Agriculture Reference
In-Depth Information
strains or strain combinations that are considerably less damaging than those
encountered earlier. This was demonstrated by Pita
et al
. (2001) and also in a recent
study of avirulent virus isolates from Ebwanateraka which provided some degree of
protection from damaging virulent strains (Owor
et al.,
2004). Another feature of the
post-epidemic phase is that there has been an increase in the proportion of single
virus infections and a decrease in the prevalence of the particularly damaging
combination of viruses that predominated at the height of the epidemic (Sseruwagi
et al.,
2004). The emergence of somewhat tolerant landraces and of avirulent virus
strains or strain combinations explains why the recovery in cassava production that
has occurred in Uganda is not confined to areas where CMD-resistant varieties have
been widely adopted.
The 1997 and subsequent surveys show a progressive increase in the adoption of
resistant varieties and overall these predominated in about one third of all plantings
assessed in 2003 (Bua
et al.,
2005). However, uptake was variable and the proportion
ranged from less than 10% in six of the 21 districts surveyed to more than 50% in six
other districts. The highly resistant Nase 3 has been the most successful of the
varieties released officially in the 1990s and it predominated in seven of the
21 districts surveyed in 2003. However, in several districts the uptake of resistant
varieties was limited by a shortage of planting material, or because the varieties
released originally did not meet the requirements of farmers or consumers; especially
after the epidemic had abated, the need for resistant varieties had lessened and
farmers became more concerned with other attributes. Increasing attention is now
being given to the quality and other features of CMD-resistant varieties and TME 14
and some of the other recent selections already feature prominently in some districts
(Bua
et al.,
2005). This suggests that the use of resistant varieties will continue to
increase, even though there is likely to be a decrease in the funds available for
rehabilitation projects of the type mounted during the 1990s crisis. However, it is
unclear whether CMD-resistant varieties will eventually displace the local mainly
susceptible ones grown previously, or whether the two types of material will continue
to co-exist. Much will depend on the success of the cassava breeding and selection
programmes and of any attempts made to improve the current unsatisfactory health
status of the many popular local varieties that are still widely grown.
20.4.8 The impact of the epidemic in Uganda
In attempts to assess the impact of the epidemic in Uganda, there is general
agreement on:
•
the drastic decline in cassava production and the food shortages that occurred in
many districts during the 1990s following the onset and spread of the epidemic;
•
the big decrease in the area of cassava being grown at the height of the
epidemic, especially in the worst-affected areas;
•
the high and largely unfulfilled demand for cassava at the height of the
epidemic which led to a big increase in theft and in the prices of cassava roots
for consumption and of cuttings for new plantings;
