In New Zealand healthy seedlings of purple passionfruit Passiflora edulis are the recommended planting material. These should be grown from seed produced on parent plants that are healthy and producing consistent yields of large well filled fruit.

The usual method of propagation is to raise plants from seed, but they can also be raised vegetatively by grafting or from cuttings.

SEED

Choose ripe fruit from a vine that has a desirable fruit type and has cropped well in previous seasons. Seed collected from the main crop during February-March gives the most reliable germination. Make sure that the fruit is free from disease.

Normal-size fruit strains of Passiflora edulis are superior to larger-fruited "mammoth" types, which are shy bearing and often produce fruit that is incompletely filled with pulp.

Extract the seed from the fruit, using the acid process. Scoop the pulp into a glass or acid-proof container. To the pulp of every 2.5 kg of fruit add 60 ml of commercial hydrochloric acid and mix well. Stir every half hour for 3 hours, and then transfer the mixture to a large container, add water, and stir vigorously or rub the seeds together. Seeds and pulp should then separate freely. The seed sink and the pulp floats and can be decanted off.

Repeat washing and decanting until all waste is removed, then strain the seed in a fine sieve or muslin to remove water.

Seed may also be extracted by fermentation. Mix the pulp with an equal quantity of water and hold at 21°C. Stir periodically. The fermentation period should not be longer than 3 days otherwise germination may be adversely affected.

After cleaning, spread the seed out thinly on absorbent paper to dry in a cool shady place. Do not dry the seed in the sun or in hot air as this considerably reduces its viability and may even kill it.

For best results sow the seed as soon as possible after collection, as it loses viability rapidly after the first year. If it must be stored keep it in a airtight container in a cool dry place.

RAISING SEEDLINGS

With good germination 1 kg of seed should yield over 28 000 plants. The seedlings may be produced under glass or outdoors.

Under glass:
Sow in seed boxes in autumn (mid March). When the seedlings are 40-50 mm high (May), transplant them into seedling boxes or individual pots; discard weak plants.

By spring (October) the plants are ready for transplanting in the field. With individual pots the vines can be planted in their permanent positions with minimum root disturbance and little check to their growth.

Outdoors:
Sow in beds in October. Sow thinly in shallow drills 20-30 cm apart. Thin the young seedlings to 10-15 cm apart to prevent overcrowding.

The first seedlings may appear in 14 days, but the main flush of germination will be about 3-4 weeks after sowing.

The seedlings are ready for planting out by mid summer, but if necessary they can be held in nursery rows over winter ready for spring planting’s.

CUTTINGS

This method of propagation is generally used only for non-fruiting species and hybrids. It has been used for raising selected clones of P. edulis, but care must be taken not to select cuttings from a virus-infected plant.

Tip cuttings, about 8 cm long, are best. They should be taken in October or March, following the two main growing flushes.

Leave one or two small leaves attached, treat the cutting with a rooting hormone, and plant it about 5 cm deep in the rooting medium. A mixture of peat, sand, and perlite at a ratio of 2:2:1 is suitable.

Then place the cuttings in a mist propagation unit with bottom heat until they root. Roots begin to appear in about 28 days.

GRAFTING

Field trials by the Plant Disease Division of the Department of Scientific and Industrial Research have shown that using various Passiflora species as rootstock’s for the purple passionfruit is not satisfactory for improving resistance to crown canker and dieback associated with Fusarium species and resistance to black root rot (Thielaviopsis basicloa).

Grafting is therefore not recommended for propagation of passionfruit vines for commercial planting’s in this country.

The pink-flowered banana passionfruit (Passionflora millissima), appears to be resistant to root rot and, when used as a rootstock, also induced a measure of resistance in the purple passionfruit to grease spot (Pseudomonas passiflorae) a serious bacterial disease. However, incompatibility sometimes occurs in vines worked on this rootstock, and infections from crown canker disease will still occur in the purple passionfruit scion just above the graft union, even when the vines are grafted well above ground level.

Yellow passionfruit (Passiflora edulis var. flavicarpa) has proved unsuitable as a rootstock for, although the grafted vines grow well during warm summer weather, they do not survive normal winter conditions in New Zealand.

The hardy blue-flowered ornamental species (Passiflora caerulea) is unsuitable as a rootstock for the purple passionfruit, owing to incompatibility. Death of the scion after infection with the "woodiness virus" may result.

A young block of passionfruit being trained on a two-wire fence

Grafting procedure:
Grafting may be carried out in the glasshouse or outdoors, but it is more difficult to prevent newly grafted scions wilting outdoors.

Cleft or wedge grafting is the most efficient method. Cut off the top of the rootstock seedlings at a suitable height, and with a sharp knife remove all leaves and leaf buds on the remaining portion of the stock. Make a split 25-40 mm long in the cut end of the stock and insert the scion.

In the glasshouse use tip scions 5-8 cm long with the terminal leaves still attached. Scions should be the same diameter as the stock.

For outdoor grafting use more mature nodal scions with one leaf attached.

Cut the scions with the wedge the same length as the split in the stock and insert to the full length of the cut. Self-adhesive crepe bandage is very successful for holding stock and scion together. Fold pieces of suitable size in a U-shape around the graft union and press the free ends together.

Scion material is best obtained from young seedlings raised for this purpose. This avoids the pollination problems which would occur should all the scions be taken from one self-sterile plant, and also reduces the risk of transmitting virus disease.