Plant Pathogenic Fungi Research Articles

Development of a qPCR Assay for Species-Specific Detection of the Tar Spot Pathogen Phyllachora maydis

Phyllachora maydis is a fungal plant pathogen that causes tar spot of corn ( Zea mays) in North and South America, causing devastating yield losses under favorable conditions. Although the causal agent is relatively easy to diagnose via macroscopic and microscopic observations, other diseases and conditions, such as insect frass, have been mistaken for tar spot of corn. Furthermore, conidia and ascospores in isolation can be difficult to visually distinguish from other fungi, and the development of signs and symptoms of the disease may not be observed until 12 to 20 days after infection. Therefore, we developed a TaqMan quantitative polymerase chain reaction (qPCR) assay for the detection and quantification of this pathogen to be used for diagnostics and airborne spore quantification. The assay was designed for the internal transcribed spacer region of P. maydis. The specificity of the assay was confirmed and tested against various nontarget Phyllachora species, corn pathogens, endophytes, and P. maydis samples from several states in the Midwest and from Mexico. The detection limit of this assay was determined to be 100 fg of genomic P. maydis DNA. To demonstrate the transferability of this technology, the assay was tested in different labs using various qPCR thermal cyclers. This assay can be used in downstream research involving latency period, disease prediction, and diagnostics. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

The mitogen-activated protein kinase module CcSte11-CcSte7-CcPmk1 regulates pathogenicity via the transcription factor CcSte12 in Cytospora chrysosperma

The pathogen Cytospora chrysosperma is the causal agent of poplar canker disease and causes considerable economic losses in China. Mitogen-activated protein kinase (MAPK) cascades play a crucial role in mediating cellular responses and Pmk1-MAPKs are indispensable for pathogenic related processes in plant pathogenic fungi. In previous studies, we demonstrated that the CcPmk1 acts as a core regulator of fungal pathogenicity by modulating a small number of master downstream targets, such as CcSte12. In this study, we identified and characterized two upstream components of CcPmk1: MAPKKK CcSte11 and MAPKK CcSte7. Deletion of CcSte11 and CcSte7, resulted in slowed growth, loss of sporulation and virulence, similar to the defects observed in the CcPmk1 deletion mutant. In addition, CcSte11, CcSte7 and CcPmk1 interact with each other, and the upstream adaptor protein CcSte50 interact with CcSte11 and CcSte7. Moreover, we explored the global regulation network of CcSte12 by transcriptional analysis between CcSte12 deletion mutants and wild-type during the simulated infection process. Two hydrolase activity GO terms (GO:0004553 and GO:0016798) and starch and sucrose metabolism (mgr00500) KEGG pathway were significantly enriched in the down-regulated genes of CcSte12 deletion mutants. In addition, a subset of glycosyl hydrolase genes and putative effector genes were significantly down-regulated in the CcSte12 deletion mutant, which might be important for fungal pathogenicity. Especially, CcSte12 bound to the CcSp84 promoter region containing the TGAAACA motif. Moreover, comparison of CcSte12-regulated genes with CcPmk1-regulated genes revealed 116 overlapping regulated genes in both CcSte12 and CcPmk1, including some virulence-associated genes. Taken together, the protein complexes CcSte11-CcSte7-CcPmk1 receive signals transmitted by upstream CcSte50 and transmit signals to downstream CcSte12, which regulates hydrolase, effectors and other genes to promote virulence. Overall, these results indicate that the CcPmk1-MAPK signaling pathway of C. chrysosperma plays a key role in the pathogenicity.

Grapevine Leaf Epiphytic Fungal and Bacterial Communities Are Influenced More by Spatial and Temporal Factors than by Powdery Mildew Fungicide Spray Programs

