DOWNGRADING of wheat due to low falling numbers tests and poor starch viscosity is a major burden on the Australian wheat industry, costing millions of dollars a year.
Generally, it is attributed to sprouted grain, caused by harvest rain, but the Grains Research and Development Corporation (GRDC) warns there is also a hidden culprit.
Late maturity alpha-amylase (LMA) was discovered by grains scientists in the 1990s.
Alpha-amylase is an enzyme which can degrade grain starch which is measured by falling number tests at delivery.
LMA is a genetic defect in some wheat varieties that can be triggered by a cool temperature shock during the middle stages of grain filling.
It is similar to the alpha-amylase produced by the wheat plant when it is receives excess rain at harvest.
But unlike harvest sprouting, there is no physical evidence of the defect on the grain itself.
LMA has therefore traditionally been very difficult to screen for and eliminate.
There is a range of levels of LMA expression in wheat varieties – high, medium and low to zero – and commercial lines require a trigger before they express LMA.
By 2004, research funded by the Grains Research and Development Corporation (GRDC) had established that about 20 per cent of then current varieties and advanced breeding lines were susceptible to LMA.
Work out of the University of Adelaide, funded by GRDC, identified several genetic traits that control LMA.
Molecular markers linked to those loci are being fine-mapped.
In collaboration with local researchers, UA pre-breeders embarked on a GRDC-funded project to develop new molecular marker tools to reduce the time it takes for breeders to identify wheat lines with low risk of LMA, as well as enhanced resistance to sprouting and black point.
There was also work into why the cool temperature shock can produce this undesirable effect on wheat quality.
Results indicated that the cool temperature shock increases the sensitivity of the grain to a plant hormone normally present in grains of varieties prone to LMA. In turn this leads to changes within the grain that result in a low falling number.
In order to assess the risk of LMA occurring in the field in current wheat varieties in different regions, the GRDC is supporting a number of trials across Australia through the National Variety Trials (NVT).
This will provide evidence on the risk of LMA occurring in a range of environments compared with ideal conditions in a glasshouse, and will identify the locations where it poses most risk, and for which varieties.
Research funded by the GRDC has produced new germplasm, screening methods and selection tools to speed up the production of varieties less susceptible to LMA.
LMA test kits are also being made available to scientists and wheat breeding programs in Australia.
Into the future, the GRDC is hopeful selective breeding will be able to significantly reduce the incidence and severity of defects at harvest.