Powdery mildew-induced changes in phyllosphere microbial community dynamics of cucumber

Abstract

As an important habitat for microorganisms, the phyllosphere has a great impact on plant growth and health, and changes in phyllosphere microorganisms are closely related to the occurrence of leaf diseases. However, there remains a limited understanding regarding alterations to the microbial community in the phyllosphere resulting from pathogen infections. Here, we analyzed and compared the differences in phyllosphere microorganisms of powdery mildew cucumber from three disease severity levels (0% < L1 < 30%, 30% ≤ L2 < 50%, L3 ≥ 50%, the number represents the lesion coverage rate of powdery mildew on leaves). There were significant differences in α diversity and community structure of phyllosphere communities under different disease levels. Disease severity altered the community structure of phyllosphere microorganisms, Rosenbergiella, Rickettsia, and Cladosporium accounted for the largest proportion in the L1 disease grade, while Bacillus, Pantoea, Kocuria, and Podosphaera had the highest relative abundance in the L3 disease grade. The co-occurrence network analysis of the phyllosphere microbial community indicated that the phyllosphere bacterial community was most affected by the severity of disease. Our results suggested that with the development of cucumber powdery mildew, the symbiotic relationship between species was broken, and the entire bacterial community tended to compete.

Keywords: co-occurrence network; cucumber powdery mildew; degree of disease; diversity; phyllosphere microbiota; relative abundance.

Figure 1.

Observations of the cucumber powdery mildew pathogen by optical microscope (10 × 40x). (A) Conidia, Arrows point to fibrous bodies. (B) Conidiophores. Scale Bar: 10 µm.

Figure 2.

α diversity analysis in different degrees of disease. The α diversity indices including Shannon, Simpson indice, ACE and Chao in bacteria (A) and fungi (B) (Levels of significance are indicated as follows: P < 0.05 marked as *, P < 0.01 marked as ** and P < 0.001 marked as ***).

Figure 3.

PCoA under different degrees of disease. (A) Bacteria. (B) Fungi.

Figure 4.

Phyllosphere microbial communities had unique or shared OTUs Venn diagrams at different disease levels. (A) Bacteria. (B) Fungi.

Figure 5.

The relative abundance of bacteria (A and C) and fungi (B and D) at phylum and genera level under different incidence levels.

Figure 6.

Analysis of differences in dominant genera under different disease levels. (A) Bacteria. (B) Fungi.

Figure 7.

Discriminant analysis of species differences in phyllosphere community composition of cucumber powdery mildew under different degrees of incidence. The taxon from the inside to the outside of the branching diagram represents phyla, class, order, family, and genus respectively. The red, green, and blue nodes represent significantly different taxonomic levels in the three incidence levels (LDA threshold of 4). The yellow node indicates that there is no significant difference in the different groups. (A, B) Bacteria (C, D) Fungi.

Figure 8.

The co-occurrence network of OTUs with the top 300 relative abundance of bacteria (A) and fungi (B) in the phyllosphere under different degrees of disease. The size of each node is proportional to the number of connections. The color of nodes indicates their classification at the gate level. The red line and the blue line represent strong positive linearity (r > 0.6) and strong negative linearity (r < − 0.6) and relationships, respectively.