Controlled environment evaluation of barley germplasm in conjunction with field trials in varying climates across South Australia have validated previous research into heat stress affecting wheat and that high temperatures are “very important” for driving grain yield during anthesis and grain filling.
The two-year ‘Genetic Characterization and Exploitation of Heat Stress Tolerant Barley Germplasm’ project concluded at the end of 2016, which was a very wet year with unusually mild temperatures during the latter part of the growing season, but it was still shown that increasing temperatures during sensitive growth stages resulted in decreased grain yield.
“So, there’s a negative correlation there, which is what we expect. Often as grain yield goes down, in part that is driven by grain size, as you get hotter temperatures you’ll get smaller grain and more screenings,” said Australian Grain Technologies barley breeder Paul Telfer, who led the project.
The controlled environment component of the project consisted of comparing an unstressed control treatment of 101 genotypes in 2015 and 2016 to a heat stress treatment, within a greenhouse, to three consecutive eight-hour days at 36oC and wind speeds of 40kph.
“Generally, we are interested in how plants respond to heat stress during grain filling, so the protocol is to stress plants 10 days after the end of anthesis, corresponding with early grain filling,” Mr Telfer said.
“The intention of this is to mimic the periods of hot north winds that we typically get in late September and during October. And by having plants that undergo this stress treatment and plants that are not stressed – unstressed control – we were able to compare the varietal responses to the heat stress conditions.
“We found that 1000 grain weight, harvest index and green leaf area were adversely affected by this heat stress treatment, and we were able to identify variety differences.”
Four field environments, at Booleroo (southern Flinders Ranges), Roseworthy (University of Adelaide, Roseworthy Campus), Winulta (Yorke Peninsula) and Angas Valley (mid Murray) were used to validate tools for the “real world” on-farm. At each location, climatic co-variates were measured to enable evaluation of the impact of stress across environments and evaluate individual genotype response to changing temperature conditions.
“If we go to 2015, it was a really hot finish and we had a lot of heat stress, so we saw a very large negative impact on grain yield,” Mr Telfer said.
“But last year, everything was a lot cooler and increases in temperature may have been favourable at sub-stressful levels. And decreases in rainfall may also have been favourable because it might have led to less lodging or perhaps less waterlogging in some of the environments.”
Mr Telfer said the project had reaffirmed previous research into wheat (AGT031) that optimizing crop management to ensure flowering in the ‘minimum risk window’, balancing heat and frost risks, was incredibly important.
“In terms of a take-home point for growers, it’s about minimizing exposure to both frost and heat.
“And the understanding of how different genotypes have different mechanisms at different growth stages might allow the breeding community to improve variety adaptation in the future.”