Harnessing Pseudomonas protegens to Control Bacterial Panicle Blight of Rice

Molecular insights into PGPR fluorescent Pseudomonads complex mediated intercellular and interkingdom signal transduction mechanisms in promoting plant's immunity

The growth-promoting and immune modulatory properties of different strains of plant growth promoting rhizobacteria (PGPR) fluorescent Pseudomonads complex (PFPC) can be explored to combat food security challenges. These PFPC prime plants through induced systemic resistance, fortify plants to overcome future pathogen-mediated vulnerability by eliciting robust systemic acquired resistance through regulation by nonexpressor of pathogenesis-related genes 1. Moreover, outer membrane vesicles released from Pseudomonas fluorescens also elicit a broad spectrum of immune responses, presenting a rapid viable alternative to whole cells. Thus, PFPC can help the host to maintain an equilibrium between growth and immunity, ultimately leads to increased crop yield.

A laudable strategy to manage bacterial panicle blight disease of rice using biocontrol agents

Bacterial panicle blight (BPB) disease is a dreadful disease in rice-producing countries. Burkholderia glumae, a Gram-negative, rod-shaped, and flagellated bacterium was identified as the primary culprit for BPB disease. In 2019, the disease was reported in 18 countries, and to date, it has been spotted in 26 countries. Rice yield has been reduced by up to 75% worldwide due to this disease. Interestingly, the biocontrol strategy offers a promising alternative to manage BPB disease. This review summarizes the management status of BPB disease using biological control agents (BCA). Bacteria from the genera Bacillus, Burkholderia, Enterobacter, Pantoea, Pseudomonas, and Streptomyces have been examined as BCA under in vitro, glasshouse, and field conditions. Besides bacteria, bacteriophages have also been reported to reduce BPB pathogens under in vitro and glasshouse conditions. Here, the overview of the mechanisms of bacteria and bacteriophages in controlling BPB pathogens is addressed. The applications of BCA using various delivery methods could effectively manage BPB disease to benefit the agroecosystems and food security.

Biocontrol of bacterial seedling rot of rice plants using combination of Cytobacillus firmus JBRS159 and silicon

Burkholderia glumae causes bacterial panicle blight (BPB) and bacterial seedling rot (BSR) which are difficult to control in rice plants. Seed disinfection using microbes and eco-friendly materials is an efficient alternative practice for managing BPB and BSR. In this study, we applied Cytobacillus firmus JBRS159 (JBRS159) in combination with silicon dioxide (SiO2) nanoparticle or potassium silicate (K2SiO3) solution to control BSR. JBRS159, SiO2 nanoparticle, and K2SiO3 independently suppressed the BSR disease and promoted growths of rice and Arabidopsis. Population of B. glumae in the treated rice seeds was suppressed by the application of JBRS159 via competitions for nutrients and niches. The mixture of JBRS159 and each Si compound (SiO2 nanoparticle or K2SiO3) was complementary for disease-suppressing and growth-promoting activities of individual treatment. The results of this study indicate that mixture of JBRS159 with each Si compound can be harnessed for disease control and growth promotion as efficient alternatives to chemical pesticides and synthetic fertilizers. The efficacy of JBRS159 and Si compounds in the control of BSR and BPB in the field remains to be evaluated.

Function of the algicidal bacterium Pseudomonas sp. Go58 isolated from the biofilm on a water plant, and its active compounds, pyoluteorins

In the development of applications to mitigate nuisance cyanobacterial blooms, environmentally friendly approaches have gained much attention. Recently, we found a bacterial strain Go58, which was isolated from the biofilm of a water plant, that showed potent algicidal activity against the bloom-forming cyanobacterium Microcystis aeruginosa. Whole genome sequencing of strain Go58 suggested that it is potentially a novel species closely related to Pseudomonas protegens. Pyoluteorins were obtained from the culture broth of this strain, and they demonstrated high toxicity against cultured cyanobacterial species, including M. aeruginosa and Anabaena cylindrica, but less toxicity against eukaryotic microalgae and other aquatic organisms. The production of pyoluteorin was enhanced by the presence of the target cyanobacterium. When a wild-caught microalgal consortium was treated with either strain Go58 or pyoluteorin, both efficiently suppressed the growth of harmful wild cyanobacteria, but promoted the growth of some specific eukaryotic microalgae. Since P. protegens is globally ubiquitous and highly anticipated to be a biopesticide for infectious diseases in the field of agriculture, the similar bacterial group identified in this study may also have potential as a safe on-site collectable biological countermeasure for controlling cyanobacterial blooms.

Draft Genome Sequence of Pseudomonas protegens Strain MWU12-2233, Isolated from Wild Cranberry Fruit in Provincetown, Massachusetts

Pseudomonas protegens strain MWU12-2233 was isolated from wild cranberry fruit surfaces in Provincetown, MA. The genome contains putative hydrogen cyanide synthase and type VI secretion systems which can act symbiotically on plant health by suppressing competitors, indicating a role in indigenous microfloral disease and insect pest suppression.

Bacterial Panicle Blight and Burkholderia glumae: From Pathogen Biology to Disease Control

Bacterial panicle blight (BPB), caused by the bacterium Burkholderia glumae, has affected rice production worldwide. Despite its importance, neither the disease nor the causal agent are well understood. Moreover, methods to manage BPB are still lacking. Nevertheless, the emerging importance of this pathogen has stimulated research to identify the mechanisms of pathogenicity, to gain insight into plant disease resistance, and to develop strategies to manage the disease. In this review, we consolidate current information regarding the virulence factors that have been identified in B. glumae and present a model of the disease and the pathogen. We also provide an update on the current research status to develop methods to control the disease especially through biological control approaches and through the development of resistant cultivars.