Early heat waves hit wheat yields hardest but boost resilience to subsequent heat waves
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New research published in the Journal of Experimental Botany reveals that wheat crops are more sensitive to grain yield losses from heat waves that occur before reaching their flowering stage than those occurring later. However, exposure to heat waves early in the growing season may reduce yield losses during additional heat waves through a protective “priming” effect.
A team of researchers from the University of Lleida in Catalonia, Spain, investigated the roles of heat wave intensity, frequency and timing relative to crop flowering during the growing season to identify how these factors interacted to affect wheat crop yield.
Heat waves are increasing in frequency and intensity around the world, and their durations are expanding to cover more of the wheat crop growing season, which can include the pivotal flowering stage, when wheat shifts from setting grains to grain growth.
This research demonstrates that heat wave damage in wheat depends not only on the intensity of the heat wave but also on when it occurs and whether the crop has experienced a heat wave earlier in the season.
“Most studies have examined heat stress as a single event, and have done so under controlled conditions rather than under field conditions,” says co-author Dr. Gustavo Slafer. “We investigated whether an earlier heat wave could alter how wheat responds to a later one during reproductive development.”
Field experiments were carried out across two growing seasons using two modern wheat varieties. Both varieties responded similarly to the heat wave treatments, despite having contrasting yield-building strategies.
Heat wave treatments were created by growing wheat inside transparent tents that produced a daily temperature rise through a greenhouse effect. The pre-flowering and post-flowering conditions were standardized for relative heat load to allow comparisons. Heat load was measured as the additional hourly degrees of temperature accumulated over an average day compared with the control treatment, with greater emphasis on heat load above 32 °C.
The major findings of this study are that wheat grain yield is more sensitive to heat waves that occur before flowering than after flowering and that, while earlier heat waves reduced the overall number of grains produced, later heat waves reduced the weight of those grains.
Surprisingly, the team also found that when exposed to sequential heat waves in one season, wheat appears to be primed by early pre-flowering heat waves to reduce the impact of later post-flowering heat waves, compared with wheat experiencing only post-flowering heat waves.
Priming is a type of physiological memory in which exposure to an initial stress can trigger protective responses that remain partly active, allowing the plant to respond more effectively to a later stress.
“To our knowledge, this is the first evidence of this type of antagonistic interaction between successive heat waves in field-grown crops,” Slafer says.
These findings can help farmers improve predictive models of crop yields and identify where and when adaptation measures will be most useful.
“This study reinforces the importance of protecting wheat during the stages when grain number is determined, particularly around flowering,” Slafer says. “The most effective adaptation measures are therefore likely to be those that reduce exposure during the most sensitive reproductive stages.”
These findings are not expected to be unique to wheat and may be relevant to other temperate field crops such as barley, oats and rye, but specific heat thresholds are likely to differ among a wide range of crop species.
This study also highlights the importance of considering multiple heat wave events when predicting crop yield damage under future climate scenarios.
“Wheat is one of the world’s most important staple crops, so safeguarding its yield under climate change is a major priority,” Slafer says. “As a crop of temperate origin, wheat is generally less adapted to high-temperature episodes than crops with tropical origins, such as maize or rice.”
Publication details
Heat waves at pre-anthesis, post-anthesis, and sequentially across both stages on wheat yield under field conditions, Journal of Experimental Botany (2026).
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Society for Experimental Biology
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Early heat waves hit wheat yields hardest but boost resilience to subsequent heat waves (2026, September 18)
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