CHAPTER ONE
INTRODUCTION
Tomato (Solanum lycopersicum L., 2n=24), is a natural red edible fruit which has its place in the Solanum family. It is one of the most adaptable crops in terms of agricultural significance and the third most important crop family, topped only by grasses and legumes. It is the most valuable in terms of vegetable crops (Van der Hoeven et al. 2002) and a food security crop in Ghana (Horna et al., 2007). The Tomato fruits are eaten fresh or cooked. They are added to sauces and soups as flavouring. In addition, they are processed into different forms such as candies, dried tomato fruits, powdered, paste, puree, ketchup and canned tomato fruits which are also equally important economically. As a matter of fact, it forms part of the food consumed in Ghana and this is clear in the fact that, a lot of Ghanaian dishes have tomatoes as a basic ingredient (Tambo and Gbemu, 2010).Tomato provides a rich supply of folate and with phytonutrients, the most abundant in tomatoes are the carotenoids, lycopene being the most well-known, followed by beta-carotene and gamma-carotene, photogene as well as several minor carotenoids (Beecher, 2009).Tomato is produced all over the country but the leading producing areas are located in the Northern regions (Horna et al., 2007). It is also an equally important cash crop in the outskirts of urban areas in the forest zone. A booming, money-making tomato production also takes place in the Greater Accra area and in the Akumadan and Wenchi districts in the Ashanti and Brong Ahafo regions, respectively (Obeng-Ofori et al., 2007).
PROBLEM STATEMENT
In Ghana, the focus and attention of the several interested participants in the tomato industry has routinely been on better production capacities of farmers leading to increased yields in order to provide for the growing population, with relatively less emphasis on fruit quality and
shelf life. According to Robinson and Kolavalli, (2010), tomato production seems to be falling since 2000. Unlike other countries, the tomato sector in Ghana has failed to reach its potential, in terms of increased yields, ability to reduce postharvest losses and in terms of improving the livelihoods of the many households involved in tomato production (Robinson and Kolavalli 2010).Agreeing to these authors, farmers do not only refuse to grow the right quality but also most importantly, they cannot produce the right quantity and quality to meet the demands of the tomato market. Robinson and Kolavalli (2010) also stated that average yields for tomatoes in Ghana are declining, typically, less than ten tonnes per hectare and that, due to production seasonality, high perishability, and competition from imports, some farmers are unable to sell their tomatoes, which are left to rot in their fields. The increase in postharvest losses, low yields, pooled with the high demand for tomatoes have given rise to the importation of fresh tomatoes and processed tomato products into the country (Horna et al., 2007).
In Ghana, loss of fresh fruits is projected to be about 20-50 percent (MOFA, 2010). In addition, consumers’ interest in the quality of tomato fruit products have also increased tremendously. Quality is an all-embracing term and it includes physical properties (size, shape, color, and absence of defects and decay, firmness, texture), flavor (sugar, acids, and aroma volatiles) and health-related compounds (desired compounds such as minerals, vitamins, and carotenoids as well as undesired compounds such as heavy metals, pesticides and nitrates) (Rouphael et al., 2010).Since consumers demand for more varieties of higher quality and longer shelf life, strategies committed to increasing fruit quality and longer shelf life continue to be of great interest. (Dorais et al., 2001; Gruda, 2005)
By the same token, the tomato market industry (fresh market, the fresh cut market and the food industry) have transformed in the sense that, the demand for products with better quality traits such as flavour, taste, texture, firmness and longer shelf life are sought after. This has
led to the adaptation of breeding goals towards increased quality traits which are pooled together with high yield and extended shelf life. Yet, these breeding goals meant for increasing tomato fruit quality and shelf life are virtually slow. More or less breeders have had some amount of feats increasing the quality of fruits with extended shelf life without losing other production traits due to the high variability that exist in the solanum group, to which tomatoes is an important affiliate (Caliman et al., 2010). Similarly, the use of plant modification tools to obtain genetically modified tomato plants that are high yielding with improved quality and extended shelf life, gives rise to socio-economic issues, as a result of the fact that, consumers are not willing to accept the use of genetically modified organisms in food production systems. An integrated approach to enhance fruit quality, increased productivity with extended shelf life is very important, for a doable and sustainable tomato production, particularly, in Ghana.
