How will our crop seeds cope with a warming world?
Molecular biology and an old Soviet seedbank may hold the key to future food production. Fiona McMillan reports.
How do you find seeds that will thrive in the climate of the future? Robert Sharwood doesn’t have a time machine, but he does have access to a very old seed bank and a glasshouse that can simulate future temperatures and carbon dioxide levels. For an agricultural scientist, that’s the next best thing.
If all goes to plan, Sharwood and his colleagues will breed crops that can cope with future droughts and heatwaves. They must work quickly, though: time is short.
Plant scientists around the world agree that global food security faces multiple challenges in the coming decades. In the first instance, current crop production can’t keep up with impending demand.
“We need to increase our productivity by 70% by 2050 in our food crops to be sure we can feed our growing population in the world,” says Sharwood, who works in the ARC Centre of Excellence for Translational Photosynthesis at the Australian National University.
We’ve faced the threat of world hunger before. In the mid-20th century, when the world population was just three billion, it seemed it would soon be impossible to feed everyone. However, Norman Borlaug and fellow scientists used selective plant breeding to produce more grain per acre.
Today, the global population is nearly 7.5 billion and is likely to approach 10 billion by 2050. Meanwhile, agricultural scientists are beginning to struggle with increasing yield in wheat and rice, which are the most critical crops.
Each year improvements in yield decline, says Sharwood. While we are approaching a theoretical limit on calorie production, there is a more pressing problem.
“What’s really impacting production is the climate extremes,” says Sharwood. “Over the last 10 years the intensity and frequency of heatwaves and droughts have increased dramatically.”
With rising anthropogenic carbon dioxide this is predicted to only get worse. “It’s really important that we make our crops flexible to cope with these extreme events,” he says.
Sharwood and others are hoping to accomplish this by ensuring the heart of the photosynthesis engine in crop plants is as robust as possible.
During photosynthesis, plants use sunlight to fix carbon dioxide into carbohydrate building blocks which are essential for plant growth.
An enzyme called ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO for short) plays a critical role in the conversion of carbon dioxide to carbohydrate, and Sharwood has spent much of his career investigating how RuBisCO behaves differently in a variety of plant species, particularly grasses.
Recently, when investigating native Australian grasses, he and his colleagues discovered something intriguing. Not only do different native grasses possess variations in their RuBisCO enzymes, they also respond differently to temperature.
Sharwood is now collaborating with Dr Gonzalo Estavillo at CSIRO to find out if wheat varieties also display such natural variability. To explore this possibility, they needed to find a wide range of different varieties of wheat from different climates. Thanks to a group of farsighted, self-sacrificing Russian scientists, Sharwood and Estavillo found the perfect resource.
In the early 1920s, Russia experienced famine after its civil war. In an effort to prevent another agricultural disaster, a young Russian botanist named Nikolai Vavilov travelled the world collecting seeds of wild wheat and other food crops. He and his colleagues collected nearly 200,000 specimens, to produce the largest seed bank the world had ever known.
During World War II the city of Leningrad, where the seeds were stored, came under prolonged siege from German forces. A group of scientists remained behind to protect the collection, and went hungry, refusing to consume any of the seeds. Ultimately, nine starved to death. Meanwhile, during the Lysenkoist backlash against plant genetics under Stalin, Vavilov was sent to prison where he, too, died of starvation.
Now, the Vavilov seeds could help feed the world.
The wheat lines in the collection originate from incredibly diverse habitats, says Sharwood. He and Estavillo are exploring how individual wheat lines adapted to their climates of origin.
“At the moment we’re just searching for natural variation in carbon dioxide fixation and photosynthesis properties,” he says.
In a carefully monitored glasshouse, they are growing 60 Vavilov wheat lines from 11 different biogeographical origins. Early results indicate there is diversity in photosynthesis function in the Vavilov lines, and Sharwood is keen to see if this is due to differences in RuBisCO performance.
He also wants to know how much RuBisCO is present, because levels can vary between varieties. This is important because RuBisCO contains a significant amount of nitrogen, and a lot of the nitrogen in fertilisers ends up there. Thus, a wheat line with low levels of highly efficient RuBisCO that functions well under higher temperatures would let farmers reduce fertiliser and water use, while improving crop yields.
Sharwood says that once they have a better understanding of the biochemistry of the Vavilov lines, they can make predictive models to see which lines would be good candidates for breeding with existing commercial wheat to produce high-yield crops.
The critical test will be developing the new breeds, and growing them over multiple seasons in the current climate. However the ultimate goal, he says, is to test them under future climates.
“We can use glasshouses to test future environments where we can supplement carbon dioxide and different temperatures,” he says.
As ever, plant breeding requires patience. “It will take about seven years to develop a line that we can use,” he says.
This, says Sharwood, is why they are working on this now, because time is a luxury global agriculture doesn’t have.
Suddenly, 2050 doesn’t seem so far away.