ASHS 2025 Conference

Citrus production in the State of Florida has been decimated by the disease Huanglongbing (HLB). This disease is associated with the phloem-limited, gram-negative bacteria Candidatus Liberibacter asiaticus (CLas) and is vectored by the Asian citrus psyllid (Diaphorina Citri). Since HLB was first identified in Florida in 2005 it spread rapidly and was considered endemic in the state by 2013, resulting in a nearly 90% decline in citrus fruit production. While breeding more tolerant or fully resistant cultivars is likely the best long-term solution, trunk injections of the antibiotic oxytetracycline were granted emergency use approval in October 2022 to combat the bacteria. Historically most of Florida’s citrus production has been sweet orange (Citrus sinensis (L.) Osbeck) cultivars including ‘Hamlin’ and ‘Valencia’ which were primarily destined for juice processing. Unfortunately, all known commercial sweet orange cultivars are susceptible to HLB infection leading to the rapid and drastic decrease in production across the state. Of the sweet orange cultivars that have been released by the University of Florida Institute of Food and Agricultural Sciences (UF-IFAS), Orie and Louise Lee (‘OLL’) lines have shown some degree of tolerance to HLB in cultivar field trials. In our experiment we evaluated the effects of rootstock selection and oxytetracycline (OTC) trunk injections on the fruit and juice quality of the ‘OLL-8’ sweet orange scion. Three of the evaluated rootstocks (‘US-942’, ‘US-897’, and ‘Swingle’) are industry standard diploids, while the other three rootstocks (‘UFR-2’, ‘UFR-4’, and ‘UFR-6’) are tetraploids released by the University of Florida. For each of these rootstocks there were trees that were injected with OTC and untreated control trees. Fruit were harvested at several time points and data were collected on juice quality attributes including titratable acidity in citric acid equivalents, total soluble solids, sugar/acid ratio, pounds-solids per box, and juice color, as well as fruit characteristics including mass, diameter, total yield, and premature fruit drop. The trees that were injected with OTC had significantly larger mean fruit diameter, higher mean ratio, and lower premature fruit drop than untreated controls. There was also evidence for statistically significant differences among rootstock selections in conjunction with the ‘OLL-8’ scion for each of the characteristics that were evaluated. These results indicate that rootstock selection and OTC-trunk injections can significantly improve fruit and juice quality of the ‘OLL-8’ sweet orange scion. However, more research is needed on the effects of OTC injections in different rootstock-scion combinations.