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

Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases
PVX’s host range to members of family Solanaceae (Green, 1991) may be responsible
for its observed low incidence in Uganda. In contrast, the high incidence of ToMV in
Uganda, could have been due to its being seed-borne (Brunt et al., 1990), and due to the
fact that some farmers, especially in Rakai district, extract their own seed for subsequent
cropping cycles (Annex 3). The survey showed that in Iganga district, where farmers only
used certified seed, ToMV did not occur. ToMV was observed to cause severe mosaic
symptoms, which were earlier on reported by Defrancq (1989) and Hansen (1990). The
wide distribution and high incidence of ToMV were considered a big threat to tomato
growers, and chances of spreading the disease farther are very high in a situation where
farmers collect and preserve their own seeds. Broadbent (1965, 1976) reported that
ToMV was easily spread with seed, running water and wind. Consequently, it is
recommended to identify ToMV strains existing in Uganda in order to compare them
with strains present elsewhere in the region.
Furthermore, Tomato spotted wilt virus was detected in only three of the eight districts
surveyed despite high thrips populations at the time (Annex 3). It could have been
possible that some of these thrips were feeding on tomatoes, and were not carrying any
TSWV inoculum. Literature revealed that TSWV was identified in East Africa as early as
1969 (CMI, 1969). Therefore, the need to study the vector Frankliniella spp., and to
identify TSWV strains, using procedures reported by Verkleij and Peters (1983),
Gonslaves et al. (1989), and Wijkamp et al. (1995), is recommended for future research
activities.
Likewise, Brunt et al. (1990) reported Pepper veinal mottle virus in Kenya. Even though
Kenya is a neighbour of Tanzania, Nono-Womdim et al. (1996) did not detect it on
tomato in Tanzania. However, during our study, PVMV was also identified in Ugandan
tomato. During the survey, PVMV incidence was only 8%. Most times PVMV was
occurring in combination with ToMV. This was the most frequent mixed tomato virus
infection, as shown in table 3.8. PVMV symptoms were observed to be mild everytime it
was singly infecting a tomato plant, but showed severe green mosaic or mottling
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