Branching agent discovered by chance
When Don Elfving began testing cyclanilide on fruit trees, no one knew what effect it would have.
Pete Van Well was one of the first in the industry to recognize the potential role of Tiberon in the production of feathered nursery trees.
Photo by Geraldine Warner
The discovery that the plant growth regulator cyclanilide could induce branching in fruit trees was made, serendipitously, by Washington State University horticulturist Dr. Don Elfving.
In 2000, he had a phone call from a representative of Aventis, an agricultural chemical supplier which at the time sold Finish, a product containing cyclanilide and Ethrel (ethephon), as a defoliant for cotton. Another Aventis employee had noticed that the molecular structure of cyclanilide was similar to that of the growth regulator Alar, and they wondered if Elfving could test cyclanilide on apple trees to see if it had similar effects as Alar on fruit maturity.
Elfving was interested in testing it—not so much because of its potential effect on fruit, but because he had previously studied Alar as a retardant of vegetative growth in apple trees. The company agreed to supply product for a trial in 2000 in which he compared Alar (daminozide), Apogee (prohexadione calcium), and cyclanilide.
He found that Alar inhibited elongation of the shoots while Apogee also inhibited growth, but, to his surprise, cyclanilide induced lateral branching.
“When I discovered the effect it had in our very first trial, I said, ‘This looks interesting,’ because I had been working on branching of apple trees all the way back as far as the mid- to late 1970s,” said Elfving.
Cyclanilide also induced branching when he tested it on cherry and pear trees. “I was enthused,” he recalled.
As requested by Aventis, he also did two years of extensive trials in which he applied cyclanilide preharvest to test its effect on fruit maturity before harvest and in storage. It didn’t have the slightest effect.
Later, as he was poring over a book of growth regulator structures, Elfving noticed that the structure of cyclanilide had no relationship to that of Alar, but it did have similarities to the synthetic auxins 2,4-D and 2,4,5-T. That explained why it had no effect on fruit but did stimulate branching.
Fruit trees are apically dominant. The apical bud produces indoleacetic acid, which is an auxin, or plant hormone, that moves down the shoot, inhibiting growth of the lateral buds. Branching can be stimulated either by removing the top leaves, which is one of the methods nurseries have traditionally used to stimulate branching, or by applying an auxin transport inhibitor or an auxin action inhibitor. Elfving said that the synthetic auxins bind to the auxin receptor sites in the plant, preventing the action of the natural auxin and allowing the lateral buds to grow.
In 2002, Bayer CropScience acquired Aventis. Elfving continued to test cyclanilide, in cooperation with several nurseries in central Washington, and sent Bayer his reports. His work was partially funded by the Washington Tree Fruit Research Commission and the Northwest Nursery Improvement Institute, with in-kind contributions from nurseries.
“It was Pete Van Well and his observations that really started to push this thing down the road because he went from being a typical skeptical nurseryman to being a very strong advocate, when he saw what it could do,” Elfving recalled.
Van Well, president of Van Well Nursery in East Wenatchee, saw it as a potential tool that nurseries could use to provide the well-feathered trees that most growers were wanting for their high-density plantings.
After reviewing the products it acquired from Aventis, Bayer became interested in the branching effect of cyclanilide. The company obtained registration from the U.S. Environmental Protection Agency in 2009 for use on nonbearing tree fruits, and marketed it as Tiberon.
Elfving said cyclanilide was tested in Oregon and California on ornamental nursery plants. Although he did not see results of those tests, he learned that cyclanilide would induce branching on some species of plants, but not on others, which is possibly why it was not registered for ornamentals.
Though it appears to be effective on apples, pears, and cherries, some species are particularly sensitive to the product. Elfving found through his trials that a rate of only 10 to 20 parts per million—a tenth of the rate used on apples—produced good branching on pear trees.