Greenhouse Tomato Production for Sustainable Food and Nutrition Security in the Tropics

Abstract

Greenhouse vegetable cultivation offers one of the optimistic approaches to ensuring sustainable food and nutrition security in the tropics. Although greenhouse vegetable production is known to be costly, this system of production is gaining popularity and contributes to sustainable tomato production with improved fruit quality and productivity, which results in higher economic returns. Among vegetable crops, tomato is the most cultivated under this system. A study was conducted to identify suitable soilless media for regenerating tomato cuttings from axillary stem of tomato plants and to assess the agronomic performance of the regenerated cuttings under greenhouse condition. The tomato cuttings were raised using 100% rice husk biochar, 100% rice husk, 100% cocopeat, 50% biochar +50% cocopeat, 50% cocopeat +50% rice husk. Two tomato hybrid varieties (Lebombo and Anna) were used. Cuttings from axillary stems were compared with those raised from seed. A 2 × 2 factorial experiment was arranged in a Completely Randomized Design (CRD) with four replications. From the study, 100% rice husk biochar was found to induce root development in stem cuttings of tomato. However, no significant differences in yield and fruit quality were found between plants raised from seed and those from stem cuttings.

1. Introduction

Tomato (Solanum lycopersicum) is a flowering plant belonging to the Solanaceae family, also known as Nightshade. It is one of the most popular vegetable crops grown in the world due to its fruit quality—taste, color, flavor and nutritional content [1]. Tomato fruits can be consumed in different forms; either fresh, partially cooked or processed. Tomatoes provide carotenoids, flavonoids, phytosterols, vitamins, and minerals which are essential in human nutrition. Carotenoids are the most abundant in tomatoes with the most common one being lycopene, followed by beta-carotene, gamma-carotene, lutein, phytoene, and a few other minor carotenoids [2, 3] which have anti-cancer properties [4, 5]. It is also a great source of carbohydrates, fiber and a small amount of vitamin A, vitamin B complex (thiamin, riboflavin, and niacin) and vitamin C [6] and is also rich in iron, copper, phosphorus, manganese and potassium [7].

According to the statistical agency of the Food and Agriculture Organization of the United Nations (FAOSTAT) (2020), the world’s total tomato production is estimated at 186,821 million tonnes with a cultivated area of about 5,051,983 hectares. In comparison, there has been a 3.35% increase in production from 180,766 million tonnes in 2019 to 186,821 million tonnes produced in 2020. China is the leading producer of tomatoes in the world accounting for about 34.67%. Egypt ranked fifth in global tomato production contributing 3.6% whiles leading the tomato production in Africa estimated at 6731.22 million tonnes cultivated on an area of 170.862 hectares. In addition to Egypt, other North African countries with both tropical and temperate conditions including Algeria, Tunisia and Morocco accounted for about 2.39% of the world’s tomato production. Among the West African countries, the leading producers, Nigeria and Cameroun produced 3693.72 million and 1.246.65 million, respectively, whiles Kenya produced 1056.18 million to lead tomato production in East Africa [8]. In Ghana, according to the Ministry of Food and Agriculture (MoFA), tomato production is estimated at 420,000 tonnes in 2019 cultivated on 47,000 hectares [9, 10].

