Effect of Ppd-1 photoperiod sensitivity genes on dry matter production and allocation in durum wheat

Understanding the effect of genetic factors controlling flowering time is essential to fine-tune phenological development and to maximize yield. Thirty-four spring durum wheat genotypes classified in five allelic combinations for Ppd-A1/Ppd-B1 loci were grown for two years at three contrasting latitudes: Mexico-North, Spain-South and Spain-North. In all them, a delay in flowering date due to the presence of photoperiod sensitivity alleles Ppd-A1b and Ppd-B1b resulted in lower yields. The number of days to flowering, determined by an increasing number of photoperiod sensitivity alleles, accounted in all sites for more than 80% of the variation in the contribution of translocation of pre-flowering assimilates to grain yield. In Mexico and Spain-North late-flowering resulted in decreased harvest index as influenced by high temperatures during grain filling. In Mexico, where grain filling occurred under high temperatures and solar radiation, translocation of pre-flowering assimilates accounted from 55 to 63% of yield, independently of the flowering date of the genotype. In Spain-North, where water was available during grain filling, current photosynthesis was the main contributor to yield (57–73%), with independence of the allelic combination at Ppd loci. In Spain-South, the relative contribution of photosynthesis and translocation depended on the allelic composition at Ppd loci, with translocation increasing by 24% in the latest-flowering genotypes compared with the earliest ones. In all sites the limiting factor for attaining high yields was the capacity of the plant canopy to photosynthesize after anthesis. This study suggests that the expression of genes Ppd-A1 and Ppd-B1 regulating the response to photoperiod modulates the physiological strategy adopted by durum wheat to fill its grains, underlining the importance of phenology fitting in maximizing grain yield.