Correlation between abnormal leaf color phenomenon and endophytic bacteria of Loropetalum chinense var. rubrum

In this study, in order to to investigate the correlation between endophytic bacteria in the leaves of Loropetalum chinense var. rubrum and the seasonal abnormal leaf coloration phenomenon of this plant, we performed plate isolation and culturing and subsequent 16S rDNA sequence analysis to isolate and identify endophytic bacteria from five types of abnormally colored leaves and normally red-colored leaves of L. chinense var. rubrum; we also analyzed differences in bacterial diversity, community structure, and functional levels among differently colored leaves. The results were as follows:(1)Compared with the normally red-colored leaves, we detected higher biomass of endophytic bacteria in the five types of abnormally colored leaves. Among the isolated bacteria, 16S rDNA sequence alignment and phylo-genetic tree analysis revealed that the presence of 906 bacterial strains were classified into 26 genera and 40 species.(2)While the smaller leaves were colonized by the largest number of endophytic bacterial species with a relatively uniform community structure, the opposite was true for bacteria isolated from the red- and yellow-pigmented leaves.(3)Comparison of the bacterial community data for abnormally colored leaves and those with the normally red-color revealed that not only were there significant differences with respect to the dominant genera and species, but also an enrichment of numerous bacterial species in the genera Methylobacterium and Pseudomonas in the five types of abnormally colored leaves. Particularly, we detected significantly larger numbers of Pseudomonas oryzihabitans.(4)We established that abnormally colored leaves(smaller, red spotted, and the red and yellow types)were characterized by an enrichment of bacteria with phosphorus solubilization, nitrogen fixation, IAA production, and salt tolerance functions, among which, four strains were found to have all four of these functions. Accordingly, we speculate that the abnormal leaf coloration of L. chinense var. rubrum is closely associated with the activities of these enriched functional bacteria. Our findings in this study indicate that the abnormal leaf coloration of L. chinense var. rubrum is closely associated with the enrichment of specific endophytic bacterial communities, which can thus provide clues for elucidating the mechanisms underlying the development of abnormal leaf color in this plant. Moreover, this may have important application value for the efficient cultivation of high-quality L. chinense var. rubrum.