Trials point to Spear genetics
Wheat varieties containing genetic material from the Spear family have a greater tolerance to heat stress, according to Dion Bennett, Australian Grain Technologies' recently appointed heat and drought tolerance expert.
Mr Bennett held a series of trials over three years using a heat chamber designed to replicate temperatures and wind speeds in a normal paddock environment.
Results from the trials indicated that varieties such as Yitpi and Mace, both of which contain genetic material from the Spear parental line, were able to withstand heat stress events better than other varieties, such as Wyalkatchem.
"Mace and Yitpi appeared to be able to maintain a greater spikelet fertility rate, meaning they were still able to set a higher number of grains within in the spike despite the onset of heat stress," Mr Bennett said.
"Through the selection of their breeding program, just being that little bit later in flowering, it has meant they've been exposed to some heat stress through the generations, so their ability to have that superior yield despite the heat stress might be a reflection of that.
"The next stage is to start doing genetic dissections to understand the underlying genetics of the heat stress tolerance that we are seeing."
Mr Bennett said the experiment included 120 different wheat varieties, and while Mace and Yitpi were not the best performers overall, they showed the strongest tolerance out of the WA commercial varieties included in the trial.
"The best commercial variety that I looked at was Gladius, which is a South Australian variety that is related to Espada, but hasn't had a big uptake in WA," he said.
Mr Bennett said the optimum daytime temperature for wheat reproduction development was 20 to 22C.
"I consider heat stress to be anything above 30C, and a heat stress event is anything above 34C. The other characteristic of a heat stress event is strong wind speeds, anything above 40km/h," he said.
Mr Bennett said the impact of a heat stress event could take several weeks to be visible.
"Straight away you might not see that much, you might see some mechanical damage from the plants hitting each other, but you might not notice much else," he said.
"Over the next week or two, you would probably notice the plants start to turn yellow, called leaf debt, and after that, depending on the stage that the heat stress hits, you might see some spikelet sterility, meaning that some of the spikelets haven't set grain because the plant was in that very sensitive stage at the time of the stress event.
"Depending on how the rest of the season develops, it could set up the plant to have a high level of grain screenings."
The three-year experiment is the first stage in a long-term trial that aims to identify the genes that allow wheat to withstand heat stress events.
"We want to start identifying some of the genomic regions within wheat that control heat stress tolerance," Mr Bennett said.
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