Pathogenicity of Three Entomopathogenic Fungi to Matsucoccus matsumurae

Matsucoccus matsumurae (Kuwana) (Hemiptera: Coccoidea: Matsucoccidae) is an invasive alien species and a destructive pest of two native Chinese pines, Pinus tabulaeformis Carr. and P. massoniana Lamb., throughout the eastern regions of China. The pathogenicity of three entomopathogenic fungi, Lecanicillium lecanii strain V3.4504 and V3.4505, Fusarium incarnatum-equiseti strain HEB01 and Lecanicillium fungicola strain HEB02, against M. matsumurae was tested in four instars, to evaluate their potential as a biological control agent. The results showed that the four strains caused disease and death of the scale insect, among which the L. lecanii strains V3.4504 and V3.4505 displayed stronger virulence than the F. incarnatum-equiseti strains HEB01 and L. fungicola strain HEB02 to M. matsumurae in the 2^nd-instar nymphs and the adult females. Furthermore, L. lecanii V3.4505 was most virulent to M. matsumurae. The adult females and the male 3^rd-instar nymphs of M. matsumurae were susceptible to L. lecanii V3.4505; the adult females were more susceptible at LT₅₀ = 1.96 than the 3^rd-instar nymphs at LT₅₀ = 5.67. The body surface structure, cuticle thickness and wax secretions of M. matsumurae impacted the fungal infection. L. lecanii is a promising biocontrol agent, and newly emerged male 3^rd-instar nymphs and adult females are a crucial period of the insect’s life cycle for M. matsumurae biocontrol.     

Effect of sodium chloride concentration in the medium on the composition of the membrane lipids and carbohydrates in the cytosol of the fungus Fusarium sp.

The fungus Fusarium sp. isolated from saline soil was identified by the ITS1-5.8S-ITS2 and the D1/D2 domains of LSU RNA as a member of the Fusarium incarnatum-equiseti species group. Its growth patterns on media with different NaCl concentrations indicated its adaptation as halotolerance. The mechanisms of halotolerance included accumulation of arabitol (a five-atom noncyclic polyol), a decreased sterols/phospholipids ratio, elevated level of phosphatidic acids in the phospholipids, and increased unsaturation of phospholipids, which was especially pronounced in the idiophase. The mechanisms of halotolerance of the mycelial fungus Fusarium sp. are discussed in comparison with yeasts and yeastlike fungi.     

Fungi Associated with Females and Cysts of Heterodera glycines in a Florida Soybean Field

Fungal colonization was determined for females and cysts of Heterodera glycines on soybean roots or in rhizosphere soil from a Florida soybean field. A total of 1,620 females and cysts were examined in 1991, and 1,303 were examined in 1992. More than 35 species of fungi were isolated from females and cysts. The frequency of fungi colonizing white and yellow females was low, but a high frequency of fungi was encountered in brown cysts, which increased with time of exposure of the cysts to the soil. No single fungal species predominated in the nematode females or cysts in this field. Rarely was a female or cyst colonized by more than one fungus. The common fungi isolated from the females and cysts were Neocosmospora vasinfecta, Fusarium solani, Fusarium oxysporum, Dictyochaeta coffeae, Dictyochaeta heteroderae, Pyrenochaeta terrestris, Exophiala pisciphila, Gliocladium catenulatum, Stagonospora heteroderae, and a black yeast-like fungus. The communities of common fungal species isolated from cysts in several regions in the southeastern United States appear to be similar.     

Identification and characterization of ethanol utilizing fungal flora of oil refinery contaminated soil

The indigenous fungal flora of three oil refinery contaminated sites (Bharuch, Valsad and Vadodara) of India has been documented in the present investigation. A total seventy-five fungal morphotypes were isolated from these sites and out of them, only fifteen isolates were capable of utilizing ethanol (0–8 %; v:v) as a sole source of carbon and energy for growth. Ten percent ethanol was completely lethal for the growth of all the isolated fungus. Biochemical characterization of the potent ethanol utilizing fungal isolates was studied based on substrate utilization profiles using BIOLOG phenotype microarray plates. Based on the morphological characters and Internal Transcribed Spacer region of ribosomal DNA, the fungal isolates were identified as Fusarium brachygibbosum, Fusarium equiseti, Fusarium acuminatum, Pencillium citrinum, Alternaria tenuissima, Septogloeum mori, Hypocrea lixii, Aureobasidium sp., Penicillium sp., and Fusarium sp. Intra-species genetic diversity among Fusarium sp. was evaluated by whole genome analysis with repetitive DNA sequences (ERIC, REP and BOX) based DNA fingerprinting. It was found that these fungus use alcohol dehydrogenase and acetaldehyde dehydrogenase enzymes based metabolism pathway to utilize ethanol for their growth and colonization.     

