THE INFLUENCE OF DAYLENGTH ON FINAL LEAF NUMBER IN SPRING WHEAT

The influence of daylength on final leaf number was determined in four field-sown wheat cultivars with no vernalisation requirement Leaf and primordium appearance was monitored in plots sown at two-month interv als during an annual cycle. The timing of the response to daylength va ried substantially among cultivars. In one, final commitment of the la st leaf primordium occurred close to the time of initiation of that pr imordium while, in another cultivar, commitment did not occur until te rminal spikelet or later. In the other two cultivars, commitment occur red midway through spikelet initiation. Late timing of response to day length is a useful adaptation that allows cultivars with no vernalisat ion response sown in autumn to set more leaves than when sown in sprin g, and hence to delay flowering. Based on the analysis, a simple itera tive procedure was developed that successfully predicted final leaf nu mber, the dares of appearance of the flag ligule and anthesis for one of the cultivars grown in an independent experiment.