If fruit trees grow from seeds, how do you grow seedless fruit? It's not unusual for plants to produce mutant fruit that lacks seeds, but these fruits are usually the end of their line. Naturally occurring hybrids can also make sterile fruit. The varieties that we eat are specifically hybridized to be seedless, like seedless watermelon or bananas, or grafted onto host root stocks, like seedless oranges.
Navel oranges (named for the belly-button shaped indentation in the peel; did everyone else already know this?) were first planted in California in 1872; the New York Times looked back on the fruit's origins in an article from 1902 (pdf).
The fine original seedless orange trees came from Bahia, Brazil, and were imported through the sense of a woman. Mr. Nellie Desmond of Syracuse, N.Y., was visiting her brother in a rubber camp along the Amazon. The natives brought her several seedless oranges, which were a curiosity to her. She inquired whence they came, and found they grew upon a clump of freak orange trees in the neighborhood.
The woman with sense brought some fruit back to the United States, and word got to the Commissioner of Agriculture, who instructed the consulate at Brazil to ship him some trees. A few years later, Mrs. Luther C. Tibbets, who was well-connected, procured three trees from an experimental USDA garden for land her husband was homesteading in what is now downtown Riverside, California. One of the trees was eaten by a cow, but after five years the others bore fruit. "On Jan. 22, 1878, two of the new oranges were cut open and critically tasted by a little company of orange growers at Riverside. A new star of the first magnitude rose that day in the horticultural firmament."
Another star of the first magnitude might well arise from a recent report in PNAS. A mutant seedless sugar apple (Annona squamosa) from Thailand was found to have a genetic disruption that blocks ovule development. Fortuitously, similar mutations have been intensively studied in Arabidopsis, a mustard plant that is the lab rat of botany. Understanding this genetic pathway could lead to seedless sugar apples or soursops. Fruits in this genus "have a meat with a sherbet-like texture and a flavor that has been compared with a mixture of banana and pineapple," the authors write, but huge seeds make these fruits a bit of a chore to eat or process. They also point out that Mark Twain described Annona as "the most delicious fruits known to men."
Has anyone tried these fruits? I'm intrigued—and wouldn't mind fighting through the seeds while the seedless varieties are in development.