Detection, Diagnosis, and Preventive Management of the Bacterial Plant Pathogen Pseudomonas syringae

Plant Growth Promotion and Plant Disease Suppression Induced by Bacillus amyloliquefaciens Strain GD4a

Botrytis cinerea, the causative agent of gray mold disease (GMD), invades plants to obtain nutrients and disseminates through airborne conidia in nature. Bacillus amyloliquefaciens strain GD4a, a beneficial bacterium isolated from switchgrass, shows great potential in managing GMD in plants. However, the precise mechanism by which GD4a confers benefits to plants remains elusive. In this study, an A. thaliana-B. cinerea-B. amyloliquefaciens multiple-scale interaction model was used to explore how beneficial bacteria play essential roles in plant growth promotion, plant pathogen suppression, and plant immunity boosting. Arabidopsis Col-0 wild-type plants served as the testing ground to assess GD4a's efficacy. Additionally, bacterial enzyme activity and targeted metabolite tests were conducted to validate GD4a's potential for enhancing plant growth and suppressing plant pathogens and diseases. GD4a was subjected to co-incubation with various bacterial, fungal, and oomycete pathogens to evaluate its antagonistic effectiveness in vitro. In vivo pathogen inoculation assays were also carried out to investigate GD4a's role in regulating host plant immunity. Bacterial extracellular exudate (BEE) was extracted, purified, and subjected to untargeted metabolomics analysis. Benzocaine (BEN) from the untargeted metabolomics analysis was selected for further study of its function and related mechanisms in enhancing plant immunity through plant mutant analysis and qRT-PCR analysis. Finally, a comprehensive model was formulated to summarize the potential benefits of applying GD4a in agricultural systems. Our study demonstrates the efficacy of GD4a, isolated from switchgrass, in enhancing plant growth, suppressing plant pathogens and diseases, and bolstering host plant immunity. Importantly, GD4a produces a functional bacterial extracellular exudate (BEE) that significantly disrupts the pathogenicity of B. cinerea by inhibiting fungal conidium germination and hypha formation. Additionally, our study identifies benzocaine (BEN) as a novel small molecule that triggers basal defense, ISR, and SAR responses in Arabidopsis plants. Bacillus amyloliquefaciens strain GD4a can effectively promote plant growth, suppress plant disease, and boost plant immunity through functional BEE production and diverse gene expression.

Plant Growth Promotion and Stress Tolerance Enhancement through Inoculation with Bacillus proteolyticus OSUB18

The isolation of B. proteolyticus OSUB18 from switchgrass unveiled its significant potential in both the enhancement of plant growth and the suppression of plant diseases in our previous study. The elucidation of the related mechanisms governing this intricate plant-microbe interaction involved the utilization of the model plant Arabidopsis thaliana. In our comprehensive study on Arabidopsis, OSUB18 treatment was found to significantly alter root architecture and enhance plant growth under various abiotic stresses. An RNA-seq analysis revealed that OSUB18 modified gene expression, notably upregulating the genes involved in glucosinolate biosynthesis and plant defense, while downregulating those related to flavonoid biosynthesis and wound response. Importantly, OSUB18 also induces systemic resistance in Arabidopsis against a spectrum of bacterial and fungal pathogens and exhibits antagonistic effects on phytopathogenic bacteria, fungi, and oomycetes, highlighting its potential as a beneficial agent in plant stress management and pathogen resistance. Overall, our findings substantiate that OSUB18 exerts a stimulatory influence on plant growth and health, potentially attributed to the remodeling of root architecture, defense signaling, and the comprehensive mitigation of various biotic and abiotic stresses.

Botrytis cinerea in vivo Inoculation Assays for Early-, Middle- and Late-stage Strawberries

Strawberries are delicious and nutritious fruits that are widely cultivated and consumed around the world, either fresh or in various products such as jam, juice, and ice cream. Botrytis cinerea is a fungal pathogen that causes gray mold disease on many crops, including strawberries. Disease monitoring is an important aspect for growing commercial crops like strawberry because there is an urgent need to develop effective strategies to control this destructive gray mold disease. In this protocol, we provide an important tool to monitor the gray mold fungal infection progression in different developmental stages of strawberry. There are different types of inoculation assays for B. cinerea on strawberry plants, such as in vitro (in/on a culture medium) or in vivo (in a living plant). In vivo inoculation assays can be performed at early, middle, and late stages of strawberry development. Here, we describe three methods for in vivo inoculation assays of B. cinerea on strawberry plants. For early-stage strawberry plants, we modified the traditional fungal disc inoculation method to apply to fungal infection on strawberry leaves. For middle-stage strawberry plants, we developed the flower infection assay by dropping fungal conidia onto flowers. For late-stage strawberry plants, we tracked the survival rate of strawberry fruits after fungal conidia infection. This protocol has been successfully used in both lab and greenhouse conditions. It can be applied to other flowering plants or non-model species with appropriate modifications. Key features • Fungal disc inoculation on early-stage strawberry leaves. • Fungal conidia inoculation on middle-stage strawberry flowers. • Disease rating for late-stage strawberry fruits. • This protocol is applicable to the other flowering plants with appropriate modifications.