A genetic, environmental and functional investigation of late-maturity alpha-amylase (LMA), and its implications for wheat breeding

Abstract

Late maturity α-amylase (LMA) is a grain quality defect that has been identified as an economically important issue for the Australian wheat industry. Therefore, Grains Australia seeks to reduce the risk of low falling number (FN) experienced by growers, by mandating LMA risk assessment prior to assigning milling quality classifications. This requires an expensive induction assay with limited throughput to be used to screen latestage breeding material. This acts as a genetic bottleneck at the end of the breeding pipeline, reducing the rate of genetic gain for other economically important traits targeted by wheat breeders. For the benefit of all stakeholders, a greater understanding of how LMA expression affects wheat quality, and improved methods for breeding and risk assessment are required. The body of work presented herein focuses on answering longstanding questions, including: 1) what genotype-by-environment (G×E) interactions are present for LMA and how can this G×E be characterised, 2) can the current LMA induction assay be improved so it may be applied earlier within the breeding program, 3) are there genes in addition to those already known to affect LMA expression, and 4) does LMA have an effect on the end-use quality of wheat? In the first component of the project, we confirm that LMA is responsible for an increased risk of low FN and reduced overall FN performance, and is subject to G×E. Furthermore, weather conditions that were associated with LMA expression were elucidated. This provided a foundation for the second component of research, in which various temperature and cool shock treatments within controlled environments were evaluated as potential improvements to the LMA assessment method. These alternative regimes were compared with LMA expression at the field level to determine the most correlated screening conditions. The third component used a high throughput assay to validate genes previously shown to reduce LMA expression, while also identifying other potential genetic loci associated with LMA expression. The fourth and final component investigated the effect of LMA expression on end-use quality. We found that low FN resulting from LMA expression may not be as detrimental to end-products as has been previously observed for wheat with low FN due to pre-harvest sprouting. However, LMA negatively affected yellow-alkaline noodles, reducing the overall utility of wheat flour for specific end-products, thus selection against LMA should continue. The work presented here represents a substantial increase in the knowledge base available for LMA in wheat breeding. It should assist industry in making informed decisions about: 1) the importance of selection against genotypes at a high risk of LMA expression to reduce risk of low FN, 2) improvements that could be made to the assessment methods used for managing LMA expression risk, 3) genetic loci that could be targeted to achieve a reduction in LMA expression, and 4) to demonstrate the importance of achieving low LMA levels within grain parcels to suit end-users.