Granadilla

Cross-section of granadilla fruit.

Granadillas, known scientifically as Passiflora ligularis, are tropical fruits revered for their distinctive flavour and versatility in culinary applications. Granadillas trace their roots to the vast tropical regions of South America, particularly the Andes Mountains. Indigenous to countries like Peru, Ecuador, and Colombia, these fruits have a rich history dating back centuries. Early South American civilisations, such as the Inca and Aztec cultures, cultivated granadillas for their nutritional value and unique taste.

European explorers, including Christopher Columbus and Hernán Cortés, encountered granadillas during their voyages to the New World in the late 15th and early 16th centuries. These explorers introduced the fruit to Europe, where it garnered attention for its exotic flavour and striking appearance. Over time, granadillas found their way to various parts of the world, including Africa, Asia, and Australia. Today, granadillas have become an integral part of the agricultural landscape in South Africa and many other regions, playing a crucial role in local economies and international trade.

Botany and Taxonomy

Granadilla plants belong to the Passifloraceae family and the Passiflora genus. These perennial vines are characterised by their vigorous growth, heart-shaped leaves, and showy, fragrant flowers. Granadilla fruits are typically spherical to oval, with a tough outer rind that encases numerous edible seeds and translucent, sweet-tasting pulp. Within the Passiflora genus, granadillas fall under the subgenus Tacsonia, making them closely related to other passion fruits. Taxonomically, Passiflora ligularis is the scientific name for granadillas. Understanding the genetic makeup of granadilla plants is essential for successful cultivation and breeding efforts.

Granadillas exhibit genetic diversity, which is valuable for improving fruit quality, disease resistance, and yield. Research into the genetic characteristics of granadillas has led to the development of improved varieties and cultivation techniques, contributing to their continued popularity in the agricultural sector.

Table 6.19: Taxonomy of granadilla.

Scientific Classification
Kingdom	Plantae
Phylum	Angiosperms
Class	Eudicots
Order	Malpighiales
Family	Passifloraceae
Genus	Passiflora
Species	P. ligularis

Ecology

A. Soil

Granadilla plants have specific soil preferences to ensure healthy growth and fruit production. They thrive in well-draining soil, which means the soil allows excess water to flow away. This prevents the roots from becoming waterlogged, which can harm the plants. Granadillas also do best in soil with a pH level between 6.0 and 7.5, which falls within a slightly acidic to neutral range. This pH range helps the plants absorb the nutrients they need from the soil effectively. Additionally, granadilla plants benefit from soil rich in organic matter, like compost or decomposed plant material. Organic matter improves soil fertility, helps retain moisture, and supports beneficial microorganisms in the soil.

However, several factors can negatively affect granadilla plants if not managed properly. One of these is soil salinity, where the soil contains too much salt. High salt levels can disrupt how the plants take in water and nutrients, leading to poor growth. Another concern is soil compaction, which happens when the soil is compressed too tightly. This can restrict the growth of granadilla roots, as they need space to spread out and access nutrients in the soil. Nutrient imbalances in the soil, where there is too much or too little of certain nutrients, can also harm the plants. Finally, soil-borne diseases like root rot can pose a threat to granadilla plants. To ensure healthy growth, growers must maintain well-drained soil and address these concerns to protect their granadilla plants.

B. Climate

Temperature:

Given their tropical origins, granadillas thrive in warm temperatures. They require a minimum annual temperature of around 20°C (68°F) for optimal growth. However, what makes granadilla production interesting is its adaptability to subtropical climates, such as those found in South Africa. Subtropical regions in South Africa experience milder winters and warm to hot summers, which create a suitable environment for granadilla cultivation.

Granadilla plants are vulnerable to cold temperatures, especially frost, due to their tropical origins. When exposed to cold weather, they can experience a range of negative effects. The most significant concern is frost damage, which can harm their leaves, stems, and fruit. This damage includes tissue injury and browning, resulting in reduced growth and photosynthesis. Extended exposure to cold conditions can slow down or halt the growth of granadilla plants. This can lead to delays in flowering and fruiting, impacting the overall yield.

