Brassinosteroids (Brs), a class of plant steroidal hormones, protect various crop species, including maize, wheat, strawberries, and grapes, from biotic and abiotic stress. However, their impact on citrus remains unexplored. The Florida citrus industry faces a significant threat from Huanglongbing (HLB), a devastating disease that deteriorates tree health and affects overall yield. Given the efficacy of Brs in enhancing stress tolerance in other crops, their potential role in citrus resilience needs an investigation. To address this knowledge gap, we examined the plant's performance after foliar application of Brs at different intervals. Three-year-old Valencia sweet oranges grafted onto UF-R5 rootstock were grown in pots and treated with Brs at three intervals: every two weeks, once a month, and every other month. Key parameters, including shoot and root biomass, canopy volume, scion and rootstock diameters, specific leaf area, total phenolic content, and flavonoid content were assessed. After one year, there was a significant increase in flavonoid content in Brs-treated plants, regardless of application frequency. There was a positive trend on the response to the treatment of the other parameters studied, althoughnot statistically significant by the first year of treatment. This finding suggests that Brs may quickly enhance secondary metabolite production in citrus, but their impact on overall growth may require longer time of exposure to the treatment. Further investigation will elucidate this.