Susceptibility of nontarget organisms to Nosema algerae (Microsporida: Nosematidae), a parasite of mosquitoes.

Host response of two penaeid species, Penaeus aztecus and P. setiferus, from the Gulf of Mexico to the pathogenic fungus Fusarium sp. isolated from the California brown shrimp, P. californiensis, was studied in vivo. The hemocytic response to this fungus was traced histologically in the gills. Both species showed complete resistance to infection by the fungal spores when normal or wounded shrimp were held in seawater containing the spores or when spores were injected directly into the shrimp in low concentrations. Complete melanization and encapsulation of the micro- and macroconidia were observed. Spore dosages of 3.2 × 10⁶ or more were lethal, apparently due to mechanical blockage of the blood sinuses of the gills.     

A Nitrogen Response Pathway Regulates Virulence Functions in Fusarium oxysporum via the Protein Kinase TOR and the bZIP Protein MeaB

During infection, fungal pathogens activate virulence mechanisms, such as host adhesion, penetration and invasive growth. In the vascular wilt fungus Fusarium oxysporum, the mitogen-activated protein kinase Fmk1 is required for plant infection and controls processes such as cellophane penetration, vegetative hyphal fusion, or root adhesion. Here, we show that these virulence-related functions are repressed by the preferred nitrogen source ammonium and restored by treatment with l-methionine sulfoximine or rapamycin, two specific inhibitors of Gln synthetase and the protein kinase TOR, respectively. Deletion of the bZIP protein MeaB also resulted in nitrogen source–independent activation of virulence mechanisms. Activation of these functions did not require the global nitrogen regulator AreA, suggesting that MeaB-mediated repression of virulence functions does not act through inhibition of AreA. Tomato plants (Solanum lycopersicum) supplied with ammonium rather than nitrate showed a significant reduction in vascular wilt symptoms when infected with the wild type but not with the ΔmeaB strain. Nitrogen source also affected invasive growth in the rice blast fungus Magnaporthe oryzae and the wheat head blight pathogen Fusarium graminearum. We propose that a conserved nitrogen-responsive pathway might operate via TOR and MeaB to control virulence in plant pathogenic fungi.     

Process of infection of armored scale insects (Diaspididae) by an entomopathogenic Cosmospora sp

Several species in the fungal genus Cosmospora (synonym Nectria) (anamorph Fusarium) are specialist entomopathogens of armored scale insects (Diaspididae), known to cause periodic epizootics in host populations. Inconsistent mortality rates recorded under laboratory conditions prompted a study into the process of infection of armored scale insects by this fungus. Scale insect mortality following exposure to a Cosmospora sp. (Culture Collection Number: CC89) from New Zealand was related to insect age, with reproductively mature insects having a significantly higher infection rate than immature insects. Examination using scanning electron microscopy found no evidence that the fungus penetrated directly through the wax test (cap) of the scale insect or through the un-lifted interface between the test and the substrate on which the insect resided. However, fungal hyphae were observed growing beneath the test when the test of the reproductively mature insect lifted away from the substrate for the purpose of releasing crawlers, the mobile pre-settled juveniles. Once the hyphae of CC89 advanced under the test, germ-tubes readily penetrated the insect body through a number of natural openings (e.g. spiracles, vulva, stylet), with mycosis observed within seven days after inoculation. Direct penetration through the cuticle of the scale insect was not observed.     

Effect of proteinaceous proteinase inhibitors from potato tubers on the growth and development of phytopathogenic microorganisms

We studied the effect of two proteins, PSPI-21 and PKSI, on the growth and development of phytopathogenic microorganisms (Phytophthora infestans oomycete and Fusarium culmorum fungus). Both proteins were isolated from potato tubers (Solanum tuberosum L., cv. Istrinskii) and served as inhibitors of serine proteinases. These proteins differed in the ability to inhibit growth of Phytophthora infestans oomycete and Fusarium culmorum fungus. PSPI-21 was the most potent in modulating the growth of oomycete mycelium. PKSI primarily affected the growth of the fungal mycelium. The proteins under study induced complete destruction of oomycete zoospores and partial destruction of fungal macroconidia. Our results suggest that these proteins are involved in the protection of potato plants from phytopathogenic microorganisms.     