Synthetic fungicide treatments for managing grapevine powdery mildew have been widely applied in vineyards for decades, yet their ecological impacts on microorganisms in the phyllosphere have not been sufficiently studied. To investigate the impact of fungicide sprays on the grapevine leaf microbiota, grapevine leaf epiphytes were collected throughout the growing season from two California vineyards, each treated with identical spray programs. Each spray program was designed to control grapevine powdery mildew and contained five rotating synthetic fungicides. Leaf samples were collected before the first spray and between subsequent spray applications. Amplicon sequencing of ITS2 and 16S rRNA V4 regions was used to compare leaf epiphytic fungal and bacterial/archaeal diversities, taxonomic compositions, and differential abundances of taxa among treatments, locations, and sampling time points. Location (vineyard) and time significantly affected bacterial and fungal community compositions, whereas spray treatment did not. Plant-pathogenic fungi were the dominant fungal guild in both locations, and, in one location, their dominance increased significantly as the season progressed. Botrytis, an important postharvest pathogen in grapes, was significantly higher in relative abundance in one of the locations in the late season and acted as a hub genus in a co-occurrence network. In summary, the overall impact of the different spray programs on microbial community compositions was not significant, suggesting that the shifts of grapevine foliar microbial communities may be driven mainly by spatial and temporal factors rather than specific fungicide applications. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Positive selection and functional diversification of transcription factor Cmr1 homologs in Alternaria

Transcription factor Cmr1 (Colletotrichum melanin regulation 1) and its homologs in several plant fungal pathogens are the regulators of the 1,8-dihydroxynaphthalene (DHN)-melanin biosynthesis pathway and have evolved functional diversification in morphology and pathogenicity. The fungal genus Alternaria comprises the group of “black fungi” that are rich in DHN-melanin in the primary cell wall and septa of the conidia. Some Alternaria species cause many economically important plant diseases worldwide. However, the evolution and function of Cmr1 homologs in Alternaria remain poorly understood. Here, we identified a total of forty-two Cmr1 homologs from forty-two Alternaria spp. and all contained one additional diverse fungal specific transcription factor motif. Phylogenetic analysis indicated the division of these homologs into five major clades and three branches. Dated phylogeny showed the A and D clades diverged latest and earliest, respectively. Molecular evolutionary analyses revealed that three amino acid sites of Cmr1 homologs in Alternaria were the targets of positive selection. Asmr1, the homolog of Cmr1 in the potato early blight pathogen, Alternaria solani was amplified and displayed the sequence conservation at the amino acid level in different A. solani isolates. Asmr1 was further confirmed to have the transcriptional activation activity and was upregulated during the early stage of potato infection. Deletion of asmr1 led to the decreased melanin content and pathogenicity, deformed conidial morphology, and responses to cell wall and fungicide stresses in A. solani. These results suggest positive selection and functional divergence have played a role in the evolution of Cmr1 homologs in Alternaria.Key points• Cmr1 homologs were under positive selection in Alternaria species• Asmr1 is a functional transcription factor, involved in spore development, melanin biosynthesis, pathogenicity, and responses to cell wall and fungicide stresses in A. solani• Cmr1 might be used as a potential taxonomic marker of the genus Alternaria

Silver nanoparticles improve the fungicidal properties of Rhazya stricta decne aqueous extract against plant pathogens

One of the most promising, non-toxic, and biocompatible developments for many biological activities is the green synthesis of nanoparticles from plants. In this work, we investigated the antifungal activity of silver nanoparticles (AgNPs) biosynthesized from Rhazya stricta aqueous extract against several plant pathogenic fungi. UV–visible spectroscopy, Zeta potential analysis, Fourier-transform infrared spectroscopy (FTIR), and transmitted electron microscopy (TEM) were used to analyze the biosynthesized AgNPs. Drechslera halodes, Drechslera tetramera, Macrophomina phaseolina, Alternaria alternata, and Curvularia australiensis were tested for their potential antifungal activity. Surface Plasmon Resonance (SPR) of Aq. AgNPs and Alkaline Aq. AgNPs was observed at 405 nm and 415 nm, respectively. FTIR analysis indicated hydroxyl, nitrile, amine, and ketone functional groups. Aq. AgNPs and Alka-line Aq. AgNPs had velocities of − 27.7 mV and − 37.9 mV and sizes of 21–90 nm and 7.2–25.3 nm, respectively, according to zeta potential studies and TEM. The antifungal examination revealed that all species' mycelial development was significantly inhibited, accompanied by severe ultra-structural alterations. Among all treatments, Aq. AgNPs were the most effective fungicide. M. phaseolina was statistically the most resistant, whereas A. alternata was the most vulnerable. To the best of our knowledge, this is the first report on R. stricta's antifungal activity against these species.

