Field performance of novel citrus rootstocks grafted with Valencia orange and their response to systemic delivery of oxytetracycline

Authors: TARDIVO, CAROLINE - University Of Florida; PUGINA, GABRIEL - University Of Florida; Bowman, Kim; ALBRECHT, UTE - University Of Florida

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2025
Publication Date: 9/29/2025
Citation: Tardivo, C., Pugina, G., Bowman, K.D., Albrecht, U. Field performance of novel citrus rootstocks grafted with Valencia orange and their response to systemic delivery of oxytetracycline. Plants. 14(19):3020. 2025. https://doi.org/10.3390/plants14193020.
DOI: https://doi.org/10.3390/plants14193020

Interpretive Summary: The global citrus industry faces unprecedented challenges due to Huanglongbing (HLB), a devastating bacterial disease. This study evaluates the field performance of Valencia sweet orange grafted on nine novel USDA hybrid rootstocks as compared with two commercial standard rootstocks under Florida’s HLB-endemic conditions, while also examining the impact of systemic oxytetracycline (OTC) trunk injections, a recently approved and available commercial treatment. In both the first and second year of the study, OTC-injection had a significant positive influence on tree health, vigor, fruit quality, and fruit productivity, increasing yield in the second year by 51% as compared with untreated control trees. In both the first and second year of the study, rootstock also had a significant effect on tree health, vigor, fruit quality, and fruit productivity, with the new rootstock 'US SuperSour 4', exhibiting the best positive influence on fruit yield among the rootstocks, and increasing yield in the second year by 43% as compared with the common commercial rootstock 'Swingle'. The positive effects from rootstock and OTC-injection did not interact and appeared additive. The results from this research demonstrate that a combination of superior rootstock selection and the systemic delivery of OTC are effective tools to manage HLB and maximize the resilience of citrus trees to this devastating disease.

Technical Abstract: The global citrus industry faces unprecedented challenges due to Huanglongbing (HLB), a devastating disease caused by Candidatus Liberibacter asiaticus (CLas). This study evaluates the field performance of nine novel hybrid rootstocks, grafted with ‘Valencia’ sweet orange, under Florida’s HLB-endemic conditions, while also examining the impact of systemic oxytetracycline (OTC) trunk injections. Rootstocks with diverse genetic backgrounds, including Citrus maxima, C. tachibana, C. reticulata, and Poncirus trifoliata, were tested alongside two commercial standards, sour orange (C. aurantium) and Swingle (C. paradisi × P. trifoliata). Mature trees received annual OTC injections and were assessed over two years. In the first year of injection, OTC-treated trees exhibited significant improvements regardless of the rootstock, including a 36% increase in yield, an 11% increase in juice total soluble solids, and reduced CLas bacterial titers in leaves. The rootstock also influenced the grafted tree response, with US-1688 (‘US SuperSour 4’) demonstrating the most vigor and highest productivity. In the second year of injection, the positive effects of OTC were sustained, or even enhanced. Yield increased by 51% in OTC-injected trees compared to non-injected trees, and fruit weight, juice color, and total soluble solids (TSS) also improved significantly. A cumulative reduction in CLas titers was observed for leaves and roots, particularly in fibrous roots, indicating the benefits of repeated application. In addition, a larger percentage of finer roots was measured in response to the injections. Rootstock cultivar remained an important determinant of tree responses, with US-1688 and US-1672 emerging as the most productive under HLB pressure. The results from this research demonstrate the importance of rootstock selection for sustainable citrus cultivation while highlighting the benefits of integrating the systemic delivery of antibacterial therapies to manage HLB and maximize the resilience of citrus trees to this devastating disease.