Great Plains, often experiences temperatures of 30 °C during grain filling, leading to lower productivity. Thus, characterizing Kansas prominent and newly released varieties for post-flowering heat stress will define the gap in heat tolerance that will need to be addressed through breeding. In the present study, seven Kansas varieties were phenotyped for heat tolerance under a controlled chamber study and two field experiments. To impose heat stress in the controlled chambers, plants grown at 25 °C were transferred to high day temperature (35 °C) chambers, 10 days after first sign of anthesis. Under field conditions, custom built “heat tents” were placed over the plots ten days after 50% flowering and remained until maturity. Plants grown under heat stress exhibited early senescence indicating a shorter grain filling period compared to control. Early maturing varieties recorded higher percent reduction in grain yield under heat stress. Post-flowering heat stress induced significant reduction in thousand kernel weight, grain number, harvest index and grain yield over control. Percent reduction in yield ranged from 6 to 51% under severe heat stress exposure in controlled environments and 2-27% with heat stress exposure using field based tents. Among the varieties tested SY Monument and Larry performed well under both conditions suggesting that they are relatively better suited for locations that face consistent heat stress exposure during the post-flowering stage. Our findings highlight the need to explore wider genetic diversity including wild wheat to infuse greater heat stress resilience into ongoing wheat breeding programs.