The rapid increase in tomato consumption in the tropics is one of the factors influencing emerging production practices and strategies to meet local and export demands. Thus, many tropical countries have expanded their tomato acreage to meet local needs and, in some cases, to generate foreign exchange due to the increased importance of tomatoes in food and nutrition security. Several different production systems have been used successfully in different parts of the world to produce tomatoes. For instance, in the tropics, particularly in Africa, the open field cultivation system is mostly adopted whereas, in the developed countries, there is a massive shift to controlled environment systems [11]. Tomato cultivars with a determinate or semi-determinate growth habit are typically grown in open fields which are usually for fresh consumption. This system is also distinguished by the use of either direct sowing or transplanting where a nursery is established. Currently, transplanting is commonly practiced since it ensures good stand establishment, uniformity, reduced weed competition, and improved survival rate and yield compared to direct sowing [12]. Nonetheless, open-field tomato seedlings tend to be weaker and have a lower rate of transplant survival, resulting in low yields [13]. Other constraints such as biotic (high incidence of pests and diseases) and abiotic stresses (such as drought and high temperature) pose serious threats to open-field tomato production [14]. Root-knot nematodes (including Meloidogyne incognita, M. javanica and M. arenaria) are soil-borne pathogens that cause yield losses of about 30% in tomatoes in the tropics [5]. Thus, they cause stunted growth making the tomato plants more susceptible to soil-borne fungal (such as Fusarium wilt caused by Fusarium oxysporum) and bacterial diseases (such as bacterial wilt caused by Ralstonia solanacearum) [5]. Several studies on grafting techniques to combat these soil-borne root-knot nematodes and fungal diseases have resulted in the identification of potential rootstocks such as Solanum torvum, Solanum macrocarpon, and Solanum aethiopicum [15] that confer tolerance to these soil-borne problems. However, due to the high cost of producing grafted seedlings in large quantities, grafting is not widely used in large-scale production in the tropics [16]. Furthermore, open-field tomato cultivation exposes the plants to a variety of stinging and sucking insects, such as whitefly, thrips, and aphids, which cause moderate to severe physical damage as well as contribute to the transmission of viruses [5]. High temperatures observed in open-field tomato production in the tropics cause heat stress [17]. Tomato is an extremely sensitive crop to heat stress, which can lead to total yield loss [18]. A slight increase in night temperature especially can decrease pollen viability and female fertility thereby impairing fruit set and consequently yield reduction [19].

Increased tomato consumption [20] combined with unfavorable climatic conditions necessitates the development of urgent strategies to boost production whiles improving fruit quality in the tropics. Open field tomato production is hampered by climate change-related factors such as high temperatures, drought and high incidence of pests and diseases. In recent years, greenhouse tomato farming has proven to be the most efficient method of producing high-quality fresh tomatoes for both domestic and international markets [1]. In addition, it provides the opportunity for year-round production. Indeterminate tomato cultivars are usually used in this system, allowing the harvesting period to be extended, thereby, increasing the tomato productivity and revenue as well as improving the livelihood of farmers. This chapter discusses greenhouse structures and systems, agronomic practices, postharvest handling, prospects and challenges of greenhouse tomato production in the tropics and the use of axillary stem cuttings as an alternative method of producing true-to-type tomato seedlings for cultivation.

2. Greenhouse structures

Greenhouse farming systems have been adopted in some African countries, especially in Northern Africa (Algeria, Egypt, Morocco, and Tunisia), Eastern Africa (Kenya, Ethiopia, Uganda, and Rwanda), Western Africa (Ghana) and South Africa. In Northern Africa, the greenhouse system is mainly used for vegetable production whiles that of Eastern Africa (for e.g., Kenya), is for flower production. Furthermore, in Rwanda, South Africa and Ghana greenhouse system is mainly used for tomato production [21]. In all these countries, the greenhouse specifications are dependent on the availability of construction inputs, local climatic conditions and socio-economic status [11]. Generally, the initial investment cost of greenhouse construction is very high. Galvanized metals including steel or aluminum are the preferred construction material as they are durable and require less amount of material for construction thereby increasing light transmission (Figure 1). Wood such as bamboo is an alternative material (Figure 2). Though it is less expensive, more wooden materials are required to ensure a solid and firm structure. This, however, reduces light transmission. Also, the cost of maintenance in using bamboo is relatively higher compared to those constructed from metals [21].

Figure 1.

Greenhouse of West Africa Center for Crop Improvement (WACCI), University of Ghana built from galvanized metals including steel or aluminum.

Figure 2.

Greenhouse of Institute of Applied Science and Technology (IAST), University of Ghana built from bamboo.

