Floret development and grain setting differences between modern durum wheats under contrasting nitrogen availability

Wheat yield depends on the number of grains per square metre, which in turn is related to the number of fertile florets at anthesis. The dynamics of floret generation/degeneration were studied in contrasting conditions of nitrogen (N) and water availability of modern, well-adapted, durum wheats in order to understand further the bases for grain number determination. Experiments were carried out during the 2008-2009 and 2009-2010 growing seasons at Lleida (NE Spain). The first experiment involved four cultivars (Claudio, Donduro, Simeto, and Vitron) and two contrasting N availabilities (50 kgN ha(-1) and 250 kgN ha(-1); N50 and N250) while experiment 2 included the two cultivars most contrasting in grain setting responsiveness to N in experiment 1, and two levels of N (N50 and N250), under irrigated (IR) and rainfed (RF) conditions. In addition, a detillering treatment was imposed on both cultivars under the IR+N250 condition. The number of fertile florets at anthesis was increased by ~30% in response to N fertilization (averaging across treatments and spikelet positions). The effect of N and water availability was evident on floret developmental rates from the third floret primordium onwards, as these florets in the central spikelets of all genotypes reached the stage of a fertile floret in N250 while in N50 they did not. In this study, clear differences were found between the cultivars in their responsiveness to N by producing more fertile florets at anthesis (through accelerating developmental rates of floret primordia), by increasing the likelihood of particular grains to be set, or by both traits.