Introduction

Solanum macrocarpon is a species of flowering plant in the Solanaceae family, which is native to Africa. It belongs to the genus Solanum, which includes over 1,400-1,500 species of plants, including popular foods such as tomatoes, potatoes, and peppers. Within the Solanum genus, S. macrocarpon is part of the Leptostemonum clade, which includes other edible plants like S. aethiopicum, S. anguivi, and S. torvum.

Gboma eggplant is a highly variable plant species, with different varieties grown and consumed throughout Africa. The plant is a shrub that can grow up to 2 metres tall, and its leaves, young shoots, and fruits are the most commonly consumed parts. Gboma eggplant leaves, and young shoots are cooked and consumed as a vegetable. These leaves are used in a variety of dishes, including soups, stews, and sautés, and are known for their rich nutritional content. The taste is more or less bitter and very much liked. The leaves can either be steamed as practised in Uganda or fried in oil with onions. They are a good source of vitamins A and C, calcium, and iron, making them an essential dietary component for many people in Africa.
In addition to its use as a leafy vegetable, Gboma eggplant also produces fruit commonly consumed raw or cooked. The fruit is large and has a long storage life of up to three months, making it an important food source in areas with limited access to fresh produce. It can be stuffed or used as a pasta substitute, and is an essential ingredient in many traditional African dishes. In addition to its culinary uses, Gboma, has been used in traditional medicine for treating a variety of ailments such as skin infections, asthma, rheumatic diseases, constipation, diabetes, and weight reduction. Its uses vary across different African countries. In Sierra Leone, the boiled leaves are chewed to treat throat problems, while in Kenya, the crushed leaves are taken to treat stomach problems. The fruits are consumed in Nigeria as a laxative and to treat cardiac diseases. Additionally, the juice of the boiled fruit is consumed in Kenya to get rid of hookworms. Recent studies have suggested that Gboma eggplant may have anti-inflammatory and antioxidant properties, which makes it a promising candidate for further research. In Ghana and Nigeria, the fruits of the Gboma plant are considered symbols of blessings and fruitfulness and are often offered as tokens of goodwill during social events such as visits and marriages.
(Bukenya. & Bonsu, 2004, Specialty produce, 2021, Food from Africa., 2021).

General Information (Species account and Ecological conditions)

Species account

Gboma eggplant plant can grow up to 1.5 meters tall. It has smooth stems or stems with small hairs, and its leaves are simple and alternate. Leaves can grow up to 46cm long and 30cm wide and may have parts that stick out up to 8cm long. The flowers have five or six parts, and the female flowers are bigger than the male flowers. The fruit is round and can be green when it's young and yellow or brown when it's ripe. The fruits are of different shapes and colors depending on the choice of the farmer. The size, usefulness, and shape of African eggplant lead to its four main classifications; Aculeatum, Gilo, Kumba, and Shum. The first leaves are narrow and almost without stems (Schippers, 2000).

The Gboma eggplant plant can be divided into two main groups: the leafy group and the fruity group. The leafy group is commonly found in West and Central Africa, while the fruity group is mainly found in the humid coastal areas of West Africa, with less frequency in East Africa. However, the distinction between the two groups is not strict, as the leaves of the fruit varieties are also consumed.
The leafy group can be recognized by its mature fruit, which can be yellow, brown, or orange-brown in color. These fruits are often cracked and filled with seeds, making them bitter and unsuitable for eating. The leaves of this group are relatively small, not divided into lobes, and usually don't have thorns.
On the other hand, the fruity group has larger fruit with a round shape and a smooth, uncracked surface. The calyx (the part at the base of the fruit) is soft and wide, and the fruit has fewer seeds. The large leaves of this group are edible when young and may have prickles, usually along the midrib or larger veins. Some leaves may also have hairs, especially along the veins and on the lower surface.  (Schippers, 2000).

Ecological information 
Optimal growth of Gboma eggplant is dependent on favourable climatic conditions, proper soil management, and efficient water management. Climatic conditions suitable for growing Gboma eggplant include a tropical sub-humid climate with a temperature range of between 20°C to 30°C. It requires well-drained soils with good organic matter content, a pH range of 5.5-6.5, and moderate soil fertility. 
Water management is critical for Gboma eggplant cultivation. Irrigation should be done at optimal intervals and depths to ensure the crop receives the required amount of water to support growth and development. Organic matter can be used to improve soil water retention capacity and reduce water loss through evaporation. Proper water management reduces the risk of waterlogging, which can negatively affect the growth and yield of Solanum macrocarpon.