High sidewalls in greenhouse construction are critical for maximizing the effectiveness of natural ventilation in greenhouses with roof venting. The direct/diffuse ratio in incident light, as well as the diffusion properties of covering materials [22, 23], greenhouse design, time of day, season, and location, all influence light transmission and spatial uniformity of light intensity inside the greenhouse [11]. To promote plant growth and development, an ideal greenhouse ensures that light is evenly distributed. Again, to ensure optimal light transmission in the greenhouse, the type of covering material should be considered. These include; (1) a non-waterproof net which provides partial shade and protection against insect permeability; (2) a plastic film for protection against insects and rains and (3) a glass which is more durable and effective than plastic films. Glass is mostly used for high-tech greenhouses [21]. In most greenhouses in Africa, side nets are fixed to provide natural ventilation (Figure 3). Circulation fans (chimney) (Figure 4), misting/fogging and hosing (Figure 5) can also be used to regulate/manage the climatic conditions in the greenhouse. In addition, shade screens/nets are also used to reduce the intensity of solar radiation in the greenhouse (Figure 5) [21].

Figure 3.

Fixing of side nets (indicated with the arrow) to provide natural ventilation.

Figure 4.

Circulation fans (chimney) are fixed on greenhouses of IAST to regulate the climatic conditions in the greenhouse.

Figure 5.

Misting/fogging and hosing (blue arrow) are used to regulate the climatic conditions as well a shade net (red arrow) is used to reduce the intensity of solar radiations in the greenhouse.

2.1 Greenhouse agronomic practices

Good greenhouse crop management practices serve as a gateway for ensuring sustainable production, increasing yield and high fruit quality, concomitant with increased income generation. Before plant establishment; raising vigorous and healthy seedlings, greenhouse fumigation media selection and sterilization, fertigation and irrigation, etc. need to be considered. In addition, other recommended greenhouse cultural practices such as plant spacing, pruning, topping, training/trellising and hormone application and pollination should be performed.

2.2 Tomato varieties and propagation

The cultivation of tomatoes in the tropics is solely by using seeds; either open-pollinated (OPV) or hybrids. Hybrid seeds of tomatoes are the most suitable planting materials because of their vigor and high yielding potential [24]. Since greenhouse cultivation is done in a limited area, indeterminate hybrid tomato varieties are cultivated [11]. For instance, in Ghana, hybrid tomatoes such as Cobra, Anna F1, Lebombo, Kwando, Jaguar, Gamharr, Jarrah, Eva, Ranja, and Sodaja are being introduced by seed companies for greenhouse cultivation. Several greenhouse screenings and evaluations of exotic tomato lines are being carried out to identify adaptable high yielding types with excellent fruit quality. However, cultivating these hybrid tomatoes in the tropics could be very expensive and as such, vegetative propagation of tomatoes could be a viable option for producing true-to-type tomato hybrid planting materials [25] to ensure sustainable production.

A study was conducted to identify a suitable soilless medium for regenerating tomato seedlings from axillary stem cuttings and to assess the agronomic performance of the regenerated seedlings under greenhouse condition. Cuttings (12–15 cm long) from mature tomato plants were taken and raised using 100% rice husk biochar, 100% rice husk, 100% cocopeat, 50% biochar + 50% cocopeat, 50% cocopeat + 50% rice husk. A 2 × 2 factorial experiment arranged in a Completely Randomized Design (CRD) with four (4) replications was used. Treatments consisted of two factors; two tomato hybrid varieties (Lebombo and Anna) and planting materials (cuttings and seeds). Seedlings were also raised using 100% rice husk biochar. Seedlings and rooted cuttings were sown and transplanted 28 days respectively into pots (22 × 25 cm) half filled with 100% cocopeat. The study identified rice husk biochar (Table 1) as a suitable medium for generating vigorous and healthy tomato stem cuttings obtained from pruned axillary shoots of tomato varieties, Lebombo and Anna F1 (Figure 6). Further evaluation using tomato plants generated from seeds and stem cuttings indicated that there were no significant differences in yield (Table 2) and fruit quality (Table 3). Hence, vegetative propagation via axillary stem cuttings could be used as an alternative method of raising tomato seedlings in the tropics. Seed companies and tomato nursery production operators can collaborate to leverage this method to supply tomato seedlings at affordable rates to ensure sustainable greenhouse tomato production in the tropics.

