I hope you can help with our “mystery.” I planted this navel orange tree approximately 20 years ago and, year after year, we got many delicious navel oranges. Last year, it sent up a lot of new shoots and the tree got considerably larger in one year. The navel oranges were plentiful and delicious again, but there is fruit on the new growth that looks more like a Valencia orange or lemon; it is much smaller than the navel oranges. Any ideas on what’s going on here? Is it possible that when I purchased this tree there was also a different citrus tree in the pot that didn’t surface for 20 years?
Judy Schillace, Orangevale
According to UC master gardener Carol Rogala, you most likely can trace the issue to suckers from the rootstock.
Orange trees generally are grafted. The bottom of the tree, including the roots and bottom portion of the trunk, is called rootstock, while the fruit-bearing top has two different names: budwood (when referring to the process of grafting) and scion (when mentioning the variety of orange).
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Tree grafting is an excellent way to bring the best of two varieties together into a single tree. Grafting trees is a practice that has been done by farmers and gardeners for hundreds of years. But the method is not foolproof.
Sometimes grafted rootstocks can sucker and send out shoots that revert to the type of growth of the original tree. If these suckers are not cut off and removed, they can overtake the growth of the graft.
The best way to prevent the rootstock from taking over is to remove any new sucker growth that appears below the graft line, where the rootstock and budwood were joined together. If the graft line goes below the ground, the tree may revert to its rootstock through suckers and give the wrong fruit.
There are various reasons for a reversion in grafted trees. For instance, grafted trees respond to severe pruning by sprouting from below the graft and reverting back to the rootstock. Sometimes scion branches on grafted trees simply die, and the rootstock is free to regrow.
Also for reasons that remain a mystery, a limb may suddenly begin to produce a different kind of fruit from that on the rest of the tree; that’s called a “sport” or “mutation.”
For instance, a tree that formerly produced all yellow apples with red stripes may “sport” a branch that has solid red fruit. Such a mutation also may produce fruit that is noticeably different in size or quality, as well as color. The fruit may be better or worse than the fruit of the rest of the tree. Sports are not common, although they happen more often in some varieties of trees than in others. Citrus trees are notorious for mutations and reversions.
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