Wheat breeding field plots in Narrabri, northwestern NSW. Credit: Professor Richard Trethowan
Some of the most popular wheat varieties in Australia cannot withstand our warming world, new University of Sydney research finds. Sensitive heat-stressed varieties produce significantly lower yields, suggesting further careful plant breeding and selection is urgently needed.
Researchers at the University of Sydney Plant Breeding Institute tested 23 varieties of Australian wheat at an atmospheric CO2 level of 800 parts per million - over double our current global average concentration - and at a temperature of 35°C.
They found elevated CO2 led to higher leaf temperatures by closing the wheat's stomata - holes used to transpire (or 'sweat'). This then reduced the viability of the wheat's pollen, resulting in reduced grain yields.
The relationship between CO2 and temperature, and grain yield.
"At below 40 percent pollen viability, for example, grain kernels of heat sensitive wheat varieties may be up to half empty or pinched (shrivelled or shrunk)," said lead researcher, Professor Daniel Tan, who labelled the relationship between high leaf temperatures and fewer viable pollen "significant".
The findings under the higher temperature of 35°C were similar - with and without elevated CO2.
Common wheat varieties tested include Suntop - one of the most widely adapted wheat varieties on Australia's east coast - and Mace and Scepter in Western and South Australia.
The Australian varieties found to be heat intolerant included Phantom, Emu Rock, Cobra and Coolah. Flanker, Lancer, Mustang, Suntime, Cutlass, Mace and Condo, by contrast, coped better with high temperatures.
"The hardy varieties are now candidates for genetic selection," said Professor Tan, whose results have been published in the Journal of Agronomy and Crop Science.
Stress-testing wheat
Stress-testing wheat to 4°C above the ambient temperature in in-field chambers. Credit: Dr Rebecca Thistlethwaite.
The researchers conducted their research in three locations: Narrabri in north-western New South Wales; Horsham in Victoria; and Merredin in Western Australia.
They subjected the wheat to temperatures of 35°C at meiosis (flower formation), as "this is closer to what it will be in these growing areas in around 10-20 years' time," Professor Tan said. The carbon dioxide level of 800 parts per million reflects an atmospheric concentration projection, 80 years into the future, in a business-as-usual (no climate change action) scenario.
Already, wheat-growing regions such as Narrabri in north-western New South Wales experience intermittent temperatures of up to 40°C - a temperature at which, if sustained for more than a few hours, most wheat die, especially during a drought.
Studies were carried out in three ways: in the field with normal and late planting times, in the field under field heated chambers, and in a greenhouse. Under the first method, a control group was planted at the normal time, in May. These same varieties were then also planted later than usual, in June, exposing them to higher temperatures as they were only harvested in late as opposed to early spring. A second lot of plants were enclosed in in-field chambers that were heated to 4°C higher than outside temperatures for three days. In the third method, this was replicated in a greenhouse, with half of the plants also exposed to additional in-chamber elevated CO2.
Efforts are now being made to develop more heat tolerant varieties from high temperature-tolerant breeding lines (genetically identical individuals) and varieties.
See the heat tolerance ratings of Australian wheat varieties (at "Table 5", p.55).
Declaration: This research received funding from the Grains Research and Development Corporation.
Hero image: Pierre Herman on Unsplash.
