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

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ix 9 Consequently, our findings concur with hypotheses formulated at the onset of the study, and the following is the summary of our key conclusions and recommendations: 1- Several viruses, including those already reported in East Africa, infect tomato in Uganda. 2- A number of viruses infect Ugandan tomato, and cause virus diseases, which are characterized by symptoms such as leaf curl, mosaic and mottling. These viral disease symptoms are not specific to a particular virus. 3- Viruses responsible for a number of leaf curl, mosaic and mottling virus symptoms observed on tomato were reported for the first time, in Uganda, i.e. RNA viruses ChiVMV, PVMV, AMV, CMV, TSWV, PVY and PVX, as well as begomoviruses, i.e. ToLCV-UG and TYLCV-UG. Basing on the genetic composition of the replication gene and coat protein gene, and to the best of our knowledge, ToLCV-UG is a new virus and reported for the first time in Uganda. Whiteflies were established to be vectors of identified begomoviruses. Whitefly adults are not easy to count because they fly away immediately when their resting ground is disturbed. A new sampling tool, i.e. the Kubwa sticky trap, for trapping adult whiteflies on individual tomato plants, and made from locally available plastic materials, would serve as new format of sticky traps to be used for whitefly monitoring before farmers decide to spray. This way, farmers would minimize amount of pesticides applied and leaking to the environment. 4- Combinations of two to five viruses exist in individual tomato plants. In one experiment, it was observed that PVMV alone caused no visible significant damage to the crop, but co-existence with ChiVMV in the same plant showed significantly severe and synergistic effects on tomato crop performance. These mixtures could be contributing to the severity of tomato virus diseases in Uganda. 5- Tomato yellow leaf curl viruses are amongst major viruses whose incidence and spread are influenced by presence of the whitefly vector (Bemisia tabaci) as well as weather conditions within the agro-ecosystem in Uganda.
x 10 6- We established that weeds act as alternative hosts to some tomato viruses identified, which lead to a clear understanding of the necessity for timely weeding of tomato fields as an option for virus disease management. 7- Majority of Ugandan tomato growers are smallholder farmers. They try to avoid risks related to farming by growing a multiplicity of crops, and this practice contributes to creating a complex nature of the agro-ecosystem favourable for both tomato viruses and their vectors. 8- It was found that whiteflies preferred young tomato plants to old plants. It is recommended that whiteflies be controlled at nursery stage before transplanting seedlings, before infection or when vector and disease levels are still very low. 9- Uprooting diseased plants and applying dimethoate was an effective control for whitefly vectors. Tomato growers are advised to apply this integrated management package for TYLCV (sensu lato) and whitefly vector control, especially if done during the dry season and the first part of the rainy season when whitefly populations are high. In this way, farmer expenditure on pesticides would be minimized and the amount of pesticides filtering through to the environment would be tremendously reduced, even though both economic analysis and evaluation of pesticide pollution were not conducted. 10- Having known major viruses infecting tomato, identified causal organisms of yellow leaf curl symptoms and their vector, and established appropriate integrated management practices, future research efforts should focus on the following; conduct a survey of tomato viruses to cover agro-climatic zones that were not surveyed during our study; investigate further the biodiversity, incidence, host range and mode of transmission of ChiVMV in Uganda; investigate the occurrence of TYLCV-UG and ToLCV-UG in other districts of Uganda; and study its biodiversity in relationship with whitefly vectors observed on tomato and on other plants within the tomato agro-ecosystem. evaluate tomato varieties, both transgenic and non-transgenic, for resistance to TYLCV-UG and ToLCV-UG.
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
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Page 20 and 21: LIST OF TABLES xvii 17 Table Page 1
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