Cultivar- and phase-specific effects of light on kernel number and compensation via kernel weight in wheat

Kernel number per spike (KpS) and floret fertility are critical traits for enhancing wheat (Triticum aestivum) grain yield under climate variability. The effects of light on KpS and other yield-related traits depend on intensity, duration, developmental phase, and genotype characteristics. Here, we investigated the effects of low light during a pre-anthesis period around 100 °Cd before heading and a post-anthesis period around 240 °Cd after heading. Five light regimes were applied in split-plot experiments under controlled conditions, and 16 genotypes were tested to demonstrate the genetic diversity in response to phase-specific light regimes. The pre-anthesis subphase between yellow anther and tipping (YA-TP) was most crucial for floret fertility and kernel number. Also, the ability to compensate the loss in grain number through increased thousand kernel weight was genotype specific, especially between YA-TP. No effects correlated with the length of any phenological subphase, indicating that the differences in sensitivity are not simply a consequence of genotypic variations in phenological duration. This allowed us to identify insensitive and sensitive genotypes to low light. Furthermore, insensitive genotypes showed increases in kernel number at top spikelet positions in comparison to the sensitive genotypes. Also, both modern and older genotypes included sensitive as well as insensitive genotypes. Our results suggest genotypic differences in environmental sensitivity during the YA-TP subphase that could be further targeted for enhancing yield stability.