Occurrence, Distribution, and Alternative Hosts of Viruses of Irrigated Tomato (Solanum Lycopersicum L.) Fields in Sokoto and Zamfara States, Nigeria
Chapter One
Objectives of the Study
The objectives were to identify:
- The occurrence and distribution of viruses of irrigated tomato in Sokoto and Zamfara States, Nigeria.
- The alternative hosts of the virus.
CHAPTER TWO
LITERATUREREVIEW
The Tomato Plant
Origin and distribution of tomato
The present day Tomato (Solanum lycopersicum L.) has a very short history of human consumption (Tan et al., 2010). It was believed to have its origin in the South American Andes (Naika et al., 2005) which is in present day Peru where it was growing in wild at the foot of hills. It was then taken to other parts of the world by early explorers where it was planted as ornamental curiosities but not eaten. In Europe for instance it was planted in gardens as decorative plants and was considered poisonous. Although tomato was accepted later as an edible crop in Europe in about 1840 (Paran and van der Knaap, 2007) there was still strict opposition to its consumption in other parts of the world. Global tomato production increased during the 1920s as a result of breakthroughs in technologies that made mechanised processing possible (Tan et al., 2010). Itis one of the most popular and widely grown fruits in the world including Africa (Osemwegi et al., 2010).
In Nigeria, production spreads all over the country, however, the major producing areas lie between latitudes 7.5 °N and 13 °N, and within a temperature range of 25–34
°C (Villareal, 1980). The areas comprises most States in northern Nigeria such as Bauchi, Benue, Borno, Gombe, Kaduna, Kano, Kwara, Plateau, Sokoto, Zamfara and the south western States:Oyo, Osun, Ogun, Ekiti and Ondo (Denton and Swarup, 1983; Olaniyi et al., 2010; Adekiya et al., 2009).
Taxonomy and morphology of tomato
lycopersicumwith approximately 1,500 species (Knapp, 2006), represents one ofthe largest genera of the angiosperms and is the largest genus in the Solanaceae.The genus is widespread, but circum-Amazonian tropical South America is the center of diversification and species richness (Knapp, 2002).In the most recent traditional classification of the entire genus based on overall morphology, D’Arcy (1972) distinguished seven subgenera and 52 sections. Solanum includes valuable crops, such as tomato (S. lycopersicum L.), eggplant (S. melongena L.), potato (S.tuberosum L.), other edible species like pepino (S. muricatum Ait.), naranjilla (S. quitoense Lam.), cocona (S. sessiliflorum Dunal), and species used for medicinal or ornamental purposes.
From botanical point of view, the tomato is a berry fruit. Nevertheless, it contains a much lower sugar content compared to other fruits. It is a diploid plant with 2n = 24 chromosomes. Tomato belongs to the Solanaceae family, which contains more than 3,000 species, including plants of economic importance such as potatoes, eggplants, tobacco, petunias and peppers (Bai and Lindhout, 2007). In 1753, Linnaeus placed the tomato in the Solanum genus (alongside with potato) under the specific name S. lycopersicum. In 1754, Philip Miller moved it to its own genus, naming it Lycopersicum esculentum (Foolad, 2007; Perlata and Spooner, 2007).
CHAPTER THREE
MATERIALSAND METHODS
Survey and sampling of tomato fields
Surveys were conducted in the month of February, 2016 dry season to document the occurrence, distribution and alternative hosts of viruses on plants in Sokoto and Zamfara States. Three Local Government Areas (LGAs) were surveyed per state for disease incidence and three farms were visited per LGA. The LGAs were selected on the basis of high production figuresand with advice of Extension Agents. For Sokoto State, the LGAs were Raba, Kware and Tureta while Tsafe, Talata Mafara and Bakura LGAs were surveyed in Zamfara State. The maps of Local Government Areas in Sokoto and Zamfara States surveyed are shown in Figures 1 and 2 respectively. In each farm, five quadrants 4 m x 4 m were demarcated at four ends of the field and one at the centre. Total number of plants was recorded using the method of Kashina et al. (2002a) and field disease incidence was calculated.
Virus incidence (VI) in laboratory was recorded as the number of positive samples in the total number of samples in the study plot. The percentage incidence was calculated using the formula below (Chaube and Pundhir, 2005);
CHAPTER FOUR
RESULTS
Incidence of Tomato Viruses in Sokoto and Zamfara States.
