The citrus industry across the globe, including Florida, has been severely affected by the citrus greening disease (Huanglongbing, HLB), which is associated with the bacterium Candidatus Liberibacter asiaticus (CLas) and vectored by the Asian citrus psyllid. While no single method has been found to completely control CLas, ways to mitigate its effects on citrus trees have been increasingly studied. One recent management method that has been attracting attention is oxytetracycline (OTC) trunk injections. While initial research has shown that OTC trunk injections have been able to reduce HLB symptoms, there have been some inconsistencies about the extent of that reduction between different cultivars. A limited number of cultivars have been studied, mainly focusing on the sweet oranges ‘Valencia’ and ‘Hamlin’. The limited cultivars injected that are closely genetically related may cause differences in the effectiveness of treatment. There is a gap in knowledge about how OTC treatments affect cultivars with diverse genetic backgrounds. The aim of this study was to investigate the effects of OTC trunk injections on above and belowground tree health of various United States Department of Agriculture developed citrus cultivars. A completely randomized experimental design comprising 10-year-old mandarin, grapefruit, and sweet orange-like cultivars grafted on ‘US-942’ and ‘US-812’ rootstocks was used to study OTC trunk injection rates applied once a year at the recommended label concentrations (n = 21). Similarly, trees from the same cultivars grafted on the same rootstocks not receiving any injections were used as controls (n = 21). Throughout the experiment, above and belowground components were analyzed for any changes. Aboveground measurements included tree health within and between cultivars: canopy dimensions, leaf CLas titer, fruit size, drop and harvest count, and OTC residue in leaves. Belowground measurements included analysis of root and microbiome health by observing root density, root CLas titer, root OTC residue, and microbiome population diversity. The results are helping researchers to utilize OTC trunk injections more effectively.
