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Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases 116 cylindrica as major weeds (Annex 1 and 3). It also experiences a characteristic bi-modal rainfall regime (Annex 1). 5.2.2 Experimental Design and Layout The experiment was repeated three times between 1999 and 2000 to take care of annual dry and wet seasonal variations (Moustafa, 1991). As such, this period included two dry seasons and two rainy seasons, i.e. March to June (rainy season) and July to August 1999 (dry season), September to December 1999 (rainy season) and January to February 2000 (dry season). Each planting was done at the beginning or end of the wet season and ended in the dry season. In all cases, variety Heinz was grown. Seedlings were raised on farm and sprayed once a fortnight with Dimethoate (30 ml in 15 l of water) against whiteflies. In the field, a spacing of 90 x 45 cm (Rice et al., 1987; Mwaule, 1995) was used. This resulted into a plant density of 50 plants per 30 m², including guard rows. A randomized complete block design was used, and six treatments referred to as n1-n6 were applied, i.e., a) a tomato monocrop without spraying dimethoate, as a control treatment (n1); b) a tomato monocrop with uprooting of TYLCV symptom-bearing plants (n2); c) a tomato-bean intercrop without spraying dimethoate (n3); d) a tomato monocrop with dimethoate sprayed once a week (n4); e) a tomato monocrop with uprooting and dimethoate sprayed once a week (n5); f) a tomato-bean intercrop with bean rows sprayed once a week with dimethoate (n6). Treatments were planted in three blocks, and therefore treatments were replicated three times in plots of 6 m x 5 m each. Guard rows, which are normally planted with another crop that is not an alternative host e.g., maize, were established around experimental plots to minimize inter-treatment effects and also provide food to farmers. A blanket application of Mancozeb fungicide (50 g/15 l of water) was fortnightly done for all experimental treatments. The experiment was weeded regularly with a hand hoe.
Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases 117 5.2.3 Whitefly Population Monitoring To keep track of whitefly population changes in the field as an alternative to turning over tomato leaves to count whiteflies present, or to using sunmica plates, vacuum collector and passive fan traps (Butler and Henneberry, 1989), cheap sticky Vaseline traps were used to trap and monitor whiteflies. Blue and yellow sticky traps (Figure 5.1), with surfaces smeared with Vaseline, were fixed in the middle and at each corner of each treatment plot to guarantee maximum trapping of whiteflies in the general tomato ecosystem. These traps were made out of used 5 l plastic jerry cans. They were modified from sticky traps reported earlier by Lewis (1973), Raccah (1986) and Green (1991). Thus, containers were cut into two pieces. Of the two pieces, the top part had a surface area of 0.015 m², whereas the bottom part had a surface area of 0.075 m² (Figure 5.1). Traps made out of top parts were used at plots’ corners, while those from bottom parts formed traps fixed in the middle of plots. Blue and yellow sticky plastic traps were repeated in all treatment plots. Note was made of number of whiteflies trapped per m² every week. Counted whiteflies were removed from traps, which were then re-surfaced with fresh Vaseline to maintain stickiness. Traps made out of 5 l plastic jerry cans trap flying whiteflies only, and were therefore used to monitor the general field whitefly population. To monitor whitefly population on individual plants per plot, another type of trap that could be used to estimate number of whiteflies infesting a tomato plant was necessary. Consequently, the Kubwa sticky trap was made out of a plastic basin and a translucent bucket with a bottom diameter of 100 cm, lower height of 45 cm, upper diameter of 25 cm, plus an upper height of 30 cm, and with a translucent top inner wall surface smeared with Vaseline (Figure 5.2). The Kubwa trap was purposely made to trap whiteflies as an estimate of the whitefly population density on individual tomato plants. This was to take care of the fact that whiteflies rarely lay eggs on tomato leaves. Therefore, counting of nymphs could not be performed as recommended by Butler and Henneberry, (1989). Counting adult whiteflies
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Incidence, Distribution and Charact
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Charles SSEKYEWA Incidence, Distrib
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CONTENTS 1 CHAPTER 1...............
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ACKNOWLEDGEMENT The following perso
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vii 7 mosaic virus (CMV), Alfalfa m
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ix 9 Consequently, our findings con
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SAMENVATTING Tomaat is een economis
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xiii 13 Beide genhomologie percenta
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xv 15 dit onderzoek geven ook aan d
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LIST OF TABLES xvii 17 Table Page 1
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ACRONYMS AND ABBREVIATIONS xix 19 A
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Abbreviation Word in full PCR Polym
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Incidence, distribution and charact
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8 ANNEXES Incidence, distribution a
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Books Incidence, distribution and c
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