The production of sporostatic factors in soil

Summary Sixteen species of fungi were isolated from a park-land soil. When inoculated back into a sterilized sample of this soil three sporostatic factors, acetaldehyde, n-propanol and nonanoic acid were found to accumulate and the soil became inhibitory to the germination of test spores. The level of inhibition recorded could be explained wholly in terms of the prevailing levels of the identified sporostatic factors.     

The identification of a self-inhibitor from Syncephalastrum racemosum and its effect upon sporangiospore germination

High concentrations of Syncephalastrum racemosum spores germinated less readily than low concentrations. Extensive washing of spores alleviated this inhibition of germination. Analysis of the spore washings revealed the main constituent to be nonanoic acid. Exogenously added nonanoic acid was found to mimic the self-inhibition, in that it delayed the time of germ tube emergence and increased the lag before spore swelling commenced.     

Sporostatic and Sporocidal Properties of Aqueous Formaldehyde

Aqueous formaldehyde is shown to exert both sporostatic and sporocidal effects on Bacillus subtilis spores. The sporostatic effect is a result of the reversible inhibition of spore germination occasioned by aqueous formaldehyde; the sporocidal effect is due to temperature-dependent inactivation of these spores in aqueous formaldehyde. The physicochemical state of formaldehyde in solution provides a framework with which to interpret both the sporostatic and sporocidal properties of aqueous formaldehyde.     

Production of volatile organic compounds by an antagonistic strain Paenibacillus polymyxa WR-2 in the presence of root exudates and organic fertilizer and their antifungal activity against Fusarium oxysporum f. sp. niveum

The volatile organic compounds (VOCs) produced by antagonistic microbes have great antifungal potential against soil-borne fungal pathogens. The VOCs produced by Paenibacillus polymyxa strain WR-2 in the presence of root exudates and organic fertilizer were identified and their effects on the growth and spore germination of Fusarium oxysporum f. sp. niveum were evaluated. The VOCs produced by WR-2 inhibited the growth of F. oxysporum by 38%, 36% and 40% in agar medium, sterilized soil and natural soil, respectively. This inhibitory effect was increased to 60%, 58% and 64% with the addition of organic fertilizer in agar medium, sterilized soil and natural soil, respectively. The addition of root exudates did not affect the production of antifungal VOCs by WR-2. The VOCs produced by WR-2 completely inhibited the germination of F. oxysporum spores. Out of 42 identified VOCs, seven VOCs; benzothiazole, benzaldehyde, undecanal, dodecanal, hexadecanal, 2-tridecanone and phenol were found to inhibit the growth of F. oxysporum. The results of these experiments suggest another significance of using organic fertilizer as a carrier material with the biocontrol agents to control soil-borne fungal pathogens.     

The effect of volatile and gaseous metabolites of swelling seeds on germination of fungal spores

Effects of volatile and gaseous metabolites of swelling seeds of pea, bean, wheat, corn, cucumber, tomato, lentil, carrot, red pepper and lettuce on germination of spores of five genera of fungi were found to depend rather on the fungal than on the plant genus. Germination of spores ofBotrytis cinerea, Mucor racemosus andTrichoderma viride was most severely inhibited. Spores ofVerticillium dahliae were less sensitive and germination of spores ofFusarium oxysporum was inhibited only in two cases. On the other hand, exudates of pea and bean stimulated germination of spores ofFusarium oxysporum. Also spores ofTrichoderma viride germinated better in an atmosphere enriched with exuded metabolites of swelling lettuce seeds. When carbon dioxide produced by the swelling seeds was absorbed in potassium hydroxide, spores ofTrichoderma viride andVerticillium dahliae did not germinate at all, the inhibitory effects of volatile and gaseous exudates on germination of spores ofMucor racemosus were accentuated, and also the percentage of germinated spores ofFusarium oxysporum decreased. Germination of spores ofBotrytis cinerea was not influenced. Absorption of volatile and gaseous metabolites in a solution of potassium permanganate decreased in most cases their inhibitory effects, particularly inBotrytis cinerea.     

Isolation and Characterization of a Spore Germination Inhibitor from Streptomyces sp. CB-1-1, a Phytopathogen Causing Root Tumor of Melon

The germination rate and activation conditions of spores were examined for four strains of Streptomyces sp., a phytopathogen causing root tumor of melon. An inhibitor was isolated from the agar-cultured material of strain CB-1-1 and then characterized. The inhibitor selectively acted on spore germination and did not affect hyphal growth, and inhibition was abolished by washing the spores in water. The inhibitor was produced by an agar culture, and most of the inhibitor existed in the spores. The IC₅₀ value for the inhibitor was approximately 0.25 μg/ml.     

