zingiberi Is Associated with Cultivar-Specific Expression of Defense-Responsive Genes

Ginger (Zingiber officinale Roscoe) is an important horticultural crop, valued for its culinary and medicinal properties. Fusarium yellows of ginger, caused by Fusarium oxysporum f. sp. zingiberi (Foz), is a devastating disease that has significantly reduced the quality and crop yield of ginger worldwide. The compatible interaction between ginger and Foz leading to susceptibility is dissected here. The pathogenicity of two Foz isolates on ginger was confirmed by their ability to colonise ginger and in turn induce both internal and external plant symptoms typical of Fusarium yellows. To shed light on Foz susceptibility at the molecular level, a set of defense-responsive genes was analysed for expression in the roots of ginger cultivars challenged with Foz. These include nucleotide-binding site (NBS) type of resistant (R) genes with a functional role in pathogen recognition, transcription factors associated with systemic acquired resistance, and enzymes involved in terpenoid biosynthesis and cell wall modifications. Among three R genes, the transcripts of ZoNBS1 and ZoNBS3 were rapidly induced by Foz at the onset of infection, and the expression magnitude was cultivar-dependent. These expression characteristics extend to the other genes. This study is the first step in understanding the mechanisms of compatible host-pathogen interactions in ginger.

Second-Generation Enamine-Type Schiff Bases as 2-Amino Acid-Derived Antifungals against Fusarium oxysporum: Microwave-Assisted Synthesis, In Vitro Activity, 3D-QSAR, and In Vivo Effect

In this manuscript, the synthesis of enamine-type Schiff bases 1−48 derived from the amino acids L-Ala, L-Tyr, and L-Phe was carried out. Their in vitro activity and in vivo protective effect against Fusarium oxysporum were also evaluated through mycelial growth inhibition and disease severity reduction under greenhouse conditions. The in vitro activity of test compounds 1−48 showed half-maximal inhibitory concentrations (IC50) at different levels below the 40 mM range. Deep analysis of the IC50 variations indicated that the size of the substituent on the acetylacetone derivatives and the electronic character on the cyclohexane-3-one fragment influenced the antifungal effect. 3D-QSAR models based on atoms (atom-based approach) were built to establish the structure−activity relationship of the test Schiff bases, showing a good correlation and predictive consistency (R2 > 0.70 and Q2 > 0.60). The respective contour analysis also provided information about the structural requirements for potentiating their antifungal activity. In particular, the amino acid-related fragment and the alkyl ester residue can favor hydrophobic interactions. In contrast, the nitrogen atoms and enamine substituent are favorable regions as H-donating and electron-withdrawing moieties. The most active compounds (40 and 41) protected cape gooseberry plants against F. oxysporum infection (disease severity index < 2), involving adequate physiological parameters (stomatal conductance > 150 mmol/m2s) after 45 days of inoculation. These promising results will allow the design of novel Schiff base-inspired antifungals using 2-amino acids as precursors.

Antifungal Activity of Selenium Nanoparticles Obtained by Plant-Mediated Synthesis

The continuous need to satisfy world food demand has led to the search for new alternatives to combat economic losses in agriculture caused by phytopathogenic fungi. These organisms cause plant diseases, reducing their productivity and decreasing fruit quality. Among the new tools being explored is nanotechnology. Nanoparticles with antimicrobial properties could be an excellent alternative to address this problem. In this work, selenium nanoparticles (SeNPs) were obtained using plant extracts of Amphipterygium glaucum leaves (SeNPs-AGL) and Calendula officinalis flowers (SeNPs-COF). Characterization of the SeNPs was performed and their ability as antifungal agents against two commercially relevant plant pathogenic fungi, Fusarium oxysporum and Colletotrichum gloeosporioides, was evaluated. Assays were performed with different concentrations of SeNPs (0, 0.25, 0.5, 1.0, and 1.7 mg/mL). It was observed that both SeNPs had antifungal activity against both plant pathogens at concentrations of 0.25 mg/mL and above. SeNPs-AGL demonstrated better antifungal activity and smaller size (around 8.0 nm) than SeNPs-COF (134.0 nm). FTIR analysis evidenced the existence of different functional groups that constitute both types of SeNPs. There are factors that have to be considered in the antimicrobial activity of SeNPs such as nanoparticle size and phytochemical composition of the plant extracts used, as these may affect their bioavailability.

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.

[Effects of temperature and humidity on infection of Fusarium oxysporum in seedlings of Salvia miltiorrhiza]

Wilt disease is a major disease of cultivated Salvia miltiorrhiza, which is caused by Fusarium oxysporum. Since the infection process of F. oxysporum in plants is affected by environment factors, this study was conducted to reveal the relationship between disease severity and concentration of the pathogen in plants in the infection process of F. oxysporum in seedlings of S. miltiorrhiza by pot experiments and to reveal the effects of temperature and humidity on the infection process. The results showed that, after inoculation of S. miltiorrhiza seedlings with F. oxysporum, the pathogen in different parts was detected at different time, and it was first detected in substrates. With the continuous propagation of the pathogen(4-5 d), it gradually infected the roots and stems of the seedlings, and the plants had yellowing leaves and withering. The number of the pathogen reached the maximum in each part after 7-8 d, and then gradually decreased in the later stage of the disease. The concentration of the pathogen in substrates, roots and stems of S. miltiorrhiza showed a trend of decreasing after increasing with the aggravation of the disease and reached the maximum in the samples of moderate morbidity, while the concentration in the samples of severe morbidity decreased. In addition, the infection of F. oxysporum in seedlings of S. miltiorrhiza was affected by temperature and humidity. The suitable temperature was 25-30 ℃ and the suitable humidity was 80%-90%. This study could provide guidance for the experiments on pathogenicity of F. oxysporum, screening of biocontrol bacteria and controlling of wilt.

Screening, synthesis optimization, and scaling-up of phytopathogen antifungals derived from natural hydroxycinnamic acids

A simple screening methodology was employed to correlate the structures of hydroxycinnamic acids (HCAs) and their esterified derivatives with their in vitro antifungal activity over Fusarium oxysporum f. sp. lycopersici. The antifungal activity of the tested HCAs, i.e., coumaric > ferulic > sinapinic > caffeic acid, was higher after esterification and when the coumaric acid hydroxyl group was at the ortho-position. This outcome was strengthened by the elongation of the alkyl chain to 4-carbons and, particularly, by the esterification with isobutyl alcohol. The highest antifungal activity was obtained from isobutyl o-coumarate (iBoC), which inhibits 70% of mycelial growth at 1.2 mM. Thereby, a heterogeneous catalysis strategy was optimized by using the response surface methodology. At the best conditions found, the synthesis of iBoC was scaled up to 15 g, achieving 96% conversion yield in 48 h in a stirred batch reactor. This study reveals for the first time the potential of iBoC to provide commercial materials as antifungal agents to control F. oxysporum and other phytopathogenic fungi.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03425-7.

Live-Cell Visualization of Early Stages of Root Colonization by the Vascular Wilt Pathogen Fusarium oxysporum

Fungal phytopathogens induce a variety of pathogenicity symptoms on their hosts. The soilborne vascular wilt pathogen Fusarium oxysporum infects roots of more than 150 different crop species. Initial colonization stages are asymptomatic, likely representing a biotrophic phase of infection, followed by a necrotrophic switch after vascular colonization which results in blockage of the plant xylem and killing of the host. Live-cell microscopy techniques have been successfully employed to study interaction events during fungal colonization of root tissues. This technique is widely used to track fungal development during disease progression. Here, we describe a well-established protocol for generation and screening of fluorescently tagged F. oxysporum transformants, as well as for live-cell imaging of the early colonization stages of F. oxysporum on tomato (Solanum lycopersicum) seedlings. The presented experimental design and techniques involved are also applicable to other root infecting fungi.

Study on the interaction mechanism between Crocus sativus and Fusarium oxysporum based on dual RNA-seq

The saffron phenylpropane synthesis pathway and Fusarium oxysporum cell wall-degrading enzymes play key roles in their early interactions. Saffron (Crocus sativus) is a highly important crop with diverse medicinal properties. F. oxysporum is a widely-distributed soil-borne fungus, causing the serious saffron rot disease. Currently, there is no effective management strategy to control this disease because of no resistant cultivars and limited information about the resistance and pathogenic mechanisms. In this study, we first characterized the infection process and physiological responses of saffron infected by F. oxysporum. The molecular mechanism of these infection interactions was revealed by dual RNA-seq analysis. On the 3rd day of infection, the hyphae completely entered, colonized and spread in the corm cells; while on the 6th day of infection, hyphae had appeared in the xylem cells, blocking these vessels. Transcriptome results indicate that within the host, phenylpropanoid metabolism, plant hormone signal transduction and plant pathogen interaction pathways were activated during infection. These pathways were conducive to the enhancement of cell wall, the occurrence of hypersensitivity, and the accumulation of various antibacterial proteins and phytoantitoxins. Meanwhile, in the fungus, many up-regulated genes were related to F. oxysporum cell wall degrading enzymes, toxin synthesis and pathogenicity gene, showing its strong pathogenicity. This study provides new ideas for the control of saffron corm rot, and also provides a theoretical basis for mining the key functional genes.

