After many years of hearing stories about wheat varieties with different-shaped ears being more tolerant to frost, CSIRO wheat geneticist Dr Greg Rebetzke is excited to be able to study them as part of a new national project.

Entitled ‘Determining the effect of wheat morphological and anatomical traits on frost susceptibility of wheat’, the project is one of three GRDC investments – collectively valued at $10 million – researching methods of reducing the impact of spring frosts on wheat yields.

Dr Rebetzke says the catalyst for the research was the expectation of greater climate variability and increasingly intense extreme weather events resulting from higher carbon emissions.

“We expect to see increased variability around rainfall and water,” he says.

“But, equally, we will see greater variability in frost events. It is predicted there may be slightly fewer frosts, but these frosts will be earlier and later. They are likely to be more extreme in their damage because of the influence of increasing air temperature on crop growth.”

Dr Rebetzke, who is a CSIRO Agriculture and Food chief research scientist, says reducing the damaging effects of frost is a Holy Grail for avoiding or reducing the impact of extreme drought and warm air temperatures later in the season.

“Frost is interesting because it has always been an issue, but some years it’s much worse than others,” he says.

“Whereas we know heat and drought are always affecting yield potential in our rainfed systems, we rarely see the catastrophic 100 per cent crop loss with heat and drought, like we do with frost. It’s about finding that fine balance around optimising flowering time for frost. But by optimising for frost, we need to be mindful of the need for optimising flowering time for drought and heat at the end of the season.”

The three-year project is focused squarely on flowering, the most vulnerable crop stage where the worst frost damage occurs.

Researchers across Australia will study about 400 different lines of wheat, including germplasm collected by Dr Rebetzke during previous projects and commercial varieties Scepter , Young, Vixen, Beckom and Dual to provide a performance benchmark.

The lines come from a range of genetic backgrounds – some older, some modern, and most with the same flowering time, height and spike number, but different ear architecture such as the absence of awns, a bolder head, larger spikelets, hairy ears or pubescent glumes.

These characteristics have been anecdotally linked to greater frost tolerance, but Dr Rebetzke says they have not previously been scientifically validated.

“The science indicates a benefit in greater floret temperature, owing to the ear architecture factors being linked to the physics of ear temperature and the dissipation of heat,” he says.

“In some instances, the ear structures are not conducive to the formation and growth of ice crystals into the florets.”

Frost on wheat. Photo: GRDC

So far seed from the breeding lines has been increased, cleaned and distributed to three collaborators: the Department of Primary Industries and Regional Development in Western Australia, the South Australian Research and Development Institute, and Charles Sturt University at Wagga Wagga.

Once the experimental designs are completed, the first batches of seed were scheduled to be planted in mid-April at the earliest of three times of sowing at each location.

Two years of field trials are planned. Some selected lines will be grown in frost chambers at Charles Sturt University next year, using modern thermal imaging techniques to try to better understand how the different characteristics regulate ear temperature.

Non-destructive measurements of floret abortion and grain damage with frost will be assessed using high-throughput X-ray CT scanning at the Australian Plant Phenomics Facility at the University of Adelaide. The CT scanner was bought with the help of GRDC funding in 2021 especially for frost and heat research.

“Measurements will be quicker and more accurate than previously,” Dr Rebetzke says.

Researchers will also link with commercial breeding companies to focus on a subset of the lines and the traits they contain, and grow them in the field under conditions of increased frost risk.

Some existing varieties, such as Bale and Dual, already have the awnless trait, but it could be another 10 years before growers can access varieties with other traits or combinations of traits. Nonetheless, the potential benefits of the research are massive.

“There hasn’t been a great deal of success in breeding for greater tolerance to the direct impacts of frost in wheat,” Dr Rebetzke says.

“Research shows that if we were able to identify one characteristic that could increase the tolerance of wheat to frost damage by 1°C, nationally it’s worth about $400 million a year.”

Records show that by 2016, the frost season was 26 days longer, on average, across southern Australia compared with the 1960–1990 mean, and some areas experience their last frost four weeks later, on average, than during the 1960s.

Dr Rebetzke says he would not be advocating that growers in frost-prone areas only plant the genetics the project is hoping to identify.

“The ultimate aim is for wheat breeders to develop improved frost-resilient varieties that can be sown in those parts of the paddocks where growers see increased frost risk, and they’re likely to be areas that are already well-known by the growers,” he says.

“Growers won’t experience frost every year. It’s about reducing the frost risk by planting paddocks with the right combination of genetics for the time of sowing. I’m really excited by this one. I think we can do something special here for growers.”

South Australian growers, in particular, will be keenly awaiting the results.

Last year, frost in early September cut wheat yields on the Upper Eyre Peninsula to below average, and crops that were well past flowering experienced significant damage from a very late frost in October in parts of the Upper North, Mid North, Murray Plains and Upper South-East.

Bureau of Meteorology records show the temperature dropped to minus 3.3°C at Keith on 26 October. This was the equal-fourth-lowest temperature on record in SA during October. Keith, which is known to be frost-prone, also recorded the coolest night-time average for October of 4.9°C.

Dr Rebetzke says factors influencing the incidence of frost in SA include prevailing weather patterns, altitude and topography, with cold air drainage occurring as cold air moves down slopes to increase the risk of frost.

More information: Greg Rebetzke,  greg.rebetzke@csiro.au