Researchers at the University of California, Davis, and the University of California, Riverside, have identified a single gene, SDMYB, that controls the alternating daily sex cycle of avocado flowers. Published in the Proceedings of the National Academy of Sciences, the discovery allows breeders to determine tree flowering types via DNA testing years before maturity.
For more than a century, growers have managed orchards around a biological quirk: avocado trees are hermaphrodites whose flowers alternate between functioning as males and females over a two-day period. While the timing has long guided how farmers pair cultivars to maximize cross-pollination, the genetic mechanism behind it remained a mystery until now. A team of researchers has mapped the trait to a single floral transcription factor, resolving a century-old puzzle in horticulture.
How the SDMYB Gene Controls Avocado Flowering Schedules
All avocado trees share an unusual reproductive rhythm designed to prevent self-pollination and inbreeding. Each individual flower opens twice across two consecutive days. During its first opening, the flower functions exclusively as a female, capable of receiving pollen but unable to release it. The flower then closes for the night before reopening the following afternoon as a male to shed pollen.
While every flower follows this sequence, entire trees divide into two distinct operational schedules. A-type trees open their flowers as females in the morning and reopen as males the following afternoon. B-type trees execute the exact reverse pattern, starting their female phase in the afternoon and completing their male phase the next morning. To uncover why trees partition themselves this way, researchers sequenced the genomes of hundreds of avocado trees representing both categories according to published findings.
The genetic analysis traced the entire behavioral difference to a single locus: the SDMYB gene. This gene acts as a molecular switch, turning on a broader network of regulatory instructions that coordinate when individual flowers open, close, and transition between their sexual phases. A dominant version of the SDMYB gene produces A-type flowering behavior, whereas a recessive version results in B-type trees. This discovery demonstrates how a single genetic polymorphism accounts for an ancient rhythm that evolved approximately 42 million years ago.
DNA Testing Solves a Multi-Year Breeding Bottleneck
The identification of the floral transcription factor carries immediate practical applications for agricultural research and commercial cultivar development. Traditionally, avocado breeding programs faced a frustrating waiting game. Seedlings had to mature over several years before they produced their first blossoms, allowing scientists to observe whether a young tree followed an A-type or B-type schedule.
Because the new study links flowering behavior directly to the SDMYB gene, breeders can bypass years of waiting by screening young plants in a laboratory setting as detailed in the scientific reports. Instead of cultivating hundreds of immature plants to field size, researchers can use targeted DNA screening during the earliest stages of growth.
“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.”
Dr. Marllon Soares dos Santos, postdoctoral researcher in at UC Riverside and a co-author on the study
The selection hurdle is particularly steep during early cultivation phases. Ensuring that the surviving seedlings already possess targeted genetic traits significantly streamlines the development of more productive cultivars.
The research suggests that identifying these flowering combinations earlier can save both time and resources during the breeding process.
Optimizing Orchard Yields and Future Cultivar Development
Commercial avocado production relies heavily on the complementary relationship between the two flowering types. If an orchard consisted entirely of a single tree type, the simultaneous opening of flowers would restrict cross-pollination opportunities. By interplanting A-type and B-type cultivars, growers ensure that female-phase flowers on one set of trees overlap with pollen-releasing flowers on the adjacent set throughout the day.
With the genetic switch now identified, researchers plan to investigate the broader protein interactions and evolutionary origins of the SDMYB gene according to university disclosures. For commercial growers and agricultural scientists, the discovery translates into immediate utility, shortening a breeding cycle that has constrained orchard development for generations.