Flowering is the critical growth stage for adverse effects of salinity on the grain yield of sunflower

Abstract Purpose Crop sensitivity to root zone salinity can vary over time during a cropping season, which can lead to severe damage when high sensitivity coincides with high soil salinity. The variation in salinity sensitivity of sunflower ( Helianthus annuus L.) during its growth cycle is not known. Methods Two pot experiments were conducted in sand culture with a complete nutrient solution to test the response of sunflower to salinity at different growth stages. Solutions were repeatedly flushed through pots in excess to maintain the specified salt concentrations in the soil solution. In Experiment 1, salt-sensitive growth stages were determined by applying solutions of increasing electrical conductivity (EC < 0.7, 2, 4 or 8 dS m -1 ) throughout vegetative, flowering or grain filling stages based on well-defined phenology. In Experiment 2, the most sensitive stage to root-zone salinity was determined by exposing the plants to 10-day periods of salinity (EC < 0.7, 8, 16 and 24 dS m -1 ) overlapping by 4 days starting from the 13-leaf to grain filling. Results In both experiments, decreases in seed yield were associated with exposure of plants to elevated EC during the period when the disk flower was opening to ~95% anthesis, while grain filling was the least sensitive. In experiment 2, measurements of ion concentrations and rates of photosynthesis in leaves suggested that Na + toxicity decreased yield due to decreases in the availability of photosynthates to flowers. Conclusion To maximise sunflower yield in saline soils, crop management should minimise salinity stress from flower opening to anthesis.