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THE HIGH YIELD offspring of Yaqui 50 were wildly successful, and as part of the Green Revolution, ended up ended dominating wheat fields around the world. But breeders never rest. They're always looking to improve wheat – to make it yield more, make it more pest resistant, more salt tolerant or produce better quality flour.
But every time they perform a cross to gain something new, they are also likely to lose something old. In this case, the thing they lost over time was the 'royal flush' that Borlaug had captured in the Mexican wheat.
Most breeders have relied on a single defensive gene against rust, known as Sr31. And that was just sweet temptation to a microbe. With its formidable mutagenic powers, it was only a matter of time before stem rust overwhelmed Sr31.
It was no surprise that it happened in East Africa. The rift valley countries of Uganda, Kenya and Ethiopia grow wheat year round – in the valleys in winter and up on the escarpment in summer. So rust gets year-round lodgings. And even if the wheat varieties being planted are unwelcoming, rust can always find a few wild relatives to hole up in. Because rust never sleeps in such a place, the chances of developing a new resistant strain are high.
What was a surprise was that wheat breeder William Wagoire even recognised the red pustules growing on wheat stems in a test plot in Uganda. His generation had never seen stem rust. Wagoire sent a sample to Zak Pretorius' lab at the University of the Free State in Bloemfontein, South Africa, who in 1999 confirmed that the pustules were indeed stem rust.
Most worryingly, he showed that this new strain, named Ug99 (for Uganda 1999), could overwhelm the main defence of much of the world's wheat: Sr31. Across vast tracts of the Punjabi plain in Pakistan and India, in Kazakhstan, China, Canada, America and Australia, wheat is a sitting duck for Ug99.
At Obregón, the coalition of the willing met to discuss the progress of the battle. The main plan is to defend the world's wheat by giving it back a royal flush of rust-resistance genes. They no longer have to do it the way Borlaug did: through brute force and feel. Today's breeders have a short cut: they can virtually peer into the seed to determine the gene sets it carries.
Genes come naturally tagged by stretches of a unique sequence of DNA letters, like a barcode, and modern DNA labs can read those barcodes in a matter of days. The breeder need only shave a snippet off the seed and send it off. If the reading shows it carries a winning combination of resistance genes, the breeder can plant what remains of the shaved seed. With these shortcut techniques, CIMMYT has bred wheat carrying new sets of rust-resistance genes.
They have been tested against Ug99 in the heavily infested test plots of Njoro, Kenya, and the winning strains distributed across the world as part of a travelling wheat nursery. Breeders in Kenya, Iran, Pakistan and India have selected the babies they liked best and are busily multiplying them. They expect to have enough seed to replace their susceptible fields within three years.
But the mood at Obregón was far from breezy. There was a sense of relief that the world was getting together at last, but there was also fear that something sinister was brewing, and that victory was far from certain.
The weak link in the defensive chain is getting the resistant new seed into the fields to farmers. Poor farmers in Pakistan and Kenya traditionally save their seed – they don't have the money to buy new seed varieties from the companies who will multiply the seed. And wealthier ones may be loathe to change varieties that, so far, are still providing handsomely.
In the U.S. for instance, "they would rather just spray fungicides", says Brian Steffenson, a plant pathologist at the University of Minnesota. But that's not a solution, he says. "Serious rust epidemics need heavy spraying, and that runs the risk of resistance to the chemicals. It's not easy to develop new fungicides." And it's certainly not a solution for the poor farmers who farm most of the land across Asia and Africa. They can't afford it.
Black Harvest Report
Congratulations to Elizabeth Finkel for this report. I just StumbledUpon the article and it is the most interesting article that I have read in years.
Well Done.
George
Scary - and what about the economics of it all?
I would love to hear more about this scary issue, especially about the economic aspects. At first sight it sounds like only the big companies like Monsanto will be able to produce resistant wheats continually. They will probably patent all that - won't they? Isn't it ironic that our stock market driven greed in the north will not be able to protect us from possible starvation, but just helps the rust to grow stronger in the South and spread from there? Isn't it time that all this information becomes open source? Should we really keep on allowing patents on plants, genes etc?
Goetz
Public vs Private sector wheat improvement
Turns out that other than Western Europe and Australia, world wheat improvement (breeding, pathology, seed systems, etc.) is primarily in the hands of the public sector. Catalyzing synergies and focus within and among the enormous array of public sector science and technology capacities in wheat is largely what the Borlaug Global Rust Initiative is about. But Goetz is right to flag the risk of restrictions on use of valuable genetic resources, as IP encumbrances are as likely to emerge from the public sector as they are from the private.
Rick Ward, BGRI/Cornell
Excellent article
Great job Elizabeth Finkel, this was a great read. Until today I did not know Norman Borlaug played such a key role in solving the rust problems several decades ago. We can only hope someone is willing to put in the effort to carry on his work, whether its public or private. With current global grain reserves being so low, farmers holding off on using potash fertilizer because of high prices and less than ideal growing conditions this year for north american crops those reserves are shrinking rapidly on their own. I don't think the world can handle another grain shock due to wheat rust in the next 2 years. A grain crisis could be the next black swan.
sr31
This is a fantastic article which I thoroughly enjoyed reading. In lectures I prepared for my students last year, I concluded Ug99 is probably not a major threat to Australia, in the sense that sr31 and sr24 arn't widely used genes in our common varieties here. Lets hope so anyway.
Karen Barry, UTAS, Lecturer (Plant Pathology)
Park (2007) Stem rust of wheat in Australia. Australian Journal of Agricultural Research, 58: 558-566.