Substrate	Root length (cm)	Survival (%)	Root volume (cm^3)	Shoot dry weight (g)	Root dry weight (g)	Total dry weight (g)
Rice husk biochar/Lebombo	16.6 b	95.8 de	1.71 b	1.74 bc	0.26 ab	1.44 b
Cocopeat/Lebombo	10.4 a	29.2 a	1.89 b	1.41 b	0.14 a	1.55 b
Biochar + Cocopeat/Lebombo	10.1 a	40.6 ab	1.66 b	0.96 a	0.15 a	1.11 a
Cocopeat + Rice husk/Lebombo	13.0 ab	45.8 ab	1.55 b	1.35 ab	0.20 a	1.52 b
Rice husk biochar/Anna	17.4 b	100.0 e	1.89 b	2.13 c	0.38 b	2.54 c
Cocopeat/Anna	10.4 a	50.0 abc	1.71 b	1.40 b	0.17 a	1.56 b
Rice husk biochar + Cocopeat/ Anna	10.7 a	83.3 cde	0.97 a	1.37 ab	0.14 a	1.51 b
Cocopeat + Rice husk/Anna	10.6 a	72.9 bcd	1.58 b	1.45 b	0.20 a	1.62 b

Table 1.

Mean Root length, Survival plants per replication, Root volume, shoot dry weight, root dry weight and Total dry weight. Means followed by the same letters within a column are not significantly different according to Fisher’s Protected LSD at 5%.

Treatments	Days to 50% flowering	Days to 50% fruiting	Total number of fruits	Fruits per plant	Fruit weight per Plant (g)	Yield (kg/ha)	Shelf life (days)
Variety
Anna	25	32 a	24 b	5 b	96.5	6431.0	5
Lebombo	27	34 b	21 a	4 a	97.6	6506.0	5
P ≤ 0.05	0.143	<0.001	0.043	0.043	0.895	0.895	0.199
Propagule
Seeds	32 b	37 b	23	5	97.6	6503.0	5
Cuttings	21 a	28 a	22	4	96.5	6434.0	5
p ≤ 0.05	<0.001	<0.001	0.689	0.689	0.902	0.902	0.019
Variety * Propagule	NS	0.021	NS	NS	NS	NS	NS

Table 2.

Days to 50% flowering and fruiting, the total number of fruits, number of fruits per plant, fruit weight per plant, yield and shelf life of tomato plants. Means followed by the same letters within a column are not significantly different according to Fisher’s Protected LSD at 5%.

Treatments	Fruit girth (mm)	Fruit length (mm)	Brix (%)	Firmness (kg/lb)	Pericarp thickness (mm)	Juice volume (cm^3)	pH	Titratable acidity
Variety
Anna	34.66 a	44.16	6.64	7.06	4.43 a	26.8	4.12	0.56 a
Lebombo	38.05 b	46.24	6.45	6.66	5.11 b	27.4	4.12	0.73 b
p ≤ 0.05	<0.001	0.036	0.567	0.438	0.050	0.874	0.947	0.028
Propagule
Seeds	36.20	44.50	6.47	6.73	4.49	27.8	4.13	0.58
Cuttings	36.51	45.90	6.62	6.99	5.05	26.4	4.10	0.71
p ≤ 0.05	0.587	0.137	0.653	0.622	0.100	0.684	0.217	0.083
Variety * Propagule
Anna * seeds	34.59	43.63	7.02 b	7.51 b	3.75 a	26.4	4.12	0.71 b
Anna * cuttings	34.73	44.69	6.27 ab	6.61 ab	5.11 b	27.3	4.11	0.41 a
Lebombo * seeds	37.82	45.37	5.93 a	5.95 a	5.23 b	29.2	4.09	0.71 b
Lebombo * cuttings	38.28	47.10	6.98 b	7.36 ab	4.99 b	25.6	4.14	0.75 b
p ≤ 0.05	0.776	0.706	0.017	0.042	0.026	0.510	0.112	0.022

Table 3.

