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

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Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases (PVMV) (Zitter, 1974; Nono-Womdim, 1994). Potato virus Y, a member of the genus Potyvirus that infects tomato, has long flexuous rod-shaped particles (730 x 11 nm) containing single-stranded RNA. Potato virus Y occurs in several pathotypes (Jones et al., 1991), which are transmitted by aphids in a non-persistent manner. Typical symptoms of PVY in tomato include mosaic, vein chlorosis, mild mottling, dark brown necrosis on leaflets, severe necrosis, leaf crinkling, and drooping (Jones et al., 1991). The virus occurs worldwide, but has a narrow host range in the tropics. Tanzania, Malawi and Zambia are among the few countries where PVY occurs in tomato and pepper (AVRDC, 1985, and 1993; Nono-Womdim et al., 1994). It has also been evidenced in Apulia, Italy in tomato (Gallitelli, 1982). There are, however, no reports of PVMV in tomato in East Africa, although Nono-Womdim et al. (1994) reported it in sweet pepper (Capsicum annum) in the SADC region. 2.1.1.1.2.4 Family Bromoviridae Family Bromoviridae has five genera that infect plants, i.e. Alfamovirus, Ilarvirus, Bromovirus, Cucumovirus and Oleavirus (Pringle, 1999). Two of these genera include viruses known to infect tomato, i.e. genera Alfamovirus and Cucumovirus (Brunt et al., 1990; Jones et al., 1991). 2.1.1.1.2.4.1 Genus Cucumovirus Cucumoviruses have three functional pieces of ssRNA, i.e. RNA 1, 2 and 3, which determine virus virulence (Jones et al., 1991). These virus particles are isometric and measure on average 28 nm in diameter (Jones et al., 1991). In addition to the three RNAs, cucumoviruses have a fourth RNA (RNA 4), which acts as a subgenomic coat protein messenger, and also a fifth RNA (CARNA 5) or satellite RNA. There are two major tomato viruses in this genus: Cucumber mosaic virus (CMV) and Tomato aspermy virus (TAV). According to Green and Kim (1991) and Jones et al. 26
Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases (1991), of the two species CMV is the most common in the tropics. It causes mottling, mosaic, yellow discolouration, vein-clearing, stunting, and leaf deformation, with extreme filiformity or shoestring leaf appearance. In severe infections, plants produce no fruits or only very few fruits, which are of small size (Green and Kim, 1991; Jones et al., 1991). These cucumoviruses are transmitted in a non-persistent manner by aphids (Green and Kim, 1991). CMV is present in the tropics. In Africa it has been evidenced in Tanzania, Malawi and Zambia (AVRDC, 1987, 1993; Nono-Womdim et al., 1994). 2.1.1.1.2.4.2 Genus Alfamovirus Members of this group, according to Green and Kim (1991) and Jones et al. (1991), contain four ssRNAs, with every each RNA consisting of five different components. One of the RNA components is isometric and 18 nm in diameter. The other four components are bacilliform with lengths of 58, 49, 38 and 29 nm, respectively and a width of 18 nm. Vacuole inclusions are found in cell cytoplasm (Green and Kim, 1991; Jones et al., 1991). One of the member species is Alfalfa mosaic virus (AMV), which infects tomato. AMV causes tomato leaf mottling, interveinal yellowing, yellow whitish mosaic, veinal necrosis, chlorotic line patterns, chlorotic rings and black spots. Fruits of AMV-infected plants are small (Jones et al., 1991). AMV is transmitted by 14 aphid species in a nonpersistent manner and through infected seed (Brunt et al., 1990; Green and Kim, 1991; Jones et al., 1991). It occurs worldwide, but before this study no report had been made of AMV in tomato in Uganda. 2.1.1.1.2.5 Family Bunyaviridae The family is divided into five genera, i.e. Bunyavirus, Hantavirus, Nairovirus, Phlebovirus and Tospovirus (Pringle, 1999). Of these, only genus Tospovirus has viruses that infect plants and especially tomato. Other genera have viruses that infect animals. 27
Page 1: Incidence, Distribution and Charact
Page 4 and 5: Charles SSEKYEWA Incidence, Distrib
Page 6 and 7: CONTENTS 1 CHAPTER 1...............
Page 8 and 9: ACKNOWLEDGEMENT The following perso
Page 10 and 11: vii 7 mosaic virus (CMV), Alfalfa m
Page 12 and 13: ix 9 Consequently, our findings con
Page 14 and 15: SAMENVATTING Tomaat is een economis
Page 16 and 17: xiii 13 Beide genhomologie percenta
Page 18 and 19: xv 15 dit onderzoek geven ook aan d
Page 20 and 21: LIST OF TABLES xvii 17 Table Page 1
Page 22 and 23: ACRONYMS AND ABBREVIATIONS xix 19 A
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Isolate IG1 Incidence, distribution
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1200 1200 (A) IG1 (ToLCV-UG) PAL1v
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Opaque and not smeared Translucent
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8 ANNEXES Incidence, distribution a
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Table A.1.1 continued Incidence, di
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