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

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Abstract
The chlorophyll fluorescence parameter Fv/Fmreflects the maximum quantum efficiency of photosystemII(PSII) photochemistry and has been widely used for early stress detection in plants. Previously, we have used a three‐tiered approach of phenotyping by Fv/Fmto identify naturally existing genetic variation for tolerance to severe heat stress (3 days at 40°C in controlled conditions) in wheat (Triticum aestivumL.). Here we investigated the performance of the previously selected cultivars (high and low group based on Fv/Fmvalue) 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 Fv/Fm. The high Fv/Fmgroup maintained significantly higher total chlorophyll and net photosynthetic rate (PN) than the low group, accompanied by higher stomatal conductance (gs), transpiration rate (E) and evaporative cooling of the leaf (ΔT). The difference inPNbetween the groups was not caused by differences inPSIIcapacity or gsas the variation in Fv/Fmand intracellularCO2(Ci) was non‐significant under the given heat stress. This study validated that our three‐tiered approach of phenotyping by Fv/Fmperformed 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.
Funding Information
  • Food Research Program 2009 of the Ministry of Food, Agriculture and Fisheries, Denmark (3304-FVFP-09-B-008)

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