Temperature sensitivity of soil-borne fungal phytopathogens depends on niche breadth and land use types

Soil-borne fungal plant pathogens pose great threats to agricultural productivity and native ecosystems. However, the roles of niche breadth and land-use types in regulating the response of soil-borne fungal plant pathogens to temperature changes largely remain unclear. Here, we surveyed soil pathogens from different valleys where croplands, grasslands, and woodlands scattered in mosaic patterns. We found that pathogen richness increased with increasing temperature in grasslands but not in croplands and woodlands. After classifying the pathogens based on temperature niche, we found that the richness of specialists was sensitive to temperature changes and increased with increasing temperature in grasslands and croplands. By contrast, the richness of neutrals (those taxa not defined as generalists or specialists) did not change with temperature gradients regardless of land-use types. Additionally, pathogens were more abundant and diverse in croplands than those in grasslands and woodlands, and this pattern persisted across the temperature gradient. Our results provide evidence that temperature change and land use types could additively affect the diversity of plant pathogens in soils. This work advances our understanding of how niche breadth affects the response of pathogens to temperature, highlighting the importance of climate change and land use in regulating the abundance and diversity of pathogens.

Total Synthesis of Fusaramin, Enabling Stereochemical Elucidation, Structure-Activity Relationship, and Uncovering the Hidden Antimicrobial Activity against Plant Pathogenic Fungi.

Fusaramin (1) was isolated as a mitochondrial inhibitor. However, the fungal producer stops producing 1, which necessitates us to supply 1 by total synthesis. We proposed the complete stereochemical structure based on the biosynthetic pathway of sambutoxin. We have established concise and robust total synthesis of 1, enabling us to determine the complete stereochemical structure and to elucidate the structure-activity relationship, and uncover the hidden antiplant pathogenic fungal activity.

The fatty acid 2-hydroxylase CsSCS7 is a key hyphal growth factor and potential control target in Colletotrichum siamense.

SCS7 is a fatty acid 2-hydroxylase required for the synthesis of inositol phosphorylceramide but is not essential for normal growth in Saccharomyces cerevisiae. Here, we demonstrate that the Colletotrichum siamense SCS7 homolog CsSCS7 plays a key role in hyphal growth. The CsSCS7 deletion mutant showed strong hyphal growth inhibition, small conidia, and marginally reduced sporulation and also resulted in a sharp reduction in the full virulence and increasing the fungicide sensitivity. The three protein domains (a cytochrome b5 domain, a transmembrane domain, and a hydroxylase domain) are important to CsSCS7 protein function in hyphal growth. The fatty acid assay results revealed that the CsSCS7 gene is important for balancing the contents of multiple mid-long- and short-chain fatty acids. Additionally, the retarded growth and virulence of C. siamense ΔCsSCS7 can be recovered partly by the reintroduction of homologous sequences from Magnaporthe oryzae and Fusarium graminearum but not SCS7 of S. cerevisiae. In addition, the spraying of C. siamense with naked CsSCS7-double-stranded RNA (dsRNAs), which leads to RNAi, increases the inhibition of hyphal growth and slightly decreases disease lesions. Then, we used nano material Mg-Al-layered double hydroxide as carriers to deliver dsRNA, which significantly enhanced the control effect of dsRNA, and the lesion area was obviously reduced. These data indicated that CsSCS7 is an important factor for hyphal growth and affects virulence and may be a potential control target in C. siamense and even in filamentous plant pathogenic fungi.IMPORTANCECsSCS7, which is homologous to yeast fatty acid 2-hydroxylase SCS7, was confirmed to play a key role in the hyphal growth of Colletotrichum siamense and affect its virulence. The CsSCS7 gene is involved in the synthesis and metabolism of fatty acids. Homologs from the filamentous fungi Magnaporthe oryzae and Fusarium graminearum can recover the retarded growth and virulence of C. siamense ΔCsSCS7. The spraying of double-stranded RNAs targeting CsSCS7 can inhibit hyphal growth and reduce the disease lesion area to some extent. After using nano material Mg-Al layered double hydroxide as carrier, the inhibition rates were significantly increased. We demonstrated that CsSCS7 is an important factor for hyphal growth and affects virulence and may be a potential control target in C. siamense and even in filamentous plant pathogenic fungi.

