Characteristics of biological control and mechanisms of Pseudomonas chlororaphis zm-1 against peanut stem rot

Screening of rhizobacteria for multi-trait plant growth-promoting ability and antagonism against B. fabae, the causative agent of chocolate spot disease of faba bean

This study aimed to isolate and characterize plant growth-promoting rhizobacteria from the faba bean rhizosphere for future inoculum production. For this purpose,127 dissimilar rhizobacterial colonies were isolated. All isolated colonies were tested for plant growth-promoting traits. Based on their multiple plant growth-promoting traits, eight potential isolates were selected and identified GY01, GY03, and GY08 are affiliated with Acinetobacter sp. GY04 and GY05 are affiliated with Chryseobacterium sp. GY06 and GY07 are affiliated with Pseudomonas costantinii and Pseudomonas chlororaphis, respectively; and GY02 is affiliated with the Bacterium strain. All eight isolates were evaluated for their effects on seed germination and vigor index and potential antagonism against Botrytis fabae. Selected isolates showed positive effects on seed germination and vigor index with different potentials. Isolate GY04 resulted in the highest vigor index (501), while isolate GY08 achieved the lowest (218). B. fabae radial growth inhibition was found in all eight isolates. The isolates inhibited the radial growth of the test pathogen with an inhibition efficacy of 72.38 % in GY04 to 25.57 % in GY-03. Generally, the results of this study indicated the potential of these isolates as a microbial inoculant with multiple functions for faba beans.

Choreographing root architecture and rhizosphere interactions through synthetic biology

Climate change is driving extreme changes to the environment, posing substantial threats to global food security and bioenergy. Given the direct role of plant roots in mediating plant-environment interactions, engineering the form and function of root systems and their associated microbiota may mitigate these effects. Synthetic genetic circuits have enabled sophisticated control of gene expression in microbial systems for years and a surge of advances has heralded the extension of this approach to multicellular plant species. Targeting these tools to affect root structure, exudation, and microbe activity on root surfaces provide multiple strategies for the advancement of climate-ready crops.

Potential functions of the shared bacterial taxa in the citrus leaf midribs determine the symptoms of Huanglongbing

Instruction

Citrus is a globally important fruit tree whose microbiome plays a vital role in its growth, adaptability, and resistance to stress.

Methods

With the high throughput sequencing of 16S rRNA genes, this study focused on analyzing the bacterial community, especially in the leaf midribs, of healthy and Huanglongbing (HLB)-infected plants.

Results

We firstly identified the shared bacterial taxa in the midribs of both healthy and HLB-infected plants, and then analyzed their functions. Results showed that the shared bacterial taxa in midribs belonged to 62 genera, with approximately 1/3 of which modified in the infected samples. Furthermore, 366 metabolic pathways, 5851 proteins, and 1833 enzymes in the shared taxa were predicted. Among these, three metabolic pathways and one protein showed significant importance in HLB infection. With the random forest method, six genera were identified to be significantly important for HLB infection. Notably, four of these genera were also among the significantly different shared taxa. Further functional characterization of these four genera revealed that Pseudomonas and Erwinia likely contributed to plant defense against HLB, while Streptomyces might have implications for plant defense against HLB or the pathogenicity of Candidatus Liberibacter asiaticus (CLas).

Disccusion

Overall, our study highlights that the functions of the shared taxa in leaf midribs are distinguished between healthy and HLB-infected plants, and these microbiome-based findings can contribute to the management and protection of citrus crops against CLas.

Why Do We Need Alternative Methods for Fungal Disease Management in Plants?

Fungal pathogens pose a major threat to food production worldwide. Traditionally, chemical fungicides have been the primary means of controlling these pathogens, but many of these fungicides have recently come under increased scrutiny due to their negative effects on the health of humans, animals, and the environment. Furthermore, the use of chemical fungicides can result in the development of resistance in populations of phytopathogenic fungi. Therefore, new environmentally friendly alternatives that provide adequate levels of disease control are needed to replace chemical fungicides-if not completely, then at least partially. A number of alternatives to conventional chemical fungicides have been developed, including plant defence elicitors (PDEs); biological control agents (fungi, bacteria, and mycoviruses), either alone or as consortia; biochemical fungicides; natural products; RNA interference (RNAi) methods; and resistance breeding. This article reviews the conventional and alternative methods available to manage fungal pathogens, discusses their strengths and weaknesses, and identifies potential areas for future research.

