Intermittent wetting of soils at high temperature reduces survival of the take-all fungus

Two pot experiments using naturally infested soil and a range of watering regimes were conducted to study the possible effect of level and frequency of wetting of hot soil (to simulate the period between growing seasons in Western Australia) on inoculum of the take-all fungus (Gaeumannomyces graminis var.tritici). In combination with the high soil temperatures, all watering regimes reduced infectivity and propagule number of the take-all fungus, this reduction being absent in dry soils.     

Effect of certain herbicide treatments on pasture composition and inoculum of the take-all fungus

The improvement of pastures by the use of a range of herbicides to eliminate grasses, and their effect on populations of the take-all fungus (Gaeumannomyces graminis vartritici=Ggt) were studied in the field (at Esperance Downs, on the south-coast of Western Australia) from 1982 to 1985. Field trials were conducted to evaluate three herbicide treatments (2,4-D amine+propyzamide; 2,4-D amine+paraquat; paraquat/ diquat) and an unsprayed control. A pot trial involving these treatments with two levels of nitrogen was undertaken to confirm treatment effects observed in the field trial. All herbicide treatments resulted in reduced grass composition of pastures, in both the year of spraying and in the second year of pasture, but reduced dry matter production in the year of spraying. In the year of spraying, however, inoculum ofGgt was reduced (P<0.1) only following the 2,4-D amine+propyzamide treatment and was greater (P<0.1) after 2,4-D amine+paraquat treatment than the unsprayed treatment. Despite reduced grass levels in the herbicide-treated plots in the second year of pasture,Ggt inoculum did not differ between treatments, nor did it after a wheat crop which followed a second year pasture. There was high correlation (P<0.001) between disease levels and dry weights of grasses in the pot trial. There was significantly less (P<0.001) grass in pots treated with herbicides compared to the unsprayed control but no difference (P>0.05) was evident between treatments. Inoculum levels were lower (P<0.05) in the treated pots than the unsprayed control with no evidence of differences among treatments (P>0.05). Nitrogen level had no effect on disease (P>0.05). All herbicide treatments tested reduced grass level and total dry matter, both in the field and in pots. Whereas in the pot trial reduced grass levels resulted in reducedGgt inoculum, in the field such a reduction occurred only with the 2,4-D amine+propyzamide treatment and only in the year of spraying. Herbicide treatments had no effect onGgt inoculum in second year of pasture or crop. Unknown soil and environmental factors in the field precluded a simple relationship between grass level in pasture and subsequent level ofGgt inoculum, and where such a relationship did occur (2,4-D amine+propyzamide treatment) it appeared to be shortlived.     

Gluconic acid: an antifungal agent produced by Pseudomonas species in biological control of take-all

Pseudomonas strain AN5 (Ps. str. AN5), a non-fluorescent Australian bacterial isolate, is an effective biological control (biocontrol) agent of the take-all disease of wheat caused by the fungus Gaeumannomyces graminis var. tritici (Ggt). Ps. str. AN5 controls Ggt by producing an antifungal compound which was purified by thin layer and column chromatography, and identified by NMR and mass spectroscopic analysis to be d-gluconic acid. Commercially bought pure gluconic acid strongly inhibited Ggt. Two different transposon mutants of Ps. str. AN5 which had lost take-all biocontrol did not produce d-gluconic acid. Gluconic acid production was restored, along with take-all biocontrol, when one of these transposon mutants was complemented with the corresponding open reading frame from wild-type genomic DNA. Gluconic acid was detected in the rhizosphere of wheat roots treated with the wild-type Ps. str. AN5, but not in untreated wheat or wheat treated with a transposon mutant strain which had lost biocontrol. The antifungal compounds phenazine-1-carboxylic acid and 2,4-diacetylphloroglucinol, produced by other Pseudomonads and previously shown to be effective in suppressing the take-all disease, were not detected in Ps. str. AN5 extracts. These results suggest that d-gluconic acid is the most significant antifungal agent produced by Ps. str. AN5 in biocontrol of take-all on wheat roots.     

