I've been practicing my approach grafts by planting all the seeds from jackfruit I've eaten this summer. I've got a number of little "Frankenstein" jackfruit plants with 3, 4, 5 and 6 rootstocks (mostly not siblings) grafted onto a single top. My observation so far is that the multi-rootstock plants are sending out larger leaves with shorter internodes than single-rootstock seedlings, and are starting to send out side branches where similar-age single rootstock seedlings are not. The oldest of my seedlings are only 14 weeks old at this point, so it's still too early to tell if the 6-rootstock plants are different or better than the 3-rootstock plants.
Sample 3-rootstock plant (with two more seedlings to be grafted on):
Sample 5-rootstock plant, with 3 more seedlings:
Sadly I don't have the room to run a proper experiment to see what various numbers of rootstocks would do over time... But if 2 rootstocks is better than 1, is 3 better than 2? Is 5 better yet? How about 10 or 20? At what point would adding more rootstocks be detrimental?
I'm thinking of grafting a few of my existing multi-rootstock plants together to form a plant with 10 or 15 rootstocks (from 9 different fruits, so there will be some sibling rootstocks) just to see what it would do, but I'm curious if anyone has any experience with large numbers of rootstocks on a single plant.
I'll be breaking my own rule of not growing fruit I can get in a "decent" form in local stores if I keep a jackfruit plant over the winter, but perhaps I can make an exception for one with a large number of rootstocks just for the curiosity factor.
Incidentally, after doing about 150 approach grafts so far, I've found on jackfruits that they take much better if the trunk is still green; once it is woody it takes a lot longer to heal and the success rate drops from about 90% to around 50%. If the supplemental rootstock is still green but being grafted onto a woody trunk, I get about 75% take. If I was doing the grafting late at night when I was tired, that also negatively affects the success rate.