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The rock doc: A threat to the worlds wheat

By
June 10, 2010 |

Special to the Democrat

If you like eating hotcakes or bread (or my own personal favorite, huckleberry muffins), you might want to pay attention to a problem thatÕs looming over wheat worldwide. ItÕs a new type of Òstem rustÓ caused by a fungus that cripples wheat plants.

Throughout history, stem rusts have created major famines. Even in the United States, wheat harvests in parts of the country were hit hard by stem rust in 1903, 1905 and 1950-1954. Localized outbreaks affected American wheat as recently as 1985-1986.

Throughout the 20th century, agronomists bred better wheat to be more resistant to a variety of fungal threats. They were successful Ð score a big one for science.

But out there in the wheat fields, thereÕs always an arms race afoot. As the agronomists did their job, fungus was shaped by random mutations and natural selection. When those two natural forces combined to create a fungus that could successfully live on the new wheat varieties, then the fungus came roaring back in the fields. Score one for natural evolutionary forces and stem rust.

In Ethiopia and Uganda in 1998 and 1999, a new type of stem rust was identified, one we can informally call Ug99 although its technical name is a tad longer. The new rust can live on most varieties of wheat grown in the world, and it can bring up to 100 percent crop loss. (ThatÕs not a typo.)

The rust has spread on the winds to Yemen, north to Sudan, and now quite possibly to Iran. ThereÕs some evidence itÕs becoming more virulent as it spreads. Next itÕs likely to move to Pakistan and Afghanistan, and from there onward to China. In time it will cross the Pacific, perhaps on the clothes and shoes of people, perhaps via air currents.

ÒThe good news is that in the developed world farmers can afford to spray fungicide to combat rusts like Ug99,Ó Dr. Tim Murray of Washington State University said to me recently. ÒBut thatÕs not true in other parts of the world where farmers rely solely on resistance in the variety of wheat they plant.Ó

To put it another way, in the developing world, thereÕs a real risk of famine. Major breadbaskets and population centers of the world, including Pakistan, India and China, could be hit hard.

Breeding in resistance to Ug99 in wheat is, in the long run, the cheapest way to give wheat the upper hand in the current arms race. Scientific crop breeders do exactly that sort of work all the time, working to understand plant disease and improve crop plants. Depending on a variety of factors, crops can be improved via simple selection, hybridization or through genetic engineering. The total effect of scientific breeding on crop plants is one of the reasons that global agricultural productivity skyrocketed in the 20th century and is still doing so today.

But Ug99 has some advantages over science. Part of its life cycle occurs each year in a bush called barberry Ð an Òalternate hostÓ for the rust. That gives the Ug99 a place to survive and flourish, quite apart from wheat.

And on barberry leaves, the rust spores reproduce sexually, which means they become more varied than in their non-sexual reproduction on wheat. Being more varied is an advantage if you are a population of rust in a life-and-death arms race and a single spore thatÕs virulent to a strain of wheat will allow your next generation to survive and flourish.

Also to the advantage of the fungus is that, in warm weather, it grows quickly and creates a new generation every 10 days or so. That gives the fungus a chance for a new set of mutations, on which natural selection can work.

But scientific wheat breeders have one enormous advantage Ð their smarts. And they are working diligently to try to resist the rising tide of Ug99 in the fields halfway around the world from where I write.

We must hope they will be successful, not for the sake of my own personal huckleberry muffins Ð but for the very lives of the poor of the world.

Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. Follow her on the Web at rockdoc.wsu.edu and on Twitter @RockDocWSU. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.

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