Worldwide citrus production faces significant challenges from the devastating disease Huanglongbing (HLB), necessitating innovative management strategies. This study aimed to assess the performance of novel rootstocks under natural HLB-endemic conditions using regular management practices and the recently registered practice of delivering oxytetracycline (OTC) through trunk injection to reduce pathogen load. Nine novel rootstocks, US-1673, US-1676, US-1680, US-1672, US-1687, US-1688, US-2111, US-2132, and US-2137 with different genetic backgrounds, including Citrus maxima, C. tachibana, C. reticulata, and Poncirus trifoliata were included in the study. Also included were two commercial rootstock standards, sour orange (C. aurantium) and Swingle (C. paradisi × P. trifoliata). The rootstocks were grafted with ‘Valencia’ sweet orange (C. sinensis) scion and planted in 2014 in a randomized complete block design and 12 single-tree replications in an open field in St. Lucie County, Florida. In July 2023, half of the trees were injected with ReMedium TI® (95.0% oxytetracycline hydrochloride) dissolved in reverse osmosis water acidified with muriatic acid to a pH of 2.0. Each tree received 0.75 g OTC dissolved in a volume of 75 ml (10,000 ppm) administered using FlexInject injectors. Injections were performed in the scion, approximately 5 cm above the graft union. Tree measurements included tree size, canopy health, pathogen titers, fruit yield, and juice quality. Significant differences among rootstocks were observed in the years before injection. In the 2022-2023 production season, US-1688 induced the highest yield, and US-2132 induced the best juice quality. Preliminary results indicate an overall positive response to the OTC treatment across all rootstocks. Injected trees had a 36% increase in yield, an 11% increase in juice brix, and a significant reduction in leaf and root pathogen titers. As in the previous years, growth and productivity varied significantly among the rootstock cultivars. US-1688, a new release by USDA under the name SuperSour 4, continued to be among the largest, healthiest, and most productive trees. The results from this research demonstrate the importance of rootstock selection for sustainable citrus cultivation. It also highlights the benefits of integrating the systemic delivery of antibacterial therapies to maximize the resilience of citrus trees to HLB.