Insights from the draft genome of Paenibacillus lentimorbus NRRL B-30488, a promising plant growth promoting bacterium

Paenibacillus lentimorbus NRRL B-30488, a plant growth-promoting bacterium was isolated from Sahiwal cow's milk. The strain shows antagonism against phytopathogens, Fusarium oxysporum f. sp. ciceri and Alternaria solani. Its genome contains gene clusters involved in nonribosomal synthesis of secondary metabolites involved in antimicrobial activities. The genome sequence of P. lentimorbus NRRL B-30488 provides the genetic basis for application of this bacterial strain in plant growth promotion, plant protection and degradation of organic pollutants.     

Promotion of growth of wheat seedlings by a sterile red fungus in relation to plant density and soil fertility

Enhancement of shoot and root growth of wheat seedlings by a sterile red fungus was evident even when sufficient nutrients were supplied and density of plants per pot was increased (from 15 to 30 plants per pot of 400 g soil). It is likely that production of hormonal-type substances by these fungi may be involved in the phenomenon observed.     

Natural suppression of take-all disease of wheat in Montana soils

This research was initiated to determine whether soils suppressive to take-all of wheat caused by Gaeumannomyces graminis var. tritici (Ggt) occur in Montana, and to identify the organisms most likely involved in this suppression. From an initial screening of eight soils collected from different wheat growing areas of Montana, two were highly suppressive to take-all. Microbial characterization of these soils indicated that different mechanisms were involved in the suppression. In Larslan soil, mycoparasitism appeared to be the main mechanism. Two different fungi with exceptional ability to reduce the severity of take-all were isolated from this soil. One of these fungi could parasitize the hyphae of Ggt. Field tests with these fungi in Ggt infested soil showed increases of over 100% in both harvestble tillers and grain yield as compared to treatments without these two fungi. In tests with 48 different bacteria and 10 actinomycetes from Larslan soil, none were able to consistently reduce severity of take-all alone, or in mixtures. In Toston soil, antibiosis by actinomycetes and perhaps the involvement of Pseudomonas spp. in production of antibiotics and/or siderophores appeared to be the most likely mechanisms involved in take-all suppression. Increases in shoot dry weight over that in the Ggt infested control using mixtures of pseudomonads and actinomycetes ranged from 25% to 87%. Actinomycetes added individually or in mixtures to soil infested with Ggt consistently reduced the severity of the disease to a greater extent than did mixtures of Pseudomonas spp.     

The attack of the phytopathogens and the trumpet solo: Identification of a novel plant antifungal peptide with distinct fold and disulfide bond pattern

Phytopathogens cause economic losses in agribusiness. Plant-derived compounds have been proposed to overcome this problem, including the antimicrobial peptides (AMPs). This paper reports the identification of Ps-AFP1, a novel AMP isolated from the Pisum sativum radicle. Ps-AFP1 was purified and evaluated against phytopathogenic fungi, showing clear effectiveness. In silico analyses were performed, suggesting an unusual fold and disulfide bond pattern. A novel fold and a novel AMP class were here proposed, the αβ-trumpet fold and αβ-trumpet peptides, respectively. The name αβ-trumpet was created due to the peptide's fold, which resembles the musical instrument. The Ps-AFP1 mechanism of action was also proposed. Microscopic analyses revealed that Ps-AFP1 could affect the fungus during the hyphal elongation from spore germination. Furthermore, confocal microscopy performed with Ps-AFP1 labeled with FITC shows that the peptide was localized at high concentration along the fungal cell surface. Due to low cellular disruption rates, it seems that the main target is the fungal cell wall. The binding thermogram and isothermal titration, molecular dynamics and docking analyses were also performed, showing that Ps-AFP1 could bind to chitin producing a stable complex. Data here reported provided novel structural–functional insights into the αβ-trumpet peptide fold.     

