Seasonal Variation in the Rhizosphere and Non-Rhizosphere Microbial Community Structures and Functions of Camellia yuhsienensis Hu

Dynamic changes of endophytic bacteria in the bark and leaves of medicinal plant Eucommia ulmoides in different seasons

The bark and leaves of the Eucommia ulmoides Oliv. (E. ulmoides) have good medicinal value. Studies show endophytes play important roles in host medicinal plant secondary metabolite synthesis, with season being a key influencing factor. Therefore, we used 16 S rRNA to detect endophytic bacteria (EB) in E. ulmoides bark and leaves collected in winter, spring, summer, and autumn, and analyzed the contents of major active components respectively. The results showed that the species diversity and richness of EB of the E. ulmoides bark were higher than those of leaves in all seasons except fall. Among them, the higher species diversity and richness were found in the E. ulmoides bark in winter and spring. EB community structure differed significantly between medicinal tissues and seasons. Concurrently, the bark and leaves of E. ulmoides showed abundant characteristic EB across seasons. For active components, geniposidic acid showed a significant positive correlation with EB diversity and richness, while the opposite was true for aucubin. Additionally, some dominant EB exhibited close correlations with the accumulation of active components. Delftia, enriched in autumn, correlated significantly positively with aucubin. Notably, the impact of the same EB genera on active components differed across medicinal tissues. For example, Sphingomonas, enriched in summer, correlated significantly positively with pinoresinol diglucoside (PDG) in the bark, but with aucubin in the leaves. In summary, EB of E. ulmoides was demonstrated high seasonal dynamics and tissue specificity, with seasonal characteristic EB like Delftia and Sphingomonas correlating with the accumulation of active components in medicinal tissues.

Diversity of Endophytes of Actinidia arguta in Different Seasons

The seasonal changes in environmental conditions can alter the growth states of host plants, thereby affecting the living environment of endophytes and forming different endophytic communities. This study employs Illumina MiSeq next-generation sequencing to analyze the 16SrRNA and ITS rDNA of endophytes in 24 samples of Actinidia arguta stem tissues across different seasons. The results revealed a high richness and diversity of endophytes in Actinidia arguta, with significant seasonal variations in microbial community richness. This study identified 897 genera across 36 phyla for bacteria and 251 genera across 8 phyla for fungi. Notably, 69 bacterial genera and 19 fungal genera significantly contributed to the differences in community structure across seasons. A distinctive feature of coexistence in the endophytic community, both specific and conservative across different seasons, was observed. The bacterial community in winter demonstrated significantly higher richness and diversity compared to the other seasons. Environmental factors likely influence the optimal timing for endophyte colonization. Solar radiation, temperature, precipitation, and relative humidity significantly impact the diversity of endophytic bacteria and fungi. In addition, seasonal variations show significant differences in the nutritional modes of fungal endophytes and the degradation, ligninolysis, and ureolysis functions of bacterial endophytes. This study elucidates the potential role of endophytes in assisting Actinidia arguta in adapting to seasonal changes and provides a theoretical basis for further exploration of functional microbial strains.

Seasonal changes in the abundance Fusarium proliferatium, microbial endophytes and nutrient levels in the roots of hybrid bamboo Bambusa pervariabilis × Dendrocalamopsis grandis

Plant root pathogens invade the soil around plant roots, disturbing the systemic balance, reducing plant defenses, and causing severe disease. At present, there are few studies on the severity of plant diseases caused by pathogen invasion in different seasons and how pathogens affect root microecology. In this study, we compared the levels of nutrients in the root tissues of the two groups of plants. We used 16S and ITS amplicon sequencing with Illumina NovaSeq 6000 to compare seasonal changes in the composition and structure of microbial communities from healthy roots of bamboo Bambusa pervariabilis × Dendrocalamopsis grandis and roots infected by the soilborne pathogen Fusarium proliferatum. We have found that the invasion of the pathogen led to a substantial decrease in nutrient elements in bamboo roots, except for nitrogen. The pathogen presence correlated with seasonal changes in the bamboo root microbiome and decreased bacterial richness in diseased plants. The root microbial community structure of healthy plants was more stable than that of their diseased counterparts. Furthermore, we identified the lesion area and relative abundance of F. proliferatum were significant predictors of disease progression. The potassium tissue content and the disease lesion area were identified as factors linked with the observed changes in the bamboo root microbiome. This study provides a theoretical foundation for understanding the seasonal dynamics F. proliferatum, an economically important soilborne pathogen of hybrid bamboo grown in Sichuan Province, China.

