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Global Fight to Preserve Daily Bread

Sustainable Solutions to Combat Wheat Black Stem Rust

Participants of the Second Coordination Meeting in Kenya, analyzing the first batch of mutant wheat and barley in an endemic hotspot at Kenya Agricultural Research Institute (KARI), Njoro. The participants are wearing protective suits that are part of the quarantine drill. The suits protect the clothes of the visiting wheat breeders, so that they do not carry spores back to their wheat producing regions. (Photo: Prof. M.G. Kinyua, Moi University, Kenya)

Wheat farmers have battled plant-killing fungi since the grain was domesticated over 10,000 years ago. One deadly nemesis, wheat black stem rust, or Puccinia graminis, has been capable of spreading across continents and destroying wheat crops in its path. This lethal fungus was stopped in its tracks 30 years ago by Norman Borlaug, the 1970 Nobel Peace Prize laureate. He developed wheat varieties that resisted the fungal attack. The world wheat production seemed safe for a time.

Breaking Through Defences

In 1998, stem rust with new mutations breached the resistant wheat varieties´ defences. First spotted in Uganda, and then officially named in 1999, "Ug99" infects and destroys resistant wheat, spreading rapidly. Stem rust, an old plague, has re-emerged with particularly alarming mutations. Now, it is "knocking at the door of the bread basket," says Pierre Lagoda, head of the International Atomic Energy Agency´s (IAEA) Plant Breeding and Genetics Section.

In May, the IAEA and the Food and Agricultural Organization marshalled wheat mutation breeding experts from 26 countries, meeting again in November in Njoro, Kenya, to join the ranks of wheat black stem rust fighters, mobilized by the Borlaug Global Rust Initiative. Lagoda says that this interregional Technical Co-operation (TC) project is at its early stages and has to smooth out some wrinkles, but it has already made surprising progress and shows promise to stall Ug99´s march.

A devious foe, Ug99 overcomes the elite wheat varieties´ rust resistance - a trait that was introduced into their genomes through breeding. Lagoda explains that the genes conferring resistance combat stem rust like the border police who has the photo of the enemy and can stop him on sight. But, Ug99 has been able to sneak past this defensive cordon unnoticed, decimating the crops that fail to recognise the fungal attack.

From the time Borlaug´s solution was used, wheat resistance in elite lines has comprised "two major genes and one minor gene complex that defeated wheat black stem rust. But now all three have been overcome," Lagoda informs.

The fungus infects the wheat stem (and also barley), feeding on the sap rich in nutrients. The plant, deprived of nutrients, either produces only shrivelled and nutritionally deficient seeds or none at all. And stem rust is mutating at an ever faster pace. It is becoming a more ravenous and tenacious threat. "Is this due to climate change or other factors?" asks Lagoda. "We do not know yet," he says, but he is sure that stem rust is "more aggressive and propagating quicker and even finding ways to attack regions it could not reach before."

Need for a Global Initiative

Ug99 spread from Uganda to Kenya, then leaping from Africa to Asia it arrived in Iranian wheat fields in 2008. Scientists have forecast the route of the fungus´ continuing, devastating march, which Lagoda says Ug99 is following with an "eerie precision." If Ug99 spreads further along this predicted path, it will soon strike crops in Ukraine and Kazakhstan, and then India and China, some of the world´s major wheat producers.

Emphasising the need for a global effort against Ug99, John Perry Gustafson of the United States Department of Agriculture says, "There are roughly 660 million metric tons of wheat produced in the world every year. It is the most important food crop for humanity, and anything that lowers the amount of food for humanity is going to affect all of us."

The damage to wheat production in Kenya was but a glimpse of the devastation Ug99 is capable of causing. Miriam Kinyua, Associate Professor from Moi University, Eldoret, calculates that the cost of Kenyan wheat production has almost doubled because farmers are now forced to purchase ever more fungicides to keep Ug99 at bay. "If it were left unchecked about 80% of the crops would have been lost," she points out.

"The most nightmarish scenario that could have been imagined has arrived," says Lagoda. To prevent a catastrophic collapse in wheat production the farming community foresaw the danger and he says they began "massive fungicide spraying and massive preventive destruction of the affected fields to stop the scourge from fully developing."

Working Out a Planned Response

But the experts point out that use of fungicides and destruction of diseased crops are just ad-hoc responses.

One sustainable solution is the very solution that worked the first time - surveying for resistant wheat varieties, crossing them with commercial domesticated varieties, and then breeding these varieties at a quicker rate. Another solution, suggests Lagoda, would be to develop plants with favourable mutations.

Spontaneous mutations occur in nature, and a mutation that allows an organism to survive better, for example, a mutation that will allow plants to resist pests, will eventually become preeminent. Induced mutations are brought about by agents such as gamma rays, and have been used in plant breeding techniques to obtain more varieties of a crop, especially varieties showing traits such as higher yield, increased adaptability, and also enhanced pest resistance or drought and salinity tolerance.

Ug99-resistant wheat varieties can also be produced in the lab by inducing mutations. "We take a handful of wheat seeds and irradiate them, sow them out, select the kind that shows resistance to Ug99 and breed the resistant variety."

But the task is not easy: at least 50 000 to 100 000 individual mutant plants have to be sown to find a few that show increased resistance to the rust. These individuals are tested by growing them in greenhouses or endemic hotspots to select the hardiest varieties. Lagoda estimates that "up to 300 000 individuals [of barley and wheat] from 20 different countries can be tested in the framework of this interregional TC project, and chances are good that we find resistant mutants."

The IAEA is applying its unique technological approach to fight Ug99´s spread, and Lagoda says that the Agency "ensures the technology reaches developing countries, and more importantly, the farmers who need it most."

IAEA stepped into the fight in 2007. "We are adding but a small part to the puzzle. We are offering the world community that has already gathered to fight Ug99 a tool, mutation induction, that can broaden the genetic sources to find resistance to Ug99," Lagoda says. "We have the capacity, the potential for capacity building and trained experts who can be part of the solution to defeat Ug99."

Last update: 27 July 2017