Abstract:
In this study, we sought to investigate the correlation between endophytic
bacteria colonizing the leaves of Loropetalum chinense var. rubrum and the seasonal
abnormal leaf coloration characteristic of this plant. Hence, we performed plate
isolation and culturing and subsequent 16S rDNA sequence analysis to isolate and
identify endophytic bacteria from leaves with five abnormal colors and normal
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 normal
red-colored leaves, we detected higher biomasses 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 the presence of 906 bacterial
strains 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 redand
yellow-pigmented leaves. (3) Comparison of the bacterial community data for
abnormally colored leaves and those with the normal 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
pigmentation in this plant. Moreover, this may have important application value for
the efficient cultivation of high-quality L. chinense var. rubrum.