The effect of wheat genotype on the microbiome is more evident in roots and varies through time

Crop breeding has traditionally ignored the plant-associated microbial communities. Considering the interactions between plant genotype and associated microbiota is of value since different genotypes of the same crop often harbor distinct microbial communities which can influence the plant phenotype. However, recent studies have reported contrasting results, which led us to hypothesize that the effect of genotype is constrained by growth stages, sampling year and plant compartment. To test this hypothesis, we sampled bulk soil, rhizosphere soil and roots of 10 field-grown wheat genotypes, twice per year, for 4 years. DNA was extracted and regions of the bacterial 16 S rRNA and CPN60 genes and the fungal ITS region were amplified and sequenced. The effect of genotype was highly contingent on the time of sampling and on the plant compartment sampled. Only for a few sampling dates, were the microbial communities significantly different across genotypes. The effect of genotype was most often significant for root microbial communities. The three marker genes used provided a highly coherent picture of the effect of genotype. Taken together, our results confirm that microbial communities in the plant environment strongly vary across compartments, growth stages, and years, and that this can mask the effect of genotype.

Community differentiation of rhizosphere microorganisms and their responses to environmental factors at different development stages of medicinal plant Glehnia littoralis

Rhizosphere microorganisms play a key role in affecting plant quality and productivity through its interaction with plant root system. To figure out the bottleneck of the decline of yield and quality in the traditional Chinese medicinal herbs Glehnia littoralis they now encounter, it is important to study the dynamics of rhizosphere microbiota during the cultivation of G. littoralis. In the present study, the composition, diversity and function of rhizosphere microbes at different development stages of G. littoralis, as well as the correlation between rhizosphere microbes and environmental factors were systematically studied by high-throughput sequencing. There were significant differences between the rhizosphere microbes at early and middle-late development stages. More beneficial bacteria, such as Proteobacteria, and more symbiotic and saprophytic fungi were observed at the middle-late development stage of G. littoralis, while beneficial bacteria such as Actinobacteria and polytrophic transitional fungi were abundant at all development stages. The results of redundancy analysis show that eight environmental factors drive the changes of microflora at different development stages. pH, soil organic matter (SOM) and available phosphorus (AP) had important positive effects on the bacterial and fungal communities at the early development stage; saccharase (SC) and nitrate nitrogen (NN) showed significant positive effects on the bacterial and fungal communities at the middle and late stages; while urease (UE), available potassium (AK), and alkaline phosphatase (AKP) have different effects on bacterial and fungal communities at different development stages. Random forest analysis identified 47 bacterial markers and 22 fungal markers that could be used to distinguish G. littoralis at different development stages. Network analysis showed that the rhizosphere microbes formed a complex mutualistic symbiosis network, which is beneficial to the growth and development of G. littoralis. These results suggest that host development stage and environmental factors have profound influence on the composition, diversity, community structure and function of plant rhizosphere microorganisms. This study provides a reference for optimizing the cultivation of G. littoralis.

Populus root exudates are associated with rhizosphere microbial communities and symbiotic patterns

Introduction

Microbial communities in the plant rhizosphere are critical for nutrient cycling and ecosystem stability. However, how root exudates and soil physicochemical characteristics affect microbial community composition in Populus rhizosphere is not well understood.

Methods

This study measured soil physiochemistry properties and root exudates in a representative forest consists of four Populus species. The composition of rhizosphere bacterial and fungal communities was determined by metabolomics and high-throughput sequencing.