Physiological race characterisation of Fusarium oxysporum strains infecting tomato employing candidate pathogenicity genes and host resistance

Physiological races of 14 strains of Fusarium oxysporum f.sp. lycopersici were established by PCR profiling SIX gene expressions. No amplification of the SIX4 (Avr1) gene was observed in any of the 14 strains. Based on amplification of the SIX3 (Avr2) gene, 6 strains were distinguished as race 2. Race 2 strains are known to contain identical SIX3 sequences and differ from race 3 strains by single point mutations. Hence, based on polymorphic amplicons of the SIX3 gene detected by stringent PCR conditions, 8 strains were identified as race 3. The identity of the physiological races of the strains was validated by inoculating on three germplasm lines, EC-814916, FEB-2 and Pusa Rohini carrying I-2, I-3 and no I gene, respectively. The race 2 and race 3 strains were avirulent on EC-814916 and FEB-2 lines, respectively. All the 14 fungal strains were pathogenic on Pusa Rohini, the Fusarium wilt susceptible cultivar lacking R genes and exhibited different levels of virulence. In evaluating two other potential pathogenicity genes, Fow1 and Fow2 as markers for virulence, their expressions were observed among both the races of the Fol strains, and hence are not potential candidates for physiological race discrimination. However, strong expressions of the genes in the root tissues inoculated with the highly virulent strain, TOFU-IHBT in comparison to the uninoculated control indicated their roles in fungal pathogenicity. To understand the role of these pathogenicity genes in countering the host defence mechanisms, their expressions in response to ROS and phenolics, the earliest known defence mechanisms of host plants were assessed. In H₂O₂, the Fow2 gene expressed 1.4-fold greater than that of the control. On the contrary, in relation to the control, the expressions of Fow1 were strongly repressed exhibiting 0.7-to 0.8-fold lesser at 0.1 mM through 3 mM concentrations than that of the control indicating that the gene is modulated by the phenolic acid indicating the roles of Fow2 and Fow1 in alleviating oxidative stress and targeted by the phenolic acid, respectively.

Persistence as a Constituent of a Biocontrol Mechanism (Competition for Nutrients and Niches) in Pseudomonas putida PCL1760

Competition for nutrients and niches (CNN) is known to be one of the mechanisms for biocontrol mostly exhibited by Pseudomonas strains. Phenotypic and full genome analysis revealed Pseudomonas putida PCL1760 controlling tomato foot and root rot (TFRR) solely through CNN mechanism. Although the availability of nutrients and motility are the known conditions for CNN, persistence of bacteria through dormancy by ribosomal hibernation is a key phenomenon to evade both biotic and abiotic stress. To confirm this hypothesis, rsfS gene knockout mutant of PCL1760 (SB9) was first obtained through genetic constructions and compared with the wild type PCL1760. Primarily, relative expression of rsfS in PCL1760 was conducted on tomato seedlings which showed a higher expression at the apical part (1.02 ± 0.18) of the plant roots than the basal (0.41 ± 0.13). The growth curve and persistence in ceftriaxone after the induction of starvation with rifampicin were performed on both strains. Colonization on the tomato root by CFU and qPCR, including biocontrol ability against Fusarium, was also tested. The growth dynamics of both PCL1760 and SB9 in basal and rich medium statistically did not differ (p ≤ 0.05). There was a significant difference observed in persistence showing PCL1760 to be more persistent than its mutant SB9, while SB9 (pJeM2:rsfS) was 221.07 folds more than PCL1760. In colonization and biocontrol ability tests, PCL1760 was dominant over SB9 colonizing and controlling TFRR (in total, 3.044 × 10⁴ to 6.95 × 10³ fg/µL and 55.28% to 30.24%, respectively). The deletion of the rsfS gene in PCL1760 reduced the persistence and effectiveness of the strain, suggesting persistence as one important characteristic of the CNN.

Fusarium oxysporum Casein Kinase 1, a Negative Regulator of the Plasma Membrane H+-ATPase Pma1, Is Required for Development and Pathogenicity

Like many hemibiotrophic plant pathogens, the root-infecting vascular wilt fungus Fusarium oxysporum induces an increase in the pH of the surrounding host tissue. How alkalinization promotes fungal infection is not fully understood, but recent studies point towards the role of cytosolic pH (pH_c) and mitogen-activated protein kinase (MAPK) signaling. In fungi, pH_c is mainly controlled by the essential plasma membrane H⁺-ATPase Pma1. Here we created mutants of F. oxysporum lacking casein kinase 1 (Ck1), a known negative regulator of Pma1. We found that the ck1Δ mutants have constitutively high Pma1 activity and exhibit reduced alkalinization of the surrounding medium as well as decreased hyphal growth and conidiation. Importantly, the ck1Δ mutants exhibit defects in hyphal chemotropism towards plant roots and in pathogenicity on tomato plants. Thus, Ck1 is a key regulator of the development and virulence of F. oxysporum.

Effect of synthetic fatty liquor and neatsfoot oil as co-contaminants on the reduction of hexavalent chromium using Fusarium oxysporum and its kinetic study

The hexavalent chromium is one of the major carcinogenic components released during the tanning process and lots of work have been carried out on the reduction of hexavalent chromium via chemical and biological routes. Different fatty oils are also employed in the tanning process and have also been released as an effluent along with chromium. However, it is difficult to find a study on the reduction of chromium in the presence of other contaminant which would help to mimic the real-time complication of treating the tannery effluent. It is the first attempt on the reduction of hexavalent chromium in the presence of synthetic fatty liquor and neatsfoot oil using Fusarium oxysporum. The maximum percentage of chromium reduction was 73.62% and 60.28% in neatsfoot oil and synthetic fatty oil, respectively, for the initial chromium concentration of 25 mg/L. The biomass productivity was better with both neatsfoot oil and synthetic fatty oil, whereas the same has decreased with the presence of chromium. The reduction of chromium was found to follow the uncompetitive substrate inhibition kinetics than the general Michaelis-Menten kinetics. The kinetic parameters were calculated using particle swarm optimization algorithm, which were compared with the already reported data. The uncompetitive substrate inhibition kinetics was represented the experimental data in both the cases and the value of substrate inhibition constant was low in the case of neatsfoot oil compared with the synthetic fatty liquor.

The Gal4-Type Transcription Factor Pro1 Integrates Inputs from Two Different MAPK Cascades to Regulate Development in the Fungal Pathogen Fusarium oxysporum

Mitogen-activated protein kinase (MAPK) signaling pathways control fundamental aspects of growth and development in fungi. In the soil-inhabiting ascomycete Fusarium oxysporum, which causes vascular wilt disease in more than a hundred crops, the MAPKs Fmk1 and Mpk1 regulate an array of developmental and virulence-related processes. The downstream components mediating these disparate functions are largely unknown. Here we find that the GATA-type transcription factor Pro1 integrates signals from both MAPK pathways to control a subset of functions, including quorum sensing, hyphal fusion and chemotropism. By contrast, Pro1 is dispensable for other downstream processes such as invasive hyphal growth and virulence, or response to cell wall stress. We further show that regulation of Pro1 activity by these upstream pathways occurs at least in part at the level of transcription. Besides the MAPK pathways, upstream regulators of Pro1 transcription also include the Velvet regulatory complex, the signaling protein Soft (Fso1) and the transcription factor Ste12 which was previously shown to act downstream of Fmk1. Collectively, our results reveal a role of Pro1 in integrating the outputs from different signaling pathways of F. oxysporum thereby mediating key developmental decisions in this important fungal pathogen.

First Report of Fusarium oxysporum Causing Stem Rot on Mammillaria humboldtii in China

Mammillaria humboldtii found in Mexico is a short-globose ornamental cactus species of the Cactaceae family, which has gained increasing popularity in China. It is characterized by tuberculate stems, dimorphic areoles, small pink flowers and pitted seed cell walls. The populations of wild M. humboldtii are critically endangered and are now of international conservation concern. In July 2021, stem rot symptoms were observed on M. humboldtii in a commercial greenhouse located in Zhangzhou (117°39'44.0064″E, 24°28'3.7236″N), Fujian Province (southern China). The typical symptoms were water-soaking, rotting and wilting on the stem, eventually leading to necrosis of the plants within 20 to 30 days. The vascular system of infected stems and roots showed a reddish-brown discolouration. The disease affected approximately 10% of 1000 plants. Fungi were isolated from the diseased stems of 26 samples, which were chopped into small pieces (5 × 5 mm), surface-sterilized with 75% ethanol for 40 s, and placed onto potato dextrose agar (PDA). After seven days of dark culture at 28°C, morphologically similar fungal isolates with whitish aerial mycelium and purple pigment were observed. On carnation leaf agar (CLA), isolates produced sickle and slightly curved macroconidia with three to four septa, measuring 12.8 to 27.9 × 1.9 to 3.8 μm (n = 15), and unicellular, ovoid to elliptical microconidia measuring 3.8 to 7.7 × 1.4 to 2.5 μm (n = 30). Smooth walled chlamydospores were terminal or intercalary, single or in pairs, measuring 9.2 to 13.1 μm (n = 15) in diameter. For molecular identification, the internal transcribed spacer (ITS) region of rDNA (Schoch et al. 2012), translation elongation factor-1α (EF1-α) (Maryani et al. 2019) and gene coding endopolygalacturonase 1 (PG1) (Hirano et al. 2006) of the representative isolate FJMH7 were amplified, purified and sequenced. BLASTn analysis of the ITS, EF1-α and pg1 sequences (GenBank accession numbers: ON832660, ON843495 and ON843496) showed 100%, 99.70% and 98.96% identity with F. oxysporum (GenBank accession numbers: KX611626, OM801797 and KF437345), respectively. Phylogenetic analysis based on the the concatenated ITS and EF1-α sequences and pg1 genes placed isolate FJMH7 with F. oxysporum reference strains in the phylogenetic trees. Based on morphological identification and sequence analysis, this isolate was identified as F. oxysporum. For the pathogenicity assay, six 6-month-old healthy plants of Mammillaria humboldtii were inoculated by dipping roots in a conidial suspension (106 conidia/mL) of isolate FJMH7 cultured in Bilai's medium for three days. Six noninoculated plants treated with Bilai's medium served as a control. Plants were transplanted into pots filled with sterilized soils and placed in a glasshouse at 25°C. After 15 days, all the inoculated plants exhibited rot symptoms on stems, which were similar to those observed in the commercial greenhouses. All inoculated plants were dead 30 days after inoculation. Control plants did not show any symptoms. F. oxysporum was reisolated and confirmed based on morphology and sequencing. No fungi were reisolated from control plants. To fulfil Koch's postulates, the pathogenicity assay was repeated twice with the same results. To date, F. oxysporum isolates have been reported on golden barrel cactus (Echinocactus grusonii) (Polizzi et al. 2004), night-blooming cereus (Hylocereus undatus) (Wright et al. 2007), apple cactus (Cereus peruvianus monstruosus) (Garibaldi et al. 2011), Schlumbergera truncate (Lops et al. 2013), Astrophytum ornatum (Quezada-Salinas et al. 2017) and Nopalea cochenillifera (Santiago et al. 2018). To our knowledge, this is the first report of F. oxysporum on M. humboldtii in China, indicating that this pathogen could cause wilt and rot disease on different cactus hosts.

