Watermelon is a refreshing and succulent fruit known for its vibrant red or pink flesh, dotted with black seeds or seedless varieties. With its high water content, typically around 92%, watermelon is a hydrating treat, especially during hot summer days. The crisp and juicy texture, coupled with a sweet flavour, makes it a popular choice for cooling down and satisfying sweet cravings. The green rind, often striped or speckled, encases the sweet interior, and the fruit is typically enjoyed in slices or diced chunks. Besides being a delicious snack, watermelon is a good source of vitamins A and C, and it contributes to overall hydration due to its water content. Whether enjoyed at picnics, barbecues, or as a simple snack, watermelon remains a quintessential summer fruit.
Watermelon
The history of watermelon dates back thousands of years, originating in the hot and arid regions of Africa. The first recorded cultivation of watermelon can be traced to the Nile Valley in ancient Egypt, where it was depicted in hieroglyphics on walls of tombs and mentioned in ancient texts. From Egypt, the cultivation of watermelon spread through trade routes into other parts of Africa, the Middle East, and eventually to Europe. In the 10th century, watermelon made its way to China, and by the 17th century, it had reached the Americas through European colonisation. Over time, selective breeding led to the development of sweeter and seedless varieties. Watermelon gained popularity as a refreshing and nutritious fruit, particularly in warm climates. Today, it is enjoyed globally, with numerous varieties and uses, and remains a symbol of summertime refreshment.
Botany and Taxonomy
Watermelon plants are annuals, completing their life cycle within a single growing season. They are characterised by their sprawling vines with lobed leaves that have a coarse texture. The plant exhibits a monoecious reproductive system, meaning it produces both male and female flowers on the same plant. The large yellow flowers are typically unisexual, and pollination is often aided by bees.
The growth cycle of the watermelon
Watermelon, scientifically known as Citrullus lanatus, is a member of the Cucurbitaceae family, which includes other well-known fruits and vegetables such as cucumbers, pumpkins, and squash. This family is characterised by its vining or trailing growth habit and is part of the order Cucurbitales. The genus Citrullus encompasses various species, but the cultivated watermelon belongs to the lanatus species.
Taxonomy of watermelon.
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Scientific Classification |
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Kingdom |
Plantae |
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Phylum |
Angiosperms |
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Class |
Rosids |
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Order |
Cucurbitales |
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Family |
Cucurbitaceae |
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Genus |
Citrullus |
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Species |
C. lanatus |
Ecology
A. Soil
Watermelon plants thrive in well-drained, loamy soils that offer a balance of texture, fertility, and moisture retention. Ideally, the soil should be loose and friable to allow for proper root development and ease of water movement. A pH range between 6.0 and 7.5 is generally preferred, indicating a slightly acidic to neutral environment. This pH range facilitates nutrient availability and absorption, crucial for the healthy growth and fruit development of watermelon.
Good drainage is a key factor in watermelon cultivation, as these plants are susceptible to root rot and other diseases in waterlogged conditions. Sandy soils, which naturally have excellent drainage, are often favoured for watermelon cultivation. However, incorporating organic matter, such as well-rotted compost or aged manure, into heavier soils can improve their drainage and overall structure.
While watermelons are known for their high water content, excessive moisture in the soil can lead to issues such as fruit cracking and reduced fruit quality. Therefore, a balance must be maintained to ensure an adequate water supply without waterlogging. Drip irrigation systems or soaker hoses are commonly used to deliver consistent moisture to the roots without wetting the foliage excessively, reducing the risk of fungal diseases.
In terms of fertility, watermelon plants benefit from soils rich in organic matter and essential nutrients. Before planting, incorporating a balanced fertiliser with a slightly higher phosphorus content can promote strong root development and fruit set. Regular soil testing is advisable to monitor nutrient levels, allowing for adjustments based on the specific needs of the growing watermelon plants.
B. Climate
Watermelons are warm-season crops that thrive in regions with a hot and sunny climate. A temperature range between 21°C to 32°C is considered ideal for their growth and development. These plants are highly sensitive to frost, and exposure to temperatures below 10°C can lead to chilling injury, adversely affecting plant growth and fruit production. Therefore, watermelon cultivation is typically limited to areas with a frost-free growing season.
Sunlight is a crucial factor in the successful cultivation of watermelons. These plants require full sunlight, meaning they should receive at least 6 to 8 hours of direct sunlight daily. Adequate sunlight is essential for photosynthesis, promoting healthy foliage, and ensuring the development of sweet and flavourful fruits. In regions with extended periods of sunlight, watermelons tend to thrive, provided other environmental conditions are favourable.
