Comparative analysis of bacterial and fungal endophytes responses to Candidatus Liberibacter asiaticus infection in leaf midribs of Citrus reticulata cv. Shatangju

Abstract

The endophytic bacterial and fungal profiles were comparatively studied between Citrus Huanglongbing (HLB) infected and uninfected healthy leaves of a mandarin cultivar, Shatangju (Citrus reticulata Blanco), by using the next generation sequencing technology. A total of 53 endophytic bacterial orders in12 phyla and 24 endophytic fungal orders in 2 phyla were detected in healthy, asymptomatic and symptomatic leaf midribs. It was found that the predominant endophytic bacteria belonged to Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes and the predominant endophytic fungi belonged to Ascomycota and Basidiomycota. Operational taxonomic unit (OTU) analysis showed that OTU_2 and OTU_6 were the core endophytic fungal OTUs, and OTU_10, OTU_4 and OTU_141 were the core endophytic bacterial OTUs. The richness and diversity of the endophytic microbes were affected by infection of the HLB bacterium, Candidatus Liberibacter asiaticus (CLas). The most significant change was the reduction in endophytic fungal OTUs following CLas infection. Eleven endophytic fungal OTUs and 24 endophytic bacterial OTUs were found to be associated with tree healthy status in citrus. Some of the healthy and HLB disease specific OTUs were discussed, with emphasis on their possible roles in HLB pathogenesis.