Field surveys were conducted during the 2016 dry season in three Local Government Areas in Sokoto and Zamfara States of Nigeria to determine the occurrence, distribution and alternative hosts of viruses of tomato [Solanum lycopersicum (L.)]. A total of 18 tomato farms were surveyed in the two States, 9 in each of the States. Sampling was done in five 4×4 m2 quadrants in the three selected fields per Local Government Area. Tomato plant with curl, mosaic, mottling, distortion, stunting, chlorosis and necrotic symptoms, as well as, asymptomatic plants were sampled. A total of ninety weed samples,forty five from each of the States were also collected during both dry and rainy seasons.The presence of tomato viruses was detected using the Double antibody sandwich enzyme linked immunosorbent assay (DAS-ELISA) forTomato aspermy virus (TAV) and Tomato mosaic virus (ToMV) and the Triple antibody sandwich- enzyme linked immunosorbent assay (TAS-ELISA)for Tomato leaf curl virus (TYLCV).Tomato aspermy virus, Tomato mosaic virus and Tomato yellow leaf curl virus were detectedeither singly or in mixed infections in all the three Local Government Areas each of Sokoto (TAV 17 %, ToMV 19.3 %, TYLCV 3.7 %, TAV + ToMV 7.4 %, TAV + TYLCV 3.7 %, ToMV + TYLCV 8.9% and TAV + ToMV + TYLCV 2.2 %) and Zamfara (TAV 20 %, ToMV 17.8 %, TYLCV 11.9 %, TAV + ToMV 3.7 %, TAV + TYLCV 12.6 %, ToMV + TYLCV 5.2 % and TAV + ToMV + TYLCV 2.2 %) states respectively. In Sokoto State, one weed species (Ludwigia decurrensWalter.) from the family Onagraceae,was establishedas a host of Tomato aspermy virus (TAV). Twoweed species (Thelepogon elegans L. andPennisetum pedicellata Trin)and one weed species (Vigna ambasensisVigamb.) from the Poaceae and Fabaceaerespectivelywere hosts of Tomato mosaic virus (ToMV). Three weed species (Euphorbia hirta L., Physalis peruviana L. and Eclipta alba L.) from three different families (Euphorbiaceae,Solanaceaeand Asteraceaerespectively) were found to be hosts ofTomato yellow leaf curl virus (TYLCV). In Zamfara State, one weed species (Phyllanthus amarus Schum & Thonn.) from the family Euphorbiaceaeidentified as a host of Tomato aspermy virus (TAV). Two weed species (Pennisetum pedicellata Trin. and Portulaca oleraceaL.) from the families (Poaceae and Portulacaceae, respectively) and one (Euphorbia hirta L.) from the family Euphorbiaceae were identifiedas ahosts ofTomato mosaic virus (ToMV) and Tomato yellow leaf curl virus (TYLCV) respectively.
TABLE OF CONTENTS
Title Page ———————————————————————————–
Table of Contents—————————————————————————
List of Tables ——————————————————————————-
List of Figures——————————————————————————-
List of Plates ——————————————————————————–
List of Appendices ————————————————————————-
List of Virus Abbreviations—————————————————————
1.0 INTRODUCTION ——————————————————————-
1.1 Justification of the Study————————————————————
1.2 Objectives of the Study————————————————————–
2.0 LITERATURE REVIEW ———————————————————-
2.1 The Tomato Plant———————————————————————
2.1.1 Origin and distribution of tomato ————————————————-
2.1.2 Taxonomy and morphology of tomato ——————————————-
2.1.3 Botanical description of tomato plant———————————————
2.1.3 Production of tomato —————————————————————
2.1.5 Cultivation of tomato —————————————————————
2.1.6 Nutritional composition tomato —————————————————
2.1.7 Uses of tomato ———————————————————————–
2.2 Constraints to Tomato Production————————————————
2.2.1 Pests and diseases of tomato——————————————————-
2.3 Viruses of Tomato ——————————————————————–
2.4 Management of Tomato Viruses—————————————————
2.5 Alternative hosts of viruses of Tomato——————————————-
2.6 Diagnosis of Tomato Viruses——————————————————-
3.0 MATERIALS AND METHODS————————————————–
3.1 Surveys for Tomato Viruses——————————————————–
3.2 Laboratory Detection of Viruses of Tomato————————————-
3.2.1 Double antibody sandwich Enzyme-Linked Immunosorbent Assay (DAS-ELISA) for Tomato aspermy virus and Tomato mosaic virus detection——–
3.2.2 Triple antibody sandwich Enzyme-Linked Immunosorbent Assay (TAS-ELISA) for Tomato yellow leaf curl virus detection——————————-