Watermelons are well-suited to regions with low humidity, as high humidity levels can contribute to the development of fungal diseases. However, they can still be grown in areas with higher humidity if proper measures are taken to manage moisture around the plants. Adequate spacing between plants, well-drained soils, and strategic irrigation practices can help mitigate the risk of humidity-related issues.
In terms of rainfall, watermelons benefit from consistent and even moisture, particularly during the fruiting stage. However, excessive or uneven rainfall can lead to problems such as fruit cracking and diseases. In areas where rainfall is unpredictable, supplemental irrigation becomes crucial to maintain optimal soil moisture levels.
Morphology and Characteristics
A. Stem and Vines
Watermelon vine grows low on the ground
The stems of watermelon plants are typically characterised by their vigorous growth and tend to be angular and ridged. These stems emerge from the base of the plant and give rise to both primary and secondary vines. The vines of watermelon plants exhibit a trailing or creeping growth habit, sprawling across the soil and covering a considerable area. They are covered with coarse, hairy structures that help deter pests and reduce water loss through transpiration. These vines can extend several feet from the central plant, requiring ample space for unrestricted growth. The tendrils produced by the vines aid in climbing and provide support, allowing the plant to latch onto nearby structures or vegetation. The vines produce large, lobed leaves that provide an expansive surface area for photosynthesis, contributing to the plant’s energy production and the development of robust fruits.
The stems of watermelon plants house the vascular system responsible for the transport of water, nutrients, and sugars throughout the plant. The efficient vascular system enables the rapid growth and development of both the vines and the fruit. As the watermelon fruit develops, the stems undergo an increase in girth to support the additional weight.
Watermelon vines exhibit determinate growth, meaning that they have a predetermined length of growth before they produce flowers and set fruit. Once the vines reach maturity, they focus energy on fruit development. Pruning, trellising, or providing adequate space are common practices to manage the sprawling growth of watermelon vines and enhance air circulation, reducing the risk of diseases.
B. Inflorescence and Flowering
Male and female flowers of watermelons
Watermelon inflorescence and flowering are critical stages in the reproductive cycle of the plant, marking the onset of fruit development. The watermelon plant produces distinct male and female flowers on the same plant, a characteristic known as monoecy. The male flowers typically appear in greater numbers and precede the female flowers. They are borne on long, slender stalks and consist of stamens, which are the male reproductive organs responsible for producing pollen. The female flowers, on the other hand, are identified by the presence of a miniature fruit structure at the base, known as the ovary. The ovary contains the potential seeds, and when fertilised, it develops into the iconic watermelon fruit. Female flowers are fewer in number compared to male flowers and are borne on shorter stalks. Watermelon inflorescence occurs in the form of axillary racemes, where clusters of flowers develop along the vine in the leaf axils. The plant’s energy is directed towards flower production during this stage, and the inflorescence contributes to the overall aesthetic of the watermelon plant. The flowers themselves are typically bright yellow, attracting pollinators with their vibrant colour and nectar.
Watermelon plants exhibit indeterminate growth, meaning that they continue to produce new flowers throughout the growing season. This extended flowering period allows for a staggered and prolonged harvest. The timing of flowering is influenced by environmental factors such as temperature, sunlight, and soil conditions. Warm temperatures and an abundance of sunlight are particularly favourable for robust flowering and fruit set.
C. Pollination and Fruit Set
Watermelon pollination is a crucial phase in the reproductive cycle, determining the successful development of the fruit. Watermelon plants are primarily pollinated by insects, with bees being the most effective pollinators. The bright yellow colour of the flowers attracts bees, which collect nectar and inadvertently transfer pollen between male and female flowers. While watermelon plants are capable of self-pollination, the cross-pollination facilitated by bees generally results in a more reliable and consistent fruit set. Adequate spacing between plants and the provision of a pollinator-friendly environment contribute to successful pollination.
The male flowers of watermelon bear stamens that produce pollen, while the female flowers have an ovary at the base, which contains the potential seeds. For successful pollination and fruit set, pollen must be transferred from the male flowers to the stigma of the female flowers. Once the pollen reaches the stigma, it travels down the style to fertilise the ovules within the ovary. This fertilisation process triggers the development of the watermelon fruit.
Environmental factors play a significant role in watermelon pollination and fruit set. Warm temperatures and sunny conditions are favourable, promoting the activity of pollinators and ensuring the viability of pollen. Adequate soil moisture is also crucial during this period to support healthy flower development and facilitate the movement of pollen.