Penicisteroids A and B, antifungal and cytotoxic polyoxygenated steroids from the marine alga-derived endophytic fungus Penicillium chrysogenum QEN-24S

Two new polyoxygenated steroids, namely, penicisteroids A and B (1 and 2), were obtained from the culture extract of Penicillium chrysogenum QEN-24S, an endophytic fungus isolated from an unidentified marine red algal species of the genus Laurencia. In addition, seven known steroids (3-9) were also isolated and identified. The structures of these compounds were established on the basis of extensive spectroscopic analysis. The absolute configuration for compound 1 was determined by application of the modified Mosher’s method. Penicisteroid A (1), which is a structurally unique steroid having tetrahydroxy and C-16-acetoxy groups, displayed potent antifungal and cytotoxic activity in the preliminary bioassays. Preliminary structure-activity relationships are discussed.     

Antiplasmodial and antifungal activities of iridal,a plant triterpenoid

Iridal, a triterpenoidic compound extracted from Iris germanica L., was previously shown to have an interesting activity on two cultured human tumor cell lines (A2780 and K562). In the present work, this same product was tested in vitro on Plasmodium falciparum chloroquine-resistant and -sensitive strains, in vivo on P. vinckei, and on some Candida albicans and C. parapsilosis strains too. The IC(50) obtained in vitro on human malaria strain ranged from 1.8 to 26.0 microg/ml and the ED(50) in vivo is about 85 mg/kg/day by intraperitoneal route. The minimal inhibitory concentrations were higher than to 50 microg/ml, whatever the strain of yeast tested. This product presents an antiplasmodial activity similar to that obtained with extracts from the plant Azadirachta indica classically taken as reference in malaria phytomedicine. Conversely iridal shows no important antifungal activity. The specific activity of iridal on human malaria parasite and on tumor cell lines is discussed.     

Isolation and characterization of a 29-kDa glycoprotein with antifungal activity from bulbs of Urginea indica

In this study an antifungal protein from Urginea indica bulbs was purified to homogeneity by acid precipitation, Diol 300 Gel-filtration, and C(18) reverse phase HPLC. Its molecular mass was estimated to be 29 kDa and periodic acid-Schiff (PAS) staining showed that identified antifungal molecule is a glycoprotein. The neutralization of antifungal activity after periodate oxidation of 29 kDa glycoprotein suggests that the glycan part of the molecule appears to be involved in antifungal activity. N-terminal amino acid sequence of the purified protein was determined as SQLKAXIXDF. This sequence had no sequence similarity with any antifungal proteins. A polyclonal antiserum was raised against purified protein and used in immunolocalization analysis. Results suggest that it is localized to the cell wall of the bulb. Antifungal tests have demonstrated that U. indica protein exerts a fungistatic effect. It completely inhibits the germination of spores and hyphal growth of Fusarium oxysporum.     

An S-locus receptor-like kinase plays a role as a negative regulator in plant defense responses

Plant cells often use cell surface receptors to sense environmental changes and then transduce external signals via activated signaling pathways to trigger adaptive responses. In Arabidopsis, the receptor-like protein kinase (RLK) gene family contains more than 600 members, and some of these are induced by pathogen infection, suggesting a possible role in plant defense responses. We previously characterized an S-locus RLK (CBRLK1) at the biochemical level. In this study, we examined the physiological function of CBRLK1 in defense responses. CBRLK1 mutant and CBRLK1-overexpressing transgenic plants showed enhanced and reduced resistance against a virulent bacterial pathogen, respectively. The altered pathogen resistances of the mutant and overexpressing transgenic plants were associated with increased and reduced induction of the pathogenesis-related gene PR1, respectively. These results suggest that CBRLK1 plays a negative role in the disease resistance signaling pathway in Arabidopsis.     

