Evaluation of trunk-injected antibiotics for huanglongbing management in citrus

Huanglongbing (HLB) is a devastating citrus disease caused by Candidatus Liberibacter asiaticus (CLas) and transmitted by the Asian citrus psyllid (ACP), Diaphorina citri Kuwayama. The disease has had a profound impact on citrus production in Florida since its discovery in 2005. The disease has become ubiquitous across the state, with nearly 100% of citrus trees estimated to be currently infected. Recent studies have demonstrated that trunk-injected oxytetracycline (OTC) can effectively reduce CLas levels in mature citrus trees, leading to improved yield. Furthermore, OTC treatments have been shown to decrease CLas acquisition by both adult and nymph ACP, thereby disrupting pathogen transmission. However, the development of resistance to OTC necessitates exploration of alternative antimicrobial treatments to rotate with OTC. In this context, streptomycin has emerged as a potential rotational candidate for trunk injection. The objective of this investigation was to evaluate the efficacy of streptomycin with and without co-injected OTC, as an alternative treatment for remediation of HLB symptoms in commercial citrus. We monitored CLas infection in treated trees up to 300 days post-injection and quantified the effects of the treatments on pathogen acquisition, tree growth, and yield. Our results indicate that both streptomycin and OTC similarly reduce CLas abundance in trees, disrupt pathogen acquisition by ACP, and increase yield as compared with non-injected controls.