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

Reserves of assimilate present in wheat and barley crops a flowering, and available for later translocation to the grains could buffer grain yield against environmental stresses durin; grain filling. This so-called pre-anthesis assimilate contributioi to grain yield can be expressed as a percentage of yield (Pj Archbold1, and later Thome2, concluded. that Px was small being no more than 20%2. But only one result (12 % for irrigate! wheat at Cambridge3) refers to a crop in the field as distinc from plants in pots, and no studies considered the effect o stress during grain filling. Recently Gallagher et a/.4,B reports substantial contributions: Px averaged 43% over six crops o wheat and barley at Nottingham; this amounted to more thai 300 g per ms of dry material in two crops and, in the sever drought of 1970, 39% of total dry matter present at anthesis They assumed, with some supporting evidence from one bade; crop8, that the pre-anthesis contribution was given by th decrease from anthesis to maturity in dry weight of non-graii parts of the crop. In situ labelling with 14C02 of the whole croj canopy at frequent intervals before and after anthesis woul« seem to be the least equivocal way of estimating Px. Using thi method we have determined i\ in wheat and barley. It averagei only 12% (watered crops) and 22% (draughted crops), and di* not agree with estimates for the same crops obtained by th method of Gallagher et a/.**6