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

Purpose Crop sensitivity to root zone salinity can vary over time, which can lead to severe damage when high sensitivity coincides with high soil salinity. The variation in salinity sensitivity of sunflower during its growth cycle is unknown. Methods Two pot experiments were conducted in sand culture with a complete nutrient solution. Solutions were flushed through pots in excess to maintain specified salt concentrations in the soil solution. In Experiment 1, salt-sensitive stages were determined by applying solutions with an electrical conductivity of < 0.7, 2, 4 or 8 dS m − 1 through the vegetative, flowering or grain filling stages. In Experiment 2, the most sensitive stage to root-zone salinity was determined by exposing plants to 10-day periods of salinity (< 0.7, 8, 16 and 24 dS m − 1 ) overlapping by 4 days starting from 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 before opening of disk flower to ~ 95% anthesis, while grain filling was the least sensitive. The decline in yield was correlated with a decrease in mature seed number. Increasing salinity from 4 to 8 dS m − 1 during flowering increased the area without seeds at the centre of the disk. In experiment 2, measurements of leaf ion concentrations and photosynthesis suggested that Na + toxicity decreased yield due to decreases in availability of photosynthate to flowers. Conclusion To maximise sunflower yield in saline soils, it is important to minimise salinity stress from before flower opening to anthesis.