Results

Luvangetin, salicylic acid, gentisic acid, oleuropein, strigol, chrysin, and linoleic acid were the differential root exudates extracted in the rhizosphere of four Populus species, which explained 48.40, 82.80, 48.73, and 59.64% of the variance for the dominant and key bacterial or fungal communities, respectively. Data showed that differential root exudates were the main drivers of the changes in the rhizosphere microbial communities. Nitrosospira, Microvirga, Trichoderma, Cortinarius, and Beauveria were the keystone taxa in the rhizosphere microbial communities, and are thus important for maintaining a stable Populus microbial rhizosphere. The differential root exudates had strong impact on key bacteria than dominant bacteria, key fungi, and dominant fungi. Moreover, strigol had positively effects with bacteria, whereas phenolic compounds and chrysin were negatively correlated with rhizosphere microorganisms. The assembly process of the community structure (keystone taxa and bacterial dominant taxa) was mostly determined by stochastic processes.

Discussion

This study showed the association of rhizosphere microorganisms (dominant and keystone taxa) with differential root exudates in the rhizosphere of Populus plants, and revealed the assembly process of the dominant and keystone taxa. It provides a theoretical basis for the identification and utilization of beneficial microorganisms in Populus rhizosphere.

A High-Quality Genome Assembly of the Mitochondrial Genome of the Oil-Tea Tree Camellia gigantocarpa (Theaceae)

Camellia gigantocarpa is one of the oil-tea trees whose seeds can be used to extract high-quality vegetable oil. To date, there are no data on the mitochondrial genome of the oil-tea tree, in contrast to the tea-tree C. sinensis, which belongs to the same genus. In this paper, we present the first complete mitochondrial genomes of C. gigantocarpa obtained using PacBio Hi-Fi (high-fidelity) and Hi-C sequencing technologies to anchor the 970,410 bp genome assembly into a single sequence. A set of 44 protein-coding genes, 22 non-coding genes, 746 simple sequence repeats (SSRs), and more than 201 kb of repetitive sequences were annotated in the genome assembly. The high percentage of repetitive sequences in the mitochondrial genome of C. gigantocarpa (20.81%) and C.sinensis (22.15%, tea tree) compared to Arabidopsis thaliana (4.96%) significantly increased the mitogenome size in the genus Camellia. The comparison of the mitochondrial genomes between C. gigantocarpa and C. sinensis revealed genes exhibit high variance in gene order and low substitution rate within the genus Camellia. Information on the mitochondrial genome provides a better understanding of the structure and evolution of the genome in Camellia and may contribute to further study of the after-ripening process of oil-tea trees.

Differed Growth Stage Dynamics of Root-Associated Bacterial and Fungal Community Structure Associated with Halophytic Plant Lycium ruthenicum

Lycium ruthenicum, a halophytic shrub, has been used to remediate saline soils in northwest China. However, little is known about its root-associated microbial community and how it may be affected by the plant’s growth cycle. In this study, we investigate the microbial community structure of L. ruthenicum by examining three root compartments (rhizosphere, rhizoplane, and endosphere) during four growth stages (vegetative, flowering, fruiting, and senescence). The microbial community diversity and composition were determined by Illumina MiSeq sequencing of the 16S V3–V4 and 18S ITS regions. Proteobacteria, Actinobacteria, Bacteroidetes, Planctomycetes, and Acidobacteria were the dominant bacterial phyla, while Ascomycota, Basidiomycota, and Mortierellomycota were the most dominant fungal phyla. The alpha diversity of the bacterial communities was highest in the rhizosphere and decreased from the rhizosphere to the endosphere compartments; the fungal communities did not show a consistent trend. The rhizosphere, rhizoplane, and endosphere had distinct bacterial community structures among the three root compartments and from the bulk soil. Additionally, PERMANOVA indicated that the effect of rhizocompartments explained a large proportion of the total community variation. Differential and biomarker analysis not only revealed that each compartment had unique biomarkers and was enriched for specific bacteria, but also that the biomarkers changed with the plant growth cycle. Fungi were also affected by the rhizocompartment, but to a much less so than bacteria, with significant differences in the community composition along the root compartments observed only during the vegetative and flowering stages. Instead, the growth stages appear to account for most of the fungal community variation as demonstrated by PCoA and NMDS, and supported by differential and biomarker analysis, which revealed that the fungal community composition in the rhizosphere and endosphere were dynamic in response to the growth stage. Many enriched OTUs or biomarkers that were identified in the root compartments were potentially beneficial to the plant, meanwhile, some harmful OTUs were excluded from the root, implying that the host plant can select for beneficial bacteria and fungi, which can promote plant growth or increase salt tolerance. In conclusion, the root compartment and growth stage were both determinant factors in structuring the microbial communities of L. ruthenicum, but the effects were different in bacteria and fungi, suggesting that bacterial and fungal community structures respond differently to these growth factors.

