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

Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases 100
4 CHAPTER 4
Homology Between Tomato Leaf Curl Viruses Identified in
Uganda and Other Tomato Leaf Curl Virus Isolates Identified
Elsewhere in The World
4.1 Introduction
Variations and similarities have been reported among tomato yellow leaf curl viruses
(TYLCVs) and tomato leaf curl viruses (ToLCVs) in both New and Old World (Padidam
et al., 1997). Padidam et al. (1995) found that phylogenetic trees obtained from the
alignment of nucleotide sequences of 36 geminiviruses using the Phylogenetic Analysis
Using Parsimony (PAUP) programme and the Un Weighted Pair Group Method with
Arithmetic mean (UPGMA) distance matrix/neighbourhood-joining method of the
MegAlign programme, had New and Old World viruses clustering separately. On the
same phylogenetic trees, TYLCVs and ToLCVs clustered together within the old world
geminiviruses cluster, but formed separate subclasses. Brown (1997) argued that these
similarities and variations could still be detected using partial sequences of the intergenic
region and the coat protein gene. Gorsane et al. (2003) used the same approach to
differentiate members of the tomato yellow leaf curl virus complex in Tunisia. Following
Brown’s argument, TYLCVs and ToLCVs were identified to be begomoviruses and
members of sub-group III of the Old World begomoviruses, but were genetically
different.
Begomoviruses have spread within the Old World and have also been identified on
tomato and capsicums in the New World. Thus, in the New World, TYLCV was
identified in Cuba (Accotto et al., 2001), in southern Florida (Ying and Davis, 2000), and
in Mexico (Ascencio-Ibanez et al., 1999). In the Old World, TYLCV (sensu lato) strains,
which are members of genus Begomovirus, have been reported in South Africa, Senegal,
Tanzania, Malawi, Zambia, Zimbabwe, Nigeria, Ivory Coast, Egypt and Sudan (Yassin et