Scientists have identified a genetic switch that determines whether avocado trees flower as A-type or B-type—an advance that could compress breeding timelines by years. The discovery, led by researchers at UC Davis with key contributions from UC Riverside, explains a long-standing question about how avocado pollen and fertilization schedules are coordinated in orchards.
Avocado production depends on compatibility between neighboring trees. A- and B-type trees differ in when flowers open and close across the day, shaping whether one variety’s pollen is available when another variety is receptive. This timing largely prevents self-fertilization and improves the chances of successful cross-pollination and fruit set.
All avocado flowers begin life as female and later reopen as male, but the length and timing of these phases vary by cultivar group. Breeders have long used flowering behavior as a practical classification tool; however, predicting whether a seedling will become A or B has required waiting until maturity.
The new study pinpoints SDMYB, a floral transcription factor that acts as the central regulator of the flowering rhythm underlying daily sex alternation. Genetic analyses show that one allele is dominant, and that allele-specific temporal regulation aligns with the distinct opening/closing schedules of A- versus B-type flowers.
To connect genotype to phenotype, the UCR team provided hundreds of genetically diverse trees and conducted intensive field observations. Researchers tracked thousands of blossoms hour by hour, often overnight, because small environmental shifts—especially temperature—can shift the flowering timetable by hours.
Confirming Mendelian inheritance patterns, the researchers demonstrated that the flowering-type trait follows classic genetic expectations, consistent with control by a single gene. Comparative genomics further suggests the SDMYB variants have persisted through evolution: the same two versions appear across at least 26 related relatives, implying the reproductive strategy may date back roughly 42 million years.
The most immediate impact is practical. With the SDMYB marker, breeders can screen seedlings using DNA rather than waiting five to 10 years for flowering maturity. This accelerates selection decisions, reduces wasted orchard space, and enables more targeted development of pollinizer trees with commercially valuable fruit.
While genome editing to reprogram flower type is likely still distant, the marker already functions as a shortcut for modern breeding programs. Researchers aim to intentionally design orchards and varieties that deliver both improved pollination and fruit quality—transforming a once unpredictable trait into a controllable breeding target.
Subject of Research: Avocado flowering type determination (A/B) and breeding efficiency via genetic marker
Article Title: Balanced polymorphism in a floral transcription factor underlies the ancient rhythm of daily sex alternation in avocado
News Publication Date: 28-Jul-2026
Web References: https://www.pnas.org/doi/10.1073/pnas.2606876123
References: Proceedings of the National Academy of Sciences (PNAS), doi:10.1073/pnas.2606876123
Image Credits: Marllon Soares dos Santos/UCR
Keywords: avocado, flowering type, A/B, SDMYB, floral transcription factor, plant genetics, pollination, transcriptional regulation, breeding marker, phenotyping
