Tree injection of oxytetracycline and streptomycin reduces phytopathogen titer and transmission by Asian citrus psyllid and improves health of citrus expressing Huanglongbing

Since its discovery in 2005, huanglongbing (HLB) has devastated citrus production in Florida. The disease is caused by the bacterium Candidatus Liberibacter asiaticus (CLas) and is transmitted by the Asian citrus psyllid, Diaphorina citri Kuwayama. Nearly 100% of citrus trees in Florida are currently infected. Recent studies have shown that trunk-injected oxytetracycline (OTC) effectively reduces CLas titer in mature citrus trees and improves yield. Furthermore, trunk injections of OTC can decrease acquisition of CLas by D. citri. An immediate concern associated with using broad-spectrum antibiotics in agriculture is the potential to select for evolution of antibiotic resistance. Therefore, we compared the effectiveness of streptomycin with OTC to determine if this antibiotic could be useful as a potential rotational treatment. Injection of trees with antibiotics reduced CLas infection and in some cases improved fruit yield and quality above control levels Reduced pathogen titers following injection of antibiotics were coincident with lower CLas acquisition and inoculation by laboratory deployed and wild-type D. citri collected from the field, respectively. Our results indicate that trunk injection of OTC in rotation with streptomycin may be useful in management of HLB by reducing CLas infection in trees and disrupting CLas transmission by the ACP vector.