|
Performance of
improved clones tolerant of cassava brown streak disease in Zanzibar
E. Kanju,
H. Saleh, E. Masumba, S. Mohammed, F. Hamis
Tanzania is one of Africa’s biggest cassava-producing countries, and the
crop is the main food staple in the Lake Victoria Basin of the northwest
and in eastern coastal areas. This vital production is currently
threatened by the dangerous spread of a devastating virus, cassava brown
streak disease (CBSD).
Although CBSD has been known from Tanzania for more than 70 years, only
limited attention has been given to managing it. The disease appears to be
increasingly damaging in the coastal districts, where it occurs most
frequently. It commonly leads to production losses as the roots are
spoiled by a dark brown, necrotic rot. Farmers in Zanzibar depend mostly
on two popular local cultivars, Boma and Kibiriti, both highly susceptible
to CBSD. Many farmers have lost almost all their yield, and many farmers
are abandoning cassava.
Three farmer groups were selected to participate in the on-farm evaluation
of
fi
ve CBSD-tolerant clones. Farmers selected KBH 2002/344, KBH 2002/477, KBH
2002/482, KBH 2002/494 and KBH 2002/517 as the best among 26 clones
evaluated on-station during 2003/04. Each farmer group constituted a
replication. Planting was done in October 2005. Forty cuttings per clone
were planted at the spacing of 1 m x 1 m. The same clones were also
evaluated on-station in a random complete block design with four
replications. Harvesting was done in September 2006. At harvest data were
recorded on yielding ability and CBSD severity. Root samples were taken to
the lab for determination of dry matter and cyanogenic potential. Roots
were also boiled and farmers were asked to taste and compare pairs to rank
the clones for cooking quality.
Statistical analysis of fresh and dry root yield data revealed significant
differences among the clones both on-farm and on-station. The mean fresh
root yield obtained on-farm was
15.2 t ha–1 (6.3
t ha–1 dry
weight), ranging from 8.5 to 23.8 t ha–1 (3.4
to 10 t ha–1 dry
weight). The average fresh root yield of the clones on-station was 14 t ha–1 (4.8
t ha–1 dry
weight), ranging from 10.3 to 20.9 t ha–1 (3.8
to 7.5 t ha–1 dry
weight). Clone KBH 2002/482 performed significantly
better than the local checks both on-station and on-farm. Incidence of
CBSD root necrosis was low among the improved clones but was high for the
susceptible local check, Boma. When roots of improved clones showed root
necrosis, the severity was very mild.
Clones KBH 2002/517, KBH 2002/482 and KBH 2002/494 were ranked high in
cooking qualities. In the overall assessment by farmers, all
five
improved clones were recommended for wider dissemination and official
release. Demand for planting material of these improved clones is high.
Interested stakeholders need to embark on wide multiplication and
distribution of planting material of these improved clones.
|
