Background: Endophytic bacteria are considered as symbionts living within plants and are influenced by abiotic and biotic environments. Pathogen cause biotic stress, which may change physiology of plants and may affect the endophytic bacterial communiy. Here, we reveal how endophytic bacteria in tumorous stem mustard (Brassica juncea var. tumida) are affected by plant physiological changes caused by Plasmodiophora brassicae using 16S rRNA high-throughput sequencing. Results: The results showed that Proteobacteria was the dominant group in both healthy roots and clubroots, but their abundance differed. At the genus level, Pseudomonas was dominant in clubroots, whereas Rhodanobacter was the dominant in healthy roots. Hierarchical clustering, UniFrac-weighted principal component analysis (PCA), non-metric multidimensional scaling (NMDS) and analysis of similarities (ANOSIM) indicated significant differences between the endophytic bacterial communities in healthy roots and clubroots. The physiological properties including soluble sugar, soluble protein, methanol, peroxidase (POD) and superoxide dismutase (SOD) significantly differed between healthy roots and clubroots. The distance-based redundancy analysis (db-RDA) and two-factor correlation network showed that soluble sugar, soluble protein and methanol were strongly related to the endophytic bacterial community in clubroots, whereas POD and SOD correlated with the endophytic bacterial community in healthy roots. Conclusions: Our results illustrate that physiologcial changes caused by P. brassicae infection may alter the endophytic bacterial community in clubroots of tumorous stem mustard.

It is well known that plant genotype can regulate phyllosphere fungi at the species level. However, little is known about how plant varieties shape the fungal communities in the phyllosphere. In this study, four types of maize varieties with various levels of resistances to Exserohilum turcicum were subjected to high−throughput sequencing to reveal the properties that influences the composition of phyllosphere fungal communities. The dominant fungi genera for all four maize varieties were Alternaria at different relative abundances, followed by Nigrospora. Hierarchical clustering analysis, non-metric multidimensional scaling and similarity analysis confirmed that the fungal communities in the phyllosphere of the four varieties were significantly different and clustered into the respective maize variety they inhabited. The findings from Redundancy Analysis (RDA) indicated that both maize resistance and leaf chemical constituents, including nitrogen, phosphorus, tannins, and flavonoids, were the major drivers in determining the composition of phyllosphere fungal communities. Among these factors, maize resistance was found to be the most influential, followed by phosphorus. The co-occurrence network of the fungal communities in the phyllosphere of highly resistant variety had higher complexity, integrity and stability compared to others maize varieties. In a conclusion, maize variety resistance and leaf chemical constituents play a major role in shaping the phyllosphere fungal community. The work proposes a link between the assembled fungal communities within the phyllosphere with maize variety that is resistant to pathogenic fungi infection.

