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

Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases
are able to grow tomatoes throughout the year. Such a situation enhances conditions for
vector population build up and virus spread to new fields. Rotation with non-susceptible
alternative crops, especially during periods of poor returns from the tomato crop and in
the absence of susceptible weeds, breaks the epidemiological cycle (Wisler et al., 1997).
Therefore, rotation is recommended in such situations.
This study led to identification of ten tomato viruses by employing serological and
molecular tests to identify causal agents of mosaic, mottling, veinal mottle and leaf curl
symptoms on Ugandan tomato, which is grown in farming conditions such as those
mentioned in the first two paragraphs above. These ten viruses included potyviruses
ToMV, PVMV, ChiVMV and PVY, potexvirus PVX, alfalfamovirus AMV, cucumovirus
CMV, tospovirus TSWV, begomovirus TYLCV-UG (TYLCV-Is strain), plus a
begomovirus tentatively named ToLCV-UG, and were not very different from what is
reported to occur elsewhere in East Africa. Indeed, TSWV was identified in East Africa
as early as 1969 (CMI, 1969); ToMV was reported to be seed-borne and occurs
worldwide (Brunt et al., 1990); Nono-Womdim et al. (1996) reported ToMV to be widely
present in East Africa; finally PVMV was reported to infect pepper in Kenya (Brunt et
al., 1990), but Nono-Womdim et al. (1996) did not detect it in Tanzania. However,
Nono-Womdim et al. (1993) and Ladipo et al. (1979) reported PVMV to infect pepper in
West Africa, while Reccah, (1986) reported PVMV to be (Myzus persicae) aphidtransmitted
in a non-persistent manner. AMV was reported to occur in Europe and
America where mottling, interveinal yellowing, yellow-whitish mosaic and fruit
distortion were observed (Brunt et al., 1990; Jones et al., 1991). Where AMV
individually infected tomato in Uganda, symptoms observed were also typically mottling,
whitish yellow mosaic and fruit distortion.
In our experiments virus incidence was ToMV (31%), AMV (1%), PVMV (13%), CMV
(6%), TSWV (1%), and PVY (0.3%), respectively. This was the first research record on
tomato viruses in Uganda. It was also the first identification of AMV on tomato in
Uganda. PVX was also reported on tomato in Uganda for the first time. The limitation of
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