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East Africa:
Viral Disease Hampers Bean Production
 Beans
(Phaseolus vulgaris L.) are vital vegetables in eastern Africa because
they are a major source of dietary protein and are available throughout the
year. However, the bean common mosaic disease constitutes a formidable threat to
production of the crop in this region.
The disease is caused by the bean common mosaic virus (BCMV) and transmitted by
several aphid species such as Myzus persicae, Aphis crassivora,
and A. fabae. Also, the disease can be transmitted via the seeds with an
incidence of up to 83%.
In the 2001 planting season, a study was conducted in the Lake Victoria basin
area of Tanzania for the presence of the disease. In all the surveyed fields,
there was a presence of bean common mosaic disease. In some fields, the
incidence was found to be as high as 100%! In heavily aphid-colonised and
susceptible cultivars, the symptoms were serious. They consisted of severe
mosaic, leaf malformation, plant stunting and vein banding. The affected plants
produced very few pods, which had fewer seeds per pod than the healthy plants.
When the leaf samples were collected and sent to the Centro Internacional de
Agricultura Tropical (CIAT) for virus identification, they were all found to
contain BCMV.
BCMV-resistant varieties have been developed and evaluated worldwide but farmers
in the region have not adopted these varieties for various reasons. These
include their unpalatability and relatively low yields. In many cases, farmers
are not able to access the resistant varieties. So, such farmers continue to
grow susceptible cultivars and thus BCMV has continued to spread through
planting of infected seeds. Because of the high prevalence and persistence of
the virus in most local cultivars, most farmers tend to ignore the disease and
its effects.
About 60% of those interviewed during the study mentioned that they did not know
about the disease and attributed the condition to the nature of soils.
This scenario shows that there is great need to train farmers in eastern Africa,
in general, on the causes, transmission and management of BCMV. Current research
and efforts to diversify the resistant varieties should be combined with the
development and implementation of control strategies. Otherwise, these efforts
will be jeopardised since those bean varieties that the farmers have access to
and are distributing, are not BCMV-resistant.
For further information:
Joseph Ndunguru
Dept. of Microbiology & Plant Pathology
University of Pretoria
Pretoria 0002, South Africa
E-mail: ndunguru@brighton.zzn.com
Article courtesy of Agriforum Quarterly Newsletter of the Association for
Strengthening Agricultural Research in Eastern and Central Africa www.asareca.org/agriforum/
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