High temperature can impair grain development and storage compound accumulation during wheat grain filling, with responses depending on stress intensity, timing, duration, and cultivar. In this study, Saekeumkang and Hwanggeumal were selected from among major Korean wheat cultivars because they differ in grain quality- and starch-related characteristics, providing a basis for comparing cultivar-specific responses to heat stress during grain filling. Plants were exposed to 25/15, 35/25, and 40/30 °C (day/night) temperature regimes for 5 d beginning at 10 or 20 days after heading (DAH), and changes in grain morphology, endosperm and embryo development, 100-grain weight, protein concentration, and storage-related gene expression were evaluated. High temperature altered grain developmental traits and generally reduced 100-grain weight, while the magnitude of these effects differed between cultivars and treatment stages. Grain protein concentration and the expression of starch- and storage protein-related genes also showed cultivar- and stage-dependent responses. In a separate RNA-seq experiment initiated at 10 DAH, plants were exposed to the temperature treatments for either 5 or 10 d, and transcriptomic analysis revealed that heat intensity and exposure duration affected both the number and functional characteristics of differentially expressed genes, particularly those associated with protein folding and quality control, chromatin-related processes, and carbohydrate metabolism. These results indicate that heat responses during wheat grain filling are jointly influenced by developmental stage, exposure duration, and cultivar-specific molecular regulation.

Heading time is an important adaptive trait in wheat that is strongly influenced by vernalization requirement and photoperiod response and is closely associated with field growth dynamics. This study evaluated heading responses under controlled low-temperature and photoperiod conditions and monitored UAV-derived canopy development in 53 wheat genetic resources. Heading responses were assessed according to VRN1 and PPD1 genotype combinations under different low-temperature treatment durations and under 14 h and 16 h photoperiods after vernalization. Field growth was evaluated using UAV RGB images acquired in 2024–2025 and UAV multispectral images acquired in 2025–2026. Accessions lacking spring-type VRN1 alleles showed delayed heading under the control and short duration low-temperature treatments, whereas accessions carrying spring-type VRN1 alleles headed earlier. After vernalization, heading responses were more closely associated with the number of spring-type VRN1 alleles and PPD1 combinations than with the difference between the two photoperiod conditions tested. UAV RGB and multispectral variables captured temporal changes in canopy development and vegetation status. Multispectral-derived canopy coverage traits characterized variation in pre-winter establishment, relative winter decline, spring recovery, and seasonal canopy development among the wheat accessions. Overall, UAV-derived canopy traits provided complementary phenotypic information for characterizing field canopy development in wheat genetic resources.