Rhizosphere microorganisms of Crocus sativus as antagonists against pathogenic Fusarium oxysporum

INTRODUCTION

Several microorganisms in the plant root system, especially in the rhizosphere, have their own compositions and functions. Corm rot is the most severe disease of Crocus sativus, leading to more than 50% mortality in field production.

METHODS

In this study, metagenomic sequencing was used to analyze microbial composition and function in the rhizosphere of C. sativus for possible microbial antagonists against pathogenic Fusarium oxysporum.

RESULTS

The microbial diversity and composition were different in the C. sativus rhizosphere from different habitats. The diversity index (Simpson index) was significantly lower in the C. sativus rhizospheric soil from Chongming (Rs_CM) and degenerative C. sativus rhizospheric soil from Chongming (RsD_CM) than in others. Linear discriminant analysis effect size results showed that differences among habitats were mainly at the order (Burkholderiales, Micrococcales, and Hypocreales) and genus (Oidiodendron and Marssonina) levels. Correlation analysis of the relative lesion area of corm rot showed that Asanoa was the most negatively correlated bacterial genus (ρ = -0.7934, p< 0.001), whereas Moniliophthora was the most negatively correlated fungal genus (ρ = -0.7047, p< 0.001). The relative lesion area result showed that C. sativus from Qiaocheng had the highest resistance, followed by Xiuzhou and Jiande. C. sativus groups with high disease resistance had abundant pathogen resistance genes, such as chitinase and β-1,3-glucanase genes, from rhizosphere microorganisms. Further, 13 bacteria and 19 fungi were isolated from C. sativus rhizosphere soils, and antagonistic activity against pathogenic F. oxysporum was observed on potato dextrose agar medium. In vivo corm experiments confirmed that Trichoderma yunnanense SR38, Talaromyces sp. SR55, Burkholderia gladioli SR379, and Enterobacter sp. SR343 displayed biocontrol activity against corm rot disease, with biocontrol efficiency of 20.26%, 31.37%, 39.22%, and 14.38%, respectively.

DISCUSSION

This study uncovers the differences in the microbial community of rhizosphere soil of C. sativus with different corm rot disease resistance and reveals the role of four rhizospheric microorganisms in providing the host C. sativus with resistance against corm rot. The obtained biocontrol microorganisms can also be used for application research and field management.

Endophytic Beauveria bassiana Induces Oxidative Stress and Enhances the Growth of Fusarium oxysporum-Infected Tomato Plants

Studying the mechanisms through which endophytic fungi confer protection to host plants against parasites will contribute toward elucidating the endophytic fungi−plant−pathogen relationship. In this study, we evaluated the effects of endophytic Beauveria bassiana on the antioxidant activity, oxidative stress, and growth of tomatoes infected with the fusarium wilt pathogen, Fusarium oxysporum f. sp. lycopersici (FOL). Tomato seedlings were inoculated with B. bassiana conidia and then contaminated with FOL experimentally. Four treatments (Control [T1], FOL only [T2], B. bassiana only [T3], and B. bassiana and FOL [T4]) were assessed. The plants from the B. bassiana and FOL treatment (T4) were significantly taller (DF = 3, 56; p < 0.001) and produced more leaves and aerial part biomass than those treated with only FOL (T2). Remarkably, plants in the two treatments with FOL (T2 and T4) had the lowest antioxidant activities; meanwhile, plants from the FOL treatment (T2) had the lowest ROS (superoxide and hydroxyl radicals) contents. Broadly, strong positive correlations between ROS and all the plant growth parameters were recorded in this study. While the current results revealed that the endophytic entomopathogen B. bassiana enhanced antioxidant capacity in plants, it did not improve the antioxidant capacity of F. oxysporum-infected plants. It is possible that the pathogenic FOL employed a hiding strategy to evade the host immune response and the antagonistic actions of endophytic B. bassiana. In conclusion, B. bassiana inoculum enhanced the growth of tomatoes infected with FOL, induced higher oxidative stress in both F. oxysporum-infected and -uninfected tomatoes, and improved antioxidant activities in plants inoculated with B. bassiana only.

First report of Fusarium oxysporum causing stem spots on Polygonatum odoratum in China

Polygonatum odoratum (Mill.) Druce is a perennial herb in the Liliaceae family and it is one of the traditional Chinese medicinal plants. Modern pharmaceutical studies demonstrate that P. odoratum contains polysaccharides, saponins, alkaloids, flavonoids, volatile oil, and other active components (Jiang-Nan, et al., 2018). From May to June 2022, the stem spot disease was discovered on P. odoratum in the planting demonstration garden in Changsha (28°20N; 113°07E), Hunan province of China. The disease seriously retarded plant growth and was estimated to have affected approximately 40-50% of the plants, significant economic losses to growers. Plants had oval tan spots on the stems, which were light in the center and dark at the margin. The spots in the back expanded and joined together, where the disease was severe, and chlorosis was near the stem spot, while many leaves turned completely yellow and withered before falling to the ground. Finally, the whole plant faded to light green and dried up. In order to isolate pathogens, symptomatic stem samples (5×5 mm) were collected from the edges of the lesions and excised symptomatic tissues consisting of diseased and healthy parts were surface-sterilized with 2% solution of sodium hypochlorite (0.1% active ingredient of chlorine) for 1 min and 75% ethanol for 30 s. The samples were then washed thrice with sterile distilled water, air-dried on the sterile filter papers under aseptic conditions, and finally plated onto Potato Dextrose Agar (PDA) plates, which were incubated at 25 °C for 24 h to 36 h in the dark. Additionally, the emerging fungal hyphal tips were transferred to PDA and purified by the single-spore method. Next, forty plants with stem spots were isolated, and 8 cultures with the same appearance were obtained. Two strains coded hnxryzj and hnxryzj1 were randomly selected, for identification. With a mean radial growth rate of 7.5 mm/day, white and dense colonies were observed after 6 days of culture on PDA. After hnxryzj was cultured on SNA, microconidia were oval or ovate (9.25-14.8µm × 2.18-3.76µm), macroconidia were sickle-shaped and slightly curved, with 2-5 septa (21.52-23.49µm × 2.64-4.51µm (n = 50)). These morphological characteristics were consistent with the description of Fusarium oxysporum (Mirghasempour, et al., 2022) Furthermore, we amplified the partial region of the internal transcribed spacer (ITS) region, the translation elongation factors EF-1α, β-tubulin, polymerase II largest subunit (RPB1) and RNA polymerase II second largest subunit (RPB2) genes from strain hnxryzj and hnxryzj1, based on the primer pairs ITS1/ITS4, EF728F/EF986R, Bt2a/Bt2b, RPB1-F5/RPB1-R8 and fRPB2-5F2/fRPB2-7cR (Li, et al., 2013, Xie, et al., 2022), and amplicons were sequenced by Tsingke Biotechnology Co. Ltd. By sequence alignment, the ITS, EF-1α, β-tubulin , RPB1 and RPB2 of hnxryzj and hnxryzj1 were identical, respectively. The sequence alignment of hnxryzj and hnxryzj1 with the Fusarium ID database and NCBI shows the following results: the ITS region, EF-1α, RPB1 and RPB2 sequences of the strain hnxryzj (GenBank accession nos. ON872218, ON897740, OP467556 and OP467557) and hnxryzj1 (GenBank accession nos. OP071248, OP087208, OP467558 and OP467559) were 100% identical to those of F. oxysporum (GenBank accession nos. MZ890536, LC469784 , MT179509 and MW368380, respectively); whereas the β-tubulin sequences of the strain hnxryzj (GenBank accession nos. ON897741) and hnxryzj1 (GenBank accession nos. OP087207) were 96.9% identical to those of F.oxysporum (CBS144135 GenBank accession nos. MH485136). Subsequently, a phylogenetic tree was established combining EF-1α, RPB1, and RPB2. Strains hnxryzj and hnxryzj1 were F.oxysporum (JW257006 GenBank accession nos. MZ921883, MZ921657 and MZ921752)(Torres-Cruz, et al., 2022), with bootstrap values 100%. The pathogenicity test was carried out by placing mycelial discs obtained from colonies that had been actively growing on PDA for 6 days. In the pathogenicity test, two sets (5 plants in each set) of potted plants, whose stems were wounded, were taken. In one set (5 plants), the PDA cakes with F. oxysporum (d=5mm, the same below) were inoculated on the stems scratched by an inoculation needle (sterilized) (the front of the colony was close to the wound of the stem). In the other set (5 plants), potted plants inoculated with the sterile PDA cakes were served as controls. In a 25 °C greenhouse, each treatment was given a 12h/12h light/dark cycl(Nabi, et al., 2019). The symptoms were observed, and the fungus cake was removed 5 days after inoculation. Then, after 18 days, typical symptoms of oval tan spots similar to original diseased plants in the field were found on the inoculated stems, and 32 days later, the inoculated plant died, while the control stems remained asymptomatic. In addition, F. oxysporum was isolated and identified from the inoculated, symptomatic stems, verifying Koch's postulates. Based on our knowledge, this is the first report of F. oxysporum causing stem spots on P. odoratum in China. Only one other study from China that root rot of Phyllostachys officinalis also resulted from F. oxysporum (Pang, et al., 2022). Furthermore, P. odoratum is an medicinal material in Hunan province. Therefore, comprehensive prevention and control methods are required.

