Wet wheat launched in Wagga

It looks like any other wheat variety, and it's not genetically engineered, but Drysdale, a new semi-dwarf wheat cultivar launched today in Wagga Wagga, is a harbinger of an agricultural revolution.

Its name pays homage to the great Australian artist, Russell Drysdale, but the new cultivar's unique drought-defying capabilities are rooted deep in the strange science of quantum physics.

Developed by the Graingene consortium -- CSIRO Plant Industry, AWB Ltd and the Grains Research and Development Corporation (GRDC) -- Drysdale excels in dry conditions.

In drought conditions, it will provide a 10 per cent yield advantage over most other cultivars. It's highly resistant to all the major wheat diseases, very tolerant of acid soils, and produces high-protein grain that will command premium prices in years of scarcity.

CSIRO wheat researcher Dr Richard Richards says the secret of the new cultivar's exceptional drought tolerance is its hunger for carbon. Unlike most wheat cultivars -- indeed, most crop plants -- it's not picky about which form of carbon it assimilates during photosynthesis.

During photosynthesis, all plants use energy from sunlight to react carbon dioxide from the atmosphere with water, yielding energy-rich sugars, with oxygen as a by-product.

The central carbon atom in carbon dioxide molecules occurs naturally in one of three forms, or isotopes, -- 'lite' C12, 'medium' C13 or, rarely, the heavy and unstable C14 isotope.

C13 has one more neutron in its nucleus than C12, and it takes a sensitive mass spectrometer to distinguish the tiny difference in weight.

Yet Australian National University (ANU) researcher Dr Graham Farquhar discovered in the mid-1980s that the photosynthesis reaction in plants can somehow distinguish between them.

Since the difference between the two isotopes amounts to one sub-atomic particle, the explanation for the preference lies in the weird world of quantum physics, rather than in chemistry, but as Farquhar discovered, this seemingly insignificant difference has surprising consequences for water-use efficiency in the macro-world.

Thirsty work

Richards says that in dry conditions, wheat cultivars that prefer the C12 isotope require more water to produce the same yield of grain.

His CSIRO team worked with Farquhar's group at the ANU, and with wheat breeders in the NSW Department of Agriculture, to develop a superior new variety that would show no preference for either carbon isotope.

The trait's presence in breeding lines could only be confirmed by using a mass spectrometer to measure the tiny mass differences between the sugar molecules produced by photosynthesis. The use of a mass spectrometer has added another dimension to conventional hybridisation, the science of unnatural selection.

Richards says Hartog, a formerly popular cultivar noted for its drought tolerance, figures prominently in Drysdale's pedigree -- Harton is now obsolescent, because it has succumbed to stem rust.

Given the potential value of drought tolerant varieties to the Australian wheat industry, it could be expected that a century of breeding and selection would have randomly bred the trait into other cultivars. Yet it has been detected in only one other cultivar apart from Hartog.

Given that Drysdale has a 10 per cent yield advantage over its already drought-tolerant progenitor, Hartog, its advantage over most other cultivars currently grown around Australia is likely to be even greater.

That yield advantage will decline progressively as rainfall increases, and will be negligible in very wet years. But because very wet years are the exception across much of the Australian wheat belt, Drysdale will have a yield advantage in most years, Richards says.

Breeding pipeline

CSIRO and Graingene expect to release another drought-tolerant cultivar in Queensland next year, and Richards says other "non-discriminator" varieties are in the breeding pipeline.

Because they provide a measure of insurance against drought, they are likely to dominate wheat production in Australia within a decade. Richards believes that in drought years, they could add as much as $2 to $3 billion to the value of the wheat crop.

Its rarity in traditional cultivars indicates it's not a single-gene trait, but Richards says it is nevertheless highly heritable, indicating that as few as three or four genes are involved.

Work is underway to identify these genes, so that breeders would then be able to select highly drought-tolerant hybrids by DNA testing -- one is known to be a variant of the gene for the rubisco enzyme, which performs the initial carbon-capture reaction in photosynthesis.

Drysdale is a landmark advance in plant breeding, and not just for the wheat industry, says Richards. Most temperate crop plants that employ the C3 photosynthesis pathway, including rice, the world's most important human food crop, and most fruit and vegetable crops, discriminate to some degree against the C13 isotope.

"The technology is attracting a lot of international interest as it offers tremendous promise for improving the potential to grow high yielding crops in the world's dry areas," he says.

More efficient

Tropical cereals like maize and sorghum, and tropical pasture grasses, already use water more efficiently because they employ the so-called C-4 photosynthesis pathway.

Richards believes the same approach used to develop Drysdale can be applied to other temperate cereals and grasses, as well as to broad-leaf fruit and vegetable crops that use the less water-efficient C-3 photosynthesis pathway. Lawn and pasture grasses that used water more efficiently would also yield major water savings.

A 'reverse discrimination' approach could be advantageous for irrigated crops like rice. In regions where water is abundant, crops bred to discriminate strongly against the C13 isotope should produce higher yields.

Richards says rice is a particularly promising candidate for selection and breeding in either direction -- towards higher-yielding drought-tolerant dryland cultivars, or varieties bred to 'max out' in irrigated rice paddies.

"Most of the world's rice is rain-grown," he says. "Tony Condon in our research group has identified some very exciting variation that could be exploited, and it should be easier than in wheat because the rice genome has already been sequenced."