Objective To reveal the endosphere bacterial diversity and community structure of needle leaves of Pinus densiflora under different disease levels.

Method High-throughput sequencing technology was used to sequence the v3-v4 region of the bacterial 16s rRNA gene, to determine the diversity and community structure of endophytic bacteria of P. densiflora under different disease levels.

Result There were 388 587 effective bacterial sequences in needle leaves of coniferous-broadleaved mixed forests, totaling 679 OTUs, belonging to 28 phylum, 69 classes and 205 genera. There were 336 600 effective sequences of bacteria in needle leaves of coniferous mixed forests, totaling 656 OTUs, belonging to 29 phylum, 65 classes and 190 genera. In the coniferous-broadleaved mixed forests and coniferous mixed forests, the endophytic bacterial diversity of the asymptomatic needles of P. densiflora was higher than that of the infected needles. The predominant genera of endophytic bacteria in the asymptomatic needles were Massilia, Endobacter, Bryocella and Sphingomonas, and the relative abundance of Lactobacillus, Bryocella, Endobacter, Methylobacterium and Singulisphaera increased in infected needles, while Massilia and Sphingomonas decreased. The bacteria in coniferous needles with severe infection were distinguished from that in symptomatic coniferous needles and light infected needles.

Conclusion The infection of S. sapinea affects the abundance of endophytic bacteria. The endophytic bacteria of the two type of mixed forests are consistent with the trend of the effects of S. sapinea, and the endophytic bacterial diversity in needles of P. densiflora is decreased gradually with the level of blight in the mixed forests.