Fusarium oxysporum infection on root elicit aboveground terpene production and salicylic acid accumulation in Chrysanthemum morifolium

Underground infection of Fusarium oxysporum resulted in great yield losses in chrysanthemum (Chrysanthemum morifolium Ramat.) industry. However, the effect of F. oxysporum root disease on the terpenes production in above- and below-ground parts of plant is completely unexplored. The aim of this study was to investigate the systematic impact of Fusarium infection underground on the terpene production in aboveground parts of chrysanthemum. Terpene production in above- and below-ground parts was profiled in a time series of post-inoculation by GC-MS. Total terpenes were significantly induced from roots and leaves of Fusarium-infected versus healthy plants. These terpenes included monoterpenes, sesquiterpenes and diterpenes, in which sesquiterpenes were primarily induced in roots and leaves, while monoterpenes were produced only in leaves. Through transcriptome analysis, 8 differentially expressed terpene synthase genes (TPSs) were screened out. The relative expression levels of 8 TPS genes at different developmental stage and tissues indicated the spatial delay of the TPS genes in leaves. The induced terpenes from roots and leaves showed consistency with the expression pattern of TPS genes. The biochemical function of Cm-j-TPS1/2/7 were verified by enzymatic assay. Additionally, it's found that the content of salicylic acid (SA) in root and leaf significantly increased by F. oxysporum infection, suggesting a role of the SA signaling pathway in defense. Together, these results reveal the defense response of above- and below-ground parts of plants to root fungal attack and provide a theoretical basis for the effective prediction and control of F. oxysporum infection in chrysanthemum.

[Pathogenicity and induced systemic resistance of Fusarium oxysporum and Verticillium dahlia to Salvia miltiorrhiza]

Salvia miltiorrhiza is a commonly used bulk medicinal material in China. Due to the increasing demand in recent years, the planting area is expanding. In the artificial cultivation of S. miltiorrhiza, continuous cropping obstacles are prominent, which has seriously restrained the growth of S. miltiorrhiza, resulted in serious root diseases, and affected the yield and quality of medicinal materials. The pathogen infection can induce plant resistance. Previously, this research group isolated Fusarium oxysporum and Verticillium dahlia from the roots of diseased S. miltiorrhiza. In this study, 7 days after inoculation of S. miltiorrhiza with F. oxysporum(Foc group) and V. dahlia(Vd group), the incidence rates in S. miltiorrhiza were 48% and 26%, respectively. Both the two pathogens significantly reduced the aboveground biomass of S. miltiorrhiza. Five days after inoculation, the activities of defensive enzymes, such as peroxidase(POD), phenylalanine ammonia-lyase(PAL), superoxide dismutase(SOD), and polyphenol oxidase(PPO) reached the peak. The enzyme activity of the Foc group was significantly higher than that of the Vd group. Three days after inoculation, the expression of defense genes SmPDF2.1 and SmPR10 peaked and then decreased. The results showed that F. oxysporum and V. dahlia showed pathogenicity to S. miltiorrhiza and could strongly induce systemic resistance. In terms of the above indexes, F. oxysporum was superior to V. dahlia.

Antagonistic Effect of Plant Growth-Promoting Fungi Against Fusarium Wilt Disease in Tomato: In vitro and In vivo Study

Fusarium wilt is considered one of the most destructive diseases for tomato plants. The novelty of this work was to investigate the antifungal and plant growth-promoting capabilities of some plant growth-promoting fungi (PGPF). Plant growth-promoting fungi (PGPF) improved the plant health and control plant infections. In this study, two fungal strains as PGPF were isolated and identified as Aspergillus fumigatus and Rhizopus oryzae using molecular method. The extracts of A. fumigatus and R. oryzae exhibited promising antifungal activity against F. oxysporum in vitro. Moreover, antagonistic effect of A. fumigatus and R. oryzae against F. oxysporum causing tomato wilt disease was evaluated in vivo. Disease severity and growth markers were recorded and in vitro antagonistic activity assay of the isolated A. fumigatus and R. oryzae against Fusarium oxysporum was measured. Physiological markers of defense in plant as response to stimulate systemic resistance (SR) were recorded. Our results indicated that A. fumigatus and R. oryzae decreased the percentage of disease severity by 12.5 and 37.5%, respectively. In addition, they exhibited relatively high protection percentage of 86.35 and 59.06% respectively. Fusarium wilt was declined the growth parameters, photosynthetic pigments, total soluble carbohydrate, and total soluble protein, whereas content of free proline, total phenols, and the activity of antioxidant enzymes activity increased under infection. Moreover, application of A. fumigatus and R. oryzae on infected plants successfully recovered the loss of morphological traits, photosynthetic pigment total carbohydrates, and total soluble proteins in comparison to infected control plants. PGPF strains in both non-infected and infected plants showed several responses in number and density of peroxidase (POD) and polyphenol oxidase (PPO) isozymes.

Functional analysis of Rehmannia glutinosa key LRR-RLKs during interaction of root exudates with Fusarium oxysporum reveals the roles of immune proteins in formation of replant disease

Previous studies have indicated that some Rehmannia glutinosa Leucine-rich repeat receptor-like protein kinases (LRR-RLKs) are involved in the formation of replant disease. However, it remains unclear how the interaction of LRR-RLKs with a key factor, the interaction between root exudates and Fusarium oxysporum, results in formation of replant disease. In this study, the influences of root exudates, F. oxysporum and the interaction of these two factors on expression of nine R. glutinosa LRR-RLKs (RgLRRs) were analyzed. The resulting eight RgLRRs of them were highly expressed at the early stage, and rapidly declined at later stages under mixed treatment of root exudates and F. oxysporum. The functions of nine RgLRRs under root exudates, F. oxysporum and mixed treatment of root exudates and F. oxysporum were preliminarily analyzed using transient overexpression and RNAi experiments. The results showed that high expression of RgLRR19, RgLRR21, RgLRR23 and RgLRR29 could decrease the damage to root cells from the mixed treatment of root exudates and F. oxysporum, but the interference of these genes enhanced the damage levels of root cells. Based on this, stable transgenic R. glutinosa seedlings were acquired. Overexpression of RgLRR29 conferred resistance of R. glutinosa seedlings to root exudates, F. oxysporum and mixed treatment. These results indicated that the continuous proliferation of F. oxysporum supported by root exudates altered the expression patterns of RgLRRs in R. glutinosa, then disordered the growth and development of R. glutinosa, finally leading to the formation of replant disease.

Fusarium oxysporum effector clustering version 2: An updated pipeline to infer host range

The fungus Fusarium oxysporum is infamous for its devastating effects on economically important crops worldwide. F. oxysporum isolates are grouped into formae speciales based on their ability to cause disease on different hosts. Assigning F. oxysporum strains to formae speciales using non-experimental procedures has proven to be challenging due to their genetic heterogeneity and polyphyletic nature. However, genetically diverse isolates of the same forma specialis encode similar repertoires of effectors, proteins that are secreted by the fungus and contribute to the establishment of compatibility with the host. Based on this observation, we previously designed the F. oxysporum Effector Clustering (FoEC) pipeline which is able to classify F. oxysporum strains by forma specialis based on hierarchical clustering of the presence of predicted putative effector sequences, solely using genome assemblies as input. Here we present the updated FoEC2 pipeline which is more user friendly, customizable and, due to multithreading, has improved scalability. It is designed as a Snakemake pipeline and incorporates a new interactive visualization app. We showcase FoEC2 by clustering 537 publicly available F. oxysporum genomes and further analysis of putative effector families as multiple sequence alignments. We confirm classification of isolates into formae speciales and are able to further identify their subtypes. The pipeline is available on github: https://github.com/pvdam3/FoEC2.

Silicon enhances plant resistance to Fusarium wilt by promoting antioxidant potential and photosynthetic capacity in cucumber (Cucumis sativus L.)

Fusarium wilt, caused by Fusarium oxysporum f. sp. cucumerinum (Fo), is a severe soil-borne disease affecting cucumber production worldwide, particularly under monocropping in greenhouses. Silicon (Si) plays an important role in improving the resistance of crops to Fusarium wilt, but the underlying mechanism is largely unclear. Here, an in vitro study showed that 3 mmol·l^-1 Si had the best inhibitory effect on the mycelial growth of F. oxysporum in potato dextrose agar (PDA) culture for 7 days. Subsequently, the occurrence of cucumber wilt disease and its mechanisms were investigated upon treatments with exogenous silicon under soil culture. The plant height, stem diameter, root length, and root activity under Si+Fo treatment increased significantly by 39.53%, 94.87%, 74.32%, and 95.11% compared with Fo only. Importantly, the control efficiency of Si+Fo was 69.31% compared with that of Fo treatment. Compared with Fo, the activities of peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) significantly increased by 148.92%, 26.47%, and 58.54%, while the contents of H₂O₂, O 2 · - , and malondialdehyde (MDA) notably decreased by 21.67%, 59.67%, and 38.701%, respectively, in roots of cucumber plants treated with Si + Fo. Compared with Fo treatment, the net photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), maximum RuBisCO carboxylation rates (Vcmax), maximum RuBP regeneration rates (Jmax), and activities of ribulose-1,5-bisphosphate carboxylase (RuBisCO), fructose-1,6-bisphosphatase (FBPase), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and the expression of FBPA, TPI, SBPase, and FBPase in Si+Fo treatment increased significantly. Furthermore, Si alleviated stomatal closure and enhanced endogenous silicon content compared with only Fo inoculation. The study results suggest that exogenous silicon application improves cucumber resistance to Fusarium wilt by stimulating the antioxidant system, photosynthetic capacity, and stomatal movement in cucumber leaves. This study brings new insights into the potential of Si application in boosting cucumber resistance against Fusarium wilt with a bright prospect for Si use in cucumber production under greenhouse conditions.

