Trunk-injected oxytetracycline alters the leaf endophytic microbiome and promotes health recovery in Huanglongbing-affected citrus

Huanglongbing (HLB) is a disease of citrus that is affecting citrus industries worldwide. To date, trunk-injected oxytetracycline (OTC) has shown positive effects in reducing HLB severity and improving tree health and productivity. However, reports about how OTC affects the endophytic microbiome in leaves of HLB-affected citrus have not been fully documented. We hypothesized that trunk-injected OTC alters the community and structure of the endophytic leaf microbiome of HLB-affected citrus, affecting abundance of potential beneficial bacteria that promote citrus health. In this study, HLB-affected grapefruit trees were injected with OTC (50,000 ppm) or water (Control), and the leaf endophytic microbiomes were compared at 0, 15, and 45 days after injection via 16 S rDNA amplicon sequencing. “ Candidatus Liberibacter asiaticus” (CLas) titers and agronomic traits also were measured after the injection. Our results showed that application of OTC on HLB-affected citrus trees by trunk injection can reduce the HLB-associated pathogen CLas titers, improve the field performance of the trees, and alter the leaves’ endophytic microbiome. It also revealed that the application of OTC resulted in a reduction of potential beneficial bacteria 15 days after treatment, which was subsequently enriched 45 days after the treatment. In addition, Spearman correlation analysis showed a significantly negative correlation between the relative abundance of two potential beneficial genera ( Sphingomonas , and Aermicrobium ) with CLas. The observed increase of potential beneficial bacteria at 45d after OTC injection may be involved in improving field performance. And Sphingomonas and Aermicrobium may act as potential antagonists of CLas. Therefore, this study provides valuable information about CLas-microbiome interactions that can be explored for developing strategies that suppress citrus HLB.