Agronomic aspects

a. Seed sources
African eggplant seeds can be obtained from seed companies or directly from farmers. It is advisable for farmers to produce their own seeds to ensure self-sufficiency. When cultivating plants for seed production, it is best to isolate them from other solanaceous plants such as tomatoes and potatoes, preferably on soils that have not recently grown these crops. For optimal seed production, a wider seed spacing of 60 cm x 20 cm is recommended, resulting in a seed rate of 1.5 kg seed/ha (Kalb et al., 2002).. 

b.  Planting 
African eggplants are typically cultivated from seeds, which can be directly sown or started in a nursery. They can be grown alone or as intercrops with other food crops. To ensure optimal growth, it is important to properly prepare the land. This involves digging to loosen the soil and remove any hardpan. In drylands, terracing is recommended to retain rainwater within the farm. After digging, well-decomposed manure is incorporated into the soil to create a well-drained structure with fine particles.
The prepared land is then divided into beds, preferably one meter wide. In wet and humid areas, raised beds are suitable, while sunken beds work well in dry areas or seasons. Additionally, farmyard manure or compost is applied and thoroughly mixed. To sterilize the soil, prevent soil-borne diseases, and control weeds, a layer of grass or similar material can be burned on top of the bed. This also adds a nutrient-rich ash, especially potash, to the soil. (Kalb et al., 2002).

c. Nursery Bed management 
African eggplants thrive when initially grown in a nursery bed and later transplanted to the main garden. To create the nursery bed, select a location away from drainage channels or slopes, yet accessible to a water source. In humid areas, raise the nursery bed at least 20cm above the ground to prevent waterlogging, while in arid and semi-arid regions, make it sunken to reduce water loss. Loosen the soil and incorporate well-decomposed manure before sowing the seeds.
Seeds can be sown by broadcasting or in rows (row planting). Mix the seeds with fine soil at a ratio of about 1:10 (seed to soil). If broadcasting, combine the seeds with dried poultry manure, ash, fine soil, or sand at a ratio of 1:10 to 1:20. Create 2cm deep furrows spaced 15cm apart. Sow the seeds and lightly cover them with soil. Apply mulch and water through it, preferably in the evening. Within 10-14 days, the seeds will germinate. Remove the mulch from the seedlings and place it between the rows. Provide shade over the nursery using light materials that allow sunlight to reach the seedlings.
Transplant the seedlings after 1-1.5 months of germination. Space the plants 1m apart between rows and individual plants. Prior to transplanting, add two handfuls of well-decomposed manure per planting hole (Kalb et al., 2002).

d. Transplanting and spacing 
To ensure successful transplanting, use the water stress method to harden off the plants. Gradually reduce watering and expose the seedlings to outdoor conditions over 4-6 days before transplanting. Select strong and disease-free seedlings for transplantation. Late afternoon is the preferred time for transplanting. Transplant when the seedlings are around 8 to 15 cm tall with six true leaves, typically after four weeks.
Before transplanting, thoroughly water the soil. Dig holes 30 cm x 30 cm apart and add well-decomposed manure to the holes. Alternatively, an initial spacing of 20 cm within the row and 40 cm between rows can be used. Ensure the roots are covered with soil and gently pressed for good root-to-soil contact. Avoid damaging or breaking the roots during transplanting. A hand fork can be used to carefully remove seedlings from the nursery bed, and if needed, a basin with water can be used for transportation. Replace any missing plants to maintain an even crop (Kalb et al., 2002).

Direct sowing
Direct sowing either in irrigation systems or rain-fed results in taller plants and when there is adequate room, in more and larger leaves and branches and better dry-matter content when compared with transplanting. The seeds are planted by broadcast or in lines. If by broadcast, one should ensure even distribution. A seed rate of 1.5kg/ha is used (Kalb et al., 2002).

Row planting 
To use the furrow gardening method, start by making shallow furrows with a stick or finger, leaving about 30 cm between rows. Drop your seeds evenly as you move at a steady speed along the row. After sowing, the bed should be covered with a thin layer of soil to prevent ants from carrying away the seeds or birds from picking them. Typically, it takes 5-10 days for the seeds to germinate. Water your seeds using a watering can and avoid washing them out of the furrows. Once the plants have germinated, the bed can be mulched with tall grass or a similar material to retain moisture, which can be removed later. 
Thinning
After germination, the strongest plants are retained, and the others removed for transplanting or consumption. Thinning should be done with the type of nightshade and hence its growth habit and size in mind. Four weeks after planting, the crop is thinned (starting with taller ones) to leave a spacing of about 15 cm from one plant to the other during the dry season. Thinning can be continued on regular basis until the desired spacing is reached, which depends a lot on the species. During thinning, the whole plant is uprooted. Thinned plants should be brought to the marketplace with their roots attached and moistened to retain their fresh appearance.

