The Fate of the Dry Matter, Carbohydrates and 14C Lost from the Leaves and Stems of Wheat during Grain Filling

In a field study with six winter wheat genotypes losses of dry matter from the stems between 30 June and maturity averaged 172 g m−2 (range 82–236), there being significant differences in loss between genotypes. Respiration from the stems during the same period was estimated to amount to 106 g m−2 (range 104–225). The amount of dry matter mobilized from the stems, calculated by difference, was estimated as 66 g m−2. The loss of ethanol- and water-soluble carbohydrate from the stems (170 g m−2; range 124–215) was very similar to the dry weight loss. Carbon-14 labelling was used to trace the time course and the amount of the movement of assimilates from the vegetative organs to the grain. Only 14⋅3 per cent (range 10⋅3–21⋅0) of the products of photosynthesis over the period 21 May-20 June were relocated to the grains. This relocation amounted to an average of 7 per cent (range 5⋅7–11⋅4) of the final grain weight. It was estimated that during the 18 days following anthesis on 20 June photosynthesis contributed 48 per cent (range 39–55) of the final grain dry weight. Of this, about half was translocated to the grain within 10 days of initial assimilation. The remainder appeared to be stored temporarily in the stems and leaves and translocated to the grains during the period 17–29 July. In general, relocation of dry matter from the vegetative organs to the grains, assessed by carbon-14 labelling, was greatest in those genotypes (Hobbit and Sportsman) which lost most dry weight from the stems and leaves.