Recent progress on harm, pathogen classification, control and pathogenic molecular mechanism of anthracnose of oil-tea

Oil tea (Camellia oleifera), mainly used to produce high-quality edible oil, is an important cash crop in China. Anthracnose of oil tea is a considerable factor that limits the yield of tea oil. In order to effectively control the anthracnose of oil tea, researchers have worked hard for many years, and great progress has been made in the research of oil tea anthracnose. For instance, researchers isolated a variety of Colletotrichum spp. from oil tea and found that Colletotrichum fructicola was the most popular pathogen in oil tea. At the same time, a variety of control methods have been explored, such as cultivating resistant varieties, pesticides, and biological control, etc. Furthermore, the research on the molecular pathogenesis of Colletotrichum spp. has also made good progress, such as the elaboration of the transcription factors and effector functions of Colletotrichum spp. The authors summarized the research status of the harm, pathogen types, control, and pathogenic molecular mechanism of oil tea anthracnose in order to provide theoretical support and new technical means for the green prevention and control of oil tea anthracnose.

Soil Bacterial Community Shifts Are Driven by Soil Nutrient Availability along a Teak Plantation Chronosequence in Tropical Forests in China

Simple Summary

Tropical forests play an important role in the global carbon cycle, especially in the context of global climate change. Soil microorganisms are essential to the functions, services, and productivity of terrestrial ecosystems as a link to maintain the connections and interactions between the aboveground and belowground ecosystems. The interactions between plants and the soil microbiome are crucial for plant growth, health, and resistance to stressors. However, information on the response of soil microbial communities to a chronosequence of woody plants is lacking, especially in tropical forests. This study compares the soil properties, diversity, composition, and co-occurrence patterns of bacterial communities in the rhizosphere and bulk soils along a teak plantation chronosequence. The results show that the composition and co-occurrence patterns of the bacterial communities are statistically different among the plantations, while stand age has no significant impact on soil bacterial alpha diversity. The results further show that soil nutrients play a key role in shaping the soil bacterial community. The study also provides information about the dynamics and characteristics of these soil bacterial communities and adds valuable information that may underpin new strategies for the management of teak plantations.

Abstract

Soil bacterial communities play crucial roles in ecosystem functions and biogeochemical cycles of fundamental elements and are sensitive to environmental changes. However, the response of soil bacterial communities to chronosequence in tropical ecosystems is still poorly understood. This study characterized the structures and co-occurrence patterns of soil bacterial communities in rhizosphere and bulk soils along a chronosequence of teak plantations and adjacent native grassland as control. Stand ages significantly shifted the structure of soil bacterial communities but had no significant impact on bacterial community diversity. Bacterial community diversity in bulk soils was significantly higher than that in rhizosphere soils. The number of nodes and edges in the bacterial co-occurrence network first increased and then decreased with the chronosequence. The number of strongly positive correlations per network was much higher than negative correlations. Available potassium, total potassium, and available phosphorus were significant factors influencing the structure of the bacterial community in bulk soils. In contrast, urease, total potassium, pH, and total phosphorus were significant factors affecting the structure of the bacterial community in the rhizosphere soils. These results indicate that available nutrients in the soil are the main drivers regulating soil bacterial community variation along a teak plantation chronosequence.

Molecular Characterization, Pathogenicity and Biological Characterization of Colletotrichum Species Associated with Anthracnose of Camellia yuhsienensis Hu in China