Effect of volatile substances fromOriganum majorana andOcimum basilicum on spore respiration and germination of some soil fungi

Oxygen uptake by the spores ofFusarium moniliforme, F. oxysporum, F. semitectum, F. solani, Mucor racemosus andTrichoderma viride was increased in the presence of volatile substances extracted, fromOriganum majorana andOcimum basilicum. This increase was greater in the presence of volatile substances fromO. basilicum thanO. majorana, except in the case ofF. semitectum where the reverse was true. A drop in the RQ of all the germinating spores was observed in the presence of these substances. Volatile substances fromO. majorana reduced the spore germination ofM. racemosus whereas the spores ofT. viride were stimulated to germinate. Volatile substances fromO. basilicum stimulated the spore germination ofM. racemosus whereasT. viride spores were not affected.     

<Emphasis Type="Italic">Exiguobacterium acetylicum</Emphasis> strain 1P (MTCC 8707) a novel bacterial antagonist from the North Western Indian Himalayas

Exiguobacterium acetylicum strain 1P (MTCC 8707) is a rhizospheric, Gram positive, rod shaped, yellow pigmented bacterium isolated from an apple orchard rhizospheric soil, on nutrient agar plates incubated at 4°C. The species level identification was arrived on the basis of 16S rRNA gene sequencing. The sequence showed 98% similarity with sequences of E. acetylicum available in the public domain. The strain was positive for siderophore and HCN production. In separate invitro assays it was found to inhibit the growth and development of Rhizoctonia solani, Sclerotium rolfsii, Pythium and Fusarium oxysporum. The volatile compound produced by the bacterium was found to be the most potent in inhibiting the hyphal development of R. solani, S. rolfsii, Pythium and F. oxysporum by 45.55, 41.38, 28.92 and 39.74% respectively. Commonly observed deformities caused by the diffusible and volatile compounds produced by the bacterium included hyphal inhibition, constriction and deformation. Under pot culture conditions the bacterium improved the germination and early growth parameters of pea (Pisum sativum) in the presence of R. solani and S. rolfsii.     

碎米藓属两种藓类植物孢子萌发与原丝体发育特征研究

为获取其孢子萌发类型与该属植物系统发育、生态选择以及生殖策略选择的相关性,该研究通过室内人工培养的方式,在微米量级下观察并描述了碎米藓属(Fabronia)碎米藓(F.pusilla)和东亚碎米藓(F.matsumurae)两种藓类植物孢子萌发、原丝体发育和配子体发生的过程.结果表明:(1)两种藓类植物孢子均为壁外萌发...     

Fungitoxic activity of fruit extracts of Syzygium cumini (L.) Skeels against plant pathogenic fungi Alternaria alternata and Fusarium oxysporum

This study was aimed to evaluate the effectiveness of the aqueous and ethanolic extracts of fruits of Syzygium cumini, against the mycelial growth of Alternaria alternata and Fusarium oxysporum. The results showed that ethanolic extract at the concentrations of 7.5 and 9?mg/ml completely inhibited the mycelial growth of A. alternata and F. oxysporum, respectively. While the aqueous extract at a highest tested concentration (37.5?mg/ml) exhibited only 27.86 and 37.23% inhibition of mycelial growth of A. alternata and F. oxysporum, respectively. The spore germination assay also showed the complete inhibition of spore germination of A. alternata and F. oxysporum by ethanolic extract at 50 and 60?mg/ml concentrations, respectively. Minimum inhibitory concentration was recorded as 0.039 and 0.156?mg/ml in ethanolic extract and 20 and 6.25?mg/ml in aqueous extract against A. alternata and F. oxysporum, respectively. Phytochemical analysis also showed the presence of high amount of phenolics, tannins, flavonoids, alkaloids and saponins.     

Volatile and gaseous metabolites released by germinating seeds of lentil and maize cultivars with different susceptibilities to fusariosis and smut

The effect of volatile and gaseous metabolites released by germinating seeds of lentil cultivars more and less susceptible to fusariosis on the germination of spores ofMucor racemosus, Trichoderma viride, Verticillium dahliae andBotrytis cinerea was found to depend rather on the fungal genus than on the lentil cultivar. However, spores ofFusarium oxysporum reacted more sensitively during germination to the presence of exudates of both cultivars, when the more susceptible lentil displayed a stimulation, the less susceptible one an inhibition of spore germination. The greatest difference in the effect of exudates was observed in the more and less susceptible maize cultivars with respect to the germination of chlamydospores ofUstilago maydis, especially during the first hours of seed germination. Analysis of the exudates of germinating seeds showed the release of a greater amount of ethanol and methanol with acetaldehyde by the more susceptible cultivars of lentil and particularly maize.     