The cell cycle, autophagy, and cell wall integrity pathway jointly governed by MoSwe1 in Magnaporthe oryzae

The cell cycle is pivotal to cellular differentiation in plant pathogenic fungi. Cell wall integrity (CWI) signaling plays an essential role in coping with cell wall stress. Autophagy is a degradation process in which cells decompose their components to recover macromolecules and provide energy under stress conditions. However, the specific association between cell cycle, autophagy and CWI pathway remains unclear in model pathogenic fungi Magnaporthe oryzae. Here, we have identified MoSwe1 as the conserved component of the cell cycle in the rice blast fungus. We have found that MoSwe1 targets MoMps1, a conserved critical MAP kinase of the CWI pathway, through protein phosphorylation that positively regulates CWI signaling. The CWI pathway is abnormal in the ΔMoswe1 mutant with cell cycle arrest. In addition, we provided evidence that MoSwe1 positively regulates autophagy by interacting with MoAtg17 and MoAtg18, the core autophagy proteins. Moreover, the S phase initiation was earlier, the morphology of conidia and appressoria was abnormal, and septum formation and glycogen degradation were impaired in the ΔMoswe1 mutant. Our research defines that MoSWE1 regulation of G1/S transition, CWI pathway, and autophagy supports its specific requirement for appressorium development and virulence in plant pathogenic fungi.4YLJWdgoLcEF_sT4NWF7zpVideo

Active substances of myxobacteria against plant diseases and their action mechanisms.

Myxobacteria have a complex life cycle and unique social behavior, and obtain nutrients by preying on bacteria and fungi in soil. Chitinase, β-1,3 glucanase and β-1,6 glucanase produced by myxobacteria can degrade the glycosidic bond of cell wall of some plant pathogenic fungi, resulting in a perforated structure in the cell wall. In addition, isooctanol produced by myxobacteria can lead to the accumulation of intracellular reactive oxygen species in some pathogenic fungi and induce cell apoptosis. Myxobacteria can also perforate the cell wall of some plant pathogenic oomycetes by β-1,3 glucanase, reduce the content of intracellular soluble protein and protective enzyme activity, affect the permeability of oomycete cell membrane, and aggravate the oxidative damage of pathogen cells. Small molecule compounds such as diisobutyl phthalate and myxovirescin produced by myxobacteria can inhibit the formation of biofilm and lipoprotein of bacteria, and cystobactamids can inhibit the activity of DNA gyrase, thus changing the permeability of bacterial cell membrane. Myxobacteria, as a new natural compound resource bank, can control plant pathogenic fungi, oomycetes and bacteria by producing carbohydrate active enzymes and small molecular compounds, so it has great potential in plant disease control.

Effects of Organic Fertilizer of Kitchen Waste on Soil Microbial Activity and Function

Changes in soil microbial activity and ecological function can be used to assess the level of soil fertility and the stability of ecosystems. To assess the fertility and safety of organic fertilizer of kitchen waste (OFK), soils containing 0% (CK), 1%, 3%, and 5% OFK were cultured, and the physical, chemical, and microbial properties of the soils were measured dynamically with routine agrochemical analysis measures and amplicon sequencing. The results showed that compared with those in CK, the contents of organic matter, available phosphorus, available potassium, NH4+-N, and NO3--N in soils with OFK increased by 23.80%-35.13%, 13.29%-29.72%, 16.91%-39.37%, 164.7%-340.2%, and 28.56%-32.71%, respectively. The activities of hydrolases related to the cycle of carbon, nitrogen, and phosphorus (α-glucosidase, leucine aminopeptidase, acid phosphatase, etc.) were also significantly higher than those of the CK treatment. OFK stimulated the growth of soil microorganisms and increased the carbon content of the microbial biomass. The amplicon sequencing analysis found that the microbial community structures of different treatments were significantly different at both the class and genus levels. In addition, it was found that the abundance of beneficial microbes in the soils with OFK increased, whereas pathogenic microbes decreased. RDA results confirmed that soil properties (including soil pH, organic matter, available nutrients, and microbial biomass) had a significant impact on microbial community structure. The results of investing bacterial community based on PICRUSt and FAPROTAX revealed that the function of the soil bacterial community was similar in the four treatments, but OFK supply significantly improved the microbial carbon utilization and metabolic ability. Moreover, by using the FUNGuild software, we found that the application of OFK increased the proportion of saprotroph-symbiotroph and symbiotroph and stimulated the growth of ectomycorrhizal fungi-undefined saprophytic fungi but inhibited plant and animal pathogenic fungi in soil. These results implied that OFK could promote the establishment of symbiotic relationships and inhibit the growth of pathogenic fungi. In summary, OFK could improve soil fertility and hydrolase activity, stimulate the growth of beneficial microorganisms, and defend against pathogens, indicating a promising use as safe and efficient organic fertilizer.

