RESULTS
Basic Composition and Structure of the Phyllosphere Bacteria of Rubber
Trees with Powdery Mildew
Four samples from each site region (BS, DZ, WZS, and WN), for a total of
16 tree-level leaf samples, were subjected to MiSeq high-throughput
sequencing of the phyllosphere microbial DNA of hosts with powdery
mildew. A total of 567,903 high-quality sequence fragments were read
after processing the raw data, with the number of sequences in a single
sample ranging from 30,261 to 44,775, with an average of 35,494. A total
of 520 OTUs were detected in the four regions after implementing the
quality control protocol. Across all regions, there were 36 overlapping
OTUs, constituting 6.92% of the total. This indicated that, although
all the samples were collected from a rubber powdery mildew phyllosphere
environment, there were significant differences in OTU levels among the
four regions (Figure 1).
The rarefication curves showed differences in the diversity of the
different sample phyla. The flattening of the rarefication curves for
each sample indicated that the amount of sequenced data was reasonably
sufficient, with a robust sequencing depth encompassing nearly all phyla
in the samples (Figure S1).
The community composition of each sample was tallied at various
taxonomic levels, and a total of 24 phyla, 49 classes, 100 orders, 172
families, and 256 genera of bacteria were identified. Apart from WZS_3,
the other samples were dominated at the phylum level byCyanobacteria , Poteobacteria , and Actinobacteria .
The dominant phyla in individual regions also included Firmicutesand Bacteroidetes , which had different relative abundances across
regions (Figure 2-1, 2-2). Excluding WZS_3, in the 15 samples the
relative abundance of Cyanobacteria ranged from 71.24% to
98.29%, that of Proteobacteria from 1.55% to 23.13%, and that
of Actinobacteria from 0.82% to 1.23%. The relative abundances
of Cyanobacteria , Proteobacteria , andActinobacteria in WZS_3 were 0.04%, 28.92%, and 10.59%,
respectively.
The dominant genera in BS were Cyanobacteria_norank (“norank” is used
when there is no scientific name for this level in the taxonomic
genealogy), Mitochondria_norank, and Rhodococcus ; in DZ,
Cyanobacteria_norank, Mitochondria_norank, and Curtobacteriumdominated; in WN, Cyanobacteria_norank, Pseudomonas , andPantoea dominated; and in WZS, Cyanobacteria_norank,Rhodococcus , and Pantoea dominated (Figure 2-1, 2-2). In
these regions, the most dominant communities in healthy rubber tree
leaves (Level 0) consisted of Cyanobacteria_norank, and likewise for
the dominant communities of infected leaves (Level 3). The relative
abundances (mean values) are shown in Table S2. Among subdominant
genera, the subdominant genera of both uninfected and Level 3-infected
leaves in BS were Mitochondria_norank and Rhodococcus ; the
subdominant genera in DZ were Mitochondria_norank (uninfected leaves)
and Curtobacterium (Level 3-infected leaves); the subdominant
genera in WN were Mitochondria_norank, Bacillus (uninfected
leaves), Pseudomonas , and Pantoea (Level 3-infected
leaves); and the subdominant genera in WZS were Rhodococcus(uninfected leaves) and Acidobacteria_norank (Level 3-infected leaves).
The relative abundances of subdominant genera in healthy leaves and
Level 3 leaves from the four regions are listed in Table S2.
In summary, the composition of the dominant genera varied little between
healthy leaves and Level 3-infected leaves. Although other dominant
genera were different among regions, their relative abundances were not
high. Therefore, the composition of genus-level communities of the three
levels of infected and healthy leaves of rubber trees at the same
growing site was similar, except for some differences in members’
relative abundances, while community composition at the genus level
differed markedly among regions.