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FOOD: Another strain of deadly wheat fungus in South Africa
lead photo
JOHANNESBURG, 3 September 2012 (IRIN) - As the world's supply of staple
grains grows tight, scientists are learning about the discovery in
South Africa of yet another deadly variant of Ug99 stem rust, a
virulent fungal disease that can devastate wheat crops within weeks.
The world's top wheat scientists are gathering in Beijing, China, for a
global symposium on the rapidly mutating disease, organized by the
Borlaug Global Rust Initiative (BGRI). The discovery of the new variant
brings the total number of new forms of Ug99 in South Africa to four,
scientists at the forum told IRIN.
"There are two possibilities for the [surfacing of] Ug99 variants in
South Africa," said Zacharias Pretorius, professor of plant pathology
at the University of the Free State, in South Africa. "Firstly,
migration of the fungal spores by wind movement from countries to the
north of us, where we have detected similar races [mutations].
Secondly, I believe that at least one of the four variants developed
locally through mutation."
Fortunately, Pretorius said, the wheat race that seems particularly
susceptible to the new Ug99 variant is not very popular among
consumers. Still, the emergence of this new rust variant is an
indication of how virulent the fungus remains.
It also places the wheat fields in Australia, one of the world's major
producers, under threat. Dave Hodson, a scientist with the Mexico-based
International Maize and Wheat Improvement Centre (CIMMYT), points out
that stem rust spores have travelled from South Africa to Australia
three times before - the last time in 1973.
When spores of the fungus travelled from South Africa to Australia
in 1969, it
caused outbreaks that destroyed hundreds of thousands of dollars of
wheat.
The polio of agriculture
'' Rising prices
of staple grains have added momentum to efforts to control such
outbreaks [of stem rust]
''
Wheat stem rust, also known as wheat black rust, is a windborne disease
that can destroy entire fields of crops. The pathogen enters the stems
of the plant and destroys its vascular tissue. There are three types of
rust that can harm wheat, but stem rust is the most feared, according
to the BGRI.
There have been several epidemics in East Africa, especially in Kenya,
which was the first country to be attacked by the original strain of
Ug99 after it was discovered in Uganda in 1999. Most farmers do not
recognize the early symptoms of rust or know to destroy infected crops
to eliminate spores, according CIMMYT. Epidemics in Kenya in 2007 led
to 15-30 percent losses of the wheat crop.
r-hope-against-stem-rust> The fungus has begun mutating rapidly over
the last few years, earning it the epithet "the polio of agriculture".
The new mutations, or "races", of this disease have acquired the
ability to defeat two of the most important stem-rust-resistant genes,
which are widely used in the world's wheat breeding programmes.
The new strain has also been reported in Zimbabwe.
"The right amount of humidity and temperature in the wheat growing
areas in South Africa and Zimbabwe throughout the year have allowed the
virulent strain to thrive," said Cobus le Roux, general manager of the
crop division in the Agricultural Research Council in South Africa.
More on wheat and stem rust
KENYA: Wheat stem
rust hits Rift Valley farmers
lley-farmers>
KENYA: Two new wheat
varieties offer hope against stem rust
r-hope-against-stem-rust>
All wheat varieties
will have to be replaced
Mutant wheat killer
on the prowl
SYRIA: Yellow wheat
rust hits supplies
ies>
IRAQ: Wheat rust
infection fears
Wheat in
India
Researchers have also begun to re-examine the role of barberry, a woody
plant commonly found in the wheat-growing areas, said Ronnie Coffman,
vice chair of BGRI and principal investigator and director of the
Durable Rust Resistance in Wheat Project at Cornell University.
Barberry was once eradicated in Europe and North America because it
serves as a host for stem rust, allowing the rust to survive and
propagate between wheat-growing seasons. "Researchers have found
barberry growing in the [East African] hotspots for new strains of stem
and yellow rust, are now investigating a possible link between the
plant and the increased virulence of emerging rust diseases," said
Coffman.
An ongoing battle
While fungicides remain an effective way to check stem rust, said
Pretorius, they require well-timed applications as well as good crop
coverage, especially in the lower parts of the stems of the wheat
plant.
Scientists have been developing disease-resistant varieties of wheat to
safeguard food supplies. Ravi Singh, a scientist at CIMMYT, has been
involved in developing several minor rust-resistant genes, which are
pooled together to counter the infection, giving them an edge over
single rust-resistant genes
owl> .
The best way to overcome the disease is to replace vulnerable wheat
varieties with some of the 20 new stem-rust-resistant varieties
available. But getting the new seeds to farmers has been a problem.
"We covered 10 to 15 percent of the wheat crops this year, but access
to all the farmers is a problem," said Bedada Girma, leader of the Stem
Rust Task Force in the Ethiopian Institute of Agricultural Research.
In 2010, Ethiopia's wheat crops were affected by yellow rust, another
fungal infection. But rural areas in Ethiopia do not have the
agricultural supply shops needed to distribute new seeds. Most famers
in many African countries buy their seeds from other farmers.
"We need to invest in improving our infrastructure and establish
distribution centres in villages," Bedada said.
Rising prices add urgency
Rising prices of staple grains have added momentum to efforts to
control such outbreaks.
The price of wheat has not climbed down since the 2007-2008 food price
spike, Bedada added.
But BGRI is optimistic. "Even if [the resistant seeds are] sown on as
little as five percent of the total wheat area, the resistant wheat
harvest could be used as seed, allowing complete replacement of
susceptible varieties within a year should Ug99 appear. Most countries
are set to pass the five percent mark in the 2012-2013 growing season,"
said BGRI in a statement.
CIMMYT says scientists are not aiming for total coverage with just one
or two resistant varieties. They plan to continue releasing new and
even better-yielding varieties for productivity and genetic diversity.
But in the meantime, the "vast wheat-growing region that stretches
across North Africa and Central Asia all the way to the gateway to
China - the world's largest wheat-growing nation -is still vulnerable
to the fungus," said Coffman.
To counter possible rust outbreaks, scientists announced the launch of
a global rust tracker , which can
monitor 42 million hectares of wheat in 27 developing countries
CIMMYT's Hodson and his colleagues in Beijing are developing "risk
maps" that can assist researchers in countries in the path of virulent
strains of stem rust and yellow rust. The maps will help to assess the
severity of the threat and prepare a response. Developers hope to add
data on wind speed and direction into the programme at a later stage,
turning it into an early warning tool for the fungus, Hodson told IRIN.
jk/rz
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