We’re approaching the season where many citrus trees are producing ripe fruit. Perhaps no orange cultivar has been more successful for the fresh market than the navel orange. Valencia oranges are used more for juice and juice is the biggest use for oranges. Navels are a close second in total consumption worldwide.
Unlike most of the plants we grow for food, the navel orange was never selectively bred. The first navel orange emerged in Brazil around 1820. It was a type of genetic mutation called a sport. A single bud developed abnormally and this naturally genetically modified bud grew into a branch and began producing sweet fruit with thick easy to peel skin and the characteristic navel on the blossom end.
About 50 years later the USDA imported a few rooted cuttings. Many sources claim they were seedlings, but this would not be possible as navel oranges have no seeds, or at least no viable seeds. At any rate, the California navel orange industry was born. As the story goes, a pioneer woman named Eliza Tibbets obtained two of these plants. Supposedly one is still alive and producing fruit in Riverside, California.
Since navel oranges can’t reproduce by seed we make new trees by grafting a bud onto an existing tree. Nearly any common citrus tree will work. Believe it or not oranges, lemons, limes and grapefruits all are the same species (Citrus sinensis).
Navel oranges are not only all the same species, but they are also genetically identical. This makes disease epidemics potentially problematic. If one tree was susceptible to a pathogen every other one in the grove would also be. Plants propagated by seeds vary somewhat genetically.
In addition to bud grafting, navel oranges and all citrus trees can be propagated by cuttings. A small piece of stem can be removed, treated with rooting hormone and placed in soil to produce new roots. This method is fine for amateur gardeners, but most commercial growers prefer to bud desired cultivars on rootstocks, many of which show resistance to root diseases.
After flowering, navel oranges average about nine months before the fruits are mature. Color is not a critical factor and eating quality can be excellent even if fruits are largely still green. Most growers taste the fruit or check for sugar levels about seven months after flowering. Under ideal conditions fruits might be ripe enough to harvest.
Most citrus fruits are different than apples, for example. Apples ripen over a narrow time period. If ripe specimens aren’t picked they fall. Citrus fruits will hold on trees for a long time, but the younger developing fruits might be the first to fall. Trees also may have flowers and fruit developing simultaneously.
While folks will always argue for their favorite citrus fruit, the navel orange is truly unique. It’s a genetic mistake that became very popular. Who knows, the same thing might happen to those seedy tangerines. Can you imagine how much they’d be improved if we didn’t have to fight through all the seeds?
Ted Manzer teaches agriculture at Northeastern High School. (firstname.lastname@example.org)