Leaf and Tillering Co-Ordination Under Contrasting Nutritional Conditions In Wheat and Barley.

Leaf and tillering appearance are one of the main developmental events in wheat as well as in barley. Leaf appearance not only regulates flowering date but also controls the rate of tillering appearance, which is strongly dependent on genotype and nutrients availabilities. We hypothesized that variations in nutrients availabilities will alter the dynamics of leaf and tiller appearance, affecting in a differential way wheat and barley. The general aim of the present study was to analyze leaf appearance and their coordination with tillering evolution in wheat and barley crops growing under contrasting soil nitrogen and sulphur conditions. To reach the objective we carried out two types of experiments from 2004 to 2009 at the University of Buenos Aires. One group of experiments consisted in the combination of different wheat and barley genotypes and contrasting soil N levels at sowing, and the other group was designed in order to analyze the N x S interaction. Barley and wheat differed in the dynamics of leaf and tiller appearance, and the synchrony between both processes. Barley genotypes had higher synchrony than the wheat genotypes (general mean of 1.41 vs. 1.23 tiller leaf^-1, respectively). The synchrony between leaf and tiller appearance was strongly modified by soil nutrient level as N availability strongly increased tiller appearance but not the leaf appearance, while the S availability only showed a clear effect on the dynamics of tillers when N availability was not limiting. The N or S availability did not significantly modify the duration of the different ontogenic stages in any species, nor was the phenology strongly affected by genotypes. The differences between species in leaf and tillering appearance and its co-ordination constitute the basis for understanding the adaptation of both crops to different environments and their response to nutrient fertilizer.