Agriculture Reference
In-Depth Information
•
Zone 6: a zone of recovery,
where production had been restored by farmers
introducing planting material from elsewhere or adopting improved virus-
resistant varieties.
From the experience in Kamuli and previous observations elsewhere in Uganda, it
was possible to generalize and interpret the six zones as forming a
temporal
as well
as a
spatial
series. The zones occurred as a temporal series over several years as the
epidemic passed through a particular site, or as a spatial series apparent at any one
time when travelling south to north from pre-epidemic to post-epidemic areas. An
important feature of the zonation in districts where Ebwanateraka or other
susceptible varieties of cassava were widely grown was the very obvious and abrupt
distinction between the Zone 3/Zone 4 areas and the largely unaffected Zone 1 to the
south. This created an obvious disease 'front' that was readily apparent to an
experienced observer, even when travelling in a vehicle at speeds of up to 50-60 km
h
-1
.
The approximate position of the front was mapped over substantial distances
across southern Uganda in 1994 and assessments continued in subsequent years to
record the number and overall health status of the plantings and the varieties grown.
Thus, the existence and southward movement of the epidemic was established across
Mukono, Kamuli and Iganga districts and into Pallisa and Tororo districts to the east
and into Mpigi, Mubende and Kibaale districts to the west (Legg and Ogwal, 1998;
Otim-Nape
et al.,
2000; Colvin
et al.,
2004).
The situation in the western and south-western districts of Uganda has been
difficult to interpret because the topography and patterns of land use are more varied
than in the east. Cassava is less widely grown and there are rocky outcrops and
considerable areas of coffee, tea, forest and rangeland used for cattle. An important
feature of cassava production in the western districts is that it is mainly for local
consumption and not for export to other areas. Many different varieties are grown,
often within the same plantings, and this has provided a degree of resilience in that
the more resistant varieties have been selected preferentially and adopted whenever
CMD has become a problem. This was evident in several western districts, including
Masindi, Hoima and Mubende, where farmers were seen removing the most
severely affected plants from within plantings of mixed varieties and retained plants
that were relatively unaffected and still productive. Consequently, the epidemic front
was either not apparent or ill-defined and the situation was in marked contrast to that
in Iganga, Kamuli, Kumi and Soroti districts to the east. There the vulnerable
Ebwanateraka predominated (Otim-Nape
et al
., 1998, 2001) and there was little
scope for the local selection of relatively resistant types.
20.4.7 Subsequent developments and the post-epidemic situation
Views on the nature and magnitude of the CMD problem in Uganda changed
considerably during the 1990s as additional areas were affected and further
information became available. When the first problems were reported in northern
Luwero and in West Nile in 1988-89, they were regarded as localized and unrelated.
