A wheat spike sets only about a third of the number of grains that it could potentially have, based on the number of floret primordia (i.e. potential grains). Since variation in wheat yield is mainly associated to grain number per unit area, an understanding of the regulation of the passage of florets to grains could help breed crops that are more resilient when exposed to abiotic stress, such as high temperatures, but also more responsive to improved conditions, such as increased CO₂, longer growing seasons or potential improvements in the crop’s photosynthetic capacity. Under potential conditions, wheat floret fertility has been linked to their developmental and anatomical status at the beginning of the period of rapid biomass accumulation of the spike (Vazquez et al., 2009) and (b) positively associated to increased sugar concentration in the growing spike (Ghiglione et al., 2008). In this study we investigated the relationship between floret fertility and carbohydrate levels as altered by genotype and environmental factors. The genotypes were recombinant inbred lines of the Seri/Babax population contrasting in water soluble carbohydrate accumulation and tillering. The environmental factors were mainly temperature and to a lesser extent photoperiod. We discuss how temperature and photoperiod interact to determine floret fertility in wheat via their impact on the spike carbohydrate pool.