* Corresponding and presenting author: sabir@gem.uni-hannover.de

Wheat yield is predicted to decrease globally because of climate change. Short-term environmental conditions during critical growth stages may have significant impact on grain yield. In addition to the physiological sub-phases of the plant, genotypic variation may also determine the magnitude of these effects.

A better understanding of the three-way interactions between cultivar, phenology and environmental conditions may help to reduce the gap between potential and actual yields under enhanced climatic variability. We analyzed multiple environment field trials data from three seasons (2014-2017) at six different sites throughout Germany under three different cropping intensities using a novel statistical approach to estimate the sensitivities of three yield components, to short-term variations in global radiation, temperature and precipitation in 220 cultivars across 81 time windows ranging from double ridge to seed desiccation.

The most sensitive yield component was found to be kernel number per spike (KpS) affected by short-term fluctuations of light and temperature, especially during the sub-phase between yellow anther and tipping and at pre-grain filling. We further examined the light effects on yield components of 16 cultivars during identified specific sub-phases in a growth chamber experiment under five light treatments and confirmed sub-phase and genotypic-specific sensitivity to light fluctuations. Sensitivity of KpS to light fluctuations during the yellow anther and tipping phases is explained by effects on floret development and increases kernel abortion, especially on the basal and middle spikelets.

Based on these responses, genotypic resilience or sensitivity to abiotic stress (i.e. light) was identified. Furthermore, another growth chamber experiment with seven light treatments and four cultivars was used to test if the effects of fluctuation in different sub-phases could be additive. KpS was reduced by 17% if fluctuation occurred in only one sub-phase but by 40% in two consecutive sub-phases (yellow anther and heading), showing significant additive effects. Similarly, reduction in florets per spike, kernel weight per spike and abortion rate per spike were found.

Moreover, photosynthetic parameters and carbohydrate levels were measured to interpret how the light fluctuations affect the source availability that physiologically reduces the development of sink, and therefore a two-fold reduction in yield potential.

Our results offer deep insights into complex genotype x environment interactions and highlight the significance of phase-specific sensitivity to environmental fluctuations. This knowledge can be used to mitigate effects of climate variability and maximize grain yield.