First Report of Stem and Root Rot Caused by Fusarium oxysporum on Geranium in China

Geranium (Pelargonium hortorum) is a widely cultivated ornamental plant in the world. In August 2021, geranium plants exhibited stem and root rot symptoms in a garden in Tianjin, China (117°20'E, 39°13'N) with an approximate incidence of 10%. Symptoms were rotted stem and root, chlorotic leaves, wilting, discolored vascular tissues and eventually plant death. White mycelia were observed growing on the surface of the infected stems and roots in a high humidity environment. Symptomatic plants were collected from three nurseries (20 plants per nursery) in the Tianjin garden, out of which 10 plants were arbitrarily selected for pathogen isolation. The diseased stem and root were rinsed under tap water, blotted dry, and excised into 3 mm2 pieces (three pieces per plant) at the boundary of the symptomatic area. The pieces were surface disinfected with 75% ethanol for 30 s, washed with sterile distilled water for three times, and then placed on potato dextrose agar (PDA) containing 50 mg/L of streptomycin sulfate and incubated at 26℃ in the dark. After 6 days, 24 of 30 isolates generated white to pale pink aerial hyphae on PDA. Macroconidia were slightly curved at apex, hyaline and falcate, 3 to 5 septate, 19.2 to 41.08 μm in length and 2.95 to 5.62 μm in width (n = 30). Microconidia were single-celled, hyaline, non-septate and ovoid, and measured 4.98 to 16.48 μm in length and 1.58 to 4.69 μm in width (n = 30). These characteristics matched the description of Fusarium oxysporum (Leslie and Summerell 2006). The ITS gene, TEF1-α gene, mtSSU gene and RPB2 gene of representative isolates (T7, T8 and T9) were amplified and sequenced for species identification (Carbone and Kohn 1999; Li et al. 1994; Miller and Huhndorf 2005). BLASTn analyses of the ITS amplicon (OK326801, OK326789 and OK326823), TEF1-α amplicon (OM974708, OM974710 and OM974711), mtSSU amplicon (OK330481, OM948931 and OM948932) and RPB2 amplicon (OM974709, OM974712 and OP331332) obtained with cognate sequences available in GenBank showed 99.31% to 100% identity to sequences of F. oxysporum in the NCBI database and the Fusarium MLST database. The multilocus phylogenetic analysis from the Fusarium MLST database performed by UPGMA showed that the representative isolates were assigned to the group of F. oxysporum. Ten two-month-old healthy plants of geranium (cv. Horizon Scarle) were inoculated by dipping the roots into a conidial suspension of 1×107 conidia/mL for 10 min (Monther et al. 2021). Another ten plants dipped in sterile distilled water served as controls. After inoculated or noinoculated treatments, plants were planted in sterilized nutrient soil in plastic pots (one plant per pot). Each treatment was repeated three times in a greenhouse at 28℃ and 75% relative humidity. Two weeks later, inoculated plants exhibited similar symptoms to those of diseased plants in the garden. Whereas the control plants remained healthy. To fulfill the Koch's postulates, F. oxysporum was reisolated from each inoculated, symptomatic plant, but was not recovered from any of the control plants. The experiments were repeated twice with similar results. F. oxysporum is reported to cause disease on Pelargonium graveolens in Kenya (Nattrass 1961) and on Pelargonium sp. in California (French 1989), to our knowledge, this is the first report of F. oxysporum causing stem and root rot on Pelargonium hortorum in China. Identification of disease caused by F. oxysporum on geranium will guide disease management.

spinaciae

Two pathogenicity groups of Fusarium oxysporum f. sp. spinaciae, the causal agent of Fusarium wilt of spinach (Spinacia oleracea), were described recently based on virulence of isolates on proprietary spinach inbreds. In this study, a wide range in severity of wilt was observed for 68 spinach cultivars inoculated with an isolate of each pathogenicity group, with 22 (32.4%) cultivars displaying differential responses to the isolates. In a second set of trials, seven spinach cultivars were inoculated with five isolates of each pathogenicity group. The cultivars had similar wilt responses to isolates within each group. In both sets of trials, the most severe wilt developed on cultivars inoculated with pathogenicity group 2 isolates when daylength was shorter and light intensity lower. To test whether light intensity exacerbates severity of Fusarium wilt, three spinach cultivars were inoculated with two isolates of each pathogenicity group and grown with or without shading. Shaded plants developed more severe wilt than nonshaded plants. This difference in wilt severity was greatest for plants inoculated with pathogenicity group 2 isolates. We propose naming isolates of pathogenicity groups 1 and 2 as races 1 and 2 of F. oxysporum f. sp. spinaciae, respectively, and recommend the cultivars Kiowa (susceptible to both races) and Magnetic (susceptible to race 2 and highly resistant to race 1) as differentials. Results of this study should help breeders screen spinach germplasm for resistance to both races of F. oxysporum f. sp. spinaciae.

Response of the plant core microbiome to Fusarium oxysporum infection and identification of the pathobiome

Plant core microbiomes consist of persistent key members that provide critical host functions, but their assemblages can be interrupted by biotic and abiotic stresses. The pathobiome is comprised of dynamic microbial interactions in response to disease status of the host. Hence, identifying variation in the core microbiome and pathobiome can significantly advance our understanding of microbial-microbial interactions and consequences for disease progression and host functions. In this study, we combined glasshouse and field studies to analyse the soil and plant rhizosphere microbiome of cotton plants (Gossypium hirsutum) in the presence of a cotton-specific fungal pathogen, Fusarium oxysporum f. sp. vasinfectum (FOV). We found that FOV directly and consistently altered the rhizosphere microbiome, but the biocontrol agents enabled microbial assemblages to resist pathogenic stress. Using co-occurrence network analysis of the core microbiome, we identified the pathobiome comprised of the pathogen and key associate phylotypes in the cotton microbiome. Isolation and application of some negatively correlated pathobiome members provided protection against plant infection. Importantly, our field survey from multiple cotton fields validated the pattern and responses of core microbiomes under FOV infection. This study advances key understanding of core microbiome responses and existence of plant pathobiomes, which provides a novel framework to better manage plant diseases in agriculture and natural settings. This article is protected by copyright. All rights reserved.

Bioethanol production from Ficus fruits (Ficus cunia) by Fusarium oxysporum through consolidated bioprocessing system

Fusarium oxysporum is among the few filamentous fungi capable of fermenting ethanol directly from lignocellulose biomass (LCB). It has the essential enzymatic toolbox to disintegrate LCB to its monosaccharides, which subsequently fermented to ethanol under anaerobic and micro-aerobic conditions. However, the structural complexity of LCB and modest performances of wild fungi are major limitations for application in local biorefineries. This study assessed the potential of the locally isolated Fusarium oxysporum for the production of bioethanol from Ficus fruits (Ficus cunia) using Consolidated Bioprocessing (CBP). The maximum ethanol concentration achieved was at 5% substrate loadings with pH 6 irrespective of temperature variance, attaining a concentration of 3.54 g/L and 3.88 g/L at 28 °C and 32 °C, respectively. The monitoring of analytes (glucose, arabinose, cellobiose, xylose, acetic acid, ethanol, furfural, and HMF) in this study suggests the utilization of an array of sugars released from Ficus fruits, irrespective of the difference in the process parameters. This study also shows that CBP of freshly grounded Ficus fruits was feasible employing a mild hydrothermal pretreatment (autoclaved at 121 °C for 30 min in 1:10 w/v) and without supplementing any extraneous enzymes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03234-y.

Meta-analysis of fungal plant pathogen Fusarium oxysporum infection-related gene profiles using transcriptome datasets

Fusarium oxysporum is a serious soil-borne fungal pathogen that affects the production of many economically important crops worldwide. Recent reports suggest that this fungus is becoming the dominant species in soil and could become the main infectious fungus in the future. However, the infection mechanisms employed by F. oxysporum are poorly understood. In the present study, using a network meta-analysis technique and public transcriptome datasets for different F. oxysporum and plant interactions, we aimed to explore the common molecular infection strategy used by this fungus and to identify vital genes involved in this process. Principle component analysis showed that all the fungal culture samples from different datasets were clustered together, and were clearly separated from the infection samples, suggesting the feasibility of an integrated analysis of heterogeneous datasets. A total of 335 common differentially expressed genes (DEGs) were identified among these samples, of which 262 were upregulated and 73 were downregulated significantly across the datasets. The most enriched functional categories of the common DEGs were carbohydrate metabolism, amino acid metabolism, and lipid metabolism. Nine co-expression modules were identified, and two modules, the turquoise module and the blue module, correlated positively and negatively with all the infection processes, respectively. Co-expression networks were constructed for these two modules and hub genes were identified and validated. Our results comprise a cross fungal-host interaction resource, highlighting the use of a network biology approach to gain molecular insights.

NMR Metabolomics and Chemometrics of Lettuce, Lactuca sativa L., under Different Foliar Organic Fertilization Treatments

Lettuce plants were grown in a greenhouse affected by the fungal pathogen Fusarium oxysporum to test the effects on plant metabolomics by different organic treatments. Three foliar application treatments were applied: a commercial compost tea made of aerobically fermented plant organic matter, a pure lyophilized microalga Artrospira platensis, commonly named spirulina, and the same microalga previously exposed during its culture to a natural uptake from medium enriched with F. oxysporum fragmented DNA (NAT). The experiment is the first attempt to observe in field conditions, the use and effects of a natural microbial library as a carrier of pathogenic fungal DNA for disease control. Untargeted NMR metabolomics and chemometrics showed that foliar organic application significantly reduced fumaric and formic acids, aromatic amino acids, and nucleosides, while increasing ethanolamine. A strong decrease in phenolic acids and an increase in citric acid and glutamine were specifically observed in the NAT treatment. It is noteworthy that the exposure of a known biostimulant microalga to fungal DNA in its culture medium was sufficient to induce detectable changes in the metabolomic profiles of the fertilized plants. These findings deserve further investigation to assess the potential relevance of the presented approach in the field of crop biostimulation and biocontrol of plant pathogens.

