Elsinochrome A production by the bindweed biocontrol fungus Stagonospora convolvuli LA39 does not pose a risk to the environment or the consumer of treated crops

Biological control as an alternative to chemical pesticides is of increasing public interest. However, to ensure safe use of biocontrol methods, strategies to assess the possible risks need to be developed. The production of toxic metabolites is an aspect which has so far largely been neglected in the risk assessment and the registration process for biocontrol products. We have evaluated the risks of elsinochrome A (ELA) and leptosphaerodione production by the fungus Stagonospora convolvuli LA39, an effective biocontrol agent used against bindweeds. The toxicity of the two metabolites to bacteria, protozoa, fungi and plants was evaluated in in vitro assays. The most sensitive bacteria and fungi were already affected at 0.01 0.07 μM ELA, whereas plants were far less sensitive. Leptosphaerodione was less toxic than ELA. Subsequently, it was investigated whether ELA is present in the applied biocontrol product or LA39-treated bindweed and crop plants. In plants ELA was never detected and in the biocontrol product the ELA concentration was far too low to have toxic effects even on the most sensitive organisms. We conclude that the production of ELA by biocontrol strain LA39 does not pose a risk to the environment or to the consume

Relationship between aggressiveness of Stagonospora sp. isolates on field and hedge bindweeds, and in vitro production of fungal metabolites cercosporin, elsinochrome A and leptosphaerodione

Stagonospora convolvuli LA39, an effective biocontrol agent of Convolvulus arvensis (field bindweed) and Calystegia sepium (hedge bindweed) produces phytotoxic metabolites leptosphaerodione and elsinochrome A. Stagonospora isolate 214Caa produces the toxin cercosporin. If toxic metabolite production is not linked to the pathogenic ability of the fungus on bindweeds, selection of aggressive strains with limited or no production of the metabolites would reduce any perceived risk of using strains of the fungus as a mycoherbicide. Therefore, 30 isolates of Stagonospora sp. including LA39 and 214Caa were characterised for aggressiveness on both bindweeds, and production of the three metabolites. Nine isolates were more aggressive than LA39 on both bindweeds. Classification of isolates based on metabolite type agreed largely with previous similar characterisation based on polymerase chain reaction-restriction fragment length polymorphism of internal transcribed spacer of ribosomal DNA. Cercosporin producers produced neither leptosphaerodione nor elsinochrome A and together with isolates that produce none of the three metabolites, were less pathogenic on bindweeds. Conversely, there was a positive correlation between elsinochrome A and leptosphaerodione production, and each was positively correlated with aggressiveness of isolates on both bindweeds. Generally, any isolate where elsinochrome A was not detected was not aggressive on any of the two bindweeds. This probably implies that selecting elsinochrome A-negative, but aggressive Stagonospora strain(s) may be difficult. However, aggressive isolates may not produce elsinochrome A in planta at levels that could constitute any risk in the environment. In a preliminary attempt to determine the levels of elsinochrome A and leptosphaerodione produced in diseased bindweeds, none of the toxins was detected in Stagonospora infected bindweed leaves. Detailed investigation focusing on the detection and quantification of in planta production of elsinochrome A by Stagonospora isolates, and determination of the fate of elsinochrome A in the environment, and its relationship with leptosphaerodione may be essential. Similarly, development of molecular tools to monitor the mycoherbicide following field application is vita

Evolutionary patchwork of an insecticidal toxin shared between plant-associated pseudomonads and the insect pathogens Photorhabdus and Xenorhabdus

