Contribution of stored pre-anthesis assimilate to grain yield in wheat and barley

Abstract

RESERVES of assimilate present in wheat and barley crops at flowering, and available for later translocation to the grains, could buffer grain yield against environmental stresses during grain filling. This so-called pre-anthesis assimilate contribution to grain yield can be expressed as a percentage of yield (P₁). Archbold¹, and later Thorne², concluded that P₁ was small, being no more than 20%². But only one result (12% for irrigated wheat at Cambridge³) refers to a crop in the field as distinct from plants in pots, and no studies considered the effect of stress during grain filling. Recently Gallagher et al.^4,5 reported substantial contributions: P₁ averaged 43% over six crops of wheat and barley at Nottingham; this amounted to more than 300 g per m² of dry material in two crops and, in the severe drought of 1970, 39% of total dry matter present at anthesis. They assumed, with some supporting evidence from one barley crop⁶, that the pre-anthesis contribution was given by the decrease from anthesis to maturity in dry weight of non-grain parts of the crop. In situ labelling with ¹⁴CO₂ of the whole crop canopy at frequent intervals before and after anthesis would seem to be the least equivocal way of estimating P₁. Using this method we have determined P₁ in wheat and barley. It averaged only 12% (watered crops) and 22% (droughted crops), and did not agree with estimates for the same crops obtained by the method of Gallagher et al.^4,5.