Impact of pollination on sunflower yield: Is pollen amount or pollen quality what matters?

• We tested the effect of amount and quality of pollen delivered to stigmas on three yield components of sunflower.
• Both amount and quality of pollen arriving to sunflower stigmas influence grain set.
• High amounts of a different hybrid's pollen significantly increase grain set as compared to low amounts of same hybrid's pollen.

Local and international information on sunflower pollination indicate that crop yield may be limited by the quality of the pollination service. This work focuses on the response of commercially-grown sunflower hybrids to variations in the amount and quality of the pollen delivered to stigmas, measured in terms of grain set, unit grain weight, grain oil concentration, and oil yield per plant as a way to assess the importance of entomophilous pollination for this crop. Three consecutive experiments including 2–8 experimental treatments each were conducted between 2004 and 2007 in Argentina. The results (a) demonstrate for the first time that the pollen amount and pollen quality that arrive to the stigma have a joint effect on sunflower grain set, (b) suggest that some yield crop components could be sensitive to this joint effect, and (c) remark the probable positive effect of the pollen redistribution across the head. Overall, results underline the importance of pollinators for the crop, and point out to possible mechanisms that explain their beneficial effect.