Morphological characterization and germination of aerial and submerged spores of the entomopathogenic fungus Verticillium lecanii

Under solid-state and liquid-state cultivations, the entomopathogenic fungus Verticillium lecanii F091 produced different types of spores. The aerial spores (AS) on cooked rice formed clusters on the tips of conidiophores, while the submerged spores (SS) were dispersed in the medium. The aerial spore appeared relatively uniform in size, which was 6.1 ± 0.9 m long, and 2.2 ± 0.3 m wide. The submerged spore varied in shape and size, with a mean length of 5.0 ± 1.0 m and width of 1.9 ± 0.5 m. Under scanning electron microscopy, the AS had a tendency to have rough, brittle surface characteristics; however, the SS appeared smooth on the surface. These spores were compared in two different germination media. On SMAY (Sabouraud maltose, agar, yeast extract, and neopeptone) coated coverslips, the AS did not show germ tubes until 8 h of incubation; while the SS showed many germ tubes. However, over 90% spore germination ratio was reached for both types of spores at 18-h of incubation. In the liquid medium, the SS germinated rapidly and many spores even produced spores on the spores; while the AS germinated, grew, and branched in the submerged culture gradually, and some sporulated on the tips of the short branches, or on the mycelia until 18 h of incubation. Evidently, the germination, growth patterns of aerial or submerged spores differed greatly under the different culture conditions. The virulence of the pathogen in relation to the type of spore of V. lecanii is discussed.     

Secondary leaf fall of Hevea brasiliensis: factors affecting the production, germination and viability of spores of Colletotrichum gloeosporioides

The optimum temperature for growth and sporulation of Colletotrichum gloeosporioides from Hevea brasiliensis was between 26 and 32 ^oC, whereas spore germination exceeded 90% between 21.5 and 30.5 ^oC. Germination decreased in culture after 3 days, and on exposure of spores to sunlight or oven heat (46 ^oC) for 10 min. Spore viability and germination were sensitive to atmospheric humidity; at 99% r.h. germination was half that at 100% r.h. and was negligible below 97% r.h. Germination decreased by up to 30% after 3 h storage at 80% r.h. Continuous light favoured spore production in vitro, but spores produced in the dark had a higher percentage germination. No differences were detected between the numbers of spores germinating on leaves of different ages, although there were slightly more on susceptible cultivars and in the presence of extracts of uninfected susceptible leaves. Extracts from, infected leaves depressed spore germination, as did concentrations above 5 times 10⁵ spores/ml. The highest % germination was observed when naturally infected leaves were dry-stored for up to 20 days and then incubated for 2 days in a moist chamber.     

Light dependent spore germination in Woodwardia radicans (L.) Sm

Abstract

The spores of Woodwardia radicans can germinate indifferently either in water or in culture media containing mineral salts at temperatures (15-24°C) falling within a range believed optimal for many other ferns (15-30 C).

The spores are photosensitive, will not germinate in the dark and the addition of gibberellic acid is ineffective in substituting a light requirement. Spore germination was induced by white and red light and phytochrome seems to be implicated in the control of germination since far-red light (and not the blue irradiation) can reverse the stimulating effect of the red light.

Spore morphology and spore germination pattern was studied using light and scanning electron microscopes.

It was concluded that the progressive disappearance of W. radicans from the Italian localities is not due to difficulties in spore germination but is related to problems that arise during the subsequent stages.     

Role of carbon dioxide in germination of spores of Streptomyces viridochromogenes

CO₂ in required continuously during germination of Streptomyces viridochromogenes spores. Spores incubated in a defined germination medium in the absence of CO₂ remain phase bright and do not release spore carbon. In the presence of CO₂, the spores initiate germination accompanied by loss of refractility and spore carbon. The CO₂ requirement is replaced by oxaloacetate or a mixture of tricarboxylic acid cycle (TCA) intermediates. Labeled CO₂ is taken up by germinating spores, and is incorporated into protein and RNA. TCA cycle intermediates and related amino acids contain most of the acid-soluble label following short term exposures of germinating spores to ¹⁴CO₂. TCA cycle inhibitors repress germination and ¹⁴CO₂ uptake whereas folic acid antagonists do not. The results indicate that CO₂ is incorporated into oxaloacetate which is converted to biosynthetic intermediates required for germination. Operation of the TCA cycle appears to be essential for spore germination. The conclusion is reached that CO₂ is required during germination in order to maintain the cycle by an anaplerotic reaction.Abbreviations SN sucrose-nitrate medium - TX buffer Trisbuffer pH 7.3 containing-Triton X-100 - DGM defined germination medium - TX salts TX buffer plus Mg and Ca ions - TA trichloroacctic acid - TCA tricarboxylic acid     

