Scientists have found a genetic switch that could shave years off avocado breeding by allowing researchers to identify one of a young tree's most important traits long before it flowers.
Researchers at UC Riverside helped identify the gene that controls whether an avocado tree has an A- or B-type flowering pattern. These flowering patterns determine how neighboring trees exchange pollen, making them an important factor in avocado production.
Published in the Proceedings of the National Academy of Sciences, the study was led by researchers at UC Davis in collaboration with UCR scientists, whose avocado breeding collections, field observations, and genetic analyses were essential to the discovery.
"This gives us a shortcut we've never had before," said Eric Focht, staff research associate in UCR's Department of Botany and Plant Sciences and a co-author of the study. "Instead of waiting years for a tree to flower, we can identify its flower type almost immediately using its DNA. That allows us to make much smarter breeding decisions."
Understanding these flowering patterns has long been important to growers, but until now, scientists did not know what controlled them.
Avocado growers typically plant a mix of A- and B-type trees because the two flowering patterns complement one another. When one type is releasing pollen during its male phase, the other is more likely to be receiving pollen during its female phase, increasing the chances of successful pollination and fruit production.
All avocado flowers first open as female before reopening later as male. What differs between varieties is the timing of those two phases. Trees are classified as A or B flower types based on that timing, allowing neighboring trees to exchange pollen instead of fertilizing themselves.
"Our study provides a genetic explanation for a century-old mystery of avocado pollination," said first author Jeffrey Groh, who led the project as a doctoral student at UC Davis and is now a postdoctoral fellow at UC Berkeley. "Flowers are not just static decorations; they are highly evolved and dynamic structures. We can see this in the pulsating rhythm of avocado flowers opening and closing throughout the day. Through the power of genetics, we can detect traces of this rhythm far into the ancient past."
For avocado breeders, however, the biggest impact is immediate.
Previously, there was no way to determine whether a seedling would become an A- or B-type tree until it matured, a process that can take five to 10 years. The newly identified genetic marker changes that. The gene is referred to as SDMYB, a floral transcription factor, which controls the flowering behavior in avocado trees.
"This is something we can begin using right away," said Marllon Soares dos Santos, a postdoctoral researcher in UCR's Department of Botany and Plant Sciences and a co-author of the study. "Instead of planting hundreds of seedlings and waiting years to see which flower type they become, we can make those decisions at the beginning. That makes breeding much more efficient."
Today, many California avocado growers devote about 10% of an orchard to B-type pollinizer trees that help nearby A-type trees like Hass produce more fruit. Those pollinizers often produce fruit with little commercial value.
One exception is the Luna, a commercially desirable B-type avocado developed through UCR's breeding program. Researchers say discoveries like this one could help them develop more varieties with the same combination of high-quality fruit and pollination benefits.
Breeders hope the new genetic marker will make it easier to develop high-quality B-type varieties that improve pollination while also producing fruit growers want to sell.
"Our goal is to create avocados with outstanding fruit quality," Focht said. "Now we can intentionally focus on producing the flower types we need instead of leaving it to chance."
The UCR team provided hundreds of genetically diverse avocado trees to the study, representing numerous varieties and related species. They also spent days, and often nights, documenting exactly when thousands of flowers opened and closed, because even small changes in temperature can shift flowering behavior by hours.
"We had to monitor the flowers hour by hour in the field to accurately determine whether each tree belonged to the A or B flowering group," Soares dos Santos said.
"Because flowering behavior changes throughout the day and is influenced by environmental conditions, we needed to observe the same trees repeatedly at different times. We confirmed the flowering type of more than 500 individual trees, providing the phenotypic data needed for genetic analyses."
The UCR team also confirmed that flower type follows the classic inheritance patterns first described by Gregor Mendel, helping demonstrate that a single gene controls the trait.
"One allele of this gene is dominant, and it shows a unique pattern of temporal regulation that is closely linked to the difference in the timing of flowers opening and closing between A- and B-types," Groh said.
By comparing avocado genomes with those of related tree species, the researchers also found that the same two versions of the gene are shared by at least 26 relatives, suggesting this flowering strategy has persisted for roughly 42 million years.
While using gene editing to alter flower type remains many years away, the newly identified genetic marker offers breeders an immediate tool for selecting seedlings with the traits they want before committing years of time and valuable orchard space.
"People have wondered about this trait since avocado breeding began in California," Focht said. "Now we finally understand the genetics behind it, and we can use that knowledge to build the next generation of avocados."