Cold temperatures during fruit development can compromise the quality of granadilla fruit. This can manifest as discolouration and irregularities, affecting its marketability. Cold stress weakens granadilla plants, making them more susceptible to diseases and pests. It can also result in long-term damage, hampering the plant’s overall health and productivity.

Rainfall:

Granadillas naturally receive evenly distributed rainfall throughout the year, typically ranging from 1,000 to 2,000 mm annually in tropical regions. In subtropical areas like South Africa, where rainfall patterns may vary, it is crucial to ensure adequate irrigation during dry periods. Drip or controlled irrigation systems are commonly used to supplement rainfall and maintain optimal soil moisture levels.

Granadilla plants can be vulnerable to low humidity, especially when it drops significantly below their preferred levels. In conditions of low humidity, the plants may experience increased transpiration rates, leading to water stress. This can result in wilted leaves and decreased growth. Additionally, low humidity can make the plants more susceptible to pests and diseases.

Radiation:

Sunlight is another critical ecological factor for granadillas. These plants require full sun exposure for at least 6 to 8 hours a day to maximise photosynthesis and fruit development. Subtropical regions, such as those in South Africa, often provide abundant sunlight, making them well-suited for granadilla production. Proper site selection within subtropical areas can further optimise solar exposure.

Windbreaks:

Strong winds can damage the vines and affect fruit development. In subtropical regions like South Africa, strategies such as using tall trees, wind fences, or trellising systems act as effective windbreaks, shielding granadilla crops from potential damage.

Trellised granadilla vines.

Morphology and Characteristics

A. Granadilla Vines

Under the canopy of granadilla vines.

Granadilla plants are robust perennial vines known for their vigorous, twining growth patterns. These vines can extend up to impressive lengths, often exceeding 10 meters. What sets them apart are their unique tendrils, specialised structures that aid in clinging to support systems like trellises, fences, or neighbouring plants. Tendrils, modified plant organs, have evolved for the specific purpose of ensuring stability and support. They possess touch sensitivity, enabling them to coil around nearby objects upon contact. This coiling mechanism serves a dual purpose: it helps the plant access essential sunlight for photosynthesis while also enhancing its competitive advantage for space and resources in its environment.

In some regions, these vines are deciduous, shedding their leaves during dry seasons. Granadilla leaves are characterised by their alternately arranged, simple structure, featuring prominent veins and serrated edges. These leaves play a pivotal role in the plant’s photosynthetic process, efficiently converting sunlight into the energy necessary for its growth and development.

B. Inflorescence and Flowering

Granadilla plants produce large, fragrant, and showy flowers that are typically solitary or borne in clusters of 1 to 3. The flowers are usually white or cream, with intricate, radial symmetry. Each flower consists of five sepals, five petals, and a central reproductive structure known as the gynoecium. The sepals are green and enclose the base of the flower. The petals are larger and often exhibit a delicate, wavy appearance. The gynoecium comprises three styles and stigmas, which are receptive to pollen, and a central ovary that will develop into the fruit if pollination is successful. Granadilla flowers are known for their attractive appearance and sweet fragrance.

A very fascinating granadilla flower.

Granadilla flowers, like many other plant species, exhibit diurnal (daytime) opening and closing patterns. These flowers typically open early in the morning and remain fully open during the day. As the day progresses, they gradually close in the late afternoon or early evening. This daily rhythm is often linked to pollination and the plant’s reproductive strategy.

The primary reason for the diurnal opening and closing of granadilla flowers is to facilitate pollination. By opening during the day, the flowers attract pollinators such as bees, butterflies, and other insects. These insects visit the open flowers to collect nectar, and in the process, they come into contact with the flower’s reproductive structures, transferring pollen from one flower to another. This cross-pollination is essential for fruit development.

Closing the flowers in the late afternoon or evening serves a protective function. It helps shield the reproductive organs from potential nighttime herbivores, excess moisture, or unfavourable environmental conditions. By closing, the flowers safeguard their delicate structures until the next day when they reopen to resume attracting pollinators.

C. Pollination and Fruit Set

A side-view photograph of the passion fruit flower indicating the many intricate parts. The operculum acts as a lid or protective structure over the nectary.