Mold Resistance of Bamboo after Laccase‐Catalyzed Fixation of Lignin Nanoparticles

AbstractIn this study lignin nanoparticles (LNPs) and iodolignin nanoparticles (ILNPs) were prepared in aqueous medium and subsequently deposited on the bamboo surfaces via laccase catalyzed reaction. The SEM micrographs of blocks treated with LNPs and ILNPs revealed a layer of nanoparticles with a mean particles size of 100 nm and 215 nm. Besides that, the fungal isolates from the bamboo culm of Dendrocalamus asper shared 99 %, 98 % and 100 % similarity with Penicillium sumatrense, Pleosporales and Cunninghamella species. The treatment of ILNPs exhibited maximum biocidal efficacy at 91 % against P. sumatrense, Pleosporales sp. and Cunninghamella sp. After leaching with ultrapure water, LNPs‐treated blocks exhibited a reduced biocidal effectiveness with an efficacy of 67 %. In contrast, bamboo treated with ILNPs exhibited a higher level of resistance to decay than LNPs. The reduction in mass of 2 %, 3 %, and 1 % was observed when subjecting P. sumatrense, Cunninghamella, and Pleosporales species to treatment with ILNPs. This study demonstrates the application of laccase catalysis in both LNPs and ILNPs, indicating a potentially effective approach for providing surface protection to bamboo against plant pathogenic fungi.

Comparative Assessment of Habitat Suitability and Niche Overlap of Three Cytospora Species in China.

The plant pathogenic fungus Cytospora is notoriously known for causing woody plant canker diseases, resulting in substantial economic losses to biological forests and fruit trees worldwide. Despite their strong negative ecological impact, the existing and prospective distribution patterns of these plant pathogens in China, according to climate change, have received little attention. In this study, we chose three widely dispersed and seriously damaging species, namely, Cytospora chrysosperma, Cytospora mali, and Cytospora nivea, which are the most common species that damage the Juglans regia, Malus domestica, Eucalyptus, Pyrus sinkiangensis, Populus spp., and Salix spp. in China. We utilized ecological niche modeling to forecast their regional distribution in China under four climate change scenarios (present, SSP 126, SSP 370, and SSP 585). The results show that temperature-related climate factors limit the current distribution ranges of the three species. Currently, the three studied species are highly suitable for northeast, northwest, north, and southwest China. Under future climate scenarios, the distribution ranges of the three species are projected to increase, and the centers of the adequate distribution areas of the three species are expected to shift to high-latitude regions. The three species coexist in China, primarily in the northwest and north regions. The ecological niches of C. chrysosperma and C. nivea are more similar. The distribution range of C. mali can reach the warmer and wetter eastern region, whereas C. chrysosperma and C. nivea are primarily found in drought-prone areas with little rainfall. Our findings can help farmers and planners develop methods to avoid the spread of Cytospora spp. and calculate the costs of applying pesticides to reduce contamination and boost yields.

Identification of Acetomycin as an Antifungal Agent Produced by Termite Gut-Associated Streptomycetes against Pyrrhoderma noxium.

