The demand for soybean in Africa has been increasing steadily driven by the growing feed industry for poultry and aquaculture as well as for home consumption in the form of processed milk, baked beans, and for blending with maize and wheat flour. This in turn has spurred an increase in soybean production to respond to the growing demand―the crop’s production in sub-Saharan Africa has doubled over the last fifteen years.
However, the demand for soybean in Africa still outweighs
the supply and hence a lot of soybean and soybean products are imported mostly
from India, Argentina, and Brazil. In 2011, soybean imports were estimated at
nearly 1.6 million tons, valued at US$1.22 billion with South Africa, Nigeria,
and Kenya being the top importers.
The production of soybean in the continent is low and is
greatly threatened by several biotic and abiotic stresses such as declining
soil fertility, diseases, insect pests, and weeds. Among the diseases, Soybean
rust disease, caused by the fungus Phakopsora pachyrhizi, is one of the
major threats to soybean production in Africa due to its rapid spread. The
fungus’ spores are easily blown by the wind, spreading over long distances.
According to a review paper by Harun Murithi, a plant
pathologist at the International Institute of Tropical Agriculture (IITA) soybean
rust is known to cause massive yield losses of between 10 and 90%. The paper
“Soybean production in eastern and southern Africa and threat of yield loss due
to soybean rust caused by Phakopsora pachyrhizi” was published recently
in Plant Pathology. (http://onlinelibrary.wiley.com/doi/10.1111/ppa.12457/abstract).
“With its current rapid spread, soybean rust is an
important disease that cannot be ignored,” Harun says. “Plants affected by the
disease have leaves that have tan to dark brown, or reddish brown lesions.
Soybean rust reduces yields mainly by decreasing the photosynthetic activity of
the infected leaves.
The disease was first confirmed in Uganda on experimental
plots and thereafter on farmers’ fields throughout the country in 1996 and all
the soybean grown in the country was found to be susceptible. In 1998, the
disease was reported in the major soybean growing regions in Kenya, Rwanda,
Zimbabwe, and Zambia. Other countries where the disease has been detected
include Nigeria in 1999, Mozambique in 2000, South Africa and Cameroon in 2001,
Ghana and the Democratic Republic of Congo (DRC) in Central Africa in 2007, and
Tanzania and Malawi in 2014.
The best method to control the disease is through the use
of resistant soybean varieties. However, this has been difficult due to the
presence of different populations of the fungus across the globe and at the
country level. Nevertheless, a lot of research is ongoing in East and Southern
Africa to understand the soybean pathogen. In Zimbabwe, resistant varieties
have been developed and in other countries tolerant varieties have been
identified and deployed.
“In the breeding program at IITA, soybean rust-resistant
lines have been tested and released across Africa. We also monitor annually the
spread of soybean rust in major soybean growing areas in the region and collect
spore samples for analysis. We are also evaluating the effectiveness of simple
methods to monitor the spore spread such as small-scale monitoring plots
(sentinel plots) and use of spore traps in Tanzania and Zambia. These methods
will be optimized for adaptation to the conditions in the region to contribute
to controlling soybean rust,” Harun adds.
According to the study, due to the huge potential of
soybean to improve the diet and the incomes and livelihoods of smallholder
farmers in eastern and southern Africa, efforts to protect the crop from
abiotic and biotic stresses and especially soybean rust disease, should be
enhanced to ensure sustainable increase in the crop’s production.
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