Kenyans help world fight wheat pest

Two Kenyan scientists are among researchers who have developed wheat varieties that could revolutionise production of the crop.

The role of the two in the research has been described at a global workshop as “incalculable.”

Peter Njau, a plant breeder and deputy director of Kenya Agricultural Research Institute, Njoro, and his colleague, Dr Ruth Wanyera, were among key presenters at the Borlaug Global Rust Initiative 2009 Technical Workshop in Mexico recently.

The wheat experts were invited by Nobel Prize winner Norman Borlaug. The four-day conference in Ciudad Obregón, between March 17 and 20, brought together “leading scientists from Australia, Asia, Africa, Europe and the Americas.”

The global experts “reported significant progress in developing new varieties of wheat capable of resisting a virulent form of an old disease that threatens wheat production worldwide,” said the Borlaug Global Rust Initiative.

Dr Njau’s report was “on strate- gies and progress towards development/release of rust-resistant varieties in Kenya.” Dr Wanyera’s presentation was on the field efficacy of fungicides used against stem rust.

Borlaug Global Rust Initiative secretariat director Rick Ward praised the Kenyan researchers. “Peter Njau, Ruth Wanyera and other scientists at Kari’s Njoro Centre play a central role in reducing the world’s vulnerability to stem rust Ug99,” he told The EastAfrican.

He added, “The team helped establish the true magnitude of Ug99’s threat to world food security. It evaluated various wheat varieties in Njoro’s research fields... and worked with breeders to develop the capacity to evaluate 40,000 different wheat varieties annually.

“That capacity is enabling both Kenya and the world to develop resistant varieties. Njoro and Kari staff are world class assets in the battle against Ug99. Kari-Njoro is a partner in Cornell University’s Durable Rust Resistance in Wheat Project, which is funded by the Bill and Melinda Gates Foundation.”

Last year, Dr Njau and his team worked with global experts to test 20,000 wheat lines from more than 15 countries for resistance to Ug99, the most stubborn type of stem rust disease.

Named for its discovery in Uganda 10 years ago, Ug99 is well established in Kenya, where in some areas the reddish, windborne fungus has decimated 80 per cent of wheat fields. The Ug99 was first detected in Uganda in 1998.

It was subsequently detected in Kenya in 2002 and in Ethiopia in 2003, Sudan and Yemen in 2006, and in Iran in 2007.

Stem rust was historically one of the most destructive diseases affecting wheat and barley. Successful control of the disease for over three decades through the use of genetic resistance has resulted in a sharp decline in research recently.

Detection and spread of Ug99 in East Africa is of high significance. A possible migration path of the disease to North Africa through the Arabian Peninsula and then to Middle East and Asia is envisaged.

These areas are highly susceptible to Ug99 and their environment is conducive to disease epidemics. The resurgence signals a breakdown of resistance genes that protect wheat varieties in many countries.

The Ug99, also referred to as black or brown rust, affects leaves and stems. It attacks wheat, barley, goat grass, oats and rye. It is characterised by small brown pustules that develop on leaf blades in a random distribution.

Infectious spores are transmitted via the soil.

Before the emergence of Ug99, chemical control by triazole fungicides was sufficient. The new strain is resistant to triazole.

Wheat scientists from East Africa visited Kenya to see first-hand the pathogen’s effects.

Dr Njau said research had found that Kingbird, a new variety of wheat, “can perform well in tests elsewhere where the disease has spread.”

Nakuru district in Kenya “is a hot-spot for the disease,” Njau said, adding: “Disease incidence was so intense this year that 85 per cent of the lines were susceptible, and many resistant lines showed 20 per cent greater infection than usual.”

New variants of the pathogen are appearing that overcome some of the most effective resistance genes in wheat,” he said in a newsletter.

But there is hope, too. “The experimental wheat variety Kingbird looked good under this year’s conditions and has performed well in tests elsewhere.”

Derived from International Centre for Maize and Wheat (CIMMYT) germplasm, Kingbird was being used by the centre to develop new varieties whose seed could be multiplied and distributed quickly to farmers in Ug99’s probable path of migration.

Dr Njau also identified an experimental wheat variety from CIMMYT’s international stem rust resistance screening nursery that out-yielded the best reference variety by 27 per cent and the average yield of varieties in the trial by 80 per cent.

In a new study released at the event, researchers from regional institutes described as a breakthrough their efforts to develop new varieties that are resistant to Ug99 and produce more grain than today’s most popular varieties.

Breeding materials in test fields in Ciudad Obregón and Toluca — and in Aleppo, Syria — are sent to Kenya and Ethiopia for exposure to Ug99 in real world conditions. They are then sent back to Mexico or Syria for further refinement and then back to Kenya and Ethiopia for more exposure.

Through this approach, scientists have produced new high-yield wheat varieties that contain “multiple minor genes” resistant to Ug99.

Although this strategy may not provide the same level of protection as that provided by one or two major genes, it is effective.

Researchers believe that by forcing the fungus to overcome a larger array of genetic barriers, the new wheat varieties could provide long-term protection against stem rust mutations.

There are many examples in the last century of stem rust mutating and devastating wheat plants with single resistance genes. In Kenya, Ug99 has mutated and overcome two additional resistance genes — Sr24 and Sr36.

Averting a crisis will require farmers to replace their existing varieties with resistant ones, many of which produce higher yields.

An update from the Global Cereal Rust Monitoring System shows that the mutated fungus could be headed to South Asia, where many subsistence farmers produce 19 per cent of the world’s wheat for a population of 1.4 billion people. Ug99 can cut wheat yields by 20 to 80 per cent.

The monitoring system has also implemented wind models showing that Ug99, which has moved out of East Africa to the Middle East, could soon travel to the Caucasus, Central Asia and Afghanistan.

Wheat provides 20 per cent of the world’s food calories.