Comparative transcriptome analysis reveals that ATP synthases regulate Fusarium oxysporum virulence by modulating sugar transporter gene expressions in tobacco

Fusarium oxysporum is a main causative agent of tobacco root rot, severely affecting tobacco growth. Here, 200 F. oxysporum strains were isolated and examined for their virulence toward tobacco plants. These strains were divided into disease class 1-3 (weak virulence), 4-6 (moderate virulence), and 7-9 (strong virulence). To understand the virulence mechanism of F. oxysporum, a comparative transcriptome study was performed using weak, moderate, and strong virulence-inducing strains. The results showed that expression levels of 1,678 tobacco genes were positively correlated with virulence levels, while expression levels of 3,558 genes were negatively associated with virulence levels. Interestingly, the expression levels of ATP synthase genes were positively correlated with F. oxysporum virulence. To verify whether ATP synthase gene expression is associated with F. oxysporum virulence, 5 strains each of strong, moderate, and weak virulence-inducing strains were tested using qRT-PCR. The results confirmed that ATP synthase gene expression is positively correlated with virulence levels. Knock-out mutants of ATP synthase genes resulted in a relatively weak virulence compared to wild-type as well as the inhibition of F. oxysporum-mediated suppression of NtSUC4, NtSTP12, NtHEX6, and NtSWEET, suggesting that ATP synthase activity is also associated with the virulence. Taken together, our analyses show that ATP synthases are key genes for the regulation of F. oxysporum virulence and provide important information for understanding the virulence mechanism of F. oxysporum in tobacco root rot.

in Jordan

Strawberries (Fragaria ananassa Duch.) are grown in Jordan year round due to the diversity of climatic conditions and the possibility of growing local or foreign varieties. More than six thousand greenhouses are planted with strawberries in the highlands and the Jordan Valley. About 12 thousand tons of strawberry are produced annually and 2000 tons are exported to European and Arab countries. In April and May 2019, symptoms of wiltand whole plant collapse were observed on approximately 30% of commercial strawberry cv. Deli gent crop in the Jordan Valley (Dayr Alla long.35.6188766, lat. 32.227465). Plants were either dead or showing symptoms including vascular wilt, external and internal discoloration of the stems, and dead shoots. Forty symptomatic plants were collected from 10 greenhouses, and stem fragments were surface sterilized and plated on potato dextrose agar (PDA). Six fungal isolates showed morphological characteristic of Fusarium oxysporum. Colonies on PDA were purple-violet, floccose, with abundant aerial mycelium; colony margins were irregular. Macroconidia were falcate, apical cells had a blunt or papillate shape, basal cells were foot shaped, three- to five-septate, hyaline, smooth, thin-walled, and 37 - 42 × 3 - 6.0 μm in diameter. Aerial microconidia were abundant, hyaline, ellipsoidal, zero to one-septate: 5 - 11 × 2 - 4.0 μm. Chlamydospores were globose to subglobose, intercalary or terminal, with an average diameter of 12 μm (Figure 1: A, B and C) (Nelson et al, 1983; Leslie and Summerell, 2006). Four representative isolates (FoSB2021JO-02, FoSB2021JO-06, FoSB2021JO-08 and FoSB2021JO-09) were DNA extracted, amplified with the translation elongation factor 1-α (EF1α) gene (EF1/EF2) primers (Geiser et al., 2004), and sequenced at Macrogen Inc, South Korea. Forward and reverse sequences were received, assembled and consensus sequence were produced using the BioEdit sequence alignment editor. Consensus sequences of the four isolates were used to conduct BLASTn queries of NCBI website (https://www.ncbi.nlm.nih.gov) and were 100%, 99.9%, 99.6%, 99.9% identical to F. oxysporum accessions MN417194.1, MK968948.1,MK968948.1, and MK968952.1, respectively. A phylogenetic tree with 1000 bootstraps was created using MEGA 7 software (Kumar et al. 2016) (Figure 2). Similarly, the four isolates were 99.5%, 100%, 100%, and 100% identical F. oxysporum reference accessions AF008507, FJ985275, FJ985275, and FJ985278 in the Fusarium MLST database, respectively. Consensus sequences of the four isolates were submitted to GenBank and accession numbers were assigned (OK040155 - OK040158). For pathogenicity tests on strawberries, a spore suspension of 1 × 105 conidia/ml was prepared separately for six isolates. Roots of identical 2-month-old healthy strawberry seedlings (15 plants of cv. Deli-gent) were cut and dipped in the spore suspensions for 30 min. They were then planted in 25 x 20 cm deep plastic pots filled with a sterile mixture of peat - moss, perlite, and vermiculite (60:20:20v/v). Control strawberry plants were soaked in water prior to planting. All plants were placed in a greenhouse at 25°C ±2 along with 15 uninoculated control plants. After 30 days, inoculated plants displayed similar symptoms to those observed in the green house, whereas control plants were symptomless. Roots from symptomatic plants were cultured on PDA and F. oxysporum was recovered and identified morphologically as F. oxysporum. To our knowledge, this is the first report of Fusarium wilt of strawberry in Jordan. The pathogen can cause significant economic losses to strawberries in Jordan and worldwide. Therefore, it is extremely important for disease control in nurseries to determine the infection source and possible factors that increase the incidence of infection to control the disease.

The primary function of Six5 of Fusarium oxysporum is to facilitate Avr2 activity by together manipulating the size exclusion limit of plasmodesmata

Pathogens produce effector proteins to manipulate their hosts. While most effectors act autonomously, some fungal effectors act in pairs and rely on each other for function. During the colonization of the plant vasculature, the root-infecting fungus Fusarium oxysporum (Fo) produces 14 so-called Secreted in Xylem (SIX) effectors. Two of these effector genes, Avr2 (Six3) and Six5, form a gene pair on the pathogenicity chromosome of the tomato-infecting Fo strain. Avr2 has been shown to suppress plant defense responses and is required for full pathogenicity. Although Six5 and Avr2 together manipulate the size exclusion limit of plasmodesmata to facilitate cell-to-cell movement of Avr2, it is unclear whether Six5 has additional functions as well. To investigate the role of Six5, we generated transgenic Arabidopsis lines expressing Six5. Notably, increased susceptibility during the early stages of infection was observed in these Six5 lines, but only to Fo strains expressing Avr2 and not to wild-type Arabidopsis-infecting Fo strains lacking this effector gene. Furthermore, neither PAMP-triggered defense responses, such as ROS accumulation and callose deposition upon treatment with Flg22, necrosis and ethylene-inducing peptide 1-like protein (NLP), or chitosan, nor susceptibility to other plant pathogens, such as the bacterium Pseudomonas syringae or the fungus Verticilium dahlia, were affected by Six5 expression. Further investigation of the ability of the Avr2/Six5 effector pair to manipulate plasmodesmata (PD) revealed that it not only permits cell-to-cell movement of Avr2, but also facilitates the movement of two additional effectors, Six6 and Six8. Moreover, although Avr2/Six5 expands the size exclusion limit of plasmodesmata (i.e., gating) to permit the movement of a 2xFP fusion protein (53 kDa), a larger variant, 3xFP protein (80 kDa), did not move to the neighboring cells. The PD manipulation mechanism employed by Avr2/Six5 did not involve alteration of callose homeostasis in these structures. In conclusion, the primary function of Six5 appears to function together with Avr2 to increase the size exclusion limit of plasmodesmata by an unknown mechanism to facilitate cell-to-cell movement of Fo effectors.

Plant Growth-Promoting Fungi as Biocontrol Tool against Fusarium Wilt Disease of Tomato Plant

Plant growth-promoting fungi (PGPF) improve plant health and resist plant pathogens. The present study was carried out to biocontrol tomato Fusarium wilt using PGPF through antifungal activity and enhance tomato plant immune response. Four PGPF were identified genetically as Aspergillus flavus, Aspergillus niger, Mucor circinelloides and Pencillium oxalicum. In vitro antagonistic activity assay of PGPF against Fusariumoxysporum was evaluated, where it exhibited promising antifungal activity where MIC was in the range 0.25–0.5 mg/mL. Physiological markers of defense in a plant as a response to stimulation of induced systemic resistance (ISR) were recorded. Our results revealed that A. niger, M. circinelloides, A. flavus and P. oxalicum strains significantly reduced percentages of disease severity by 16.60% and 20.83% and 37.50% and 45.83 %, respectively. In addition, they exhibited relatively high protection percentages of 86.35%, 76.87%, 56.87% and 59.06 %, respectively. With concern to the control, it is evident that the percentage of disease severity was about 87.50%. Moreover, the application of M. circinelloides, P. oxalicum, A. niger and A. flavus successfully recovered the damage to morphological traits, photosynthetic pigments’ total carbohydrate and total soluble protein of infected plants. Moreover, the application of tested PGPF enhanced the growth of healthy and infected tomato plants.

