KAMPALA, 20 May 2010 (IRIN) - Agriculture officials and researchers in
Uganda have warned of a serious threat posed by a new strain of Cassava
Mosaic Disease, saying it could wipe out at least 202,342ha of crops.
Farmers in the central district of Mukono have been hardest-hit by the
Cassava Brown Streak Disease (CBSD), a devastating viral infection that
affects the edible parts - the tuberous roots and sometimes leaves - leading
to a total loss of yields in most cases. It is spread by white flies.
Mike Thresh, a consultant on cassava viral diseases, said the disease was
now occurring in areas previously believed to be immune, such as high
altitude areas away from the Indian Ocean coastal belt of Kenya, Tanzania
and Mozambique.
"[Initially] there was a sort of dogma that built up in scientists that
there is an altitude ceiling and that it [the disease] was not a problem
once one exceeded 1,000m above sea level," Thresh said. "The gravity of the
situation is that almost all varieties bred or selected for resistance to
Cassava Mosaic Disease [CMD] are susceptible to the 'new strain' of CBSD
occurring in Uganda, inland areas of Tanzania and Western Kenya.
"Unlike [the] case of mosaic disease where the plant is affected as well as
the yields, in the case of CBSD, the plant remains extremely vigorous and
you pass by it and conclude that it is okay, but the problem comes when you
look at the roots. What is more worrying is that it takes about 10 years to
develop a variety," Thresh said.
The symptoms include root constriction and a dry hard rot when the root is
cut. It also causes cracks and discolouration in the tubers while the
harvested roots have corky, yellow-brown necrotic spots. It also causes
patches of yellow mixed with normal green on the leaves, a phenomenon
commonly referred to as chlorosis.
Rapid spread
The disease can render susceptible varieties unusable if cassava roots are
left in the ground for more than nine months.
Stephen Mukasa, the district agricultural officer for Mukono, told IRIN
that almost all the cassava crop in the area, where 85 percent of residents
are farmers, had been affected by the disease, threatening the population's
food security.
"We have tried to sensitize farmers about the disease and how to halt its
spread - like destroying affected plants - but it keeps on spreading.
Materials that we thought could be resistant have turned out to be
susceptible to it. Even clean materials are very costly because it requires
five bags costing 25,000 shillings [US$12.50] each to plant 0.4ha and very
few farmers can afford this."
Anton Bua, an agricultural economist and team leader of the cassava
programme in the Ministry of Agriculture, said CMD in the early 1990s had
reduced to zero Uganda's cassava output of six million tonnes by 1990 from
some 202,342ha with a loss of $60 million per year.
"This had recovered to one billion tonnes of yield by 2005 but by 2009 the
area under production had not decreased but the production and the quality
had gone down [due to] a new strain of the brown streak disease," Bua said.
"We are faced with a more serious situation than we witnessed with the
mosaic disease," he added. "A recent tally indicates that over 70 percent of
Ugandans feed on cassava, with the populations in the east and west Nile
regions depending on cassava 100 percent."
Titus Alicai, a plant virologist with the National Agricultural Research
Organization, told IRIN that with funding from the government of Uganda, the
Association for Strengthening Agricultural Research in Eastern and Central
Africa, as well as the International Institute for Tropical Agriculture,
research for a cassava seed variety containing some level of tolerance to
CBSD was ongoing.
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The information is from Mr. Frans Kenis from BD
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