Camellia yuhsienensis Hu, a species of tea oil tree with resistance to anthracnose, is widely used to breed disease-resistant Camellia varieties. In 2019, anthracnose symptoms were observed on Ca. yuhsienensis for the first time. However, the species and biological characteristics of Colletotrichum spp. isolated from Ca. yuhsienensis (YX-Colletotrichum spp.) have not been elucidated. In this study, five isolates (YX2-5-2, 2YX-3-1, 2YX-5-1, 2YX-8-1-1 and 2YX-8-1-2), which were consistent with the morphological characteristics of Colletotrichum spp., were obtained from Ca. yuhsienensis. A phylogenetic analysis demonstrated that YX2-5-2, 2YX-3-1 and 2YX-8-1-2 belonged to first clade along with Colletotrichum fructicola. 2YX-8-1-1 belonged to the second clade along with Colletotrichum siamense. 2YX-5-1 belonged to the third clade with Colletotrichum camelliae. Pathogenicity tests revealed that the pathogenicity of YX-Colletotrichum spp. was stronger than that of Colletotrichum spp. isolated from Camellia oleifera (GD-Colletotrichum spp.). Biological characteristics illustrated that the mycelial growth of YX-Co. camelliae (2YX-5-1) was slower than that of GD-Co. camelliae when the temperature exceeded 20 °C. In addition, in the presence of ions, the mycelial growth of YX-Co. fructicola (YX2-5-2) and YX-Co. siamense (2YX-8-1-1) was also slower than that of GD-Co. fructicola and GD-Co. siamense. Furthermore, the ability of YX-Colletotrichum spp. to utilize lactose and mannitol was weaker than that of GD-Colletotrichum spp., while the ability to utilize NH4+ was generally stronger than that of GD-Colletotrichum spp. This is the first report of anthracnose of Ca. yuhsienensis induced by Co. fructicola, Co. siamense and Co. camelliae in China. These results will provide theoretical guidance for the study of the pathogenesis and control of anthracnose on Ca. yuhsienensis.

Wheat Genotype-Specific Recruitment of Rhizosphere Bacterial Microbiota Under Controlled Environments

Plants recruit beneficial microbial communities in the rhizosphere that are involved in a myriad of ecological services, such as improved soil quality, nutrient uptake, abiotic stress tolerance, and soil-borne disease suppression. Disease suppression caused by rhizosphere microbiomes has been important in managing soil-borne diseases in wheat. The low heritability of resistance in wheat to soil-borne diseases like Rhizoctonia root rot has made management of these diseases challenging, particularly in direct-seeded systems. Identification of wheat genotypes that recruit rhizosphere microbiomes that promote improved plant fitness and suppression of the pathogen could be an alternative approach to disease management through genetic improvement. Several growth chamber cycling experiments were conducted using six winter wheat genotypes (PI561725, PI561727, Eltan, Lewjain, Hill81, Madsen) to determine wheat genotypes that recruit suppressive microbiomes. At the end of the third cycle, suppression assays were done by inoculating R. solani into soils previously cultivated with specific wheat genotypes to test suppression of the pathogen by the microbiome. Microbiome composition was characterized by sequencing of 16S rDNA (V1-V3 region). Among the growth cycling lengths, 160-day growth cycles exhibited the most distinct rhizosphere microbiomes among the wheat genotypes. Suppression assays showed that rhizosphere microbiomes of different wheat genotypes resulted in significant differences in shoot length (value of p=0.018) and had an impact on the pathogenicity of R. solani, as observed in the reduced root disease scores (value of p=0.051). Furthermore, soils previously cultivated with the ALMT1 isogenic lines PI561725 and PI561727 exhibited better seedling vigor and reduced root disease. Microbiome analysis showed that Burkholderiales taxa, specifically Janthinobacterium, are differentially abundant in PI561727 and PI561725 cultivated soils and are associated with reduced root disease and better growth. This study demonstrates that specific wheat genotypes recruit different microbiomes in growth chamber conditions but the microbial community alterations were quite different from those previously observed in field plots, even though the same soils were used. Genotype selection or development appears to be a viable approach to controlling soil-borne diseases in a sustainable manner, and controlled environment assays can be used to see genetic differences but further work is needed to explain differences seen between growth chamber and field conditions.

