Breeding effects on dry matter accumulation and partitioning in Spanish bread wheat during the 20th century

Increasing biomass accumulation is becoming a major objective of most bread wheat ( Triticum aestivum L.) breeding programs worldwide. This study addresses the changes caused by breeding in the pattern of wheat growth and its relationship with the presence of Rht dwarfing alleles. A historical series of 16 varieties representative of the most widely grown during the twentieth century in Spain, including landraces (grown before 1940’s), initial (1947–1955) and modern (1972–2001) cultivars, was characterized for Rht8c , Rht - B1b and Rht - D1b dwarfing alleles. Changes in biomass accumulation and partitioning, leaf area index (LAI) and leaf area duration (LAD) were studied in four field experiments conducted in NE Spain. Biomass and LAI at the beginning of jointing were reduced by ca. 20 and 40 % in varieties carrying one or two dwarfing alleles, respectively. The rates of biomass accumulation from the beginning of jointing to anthesis were similar for wheats from the three historical periods (ca. 1.70 g m −2 GDD −1 ), and amongst varieties carrying a different number of dwarfing alleles. Almost 80 % of absolute yield gains during the last century were due to increases in the spikes weight per unit area from milk-grain to maturity. Initial varieties maintained and modern varieties increased above-ground biomass from milk-grain stage to maturity. The contribution of photosynthesis during this last phase was enhanced in modern varieties due to increases in LAI at milk-grain stage (0.83 % y −1 ) and of LAD from it to maturity (0.79 % y −1 ). Changes on the pattern of biomass accumulation and partitioning caused by the introduction of improved varieties were related to the number of dwarfing alleles present. The contribution of photosynthesis to grain filling was increased in modern varieties due to improved LAI values at milk-grain stage and, subsequently, a longer LAD.