Researchers have solved a century-old agricultural puzzle by identifying the specific genetic mechanism that controls how avocado trees alternate between male and female phases. All avocado trees are hermaphrodites, but their flowers function either as male by releasing pollen or as female by receiving pollen at different times. Botanist A.B. Stout first documented this daily rhythmic alternation of sexes in the 1920s.
Unlocking the Century-Old Mystery of Avocado Flower Rhythms
To investigate how this process functions, a research team led by scientists from the University of California, Davis, froze the leaves of different avocado varieties to sequence their DNA. Additionally, evolutionary geneticist and lead study author Jeffrey Groh camped in a tent in an orchard for a few days, sampling flowers every couple of hours to preserve RNA and test gene expression fluctuations. Scientists from the University of California Riverside also contributed by monitoring hundreds of genetically diverse avocado trees and recording opening and closing times.
How the SDMYB Gene Controls A-Type and B-Type Schedules
The findings, published in the Proceedings of the National Academy of Sciences, reveal that variations in a single gene called cnas.ucr.edu dictate this daily rhythm. Specifically, a dominant version of the gene produces A-type flowering, while a recessive version results in B-type trees.
Avocado trees adhere to one of two distinct schedules to minimize the risk of inbreeding through self-pollination:
- A-type plants: Open female flowers in the morning and male flowers in the afternoon, or open flowers as females in the morning before reopening as males the following afternoon (varieties such as Hass follow this pattern).
- B-type plants: Follow the opposite schedule (varieties such as Bacon follow this pattern).
Because every avocado flower opens twice over two consecutive days—first functioning only as a female, closing for the night, and reopening the next day as a male—growers traditionally plant a mixture of A- and B-type trees in orchards to ensure cross-pollination. This staggered timing maintains a continuous supply of pollen throughout the day.
Implications for Future Breeding Programs and Climate Resilience
The discovery of the SDMYB gene carries major practical advantages for agriculture. U.S. consumption has quadrupled since 2000, fueling skyrocketing demand amid America’s avocado obsession. Previously, breeders could not distinguish between A and B types until a tree matured and produced its first flowers—a process that can take up to 15 years.
By linking flowering behavior directly to the SDMYB gene, breeders can now use a DNA test to determine whether a seedling will become an A-type or B-type tree long before the plant reaches maturity. According to msn.com, this breakthrough could shave off years in the process of breeding new varieties for future climates. Furthermore, UC Davis evolution and ecology professor Graham Coop noted that variations of the gene evolved over 42 million years ago, indicating that dozens of related plant species share this same mating system.
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