Effects of Secondary Metabolites from Pea on Fusarium Growth and Mycotoxin Biosynthesis

Identification and Pathogenicity of Fusarium Species from Herbaceous Plants on Grassland in Qiaojia County, China

The Fusarium species is an important plant pathogen that can cause plant diseases in grassland, leading to the degradation of grassland quality. However, the morphology of Fusarium is greatly affected by environmental factors, which makes it difficult to identify its species. In addition, the pathogenic ability of different Fusarium species in plants has not been fully studied. In this study, Fusarium isolates were obtained from grassland herbaceous plants via tissue separation. Through morphological means and based on ITS, RPB2, and TEF-1 gene sequences, we compared and constructed polygenic phylogenetic trees to classify and identify the Fusarium species. In addition, the pathogenicity of different Fusarium species was also analyzed. The results showed that a total of 24 Fusarium strains were successfully isolated from grassland, from which ten species were identified: F. flagelliforme, F. longifundum, F. clavum, F. scirpi, F. ipomoeae, F. oxysporum, etc. and were included in four complexes: Fusarium incarnatum-equiseti species complex (FIESC), Fusarium oxysporum species complex (FOSC), Fusarium tricinctum species complex (FTSC), and Fusarium sambucinum species complex (FSAMSC). Pathogenicity tests demonstrated that except for F. ipomoeae QJ5211, F. sambucinum QJ203, and F. acuminatum QJ1662, other Fusarium species had different degrees of pathogenic ability. This is the first study that discusses the effect of Fusarium on grassland disease control in this area. This study further provides clear pathogen information for the prevention and control of grassland diseases.

Flue-cured tobacco intercropping with insectary floral plants improves rhizosphere soil microbial communities and chemical properties of flue-cured tobacco

BACKGROUND

Continuous cropping of the same crop leads to land degradation. This is also called the continuous-cropping obstacle. Currently, intercropping tobacco with other crops can serve as an effective strategy to alleviate continuous cropping obstacles.

RESULTS

In this study, tobacco K326 and insectary floral plants were used as materials, and seven treatments of tobacco monoculture (CK), tobacco intercropped with Tagetes erecta, Vicia villosa, Fagopyrum esculentum, Lobularia maritima, Trifolium repens, and Argyranthemum frutescens respectively, were set up to study their effects on rhizosphere soil chemical properties and composition and structure of rhizosphere soil microbial community of tobacco. The 16 S rRNA gene and ITS amplicons were sequenced using Illumina high-throughput sequencing. tobacco/insectary floral plants intercropping can influence rhizosphere soil chemical properties, which also change rhizosphere microbial communities. The CK and treatment groups tobacco rhizosphere soil microorganisms had significantly different genera, such as tobacco intercropping with T. repens and A. frutescens significantly increased the number of Fusarium and intercropping T. erecta, V. villosa, L. maritima, T. repens, and A. frutescens significantly increased the number of Sphingomonas and unknown Gemmatimonadaceae. Additionally, intercropping T. erecta, V. villosa and L. maritima changed the rhizosphere fungal and bacteria community and composition of tobacco and the positive correlation between tobacco rhizosphere the genera of fungi and bacterial were greater than CK. The pathway of the carbohydrate metabolism, amino acid metabolism, and energy metabolism in rhizosphere bacteria were significantly decreased after continuous cropping. Fungal symbiotic trophic and saprophytic trophic were significantly increased after intercropping V. villosa, L. maritima and plant pathogen and animal pathogen were increased after intercropping T. repens and A. frutescens. Additionally, bacterial and fungal communities significantly correlated with soil chemical properties, respectively.

CONCLUSION

This study reveals that intercropping tobacco with insectary floral plants, particularly T. erecta, V. villosa, L. maritima and A. frutescens significantly affects soil chemical properties and alters rhizosphere microbial communities, increasing the abundance of certain microbial genera. Additionally, intercropping enhances pathways related to carbohydrate, amino acid, and energy metabolism in rhizosphere bacteria. These findings suggest that intercropping could provide a promising strategy to overcome challenges associated with continuous tobacco cropping by regulating the rhizosphere environment.

