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

Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases 101
al., 1982; AVRDC, 1987; Czosnek et al., 1990; Nakhla et al., 1993; AVRDC, 1993;
Nono-Womdim et al., 1996). In Tanzania, Chiang et al. (1996) identified another tomato
leaf curl virus (ATLCV-TZ). Later, a ToLCV-related virus, Tobacco leaf curl virus
(TbLCZbwV), was isolated from tobacco in Zimbabwe by Paximadis and Rey (2001),
while Pieterson et al. (2000) identified a new begomovirus, in South Africa, Tomato cury
stunt virus, which formed cluster with TYLCV-Is.
It is with a clear identification of the causal organism that appropriate virus management
options can be drawn (Bock 1982). If this can be achieved with the intergenic region and
coat protein gene sequences comparisons with sequences in the (EMBL/NCBI) genbank
(Brown, 1997), this chapter deals with comparison of begomoviruses found in Uganda
with those already identified elsewhere and that have their DNA sequence in the
geminiviruses genbank (Fauquet et al., 2003; Moriones and Navas-Castillo, 2000). If this
is successfully done, Ugandan TYLCV and ToLCV should be understood in terms of
their homology with other species of genus Begomovirus. Furthermore, the use of the
intergenic region and coat protein gene sequences would hence be proven to be useful
and cheaper, as a first step approach, than the full sequence comparison approach
(Fauquet et al., 2003).
From our tomato yellow leaf curl viruses identification molecular experiments in Chapter
3 above, many samples tested positive. However, samples IG1 and RL5 were notable
because of the different way they reacted to experimental probes. In DNA hybridization,
IG1 tested positive to the Bean golden mosaic virus degenerate probe, whereas sample
RL5 was negative in this experiment (Figure 4.1C). In another experiment where specific
TYLCV-Is probes were used, both IG1 and RL5 tested positive (Figure 4.1F). Similar
results were generated in PCR, where IG1 reacted positve to primers pairs AL1v1978:
ARc715 and ARAv494: 1048, while RL5 was negative (Figure 4.1A/B). Nevertheless,
RL5 was positive in a PCR experiment with specific primers C2v 1499: AL1c2196 and
CRv21: IRc287 (Figure 4.1D/E). Therefore, these two samples were selected for further
characterization experiments reported about in this Chapter 4.