A Burkholderia cenocepacia-like environmental isolate strongly inhibits the plant fungal pathogen Zymoseptoria tritici.

Fungal phytopathogens cause significant reductions in agricultural yields annually, and overusing chemical fungicides for their control leads to environmental pollution and the emergence of resistant pathogens. Exploring natural isolates with strong antagonistic effects against pathogens can improve our understanding of their ecology and develop new treatments for the future. We isolated and characterized a novel bacterial strain associated with the species Burkholderia cenocepacia, termed APO9, which strongly inhibits Zymoseptoria tritici, a commercially important pathogenic fungus causing Septoria tritici blotch in wheat. Additionally, this strain exhibits inhibitory activity against four other phytopathogens. We found that physical contact plays a crucial role for APO9's antagonistic capacity. Genome sequencing of APO9 and biosynthetic gene cluster (BGC) analysis identified nine classes of BGCs and three types of secretion systems (types II, III, and IV), which may be involved in the inhibition of Z. tritici and other pathogens. To identify genes driving APO9's inhibitory activity, we screened a library containing 1,602 transposon mutants and identified five genes whose inactivation reduced inhibition efficiency. One such gene encodes for a diaminopimelate decarboxylase located in a terpenoid biosynthesis gene cluster. Phylogenetic analysis revealed that while some of these genes are also found across the Burkholderia genus, as well as in other Betaproteobacteria, the combination of these genes is unique to the Burkholderia cepacia complex. These findings suggest that the inhibitory capacity of APO9 is complex and not limited to a single mechanism, and may play a role in the interaction between various Burkholderia species and various phytopathogens within diverse plant ecosystems. IMPORTANCE: The detrimental effects of fungal pathogens on crop yields are substantial. The overuse of chemical fungicides contributes not only to environmental pollution but also to the emergence of resistant pathogens. Investigating natural isolates with strong antagonistic effects against pathogens can improve our understanding of their ecology and develop new treatments for the future. We discovered and examined a unique bacterial strain that demonstrates significant inhibitory activity against several phytopathogens. Our research demonstrates that this strain has a wide spectrum of inhibitory actions against plant pathogens, functioning through a complex mechanism. This plays a vital role in the interactions between plant microbiota and phytopathogens.

A pipeline for rapidly evaluating activity and inferring mechanisms of action of prospective antifungal compounds.

BACKGROUND: Fungal phytopathogens are a significant threat to crops and food security, and there is a constant need to develop safe and effective compounds that antagonize them. In-planta assays are complex and tedious and are thus not suitable for initial high-throughput screening of new candidate antifungal compounds. We propose an in vitro screening pipeline that integrates five rapid quantitative and qualitative methods to estimate the efficacy and mode of action of prospective antifungal compounds. RESULTS: The pipeline was evaluated using five documented antifungal compounds (benomyl, catechol, cycloheximide, 2,4-diacetylphloroglucinol, and phenylacetic acid) that have different modes of action and efficacy, against the model soilborne fungal pathogen Fusarium oxysporum f. sp. radicis cucumerinum. We initially evaluated the five compounds' ability to inhibit fungal growth and metabolic activity using green fluorescent protein (GFP)-labeled F. oxysporum and PrestoBlue staining, respectively, in multiwell plate assays. We tested the compounds' inhibition of both conidial germination and hyphal elongation. We then employed FUN-1 and SYTO9/propidium iodide staining, coupled to confocal microscopy, to differentiate between fungal growth inhibition and death at the cellular level. Finally, using a reactive oxygen species (ROS)-detection assay, we were able to quantify ROS production in response to compound application. CONCLUSIONS: Collectively, the proposed pipeline provides a wide array of quantitative and qualitative data on the tested compounds that can help pinpoint promising novel compounds; these can then be evaluated more vigorously using in planta screening assays. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Fusarium Wilt of Coriander: Root Cause Analysis and Varietal Tolerance Development.

Since 2012, growers of coriander, Coriandrum sativum L., in Israel have been suffering from summer wilting that can result in entire fields collapsing. The current study aimed to determine the cause of the phenomenon and find a genetic solution to the problem. The disease was reproduced in a growth chamber using naturally-infested soil from a commercial field. Wilt became apparent within two weeks, and after ten weeks, all plants died compared to plants in sterilized soil from the same source. Fusarium oxysporum was isolated from infected plants, and Koch's postulates were completed. Sequence analysis of the Elongation Factor (EF1α) encoding gene of the pathogen had a 99.54% match to F. oxysporum f. sp. coriandrii. Several coriander varieties were screened for resistance or tolerance to the disease. In four independent experiments, only the cultivar 'Smadi' showed high tolerance, while other genotypes were susceptible. In a trial in a naturally infested field, the cultivar 'Smadi' outperformed the commercial cultivar 'Blair'. 'Smadi' provides a cropping solution to many Israeli farmers, yet this winter cultivar bolts early in the summer. There is a further need to characterize the tolerance mechanism and inheritance for informed breeding of late-bolting Fusarium-resistant coriander.

Examination of genetic lines of Myrtus communis as potential sources of organic agricultural pest control agents.

Myrtus communis is a Mediterranean shrub cultivated in Israel for traditional, ceremonial use only, with more than 98 % of the crop biomass, equivalent to 26-27 tons per ha per annum, considered agricultural waste. Therefore, potentially profitable use for this excess is being highly sought. As Myrtus is also known for its unique terpene and terpenoid content, this work evaluated the impact of essential oil (EO) extracted from several M. communis cultivars on storage insects, nematodes, fungi, and pathogens. In addition, the allelopathic effect of M. communis litter on the germination success of wheat seeds was evaluated. The EO extracts demonstrated an insecticidal effect on several storage insects in fumigation experiment and a potentially inhibiting effect on wheat development in allelopathy experiments. No significant impact of M. communis EOs on the examined fungi, pathogens, and nematodes was recorded. Additional uses of the M. communis biomass suggest supplying additional income to the farmer through the circular agriculture approach. In addition, the use of this local crop can contribute to sustainable intensification by increasing farming efficiency, providing nature-based substitutes for chemical pesticides, and possibly, improving the future design of agriculture through the integration of Myrtus in monoculture crops.