Fruit girth, Fruit length, Brix, Firmness, Pericarp thickness, Juice volume, pH and Titratable acidity of tomato fruits. Means followed by the same letters within a column are not significantly different according to Fisher’s Protected LSD at 5%.

Figure 6.

Lebombo (A) and Anna (B) tomato seedlings raised from stem cuttings.

2.3 Substrate and sterilization

Plant roots are contained within a porous rooting medium called a ‘substrate’ or ‘growing medium.’ A suitable growing medium is required to provide root anchorage and a favorable environment for healthy root development, [26]. Growing media for greenhouse cultivation in the tropics comes in two basic types: soil- and organic-based. Field soil is the main component of the soil-based media and is the most simple and cheapest. However, it is associated with a high risk of soil-borne diseases such as bacterial wilt [21]. On the other hand, organic materials such as composted waste, peat, coconut peat/coir, sawdust, wood and bark are used to prepare the organic-based media [27]. Peat moss, vermiculite, and perlite which are premixed blends of organic and inorganic materials are commercially available. These products, however, are costly and difficult to obtain locally in the tropics, especially in Africa. Agricultural and municipal wastes, which are locally available, affordable, and environmentally sustainable, should be investigated as alternatives to commercial products in the tropics. A good soil-free substrate should have excellent chemical, biological and physical characteristics with low nutrient content, low pH, a unique combination of high-water retention capacity, high air space, lightweight, pest, and disease-free [28]. Cocopeat, a waste product obtained from the mesocarp of coconut (Cocos nucifera) fruit is most widely used in Africa and Asian countries such as the Philippines, Indonesia, India and Sri Lanka, where lots of coconuts are produced [28]. It can be combined with rice husk biochar and oyster shells. Although cocopeat is a better substitute for peat moss, high levels of natural soluble salts, sodium, and chloride are present and could cause osmotic stress to plants. As a result, to make these materials suitable for crop production, they are buffered or flushed out to remove excessive salts [29]. Sterilization of growing media is required before use, especially the locally prepared ones to prevent the introduction of pathogens and weeds in the greenhouse. Heat sterilization is the most common method (Figure 7). Although the most popular and cheapest method is solar sterilization, other improvised systems have been developed. Regardless of the system, it is critical to ensure that the entire media is exposed to uniform and adequate heat for efficient and effective sterilization [27].

Figure 7.

Dry heat from a flame used for the sterilization of growing media.

2.4 Plant spacing and density

Due to the high cost of greenhouse infrastructure, increasing plant density is one strategy for maximizing the limited space [30]. However, it is also important to plant in rows at a recommended spacing (Figure 8) to achieve an optimum yield. The required spacing between tomato plants will ensure an even distribution of resources such as water, nutrients, light, and air [31]. For example, there is more competition for light due to the overlapping and shading of leaves when plants are closely spaced [32]. The amount of light intercepted by the basal leaves could be drastically reduced, lowering the plants’ photosynthetic efficiency. Consequently, the plants may be forced to trade off their energy for stem elongation and reduced assimilate transport to developing fruits [31], thereby, causing yield reduction and poor fruit quality [33]. There have been reports of great increases in tomato yield and yield components when recommended plant spacing was used [33, 34, 35]. A recent study by Nkansah et al. [36] suggested plant spacing of 0.2 × 1.3 m for greenhouse tomato production.

Figure 8.

Tomato plants planted in rows at a recommended spacing.

