The globe may have plenty of land but much of it is too dry – or too salty – to grow crops. And the problem is becoming worse as weather patterns change.
“Salinity already affects over 20 per cent of the world’s agricultural soils, and salinity poses an increasing threat to food production due to climate change,” says Dr Rana Munns, a scientist from the CSIRO Plant Industry. CSIRO, or Commonwealth Scientific and Industrial Research Organisation, is Australia’s peak scientific body.
The problem could be a matter of life and death for millions of people. As the globe’s population continues to balloon, demographers and scientists are warning that mankind is careering towards a tipping point unless we can increase our food production by more than double by 2050.
Munns is part of a team of Australian researchers who have made an important discovery that could help stave off future food shortages. Munns and her colleagues have crossbred a new wheat that can go where other high-yielding plants have failed before – into previously unsuitable salty soils. Their groundbreaking project has introduced a salt-tolerant gene into a commercial wheat variety with spectacular results. In-field tests show an improved grain yield of 25 per cent can be achieved in salty soils. Crop yield is measured by the weight of grain that is harvested per hectare.
Humans have been growing crops for about 10,000 years and have continually crossbred plants in an effort to increase the amount of food each crop can produce. However, they’ve usually done this in the best conditions available – where the land is free from salinity, drought and disease – and in many cases, this has stripped the plant of its resistance to adverse conditions.
“By continually crossing the same subset of plants we’ve lost diversity in the gene pool,” explains research leader Dr Matthew Gilliham, a senior scientist at the University of Adelaide’s Waite Research Institute and the ARC Centre of Excellence in Plant Energy Biology. “Our research is trying to bring genes back into the gene pool from either wild relatives or, if you like, the cousins of wheat to reintroduce those characters of drought and salinity tolerance into plants.”
Using age-old crossbreeding techniques, the scientists took a salt-tolerant gene from an ancestral cousin of modern wheat and added it to a commercial variety of durum wheat. Durum wheat is used to make staples such as couscous and pasta but is particularly averse to salty soil.
Durum’s ancestral cousin – Triticum monococcum – is not directly related to the commercial modern wheat variety and still has a genetically diverse set of genes. The ancient wheat originated in the Mediterranean and is still grown around the world today. While it tolerates salty soils, it has low yields that render it a poorer food source.
The researchers first had to understand exactly how T. monococcum’s genes deliver salinity tolerance, and then use the knowledge to increase the salt tolerance of higher yielding wheat varieties. Once the team identified the genes that gave the ancestor its tolerance to salinity, they used molecular markers, or DNA fragments, to track these traits as they crossed pollen from T. monococcum with a modern wheat. “By crossing pollen from the ancestor to modern wheat, we’ve transferred genes that confer salinity tolerance,” Gilliham explains.
After the initial cross with modern wheat, the resulting plant then had to be crossed to itself multiple times to remove the additional DNA from the ancestor that conferred poor traits such as low yields. And this was no simple process – all up it took 15 years.
“You have to be very careful about how you introduce these new genes so you don’t lose other favourable characteristics,” Gilliham says. “That’s why it takes such a long time, because of the multiple breeding steps and the screening processes that are involved. We can do this in a matter of two or three years with other technologies such as the use of modern genetic modification (GM) but those technologies weren’t available when this project was started.
“It does involve some molecular biology and we identified this gene by using advanced molecular techniques, but the whole process is very similar to the one that’s been used for thousands of years really. Now we know the genes that are involved in salinity tolerance we can accelerate the conventional breeding approach.”
Although the research is not the panacea to the world’s potential food shortfalls, it is a significant step forward. Past studies have shown an improvement in plants grown in salty conditions in the laboratory, often using genetic modification techniques. However, when these plants have been propagated in the field and exposed to varying climatic conditions and other natural factors, they often haven’t done as well.
“There is often a yield penalty for the introduction of a certain salinity-tolerance trait,” says Gilliham. “This is the first time that any study to our knowledge has seen such a drastic, significant improvement in yield under field conditions.”
The project brought together expertise from CSIRO, New South Wales Department of Primary Industries, University of Adelaide, Australian Centre for Plant Functional Genomics and the ARC Centre of Excellence in Plant Energy Biology. It was supported by the Grains Research and Development Corporation (GRDC) and Australian Research Council (ARC).
“It was very much a collaborative effort from a number of institutions across Australia,” says Gilliham. “There are not many labs around the world that would have been able to do this kind of work and we’re lucky to have those facilities here in Australia. Without the multidisciplinary team that we put together, we wouldn’t have been able to do this.”
There has been significant commercial interest in the research. Munns says new varieties of salt-tolerant durum wheat could be a commercial reality in the near future and create big demand. “We have produced a novel durum wheat that is not classified as transgenic, or ‘GM’, and can therefore be planted without restriction,” she says.
Buoyed by their success, the team are applying their research to other wheat varieties to gain an even deeper understanding of the “salt-defying gene”. The researchers have now crossed the salt-tolerance gene into bread wheat, and are assessing the result under field conditions.
The research is the first step in a longer journey. “We have improved the salinity tolerance of this durum wheat but we haven’t solved the problem,” says Gilliham. “There are still additional questions that need to be answered and those are the challenges that we’re setting ourselves now to improve the salinity tolerance of crop plants even further.”