Tug of War-Who is the Winner? Canker Disease Restructures the Endophytic Bacterial Community of Citrus

Abstract

High-throughput sequencing and a 16S rRNA gene clone library amplicon analysis were used to study the endophytic microbial diversity in citrus leaves in response to a Xanthomonas citri pv. Citri (Xcc) infection in an effort to develop a biocontrol scheme for citrus canker disease. There are more species of moderate citrus canker disease (MCD) than severe citrus canker disease (SCD) in terms of both Shannon and Simpson index measurements. Taxonomy has shown that the MCD Firmicutes group (25.2%) outnumber the SCD group (0.55%). Some Firmicutes can suppress Xcc, but in SCD leaves, they are in a competitive position and do not have a dominating niche; therefore, their population is greatly decreased. Sphingomonas and Methylobacterium, two genera of the phylum Proteobacteria, are growth-promoting and stress-resistant in most plants and comprise approximately 60% of the SCD group, whereas the MCD group was less abundant. In conclusion, citrus canker disease restructures bacterial communities in infected leaves, causing the endophytic community to evolve toward "weakening its spear and strengthening its shield." This research provides support for the idea that introducing helpful bacterial strains in advance may alter the relative abundance of bacteria in a given area and hence decrease the likelihood of infection by harmful bacteria. The future of sequencing technology lies in research on microbial community functions, the elucidation of plant processes and pathogen occurrence, and support for the development of plant biological control technologies.