Seeds Priming with Bio-Silver Nanoparticles Protects Pea (Pisum sativum L.) Seedlings Against Selected Fungal Pathogens

Nano-priming is a relatively new seed treatment technique using metal and metal oxide nanoparticles (NPs), and such application of NPs may support the plants' immunity. Recently we have shown that the that biologically synthesized silver nanoparticles (bio-AgNPs) used as short-term foliar treatment protect pea seedlings against D. pinodes and F. avenaceum. In the present study, the protection of peas against both fungal pathogens via seed priming with bio-AgNPs was analyzed. Moreover, the changes in the polar metabolic profiles of the seedlings caused by priming and infection were also compared. Seed priming with bio-AgNPs at concentrations of 50 and 100 mg/L considerably reduced the symptoms and infection levels of both pathogens by over 70% and 90% for F. avenaceum and D. pinodes, respectively. Pathogens infection and nano-priming affected the metabolic profile of pea seedlings. The major changes in the primary metabolism were observed among carbohydrates and amino acids. In turn, this may result in changes in the expression and accumulation of secondary metabolites. Therefore, further investigation of the effect of nano-priming should focus on the changes in the secondary metabolism.

Antifungal Properties of Bio-AgNPs against D. pinodes and F. avenaceum Infection of Pea (Pisum sativum L.) Seedlings

Ascochyta blight and Fusarium root rot are the most serious fungal diseases of pea, caused by D. pinodes and F. avenaceum, respectively. Due to the lack of fully resistant cultivars, we proposed the use of biologically synthesized silver nanoparticles (bio-AgNPs) as a novel protecting agent. In this study, we evaluated the antifungal properties and effectiveness of bio-AgNPs, in in vitro (poisoned food technique; resazurin assay) and in vivo (seedlings infection) experiments, against D. pinodes and F. avenaceum. Moreover, the effects of diseases on changes in the seedlings' metabolic profiles were analyzed. The MIC for spores of both fungi was 125 mg/L, and bio-AgNPs at 200 mg/L most effectively inhibited the mycelium growth of D. pinodes and F. avenaceum (by 45 and 26%, respectively, measured on the 14th day of incubation). The treatment of seedlings with bio-AgNPs or fungicides before inoculation prevented the development of infection. Bio-AgNPs at concentrations of 200 mg/L for D. pinodes and 100 mg/L for F. avenaceum effectively inhibited infections' spread. The comparison of changes in polar metabolites' profiles revealed disturbances in carbon and nitrogen metabolism in pea seedlings by both pathogenic fungi. The involvement of bio-AgNPs in the mobilization of plant metabolism in response to fungal infection is also discussed.

Lamium album Flower Extracts: A Novel Approach for Controlling Fusarium Growth and Mycotoxin Biosynthesis

Lamium album is a medicinal flowering plant that is rich in bioactive compounds with various biological properties. Fusarium species, known for causing significant crop losses and mycotoxin contamination, pose threats to food safety and human health. While synthetic fungicides are commonly employed for fungal management, their environmental impact prompts the ongoing development of alternative methods. This study aimed to evaluate the efficacy of L. album flower extracts in inhibiting the in vitro growth and biosynthesis of mycotoxins by Fusarium culmorum and F. proliferatum strains. The extracts were obtained by supercritical fluid extraction using CO2 (SC-CO2). The effects of various concentrations (2.5, 5, 7.5, and 10%) were assessed on a potato dextrose agar (PDA) medium using the "poisoning" technique. L. album flower extracts reduced mycelium growth by 0 to 30.59% for F. culmorum and 27.71 to 42.97% for F. proliferatum. Ergosterol content was reduced by up to 88.87% for F. culmorum and 93.17% for F. proliferatum. Similarly, the amounts of synthesized mycotoxins produced by both strains were also lower compared to control cultures. These findings are a preliminary phase for further in vivo tests planned to determine the fungistatic effect of L. album flower extracts on cereal substrates as seedlings incubated in controlled environments and under field conditions. Their phytotoxicity and biological stability, as well as the possibility of formulating a bio-preparation to protect cereals against Fusarium infections, will be evaluated.

Maize kernel metabolome involved in resistance to fusarium ear rot and fumonisin contamination

