How Avocados Switch Sex Daily: The Science Explained

Avocado pollination mechanics have finally been decoded by researchers, according to a study published in the Proceedings of the National Academy of Sciences. By combining field observations with genetic analyses, scientists mapped the genomes of hundreds of avocado trees to identify the gene variants controlling temporal dichogamy, a biological mechanism where flowers functionally switch sexes daily to prevent self-pollination.

Cracking a Century-Old Botanical Mystery

For more than a century, botanists and commercial growers puzzled over how avocado trees avoid self-pollination despite possessing both male and female reproductive organs in a single flower. According to Jeffrey Groh, an evolutionary geneticist now at the University of California, Berkeley, the new research provides a genetic explanation for this pollination puzzle. Flowers function as dynamic structures rather than static decorations, displaying a pulsating rhythm of opening and closing.

Researchers mapped genomes in varying detail and tracked the hourly opening and closing of thousands of flowers. This revealed that the activity of a single gene named SDMYB oscillates like a clock to control flowering behaviors, according to the study. The genetic blueprints appear to have emerged more than 42 million years ago.

A-Type and B-Type Flowering Schedules Explained

Avocado trees divide into two distinct functional categories that operate on complementary daily schedules. According to field observations, A-type avocado trees open their female flowers in the morning and their male flowers in the afternoon. Conversely, B-type trees execute the exact opposite schedule, opening as female in the afternoon and male the following morning.

At any given moment, a tree acts as either functionally female or male to receive or release pollen. The underlying genetics dictate these rigid schedules. A-type trees carry one copy of each SDMYB gene variant, or allele. B-type trees hold two copies of the recessive version of the gene, according to the genetic analyses.

Supercharging Commercial Avocado Breeding and Orchard Design

The discovery of these genetic markers promises to accelerate commercial breeding programs. Graham Coop, an evolutionary geneticist and professor of evolution and ecology at UC Davis and the study’s senior author, explains that previously, growers could not tell whether a plant was an A- or a B-type until it flowered years later, which constituted a major impediment for breeding.

Orchard management relies heavily on mixing these types. California growers typically stock about 10 percent of an orchard with B-type pollinizer trees to boost fruit production in neighboring A-type trees. However, the fruit of B-type trees is often commercially undesirable compared to the world-favorite Hass avocado, which is an A-type variety, according to Marllon Soares dos Santos, an agricultural engineer at UC Riverside and co-author of the study.

Frequently Asked Questions

Why do avocado trees need to switch sexes?

Because individual avocado flowers contain both male and female organs, temporal dichogamy prevents self-pollination, allowing increased gene sharing that prunes deleterious mutations and boosts overall fitness.

What is the difference between A-type and B-type avocados?

A-type trees open female flowers in the morning and male flowers in the afternoon. B-type trees open female flowers in the afternoon and male flowers the next morning. A-type trees carry one of each SDMYB gene variant, while B-type trees hold two copies of the recessive version, according to the research.

How will this study help farmers right away?

Agricultural engineers like Marllon Soares dos Santos note that growers can now determine tree flower types at the seedling stage rather than waiting years, streamlining the creation of the next generation of avocados as envisioned by UCR botany researcher Eric Focht.

What Comes Next for Avocado Genetics

While direct gene editing applications for novel traits remain years away, identifying these genetic markers provides an immediate tool for selection. According to the research team, breeders can now select desired plants without waiting for them to mature and flower. This breakthrough clears a century-old hurdle and sets the stage for faster, more predictable agricultural development in the industry.