Microbial Communities and Functions in the Rhizosphere of Disease-Resistant and Susceptible Camellia spp

Oil tea (Camellia spp.) is endemic to the hilly regions in the subtropics. Camellia yuhsienensis is resistant to diseases such as anthracnose and root rot, while Camellia oleifera is a high-yield species but susceptible to these diseases. We hypothesize that differences in the rhizosphere microbial communities and functions will elucidate the resistance mechanisms of these species. We used high-throughput sequencing over four seasons to characterize the rhizosphere microbiome of C. oleifera (Rhizo-Sus) and C. yuhsienensis (Rhizo-Res) and of the bulk soil control (BulkS). In Rhizo-Res, bacterial richness and diversity (Shannon index) in autumn and winter were both higher than that in Rhizo-Sus. In Rhizo-Res, fungal richness in autumn and winter and diversity in summer, autumn, and winter were higher than that in Rhizo-Sus. The seasonal variations in bacterial community structure were different, while that of fungal community structure were similar between Rhizo-Res and Rhizo-Sus. Gram-positive, facultatively anaerobic, and stress-tolerant bacteria were the dominant groups in Rhizo-Sus, while Gram-negative bacteria were the dominant group in Rhizo-Res. The significant differences in bacterial and fungal functions between Rhizo-Sus and Rhizo-Res were as follows: (1) in Rhizo-Sus, there were three bacterial and four fungal groups with plant growth promoting potentials, such as Brevibacterium epidermidis and Oidiodendron maius, and one bacterium and three fungi with pathogenic potentials, such as Gryllotalpicola sp. and Cyphellophora sessilis; (2) in Rhizo-Res, there were also three bacteria and four fungal groups with plant-growth-promoting potentials (e.g., Acinetobacter lwoffii and Cenococcum geophilum) but only one phytopathogen (Schizophyllum commune). In summary, the rhizosphere microbiome of disease-resistant C. yuhsienensis is characterized by a higher richness and diversity of microbial communities, more symbiotic fungal communities, and fewer pathogens compared to the rhizosphere of high-yield but disease-susceptible C. oleifera.

Spatial and Species Variations of Bacterial Community Structure and Putative Function in Seagrass Rhizosphere Sediment

Seagrasses are an important part of the coral reef ecosystem, and their rhizosphere microbes are of great ecological importance. However, variations in diversity, composition, and potential functions of bacterial communities in the seagrass rhizosphere of coral reef ecosystems remain unclear. This study employed the high-throughput sequencing based on 16S rDNA gene sequences and functional annotation of prokaryotic taxa (FAPROTAX) analysis to investigate these variations based on seagrass species and sampling locations, respectively. Results demonstrated that the seagrass rhizosphere microbial community was mainly dominated by phylum Proteobacteria (33.47%), Bacteroidetes (23.33%), and Planctomycetes (12.47%), while functional groups were mainly composed of sulfate respiration (14.09%), respiration of sulfur compounds (14.24%), aerobic chemoheterotrophy (20.87%), and chemoheterotrophy (26.85%). Significant differences were evident in alpha diversity, taxonomical composition and putative functional groups based on seagrass species and sampling locations. Moreover, the core microbial community of all investigated samples was identified, accounting for 63.22% of all obtained sequences. Network analysis indicated that most microbes had a positive correlation (82.41%), and two module hubs (phylum Proteobacteria) were investigated. Furthermore, a significant positive correlation was found between the OTUs numbers obtained and the functional groups assigned for seagrass rhizosphere microbial communities (p < 0.01). Our result would facilitate future investigation of the function of seagrass rhizosphere microbes.

First Report of Colletotrichum fructicola Causing Anthracnose on Camellia yuhsienensis Hu in China