HapX-Mediated Iron Homeostasis Is Essential for Rhizosphere Competence and Virulence of the Soilborne Pathogen Fusarium oxysporum

Soilborne fungal pathogens cause devastating yield losses and are highly persistent and difficult to control. During the infection process, these organisms must cope with limited availability of iron. Here we show that the bZIP protein HapX functions as a key regulator of iron homeostasis and virulence in the vascular wilt fungus Fusarium oxysporum. Deletion of hapX does not affect iron uptake but causes derepression of genes involved in iron-consuming pathways, leading to impaired growth under iron-depleted conditions. F. oxysporum strains lacking HapX are reduced in their capacity to invade and kill tomato (Solanum lycopersicum) plants and immunodepressed mice. The virulence defect of ΔhapX on tomato plants is exacerbated by coinoculation of roots with a biocontrol strain of Pseudomonas putida, but not with a siderophore-deficient mutant, indicating that HapX contributes to iron competition of F. oxysporum in the tomato rhizosphere. These results establish a conserved role for HapX-mediated iron homeostasis in fungal infection of plants and mammals.     

Fusarium solani, a weak pathogen of the larval stages of the large elm bark beetle Scolytus scolytus (Coleoptera: Scolytidae)

Fusarium solani, a common colonist of beetle-infested elm bark, has been isolated from dead larvae and adults of the large elm bark beetle, Scolytus scolytus. Two infectivity tests indicated that this fungus is probably a weak pathogen of the larval stages of the beetle. Total mortality was not achieved in either test, but the mortality associated with fungal inoculation was occasionally significantly greater than the mortality in the uninoculated controls in both experiments (P<0.05, experiment A; P<0.025, experiment B). Disease symptoms suggest that the larvae attacked by F. solani may have died from bacterial infection.     

Antimicrobial endophytic fungal assemblages inhabiting bark of <Emphasis Type="Italic">Taxus baccata</Emphasis> L. of Indo-Burma mega biodiversity hotspot

Fungal endophytes were isolated from inner bark of Taxus baccata L., an important source of potent anticancer drug taxol. Bark samples were collected from two locations of Arunachal Pradesh, India, part of the Indo-Burma mega biodiversity hotspot, during two seasons i.e. monsoon and winter. Altogether 77 fungal strains representing 18 genera were isolated from T. baccata bark during the present investigation. The colonizing frequency was recorded as 38.5% and the fungal community comprised of 78% of Hyphomycetes, 5.2% of Coelomycetes, 2.6% of Zygomycetes and Ascomycetes and 9.1% of sterile mycelia. Most common and frequently isolated genera were Fusarium, Penicillium and Aspergillus. Simpson and Shannon diversity indices indicated higher species diversity during monsoon than during winter seasons irrespective of the locations. The two locations harbored 5 to 37 endophyte species and the similarity index was low during winter and high during monsoon. Ethyl acetate extract of fermentation cultures of these fungi were tested for their antimicrobial activity against a panel of human pathogenic Gram-positive and Gram-negative bacteria and fungi. Fifteen fungal isolates out of the isolated strains displayed antimicrobial activity. An endophytic fungus, identified as Fusarium sp. displayed significant antimicrobial activity against all the test pathogens.     

Glucosinolate profiling of Brassica rapa cultivars after infection by Leptosphaeria maculans and Fusarium oxysporum

The glucosinolate contents of two different cultivars of Brassica rapa (Herfstraap and Oleifera) infected with Leptosphaeria maculans and Fusarium oxysporum were determined. Infection triggered the accumulation of aliphatic glucosinolates (gluconapin, progoitrin, glucobrassicanapin and gluconapoleiferin) and indole glucosinolate (4-hydroxy-glucobrassicin) in Herfstraap and of two indole glucosinolates (glucobrassicin and 4-hydroxy-glucobrassicin) in Oleifera. While total and aliphatic glucosinolates decreased significantly in Oleifera, a large increase was observed in Herfstraap after fungal infection. The indole glucosinolate glucobrassicin accumulated in Oleifera at a higher rate than Herfstraap especially after infection with F. oxysporum. Apparently the interaction between fungus and B. rapa is cultivar and fungal species specific.     