2.5 Irrigation and fertigation

Adequate water supply to plants is essential for various metabolic and physiological processes such as photosynthesis, nutrient transport, and cell expansion and development [27]. In the tropics, water for greenhouse production can be obtained from rivers, ponds or reservoirs, rain, groundwater (boreholes), and municipal sources (tap water). Unfortunately, water quantity, quality and seasonal availability are not guaranteed in most tropical environments. A good water should be free from pests (such as pathogenic bacteria, fungi, weeds and pesticide contamination) and high concentrations of dissolved salts and toxic ions (heavy metals) [27]. As a result, a thorough biological and chemical analysis of water for greenhouse tomato production is required as this can affect plant health, growth and development. The chemical property, for instance, is useful for the formulation of nutrient solutions.

In the tropics, the manual irrigation system is the cheapest but does not give precision in terms of the quantity of water and nutrients applied. Gravitational fertigation in combination with drip irrigation is the commonly adopted method. The water tank is elevated (Figure 9) to allow water and nutrients to flow naturally [37]. Water and nutrients can be reused by using a recirculation system [11]. Water recirculation, on the other hand, increases the risk of spreading soil-borne diseases, necessitating the use of a disinfection unit (UV or heat treatment) [38] which can be costly. Another means of supplying water and nutrients is using a computerized system with sensors and a pre-programmed fertigation regime (Figure 10). This system, however, is reliant on a constant supply of electricity, which is a major challenge in the tropics [21].

Figure 9.

Water tanks are elevated above the level of the field to allow for the natural flow of water and nutrients.

Figure 10.

Water and nutrients are applied using a computerized system with sensors and a pre-programmed fertigation regime.

2.6 Pruning, topping and training/trellising

Tomato cultivars are divided into two categories based on their growth habits: determinate and indeterminate. Determinate tomatoes grow in a bush-like manner, reaching a fixed mature size characterized by synchronized flower formation and fruit production. On the other hand, indeterminate tomatoes grow in a vine-like manner, continuing to grow throughout the growing season and thus, having continuous flower and fruit formation [39]. The indeterminate tomato cultivars are used in greenhouse tomato cultivation [11]. Tomato vines are pruned by removing the stem suckers (Figure 11). These are stem branches or side shoots that emerge from the leaf axils which are the junctions between the main stem and the true leaf. If not pruned, these suckers will grow into full shoots with leaves, flowers, and fruits, and even regenerate new suckers. When suckers are young and small, they can be pinched or cut using pruners such as knives, scissors and secateurs. In any of these pruning approaches, it is better to ensure decontamination either by using an alcohol-based sanitizer or washing with soap to prevent the spread of pathogens [40]. Pruning can be done on weekly basis to improve or ensure efficient air circulation/aeration [41]. In addition, pruning helps to prevent the diversion of assimilates from the developing fruits thereby, improving tomato fruit quality [40, 42].

Figure 11.

Pruning of tomato vines by removing the stem suckers.

Another important greenhouse technique is topping (Figure 12), which involves cutting or pinching off the terminal bud to break the apical dominance [43]. This technique is critical because tomato cultivars for greenhouse cultivation are indeterminate types characterized by indefinite growth. Topping has been shown to improve fruit quality and yield by causing assimilates to be redistributed to developing fruits [44, 45]. In the Solanaceae family, topping improved yield and yield components in eggplant [46], pepper [47] and tomato [36]. According to Nkansah et al. [36], tomato yields were increased by topping at truss 2.

Figure 12.

Topping tomato plants by cutting or pinching off the terminal bud.

The main stem of tomato plants is positioned upright immediately after transplanting to keep the leaves and fruits from touching the ground [48], facilitate pollination, maximize light interception of the younger leaves, and increase labor efficiency in pruning and harvesting [11]. This method known as stem training/trellising (Figure 13) is necessary for indeterminate tomato cultivars. It entails securing the main stem with a twine/rope suspended from a horizontal wire about 2.5–3.2 m above the ground [11, 49]. Non-slip loops or clips are used to secure the twine’s tip to the stem’s base. The twine is then neatly wound in two or three spirals around the stem for each truss without damaging the stem [11].

