Uncovering the effect of genetic factors controlling flowering time of wheat is essential for fitting its phenology to target environments and maximizing yield potential. Results from the detailed characterization of a set of spring durum wheat genotypes harboring known allelic variants at the photoperiod response loci (Ppd-A1 and Ppd-B1) will be presented. These were grown during several years at three sites at latitudes ranging from 41° to 19°N. Constraints to yield formation due to environmental variables associated to latitude (photoperiod, temperature and radiation) were precisely estimated. Ppd-1 genes were responsible for about half of the variability in flowering time, with the remaining variability putatively attributable to earliness per se. The expression of alleles conferring photoperiod insensitivity at Ppd-A1 was more substantial at sites where the average day-length from emergence to flowering was lower than 12 h. The effect on flowering time of the Ppd-A1 allele conferring photoperiod sensitivity was stronger than that of its homeologue at PpdB1. Based on the magnitude of their effect on flowering time, photoperiod insensitivity alleles were ranked as Ppd-A1’GS100’ > Ppd-A1’GS-105’ > Ppd-B1a. The shortest flowering time across sites corresponded to the allelic combination PpdA1’GS-100’ /Ppd-B1a.In autumn sowings, any delay in flowering date due to the presence of photoperiod sensitivity alleles Ppd-A1bor Ppd-B1b resulted in lower yields at all latitudes. Allele Ppd-A1’GS-100’ tended to increase kernel weight and yield, albeit not substantially. Allele Ppd-B1a did not affect yield. Ppd-B1b was associated with an increase in the number of spikelets per spike, hence a greater number of grains per spike and per unit area. However, this increase did not translate into higher yield due to under-compensation in kernel weight. In all experiments, the number of days from emergence to flowering was negatively correlated with kernel weight. The reason was not a shortening of the grain filling period, but a reduction of the grain filling rate coinciding with higher temperatures after anthesis. The effect of Ppd-1 and its implications for wide adaptation and regional/global breeding efforts at different latitudes will be discussed.