Cell wall synthesis in cotton roots after infection with Fusarium oxysporum

Fusarium oxysporum f. sp. vasinfectum penetration hyphae infect living cells in the meristematic zone of cotton (Gossypium barbadense L.) roots. We characterized wall modifications induced by the fungus during infection of the protodermis using antibodies against callose, arabinogalactan-proteins, xyloglucan, pectin, polygalacturonic acid and rhamnogalacturonan I in high-pressure frozen, freeze-substituted root tissue. Using quantitative immunogold labelling we compared the cell walls before and after hyphal contact, cell plates with plasmodesmata during cytokinesis, and wall appositions induced by fungal contact. In the already-existing wall, fungal contact induced only minor modifications such as an increase of xyloglucan epitopes. Wall appositions mostly exhibited epitopes similar to the cell plate except that wall appositions had a much higher callose content. This study shows that wall appositions induced by Fusarium oxysporum hyphae are the result of normal cell wall synthesis and the addition of large amounts of callose. The appositions do not stop fungal growth.     

Pathogenic ability and saline stress tolerance of two Fusarium isolates from Odontesthes bonariensis eggs

BackgroundSeveral fungal species represent a potential risk to embryos of Odontesthes bonariensis (Cuvier and Valenciennes, 1835), a euryhaline freshwater fish that lives in the Pampean inland waters and has potential economic relevance.AimsTo identify two fungi isolated from O. bonariensis eggs exposed to saline conditions and to characterize their pathogenicity and tolerance to sodium chloride solutions.MethodsThe isolates were identified by morphological features, and a preliminar phylogenetic analysis using sequences of translation elongation factor 1-alpha (EF-1α) and calmodulin (CAM) was performed. Koch's postulates were tested to identify the causative agent of fungal infection. The influence of NaCl on the fungal growth was evaluated in in vitro assays.ResultsThe isolates LPSC 1001 and 1002 were identified as representatives of the genus Fusarium, and belonging to the Fusarium incarnatum-Fusarium equiseti species complex (FIESC) and the Fusarium solani species complex (FSSC), respectively. Histological observations on eggs exposed in vitro to both isolates in infectivity assays confirmed the ability of the fungal isolates to penetrate to egg's chorionic membrane, leading to the death of embryos. Increasing NaCl concentration in the culture medium reduced the growth of the isolates LPSC 1001 and 1002, being completely inhibited at 160 and 120 g/l NaCl respectively.ConclusionsThe isolates LPSC 1001 (FIESC) and 1002 (FSSC) were identified as fungal pathogens to O. bonariensis eggs. The use of NaCl solutions as antifungal treatment was not effective to control the infection with these strains.     

Free living amoebae could enhance Fusarium oxysporum growth

Free living amoebae and Fusarium oxysporum can be recovered in the same environment and may potentially interact. The presence of these protozoa could lead to an increased development of this filamentous fungus. To assess this potential risk, the interactions between two free living amoebae, Acanthamoeba castellanii and Hartmanella vermiformis, and F. oxysporum, which can be isolated from soil and water, were studied. After 48 hr of coincubation in tap water, culturable fungi were quantified. In addition, the interactions between the free living amoebae and the fungus were investigated using electron microscopy. We show that the presence of amoeba trophozoites increased the growth of F. oxysporum without fungal influence on amoebae viability. In the same way, incubation of the fungus with culture supernatants of the two amoebae induced fungal germination and increased fungal growth. The results of this study confirm that the presence of amoebae should be taken into consideration in the different environments where they may be in contact with Fusarium.     

Rhizonin, the First Mycotoxin Isolated from the Zygomycota, Is Not a Fungal Metabolite but Is Produced by Bacterial Endosymbionts

Rhizonin is a hepatotoxic cyclopeptide isolated from cultures of a fungal Rhizopus microsporus strain that grew on moldy ground nuts in Mozambique. Reinvestigation of this fungal strain by a series of experiments unequivocally revealed that this “first mycotoxin from lower fungi” is actually not produced by the fungus. PCR experiments and phylogenetic studies based on 16S rRNA gene sequences revealed that the fungus is associated with bacteria belonging to the genus Burkholderia. By transmission electron microscopy, the bacteria were localized within the fungal cytosol. Toxin production and the presence of the endosymbionts were correlated by curing the fungus with an antibiotic, yielding a nonproducing, symbiont-free phenotype. The final evidence for a bacterial biogenesis of the toxin was obtained by the successful fermentation of the endosymbiotic bacteria in pure culture and isolation of rhizonin A from the broth. This finding is of particular interest since Rhizopus microsporus and related Rhizopus species are frequently used in food preparations such as tempeh and sufu.     