First report of Fusarium oxysporum and Fusarium solani causing root rot on trifoliate orange rootstock in China

Trifoliate orange (Poncirus trifoliata L) is a thorny tree of the Rue family, which is extensively used as citrus rootstock in China. In January 2021, several leaf yellowing, declining, and wilting citrus seedlings grafted on trifoliate orange rootstock with rotted main roots were observed in orchards located in Wuhan city, Hubei, China. In old orchards, the incidence of diseased roots was approximately 90%. Diseased roots from seven plants were collected and cut into small pieces (0.2 to 0.5 cm). These pieces were then surface-sterilized using 0.1% mercury bichloride for 3 min, 75% ethanol for 3 min, rinsed with sterile distilled water for several times, and then placed on potato dextrose agar (PDA) supplemented with 0.05% lactic acid (v/v), and incubated at at 25±2°C in dark. Fifty-threesingle-conidium isolates with morphological characteristics similar to Fusarium spp. were obtained (Leslie and Summerell 2006), which displayed two kinds of colony morphology. Thirty isolates showed white to orange-white abundant aerial mycelium in rings and acquired a yellow to orange pigmentation, tweenty-three isolates showed white to pink, fluffy aerial mycelium in rings and acquired an orange to red pigmentation. Isolate WG-1 and HrmY-9 from each group were used for future identification. The average colony growth rate of WG-1 and HrmY-9 on PDA was 0.95±0.06 and 0.69±0.11 mm/day, n=4, respectively. WG-1 produced numerous oval, unicellular microconidia without septa, 4.03-9.87×1.01-5.13 µm, n=80 and very few macroconidia with two to four septa, narrowed at both ends, 11.08-22.64×1.67-4.91 µm, n=30. HrmY-9 produced numerous curved macroconidia with three to four septa, 18.03-37.33×2.16-7.8 µm, n=80, microconidia were unicellular, oval, and 5.33-16.19×1.74-6.51 µm, n=50. Sequences of internal transcribed spacer (ITS), translation elongation factor 1-alpha (EF-1α), and DNA-directed RNA polymerase largest subunit (RPB1) genes were amplified with the primers ITS1/ITS4, EF1a-F/EF1a-R, and RPB1-F5/RPB1-R8, respectively (White et al. 1990, O'Donnell et al. 1998, O'Donnell et al. 2010), sequenced and deposited in GenBank. Sequences of isolate WG-1 (GenBank accession No. ON045437, ON063232 and ON089664) and HrmY-9 (GenBank accession No. ON045438, ON063233 and ON089665) were 100% identical with the corresponding sequences of Fusarium oxysporum (OM876904, JF430180, and MT568959) and F. solani (MT605584, MK617767, and MT305110), respectively. Based on above results, WG-1 and HrmY-9 was identified as F. oxysporum and F. solani, respectively. Pathogenicity test were performed on healthy one-year-old trifoliate orange seedlings by dipping their injured roots into conidial suspension (50 ml, 1×106 conidia/mL) for 1 h and the rest of conidial suspension was added to the pot after replanting to make sure the inoculum was in contact with the roots. Roots of control plants were inoculated with sterilized water. All experiments were repeated twice. All plants were cultured at 26°C under a 16-h light/dark cycle. Typical symptoms developed on most of inoculated seedlings two months post inoculation. No disease symptoms appeared on control plants. Same colonies were reisolated from the inoculated roots, confirming Koch's postulates. To our knowledge, this is the first report of F. oxysporum and F. solani causing root rot on trifoliate orange rootstock in China. The identification of F. oxysporum and F. solani as the causal agents of the observed root rot on trifoliate orange rootstock is critical to the prevention and control of this disease in the future.

Preliminary Studies on Detection of Fusarium Basal Rot Infection in Onions and Shallots Using Electronic Nose

The evaluation of crop health status and early disease detection are critical for implementing a fast response to a pathogen attack, managing crop infection, and minimizing the risk of disease spreading. Fusarium oxysporum f. sp. cepae, which causes fusarium basal rot disease, is considered one of the most harmful pathogens of onion and accounts for considerable crop losses annually. In this work, the capability of the PEN 3 electronic nose system to detect onion and shallot bulbs infected with F. oxysporum f. sp. cepae, to track the progression of fungal infection, and to discriminate between the varying proportions of infected onion bulbs was evaluated. To the best of our knowledge, this is a first report on successful application of an electronic nose to detect fungal infections in post-harvest onion and shallot bulbs. Sensor array responses combined with PCA provided a clear discrimination between non-infected and infected onion and shallot bulbs as well as differentiation between samples with varying proportions of infected bulbs. Classification models based on LDA, SVM, and k-NN algorithms successfully differentiate among various rates of infected bulbs in the samples with accuracy up to 96.9%. Therefore, the electronic nose was proved to be a potentially useful tool for rapid, non-destructive monitoring of the post-harvest crops.

radicis-cucumerinum

Phytopathogenic strains of Fusarium oxysporum Schlecht exhibit clear host specificity, which appears to be a persistent characteristic and a dependable base for the forma specialis system of these pathogens. Here, we report an altered host specificity of the F. oxysporum f.sp. radicis-cucumerinum strain V03-2 g (Forc V03-2 g) - a causative agent of cucumber root-rot, the clonal derivates of which acquired the ability to infect tomato plants. Since the clonal derivates of Forc V03-2 g with transformed host specificity preserved their ability to parasitize on cucumber plants, the changes that occurred can be classified as broadening of host specificity. To our knowledge, this is the first observation of pathogenicity changes in formae speciales of F. oxysporum. The clonal derivates acquired could be used to trace genetic determinants of the host specificity of phytopathogenic strains of F. oxysporum.

Protein kinase Ime2 is associated with mycelial growth, conidiation, osmoregulation, and pathogenicity in Fusarium oxysporum

Fusarium oxysporum f.sp. niveum is one of the most serious diseases impairing watermelon yield and quality. Inducer of meiosis 2 (Ime2) is the founding member of a family of serine/threonine protein kinases and plays important roles in yeasts and other filamentous fungi. In this study, we analyzed the functions of FoIme2, the ortholog of Saccharomyces cerevisiae Ime2 in F. oxysporum f.sp. niveum. The FoIme2-deleted mutants exhibited obvious morphological abnormalities, including slower vegetative growth, more branches in the edge hyphae and a reduction in conidia production. Compared to the wild type, the mutants were hypersensitive to the osmotic stressor NaCl but were more insensitive to the membrane stressor SDS. The deletion of FoIme2 also caused a reduction in pathogenicity. Transcriptional analysis revealed that FoIme2 acts downstream of FoOpy2 which is an upstream sensor of the MAPK kinase cascade. These results indicate that FoIme2 is important in the development and pathogenicity of F. oxysporum, and provide new insight for the analysis of the pathogenic mechanism of F. oxysporum.

Gene Regulatory Network Inference and Gene Module Regulating Virulence in Fusarium oxysporum

In this work, we inferred the gene regulatory network (GRN) of the fungus Fusarium oxysporum by using the regulatory networks of Aspergillus nidulans FGSC A4, Neurospora crassa OR74A, Saccharomyces cerevisiae S288c, and Fusarium graminearum PH-1 as templates for sequence comparisons. Topological properties to infer the role of transcription factors (TFs) and to identify functional modules were calculated in the GRN. From these analyzes, five TFs were identified as hubs, including FOXG_04688 and FOXG_05432, which regulate 2,404 and 1,864 target genes, respectively. In addition, 16 communities were identified in the GRN, where the largest contains 1,923 genes and the smallest contains 227 genes. Finally, the genes associated with virulence were extracted from the GRN and exhaustively analyzed, and we identified a giant module with ten TFs and 273 target genes, where the most highly connected node corresponds to the transcription factor FOXG_05265, homologous to the putative bZip transcription factor CPTF1 of Claviceps purpurea, which is involved in ergotism disease that affects cereal crops and grasses. The results described in this work can be used for the study of gene regulation in this organism and open the possibility to explore putative genes associated with virulence against their host.

Antagonistic Effect of Plant Growth-Promoting Fungi Against Fusarium Wilt Disease in Tomato: In vitro and In vivo Study

Fusarium wilt is considered one of the most destructive diseases for tomato plants. The novelty of this work was to investigate the antifungal and plant growth-promoting capabilities of some plant growth-promoting fungi (PGPF). Plant growth-promoting fungi (PGPF) improved the plant health and control plant infections. In this study, two fungal strains as PGPF were isolated and identified as Aspergillus fumigatus and Rhizopus oryzae using molecular method. The extracts of A. fumigatus and R. oryzae exhibited promising antifungal activity against F. oxysporum in vitro. Moreover, antagonistic effect of A. fumigatus and R. oryzae against F. oxysporum causing tomato wilt disease was evaluated in vivo. Disease severity and growth markers were recorded and in vitro antagonistic activity assay of the isolated A. fumigatus and R. oryzae against Fusarium oxysporum was measured. Physiological markers of defense in plant as response to stimulate systemic resistance (SR) were recorded. Our results indicated that A. fumigatus and R. oryzae decreased the percentage of disease severity by 12.5 and 37.5%, respectively. In addition, they exhibited relatively high protection percentage of 86.35 and 59.06% respectively. Fusarium wilt was declined the growth parameters, photosynthetic pigments, total soluble carbohydrate, and total soluble protein, whereas content of free proline, total phenols, and the activity of antioxidant enzymes activity increased under infection. Moreover, application of A. fumigatus and R. oryzae on infected plants successfully recovered the loss of morphological traits, photosynthetic pigment total carbohydrates, and total soluble proteins in comparison to infected control plants. PGPF strains in both non-infected and infected plants showed several responses in number and density of peroxidase (POD) and polyphenol oxidase (PPO) isozymes.

Streptomyces albidoflavus Strain CARA17 as a Biocontrol Agent against Fungal Soil-Borne Pathogens of Fennel Plants

Fennel crop is a horticultural plant susceptible to several soil-borne fungal pathogens responsible for yield losses. The control of fungal diseases occurring on fennel crops is very difficult with conventional and/or integrated means; although several chemical fungicides are able to contain specific fungal diseases, they are not registered for fennel crops. The intensive use of some fungicides causes public concern over the environment and human health. The main aims of this study were to assess the ability of a strain of Streptomyces albidoflavus CARA17 to inhibit the growth of fungal soil-borne pathogens, and to protect fennel plants against severe fungal soil-borne pathogens such as Athelia rolfsii, Fusarium oxysporum, Plectosphaerella ramiseptata, Sclerotinia sclerotiorum and Verticillium dahliae. This study confirmed that the CARA17 strain has been able to inhibit the mycelium growth of pathogens in vitro conditions with significant inhibition degrees, where S. sclerotiorum resulted in being the most controlled. The strain CARA17 was also able to significantly protect the fennel seedlings against fungal soil-borne pathogens used in vivo conditions, where the treatment with an antagonist strain by dipping resulted in being more effective at limiting the disease severity of each fungal soil-borne pathogen. Moreover, any treatment with the CARA17 strain, carried out by dipping or after transplanting, produced benefits for the biomass of fennel seedlings, showing significant effects as a promoter of plant growth. Finally, the results obtained showed that CARA17 is a valid strain as a biocontrol agent (BCA) against relevant fungal soil-borne pathogens, although further studies are recommended to confirm these preliminary results. Finally, this study allowed for first time worldwide the association of Plectosphaerella ramiseptata with fennel plants as a severe pathogen.