Fusarium verticillioides poses a threat to worldwide maize production due to its ability to infect maize kernel and synthesize fumonisins that can be accumulated above safety levels for humans and animals. Maize breeding has been proposed as key tool to decrease kernel contamination with fumonisins, but metabolic studies complementary to genomic approaches are necessary to disclose the complexity of maize resistance. An untargeted metabolomic study was proposed using inbreds genetically related but with contrasting levels of resistance in order to uncover pathways implicated in resistance to Fusarium ear rot (FER) and fumonisin contamination in the maize kernel and to look for possible biomarkers. Metabolite determinations were performed in kernels collected at 3 and 10 days after inoculation with F. verticillioides (dat). Discriminant metabolites between resistant and susceptible RILs were rather found at 10 than 3 dat, although metabolite differences at later stages of colonization could be driven by subtle variations at earlier stages of infection. Within this context, differences for membrane lipid homeostasis, methionine metabolism, and indolacetic acid conjugation seemed highly relevant to distinguish between resistant and susceptible inbreds, confirming the polygenic nature of resistance to FER and fumonisin contamination in the maize kernels. Nevertheless, some specific metabolites such as the polyamine spermidine and/or the alkaloid isoquinoline seemed to be promising indirect selection traits to improve resistance to FER and reduce fumonisin accumulation. Therefore, in vitro and in vivo experiments will be necessary to validate the inhibitory effects of these compounds on fumonisins biosynthesis.

Plant Metabolites Affect Fusarium proliferatum Metabolism and In Vitro Fumonisin Biosynthesis

Fusarium proliferatum is a common hemi-biotrophic pathogen that infect a wide range of host plants, often leading to substantial crop loss and yield reduction. F. proliferatum synthesizes various mycotoxins, and fumonisins B are the most prevalent. They act as virulence factors and specific effectors that elicit host resistance. The effects of selected plant metabolites on the metabolism of the F. proliferatum strain were analyzed in this study. Quercetin-3-glucoside (Q-3-Glc) and kaempferol-3-rutinoside (K-3-Rut) induced the pathogen's growth, while DIMBOA, isorhamnetin-3-O-rutinoside (Iso-3-Rut), ferulic acid (FA), protodioscin, and neochlorogenic acid (NClA) inhibited fungal growth. The expression of seven F. proliferatum genes related to primary metabolism and four FUM genes was measured using RT-qPCR upon plant metabolite addition to liquid cultures. The expression of CPR6 and SSC1 genes was induced 24 h after the addition of chlorogenic acid (ClA), while DIMBOA and protodioscin reduced their expression. The transcription of FUM1 on the third day of the experiment was increased by all metabolites except for Q-3-Glc when compared to the control culture. The expression of FUM6 was induced by protodioscin, K-3-Rut, and ClA, while FA and DIMBOA inhibited its expression. FUM19 was induced by all metabolites except FA. The highest concentration of fumonisin B₁ (FB₁) in control culture was 6.21 µg/mL. Protodioscin did not affect the FB content, while DIMBOA delayed their synthesis/secretion. Flavonoids and phenolic acids displayed similar effects. The results suggest that sole metabolites can have lower impacts on pathogen metabolism and mycotoxin synthesis than when combined with other compounds present in plant extracts. These synergistic effects require additional studies to reveal the mechanisms behind them.

Plant-Pathogenic Fusarium Species

Fusarium species are ubiquitous fungi, both saprotrophic and pathogenic to plants, animals and humans. They are also potent mycotoxin producers which makes them one of the most devastating plant pathogens. Mycotoxin biosynthesis and regulation has recently become one of the mainstream research topics, since knowledge concerning individual metabolic pathways became available and modern 'omics' techniques allowed us to expand this even further. Independently, high-throughput sequencing methodology helped researchers gain insight into the complex phylogenetic relationships among closely related genotypes comprising Fusarium populations, species and species complexes. Molecular tools have so far been very powerful in species identification and phylogeny, as the great diversity of the Fusarium genus has forced scientists to continuously revise previously described taxons.

In Vitro Effects of Lemon Balm Extracts in Reducing the Growth and Mycotoxins Biosynthesis of Fusarium culmorum and F. proliferatum

The objectives of this research were to obtain the extracts of lemon balm (Melissa officinalis) using supercritical CO2 (SC-CO2) and methanol as co-solvent and evaluate the antifungal activity of those extracts against two selected strains of Fusarium species (Fusarium culmorum and Fusarium proliferatum). The extraction conditions were set at 40 and 60 °C and 250 bar. The obtained extracts were characterized in terms of antifungal activity on potato dextrose agar media (PDA). The results showed that the extraction parameters had different effects on mycelium growth and mycotoxins biosynthesis reduction. All studied lemon balm extracts (1, 2.5, 5, 7.5, and 10%) inhibited the growth of F. proliferatum and F. culmorum mycelia compared to the control. The lemon balm extracts significantly reduced ergosterol content and synthesized mycotoxins in both tested strains. These findings support the antifungal activity of lemon balm extracts against F. proliferatum and F. culmorum. However, more research on other Fusarium species is needed, as well as in vivo applications, before considering lemon balm extracts as a natural alternative to synthetic fungicides.