By Noris Ledesma, Curator of Tropical Fruit
Grafting: Grafting is the most reliable means of propagating a desired cultivar. Grafting joins together a piece of a mature, bearing tree (scion) with a separate seedling tree (rootstock) to form a permanent union. The scion forms the canopy of the tree and the rootstock the lower trunk and roots. Grafted trees will bear fruit in 2 to 3 years after planting and have a more spreading and open canopy than seedling trees. Jackfruit grafting is only now becoming a viable method of propagation. Today, grafted cultivars are common in India, Indonesia, Malaysia and Thailand and increasingly in South Florida.
Rootstock: The proper rootstock provides a tree with a healthy root system and can influence growth and fruit traits such as tree vigor, size, and fruit quality. There has been little investigation into preferred rootstocks for jackfruit in the Western Hemisphere. Locally collected seed can be used, given that they form healthy and vigorous seedlings with a strong root system. Seedlings for rootstock should be grafted when less than one year old. They should be healthy and not rootbound, which will permanently weaken the jackfruit tree, resulting in poor growth and fruiting, and susceptibility to diseases. A rootstock can be grafted when the stem reaches the diameter of a pencil, or even smaller if budding techniques are used.
When to graft: Grafting is most successful when daytime temperatures are 70 to 85F and nighttime temperatures are 55 to 65F, keeping in mind that the key to successful grafting of the jackfruit is the maintenance of vigorous growth.
Veneer Graft: The modified veneer graft, with or without the retention of leaves is among the most successful techniques for grafting the jackfruit. This method requires active scions of 10 to 15 cm (4 to 6 in) with a swollen terminal bud.
The last fully expanded leaf is retained. Long, shallow veneer cuts are made on both the rootstock and scion, exposing the cambium of both. The veneer cut stops short of the terminal bud of the scion. A short flap of bark is left at the base of the veneer cut on the rootstock to secure the scion during wrapping. The cut surfaces of both the scion and the rootstock are then joined and wrapped with plastic grafting tape or a rubber band, leaving the terminal bud uncovered.
The grafted tree and container are covered with a clear plastic bag and placed in a bright, but shaded location and thoroughly watered. The terminal bud on the scion will unfold its leaf and continue to grow. Rootstock sprouts from below the graft should be removed. The bag can be removed after the scion begins to grow in 2 to 4 weeks. The height of the graft on the rootstock is not critical. The same method can be used with leaf removal on the scion, and these scions can be stored in a plastic bag at 12C (54F) for up to a week. Other successful techniques include chip budding, cleft and forkert grafts. The key to all of these methods is the vigor of the rootstock and scion, and the preparation of the budwood.
More information: Book The Exotic Jackfruit By Richard J. Campbell,Ph.D and Noris Ledesma