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Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases Others: Chaerogphyllum spp., Cynanchum acutum, Hyoscyamus desertorum, Nicandra physaloides, and Vitis vinifera (Cohen and Antignus, 1994; Nakhla et al., 1994; Mansour, 1992; Ioannu, 1987; Nakhla et al., 1978; Nitzany, 1975; Cohen and Nitzany, 1966; Nono- Womdim et al., 1996). Cohen and Antignus (1994) used viruliferous B. tabaci for inoculation of plants belonging to diverse families, such as Asclepiadaceae, Asteraceae, Fabaceae, Malvaceae, Solanaceae and Apiaceae in the greenhouse, and virus-free whiteflies for recovery tests, to determine TYLCV host range. The extensive host range has consequences for virus disease epidemiology and is worth considering while developing a system-wide management strategy for these viruses. Furthermore, it is doubtable whether crop rotation is a feasible tomato yellow leaf curl virus diseases control measure. Tomato Yellow Leaf Curl Viruses (sensu lato) Epidemiology Epidemiological studies by Moustafa (1991), in the semi-tropical climatic zone of Egypt, indicated that at the beginning of Spring and early Summer (February - April), when tomato plants have just established, TYLCV incidence is very low. The latter becomes high towards the end of Summer (September – mid-October), and then coincides with peak whitefly population density (Riley et al., 1995). This is followed by high TYLCV incidence and severe damage in the fall (Autumn) when production losses rise to 80% and almost all plants are infected. Similarly, Cohen and Antignus (1994) observed that in the Jordan Valley, the spread of TYLCV was significantly correlated with B. tabaci population size. As in Egypt, peak whitefly population occurred between the first week of September and Mid-October. In Tanzania, TYLCV symptoms and whitefly vector presence are reported to be most common during November to February (Nono-Womdim et al., 1996). Another factor contributing to high incidence of TYLCV is proximity to old host crop fields. Mazyad et al. (1994) found that adjacent old fields of vegetables and other field 20
Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases crops present at tomato planting play a big role in harbouring whiteflies, which eventually infest tomatoes. Similar observations were made in Egypt, Cyprus, Lebanon, Jordan, Saudi Arabia and Israel (loannou et al., 1991; Mazyad et al., 1986; Makkouk et al., 1979; Nitzany, 1975). Although some whitefly vector-host studies have been conducted in relation to Cassava mosaic geminiviruses (CMGs) in Uganda (Legg, 1996), there is a need to establish the relationship between whitefly vector and transmitted TYLCV in order to develop sound TYLCV management options. Management of Tomato Yellow Curl Virus The most effective way of managing Tomato yellow leaf curl virus (sensu stricto) is by use of an integrated management package, which combines cultural practices, insecticide application, UV-absorbing plastic films, insect vector proof nets, and variation of weather conditions like light intensity, photoperiod and temperature (loannou et al., 1985; Mazyad et al., 1986; Cohen and Antignus, 1994; Perring et al., 1999; Palumbo et al., 2001; Hilje et al., 2001; Mutwiwa et al., 2005; Zilahi-Balogh et al., 2006; Kumar et al., 2006). Mazyad et al. (1986), and Chan and Jeger (1994) controlled TYLCV by eliminating or reducing sources of initial inoculums through uprooting diseased plants. Chan and Jeger (1994) reported that uprooting was most effective where plants were sparsely distributed and with minimal contact. This may also relate to young plants whose canopies are still small. Ioannou et al. (1987) recommended the use of healthy transplants, and later in 1991 reported successful control of TYLCV by timely planting. Thus, the whitefly population is low during the rainy season and high in the dry season. Careful tomato seedling protection against whiteflies in the dry season, and transplanting at the beginning of the rainy season helped to avoid TYLCV infection. Sharaf et al. (1986); Prabhaker et al. (1988); Mason et al. (2000); and Palumbo et al. (2001) managed vector populations by using chemical pest control options, such as Imidacloprid (a nicotinoid), buprofezin (a chitin synthesis inhibitor), and pyriproxyfen (a juvenile hormone analog). However, Palumbo et al. (2001) recommend use of cultural and biological options for controlling B.tabaci because of pest resistance to insecticides. 21
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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1200 1200 (A) IG1 (ToLCV-UG) PAL1v
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8 ANNEXES Incidence, distribution a
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Table A.1.1 continued Incidence, di
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