Granadilla plants are generally self-sterile, meaning they require cross-pollination between different plants to set fruit. Pollination is typically facilitated by insects, particularly bees, which visit the flowers in search of nectar. As they collect nectar, pollen is transferred between flowers, leading to fertilisation. Once pollination occurs, the fertilised ovaries develop into fruit. However, the exact process can vary depending on the specific granadilla species and cultivar.

D. Fruit

Parts of a yellow passion granadilla, Passiflora edulis f. flavicarpa.

The fruit of granadilla is one of its most distinctive and appealing features. It is typically round or oval, with a tough, smooth, or slightly wrinkled outer rind, often referred to as the “shell.” The colour of the shell can vary, with shades ranging from yellow and orange to purple or even purplish-black when ripe, depending on the cultivar. The interior of the fruit contains a jelly-like pulp filled with numerous small, black seeds embedded in translucent arils. The pulp is renowned for its sweet and aromatic flavour, which is a combination of tartness and tropical sweetness. The seeds are edible but often discarded due to their bitter taste and hard texture. Granadilla fruit is enjoyed fresh, in juices, desserts, and various culinary applications.

Cultivars, Breeding and Distribution

In South Africa, the Ester cultivar (Passiflora ligularis), often referred to simply as “Ester,” holds a dominant position in commercial granadilla production. This cultivar is highly esteemed for its exceptionally sweet and aromatic flavour, making it a preferred choice for both domestic consumption and export. While Ester granadillas are the primary focus of commercial production in South Africa, it is worth noting that there are other cultivars present, including the Purple Passion (Passiflora edulis var. edulis) and Yellow Passion (Passiflora edulis var. flavicarpa). However, these cultivars are cultivated to a lesser extent compared to the Ester variety.

Ester granadilla cultivar.

Granadilla production in South Africa is primarily concentrated in regions where the Ester cultivar thrives. These production areas are chosen based on their suitability for cultivating Ester granadillas. Regions such as Limpopo, Mpumalanga, KwaZulu-Natal, and others with appropriate climatic conditions play a significant role in Ester granadilla cultivation.

The Ester cultivar’s widespread popularity and exceptional flavour have made it the cornerstone of South Africa’s granadilla industry, catering to both local and international markets. While other cultivars like Purple Passion and Yellow Passion are grown in South Africa, they do not enjoy the same level of commercial prominence as the Ester variety.

A. Breeding Objectives

South Africa has initiated granadilla breeding programs which focus on improving fruit quality, yield, and pest resistance. These programs involve selective crossbreeding and genetic selection to create new cultivars with desired traits. Research institutions and agricultural universities collaborate with growers to conduct trials and assessments to identify promising cultivars.

One of the primary breeding objectives is to develop granadilla cultivars with enhanced flavour and overall fruit quality. This includes achieving a perfect balance of sweetness and tartness, as well as improving the aroma and texture of the fruit.
Developing granadilla varieties with natural resistance or tolerance to common pests and diseases is crucial to reduce the need for chemical pesticides and ensure crop health.
Breeders aim to increase fruit production per plant and maximise overall yield, thus increasing the economic viability of granadilla farming.
Developing cultivars with a longer shelf life helps in reducing post-harvest losses and extends the availability of granadilla fruit in markets.
Breeding for climate adaptability is essential to expand granadilla cultivation into new regions with varying environmental conditions, making the crop more resilient to climate change.

B. Breeding Challenges

Granadilla exhibits significant genetic variability within its species, which poses challenges in controlled breeding programs. Due to this heterogeneity, it becomes more complex to predict the traits and characteristics of offspring resulting from controlled crosses. Identifying desirable traits and selecting them becomes a more intricate process, requiring extensive evaluation and patience. The wide genetic variability can also lead to variability in fruit quality and other important attributes, making it challenging to consistently produce granadilla cultivars with desired traits.

Granadilla plants have relatively long juvenile periods before they start flowering and bearing fruit. This extended juvenile phase lengthens the breeding cycle and delays the evaluation of new cultivars. Breeders must invest significant time and resources to bring a new cultivar from the initial crossbreeding to commercial production. This extended timeline can hinder the rapid development of improved cultivars and requires a long-term commitment to breeding efforts.