An Endophytic Sanguinarine-Producing Fungus from Macleaya cordata,Fusarium proliferatum BLH51

Fermentation processes using sanguinarine-producing fungi other than Macleaya cordata may be an alternative way to produce sanguinarine (SA), which is a quaternary benzo[c]phenanthridine alkaloid possessing antibacterial, anthelmintic, and anti-inflammatory properties. In this study, a SA-producing endophytic fungus strain BLH51 was isolated from the leaves of M. cordata grown in the Dabie Mountain, China. Strain BLH51 produced SA when grown in potato dextrose liquid medium. The amount of SA produced by this endophytic fungus was quantified to be 178 μg/L by HPLC, substantially lower than that produced by the host tissue. The fungal SA—which was analyzed by thin layer chromatography and high-performance liquid chromatography—was shown to be identical to authentic SA. Strain BLH51 was identified as Fusarium proliferatum based on the morphological characteristics and nuclear ribosomal DNA ITS sequence analysis. To the best of our knowledge, this is the first report concerning the isolation and identification of endophytic SA-producing fungi from the host plant, which further proved that endophytic fungi are valuable reservoirs of bioactive compounds.     

枝顶孢属真菌的抑菌活性及其代谢产物研究

用组织分离法从采集于广东鼎湖山的腐殖质中分离得到一株枝顶孢属真菌(Acremonium sp. SC0105),其固体发酵物的乙醇提取物对金黄色葡萄球菌(Staphylococcus aureus)有较强的抑制作用。经多种柱层析,从固体发酵物中分离得到5个化合物。通过光谱分析,分别鉴定为姜糖脂B (1)、姜糖脂C (2)、D-甘露醇(3)、酒渣碱(4)、枝顶孢素F(5)。其中酒渣碱是首次从枝顶孢属真菌中分离得到。     

Early Events in the Fusarium verticillioides-Maize Interaction Characterized by Using a Green Fluorescent Protein-Expressing Transgenic Isolate

The infection of maize by Fusarium verticillioides can result in highly variable disease symptoms ranging from asymptomatic plants to severe rotting and wilting. We produced F. verticillioides green fluorescent protein-expressing transgenic isolates and used them to characterize early events in the F. verticillioides-maize interaction that may affect later symptom appearance. Plants grown in F. verticillioides-infested soil were smaller and chlorotic. The fungus colonized all of the underground parts of a plant but was found primarily in lateral roots and mesocotyl tissue. In some mesocotyl cells, conidia were produced within 14 to 21 days after infection. Intercellular mycelium was detected, but additional cells were not infected until 21 days after planting. At 25 to 30 days after planting, the mesocotyl and main roots were heavily infected, and rotting developed in these tissues. Other tissues, including the adventitious roots and the stem, appeared to be healthy and contained only a small number of hyphae. These results imply that asymptomatic systemic infection is characterized by a mode of fungal development that includes infection of certain tissues, intercellular growth of a limited number of fungal hyphae, and reproduction of the fungus in a few cells without invasion of other cells. Development of visibly rotted tissue is associated with massive production of fungal mycelium and much less organized growth.     

Regulation of a novel Fusarium cytokinin in Fusarium pseudograminearum

Fusarium pseudograminearum is an agronomically important fungus, which infects many crop plants, including wheat, where it causes Fusarium crown rot. Like many other fungi, the Fusarium genus produces a wide range of secondary metabolites of which only few have been characterized. Recently a novel gene cluster was discovered in F. pseudograminearum, which encodes production of cytokinin-like metabolites collectively named Fusarium cytokinins. They are structurally similar to plant cytokinins and can activate cytokinin signalling in vitro and in planta. Here, the regulation of Fusarium cytokinin production was analysed in vitro. This revealed that, similar to deoxynivalenol (DON) production in Fusarium graminearum, cytokinin production can be induced in vitro by specific nitrogen sources in a pH-dependent manner. DON production was also induced in both F. graminearum and F. pseudograminearum in cytokinin-inducing conditions. In addition, microscopic analyses of wheat seedlings infected with a F. pseudograminearum cytokinin reporter strain showed that the fungus specifically induces its cytokinin production in hyphae, which are in close association with the plant, suggestive of a function of Fusarium cytokinins during infection.