Isolation and identification of a plant growth promotive substance from mixture of essential plant oils

The PCS (commercial products by Field Science Co, Japan, used for air fresheners) was analyzed for the presence of bioactive constituents and their role as root growth promoters. Chromatographic separation of the methanolic solution of PCS resulted in the isolation of an promoting active substance, which was identified using GC-mass spectrometry and NMR spectroscopy as 1,2-propanediol (CH₃CH(OH)CH₂OH). Lettuce seedling growth bioassay as test plant revealed that 1,2-propanediol can act as potent root growth promoter; enhancing the growth of lettuce seedling radicle at a concentration 0.01 ppm. The concentration of 1,2-propanediol in PCS mixture was estimated as 4 g/l. These studies suggest that 1,2-propanediol might play an important role in the plant growth promoting activity of PCS.     

Isolation and characterization of an antifungal protein from Bacillus licheniformis HS10

Bacillus licheniformis HS10 is a good biocontrol agent against Pseudoperonospora cubensis which caused cucumber downy disease. To identify and characterize the antifungal proteins produced by B.licheniformis HS10, the proteins from HS10 were isolated by using 30–60% ammonium sulfate precipitation, and purified with column chromatography on DEAE Sepharose Fast Flow, RESOURCE Q and Sephadex G-75. And the SDS–PAGE and MALDI-TOF/TOF-MS analysis results demonstrated that the antifungal protein was a monomer with molecular weight of about 55 kDa, identified as carboxypeptidase. Our experiments also showed that the antifungal protein from B. licheniformis HS10 had significantly inhibition on eight different kinds of plant pathogenic fungi, and it was stable with good biological activity at as high as 100 °C for 30 min and in pH value ranged from 6 to 10. The biological activity was negatively affected by protease K and 10 mM metal cations except Ca²⁺.     

Antibacterial and antifungal lysozyme-type activity in Cameraria ohridella pupae

Lysozyme-type antibacterial and antifungal activity in pupae of Cameraria ohridella was studied. Activity against Micrococcus luteus and Bacillus megaterium was detected in pupae extract. Also antifungal activity from C. ohridella pupae extract directed against Saccharomyces cerevisiae strain W 303 was shown. During immunoblotting two bands in pupae extract, with molecular mass of about 15 and 28 kDa were recognized by antibodies directed against HEWL. After acid electrophoresis followed by bioautography of the extract, two lytic zones showing lysozyme-type activity against M. luteus were observed. Two bacteria: Gram-positive Aerococcus viridans and Gram-negative Aeromonas salmonicida ssp. masoucida were isolated from pupae of C. ohridella. Their activity against M. luteus, B. megaterium, and S. cerevisiae W303 was detected. After immunoblotting with antibodies against HEWL, also two proteins from bacterial suspensions of A. viridans and A. salmonicida were detected, about 15 and 28 kDa.     

Botryorhodines A-D, antifungal and cytotoxic depsidones from Botryosphaeria rhodina, an endophyte of the medicinal plant Bidens pilosa

An endophytic fungus (Botryosphaeria rhodina) was isolated from the stems of the medicinal plant Bidens pilosa (Asteraceae) that is known for its anti-inflammatory, antiseptic and antifungal effects. The ethyl acetate extract of the fungal isolate exhibits significant antifungal activity as well as potent cytotoxic and antiproliferative effects against several cancer cell lines. Activity-guided fractionation resulted in the isolation of a complex of four depsidones, botryorhodines A-D and the auxin indole carboxylic acid. Botryorhodine A and B show moderate to weak cytotoxic activities against HeLa cell lines with a CC₅₀ of 96.97 μM and 36.41 μM, respectively. In addition, they also show antifungal activity against a range of pathogenic fungi such as Aspergillus terreus (MIC 26.03 μM for botryorhodine A and 49.70 μM for B) and the plant pathogen Fusarium oxysporum (MIC 191.60 μM for botryorhodine A and 238.80 μM for B). A potential role of the endophyte in modulating fungal populations living within or attacking the host plant is discussed.     

