Growth of the grain of wheat (Triticum aestivum L.). The relationship between water content and dry matter accumulation

Abstract

The dry matter and water content of grains of nine spring wheat cultivars and two breeding lines was determined at 2- to 7-days intervals throughout grain filling. The experiment was performed to (i) investigate the quantitative relationship between the relative dry matter content of grains (g g-1 fresh weight) and the state of dry matter accumulation and (ii) test the hypothesis that final grain weight is closely related to maximum grain water content, which is determined early in grain development. The relative dry matter content of grains increased continuously during grain filling. Net water deposition into grains was very rapid initially and ceased when relative dry matter content had increased to approximately 0.33 g g-1 fresh weight. Dry matter deposition stopped when grains attained a relative dry matter content of approximately 0.55. Although the genotypes differed in final grain dry weight (range 34.0 to 47.9 mg) they did not differ in the above characteristics. Final grain dry weight (y) was positively and linearly related to maximum grain water content (y = 1.24x - 1.57; r2 = 0.80). There was also a close relationship between relative dry matter content (in the range of 0.3 to 0.54) and the state of dry matter accumulation (defined as the dry weight of a grain at a given time relative to the maximum dry weight it reached near maturity). The latter relationship was well described by a third degree polynomial. The equation derived from our data and data taken from literature were used to test whether mature, i.e. maximum grain dry weights could be predicted at early developmental stages. There was a close positive and linear relationship between predicted and observed maximum grain dry weights, when predictions started from developmental stages where relative dry matter content was greater than 0.3. The precision of the prediction was poor at earlier developmental stages. Relative dry matter contents less than 0.3 were associated with the period of rapid net water deposition in grains. Termination of rapid net water uptake is known to coincide with the termination of endosperm nuclear division. The data provide evidence that spatial restrictions, reflected in the water content of grains at the end of rapid net water deposition, may be causally related to the determination of the sink capacity of grains.