Accumulation of Dry Matter and Nitrogen by Grains in Different Positions of the Wheat Ear as Influenced by Shading and Defoliation

Abstract

The order of priority for supply of assimilate and nitrogen between individual grains of the wheat ear was studied by determining their accumulation of dry matter and nitrogen when the supply was varied by shading and defoliation, alone and combined, from 2 weeks after anthesis.The production of assimilates by untreated plants was surplus to the requirements of grain filling. Treatments influenced the distribution of dry matter so as to minimize effects on grain.In one cultivar, there was no well-defined pattern of individual grain responses to treatments. In another, the data were consistent with the predominance of an effective parallel linkage of spikelets to sources, although a series-type linkage assumed some importance when there was severe shortage of assimilate (60% reduction in grain growth); upper spikelets were then more seriously affected. Within spikelets, a series effect was more evident, grains being increasingly affected by severe shortage with progression from base to apex of the spikelets; when the overall grain growth reduction was about 60%, growth of first, second, and third grains in a central spikelet was reduced by about 50, 60, and 70% respectively. There were differences between shading and defoliation in their effects on distribution of assimilate, and these differences were consistent with preferential distribution of shoot assimilate to second grains and central spikelets.The third grain of three.grain spikelets was characteristically lower in nitrogen than the others, and this difference was increased by even moderate levels of shortage.It is suggested that the fast growth rate of the second grain in central spikelets is due to its capacity for growth rather than to a favourable position vis· a-vis the vascular system.

Fixation of 14Co2 by Flowering and Non-Flowering Glumes of the Wheat Ear, and the Pattern of Transport of Label to Individual Grains

“…The 24-hr harvest of the shaded ear treatment of experiment 3b (in which flag leaves were fed) gave relative activities for a, b, and c of 100,117 and 87 respectively. Rawson and Evans' (1970) labelling studies and Bremner's (1972) grain growth studies also show that grain b gets more shoot assimilate than others.…”

“…Indeed we may infer from experiment 3b and a number of others done in similar conditions (e.g. Rawson and Evans 1970;Bremner 1972) that grain growth was not limited by the availability of assimilate from any source, but by the capacity of the grains to utilize assimilate.…”

“…Relative size is largely a function of position, and differences between grains in either or both rate and duration of growth are involved (Rawson and Evans 1970;Rawson and Ruwali 1972;Bremner 1972). Differences in growth rates between grains may be caused by their different capacities for growth (Bremner 1972) or by a pattern of assimilate distribution more favourable to some than others; or by an interaction between the two. The distribution of assimilate between grains might well be influenced by the photosynthetic capacities of the glumes, particularly if subtended grains are the exclusive or preferred sink for the assimilate of their associated glumes.…”

Simulating winter wheat spike development and growth

“…Kernel sink strength is related to location in the spike, where kernels in central spikelets, or basal kernels within a spikelet, have greater sink strengths (Fig. 5, Rawson and Evans, 1970;Bremner, 1972). This pattern of sink strength positively correlates with the fertilization pattern.…”

Plant tissue tests for predicting nitrogen fertilizer requirements in spring wheat

“…There are also varietal differences in N uptake efficiency (Seth et al 1960, Mikesell and Paulsen 1971, Noaman and Taylor 1990. The situation may be affected by leaf shading, which becomes more significant at high plant population densities leading to translocation of N from shaded leaves (Campbell and Read 1968, Willey and Holliday 1971, Bremner 1972). It has also been shown that prolonged root activity and leaf duration positively affect N accumulation into the grain (Spiertz andEllen 1978, Herzog andStamp 1983).…”