JUSTIFICATION
A rapid and an efficient alternative to achieve this, is by vegetable grafting. Grafting has been well-known to be an effective and environmentally sustainable method to provide improved resistance and/or tolerance to soil-borne diseases, nematodes, bacterial wilt, viruses (King et al., 2010; McAvoy et al., 2011; Cheng et al., 2012). A study by Nkansah et al., (2013) and Cheng et al., (2012) showed that grafting tomatoes enhances growth, increase yield and improves the quality of fruit. Presently, grafting tomatoes has demonstrated remarkable evidence to develop better resistance and/or tolerance against abiotic stress such as soil salinity, (Vanema et al., 2008); cold (Gao et al., 2006); heat and drought (Abdelmageed and Gruda 2009; Voutsela et al., 2012), waterlogging, (Black et al., 2003). In addition, grafting has been reported to improve the uptake of nutrients (Leonardi and Giuffrida, 2006), enhance water-use efficiency (Lee and Oda, 2003; Rouphael et al., 2008a), fruit quality (Balliu et al., 2008;Turhan et al., 2011), increases the rate of photosynthesis, and anti-oxidant enzyme
activities (He et al., 2009), thereby increasing crop yields under natural growing environment and heavy metal toxicity (Rouphael et al., 2008b; Edelstein and Ben Hur, 2006), longer harvest duration (Lee, 1994) and extended shelf life (Nkansah et al., 2013: Davis et al., 2008a, b).
This can be a positive tool that can help as a quick alternative to the socio-economic issues of genetically modified food and the relatively slow breeding methods aimed at improving fruit quality combined with increased productivity and extended shelf life (Nkansah et al., 2013). It may also be an alternative to crop management strategy to reduce postharvest losses due to rootstocks that can enhance fruit quality attributes of the scion with increased yields and extended shelf life. The advantages that vegetable grafting offers, primarily with high-value crops such as tomato (Solanum lycopersicum L.) point to the fact that growing tomatoes using grafting is a profitable enterprise.(Barret, 2011).It may be a ground-breaking method that can offer farmers, new profitable commercial prospects, better production solidity, increased fruit quality with longer shelf life and increased yields. (O’Connell, 2008).
In addition, grafting may provide an effective management tool for growers to control soil borne pathogens and cope with environmental stressors. But, if fruit quality is poorly affected as an outcome of grafting, farmers may be less likely to take on this technique. (Barret, 2011).Similarly, in Ghana, vegetable grafting is quite unknown. It has received limited attention not only for the effort needed to practice it, but also the delusion that grafting is a difficult practice (Alai, 2014) and cannot be applied to vegetables but to tree crops. The likelihood of applying grafting to improve fruit quality with longer shelf life and increased yields has not quite been investigated in Ghana. It is against this background that this research study was conceived to investigate the influence of grafting on the growth, yield, fruit quality and shelf life of tomatoes grafted unto different solanum rootstocks.
MAIN OBJECTIVES
- To develop an improved protocol for grafting of tomato that is successful and adaptable for farmers.
- To evaluate the grafting survival rate of grafted plants.
- To determine the effect of grafting on the period of flowering and harvesting.
- To identify the rootstock and scion/rootstock combination with positive impact on growth, yield, fruit quality and shelf life.
RESEARCH QUESTIONS
- Can grafting influence flowering and harvesting periods of tomatoes?
- Does grafting extend the shelf life of tomatoes?
- Can grafting produce tomato fruits with good fruit qualities?
- What is the best rootstock that has a positive impact on growth, yield, fruit quality and shelf life of tomatoes?