Fruit set in watermelons is marked by the enlargement of the ovary into a developing fruit. The fertilised ovules within the ovary transform into seeds, and the surrounding tissue forms the flesh of the watermelon. The rate of fruit set can be influenced by factors such as the availability of pollinators, the number of viable pollen grains, and the overall health of the plant. Uneven fruit set can occur if pollination is limited, leading to differences in size and maturity among the fruits. Growers often take measures to optimise pollination and fruit set in watermelon crops. This may include providing a pollinator-friendly environment, avoiding the use of pesticides harmful to bees, and ensuring proper spacing between plants to enhance air circulation and facilitate pollinator movement. Additionally, some varieties of watermelon are bred for seedlessness, which involves producing fruits with underdeveloped, soft seeds through specific breeding techniques.
Seedless watermelon
D. Fruit
Botanically classified as a pepo, which is a type of berry, the watermelon fruit features a thick rind, fleshy interior, and internal seeds. The rind, often green with varying patterns, protects the succulent flesh and seeds within. The botanical term “pepo” is used for fruits with a hard outer layer derived from the ovary wall, characteristic of many fruits in the gourd family to which watermelon belongs.
The fleshy interior of the watermelon is the edible part of the fruit and is classified as the mesocarp. This portion is rich in water, accounting for over 90% of the fruit’s weight, and gives watermelon its hydrating and refreshing qualities. The colour of the mesocarp can vary among cultivars, with common hues being pink and red, attributed to pigments like lycopene. In some varieties, the mesocarp can also be yellow or orange, contributing to the visual diversity of watermelon fruits.
Watermelon seeds, typically brown or black, are embedded within the flesh. Traditional varieties contain mature, hard seeds, while modern seedless cultivars are developed through selective breeding techniques. Seedless watermelons have small, soft, and often edible seeds or are entirely devoid of seeds. The presence or absence of seeds is a key botanical distinction, influencing both culinary preferences and the plant’s reproductive characteristics.
Cultivars and Breeding
Watermelon cultivation has led to the development of numerous cultivars, each with distinct characteristics, Flavors, and adaptations. Cultivars can vary in size, shape, colour, seed content, and even taste. Traditional varieties often have black seeds, while modern breeding techniques have given rise to seedless varieties, which are increasingly popular for their convenience. Seedless cultivars are produced through complex breeding processes involving controlled pollination and the incorporation of specific genetic traits.
One prevalent breeding technique for creating seedless watermelons is triploidisation. Triploid watermelon plants have three sets of chromosomes instead of the usual two. The development of triploid seeds involves crossing a diploid (normal) watermelon with a tetraploid watermelon, resulting in a seed with an uneven number of chromosomes. These triploid seeds are then planted, and the resulting plants are sterile, producing fruits without mature seeds. This process ensures seedlessness while maintaining the desirable characteristics of the parent plants.
Apart from seedlessness, breeders focus on enhancing other traits such as flavour, texture, and disease resistance. Some cultivars are bred for specific climates or growing conditions, adapting to varying temperatures, soil types, and pest pressures. Disease-resistant cultivars help mitigate the impact of common watermelon diseases, ensuring a healthier and more reliable harvest.
Cultivars are also classified based on characteristics like flesh colour. Common cultivars include those with red or pink flesh, which is the traditional and widely recognised colour. Yellow and orange-fleshed watermelons are gaining popularity for their unique appearance and distinct flavour profile. The diversity of cultivars allows consumers and growers to choose varieties that suit their preferences and growing conditions.
Miniature or “personal-sized” watermelons are another category of cultivars that have gained popularity. These smaller fruits are convenient for individual servings and have a quicker maturation period, making them well-suited for home gardens and smaller spaces. Speciality cultivars, such as those with striped or speckled rinds, are cultivated for their aesthetic appeal and unique visual characteristics.
In recent years, there has been increasing interest in heirloom or heritage watermelon varieties. These cultivars are often open-pollinated and carry historical significance, preserving genetic diversity and traditional flavours. Growers and consumers alike appreciate heirloom watermelons for their unique tastes and cultural heritage.
There are close to a hundred different varieties of watermelons with new hybrids being developed all the time as tastes change and markets evolve. The main types grown in South Africa are All Sweet, Crimson Sweet, Super Small and Seedless varieties. Some varieties available in South Africa are Sugar Sweet, Charleston, Congo, Sugar Baby, Moon and Stars, Daytona, Sensei, White Wonder, Yellow Petite and Starlight.