8th INTERNATIONAL WHEAT CONFERENCE

associated to the cultivar effect. Kcha was the cultivar with the heaviest grains (37.6 mg)
and Bman with the lowest ones (28.8 mg). There was no effect of the soil N level at sowing
on grain weight in any experiment (p> 0.10); nevertheless, the addition of N at anthesis
significantly increased grain weight (p< 0.05) in all cultivars (from 34.6 to 36.9 mg). Variations
in grain weight were explained by changes in grain filling rate (R 2 = 0.73, p< 0.01)
more than by the duration of the period between anthesis and physiological maturity
(p> 0.10). The cultivars with the most contrasting grain filling rate were Kcha and Bman
(0.089 and 0.120 mg °Cd -1 , respectively). The absolute content of N in the grain (mg N per
grain) at maturity was modified by the genotypes and by the different N levels at sowing
and at anthesis (p< 0.05), but not by the sowing dates (p> 0.10). Similar to that observed
in grain weight, the differences between treatments in the absolute content of N in the
grain were associated with variations in the rate of N accumulation during the grain filling
period (R 2 = 0.90, p