Harvest and post-harvest practices

Harvesting

The Gboma leafy vegetable is typically harvested 6-9 weeks after transplanting, generally within a week of flowering. Periodic leaf collection continues throughout the year, depending on water availability. During the initial harvest, the entire shoot, including the terminal bud and sometimes the flowers, is picked. Subsequent harvests occur every two weeks and involve gathering side shoots. This method promotes ongoing growth, allowing for extended harvesting. For Gboma eggplant, unripe fruits should be harvested 2-4 months after planting for consumption, while ripe fruits should be collected a month later for seed extraction (Bukenya & Bonsu, 2004).

Post harvesting practices 
Proper post-harvest practices are important to ensure the longevity and quality of Gboma eggplant leaves and fruits. Freshly harvested leaves and fruits can be easily transported and kept in good condition for an extended period, particularly in shaded or cool areas. To maintain the freshness of the leaves, sprinkling them with water can be effective. This not only helps to keep the leaves hydrated but also slows down their respiration rate, which can ultimately extend their shelf life.
There are various methods available for preserving vegetables. One such way is through local refrigeration. This involves constructing a 1-meter-high brick structure with two separate walls, filled with sand or charcoal dust in between. The structure should be placed under a shade and an elevated water tank installed nearby. A small pipe should be used to keep the sand or charcoal dust moist, and racks placed inside to hold the vegetables.
Another method of preservation is through the use of a pot. After harvesting the vegetables, they can be stored in a pot placed under a shade. The pot should be surrounded by sand or charcoal dust, which should be kept moist by regularly adding water. It is important not to pour water into the pot.
A third method is through the use of a solar dryer. This involves drying the vegetables using solar dryers and then packaging them for future use during the dry season. Although vegetables can be dried traditionally under the sun, using solar dryers is a more efficient method as it helps to retain more nutrients (Bukenya & Bonsu, 2004).

Value addition, value chain and markets 

Solanum macrocarpon is a widely consumed vegetable in Africa, commonly found in local markets. It is highly nutritious and valued as a food source for both humans and animals. While statistics on its production and trade are not available, some Gboma fruits are exported from countries like Senegal and Uganda to European markets such as Paris and Brussels. Similarly, Santo Domingo and Suriname export gboma fruits to the United States and Europe, including Amsterdam.
(Bukenya R. & Bonsu, K.O., 2004)

Nutritional value and recipes 

Solanum macrocarpon leaves offer a range of significant nutrients and associated benefits. They contain a moderate amount of protein, supporting muscle growth, repair, and cellular functions. The high fiber content promotes digestion, regular bowel movements, and can aid in weight management while supporting heart health. These leaves are also a notable source of calcium, contributing to the development and maintenance of healthy bones, teeth, and facilitating muscle function and nerve transmission. The leaves have a significant amount of iron, necessary for red blood cell production, preventing iron-deficiency anaemia, and supporting oxygen transport throughout the body.
Being a good source of potassium, these leaves help maintain fluid balance, support nerve function, and assist in muscle contraction. 
Additionally, Solanum macrocarpon leaves contain vitamin A, vital for vision health, immune function, and maintaining healthy skin. Vitamin A also acts as an antioxidant, protecting cells from damage. Furthermore, the presence of vitamin C in these leaves contributes to a strong immune system, collagen synthesis, antioxidant activity, and aids in the absorption of iron from plant-based sources. They also contain various B-vitamins, including thiamine, riboflavin, vitamin B6, and folate, which play essential roles in energy metabolism, neurological function, and the synthesis of DNA and red blood cells.
 

