Influence of pollinator abundance and flower visitation on seed yield in red clover

Red clover (Trifolium pratense) is an important forage crop in temperate regions. However, the seed yield in red clover, especially in tetraploid cultivars, constrains the commercial success of this crop. The relationship between seed yield and several flower and inflorescence characteristics has been investigated previously, but up to now no clear link has been identified. The central questions in this article are as follows: (1) Whether nectar production and composition are correlated with seed yield? (2) Which is the main pollinator found on red clover in Flanders? (3) Whether pollinator preferences can explain differences between high and low seed-yielding cultivars and genotypes? We found that Bombus pascuorum was the most abundant pollinator on red clover in the region considered. Nectar volume, nectar composition or pollinator preference did not explain the variation in seed yield between genotypes, nor between diploid and tetraploid cultivars. To explain seed yield differences among red clover genotypes and ploidy levels better, we believe that plant-related characteristics like problems with meiosis, low pollen or seed viability or embryo abortion need to be investigated.