Changes in Australian wheat quality over the last 150 years

Wheat occupies a prominent position in Australian agriculture and Australia is the world’s 5th largest wheat exporter. Maintenance and improvement in wheat quality is an important goal of wheat breeding in Australia along with yield and disease resistance. The main objective of this study was to investigate the changes in the grain quality of Australian wheat varieties released over the last 150 years. Grain quality was assessed in terms of grain physical quality parameters, protein content and composition, dough rheology and baking quality traits. Genome wide association study was also conducted using publicly available genotyping data with the aim of identifying the genes with a significant impact on protein content, composition and/or dough rheology traits.
Yield improvement was the main target of wheat breeding and grain quality analysis revealed that grain protein content decreased over time as a result of yield increases. A large improvement in milling extraction was observed in this study and it was most prominent in varieties released after 1960. Australian wheat is recognised as having bright white flour and colour analysis suggested brightness of Australian wheat flour has been maintained over the years. High and low fructan content cultivars were identified in the studied set of wheat varieties, however, there was no significant trend in fructan content over the years.
End use quality is directly affected both by protein content and composition. Glutenin and UPP content increased and gliadin content decreased over the years. This improvement in protein composition was associated with selection of alleles at all six glutenin loci on the chromosome group 1. Elimination of GluA1c, the consistent selection of GluB1i, GluB1u, GluA3b, GluB3h and the introduction of GluB1al was associated with improvement in protein composition. These changes in protein composition have translated into dough quality parameters. A significant improvement in dough mixing time, mixograph peak width and dough stability, and decreasing trend in weakening slope and softening value was observed. Baking quality analyses conducted with a subset of selected varieties observed no improvement in loaf volume in modern varieties compared to older varieties. A significant improvement in loaf volume per percentage of protein was observed in modern varieties which suggested that protein quality has improved. There was a positive correlation between dough extensibility and loaf volume while no relationship between dough strength (Rmax) and loaf volume was observed.

Two harvest years were used to analyse the effect of environment on grain, protein and dough quality traits. The results of this study demonstrated that the flour from 2015 harvest was stronger than the 2016 samples. The effect of harvest year was associated with higher accumulation of protein in 2015 than 2016 which may have resulted in higher polymeric protein hence improved dough quality traits. GWAS revealed significant associations of multiple genes with protein content and protein composition parameters. The genes associated with dough rheology traits such as dough stability and mixing time were also identified in the studied set of wheat varieties. This research provides evidence that due to genetic selection the protein composition of the current varieties relative to the older varieties have significantly changed and this has led to an improvement in grain quality. Moreover, high grain protein content in varieties such as Festiguay, Gabo and Timgalen have shown significant association with overlapping genes that can be used in future breeding programs to develop new varieties with higher protein content, to meet the demands of domestic and export market.