Enterobacter cloacae is a symbiotic bacterium, which is one of the species in intestinal microbiota in many humans and animals. In some cases, it causes harmful diseases in humans. More and more studies showed that E. cloacae caused disease on plants, such as macadamia, ginger, mulberry, onion, chili pepper and rice. Garlic (Allium sativum L.) is one of crops with economic importance in the world. It is also widely grown in China. During 2018 to 2020, the naturally infected garlic bulbs from garlic fields in Kaifeng of Henan Province (34.55° N; 114.78° E) showed dry brown discoloration and rot symptoms. The diseased garlic seriously affected its edible value. Voucher specimens collected on June, 2019 were deposited in Plant Disease Laboratory of Tianjin Agricultural University under accession no. PATAU190620. To identify the causal agent of this disease, the bulb tissues of infected garlic were surface-disinfested in 0.6% sodium hypochlorite, dipped in75% ethanol, and then dipped in sterile distilled water. These bulbs were plated on LB medium and incubated at 37℃. A number of white colonies grew on the medium after plating for 16 h. All colonies were round, white, opaque, smooth, and gram-negative, which is a typical characteristic of Enterobacter. To confirm the initial identification of the isolated bacterium, the fragments of 16S rRNA gene and gyrA gene of 6 colonies were amplified, respectively. The PCR products were purified and sequenced. All 16S rRNA and gyrA sequences were identical to each other. The sequences of 16S rRNA gene and gyrA gene were deposited in GenBank with accession numbers MW730711 and MW768876, respectively. BLAST searches were conducted using the sequences of 16S rRNA and gyrA. The results showed 99.72%, and 96.91% identity with the corresponding sequences of E. cloacae strain CBG15936 (CP046116.1), respectively. Phylogenetic trees were performed using the neighbor-joining (NJ) method of MAGA X based on the sequences of 16S rRNA gene and gyrA gene. Phylogenetic tree indicated that isolates are most likely E. cloacae. Pathogenicity tests were performed by puncturing garlic bulbs with a hypodermic needle, followed by dipping in bacterial suspension with the concentration of 2×108 CFU for 5 minutes. As control, the garlic bulbs were treated with sterile water. The inoculated and control were incubated at 30°C. 7 days after inoculation, brown discoloration and rot were developed on all inoculated garlic bulbs. No symptoms were observed in the control group.The symptoms were similar to that observed on the original diseased garlic bulbs. The garlic bulbs in inoculated and control were ten replicates in each independent biological experiments. The pathogenicity tests were conducted three times with similar results. The bacteria were re-isolated from the symptomatic diseased garlics and confirmed as E. cloacae by morphological and sequence analyses as above. The re-isolated bacteria were identified by biochemical and physiological characteristics using API 20E strips. The results of the identification were identical to those of the edible ginger strains and the chili pepper strains. As far as we know, this is the first report of bulb decay on garlic caused by E. cloacae. The results are of great significance not only for the management of garlic bulbs during postharvest handling and storage, but also for the further research of opportunistic human pathogens E. cloacae.

Sclerotinia sclerotiorum is one of the most damaging and economically important necrotrophic plant pathogens, infecting more than 400 plant species globally. Although the phenylpyrrole fungicide fl...

A significant population of biocontrol microorganisms resides in the rhizosphere of plants, which can be utilized for plant disease control. To explore the potential of rhizosphere soil microorganisms as biocontrol agents against pepper blight, a bacterial strain Pa608 was screened from rhizosphere soil of pepper and identified as Pseudomonas aeruginosa through morphological characteristics and 16S rRNA sequences. The result showed that the strain Pa608 demonstrated antagonistic activity against Phytophthora capsici, effectively suppressing mycelial growth. The potted experiment showed a high control efficacy of 88.0%. Remarkably, the strain Pa608 also reduced the disease index of pepper blight in the field, resulting in control efficiencies of 74.9%. Moreover, the strain Pa608 also enhanced pepper plant height and yield. GC-MS analysis revealed the production of numerous secondary metabolites by the strain Pa608, with α-pinene displaying potent anti-oomycete activity by inhibiting P. capsici growth. In conclusion, P. aeruginosa Pa608 exhibited high biocontrol activity against P. capsici and can be utilized for the management of P. capsici in pepper cultivation.

Soil nematodes are considered indicators of soil quality due to their immediate responses to changes in the soil environment and plants. However, little is known about the effects of plant genotypes on the soil nematode community. To elucidate this, high-throughput sequencing and gas chromatography/mass spectrometry analysis was conducted to analyze the soil nematode community and the structure of root exudates in the rhizosphere of tomatoes with different resistance to Meloidognye incognita. The dominant soil nematode group in the soil of resistant tomatoes was Acrobeloides, while the soil nematode group in the rhizosphere of the susceptible and tolerant tomatoes was Meloidognye. Hierarchical clustering analysis and non-metric multidimensional scaling showed that the three soil nematode communities were clustered into three groups according to the resistance level of the tomato cultivars. The soil nematode community of the resistant tomatoes had a higher maturity index and a low plant-parasite index, Wasilewska index and disease index compared to the values of the susceptible and tolerant tomatoes. Redundancy analysis revealed that the disease index and root exudates were strongly related to the soil nematode community of three tomato cultivars. Taken together, the resistance of the tomato cultivars and root exudates jointly shapes the soil nematode community. This study provided a valuable contribution to understanding the mechanism of plant genotypes shaping the soil nematode community.