Plant fungal pathogen Pyrrhoderma noxium is responsible for the destructive and invasive disease of brown root rot currently affecting the city of Brisbane, Australia. In order to address this issue, environmentally friendly and safe alternatives to chemical control are preferred due to the city's public setting. Antifungal natural products are ideal candidates as biological control alternatives and can be detected through investigating the metabolomes of microbial symbionts. Within this study, an NMR-based metabolomics approach was applied to fermentation extracts obtained from 15 termite gut-associated streptomycetes. By analysing the NMR spectra, six of the extracts which displayed similar chemical profiles exhibited antifungal activity against the P. noxium pathogen. The major compound within these extracts was identified as acetomycin using NMR and X-ray crystallography analyses. This is the first reporting of acetomycin as a potential natural product fungicide, particularly as an antifungal agent against P. noxium. Inhibitory activity was also found against other important fungal crop pathogens, including Aspergillus niger, Botrytis cinerea, and Alteranaria alternata. Further experimentation using a woodblock test found inhibitory activity on the growth of the P. noxium pathogen for up to 3 weeks and a significant difference in the integrity of the woodblocks when conducting compression strength tests after 6 weeks. Therefore, acetomycin may be used as a biological control agent and natural product fungicide against P. noxium.

Mercaptoimidazole-capped gold nanoparticles as a potent agent against plant pathogenic fungi.

Plant pathogenic fungi pose a substantial challenge to agricultural production, but the conventional fungicide-based approaches are losing importance. As agents with broad-spectrum antibacterial effects, gold nanoparticles (Au NPs) are found to have antifungal effects; however, no study has examined their application in agriculture as fungicides. Accordingly, this study investigates the activity of 2-mercaptoimidazole-capped Au NPs (MI-Au NPs) against the 'top' plant pathogenic fungi, finding that they could inhibit Magnaporthe oryzae, Botrytis cinerea, Fusarium pseudograminearum and Colletotrichum destructivum by inducing cytoplasmic leakage. Moreover, MI-Au NPs are found to protect plants from infection by B. cinerea. Specifically, pot experiments demonstrate that MI-Au NPs decrease the incidence rate of B. cinerea infection in Arabidopsis thaliana from 74.6% to 6.2% and in Solanum lycopersicum from 100% to 10.9%, outperforming those achieved by imazalil. Furthermore, the biosafety assays reveal that MI-Au NPs cannot penetrate the cuticle of plant cells or negatively influence plant growth, and it is safe to mammalian cells. In summary, the findings of this study will support the development of NP-based antifungal agents for use in agriculture.

Evaluation of the brown alga, Sargassum muticum extract as an antimicrobial and feeding additives.

Plant disease administration is difficult due to the nature of phytopathogens. Biological control is a safe method to avoid the problems related to fungal diseases affecting crop productivity and some human pathogenic bacteria. For that, the antimicrobial activity of the seaweed Sargassum muticum methanol and water extracts were investigated against human bacterial pathogens and fungal plant pathogens. By using 70 percent methanol, the seaweed powder was extracted, feeding additives assay, ultrastructure (TEM). Results revealed significant inhibition of S. muticum methanol extract against Salmonella typhi (25.66 mm), Escherichia coli (24.33 mm), Staphylococcus aureus (22.33 mm) and Bacillus subtilis. (19.66 mm), some fungal phytopathogens significantly inhibited Fusarium moniliforme (30.33mm), Pythium ultimum (26.33 mm), Aspergillus flavus (24.36mm), and Macrophomina phaseolina (22.66mm). Phytochemical investigation of S. muticum extract showed the presence of phenolic and flavonoid compounds. Results suggested that there is an appreciable level of antioxidant potential in S. muticum (79.86%) DPPH scavenging activity. Ultrastructural studies of Fusarium moniliforme hypha grown on a medium containing S. muticum extract at concentration 300mg/ml showed a thickening cell wall, disintegration of cytoplasm, large lipid bodies and vacuoles. In conclusion, our study revealed The antibacterial activity of S. muticum extract significantly against some Gram positive, Gram negative bacteria and antifungal activity against some phytopathogenic and some mycotoxin producer fungi. Flavonoids, phenolic play an important role as antioxidants and antimicrobial properties. Such study revealed that S. muticum methanol extract could be used as ecofriendly biocontrol for phytopathogenic fungi and feeding additives to protect livestock products.

Exaggerated Plurivory of Macrophomina phaseolina: Accounting for the Large Host Range Claim and the Shifting of Scientific Language.

