Complicating the problem further is the fact that the wheat genome – 40 times larger than the rice genome – has not yet been fully sequenced.

Approaching the problem from one side of the equation with traditional forward genetics techniques is Dr Delphine Fleury, while her colleagues Dr Sergiy Lopato and Dr Whitford work from a reverse genetics angle as part of the ACPFG’s partnership with DuPont Agricultural Biotechnology.

Dr Fleury’s work stems from an elite germplasm program which began in 2003 in conjunction with breeding company Australian Grain Technologies (AGT) and tested varieties already known to be relatively drought tolerant.

They recreated the southern Australian drought cycle in which plants only have a short window to make use of available moisture before the soils dry out and before the cycle starts again with the next rain event.

The researchers studied the molecular and physiological mechanisms – such as tillering, root depth, transpiration rates and chlorophyll levels – in the parent lines Kukri, Excalibur and RAC875.

In the severe 2006 drought Excalibur and RAC875 were consistently 16 per cent and 22pc higher yielding than other varieties at the trial sites. Yet the three parent varieties all displayed different strategies in responding to the drought pressures.

For example, RAC875 proved to be very robust from planting, setting itself up before the season dried out, whereas Excalibur would set a lot of tillers early and then adapt its grain set according to the availability of water.

“It was really interesting to see that both lines that were tolerant were behaving differently,” Dr Fleury said. “It means that if we can identify some genes and combine them in some other cultivars we might be able to step up their levels of tolerance.”

The process is underway again with the testing of cultivars Gladius (a cross descended from both Excalibur and RAC875) and Drysdale as drought-tolerant parent lines. These lines have different root systems and yet both yield well under drought – the question is which plant mechanism is driving that performance.

Following glasshouse and field trials here in Australia and in Mexico, the researchers set out to find the loci (sections of chromosome containing hundreds of genes) responsible for the plants’ performance under drought conditions.

It was a massive task of crossing the parent lines – producing 3000 plants from each cross – in order to study the segregating population.

Assisting the process is the Plant Accelerator at the University of Adelaide, which uses high-tech digital devices to monitor plant development over time under the drought conditions. This speeds up the process of identifying the plants carrying the active genes. By comparing the structure of the different plants, researchers can narrow the search for the location of the key genes.

From the initial trials involving Kukri, Excalibur and RAC875, the team has identified four loci “that were really key in controlling the yields in drought conditions, so now we are in the process of trying to identify the genes behind them”. Each locus has been linked to different plant responses to different drought stresses, including lack of water, heat and canopy temperature suppression.

“There’s already nice progress, and we’re getting closer to identifying one of the genes,” Dr Fleury said.

From one of the loci, the team has a candidate gene, with tests being prepared to validate the hypothesis, while the group is still in the process of mapping the genetic locations of the other two loci.

“Now we have a good understanding of the stress response of the parents at the molecular level, we have identified some key loci, and we’re also strongly involved in wheat genome sequencing,” Dr Fleury said.

“It’s still difficult because the wheat genome is a big genome and very complex. But with the new technology for genome sequencing we are starting to see light at the end of the tunnel.

“We are now going through a key phase of the project where we can start to put things together.”

It is at this point that Dr Fleury’s work converges with Dr Whitford’s and Dr Lopato’s – they use modern biotechnology techniques to drill down and modify the individual genes that are identified in Dr Fleury’s work.

“We pull multiple lines of observation together; it’s an integrative process,” Dr Whitford said. “Our biotech side looks at the gene sequence and individual genes. We can then cross-reference those two data sets.”

In conjunction with DuPont Agricultural Biotechnology, Dr Whitford is working with some newly located genes to better understand how plants respond to drought.

“The genes we’re looking at are responsible for several critical biochemical pathways that allow the plant to respond to stress,” he said.

The goal is to identify naturally occurring genes that influence drought tolerance but are not being effectively utilised. Through the use of genetic modification (GM) techniques, the action of these genes is modified to bolster performance.

But the strategy runs the risk of what the scientists refer to as deleterious pleiotropic effects – the situation where modifying a single gene can create a ripple of unwanted physiological activity throughout the plant. For example, increasing the expression of a single gene which influences transpiration could then affect the time of flowering or grain set.

“We put a lot of focus on basically trying to eliminate the unwanted effects of modifying the genes,” Dr Whitford said. “We want the genes only to take effect when the stress is present.”

“We need to know when each gene is turned on and off, and we need to fine tune that so it goes on and off at exactly the right time.”

To address this problem Dr Lopato is trying to identify gene “promoters”, which provide the internal signals that activate the necessary genes to respond to the drought stress.

Additionally Dr Lopato’s research has found a number of other factors – known as the DREB and CBF factors – that regulate the activation of key drought-tolerance genes.

“These gene switches activate a swathe of downstream genes and turn them on. We’re trying to make sure these activate at the right time and in the right place,” Dr Whitford said.

By using transgenic methods to include these factors into crossbred lines, the performance of plants under drought stress was transformed, often leading to stunted growth as the plants decrease water consumption and conserve energy.

But in one series of trials transgenic plants containing the DREB factors were found to show no signs of stress for at least 2-3 days longer than control plants, and to be able to fully recover within one to two weeks of re-watering unlike most control plants.

Interestingly, the DREB factors were also linked to improved frost tolerance.

The end goal is to breed varieties carrying multiple genes that govern different plant mechanisms for drought tolerance.

“There’s no single gene that’s going to provide a panacea to our drought problems,” Dr Whitford said. “We’re trying to cherry-pick the various mechanisms and recombine them into one elite cultivar – and that process doesn’t necessarily need to be GM.”

The whole process of breeding for enhanced drought tolerance takes many years. The time from when a gene is first identified until it is incorporated into adapted varieties can take anywhere between five and eight years. These lines then need to feed into the breeding programs and can take a further 10 years before commercial varieties are available to growers.

The end result will not be a silver bullet variety that lifts yields under all growing conditions – drought tolerance breeding will deliver farmers an extra form of insurance against yield loss in dry seasons.

In the meantime though, as the researcher’s progress along the winding road towards this Holy Grail, the genetic material and knowledge is being shared with Australia’s plant breeding companies, so that continual and incremental gains can be delivered to farmers.