The Isolate Pseudomonas multiresinivorans QL-9a Quenches the Quorum Sensing Signal and Suppresses Plant Soft Rot Disease

Quorum sensing (QS) is a communication mechanism used among microorganisms that regulate the population density and behavior by sensing the concentration of signaling molecules. Quorum quenching (QQ), a novel, eco-friendly, and efficient method for disease control, interferes with QS by disturbing the production and enzymatic degradation of signaling molecules, blocking communication among microorganisms, and thus has deep potential for use in plant disease control. Pectobacterium carotovorum can cause bacterial soft rot, resulting in yield reduction in a variety of crops worldwide, and can be mediated and regulated by the N-acyl homoserine lactones (AHLs), which are typical signaling molecules. In this study, a novel quenching strain of Pseudomonas multiresinivorans QL-9a was isolated and characterized, and it showed excellent degradation ability against AHLs, degrading 98.20% of N-(-3-oxohexanoyl)-L-homoserine lactone (OHHL) within 48 h. Based on the results of the gas chromatography-mass spectrometer (GC-MS) analysis, a possible pathway was proposed to decompose OHHL into fatty acids and homoserine lactone, in which AHL acylase was involved. Additionally, it has been demonstrated that the QL-9a strain and its crude enzyme are promising biocontrol agents that can considerably reduce the severity of the soft rot disease brought on by P. carotovorum, consequently preventing the maceration of a variety of host plant tissues. All of these results suggest promising applications of the QL-9a strain and its crude enzyme in the control of various plant diseases mediated by AHLs.

Evaluation of efficacy and mechanism of Bacillus velezensis CB13 for controlling peanut stem rot caused by Sclerotium rolfsii

Peanut stem rot, caused by Sclerotium rolfsii, considerably affects crop productivity. Application of chemical fungicides harms the environment and induces drug resistance. Biological agents are valid and eco-friendly alternatives to chemical fungicides. Bacillus spp. are important biocontrol agents that are now widely used against several plant diseases. This study aimed to evaluate the efficacy and mechanism of a potential biocontrol agent Bacillus sp. for controlling peanut stem rot caused by S. rolfsii. Here, we isolated a strain of Bacillus from pig biogas slurry that considerably inhibits the radial growth of S. rolfsii. The strain CB13 was identified as Bacillus velezensis on the basis of morphological, physiological, biochemical characteristics and phylogenetic trees based on the 16S rDNA and gyrA, gyrB, and rpoB gene sequences. The biocontrol efficacy of CB13 was evaluated on the basis of colonization ability, induction of defense enzyme activity, and soil microbial diversity. The control efficiencies of B. velezensis CB13-impregnated seeds in four pot experiments were 65.44, 73.33, 85.13, and 94.92%. Root colonization was confirmed through green fluorescent protein (GFP)-tagging experiments. The CB13-GFP strain was detected in peanut root and rhizosphere soil, at 104 and 108 CFU/g, respectively, after 50 days. Furthermore, B. velezensis CB13 enhanced the defense response against S. rolfsii infection by inducing defense enzyme activity. MiSeq sequencing revealed a shift in the rhizosphere bacterial and fungal communities in peanuts treated with B. velezensis CB13. Specifically, the treatment enhanced disease resistance by increasing the diversity of soil bacterial communities in peanut roots, increasing the abundance of beneficial communities, and promoting soil fertility. Additionally, real-time quantitative polymerase chain reaction results showed that B. velezensis CB13 stably colonized or increased the content of Bacillus spp. in the soil and effectively inhibited S. rolfsii proliferation in soil. These findings indicate that B. velezensis CB13 is a promising agent for the biocontrol of peanut stem rot.

Establishment and Application of a Multiplex PCR Assay for Detection of Sclerotium rolfsii, Lasiodiplodia theobromae, and Fusarium oxysporum in Peanut

Southern blight, stem rot, and root rot are serious soil-borne fungal diseases of peanut, which are caused by Sclerotium rolfsii, Lasiodiplodia theobromae, and Fusarium oxysporum, respectively. These diseases are difficult to be diagnosed in early stage of infection, causing the optimal treatment period was often missed. Therefore, establishing a rapid detection system is of great significance for early prevention of peanut soil-borne fungal diseases. Here, we have invented a multiplex PCR detection system to detect fungal pathogens of peanut southern blight, stem rot, and root rot at the same time. The quarantine fungal pathogen primer pairs were amplified to the specific number of base pairs in each of the following fungal pathogens: 1005-bp (F. oxysporum), 238-bp (L. theobromae), and 638-bp (S. rolfsii). The detection limit for the single and multiplex PCR primer sets was 1 ng of template DNA under in vitro conditions. Amplification of fungi of non-target species yielded no non-specific products. The validation showed that the multiplex PCR could effectively detect single and mixed infections in field samples. Overview, this study proved that this mPCR assay was a rapid, reliable, and simple tool for the simultaneous detection of three important peanut soil-borne diseases, which facilitated prompt treatment and prevention of peanut root diseases.