Figure 13.

Trellising or training of tomato plants by securing the main stem with a twine/rope suspended above the ground.

2.7 Hormone application and pollination

Heat stress is a major problem hampering tomato production in the tropics [50]. Poor fruit set occurs in greenhouse systems where the microenvironment is not fully controlled or automated. Tomato is an extremely sensitive crop to heat stress, which can lead to total yield loss. The optimal day and night temperatures for tomato production are 21–29.5°C and 18.5–21°C, respectively. However, a slight increase in night temperature especially can decrease pollen viability and female fertility thereby impairing fruit set and consequently yield reduction [19]. Pollination and fertilization must both be completed before the fruit set can occur (Figure 14) [51]. Under heat stress, however, these processes are disrupted, resulting in flower abortion and flower drop [50]. Unfortunately, the molecular mechanisms underlying tomato fruit set are unknown, despite the fact that exogenous application of auxin and gibberellin to the tomato stigma improved tomato fruit set. Bypassing pollination and fertilization, auxin or gibberellin can stimulate tomato fruit development (cell division and expansion) [51]. As a result, using these hormones can help increase greenhouse tomato production by increasing fruit set and yield [52]. The coordinated mechanism of auxin, gibberellin, and cytokinin has been investigated for the development of parthenocarpic tomato fruits [53], which improves fruit quality. Although this may be labor intensive, the high returns from increased productivity and improved fruit quality can compensate for this.

Figure 14.

Pollination and fertilization of tomato flowers before fruit set.

2.8 Greenhouse pest and disease management

One of the reasons for the rise in greenhouse tomato production in the tropics is the benefit of reducing pest and disease outbreaks, which can affect plant growth and development, resulting in lower yields and poor fruit quality. To control pest or disease outbreaks, an integrated pest management approach including cultural, biological and chemical measures (Figure 15) is used. Because prevention is the best approach, ensuring good environmental practices is an important first step [54]. Regular cleaning and washing of the greenhouse and its equipment with disinfectant (such as bleach) and fumigation prior to the start of the production cycle are examples of best practices. Another strategy is to keep a close eye on the crops in the greenhouse in case of a pest or disease outbreak [55]. Pheromone traps and sticky cards (Figure 16), for example, are used to trap, detect, and determine pest population thresholds of pests such as leaf miners, whiteflies aphids and thrips [8, 55]. A comprehensive pest management guide for tomato production is available [8]. Pruning, trellising, and proper plant density and spacing ensure good aeration. Avoidance of wet floors by preventing irrigation water spillage helps to reduce the creation of a microclimate that promotes disease outbreaks [55].

Figure 15.

Chemical application for the management of pest and disease in greenhouse vegetable production.

Figure 16.

Pheromone traps (A) and sticky cards (B) are used to trap, detect, and determine pest population thresholds in greenhouses.

2.9 Harvesting and postharvest handling

Harvesting of greenhouse tomatoes is usually done at the breaker of color or when the fruit is orange-red, by handpicking. Thus, greenhouse tomatoes are typically harvested riper than fresh market field-grown fruit, making them more susceptible to mechanical injuries due to their softer nature and shorter shelf life than mature-green fruit. Greenhouse-grown fruit harvesting is done twice or three times per week as it reaches the appropriate stage of fruit development [11]. Prior to temporary storage, tomato fruits are sorted and graded. Grading allows a grower to serve different qualities at different prices to different markets, such as a supermarket and a wet market. As such, good packaging is required to reduce losses during transportation [21]. Harvested tomato fruits are chilling sensitive. Breaker fruits can be stored at 10–12.5°C for a week whiles orange-red at 7–10°C for 3–5 days [11]. Even though greenhouse tomatoes are more expensive than field-grown fruits, they are primarily produced for local consumption in the tropics. On the other hand, Northern African countries (such as Egypt and Morocco) and South Africa, produce greenhouse tomatoes for export to Europe [21].

