Reproduction
The purple passion fruit blooms in spring and early summer and again for a shorter period in fall and early winter. Yellow passion fruits in Puerto Rico flower from April to September and yield fruits from June to October. In some areas, plants fruit twice each year. Plants usually begin blooming and fruiting in their second year. Yellow passion fruit flowers have both male and female parts but are self-sterile. They rely mainly on carpenter bees (Xylocopa spp.) for pollination. Other insects and hummingbirds also visit the flowers. The flowers of purple passion fruit can self-pollinate. Fruits of the naturalized yellow-fruited form range from about 45 to 120 g in Puerto Rico. There is a large variation between plants in size and shape of fruits. Small fruits are sometimes completely devoid of seeds, and large fruits may have over 200 seeds. A collection of seeds from naturalized plants in Puerto Rico averaged 0.0251 ± 0.0004 g/seed or 40,000 seeds/kg. Passion fruit is usually propagated from seeds but can be started from cuttings, layers, and grafts. Seeds germinate best if allowed to ferment for a few days in the fruit pulp before cleaning and are lightly scarified by clipping or sandpapering. A group of seeds in Puerto Rico were sown without pretreatment in commercial potting mix and began germinating in 14 days and completed germination in 24 days with 61 percent germinated. Plants are grown in beds or pots and transplanted when they reach about 25 cm in height. The seedlings are heavily watered after planting. Seeds are disbursed in the wild by humans, animals especially pigs, and birds, and by vine extension.
Many in vitro culture techniques have been described for the Passiflora genus including regeneration from hypocotyl, leaves and cotyledons , regeneration from leaf disks and mesophyll and cotyledon-derived protoplasts, regeneration after protoplast fusion , and micropropagation. A mature endosperm culture has been reported for P. foetida. Embryo and endosperm culture from seeds of several Passiflora species mainly collected in the wild has been attempted in this study.
Seeds of Passiflora genus vary greatly in size and shape. However, several common features are apparent, including hard seed coats surrounding a white, well-developed, straight embryo, with large flat cotyledons. A thin layer of endosperm, which can be ruminated, surrounds the embryo.
Endosperm and embryos extracted from seeds were grown in two different media, A and B. The plant growth regulator and sucrose concentration of these media have been reported to induce undifferentiated callus formation (medium A) and to stimulate in vitro germination of zygotic embryos (medium B) in rice. Twenty six species responded to either A or B medium with embryo germination or callus formation.
Undifferentiated calli were spontaneously produced especially from embryos grown on medium A. Alternatively, pieces of embryo-derived hypocotyl or root were cut and transferred to high 2.4-D to obtain calli. Different embryos from a single species and even individual embryos produced calli with different characteristics.
Ex-vitro propagation
Dehydrated seeds of many Passiflora species may require from many months up to two years to germinate. Passiflora seedcoats are very tough, in nature they're softened by the stomach acids of birds and other animals. This can be mimicked by placing them 24 hours in milk or citrus juice. Rinse the seeds and plant them immediately in an airy general-purpose seedling soil. Cover them with 5 millimeters of the same medium and gently press it down a bit, put them in a bright spot at 20°C. Use a hand sprayer to keep the substrate moist - don't let it dry out. Transplant them to individual pots after they formed a few leaves.
Cuttings
Start your cuttings from woody sections of the plant - the growing points are too soft, are difficult to root and rot easily. A 2-foot (60cm) branch yields 4 cuttings which have 2 growing points each. Cut the branch diagonally 2 cm above the upper and 3 cm below the bottom growth point. Remove the tendril and leaves from the bottom shoot by swiftly rubbing your fingers down the branch. The upper shoot remains intact but cut away half of the leaf to avoid dehydration. Put the bottom of the cutting in cold water and let them drip off in the fridge, then dab them in rooting hormone powder. Tap of the excess powder and stick them 2/3 in a sandy airy mix. Place them in a bright spot in a humid environment (under clear plastic or in a mini-conservatory), not in direct sunlight. Roots will take a few weeks to appear, don't interfere with them. Water the pot from a tray - watering from the top will collapse the airy soil.
The New-World butterflies of the genus Heliconius have developed a special relationship with Passiflora. The appearance of both organisms is the result of mutual evolution. The butterfly has specialized in Passion flowers as food for its caterpillars, which only feed on these plants. Not only does the butterfly lay eggs on the plants for the offspring to feed on, the caterpillar stores the toxic chemicals developed by the plant to ward them of. This makes the caterpillar an unattractive meal for other animals, but the toxins are passed on to the adult stage. After the metamorphosis the butterfly remains poisonous and advertises it with vivid markings on the wings: unfit for consumption.