Different symptoms observed on tomato plants duringsurvey were leaf curl, mosaic, mottling, distortion, stunting, chlorosis and necrosis. Other symptoms observed were mixture of the abovenecrotic symptoms on tomato plant infected by TAV, mosaic symptom on tomato induced by ToMV, leaf curl and distortion caused by TYLCV, mixed infection caused by TAV and TYLCV, mixed infection caused by TAV and ToMV, mixed infection caused by ToMV and TYLCV, mixed infection caused byTAV, ToMV and TYLCV. The symptoms caused by the TAV, ToMV and TYLCV are shown in Plate IA, IB and ICrespectively. In order to confirm the fact that symptoms observed on tomato were indeed due to viruses, serological tests were conducted. DAS and TAS – ELISA results indicated that samples that tested positive for TAV, ToMV and TYLCV either had curl, mosaic, mottling, distortion, stunting, chlorosis or necrosis. Viruses occurred singularly or in mixture of two or three viruses in one sample.Data collected during the survey are presented in appendices III and IV, V and VI respectively.
CHAPTER FIVE
DISCUSSION
The incidence, distribution and alternative hosts of threetomato viruses (Tomato aspermy virus, Tomato mosaic virus and Tomato yellow leaf curl virus) in Sokoto and Zamfara states were examined in this study.The symptoms observed on the samples, which included leaf curl, mosaic, mottling, distortion, stunting, chlorosis, and necrosis where the viruses were detected have been reported to be incited by the viruses (Gallitelli, 2000). Leaf curl, mosaic and mottling symptoms were very pronounced on most of the samples. These symptoms have been observed on tomato infected by these viruses (Breman, 1989; Blencowe and Caldwell, 1994; Ssekyewa, 2006;Alegbejo, 2015). The serological test conducted accurately affirmed that the causal agents of the aforementioned symptoms were the viruses. Some of the samples tested had virus-like symptoms, but no virus was detected using the serological method employed in this research. These symptoms could have been caused by other viruses whose antisera were unavailable for use in this study. Green (1991) reported about 146 viruses from tomato. These virus-like symptoms could be due to reasons other than virus infection such as abiotic factors which incite the virus-like symptoms (Alireza et al., 2012; Hull, 2002).
CHAPTER SIX
SUMMARY,CONCLUSION AND RECOMMENDATION
Summary
Tomato aspermy virus, Tomato mosaic virus and Tomato yellow leaf curl virus were detected in all the three Local Government Areas each of the two States (Sokoto and Zamfara) either singly or in mixed infections. In Sokoto state, one weed species (Ludwigia decurrens Walter.) from the family Onagraceae,detected as a host of Tomato aspermy virus (TAV), two weed species (Thelepogon elegans L. and Pennisetum pedicellata Trin) and one weed species (Vigna ambasensis Vigamb.) from the two families (Poaceae and Fabaceae respectively) as hosts of Tomato mosaic virus (ToMV) and three weed species (Euphorbia hirta L., Physalis peruviana L. and Eclipta alba L.) from three different families (Euphorbiaceae, Asteraceae and Solanaceae respectively) as hosts of Tomato yellow leaf curl virus (TYLCV). In Zamfara State, one weed species (Phyllanthus amarus Schum & Thonn.) from the family Euphorbiaceae detected as a host of Tomato aspermy virus (TAV), two weed species (Pennisetum pedicellata Trin. and Portulaca oleracea L.) from the two families (Poaceae and Portulacaceae respectively)as hosts of Tomato mosaic virus (ToMV) and one weed species (Euphorbia hirta L.) from the family Euphorbiaceae as a hosts of Tomato yellow leaf curl virus (TYLCV).
Conclusion
- TAV,ToMV and TYLCV occurred singly and in mixed infections in tomato plant in Sokoto and Zamfara States of Nigeria.
- TAVwas detected for the first time in Sokoto and Zamfara States of
- It was found that Ludwigia decurrens Walter acted as alternative host for TAV,Thelepogon elegans L., and Vigna ambasensis Vigamb for ToMV, Physalis peruviana and Eclipta alba L. for TYLCV in Sokoto while Phyllanthus amarus Schum & Thonn.acted as alternative host ofTAV,Portulaca oleracea L. for ToMV in Zamfara State. Pennisetum pedicellata Trin. and Euphorbia hirta L. were found to be alternative hosts for ToMV and TYLCV in Sokoto and Zamfara States respectively.
Recommendations
- Farmers should employ regular weeding mechanisms to avoid weeds build up thatharbour Tomato aspermy virus,Tomato mosaic virus and Tomato yellow leaf curl virus in both dry and wet seasons.
- Tomatovarieties should be developed with multiple resistances to the three
- Molecular techniques should be employed to determine the strains and relatednessbetween TLCV and TYLCV in the study
- Studies should be conducted on the epidemiology of these viruses in order todevelop integrated management strategies for them.
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