Table 1: Approximate nutritional content of 100 g of African eggplant (Solanum macrocarpon) leaves

Source: (Nutrient data): FAO/Government of Kenya. 2018. Catalogue of Selected Indigenous Vegetables in Ghana. (Oboh et al., 2005)
$ Draining the water several times leaches away water soluble nutrients significantly.
a Lewis, J. 2019. Codex nutrient reference values. Rome. FAO and WHO
b NHS (refers to saturated fat)
c https://www.hsph.harvard.edu/nutritionsource/water/
d British Heart Foundation
e FDA
f NIH
g Mayo Clinic

Complimentary Recipes
a.    African eggplant leaves with pumpkin kernels
Cameroon recipe. 
Ingredients 
• 3 bunches African eggplant leaves 
• 1 g limestone 
• 4 cups (800 g) of pumpkin kernels/seeds 
• 1 kg meat 
• Dried shrimps (optional) 
• 1/4 refined vegetable oil 
• 1 clove of garlic, 1 small piece of ginger, 2 large onions, 1 large leek, 1 stalk celery, two yellow peppers 
• 15 - 20 grains white pepper 
• Seasoning (stock cubes, salt, pepper) 

Preparation 
•    Sort, wash, and cut the African eggplant leaves into small pieces.
•    Dilute 1 g of limestone in a cup of hot water, filter to remove grit, and pour the liquid into a pot with 1.5 - 2 litres of water. Add the leaves and cook until soft, stirring occasionally.
•    Once the leaves are soft enough, remove them from the heat, strain, and rinse with cool water.
•    Squeeze out excess water and shape the leaves into balls.
•    Boil the meat and prepare onions, leeks, and celery by slicing them.
•    Peel ginger and garlic, clean peppers, and crush them together.
•    Chop shrimps and grind pumpkin kernels/seeds.

Cooking
•    Heat some vegetable oil in a pan and sauté onions until brown.
•    Add leeks and cook for 3-5 minutes.
•    Add celery and cook for a few more minutes.
•    Mix garlic, ginger, and peppers, along with boiled meat and half a glass of water. Simmer for 10 minutes.
•    Add vegetables, stir, and pour a glass of water. Cover the pot.
•    Once the vegetables start boiling, add pumpkin powder and simmer for 10 minutes without stirring.
•    Stir the pumpkin powder into the vegetables.
•    Heat two spoonfuls of vegetable oil in another frying pan. Quickly brown the chopped shrimps for 5-10 seconds and pour over the vegetables.
•    Immediately cover the pan to allow the vegetables to absorb the aroma.
•    Boil for a few minutes.
•    Season with a teaspoon of ground white pepper and adjust the seasoning to taste.

Serving: Serve with tubers of your choice.
Source: (Chagomoka et al, 2004)

b.    Ngogwe

Ingredients
•    120 g African eggplant
•    80 g okra fruits
•    100 g carrots
•    80 g onions
•    100 g tomatoes
•    2 eggs
•    ½ cup cooking oil
•    Salt to taste
•    1 cup water
Preparation
•    Wash, peel and chop the tomatoes
•    Clean and chop the onions
•    Wash, peel and cut lengthwise the carrots
•    Wash and trim the pedicles of African eggplants
•    Wash and trim the end tips of the okra
•    Fry the onions lightly, add tomatoes, salt and stir until soft
•    Add okra, African eggplant, carrots and stir well
•    Whisk the eggs with 1 cup of water and add while stirring slowly for 5 minutes
•    Season to taste and serve while hot as a relish

Source: Traditional recipes. (AVRDC & IPGRI., 2006)

c.    African eggplant sauce 
(Kamga & Mecozzi, n.d.)
Ingredients 
• 1 kg African eggplant 
• 1 kg chopped meat or crumbled smoked fish
 • 2 large onions 
• 1/4-liter refined vegetable oil 
• 2 large tomatoes 
• 3 tablespoons mayonnaise 
• 1 clove garlic, 1 stalk celery, 1 large leek, two yellow peppers
 • Seasoning (stock cubes, salt, pepper

Preparation 
•    Wash the African eggplant, 
•    Soak for few minutes in hot water and remove the skin. 
•    Cut each fruit into four pieces. 
•    Crush together garlic, celery, leeks, peppers and tomatoes. Finely slice onions.
Cooking
•    Place a pan on the fire, add the vegetable oil, and heat. 
•    Brown the sliced onions in the oil. 
•    Add the crushed garlic, celery, leeks, peppers and tomatoes and simmer. After 3-5 minutes, add the meat or fish, and cook until done. Add African eggplant fruit and cook for about 30 minutes to reduce the amount of water. 
•    Add mayonnaise, salt and simmer to obtain the consistency you prefer. Adjust the seasoning as needed. 
•    Serve with rice or tubers of your choice.