Avocado breeding timelines could shrink by years after researchers in the United States identified a genetic switch controlling how trees alternate between opening male and female flowers daily. According to a study led by University of California, Davis researchers, variation in a single gene dictates this 42-million-year-old rhythm, allowing breeders to sort seedlings before the plants ever flower.
The Century-Old Mystery of Avocado Pollination
Avocado trees are hermaphrodites, meaning every flower functions as either male by releasing pollen or female by receiving pollen at different times. Roughly half of all avocado trees, known as A-type plants, open female flowers in the morning and male flowers in the afternoon. B-type plants follow the exact opposite schedule, opening female flowers in the afternoon and male flowers the following morning, according to data from UC Davis and UC Riverside.
This daily partitioning prevents self-pollination and subsequent inbreeding. Growers have known about this behavior for over a century. Because A-type and B-type varieties pollinate one another, commercial farmers typically plant a mix of both types in the same orchard. As UC Davis professor of evolution and ecology Graham Coop explained, having reciprocally and synchronously flowering trees allows avocados to exchange pollen throughout the entire day.
Pinpointing the SDMYB Gene in Avocado Genomes
To locate the genetic driver behind this daily rhythm, researchers analyzed the genomes of hundreds of avocado trees grown by collaborating scientists at UC Riverside. By comparing these genomes against recorded flowering behavior, the team isolated a single floral transcription factor gene called SDMYB that dictates whether a tree follows an A-type or B-type schedule, according to findings published in the Proceedings of the National Academy of Sciences.
Prior to this discovery, identifying whether a young avocado seedling would become an A-type or B-type tree was impossible without waiting for the plant to mature. Because avocado trees can take anywhere from 5 to 10 years to flower for the first time, this lag served as a major roadblock for breeders. UC Riverside staff research associate Eric Focht noted that the genetic markers give growers a direct shortcut to make smarter breeding decisions at the seedling stage.
Did you know?
Many California avocado growers typically devote about 10% of an orchard to B-type pollinizer trees to help A-type varieties like Hass set fruit. While many pollinizer trees produce low-commercial-value fruit, breeding programs have introduced commercially desirable B-type varieties such as the Luna UCR™.
Accelerating Commercial Avocado Varieties
The newly identified genetic markers allow breeders to bypass years of field waiting. According to UC Riverside postdoctoral researcher Marllon Soares dos Santos, researchers can now make selection decisions at the very beginning of the process instead of planting hundreds of seedlings and waiting up to a decade to observe their flower types.
Jeffrey Groh, who led the project as a PhD student at UC Davis and is now a postdoctoral fellow at UC Berkeley, stated that the research provides a genetic explanation for a long-standing pollination mystery. Breeders plan to use these markers to develop new high-quality B-type varieties that deliver both optimal pollination and strong commercial value.
Frequently Asked Questions
What controls the flowering schedule of avocado trees?
According to researchers at UC Davis and UC Riverside, variation in a single gene called SDMYB dictates whether an avocado tree follows an A-type or B-type flowering schedule.
Why do avocado orchards contain both A-type and B-type trees?
Farmers plant a mixture of both types because their daily pollination schedules complement one another. When A-type trees open female flowers in the morning, B-type trees are shedding pollen, which maximizes cross-pollination.
How long did it previously take to identify an avocado tree’s flower type?
Before the identification of the SDMYB genetic marker, growers had to wait for mature trees to flower, a process that takes anywhere from 5 to 10 years.
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