Time-related multivariate strategy for the comprehensive evaluation of microbial chemical data

INTRODUCTION

In microbial metabolomics, the use of multivariate data analysis (MDVA) has not been comprehensively explored regarding the different techniques available and the information that each gives about the metabolome. To overcome these limitations, here we show the use of Fusarium oxysporum cultured in the presence of exogenous alkaloids as a model system to demonstrate a comprehensive strategy for metabolic profiling.

MATHERIALS AND METHODS

F. oxysporum was harvested on different days of incubation after alkaloidal addition, and the chemical profiles were compared using LC-MS data and MDVA. We show significant innovation to evaluate the chemical production of microbes during their life cycle by utilizing the full capabilities of Partial Least Square (PLS) with microbial-specific modeling that considers incubation days, media culture availability, and growth rate in solid media.

RESULTS AND DISCUSSCION

Results showed that the treatment of the Y-data and the use of both PLS regression and discrimination (PLSr and PLS-DA) inferred complemental chemical information. PLSr revealed the metabolites that are produced/consumed during fungal growth, whereas PLS-DA focused on metabolites that are only consumed/produced at a specific period. Both regression and classificatory analysis were equally important to identify compounds that are regulated and/or selectively produced as a response to the presence of the alkaloids. Lastly, we report the annotation of analogs from the piperidine alkaloids biotransformed by F. oxysporum as a defense response to the toxic plant metabolites. These molecules do not show the antimicrobial potential of their precursors in the fungal extracts and were rapidly produced and consumed within 4 days of microbial growth.

MdBAK1 overexpression in apple enhanced resistance to replant disease as well as to the causative pathogen Fusarium oxysporum

Apple replant disease (ARD) is a complex syndrome caused by various biotic and abiotic stresses contained in replanted soil, leading to reduced plant growth and fruit yields and causing serious economic loss. Breeding disease-resistant varieties is an effective and practical method to control ARD. Effective plant defense depends in part on the plant immune responses induced by the recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs). BAK1 participates in the regulation of plant immunity as an important PRR-binding protein. In this study, MdBAK1 overexpression activated indeterminate immune responses in tissue-cultured apple plants. MdBAK1-overexpressing rooted apple plants exhibited enhanced resistance to ARD, as the inhibition of plant growth was significantly alleviated during the replanted soil treatment. In addition, MdBAK1-overexpressing apple plants showed abolished growth inhibition, wilting and root rot induced by Fusarium oxysporum, which is the main pathogen that causes ARD in China. MdBAK1 overexpression changed the microbial community structure in the rhizosphere soil, as reflected by the increase in bacterial content and the decrease in fungal content, and the root exudates of MdBAK1-overexpressing plants inhibited F. oxysporum spore germination compared with that of wild-type plants. Furthermore, the constitutive immunity and cell necrosis induced by the upregulation of MdBAK1 expression were involved in the inhibition of colonization and expansion of F. oxysporum in host plants. In short, MdBAK1 plays an important role in the regulation of apple resistance to ARD, suggesting that MdBAK1 may be a valuable gene for molecular breeding of ARD resistance.

cubense (Foc4)

Fusarium wilt of banana (Musa spp.), a typical vascular wilt disease caused by the soil-borne fungus, Fusarium oxysporum f. sp. cubense race 4 (Foc4), seriously threatens banana production worldwide. Pathogens, including vascular wilt fungi, secrete small cysteine-rich proteins during colonization. Some of these proteins are required for pathogenicity. In this study, 106 small secretory proteins that contain a classic N-terminal signal peptide were identified using bioinformatic methods in Foc4. Among them, 11 proteins were selected to show transient expressions in tobacco. Interestingly, transient expression of FoSsp1 in tobacco, an uncharacterized protein (of 145 aa), induced necrotic cell death reactive oxygen burst, and callous deposition. Furthermore, the expression of FoSSP1 in Foc4 wild type (WT) was up-regulated during the stage of banana roots colonization. A split-marker approach was used to knock out FoSSP1 in the Foc4 WT strain. Compared with the WT, the deletion mutant Fossp1 was normal in growth rate but increased in conidiation and virulence. RT-qPCR analysis showed that the expression of four conidiation regulator genes in the Fossp1 deletion mutant was significantly decreased compared to the WT strain. In addition, the expression of four pathogenesis-related genes of bananas infected with Fossp1 deletion mutant was down-regulated in comparison with that of the WT. In summary, these results suggested that FoSSP1 is a putative elicitor that negatively regulates conidiation and pathogenicity in Foc4.

Biogenic Silver Nanoparticles Strategically Combined With Origanum vulgare Derivatives: Antibacterial Mechanism of Action and Effect on Multidrug-Resistant Strains

Multidrug-resistant bacteria have become a public health problem worldwide, reducing treatment options against several pathogens. If we do not act against this problem, it is estimated that by 2050 superbugs will kill more people than the current COVID-19 pandemic. Among solutions to combat antibacterial resistance, there is increasing demand for new antimicrobials. The antibacterial activity of binary combinations containing bioAgNP (biogenically synthesized silver nanoparticles using Fusarium oxysporum), oregano essential oil (OEO), carvacrol (Car), and thymol (Thy) was evaluated: OEO plus bioAgNP, Car plus bioAgNP, Thy plus bioAgNP, and Car plus Thy. This study shows that the mechanism of action of Thy, bioAgNP, and Thy plus bioAgNP involves damaging the membrane and cell wall (surface blebbing and disruption seen with an electron microscope), causing cytoplasmic molecule leakage (ATP, DNA, RNA, and total proteins) and oxidative stress by enhancing intracellular reactive oxygen species and lipid peroxidation; a similar mechanism happens for OEO and Car, except for oxidative stress. The combination containing bioAgNP and oregano derivatives, especially thymol, shows strategic antibacterial mechanism; thymol disturbs the selective permeability of the cell membrane and consequently facilitates access of the nanoparticles to bacterial cytoplasm. BioAgNP-treated Escherichia coli developed resistance to nanosilver after 12 days of daily exposition. The combination of Thy and bioAgNP prevented the emergence of resistance to both antimicrobials; therefore, mixture of antimicrobials is a strategy to extend their life. For antimicrobials alone, minimal bactericidal concentration ranges were 0.3-2.38 mg/ml (OEO), 0.31-1.22 mg/ml (Car), 0.25-1 mg/ml (Thy), and 15.75-31.5 μg/ml (bioAgNP). The time-kill assays showed that the oregano derivatives acted very fast (at least 10 s), while the bioAgNP took at least 30 min to kill Gram-negative bacteria and 7 h to kill methicillin-resistant Staphylococcus aureus (MRSA). All the combinations resulted in additive antibacterial effect, reducing significantly minimal inhibitory concentration and acting faster than the bioAgNP alone; they also showed no cytotoxicity. This study describes for the first time the effect of Car and Thy combined with bioAgNP (produced with F. oxysporum components) against bacteria for which efficient antimicrobials are urgently needed, such as carbapenem-resistant strains (E. coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa) and MRSA.

Quantitative Proteomic Analysis Reveals Important Roles of the Acetylation of ER-Resident Molecular Chaperones for Conidiation in Fusarium oxysporum

Fusarium oxysporum is one of the most abundant and diverse fungal species found in soils and includes nonpathogenic, endophytic, and pathogenic strains affecting a broad range of plant and animal hosts. Conidiation is the major mode of reproduction in many filamentous fungi, but the regulation of this process is largely unknown. Lysine acetylation (Kac) is an evolutionarily conserved and widespread posttranslational modification implicated in regulation of multiple metabolic processes. A total of 62 upregulated and 49 downregulated Kac proteins were identified in sporulating mycelia versus nonsporulating mycelia of F. oxysporum. Diverse cellular proteins, including glycolytic enzymes, ribosomal proteins, and endoplasmic reticulum–resident molecular chaperones, were differentially acetylated in the sporulation process. Altered Kac levels of three endoplasmic reticulum–resident molecular chaperones, PDI^K70, HSP70^K604, and HSP40^K32 were identified that with important roles in F. oxysporum conidiation. Specifically, K70 acetylation (K70ac) was found to be crucial for maintaining stability and activity of protein disulphide isomerase and the K604ac of HSP70 and K32ac of HSP40 suppressed the detoxification ability of these heat shock proteins, resulting in higher levels of protein aggregation. During conidial formation, an increased level of PDI^K70ac and decreased levels of HSP70^K604ac and HSP40^K32ac contributed to the proper processing of unfolded proteins and eliminated protein aggregation, which is beneficial for dramatic cell biological remodeling during conidiation in F. oxysporum.

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Importance and levels of acetylation in conidiation of Fusarium oxysporum.

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Protein folding was regulated by acetylation during conidiation.

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Acetylation modulates activities of ER-resident molecular chaperones.

Improvement of beauvericin production by Fusarium oxysporum AB2 under solid-state fermentation using an optimised liquid medium and co-cultures

The production of beauvericin (BEA) by Fusarium oxysporum AB2 in liquid medium (SmF) was compared to that on solid medium (SSF) on inert support (polyurethane foam or PUF), using a previously optimised medium. The analysis included two different concentrations of the medium (1 × and 3 ×). Under SSF, the production of BEA (22.8 mg·L^-1) was higher relative to SmF (0.8 mg·L^-1). The production increased proportionally in the concentrated medium (3 ×) (65.3 mg·L^-1); using the concentrated medium in SmF, the production of BEA was completely inhibited, although more biomass was produced. The peak of BEA production was reached on day 7 and remained stable until day 11; sustained production after several days has not been achieved in similar reports. The presence of BEA was corroborated by high-performance liquid chromatography (HPLC) and mass spectrometry. The BEA production profile is shown performing mixed cultures of Fusarium oxysporum AB2 and Epicoccum nigrum TORT using the same system, increasing the production of BEA up to 84.6 mg·L^-1. We propose SSF using polyurethane foam (PUF) as a solid support as a new culture system for obtaining secondary metabolites such as BEA.