3.4 Data Analysis————————————————————————–
4.1 Incidence of Tomato in Viruses in Sokoto and Zamfara———————
4.1.1 Incidence of tomato viruses in three Local Governments of Sokoto State—
4.1.2 Incidence of tomato viruses in three Local Governments of Zamfara State-
4.1.3 Occurrence of viruses of tomato in Sokoto and Zamfara States—————
4.1.4 Distribution of viruses of tomato in Sokoto and Zamfara States ————-
4.2. Weed host of viruses of tomato in Sokoto and Zamfara States—————–
6.0 SUMMARY, CONCLUSION AND RECOMMENDATION —————
Tomato (Solanum lycopersicum L.), belongs to the family Solanaceae which contains more than 3,000 species, including plants of economic importance such as potatoes, eggplants, tobacco, petunias and peppers (Bai and Lindhout, 2007). It is believed to have its origin in South America (Naika et al., 2005) but cultivated and consumed worldwide. China leads world production with about 50 million tonnes followed by India with 17.5 million tonnes (FAOSTAT, 2014). Nigeria is also ranked second largest producer in Africa and fourteenth largest in the world, producing 1.56 million tonnes annually at an average of 27.5 tonnes per hectare (FAOSTAT, 2014). It is one of the most important vegetables grown for it edible fruits. Tomato is cultivated in Nigeria on an annual total area of one million hectares. It makes up about 18 per cent of the average daily consumption of vegetables in Nigerian homes (Chidi, 2012). 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 include most States in northern Nigeria such as Bauchi, Benue, Borno, Gombe, Kaduna, Kano, Kwara, Plateau, Sokoto, Zamfara and the south western States such as Oyo, Osun, Ogun, Ekiti and Ondo (Denton and Swarup, 1983; Olaniyi et al., 2010; Adekiya et al., 2009).
In the tropics, tomato grows well on most mineral soils that have proper water holding capacity and aeration, and are free of salts. It prefers deep, well drained sandy loam soils. The upper layer needs to be permeable. Soil depth of 15 to 20 cm is needed to grow a healthy crop. In heavy clay soils, deep ploughing allows better root
penetration. Tomato is moderately tolerant to a wide range of pH (level of acidity), but grows well in soils with a pH of 5.5 – 6.8 with adequate nutrient supply and availability (Shankara et al., 2005). Addition of organic matter is generally favourable for good growth. Soils with very high organic matter content, like peat soils, are less suitable due to their high water holding capacity and nutrient deficiencies (Shankara et al., 2005). Although the plant is perennial, it is grown as annual. The size, shape, colour, flavour, vitamin content, method of growth (which may be erect or sprawling) and resistance to disease vary according to the variety (Villareal, 1992). It is a branching, herbaceous plant with hairy weak trailing stems. Tomato is consumed fresh or as processed products such as canned tomato, sauce, juice, ketchup, stews and soup (Lenucci et al., 2006). It is consumed principally due to its high concentrations of vitamins A, B and C, and fair concentrations of protein, calcium and niacin (Norman, 1992; Bodunde, 2003; Kaushik et al., 2011). It has medicinal values and used for blood purification and cure of digestive ailments (Kaushik et al., 2011). Studies have shown that consumption of raw tomato and tomato based products is associated with a reduced risk of cancer and cardiovascular diseases (Clinton, 1998; Giovannucci et al., 2002). This protective effect has been mainly attributed to its valuable bioactive components with antioxidant properties (Borguini and Torres, 2009). It is also a major source of antioxidants contributing to the daily intake of a significant amount of these molecules. Tomato antioxidants include carotenoids such as β-carotene, a precursor of vitamin A and mainly lycopene, which is largely responsible for the red colour of the fruit, vitamins such as ascorbic acid and tocopherols, and phenolic compounds such as flavonoids and hydroxycinnamic acid derivatives (Clinton, 1998; Borguini and Torres, 2009).
