The easiest method for propagating cherimoya trees is by grafting a selected scion onto a seedling rootstock. When choosing potential rootstock, look for the following qualities:

–	a high germination rate
–	a low incidence of bench root (a noticeable bend in the tap root)
–	moderately vigorous seedlings, with the root and shoot growth being well balanced.

When some grafted trees begin to produce fruit, they will fail due to inadequate root systems caused by using seedlings with bench root. This is mostly the result of the seed having a thick heavy coating that restricts the emergence of the taproot, which can cause it to bend.

   A bad case of bench root

The size, shape and strength of the seed differs between varieties (such as the variety Bronceada, whose seeds have a weak coating that allows the root to emerge easily, and which probably attributes to that variety’s low incidence of bench root). Soaking seed for 24–48 hours before sowing could help lower the incidence of bench root during germination by slightly softening the seed’s coating. Any seedlings showing signs of bench root or other deformities should be discarded.

Seeds are generally collected from fruit that has been hand pollinated. They’re extracted from mature ripe fruit, washed, dried and stored at room temperature for up to 14 weeks (although seeds can remain viable for two to three years if kept dry and protected from weevil and fungi—though this is dependant on seed source, extraction and storage methods). Store the seeds in a cool place, in an airtight container and treat with a fungicide, which helps to avoid damping off in young seedlings.

Cherimoya seed have a very high germination rate (usually more than 90%), with optimum germination temperatures of 28–32ºC, while temperatures below 20ºC will delay and reduce germination chances. At 20ºC seed will germinate in about 21 days. Tests have been done on sowing seed horizontally and vertically with the results indicating that horizontally sown seeds get slightly better results, with a lower bench root incidence and an overall thicker, heavier seedling quality (although the differences are minimal).

Seeds should be planted in deep trays and then transplanted, when the seedlings are about 8cm high, to deep containers (approximately 45–50cm in depth) to promote a well-developed root system. Seeds sown in spring will produce rootstock ready for grafting the following spring (although some may need two years before grafting).

Studies show that seedling vigour, measured by weight, can vary by as much as 50% between varieties and can generally be determined by the size of the seed. This can partly be put down to some varieties having a slower taproot development, which can inhibit seedling growth. Of the common commercial

Variety		Germination (%)		Seedling weight (g)		Bench root incidence (%)
Bays		95		1.55		40
Bronceada		94		1.74		20
Burtons		97		1.96		41
Burtons favourite		99		1.58		39
Jete		95		1.84		27
Reretai		96		1.35		38
Smoothey		96		1.70		42
White		96		1.83		34

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Variety		Stem length (mm)		Taproot length (mm)		Lateral root*
Bays		133		155		1.7
Bronceada		131		149		2.0
Burtons		144		176		2.4
Burtons favourite		139		162		1.8
Jete		140		164		2.0
Reretai		117		157		1.8
Smoothey		142		147		1.9
White		148		166		1.8

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Seedling taproot length and lateral root development can also vary considerably between varieties. Burtons, Burtons favourite and Jete have much longer taproots than other varieties, while Bronceada and Smoothy have short taproots but similar lateral root development. Almost all seedlings have a higher mass of shoot than root. Some varieties can be less stable than others, and may fail or collapse due to naturally poor root systems in proportion to the shoot.

Grafting is done when seedlings are 1–2 years old and dormant, and is most successful from July to October, provided the previous year’s leaves have not dropped from the potential scionwood. During this period no scion preparation is required other than the removal of leaves. All normal grafting techniques seem to work equally well. To bud, collect budwood in July and store refrigerated for 10 days in plastic. The leaves will then drop and expose the dormant buds. Graft at once and wrap well to protect from dehydration. It is necessary to protect the trunk of topped trees to avoid sunburn. If topworking, nurse branches are desirable, if not essential for success. Grafted plants should be allowed to grow for another year until they’re 0.9–1.2m before planting out in the orchard, and should bear fruit in about two to three years.

In India, cherimoya have been grafted onto custard apple (A.reticulata) rootstock with a 90% success rate.

Other methods of propagating
Cherimoya have been known to root from cuttings, but only from plants less than 6–12 months of age, which isn’t commercially viable as knowledge of the tree’s qualities and production potential take from 1–5 years. Cuttings tests on juvenile trees achieved 5–10% rooting (not a commercially viable result) and adult trees gave 0%. The use of indolebutyric acid (IBA – rooting hormone) on cuttings may help, as may retaining some leaves that are then cut in half so more energy is given to promoting root development. One study found mature wood cuttings of healthy cherimoya trees have rooted in propagating sand, with bottom heat, in 28 days.

Meristem culture (using cuttings from the growing tips) apparently gives faithful propagation and tests obtained 80% rooting with adult soursop (A.muricata) trees.

Cherimoya trees aren’t easily propagated from tissue culture.

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Next – planting your new cherimoya trees out

Description		Growing conditions
Tree management		Hand pollinating
Harvest to selling		Ripening and eating
Varieties

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Last modified 21/11/02