CHAPTER ONE INTRODUCTION
Tomato (Solanum lycopersicum L) is the second most cultivated vegetable worldwide after potato, and the most important vegetable in terms of value (Hanson et al., 2001). The global land area for crop production in 2012 was 4,803,680 ha, with a production volume of 161,793,834 tons amounting to US$59,108,521 (FAOSTAT, 2013). Tomato production in recent times, has observed a growth of about 10% due to demand for its rich source of vitamins, minerals and antioxidants with greenhouse cultivation becoming significant (FAOSTAT, 2009; HE et al., 2009; Shalaby and El-Banna, 2013). Nutritionally, tomato fruits and products are described as “protective foods”, owing to the presence of lycopene and other anticarcinogenic and antioxidant compounds (Alam et al., 2007). A positive correlation between the consumption of tomato fruits and incidence of some chronic and degenerative diseases, such as cardiovascular diseases and aging condition has been observed (Ishida and Chapman, 2004; Rao and Rao, 2007).
The total land area under tomato production in Ghana in 2017 was 47,932 ha yielding 321,000 tons (FAOSTAT, 2017). Tomato is regarded as a high-value crop cultivated mainly by smallholder farmers in all the agro-ecological zones in Ghana (Diao, 2010) and the monetary expenditure on tomatoes exceeds any other vegetable in the country (Osei et al., 2010). In Ghana, the crop is prone to a myriad of fungal, virial, bacterial, nematodes and insect pests (Sasser et al., 1983), and over 30 diseases have also been reported (Oduro, 2000; Offei et al., 2008). Diseases and other constraints on production of the crop in the country has resulted in a high yearly importation from neighbouring countries especially Burkina Faso (Robinson and Kolavalli, 2010).
The Government of Ghana in collaboration with relevant stakeholders, launched the Export Marketing and Quality Awareness Project (EMQAP) under the Ministry of Food and Agriculture (MOFA) in January, 2007 to enhance productivity and ensure a secure and sustained supply of tomatoes and other vegetables throughout the year (Harry Bleppony, personal communication, June 5, 2017). The project included the setting up of greenhouses at Vakpo (Volta region), Kade (Eastern region), Okyereko (Central region) and Amrahia (Greater Accra Region) to address the constraints and to increase export earnings from non-traditional agricultural produce. Similarly, the Forest and Horticultural Crops Research Centre, Kade, under the Envirodome project, University of Ghana in 2012 established some domes at the Centre, and later in other parts in the country (Dr. Stephen Torkpo, personal communication, July 4, 2018).
In 2016, the World Bank also donated over USD$2 million to the West African Agricultural Productivity Program (WAAPP) in support of a Greenhouse Project to boost vegetable production in Ghana. This project supported the construction and operation of over 260 greenhouses across the country to grow vegetables under fully controlled environmental conditions for optimum growth and productivity (Ali Azara, personal communication, June 9, 2017).
Unfortunately, the greenhouses of EMQAP and WAAPP alongside with private ones established in the country have reported high incidence and severity of a devastating bacterial wilt disease of tomato. The disease is expressed by an overnight irreversible wilting without leaf yellowing or necrosis and the browning or discoloration of xylem tissue, with visible bacterial ooze (streaming) in water upon preliminary investigation. Wilting symptoms typically occurs first on the top young leaves and fits that of the bacterial wilt disease of tomato caused by
Ralstonia solanacearum (Smith, 1984; Agrios 2005). The disease was reported in tomato fields
in the Ashanti (Agogo, Akumadan) , Northern (Vea, Tono, Pwalugu), and Brong Ahafo (Tanoso, Tuobodom) regions of Ghana in 2012 (Subedi et al., 2014).
Genin (2010) revealed that the modus operandi of the bacterium is the invasion of the xylem vessels of infected plant through the rhizosphere, and subsequent high rate of multiplication and spread to above-ground parts of infected host plants culminating in wilting and eventual death. The bacterial disease of tomato is the most difficult to control due to the extreme aggressiveness, extensive host range, wide geographical distribution, broad genetic diversity, multiple virulence factors and the ability of the causal organism to persist in soils and water (Hayward, 1991; Prior et al., 1994; Elphinstone, 2005; Denny, 2006). Mansfield et al. (2012) ranked the bacterium worldwide as the second most scientifically and economically important phytopathogenic bacterium in 2012, after Pseudomonas syringae. This ranking was voted for by plant bacteriologists associated with the journal Molecular Plant Pathology worldwide.
