Killer fungus spells disaster for wheat
May 6, 2008 by John
A WHEAT disease that could destroy most of the world’s main wheat crops could strike south Asia’s vast wheat fields two years earlier than research had suggested, leaving millions to starve. The fungus, called Ug99, has spread from Africa to Iran, and may already be in Pakistan. If so, this is extremely bad news, as Pakistan is not only critically reliant on its wheat crop, it is also the gateway to the Asian breadbasket, including the vital Punjab region.
Scientists met this week in Syria to decide on emergency measures to track Ug99’s progress. They hope to slow its spread by spraying fungicide or even stopping farmers from planting wheat in the spores’ path. The only real remedy will be new wheat varieties that resist Ug99, and they may not be ready for five years. The fungus has just pulled ahead in the race.
Ug99, a virulent strain of black stem rust (Puccinia graminis) was identified in Uganda in 1999. Since then it has invaded Kenya and Ethiopia and, last year, Yemen. From previous fungal invasions, scientists expected the prevailing winds to carry Ug99 spores to Egypt, Turkey and Syria, and then east to Iran, a major wheat-grower, buying them some time. But on 8 June 2007, Cyclone Gonu hit the Arabian peninsula, the worst storm there for 30 years.
“We know it changed the winds,†says Wafa Khoury of the UN Food and Agriculture Organization in Rome, because desert locusts the FAO had been tracking in Yemen blew north towards Iran instead of northwest as expected. “We think it may have done that to the rust spores.†This means, she says, that Ug99 has reached Iran a year or two earlier than predicted. The fear is that the same winds could have blown the spores into Pakistan, which is also north of Yemen, and where surveillance of the fungus is limited.
There could be more unpleasant surprises in store. On mature wheat, the fungus reproduces asexually to release billions of identical spores. If the spores drift onto a barberry bush (Berberis vulgaris), however, they switch to sexual reproduction, and so could swap genes with other stem rusts to produce completely new variants. Iran is a hotspot for barberry.
Scientists have now found out how Ug99 took hold, says Rick Ward of CIMMYT, the wheat breeding institute in Mexico that started the Green Revolution. “It turns out most of Kenya was planted with a wheat variety that contained only one gene for rust resistance, SR24,†he told New Scientist.
“We advise at least two resistance genes,†says Ward. Wheat with the SR24 gene alone gives any Ug99 strains resistant to SR24 a huge advantage, just as misuse of antibiotics selects for antibiotic-resistant bacteria, says Ward. Farmers then switched to using wheat with other resistance genes and the same thing happened.
Ug99 is now resistant to the three major anti-rust genes used in nearly all the world’s wheat. “The real solution is disease resistance that relies on a number of genes,†says Ward. Wheat with multigene resistance does not so much destroy the fungus as slow it down. The hope is that with several genes involved it will be much harder for the fungus to become resistant and there will be less selection pressure for it to do so.
A breeding programme by CIMMYT and others has now uncovered some wheat types which “show promise†in tests against Ug99 in Kenya and Ethiopia, says Ronnie Coffman of Cornell University in Ithaca, New York, who chairs the programme. Funding has increased, as rich countries such as Canada and the US worry that Ug99 could hit their breadbaskets, accidentally or deliberately.
Without such fears, says Khouri, “it is hard to convince donors to take preventive actions, when people are not starving nowâ€. But that may not be far off. “People will start starving if Ug99 cuts harvests enough to push up grain prices,†warns Ward.
The problem is that crop breeding is slow. It usually takes at least five years to cross disease-resistant lines with wheat varieties adapted to local conditions in the world’s wheat-growing countries, then grow enough seed to plant fields threatened by Ug99.
New Scientist has learned that China started a crash programme to breed resistance into Chinese wheat varieties last year, after an article on Ug99 in this magazine was translated into Chinese and circulated to top agriculture officials.
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Ug99 tops Mideast bad news
The news from the Middle East is bad almost everywhere. Iran is tripling its number of centrifuges for processing nuclear fuel. Egypt’s municipal elections have seen independent poll monitors arrested amid boycott calls and a very low turnout. And then there are new rumors of military confrontation over Lebanon, with Syria reinforcing its troops in the Bekaa Valley, extraordinary civil defense exercises in Israel, and American warships off the Lebanese coast.
But all these threats pale almost into insignificance by comparison with the confirmation by the U.N.’s Food and Agricultural Organization (FAO) that an organism with the ugly name of Ug99 has crossed the Red Sea.
Ug99 threatens global famine.
It is the name for a variant of stem rust, a form of wheat disease, which was first identified in Uganda in 1999, hence its name. It is devastatingly damaging to wheat, and so far agricultural scientists have not been able to find an effective defense against it. Ug99 has defeated the two main gene complexes, Sr 31 and Sr 24, which protect most wheat strains from stem rust. It appears to resist most fungicides.
Of the 50 genes we know for resistance to stem rust, only 10 work even partially against Ug99, warns Rock Ward, leading the fight against it at the international Maize and Wheat Improvement Center. Less than 1 percent of the world’s wheat crops contain these genes.
After being restricted to East Africa, Ug99 has now been identified in Yemen, and the FAO now reports that it (or something very like it) has also been spotted in Iran. Spread by the wind, it is not easy to stop or to control, and the prospect that it almost inevitably spreads east into the Indian sub-continent and north in Russia and then to Europe is nothing short of nightmarish.
The FAO says that some 65 million hectares of wheat, which produce about a quarter of the global wheat harvest, are now directly under threat. It gets worse. Over two-thirds of the wheat strains in North America are vulnerable to this disease.
And this comes at a time when world wheat reserves are at their lowest level since records were first kept, and when there are global shortages of other staple foods like rice.
This thing has immense potential for social and human destruction,” says Nobel laureate Norman Borlaug, now 93 and known as the father of the Green Revolution in agriculture.
“We know what to do and how to do it. All we need are the financial resources, scientific cooperation and political will to contain this threat to world food security,” Borlaug adds.
Forget about Israel and Palestine, about Muslims and Christians. The human race could be facing mass famine. The sooner we take Borlaug’s advice with a global crash program against Ug99, the better.
http://www.metimes.com/Editorial/2008/04/11/ug99_tops_mideast_bad_news/6599/