Incidence, Distribution and Characteristics of Major Tomato Leaf ...

Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases
1.1.1.1 Social-economic Importance of Tomato in Uganda
According to FAO (1990, 2003) reports, tomato is now the most important vegetable in
the tropics. It is annually planted on almost 4 million ha worldwide. According to
statistical production data, in Tanzania which is one of the countries neighbouring
Uganda, tomato yields are estimated to be 10 to 14 t/ha (Nono-Womdim et al., 1996),
while in Sudan, tomato yields of about 20 t/ha have been reported (Yassin, 1989). In
some eastern and southern Africa countries, tomato yields on smallholder farms do not
exceed 20 t/ha. However, a smallholder commercial farmer is expected to get tomato
yields of at least 100 t/ha (AVRDC, 1994). In Uganda, by 1990, most smallholder tomato
producers were concentrated in the Lake Victoria basin region with about 150 to 500
hectares under tomato, and with an average annual production level of 10 t/ha (Ugandan
Ministry of Agriculture Animal Industry and Fisheries (MAAIF) statistics, unpublished;
Baliddawa, 1990). Since then, tomato is grown and consumed in every district of
Uganda (Mukiibi, 2001; Mwaule, 1995). According to now available data, agricultural
yields annually increase with 5% (MAAIF Planning Unit unpublished verbal
communication). In the absence of concrete data on tomato production, and taking this
growth in yield to be true also for the tomato crop, an annual production level of about
12.5 t/ha is expected by 2006, which is still very low.
1.1.1.2 Factors Limiting Tomato Yield
Low tomato yields are due to a number of factors. These include (1) lack of improved
well-performing varieties; (2) poor fruit setting due to heavy rains and excessively high
temperatures, which limit pollination, more specifically fecundation plus pollen viability;
and (3) pests and diseases (Villareal, 1979; Lyons et al., 1985; Ladipo, 1988). In eastern
and southern Africa, arthropods, and fungal as well as bacterial diseases are considered to
be the major constraints to tomato production. Viral diseases have been ranked as the
third most important constraint among tomato diseases, basically because of absence of
enough information on them (Varela, 1995).
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