RESEARCHERS say there is potential to improve the levels of heat tolerance among wheat crops to tackle the risk of heat stress.
With predictions that heat waves and temperature volatility will become more frequent in Australia, researchers are using targeted genomic selection to improve the heat tolerance of varities.
A rigorous comparison of the yield performance of thousands of wheat lines has been undertaken at the University of Sydney's Plant Breeding Institute at Narrabri, NSW, under different times of sowing, heat shock conditions and within temperature-controlled greenhouses.
Similar trials have been conducted in major growing regions in WA and Vic, delivering remarkably consistent results.
The research is a key investment for the GRDC and has been conducted by the University of Sydney's PBI with assistance from Agriculture Vic, Flinders University, Merredin Managed Environment Facility, Australian Grain Technologies and Intergrain.
University of Sydney's Richard Trethowan said the evaluation of new materials developed from diverse genetic backgrounds using field-based phenotyping and genomic selection suggested that current levels of heat tolerance could be substantially improved.
"The ultimate aim of the program is to identify lines that perform very well when sown optimally and maintain yield when temperatures are high," he said.
"While years of breeding selection has resulted in many current Australian wheat varieties possessing heat tolerance, the research has identified genetic material that offers superior heat tolerance potential, which can be used to mitigate the effects of a warming climate.
"Periods of extreme high temperature, particularly short periods of heat shock, are a major threat to wheat yield and grain quality throughout much of the Australian wheat belt.Observations at PBI since 2012 suggest that every one degree Celsius rise in average maximum seasonal temperature reduces wheat yields by 250-400 kilograms per hectare."
Heat shock occurs when there are at least three to five days of temperatures above 35C, and when this coincides with meiosis/flowering, grain number and therefore yield is reduced.Temperatures above 35C during grain fill will also impact yield by reducing grain weight and increasing screenings.
To progress genetic improvement for heat tolerance, Prof Trethowan said it was imperative for researchers to have a relevant, effective and repeatable phenotyping strategy.
"Over time, researchers at PBI have developed a three-tiered scheme for phenotyping for heat tolerance," he said.
"Stage one involves time of sowing trials under irrigation, stage two evaluates the lines which demonstrated a level of heat tolerance for response to heat shock using field-based heat chambers and stage three focuses on the delivery of controlled heat stress in glasshouses to assess the impact on pollen.
"The pollen impact is extremely important - results from one of the heat susceptible varieties showed that heat shock reduced pollen viability by two thirds.
"If we can introduce a gene for enhanced pollen viability under heat and another gene which maintains grain weight under high temperatures, then it allows the sowing window to become a little wider despite tougher growing conditions."
Prof Trethowan said the success of the phenotyping strategy was helping establish a successful genomic selection strategy for heat tolerance.
"We've reduced the cycle time of cross to cross from six to seven years to two to three years," he said.
"Because we now have an extensive genetic profile of a broad range of material, we can combine the genetics, the field responses, the heat chamber responses and the glasshouse responses to calculate genomic estimated breeding values and quantitative trait loci linked to heat tolerance traits.
"There's enormous value in that germplasm for plant breeders who are interested in heat tolerance."
Prof Trethowan said the lines with the highest breeding values from Narrabri would be tested in WA and Vic to confirm the responses were transferable across environments.
"What we've seen is good correlation in predictability across the different regions as well as good prediction accuracy when the sophisticated model is used," he said.
"Better predictions mean better germplasm and better varieties for grain growers."
- Details: For more information, read Professor Trethowan's 2020 GRDC Grains Research Update paper Maintaining wheat yield under high temperatures - how do current cultivars compare with what's coming?.
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