Leaf appearance, tillering and their coordination in old and modern barleys from Argentina

Two field experiments were carried out to evaluate the effect of the genetic improvement of barley on leaf and tiller appearance. Four malting barley cultivars were used to represent the main genotypes released from 1944 to 1998 in Argentina. One experiment was carried out with 110 kg N ha−1 of nitrogen availability at sowing, while in the other experiment cultivars were grown with 20, 50, 110 or 160 kg available N ha−1. There was no difference in final leaf number among cultivars, which ranged from 9.5 to 11.2 leaves per main stem. Differences in phyllochron between old and modern cultivars were only observed for the early leaves and under treatments of low nitrogen availability (20 and 50 kg N ha−1). Cultivars began tillering at a similar time. Nitrogen treatments modified the range of maximum tiller number per plant from three (N20) to seven (N160) across cultivars. In addition, higher nitrogen availability delayed the time to maximum tiller number. Differences in the number of tillers per plant were explained by the rate of tiller appearance. High levels of tillering were accompanied by high levels of intercepted radiation and associated with modern cultivars growing under high levels of nitrogen. Accumulated intercepted radiation during the jointing–heading period had a trend to increase with years from release, at a mean rate of 1.17 MJ m−2 per year.