Macrophomina phaseolina is a plant pathogenic fungus that is frequently described as having a broad host range encompassing more than 500 species. We noticed that citations provided in support of this statement do not actually demonstrate such a broad host range. To elucidate the true documented host range of this fungus, we initiated a literature meta-analysis of 894 publications on M. phaseolina since 1913. We discovered that the first host range summaries did not require Koch's postulates or other experimental demonstrations of pathogenicity. Most of the available early host claims were based on tenuous associations between the fungus and symptoms, sometimes without reporting isolation or morphological examination in vitro. These statements apparently led to a pattern of increasingly exaggerated host range claims, without support from a primary reference, until the claim that M. phaseolina has 500 hosts became common in the early 2000s. At present, the scientific community typically requires Koch's postulates to characterize pathogenicity on a new host. Among all the available literature, we only found primary experimental evidence for M. phaseolina's pathogenicity on 97 hosts; 74 hosts confirmed by Koch's postulates and 23 hosts with all steps from Koch's postulates completed except for recovery of the pathogen from symptomatic tissues. This study demonstrates how scientific concepts can change over time and necessitate changes to historic axioms. We propose that the hyperbole surrounding the host range of M. phaseolina has obscured an accurate depiction of its biology.

Piecing together the taxonomic puzzle of Sphaerulina

Sphaerulina species are plant pathogenic fungi causing leaf spot diseases of various hosts, including arboreous and herbaceous plants. The morphological characteristics of their asexual morphs and leaf spot symptoms are like those of Septoria spp. Due to their similar morphology, species of Sphaerulina have largely been subsumed under Septoria s. lat. A recent revision of the genus Septoria based on morphological characteristics and phylogeneticrelationships resulted in the separation of Sphaerulina from Septoria. This study reveals the diversity of the genus Sphaerulina in Japan, and the species relationships based on a multigene phylogenetic analysis. Moreover, resultsof our phylogenetic analysis revealed seven novel species (Sph. farfugii, Sph. hydrangeicola, Sph. idesiae, Sph. lapsanastri, Sph. miurae, Sph. styracis, and Sph. viburnicola) which are described, and two species (Sep. duchesnea and Sep. nambuana) which are transferred to the genus Sphaerulina.

Fungal-mediated synthesis of silver nanoparticles: a novel strategy for plant disease management.

Various traditional management techniques are employed to control plant diseases caused by bacteria and fungi. However, due to their drawbacks and adverse environmental effects, there is a shift toward employing more eco-friendly methods that are less harmful to the environment and human health. The main aim of the study was to biosynthesize silver Nanoparticles (AgNPs) from Rhizoctonia solani and Cladosporium cladosporioides using a green approach and to test the antimycotic activity of these biosynthesized AgNPs against a variety of pathogenic fungi. The characterization of samples was done by using UV-visible spectroscopy, SEM (scanning electron microscopy), FTIR (fourier transmission infrared spectroscopy), and XRD (X-ray diffractometry). During the study, the presence of strong plasmon absorbance bands at 420 and 450 nm confirmed the AgNPs biosynthesis by the fungi Rhizoctonia solani and Cladosporium cladosporioides. The biosynthesized AgNPs were 80-100 nm in size, asymmetrical in shape and became spherical to sub-spherical when aggregated. Assessment of the antifungal activity of the silver nanoparticles against various plant pathogenic fungi was carried out by agar well diffusion assay. Different concentration of AgNPs, 5 mg/mL 10 mg/mL and 15 mg/mL were tested to know the inhibitory effect of fungal plant pathogens viz. Aspergillus flavus, Penicillium citrinum, Fusarium oxysporum, Fusarium metavorans, and Aspergillus aflatoxiformans. However, 15 mg/mL concentration of the AgNPs showed excellent inhibitory activity against all tested fungal pathogens. Thus, the obtained results clearly suggest that silver nanoparticles may have important applications in controlling various plant diseases caused by fungi.

Insights into the Mechanobiology of Phytophthora

Phytophthora species, classified as oomycetes, are among the most destructive plant pathogens worldwide and pose a substantial threat to food security. Plant pathogens have developed various methods to breach the cuticle and walls of plant cells. For example, plant-pathogenic fungi use a ‘brute-force’ approach by producing a specialized and fortified invasion organ to generate invasive pressures [1]. Unlike in fungi, Phytophthora pathogens harness a specialized form of invasive tip growth to slice through the plant surface, wielding their hypha as a microscopic knife known as “naifu” invasion [2].