Evaluation of the Spatiotemporal Dynamics of Oxytetracycline and Its Control Effect Against Citrus Huanglongbing via Trunk Injection

Abstract

Citrus huanglongbing (HLB) or greening is a devastating bacterial disease that has destroyed millions of trees and is associated with phloem-residing 'Candidatus Liberibacter asiaticus' (Las) in Florida. In this study, we evaluated the spatiotemporal dynamics of oxytetracycline in planta and its control effect against HLB via trunk injection. Las-infected 'Hamlin' sweet orange trees on 'Swingle' citrumelo rootstock at the early stage of decline were treated with oxytetracycline hydrochloride (OTC) using trunk injection with varying number of injection ports. Spatiotemporal distribution of OTC and dynamics of Las populations were monitored by high-performance liquid chromatography method and qPCR assay, respectively. Uniform distribution of OTC throughout tree canopies and root system was achieved 2 days postinjection. High levels of OTC (>850 µg/kg) were maintained in leaf and root for at least 1 month and moderate OTC (>500 µg/kg) persisted for more than 9 months. Reduction of Las populations in root system and leaves of OTC-treated trees were over 95% and 99% (i.e., 1.76 and 2.19 log reduction) between 2 and 28 days postinjection. Conditions of trees receiving OTC treatment were improved, fruit yield was increased, and juice acidity was lowered than water-injected control even though their differences were not statistically significant during the test period. Our study demonstrated that trunk injection of OTC could be used as an effective measure for integrated management of citrus HLB.

Uptake, Translocation, and Stability of Oxytetracycline and Streptomycin in Citrus Plants

“…Consequently, a proper wait time should be allowed between the application of antibiotics and harvest date (i.e., preharvest interval) in order to achieve low levels of antibiotics in harvested fruits. In fact, a recent study showed that trunk injection of oxytetracycline could result in low levels (202 µg/kg) of this antibiotic in citrus fruit [37]. The detected levels of oxytetracycline in citrus fruits were far below the minimum inhibitory concentration for gut flora, indicating negligible impacts on gut flora [37].…”

Bacterial Citrus Diseases: Major Threats and Recent Progress

“…are restricted to the phloem, which makes it difficult to effectively control them using foliar applications of bactericides. Among the alternatives that have been shown to overcome these limitations are trunk injection and the use of nanoemulsion formulations that enhance bactericide penetration [104,105].…”

Choosing an Adequate Pesticide Delivery System for Managing Pathogens with Difficult Biologies: Case Studies onDiplodia corticola, Venturia inaequalisandErwinia amylovora

“…Agricultural, urban, and natural tree stands have been the focus of extensive plant pathogen diagnostic and disease management research in recent decades [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] which recorded an increase in the number of new fungal and bacterial pathogens and their detrimental impact on agroecosystems, ecosystems, and the human society. The economic effects of these pathogens are reflected in lost fresh fruit produce [17][18][19], reduced yields and quality of fruit or wood and cork products [20,21], diminished ecological tree services, and death of whole trees, stands, and forest regions or decimation of fruit industries [19,22].…”

“…The most investigated tree fruit crops and their pathogens and insect pests are citrus (e.g. Candidatus Liberibacter asiaticus) [14,15], avocado (e.g. avocado thrips, Scirtothrips perseae; Phytophthora root rot, Phytophthora cinnamomi) [49,50], apple (e.g.…”

“…While trunk injection for pesticide delivery is a relatively new technology investigated in tree-based agriculture for managing diseases like citrus greening [14][15][16][66][67][68] or fire blight [11,44], research in agricultural engineering will first need to design or invent an application system/s that allow scalability, i.e. achieving simultaneous trunk injection of large number of trees in a short period of time.…”