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:
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 varietys low incidence of bench root). Soaking seed for 2448 hours before sowing could help lower the incidence of bench root during germination by slightly softening the seeds 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. Theyre 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 fungithough 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 2832ºC, 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 4550cm 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 varieties grown in New Zealand, studies show Burtons, Burtons favourite, Jete, White and Smoothy produce seedlings with significantly longer stems.
Seedling qualities from a study done in New Zealand on commonly grown commercial varieties
* Based on a rating scale of 1 (= small) to 3 (= large).
The information for these charts has been collated from various articles published by The Orchardist of New Zealand.
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.
Other methods of propagating