Metagenomic Analysis Reveals Reduced Beneficial Microorganism Associations in Roots of Foot-Rot-Affected Citrus Trees

Abstract

Root endophytes have been shown to influence plant growth and plant responses to pathogens. Phytophthora spp. are important pathogens of citrus that cause foot rot and fibrous root decline. We hypothesize that foot rot infection by Phytophthora spp. can result in changes of the endophytic microbial community in citrus roots. Therefore, the endophytic (including bacterial and fungal) microbiome of roots from Phytophthora foot-rot-affected and healthy citrus trees were analyzed by Illumina sequencing of 16S ribosomal RNA and internal transcribed spacer amplicons. Results indicate that the composition and structure of the endophytic bacterial and fungal communities were changed in roots of foot-rot-affected citrus trees. The populations of bacterial genera Asteroleplasma, Pseudomonas, and Streptomyces were decreased in foot-rot-affected trees. Also, the relative abundance of Exophiala pisciphila and Glomeraceae spp. was significantly decreased in citrus roots. Pseudomonas and Streptomyces spp. are considered beneficial bacteria and E. pisciphila and Glomeraceae spp. are dark septate endophytes and arbuscular mycorrhizal fungi, respectively, which are involved in citrus health and growth. This study provides a baseline to continue investigating the interactions between the citrus host, Phytophthora spp., and beneficial microbes.