Due to its various uses, both for processing and fresh market has become one of the most important crops in agriculture for smallholder farmers (Anang et al., 2013). However,the yield in West Africa particularly Nigeria is not encouraging, especially when compared to developed countries. For instance, tomato production in Nigeria was estimated to be 1.56 million tonnes in 2012, while the United States of America estimate for the same year was 13.20 million tonnes (FAOSTAT, 2014). Yield per hectare in Nigeria was estimated at 1/7th of that of the U.S.A (FAO, 2010). Many factors have been reported to be responsible for this poor yield performance (Sangoyomi et al., 2011). The production of this vegetablefaced with a lot of constraints of abiotic (excessive heat, blossom end rot, fruit cracking, catfaced fruit, sunscald, blotchy fruit, physiological leafroll, herbicide injury etc.) and biotic (insects, mites, nematodes, fungi, bacteria, and viruses etc.) factors (Marjan et al., 2000; Srinivasan, 2010; Osei et al., 2012).
Tomato fields in Nigeria are known to be constantly plagued by virus diseases. While, some are prominent in the wet season others are prominent in the dry season under irrigation. The availability of the source of virus, susceptible host and presence of vectors determine the occurrence and the severity of disease. The most common and important virus diseases of tomatoes in Nigeria include: Tomato leaf curl virus (TLCV), Tomato yellow leaf curl virus (TYLCV), Tomato mosaic virus, (ToMV), Tomato bunchy top virus (TBTV), Pepper veinal mottle virus (PVMV), Cucumber mosaic virus (CMV), Tobacco mosaic virus (TMV) and Potato virus y (PVY) (Simons and Sobulo, 1975; Alegbejo, 2015). These viruses have been reported to cause serious yield losses on tomato annually. Known hosts can be cultivated vegetables, ornamentals, wild or weed plant species (Jane et al., 2007). These viruses are spread
mainly by whitefly (Bemisia tabaci Genn) or aphids (Myzus persicae) and grafting (Butter and Rataul, 1977; Sanchez et al., 2000). The whitefly has large number of hosts upon which it can feed and reproduce. Reservoirs of the vector may also vary among production regions (Jane et al., 2007). Symptoms induced by viruses of tomato vary depending on the growth stage at the time of initial infection, environmental conditions and cultivars/variety of tomato plants. These include marginal leaf yellowing/chlorosis of leaf margin of the newest leaves, interveinal chlorosis, upward curling, reduction in leaf size, puckering, shortening of internodes resulting in dwarf bushy appearance, excessive branching and stunting of the plants (Cohen and Antignus, 1994). Recommended management strategies include use of resistant varieties, virus-free transplants, management of vectors,manipulation of sowing date, intercropping, sanitation of tomato field and elimination of virus reservoir (Kashina et al., 2002a; Sastry and Zitter, 2014). 1.1 Justification of the Study Tomato is the world’s major vegetable crop and known as protective food because of its special nutritive value (Rukhsaretal., 2015). It is also the most popular vegetable crop in Nigeria dominating the largest area under production among vegetable crops (Ramalan, 1994).The popularity of tomato as fresh and processed food has made it an important source of vitamin A, B and C in diets. It is consumed throughout the world on a large scale and serves many benefits for heart and other organs and contains carotene and lycopene, one of the most powerful natural antioxidants (Mourvaki et al., 2005).
Despite its numerous uses, yield obtained per hectare is very low in Sokotoand Zamfara states. SADP (2008) reported highest yield of tomato in Sokoto to be 8 tonnes/ ha compared to average yield of 27.5 tonnes/ ha in Nigeria and 192 tonnes/ ha in United States (FAOSTAT, 2014).Viruses have been reported to be one of the most limiting factors in tomato production in the northern states of Nigeria (Alegbejo, 1995).TLCV was reported to have caused yield loss of over 23 % in northern states of Nigeria (Alegbejo and Ogunlana, 1995) whileEraslan et al. (2007) reported Tomato mosaic virus to reduce tomato yield by up to 25 %. A combination of TYLCV and ToMV cause as much as 20-90 % yield loss in West Africa (Lana and Adegbola, 1977). Tomato viruses have one of the widest reported host ranges for viruses, infecting more than 30 species in over 12 plant families (Jane et al., 2007), which harbour the viruses during both wet and dry seasons. There was no any record of survey to identify tomato viruses in the study areasdespite the great threats they pose on the crop yield’s potential prior to this work. The weed hosts, which serve as reservoir for the viruses and their vectors, need to also be identified (Narayana et al., 2002) for effective management of the virus diseases. Therefore, this study was conducted to identify the occurrence, distribution and alternative hosts of the viruses of tomato in Sokoto and Zamfara States of Nigeria.
1.2 Objectives of the Study
The objectives were to identify: 1. The occurrence and distribution of viruses of irrigated tomatoin Sokoto and Zamfara States, Nigeria.
2. The alternative hosts of the viruses.