Incidence, Distribution and Characteristics of Major Tomato Leaf ...
Incidence, Distribution and Characteristics of Major Tomato Leaf ... Incidence, Distribution and Characteristics of Major Tomato Leaf ...
Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases tomato variety Pearl Harbour (Yassin and Nour, 1965) provided a tomato crop with resistance to Tomato yellow leaf curl virus (sensu stricto). Twelve tomato lines from Israel were found to be partially resistant to TYLCV (de Catro et al., 2005). Krishna- Kumar et al.(1995) found resistance to TSWV in wild tomato species on the Hawaiian Island of Maui. Legnani (1995) reported resistance to PVY in wild tomato (Lycopersicon hirsutum), which was subsequently used in breeding programmes. Moreover, some hairy wild tomato species are said to be resistant to CMV (AVRDC, 1985). Such resistance to CMV has been identified in another wild tomato, i.e. Lycopersicon chilense, which has also got resistance to TYLCV (Zakay et al., 1991). In Thailand, the most tolerant lines of tomato to TYLCV are Fl (106) 1 (33) (21) Fireball and P1 (30) 5 (29) (16) P-1. To develop virus-resistant tomato varieties, it is necessary to understand mechanisms involved. Bejarano and Lichtenstein (1994) reported about engineering tomatoes with resistance to TYLCV. According to Aranyine-Rehak and Burgyan (1992), pseudo-recombinants, which are RNA strands forming loose bonds with complementary target virus RNA strands, were used for specific determination of virus genome sections responsible for specific functions. In their report, pseudo recombinants of Tomato aspermy virus (TAV) and Cucumber mosaic virus (CMV) were used to determine RNA responsible for cross-resistance in CMV. As a result, RNA-1 and RNA-2 were found to be responsible for resistance to CMV strain (CMV nt 80/35), which induces intense yellow mosaic symptoms. Also the use of transgenic plants for resistance to TYLCV, a method that is encouraged as the easiest way to manage TYLCV in the future (Beachy, 1997), has been researched. Bendahmane and Gronenbom (1997) used anti-sense RNA, which targeted mRNA of the replication gene (C1), to engineer resistance against TYLCV. Using N. benthamiana test plants, they found that TYLCV could be resisted. At least 21% of tested plants were found resistant to TYLCV when Antignus et al. (2004) used truncated replication associated protein (T-Rep) gene from a mild TYLCV strain. Just recently, Fuentes et al. (2006), reported transgenic tomato plants, which were transformed with an intron-hairpin genetic construction (726 nt of the 3’ end of TYLCV C1 gene) to induce post transcriptional gene silencing against early TYLCV replication 44
Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases gene (C1). This line of castor bean catalase intron-hairpin transgenic tomato plants was resistant even at high whitefly populations. These results exhibited a new trend of other possible management solutions for TYLCV (sensu lato), which are worth trying in developing countries like Uganda. Whereas many different control methods have been developed for tomato viruses elsewhere, none of them have been tested in Uganda. This study, therefore, is seeking to (1) identify tomato viruses in major tomato growing areas of Uganda; (2) generate information on one virus found to be a major virus problem on tomato; (3) establish the epidemiology of this virus in the complex small holder agro-ecosystem; and (4) investigate its relationship with the vector. Such information could eventually be utilized in the development of integrated viral disease management packages, such as transgenic plant resistance. 45
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<strong>Incidence</strong>, distribution <strong>and</strong> characteristics <strong>of</strong> major tomato leaf curl <strong>and</strong> mosaic virus diseases<br />
tomato variety Pearl Harbour (Yassin <strong>and</strong> Nour, 1965) provided a tomato crop with<br />
resistance to <strong>Tomato</strong> yellow leaf curl virus (sensu stricto). Twelve tomato lines from<br />
Israel were found to be partially resistant to TYLCV (de Catro et al., 2005). Krishna-<br />
Kumar et al.(1995) found resistance to TSWV in wild tomato species on the Hawaiian<br />
Isl<strong>and</strong> <strong>of</strong> Maui. Legnani (1995) reported resistance to PVY in wild tomato (Lycopersicon<br />
hirsutum), which was subsequently used in breeding programmes. Moreover, some hairy<br />
wild tomato species are said to be resistant to CMV (AVRDC, 1985).<br />
Such resistance to CMV has been identified in another wild tomato, i.e. Lycopersicon<br />
chilense, which has also got resistance to TYLCV (Zakay et al., 1991). In Thail<strong>and</strong>, the<br />
most tolerant lines <strong>of</strong> tomato to TYLCV are Fl (106) 1 (33) (21) Fireball <strong>and</strong> P1 (30) 5<br />
(29) (16) P-1. To develop virus-resistant tomato varieties, it is necessary to underst<strong>and</strong><br />
mechanisms involved. Bejarano <strong>and</strong> Lichtenstein (1994) reported about engineering<br />
tomatoes with resistance to TYLCV. According to Aranyine-Rehak <strong>and</strong> Burgyan (1992),<br />
pseudo-recombinants, which are RNA str<strong>and</strong>s forming loose bonds with complementary<br />
target virus RNA str<strong>and</strong>s, were used for specific determination <strong>of</strong> virus genome sections<br />
responsible for specific functions. In their report, pseudo recombinants <strong>of</strong> <strong>Tomato</strong><br />
aspermy virus (TAV) <strong>and</strong> Cucumber mosaic virus (CMV) were used to determine RNA<br />
responsible for cross-resistance in CMV. As a result, RNA-1 <strong>and</strong> RNA-2 were found to<br />
be responsible for resistance to CMV strain (CMV nt 80/35), which induces intense<br />
yellow mosaic symptoms. Also the use <strong>of</strong> transgenic plants for resistance to TYLCV, a<br />
method that is encouraged as the easiest way to manage TYLCV in the future (Beachy,<br />
1997), has been researched. Bendahmane <strong>and</strong> Gronenbom (1997) used anti-sense RNA,<br />
which targeted mRNA <strong>of</strong> the replication gene (C1), to engineer resistance against<br />
TYLCV. Using N. benthamiana test plants, they found that TYLCV could be resisted. At<br />
least 21% <strong>of</strong> tested plants were found resistant to TYLCV when Antignus et al. (2004)<br />
used truncated replication associated protein (T-Rep) gene from a mild TYLCV strain.<br />
Just recently, Fuentes et al. (2006), reported transgenic tomato plants, which were<br />
transformed with an intron-hairpin genetic construction (726 nt <strong>of</strong> the 3’ end <strong>of</strong> TYLCV<br />
C1 gene) to induce post transcriptional gene silencing against early TYLCV replication<br />
44
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