Background: Root-colonizing fluorescent pseudomonads are known for their excellent abilities to protect plants against soil-borne fungal pathogens. Some of these bacteria produce an insecticidal toxin (Fit) suggesting that they may exploit insect hosts as a secondary niche. However, the ecological relevance of insect toxicity and the mechanisms driving the evolution of toxin production remain puzzling. Results: Screening a large collection of plant-associated pseudomonads for insecticidal activity and presence of the Fit toxin revealed that Fit is highly indicative of insecticidal activity and predicts that Pseudomonas protegens and P. chlororaphis are exclusive Fit producers. A comparative evolutionary analysis of Fit toxin-producing Pseudomonas including the insect-pathogenic bacteria Photorhabdus and Xenorhadus, which produce the Fit related Mcf toxin, showed that fit genes are part of a dynamic genomic region with substantial presence/absence polymorphism and local variation in GC base composition. The patchy distribution and phylogenetic incongruence of fit genes indicate that the Fit cluster evolved via horizontal transfer, followed by functional integration of vertically transmitted genes, generating a unique Pseudomonas-specific insect toxin cluster. Conclusions: Our findings suggest that multiple independent evolutionary events led to formation of at least three versions of the Mcf/Fit toxin highlighting the dynamic nature of insect toxin evolution

Biologische Schädlingskontrolle adulter Japankäfer mit entomopathogenen Pilzen

"Der Japankäfer (Popillia japonica) ist ein invasiver Schädling, der mit seiner polyphagen Lebensweise die europäische Landwirtschaft bedroht. Mit dem Einsatz von ""attract-and-infest"" Fallen werden erwachsene Käfer als Vektoren benutzt, um einen entomopathogenen Pilz in der Population zu verbreiten.

Signaling between bacterial and fungal biocontrol agents in a strain mixture

The use of bacterial and fungal strain mixtures is a promising way to improve efficacy of biocontrol treatments. Certain Pseudomonas and Trichoderma strains belong to the most common studied biocontrol agents. One key factor for the biocontrol efficacy of several P. fluorescens strains is the synthesis of 2,4-diacetylphloroglucinol (DAPG). Production of chitinases, such as the ECH42 endochitinase and the NAG1 N-acetyl-β-d-glucosaminidase, is a primary mechanism of action for T. atroviride. We examined the molecular interactions between the DAPG-producing P. fluorescens strains CHA0 and Q2-87 and chitinase-producing T. atroviride P1. Interactions were monitored using the reporter gene constructs, phlA'-'lacZ translational fusion in P. fluorescens CHA0 and ech42-goxA or nag1-goxA fusions in T. atroviride P1. We found that DAPG enhanced nag1, but not ech42 expression, whereas an unidentified substance from P. fluorescens CHA0 repressed expression of both Trichoderma chitinases. Addition of T. atroviride P1 culture filtrates to growing cultures of P. fluorescens enhanced phlA expression transiently during growth. These results indicate that negative and positive effects on expression of key biocontrol genes may occur while mixing antagonist

Biological Control of pathogenic fungi: problems in the transfer from research to application

Im vorliegenden Beitrag werden einige erfolgreiche und nicht erfolgreiche Beispiele für die Bekämpfung pflanzenpathogener Pilze mit lebenden Organismen analysiert, und die Unterschiede zur meist erfolgreicheren biologischen Bekämpfung von Arthropoden werden aufgezeigt.In this presentation some examples of successful and unsuccessful control of phytopathogenic fungi through biological living agents are analyzed and the differences with the more successful biocontrol of arthropodes are mentioned

Draft Genome Sequence of Pseudomonas sp. Strain LD120, Isolated from the Marine Alga Saccharina latissima

We report the draft genome sequence of Pseudomonas sp. strain LD120, which was isolated from a brown macroalga in the Baltic Sea. The genome of this marine Pseudomonas protegens subgroup bacterium harbors biosynthetic gene clusters for toxic metabolites typically produced by members of this Pseudomonas subgroup, including 2,4-diacetylphloroglucinol, pyoluteorin, and rhizoxin analogs.ISSN:2576-098

The secret life of plant-beneficial rhizosphere bacteria: insects as alternative hosts

