Foliar application of isopyrazam and epoxiconazole improves photosystem II efficiency, biomass and yield in winter wheat

• Changes in chlorophyll fluorescence were related to fungicide effects on photosynthesis and yield.
• Application of isopyrazam and epoxiconazole increased PSII efficiency in the absence of biotic stress.
• High PSII efficiency of wheat was associated with greater biomass and yield.
• Efficiency of PSII photochemistry at key developmental stage of wheat can predict yield potential.

A range of fungicides including epoxiconazole, azoxystrobin and isopyrazam, were applied to winter wheat at GS 31/32 to determine their effect on photosystem II (PSII) efficiency, biomass and yield. Frequent, repeated measurements of chlorophyll fluorescence were carried on plants grown under different water regimes in controlled environment and in the field to establish the transiency of fluorescence changes in relation to fungicide application. Application of the succinate dehydrogenase inhibitor isopyrazam in a mixture with the triazole epoxiconazole increased PSII efficiency associated with a 28% increase in biomass in the controlled environment and 4% increase in grain yield in the field in the absence of disease pressure. Application of isopyrazam and epoxiconazole increased efficiency of PSII photochemistry (Fv′/Fm′) as early as 4 h following application associated with improved photosynthetic gas exchange and increased rates of electron transport. We reveal a strong, positive relationship between Fv′/Fm′ and CO2 assimilation rate, stomatal conductance and transpiration rate in controlled environment and Fv′/Fm′ detected just after anthesis on the flag leaf at GS 73 and grain yield in field. We conclude that application of a specific combination of fungicides with positive effects of plant physiology in the absence of disease pressure results in enhanced biomass and yield in winter wheat. Additionally, an accurate and frequent assessment of photosynthetic efficiency of winter wheat plants can be used to predict yield and biomass in the field.

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