Wheat cultivars selected for high Fv/Fmunder heat stress maintain high photosynthesis, total chlorophyll, stomatal conductance, transpiration and dry matter

The chlorophyll fluorescence parameter F v /F m reflects the maximum quantum efficiency of photosystem II ( PSII ) photochemistry and has been widely used for early stress detection in plants. Previously, we have used a three‐tiered approach of phenotyping by F v /F m to identify naturally existing genetic variation for tolerance to severe heat stress (3 days at 40°C in controlled conditions) in wheat ( Triticum aestivum L.). Here we investigated the performance of the previously selected cultivars (high and low group based on F v /F m value) in terms of growth and photosynthetic traits under moderate heat stress (1 week at 36/30°C day/night temperature in greenhouse) closer to natural heat waves in North‐Western Europe. Dry matter accumulation after 7 days of heat stress was positively correlated to F v /F m . The high F v /F m group maintained significantly higher total chlorophyll and net photosynthetic rate ( P N ) than the low group, accompanied by higher stomatal conductance (g s ), transpiration rate (E) and evaporative cooling of the leaf (ΔT). The difference in P N between the groups was not caused by differences in PSII capacity or g s as the variation in F v /F m and intracellular CO 2 (C i ) was non‐significant under the given heat stress. This study validated that our three‐tiered approach of phenotyping by F v /F m performed under increasing severity of heat was successful in identifying wheat cultivars differing in photosynthesis under moderate and agronomically more relevant heat stress. The identified cultivars may serve as a valuable resource for further studies to understand the physiological mechanisms underlying the genetic variability in heat sensitivity of photosynthesis.