Canopy temperature varied by time, stage, and environment in wheat

What the study found: Canopy temperature in wheat was not stable across the day or across growth stages. The study found that cooling patterns depended on time of day, phenological stage, and environment.
Why the authors say this matters: The authors conclude that single-time-point canopy temperature measurements give an incomplete picture of thermal status, and they suggest that multi-temporal protocols and context-specific measurement windows are needed for breeding and physiological interpretation under drought and heat.
What the researchers tested: The researchers monitored 184 spring wheat genotypes in two Mediterranean environments, one fully irrigated and one rainfed, using UAV-based thermal imaging. They measured canopy temperature six times per day at four reproductive stages: anthesis, milk-grain, milk-dough, and dough.
What worked and what didn't: Repeated-measures mixed models showed that location, stage, time of day, and all interactions were highly significant. Genotypic effects were strong within each stage-by-environment combination, but the best phenotyping window depended on conditions: around 15:00 h under rainfed conditions, and between 13:30 and 15:00 h under irrigation. Genotype rankings were less stable across hours under rainfed conditions, and temperatures above 32 °C were strongly influenced by time of day and stage; maximum temperature captured short heat events that daily means missed.
What to keep in mind: The abstract does not describe limitations beyond the need for context-specific, multi-temporal measurement. The reported results apply to the tested spring wheat genotypes and the two Mediterranean environments in this study.

Key points

• Canopy temperature in wheat changed with time of day, growth stage, and environment.
• The study measured 184 spring wheat genotypes in irrigated and rainfed Mediterranean conditions.
• The most informative measurement time depended on water supply and stage.
• Under rainfed conditions, genotype rankings changed more across the day.
• Temperatures above 32 °C depended strongly on time of day and stage, and maximum temperature captured brief heat events missed by daily averages.