Genetic gains in NSW wheat cultivars from 1901 to 2014 as revealed from synchronous flowering during the optimum period

Quantifying historic increases in water-limited potential yield (PYw) achieved through breeding provides insight into associated changes in physiology and can assist with future cultivar improvement. We compared PYw of bread wheat cultivars popular in southern New South Wales released between 1901 and 2014. In both 2015 and 2016, cultivars were sown at multiple sowing dates to allow comparisons to be made at a consistent optimal flowering date (early October), and thus control for the large differences in life cycle duration. Seasonal conditions were close to average in 2015 and extremely favorable in 2016. In both, grain yield increased across the historic period studied at 26 kg/ha per annum, regardless of whether a common sowing date or flowering date was used. Yield gain was not linear, and there was a period of rapid yield increase during the middle of the 20th century, that culminated with the release of semi-dwarf cultivars. Yield gain was relatively slower from the 1980s until the present day, possibly due to selection for grain quality traits (grain size) at the expense of grain number. Historic yield increases were not associated with earlier flowering, but with an interplay between greater grain number/m2 and greater grain weight which was the result of increased partitioning of assimilates to spikes, and greater number of grains per unit spike weight (fruiting efficiency). Greater partitioning to the spike in modern cultivars was associated with reduced dry matter (DM) production prior to flowering. Modern cultivars have a less stable flowering time across sowing dates, and shorter life cycle, but improved partitioning in modern cultivars appeared decoupled from shorter developmental phases prior to flowering. The performance of the novel vernalisation sensitive cultivar Longsword showed that future yield gain may be achieved through the combination of early sowing and slow development, increased DM production and superior partitioning to grain.