Can the duration of the spike construction phase increase the yield of wheat?

It is proposed that increasing the duration of the spike construction phase (CPD, i.e. beginning of stem elongation to flowering) of wheat to increase the number and size of grains per m² will significantly increase grain yield in the High Rainfall Zones (HRZ). Field experiments undertaken in Canberra, Hamilton and Hobart in 2012, demonstrated genotypic variation in CPD in the CSIRO wheat Multiparent Advanced Generation Inter Cross (MAGIC) population compared with check cultivars. Variation in CPD was determined as the difference between dates of terminal spikelet (determined by microscopic dissection) and flowering and ranged from 309 to 950 °Cd (base (Tb) = 0°C). Height of the ligule relative to the apex was investigated as a possible technique for easily estimating terminal spikelet without the need for microscopic dissection, but the results were inconclusive. This project has now entered its next phase with the testing of fifty lines selected from the MAGIC population, at multiple sites, together with commercial and nearisogenic wheat lines differing in vernalisation and photoperiod alleles. The sites used were Canberra, Hamilton, Cressy and at two sites in WA (Badgingarra and Kojonup) for up to two sowing dates (April, May) and were assessed for CPD and grain yield in 2014. These site locations were chosen to provide a range of sites that vary both in climatic and day length variation across the growing season. Implications for breeding a new ideotype of wheat for the HRZ are discussed.