Pulses in spotlight for drought and heat stress tolerance
Four years ago, the team of Associate Professor Victor Sadras from the South Australian Research & Development Institute began looking at ways to improve drought and heat stress tolerance in field peas, which began with mapping the risk of drought in Australia and its different forms.
That research determined there was three main types of drought - Environmental Types 1, 2 and 3.
“ET1 is the most favourable condition, with no stress during most of the pre-flowering phase and gradual development of mild stress after flowering,” Assoc Prof Sadras said.
“ET2 is characterised by increasing water deficit between four weeks before flowering and two weeks after flowering and rainfall that relieves stress late in the season.
“ET3 is the more stressful condition, with increasing water deficit between four weeks before flowering and maturity.”
ET3 is the most dominant environmental type in Australia with a 43 per cent frequency of occurrence, followed by 24pc and 32 pc for ET1 and ET2, respectively.
“Growers need break crops for the benefits of nitrogen replenishment and pulses are useful for that, but they are also risky as they are particularly sensitive to drought and heat stress,” Assoc Prof Sadras said.
“The crop’s response depends on the timing, duration and severity of the water deficit.”
What followed was a trial screening 29 different varieties of field peas - including both advanced breeding lines and commercially available varieties - for adaptation to water and heat stress and the associations between yield, crop growth rate and seed abortion.
One of the findings from this was the varieties more tolerant to drought were also the better performing varieties under more favourable seasonal conditions.
Assoc Prof Sadras said one of the most interesting traits was the crop growth rate four weeks before flowering to two weeks after flowering.
“We found yield was associated with a water deficit in this window when seed number is defined, and that yield was closely associated to seed number rather than to seed size,” he said.
“Whereas seed filling is an important attribute for quality and value of the crop, a yield range from 0.5t/ha to 4t/ha can only be related to growing conditions and crop traits in the critical window of grain set.
“Cropping practices should therefore increase the focus on this period, with less emphasis on seed filling.
“If the variety is under stress and you are able to maintain growth rate in that window, the variety will give better yields.”
Last year, work began seeing if these same principles apply to chickpeas.
Assoc Prof Sadras, Senior Research Officer Lachlan Lake and Dr Kristy Hobson, the leader of the chickpea Pulse Breeding Australia program at the New South Wales Department of Primary Industries, Tamworth, are conducting the project with funding from the Grains Research and Development Corporation and the Australia-India Strategic Research Fund.
With additional funding from the South Australian Government, the researchers have set up rainout shelters to simulate drought and irrigation to measure potential yield.
“We are trying to manage water supply with irrigation,” Assoc Prof Sadras said.
“We don’t want to improve adaptation to drought at the expense of performance in good seasons”
The chickpea trials are being done around the Lower North region of South Australia at Roseworthy, Turretfield and Pinery.
The rainout shelters are set up at Roseworthy, with about 50 millimetres of water applied through sprinklers during last year’s growing season, plus any additional “natural” precipitation.
“With the shelters we can target drought at any particular time of the season,” Assoc Prof Sadras said.
“Last year, we also did an experiment with shading.
“With drought in the field, it’s hard to get the intensity of stress but with the shades you can do it for a period of time, then move it to another spot in order to determine the critical window for stress response in chickpeas.”
That experiment has given the researchers information that was not previously available – the critical window of development in chickpeas.
“The critical window in chickpeas is from four weeks before flowering to three weeks after flowering,” Assoc Prof Sadras said.
“This shows you can still have yield reductions through stress three weeks before flowering. Therefore, management should be to have good growing conditions prior to flowering.
“Looking after that window is very important. Any stress – nutrient deficiencies, insects, disease or water deficiency – will impact on yield, but chickpeas are different to other crops in that the critical window starts relatively early.”
Yield penalty comes down to three factors, the timing, duration and severity of the different stresses.
“How much yield is reduced depends on the severity of the stress,” Assoc Prof Sadras said.
“If it is only minor then there is maybe 5-10pc in yield reduction, but if it is a major stress then that penalty is much larger.
“For instance, heat and frost, even if it is only for a few days, it doesn’t take a long period of stress to cause damage compared to drought. It is a matter of the timing and intensity.”
Assoc Prof Victor Sadras
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GRDC Project Code DAS00108