Early vigour clue to surviving dry start
Pre-breeders in Western Australia have made the first ever observations of varietal differences in responses to water deficit early in the season, during sowing and crop establishment.
The project has also identified a wheat trait that can lessen the damage to crops from early drought. It is an early vigour trait that may also be well suited to dry-sown crops.
The finding is in the first body of data to emerge from the specialised field trial sites – Managed Environment Facilities (MEFs) – that the GRDC established to underpin research to make dryland farming systems more resilient to water deficits and climate variability.
Three MEFs have been set up so that the level of soil moisture experienced by crops can be controlled through the use of onsite irrigation and rain-out shelters. They are located in contrasting regions of the Australian wheatbelt at Narrabri in northern New South Wales, Yanco in southern NSW and Merredin in WA.
The early drought project is led by Dr Bob French of the Department of Agriculture and Food, WA, who ran field trials in 2012, with the experiments being repeated this year. Dr French says the project is a response to the adoption of dry sowing in WA agriculture.
“Most research on crop response to water deficit in Mediterranean environments has concentrated on the end of the growing season,” he says.
“There is no doubt that terminal drought is a huge constraint to crop production in these environments. But it has become increasingly evident that crops can also be exposed to quite severe water deficits early in the growing season and these deficits are projected to become more common as a result of climate change.”
The project screened released wheat varieties and advanced breeding material for variation in the response to early drought, primarily in released wheat varieties and advanced breeding material. One experiment also included a wheat population produced by Dr Greg Rebetzke at CSIRO Plant Industry, which comprises plants that are almost genetically identical except they have varying levels of early vigour.
Overall, two experiments were run in 2012. The first involved dry sowing a range of different wheat varieties in mid-April and examining the impact of drought, primarily during establishment. The second applied the water deficit later, from crop establishment through to tillering, and examined production impact.
“To the best of my knowledge there has been no prior work comparing the response of different wheat material to these types of stresses,” Dr French says.
In the first experiment, the diverse wheat germplasm was dry sown early (in mid-April) into very dry soil and then subjected to increasing levels of irrigation (equivalent to 15 to 55 millimetres of rain). This treatment served to simulate a range of water stress conditions. Effects on early growth, crop development, heading and flowering were analysed.
Extreme climate conditions that year coincidentally served up an additional water stress – a four-and-a-half-week period from early May to June when it did not rain.Dr French says that while the results need further validation, there were some notable effects.
- Increasing the severity of water deficits had a profound effect on how quickly the crops emerged.
- The impact on emergence varied strongly in different varieties so that one week after sowing under the most severe water deficit, the proportion of emergence ranged from zero to 40 per cent.
- The most extreme water deficit resulted in delays of up to 20 days in flowering time compared with the same variety under unstressed conditions.
- Early maturing varieties tended to suffer longer delays in flowering time than later maturing varieties (almost cancelling out the growing period difference between them).
- Differences in performance among existing varieties were observed along with patchy patterns of emergence that matched anecdotal reports from growers about their experiences with dry sowing.
Until the results of the repeated experiment in 2013 are known, Dr French is reluctant to rank the performance of the tested wheat varieties.
However, he can say that among the better performers were two varieties that are grown on a wide scale in WA: MaceA and Calingiri. In contrast, varieties such as WyalkatchemA confirmed their reputation as performing poorly under these growing conditions.
As to the prolonged dry phase, it was so severe that it pushed seedlings to the point of death and yet a remarkable recovery was observed when the rain finally did come.
“It turns out wheat at that stage of its life cycle is an extremely resilient plant and it will survive some very severe water deficits without dying,” Dr French says. “But we were unable to identify any difference among varieties in the rate of survival.”
Questions remain as to why flowering was so strongly affected by the early water stress. Flowering time expert Dr Ben Trevaskis, from CSIRO, says that if early stress delays flowering it could lead to a double hit by increasing the risk of frost damage and heat stress at the end of the season.
“We have material developed in a GRDC project that could resolve which genetic traits might be affected by that early stress. If the genes can be identified, they present an opportunity to select for those variants most favourable to these growing conditions,” Dr Trevaskis says.
In the second experiment, the wheat lines were planted later into moist soil. Once the wheat had established adequately, rain-out shelters at the Merredin MEF were installed for about eight weeks to create water stress. For comparison, replicate plots received weekly irrigation.
Researchers then looked at the impact of the water stress on production criteria such as final biomass and grain yield.
Dr French says that dry matter production during the eight-week period under the rain-out shelters was reduced by 30 to 70 per cent, depending on genotype.
“In this experiment, the lines that suffered the least loss of dry matter production during the water deficit period were the lines with the highest vigour from the CSIRO wheat population provided by Dr Rebetzke,” Dr French says.
“There was also a significant relationship between higher grain yields and the presence of the early vigour trait.
“We were very pleased to get that result, because that was one of our hypotheses – that early vigour should confer better performance under early water deficits.”
He is now excited about future possibilities for further testing and developing the early vigour trait, along with validating and expanding on the 2012 trial results.
Also in 2013, a bigger range of environmental treatments have been included to get a better handle on wheat’s response to the stress patterns that growers see in their paddocks.
“It was the establishment of the MEF that made it possible to design and run these types of experiments,” Dr French says. “The MEF refines our ability to study the relationship between stress, agronomy, physiology and a plant’s genetics.”
More information:Dr Bob French,
GRDC Project Code DAW00219
Region South, North