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How real is the wheat stem rust threat?

Subhra Priyadarshini

doi:10.1038/nindia.2008.182 Published online 16 April 2008

The rust threatens to wipe off significant wheat crop.

© Getty

Wheat farmers in India have heard hushed stories of a deadly stem rust that's been traveling continents and could soon be on its way to India. The stories have been doing the rounds for a couple of years now threatening to wreak havoc on wheat crops when here. But how real are the threats of ug99, the bug identified in 1999 from Uganda?

An alarm was raised last year by the international crop protection body Global Rust Initiative (GRI) and the International Maize and Wheat Improvement Centre, better known by its Spanish acronym CIMMYT. They said spores of a new variety of black stem rust may reach India from Uganda and hit most of the wheat crop.

The new pathogen ug99 is a variant of the Puccinia graminis fungus and has been popping up in fields throughout East Africa. It entered Yemen and Sudan last years. Fresh reports suggest it might already be in neighbouring Pakistan, which is the gateway to the Asian breadbasket, and includes the significant crop region of Punjab.

A recent meeting of scientists in Syria has decided to track the bug on an emergency basis. The meet put emphasis on spraying of fungicide and stopping farmers from planting wheat in the path that the fungus is expected to take. While tracking ug99 earlier, the scientists had expected winds to carry the spores to Egypt, Turkey, Syria and Iran. But the Cyclone Gonu of June 2007 upset the wind directions blowing the spores into Iran a couple of years before expected. The UN Food and Agriculture Organization is fearing that the spores could have also flown into Pakistan during the same time.

Threat looms large

Nobel laureate Norman Borlaug has been warning the world not to get complacent. "We are too complacent to admit that this could be a calamity after all," he had said earlier. The last stem rust epidemic had hit North America in 1954, wiping out 40 per cent of the crop. Borlaug then began work in Mexico to develop stem-rust-resistant wheat. The project grew into CIMMYT, which made the rust-resistant high-yielding wheat variety and won Borlaug the Nobel peace prize in 1970.

At 93 now, Borlaug says it was a mistake to dismantle wheat testing programmes worldwide by being over-confident that the rust wouldn't strike back.

India still unsure

India is ready to fight the spores if and when they come, says B. Mishra, project director of the Directorate of Wheat Research in Karnal, Haryana. The laboratory of the Indian Council of Agricultural Research (ICAR) in collaboration with CIMMYT and GRI has started testing its own germplasm varieties in Africa and Kenya to gauge their resistance capabilities. "It takes years to make crosses and then we develop stabilized genotypes, which are then put to tests in the fields."

Historically, widespread stem rust epidemics have been reported in India and Pakistan but after the Green Revolution, there has been no report of significant losses.

Ordinarily, stem-rust spores move only short distances, one stem infecting another as they brush against each other. But ug99 makes five distinct types of spores, of which the urediniospore is especially infectious and unique in its ability to ride air currents. Winds can carry these spores over thousands of miles and this could pose a challenge for India and Pakistan, says Borlaug.

Black rust is not important for India as it has almost vanished through years of resistance breeding

About a year back, there were rumours of an outbreak of stem rust in the coastal areas of Sindh in Pakistan. "No evidence was found. Similar rumours were also spread in India. But India is lucky in that it has a mosaic of variety in wheat lines," Mishra says.

Twenty two released varieties of wheat genetic stocks were sent for testing in Kenyan hotspots and found resistant in the first year of outbreak of ug99. The very next year many of them were found to be susceptible.

Does India have a contignency plan ready if the spores cross its borders? "We would have developed some resistant varieties by then," he says. According to Mishra, black rust is 'not important' for India now because it has almost vanished through years of resistance breeding.

"In any case, only central and peninsular Indian zones produce wheat susceptible to black rust. The highest producing zone — Haryana, Punjab, plains of Jammu and Kashmir, western Uttar Pradesh and Uttarakhand — get yellow rust infections because of the temperature," he says. The northwest plains account for roughly two-thirds of India's annual wheat production on an average.