Camellia yuhsienensis Hu is an endemic species from China, where is the predominant oilseed crop due to its anthracnose resistance (Kuang 2015; J. Li et al. 2020; Nie et al. 2020). In April 2019, anthracnose symptoms were observed on C. yuhsienensis in a plantation in Youxian, Zhuzhou, Hunan Province, China (113.32°E, 26.79°N). It was detected approximately 10% anthracnose incidence in 500 two-year-old plants in a 5000 m2 cultivated area. Diseased leaves showed irregular grayish brown spots with dark brown edges and dark brown undersides. Symptomatic tissues (4 to 5 mm2) were surface-disinfected for 90 s in 75% ethanol, then rinsed twice with sterile water, and finally incubated on PDA (potato dextrose agar) at 28℃ (Jiang et al. 2018). Pure cultures were obtained by the single-spore isolation method. A total of 100 fungal isolates were obtained from 85 symptomatic leaves, from which 81 had similar colony morphology. Colonies on PDA were white, fluffy and cottony, and becoming dark gray after 5 days. The character of the reverse of the colony were similar to that of the upper of the colony, but the color was darker at the same time. The isolates produced a large number of single-celled, hyaline, straight and cylindrical conidia, with 10.35 to 17.58 length × 3.46 to 5.69 μm width (x=13.61 × 4.63 μm, n = 30). The isolates were preliminarily identified as Colletotrichum spp. according to morphological features (Weir et al. 2012). Representative isolate YX2-5-2 was used for molecular identification: internal transcribed spacer (ITS), partial actin (ACT), chitin synthase (CHS-1) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genomic DNA regions were amplified by PCR (Weir et al. 2012). Gene sequences were deposited in GenBank (GenBank accession no. MW398863 for ACT, MW886232 for CHS-1, MW398864 for GAPDH, MW398865 for ITS). BLAST analysis revealed that DNA sequences of YX2-5-2 at the ITS, GAPDH, ACT, and CHS-1 loci showed 100%, 99.25%, 100%, and 99.33% sequence identity, respectively to their corresponding loci in strains ZH6 (GenBank accession no. MT476840.1), ICKP18B4 (LC494274.1), YN17 (MN525804.1), and ICKG4 (LC469131.1) of C. fructicola. A Maximum Likelihood phylogenetic tree based on the combined ACT, CHS-1, ITS and GAPDH sequences revealed that the representative isolate YX2-5-2 clustered with C. fructicola. In addition, the morphological features of YX2-5-2 were similar to C. fructicola which has been reported (Weir et al. 2012). Pathogenicity was tested using isolate YX2-5-2 by inoculating leaves of 2-year-old C. yuhsienensis. Four leaves of each healthy C. yuhsienensis were sprayed with a conidial suspension (105 conidial/mL) of isolate YX2-5-2, and the above steps were repeated three times. Two additional mock-inoculated control plants were sprayed with sterilized liquid potato dextrose medium. The plants were incubated in a greenhouse at 28℃ and 90% humidity with a 12 h photoperiod. Anthracnose-like symptoms were observed 5 days post-inoculation. The control plant tissues remained healthy. C. fructicola was re-isolated on PDA from lesions, and the morphological features were consistent with YX2-5-2, confirming Koch's postulates. To our knowledge, this is the first report of anthracnose of C. yuhsienensis caused by C. fructicola in China. Anthracnose of Camellia. oleifera has been reported for a long time (H. Li et al. 2016). C. yuhsienensis, as a wild relative of C. oleifera (commonly known as tea-oil tree), has been concerned about its resistance to anthracnose. Therefore, the occurrence of C. yuhsienensis anthracnose hindered the control of anthracnose tea-oil tree. This finding will lay the foundation for studying the pathogenesis of anthracnose of tea-oil tree and developing effective prevention methods. References: Jiang, S. Q., et al. 2018. Plant Dis. 102: 674. Kuang, R. 2015. Forest Pest and Disease. Li, H., et al. 2016. PLoS One 11: e0156841. Li, J., et al. 2020. Microorganisms 8: 1385. Nie, Z., et al. 2020. Mitochondrial. DNA. B. 5: 3016. Weir, B. S., et al. 2012. Stud. Mycol. 73: 115.

Time outweighs the effect of host developmental stage on microbial community composition

Thousands of microbial taxa in the soil form symbioses with host plants, and due to their contribution to plant performance, these microbes are often considered an extension of the host genome. Given microbial effects on host performance, it is important to understand factors that govern microbial community assembly. Host developmental stage could affect rhizosphere microbial diversity while, alternatively, microbial assemblages could change simply as a consequence of time and the opportunity for microbial succession. Previous studies suggest that rhizosphere microbial assemblages shift across plant developmental stages, but time since germination is confounded with developmental stage. We asked how elapsed time and potential microbial succession relative to host development affected microbial diversity in the rhizosphere using monogenic flowering-time mutants of Arabidopsis thaliana. Under our experimental design, different developmental stages were present among host genotypes after the same amount of time following germination, e.g. at 76 days following germination some host genotypes were flowering while others were fruiting or senescing. We found that elapsed time was a strong predictor of microbial diversity whereas there were few differences among developmental stages. Our results support the idea that time and, likely, microbial succession more strongly affect microbial community assembly than host developmental stage.