Corresponding author: roxana.savin@udl.cat

The detrimental impact of high temperatures on crop yields has been extensively documented for over a century. Heat waves, brief periods of high temperatures, have been recognized for the past four decades, but in the last years are gaining more attention as (i) they are expected to become more frequent and severe due to climate change, and (ii) the penalty imposed by them on crop yield are different in mechanisms triggered and larger in magnitude when normalised per degree increase in average temperature, than when comparing crops grown under lower or higher temperatures throughout.

Various experimental approaches exist to determine/quantify the effects of heat waves, none being perfect. Portable polyethylene tents, when placed over plots, offer a cost-effective and convenient solution, particularly for larger plots and fields lacking electricity access. Here we summarised results from a number of field experiments in which heat wave treatments were imposed determining the effects on key physiological and morphological determinants of grain yield when applied either at pre- or/and post-anthesis.

Analysis of data from 18 experiments conducted over 7 years in NE Spain, involving across experiments 10 different genotypes under irrigated field conditions, reveals that crop yield is notably more affected by pre- than by post-anthesis heat waves. This trend remains consistent across various background conditions, locations, and genotypes. Depending on the experiment and particular heat wave treatment imposed, grain number reduction ranged from 10 to 73 %, primarily occurs through grain abortion and mortality of floret primordia.

Conversely, reduction in grain weight was between 5.5 to 10 %, does not appear to be linked to changes in source strength, but due to a direct effect on reducing potential grain weight per se. It is urgent to establish a framework for further progressing in develop both management and breeding strategies to enhance resilience under these extreme climate events.