The caterpillar's appetite can be such a drain on the plant that it is unable to produce flowers or set fruit, in extreme cases they destroy the plant completely. This has lead to a battle between the two organisms: not only does the plant produce toxins, it also takes advantage of the insect's weakness. Each Heliconius species specialize in one or a few Passiflora species and determines the host by looking at the foliage. This has lead to Passiflora species that produced a large variation in leaf so that the butterfly had difficulty in recognizing them. Other species developed small nodules on the tendril or petiole which mimic the butterfly eggs. The Heliconius only lays its eggs on “virgin” plants which haven't been visited by other females, this mechanism fools the butterfly in many cases. A third defense is the production of nectary glands on the leaves and stem which attract ants, wasps and parasites - generally speaking insects which have a strong interest in finding caterpillars on their path.
One species, Passiflora adenopoda even grows small hooklike trichomes which have proven to inflict deadly wounds upon the caterpillar. A fourth mechanism has evolved in Passiflora foetida: this species has bracts that grow as a mesh with sticky glands around the flower which act as a passive trapping mechanism such as seen in Drosera species. These glands obstruct the large-winged Heliconius butterflies from landing near the flower.
Propagation
Seeds, cuttings, grafts or layering can be used to propagate Passionfruit. The first three methods are most commonly used. The seeds are planted 1.5 cm deep on a sterile seed bed and are transplanted into individual bags containing enriched potting mixture at the three leaf stage.
All 3 passion fruits can be propagated from seed, which should be fresh (less than 1 year old) because seeds lose viability rapidly. Seeds may be sown in flats or pots of sterile soil and kept in a moist place shaded from direct sunlight. Seeds ordinarily germinate in 10-20 days and young plants grow rapidly. Seedlings should be potted individually in small containers as soon as practical after germination. They can be transferred to a permanent location when they are 25-40 cm tall.
Dehydrated seeds of many Passiflora species may require from many months up to two years to germinate. Passiflora seed coats are very tough, in nature they are softened by the stomach acids of birds and other animals. This can be mimicked by placing them 24 hours in milk or citrus juice. Rinse the seeds and plant them immediately in an airy general-purpose seedling soil. Cover them with 5 mm of the same medium and gently press it down a bit, put them in a bright spot at 20°C. Use a hand sprayer to keep the substrate moist - don't let it dry out. Transplant them to individual pots after they formed a few leaves. Plantlets are grown under shaded conditions and hardened before being transplanted into the field. It takes 6 to 8 weeks from the time of sowing to transplanting in the field.
Cuttings from young, newly mature wood with 2-3 internodes, may be rooted in about one month and ready for setting out in 90 days. The most desirable cutting material is that portion of the stem from the first fully expanded mature leaf, back to the area of the fully extended branch. The best period to obtain cutting material is when the vines are actively growing, after the summer and winter crops. Cuttings are taken from vigorous, actively growing vines. Start your cuttings from woody sections of the plant - the growing points are too soft, are difficult to root and rot easily. A 2-foot (60cm) branch yields 4 cuttings which have 2 growing points each. Cut the branch diagonally 2 cm above the upper and 3 cm below the bottom growth point. Remove the tendril and leaves from the bottom shoot by swiftly rubbing your fingers down the branch. The upper shoot remains intact but cut away half of the leaf to avoid dehydration. Put the bottom of the cutting in cold water and let them drip off in the fridge, then dab them in rooting hormone powder (eg. IBA). Tap of the excess powder and stick them 2/3 in a sandy airy mix. Place them in a bright spot in a humid environment (under clear plastic or in a mini-conservatory), not in direct sunlight. Roots will take about 4 weeks to appear, don't interfere with them. Water the pot from a tray - watering from the top will collapse the airy soil. Then it should be treated similar to seedlings. Plants from rooted cuttings are less vigorous than seedlings and could be planted at a closer spacing than seedlings.
Purple passion fruit is sometimes grafted onto a yellow passion fruit rootstock to alleviate nematode and disease problems affecting the root system of purple passion fruit. Seedlings of both stock and scion should be about 45 cm tall and have a stem diameter about that of a pencil when grafted. Scions should be about 8-10 cm long and contain at least 2 nodes. The stock should be cut off 25-30 cm above the soil line. For grafting, a long, slanting cut is made from one side to the other through the base of the scion for about half its length, and a similar cut is made through the stem of the stock. The two cut surfaces are then placed together with cambia aligned and the graft is tied firmly with budding tape. The graft is enclosed in a small plastic bag tied shut below the graft, and placed in a warm, shady location for 10-14 days or until the union takes. Then the bag is loosened to admit air and is removed when scion buds begin to grow. The budding tape is removed before it thickens the growing stem.