Basic Composition and Structure of the Phyllosphere Fungal Community of Rubber Trees with Powdery Mildew
A total of 593,237 high-quality sequence fragments were obtained from the 16 samples of rubber tree powdery mildew fungi via MiSeq high-throughput sequencing. The number of sequences in a single sample ranged from 30,129 to 44,619, with an average of 37,077, and a total of 1406 OTUs were detected. Their average sequence length was 293.01 bp, with 57.38% of the sequences being 301–320 bp in size and 26.99% being 241–260 bp. The samples’ dilution curves showed differences in their fungal diversity. The general flattening of these dilution curves indicated that the amount of sequenced data was robust, and that the depth of sequencing largely covered all species in the rubber tree leaf samples (Figure S1).
A total of 1398 OTUs were detected in the four regions after quality control, with a ranking of WZS > WN > BS > DZ (Figure 1). There were 90 overlapping OTUs across the four regions, accounting for 6.44% of the total number of OTUs in all pooled samples. This indicated that although the samples were all sourced from the rubber powdery mildew phyllosphere, there were stark differences in OTU levels among the four rubber tree-growing regions.
The community composition of each sample was calculated at different taxonomic levels, for which a total of six phyla, 26 classes, 69 orders, 157 families, and 351 genera of fungi were identified. At the phylum level, the community composition of samples from all four regions was similar, with Ascomycota and Basidiomycota dominating, though their relative abundances varied across regions (Figure 2-1). The relative abundance of Ascomycota ranged from 43.76% to 99.80%, and that of Basidiomycota ranged from 0.17% to 10.91% in the 16 samples (Figure 2-2).
The dominant genera in all four regions consisted of Erysiphe andCladosporium . In addition, the dominant fungal taxa of the regions’ healthy leaves differed (Figure 2-2). The dominant genera in the Level 3 leaves of the samples from the four regions are listed in Table S4. In addition, the healthy leaves (Level 0) and Level 3 leaves in the four regions also included a number of less abundant community members. The relative abundance of fungi (others) whose taxonomic status was unclear or not yet identified ranged from 1.04% to 10.58% (Table S4).
In summary, apart from WZS, the dominant fungal genera in the other three regions for both Level 3-infected leaves and healthy leaves consisted of Erysiphe and Cladosporium , with one to three different subdominant genera per region, albeit all at low relative abundances. Therefore, the two levels of infected and healthy leaves of rubber trees growing at the same site differed in the relative abundance of phyllosphere microbiome but not in the genus-level community composition, whereas the latter varied across the four regions. Although powdery mildew had little effect on the structure of the phyllosphere fungal community, it did affect the relative abundance of each community.