Root-colonizing bacteria have been intensively investigated for their intimate relationship with plants and their manifold plant-beneficial activities. They can inhibit growth and activity of pathogens or induce defence responses. In recent years, evidence has emerged that several plant-beneficial rhizosphere bacteria do not only associate with plants but also with insects. Their relationships with insects range from pathogenic to mutualistic and some rhizobacteria can use insects as vectors for dispersal to new host plants. Thus, the interactions of these bacteria with their environment are even more complex than previously thought and can extend far beyond the rhizosphere. The discovery of this secret life of rhizobacteria represents an exciting new field of research that should link the fields of plant–microbe and insect–microbe interactions. In this review, we provide examples of plant-beneficial rhizosphere bacteria that use insects as alternative hosts, and of potentially rhizosphere-competent insect symbionts. We discuss the bacterial traits that may enable a host-switch between plants and insects and further set the multi-host lifestyle of rhizobacteria into an evolutionary and ecological context. Finally, we identify important open research questions and discuss perspectives on the use of these rhizobacteria in agriculture

What makes a compost suppressive to soilborne pathogens?

Composts have been shown to suppress soilborne pathogens in numerous greenhouse and field experiments. However, the effectiveness of disease suppression is highly variable between composts, and we currently lack reliable indicators to select composts for plant protection. We hypothesize that disease suppression is a complex interplay between abiotic and biotic compost properties. Investigating the microbial communities may help to develop tools for predicting suppressive properties and producing composts with strong biocontrol activity. In the first part of the project, 17 composts were assessed for disease suppression in a cress–Globisporangium ultimum (syn. Pythium ultimum) system and assessed for their physico-chemical properties. Their microbial communities were analyzed using an Illumina metabarcoding approach, which identified bacterial taxa that are indicative for disease suppression. This data set has now been extended by 30 additional composts and a cucumber–G. ultimum and a cucumber–Rhizoctonia solani test system, which revealed differences in disease suppression between pathogens and plant species. The microbial communities are currently assessed by SMRT cell long-read sequencing with the goal to get a high taxonomic resolution to accurately relate the sequencing data with isolates obtained from the composts. Our comprehensive data set provides new insights into the contribution of different abiotic and biotic factors to disease-suppressive activity of composts

Relationships Between Root Pathogen Resistance, Abundance and Expression of \u3ci\u3ePseudomonas\u3c/i\u3e Antimicrobial Genes, and Soil Properties in Representative Swiss Agricultural Soils

Strains of Pseudomonas that produce antimicrobial metabolites and control soilborne plant diseases have often been isolated from soils defined as disease-suppressive, i.e., soils, in which specific plant pathogens are present, but plants show no or reduced disease symptoms. Moreover, it is assumed that pseudomonads producing antimicrobial compounds such as 2,4-diacetylphloroglucinol (DAPG) or phenazines (PHZ) contribute to the specific disease resistance of suppressive soils. However, pseudomonads producing antimicrobial metabolites are also present in soils that are conducive to disease. Currently, it is still unknown whether and to which extent the abundance of antimicrobials-producing pseudomonads is related to the general disease resistance of common agricultural soils. Moreover, virtually nothing is known about the conditions under which pseudomonads express antimicrobial genes in agricultural field soils. We present here results of the first side-by-side comparison of 10 representative Swiss agricultural soils with a cereal-oriented cropping history for (i) the resistance against two soilborne pathogens, (ii) the abundance of Pseudomonas bacteria harboring genes involved in the biosynthesis of the antimicrobials DAPG, PHZ, and pyrrolnitrin on roots of wheat, and (iii) the ability to support the expression of these genes on the roots. Our study revealed that the level of soil disease resistance strongly depends on the type of pathogen, e.g., soils that are highly resistant to Gaeumannomyces tritici often are highly susceptible to Pythium ultimum and vice versa. There was no significant correlation between the disease resistance of the soils, the abundance of Pseudomonas bacteria carrying DAPG, PHZ, and pyrrolnitrin biosynthetic genes, and the ability of the soils to support the expression of the antimicrobial genes. Correlation analyses indicated that certain soil factors such as silt, clay, and some macro- and micronutrients influence both the abundance and the expression of the antimicrobial genes. Taken together, the results of this study suggests that pseudomonads producing DAPG, PHZ, or pyrrolnitrin are present and abundant in Swiss agricultural soils and that the soils support the expression of the respective biosynthetic genes in these bacteria to various degrees. The precise role that these pseudomonads play in the general disease resistance of the investigated agricultural soils remains elusive