Culture condition-dependent metabolite profiling of Aspergillus fumigatus with antifungal activity

Three sections of Aspergillus (five species, 21 strains) were classified according to culture medium-dependent and time-dependent secondary metabolite profile-based chemotaxonomy. Secondary metabolites were analysed by liquid chromatography–electrospray ionisation tandem mass spectrometry (LC–ESI-MS–MS) and multivariate statistical methods. From the Aspergillus sections that were cultured on malt extract agar (MEA) and Czapek yeast extract agar (CYA) for 7, 12, and 16 d, Aspergillus sections Fumigati (A. fumigatus), Nigri (A. niger), and Flavi (A. flavus, A. oryzae, and A. sojae) clustered separately on the basis of the results of the secondary metabolite analyses at 16 d regardless of culture medium. Based on orthogonal projection to latent structures discriminant analysis by partial least squares discriminant analysis (PLS-DA), we identified the secondary metabolites that helped differentiate sections between A. fumigatus and Aspergillus section Flavi to be gliotoxin G, fumigatin oxide, fumigatin, pseurotin A or D, fumiquinazoline D, fumagillin, helvolic acid, 1,2-dihydrohelvolic acid, and 5,8-dihydroxy-9,12-octadecadienoic acid (5,8-diHODE). Among these compounds, fumagillin, helvolic acid, and 1,2-dihydrohelvolic acid of A. fumigatus showed antifungal activities against Malassezia furfur, which is lipophilic yeast that causes epidermal skin disorders.     

Seedling resistance of wheat to the powdery mildew fungus,Erysiphe graminis f. sp. tritici. I. Resistance of first leaves

During primary infection by conidia ofErysiphe graminis f. sp.tritici, three mechanisms of resistance operate in first leaves of 8-day-old seedlings of both resistant and susceptible wheats. The first mechanism, operating at the penetration site, is responsible for the failure of penetrations attempted by primary germ tubes (PGT). The second mechanism is concerned with the abortion of haustoria in normal-appearing host cells. The third mechanism relates to the abortion of haustoria and the hypersensitivity of the penetrated host cells.With the inoculum-level of 19–24 conidia/mm², the three mechanisms together prevented 89.3 % of the attempted penetrations by PGT from producing normal haustoria in resistant wheat Purdue 5752C1-7-5-1 and 37.4 % in the susceptible wheat Vermillion. The first mechanism accounted for the prevention of 73.3 % of the attempted PGT penetrations on Purdue 5752C1-7-5-1 and 36 % on Vermillion. The second mechanism was responsible for stopping 19 % of all the successful penetrations in Purdue 5752C1-7-5-1 and 0.8 % in Vermillion. The third mechanism accounted for the failure of 41 % of all the successful penetrations in Purdue 5752C1-7-5-1 and 1.4% in Vermillion. Thirty-six hours after inoculation, 10.7% of all the attempted PGT penetrations appeared to be developing normally in first leaves of 8-day-old seedlings of resistant wheat Purdue 5752C1-7-5-1 as compared to 62.6 % in the susceptible wheat Vermillion.This appears to be the first report showing the relative effectiveness of various mechanisms of resistance concerning any powdery mildew fungus.     

The mistletoe lectin I--phloretamide structure reveals a new function of plant lectins

The X-ray structure at 2.7 Å resolution of the complex between the European mistletoe lectin I (Viscum album, ML-I) and the plant growth hormone, 3-(p-hydroxyphenyl)-propionic acid amide (phloretamide, PA) from xylem sap has revealed the binding of PA at the so far undescribed hydrophobic cavity located between the two subunits of this ribosome-inhibiting protein. No such cavity is observed in related lectins. The binding of PA is achieved through interactions with the non-conserved residues Val228A, Leu230A, Arg388B, and the C-terminal Pro510B. It is conceivable that binding of PA to ML-I is part of a defence mechanism of the parasite against the host, whereby the parasite prevents the growth hormone of the host from interfering with its own regulatory system. The specific binding of PA to ML-I indicates that heterodimeric RIPs are multifunctional proteins whose functions in the cell have not yet been fully recognized and analyzed.