3. Prospects and challenges of greenhouse tomato production in the tropics

3.1 Prospects

In the tropics, greenhouse tomato production has the potential to create attractive jobs for youth and women in particular [56]. Greenhouse training programs have been introduced in West Africa, particularly in Ghana, to target entrepreneurs and young graduates to learn how to grow vegetables in greenhouses [57].

The increased demand for greenhouse tomatoes, owing to their superior fruit quality, benefits growers by earning appreciable income to improve their livelihoods [58]. People in urban and peri-urban cities have gradually accepted and are willing to pay more for greenhouse tomatoes, despite the fact they are more expensive than those grown in the field [59].

Greenhouse tomato production supplements local tomato production, which is primarily a field-grown system that is affected by biotic and abiotic factors. Thus, the introduction of greenhouses in the topics has helped to ensure year-round tomato production and supply of high-quality fruits, ensuring sustainable food and nutrition security [60]. Also, there will be a constant supply of tomatoes to the processing industries for various industrial activities.

In addition, the greenhouse tomato production system contributes to the economic maximization of limited land and other resources [61]. This system, for example, ensures efficient water and nutrient supply to the plants while reducing losses such as leaching, which is common in field-grown systems. Also, unproductive lands, rooftops and concreted areas can be utilized for greenhouse tomato cultivation [62].

Another advantage of greenhouse tomato production is the complete control over indiscriminate agrochemical (pesticides, fungicides and weedicides) application. Strict adherence to greenhouse agronomic practices and integrated pest management systems eliminates traces of these agrochemicals on tomato fruits, which are harmful to human health [58]. This could promote the use of traceability systems to encourage the export of greenhouse tomato fruits in order to generate foreign exchange to boost tropical economies [63].

The introduction of greenhouses has opened up new areas in the tropics for academic and research work. To improve greenhouse tomato cultivation in the tropics, researchers should look into areas such as greenhouse agronomic practices, breeding for tropics-adapted greenhouse tomatoes, commercial adoption of grafting techniques for soil-based greenhouse cultivation, development of tropical soilless media and nutrient solutions, assessment and availability of raw materials for greenhouse constructions and so on.

3.2 Challenges

The initial cost of constructing a greenhouse is high which deters average income entrepreneurs to venture into greenhouse tomato production [64]. In addition to this, accessibility to credit facilities is difficult [65]. Lack of greenhouse technical know-how has also hindered the adoption of greenhouse tomato production in most tropical countries. In some areas, there are no greenhouse training centers for hands-on training to fully equip trainees in greenhouse design, construction, repair and maintenance and cultivation [66].

The unavailability of adaptable greenhouse tomato cultivation possess a major challenge. There is a high influx of imported tomato hybrids into various countries, however, some of these tomato hybrids are not adequately evaluated or screened to identify the promising candidates for further evaluations and official release. In addition, the available tomato hybrids are generally expensive for the local growers and may have fruit quality characteristics which are not preferred by the local market [45].

There is also a lack of greenhouse cultivation inputs and important resources. For instance, poor water quality and quantity prevent seasonal and year-round greenhouse tomato cultivation. Also, the unavailability of quality soilless substrates is a major challenge [58].

4. Conclusions

In conclusion, greenhouse tomato production is a promising technology that can ensure sustainable food and nutrition security in Africa. The selection of the proper greenhouse structure and system as well as the adoption of the appropriate agronomic practices and postharvest handling techniques would ensure enhanced tomato production under greenhouse condition in the tropics. Our research findings point to tomato cuttings as a viable source for raising planting material for tomato cultivation in the developing countries. The yields and fruit quality obtained from the use of seedlings versus stem cuttings were comparable.

It is therefore essential to encourage scientific research about greenhouse production in Africa to foster its adoption. Greenhouse tomato production has the potential of creating jobs and increasing income generation thereby improving the livelihood of the people in the greenhouse tomato value chain.

Conflict of interest

The authors declare no conflict of interest.