DISCUSSION
Much research has focused on the relative macroscopic behavior of
phyllosphere microorganisms, and on the behavior of phyllosphere
microorganisms when non-specific parasitic bacteria infest plants.
However, there are no reports on obligate parasitic bacteria. In work by
Liu et al. (2022) on the community composition of phyllosphere
microorganisms of female and male ash trees (Fraxinus ), the core
phyllosphere microbiota was consistent, with the dominant phyla beingCyanobacteria and Proteobacteria ; however, some
differences were identified at the genus level, with the genusArsenophonus present in female ash only. As in the present study,
Guo (2009) collected samples from several sites and found that the
phyllosphere microorganisms of Populus tremula mainly consisted
of bacteria, followed by actinomycetes and fungi; however, the
populations and numbers of phyllosphere bacteria differed between sites.
Recently, by analyzing the structure of the phyllosphere fungal
communities of dominant tree species in broadleaf red pine forests in
Changbai Mountains, Wang et al. (2022) found that the dominant phyla
were Ascomycota and Basidiomycota and the dominant classes
were Dothideomycetes and Taphrinomycetes , and that the
canopy phyllosphere fungal communities of the six dominant tree species
differed significantly in composition. Some researchers have also
explored the complexity in host–microbe interactions and suggested that
the rational design and use of microbial tools, such as phyllosphere
probes, have broad potential for applications in economic production
activities, such as agriculture, viticulture, forestry, and biofuels,
and even for improving human health (Whitaker et al., 2019).
Sampling was based on the fact that geographical location and its
relative environment are decisive factors in the community composition
of interstitial microorganisms. Therefore, samples were collected from
four representative areas in Hainan Province, China: WN in eastern
Hainan, WZS and BS in central Hainan, and DZ in western Hainan. Sample
WZS_3 from Wuzhishan was markedly different when compared with sample
WZS_1 or WZS_2, and the sequencing results of its bacterial community
composition showed that a portion of the microorganisms came from the
soil, which might be related to the changeable climate in the field. It
was difficult to distinguish whether the samples were affected by the
nearby environment before sampling.
Only Level 3-infected leaves were collected because under field
conditions, Level 3 infections are the most common, Level 4 (entire leaf
covered with spots) infections mostly occur in greenhouse conditions,
while Level 2 (scattered spots on the surface) infections normally occur
on older leaves, or when the powdery mildew spots have faded, and only
form at the beginning or at the end of the powdery mildew period, when
the leaves age faster under higher temperatures. In addition, there were
differences in the relative abundances of the communities of Level
3-infected leaves in each region, which might be associated with the
number of environmental influences in the field. As a result, the mean
values were taken for comparison with uninfected healthy leaves (Level
0).
In this study, state-of-the-art molecular biotechnology was used to
investigate the phyllosphere microorganisms of rubber trees with powdery
mildew, to identify their dominant populations at the phylum and genus
levels, and to determine whether the incidence of powdery mildew disease
affected the phyllosphere microbial community structure and the relative
abundances of their taxa members. Because one plantation site was
sampled per region, the following inferences about regional differences
were made with caution.