The effect of root exudates from two transgenic insect-resistant cotton lines on the growth of Fusarium oxysporum

The attenuation of disease resistance in transgenic insect-resistant cotton has become one of the important factors restricting cotton production in China. Two transgenic insect-resistant cotton lines and their parental conventional cotton lines were used as the testing materials. The effects of root exudates of these cotton lines on the spore germination and mycelial growth of Fusarium oxysporum were studied and the components, contents of amino acids and sugars were determined. The results showed that the resistance of the two insect-resistant cotton lines to F. oxysporum was inferior to the parental lines, and that their root exudates promoted fungal spore germination and mycelial growth. Considerable differences in the components and contents of both, amino acids and sugars were found between the root exudates of transgenic cotton lines and their parental lines, where the disease indices were highly correlated with the total amount of sugars in the root exudates.     

Comparative studies on the effect of vitamins on sporulation in Fusarium oxysporum schlecht. ex. Fr. and Fusarium moniliforme V. subglutinans Wr. & Rg.

On the basis of sporulation (total output of all the three spore forms taken together) and fungal mat production bothF. oxysporum Schlecht ex.Fr. andF. moniliforme v.subglutinans Wr. &Rg. are auxoheterotrophic for thiamine, biotin, inositol, riboflavin and pyridoxine. The first three vitamins are selective in accelerating macro-conidial production also inF. moniliforme, which otherwise shows decrease with advance in days of incubation.F. moniliforme is an auxo-autotroph for nicotinic acid, Ca-pantothenate and folic acid and auxoheterotroph for ascorbic acid. Auxoautotrophy for Ca-pantothenate, folic acid, l-ascorbic acid and p-aminobenzoic acid cannot be suggested forF. oxysporum. Whereas nicotinic acid is a depressent of sporulation inF. oxysporum, inF. moniliforme another vitamin p-aminobenzoic acid depresses sporulation. As the two species ofFusarium show differences in preference as well as inhibition to at least five of the vitamins studied and also varied trends of pH changes exists there is full justification for their separate taxonomic placements.     

Nonanoic Acid, a Fungal Self-Inhibitor, Prevents Germination of Rhizopus oligosporus Sporangiospores by Dissipation of the pH Gradient

Germination of Rhizopus oligosporus sporangiospores is characterized by swelling of the spores and subsequent emergence of germ tubes. Changes in spore morphology and alterations in intracellular pH (pH(infin)) of the sporangiospores were assessed during the germination process by flow cytometry. Sporangiospores were stained with carboxyfluorescein by incubation with carboxyfluorescein diacetate. The nonfluorescent carboxyfluorescein diacetate is passively transported into intact cells and subsequently cleaved by esterases, which results in intracellular accumulation of the fluorescent carboxyfluorescein. Given that the fluorescence of carboxyfluorescein is pH dependent, the pH(infin) of the individual spores could be assessed simultaneously with spore size. For R. oligosporus, swelling of the sporangiospores was accompanied by an increase of pH(infin). In the presence of nonanoic acid, a self-inhibitor produced by various fungi, increase of the pH(infin) was prevented and swelling was inhibited at concentrations of less than 1 mM. Octanoic acid and decanoic acid were equally effective. Acetic acid also inhibited germination but at much higher concentrations (>8 mM). The mechanism of action of these fatty acids is most likely dissipation of the pH gradient. A model is proposed in which the pH(infin) plays a crucial role in the germination of R. oligosporus sporangiospores.     

The effect of <Emphasis Type="Italic">Baccharis glutinosa</Emphasis> extract on the growth of mycotoxigenic fungi and fumonisin B<Subscript>1</Subscript> and aflatoxin B<Subscript>1</Subscript> production

The aim of this study was to evaluate the effect of Baccharis glutinosa isolated extract on the growth of Aspergillus flavus and Aspergillus parasiticus, and their aflatoxin B₁ production; and growth of Fusarium verticillioides, and their fumonisin B₁ production. The three fungi were exposed to an antifungal fraction, designated as fraction F6-1, isolated from B. glutinosa by methanolic extraction followed by silica gel chromatography. The growth of the fungi was evaluated in kinetics of radial extension growth, kinetics of spores germination, length and diameter of hyphae, spores diameter, as well as in aflatoxin B₁ and fumonisin B₁ production. Fraction F6-1 caused radial growth inhibition of the three fungi mainly F. verticillioides. Spores germination of A. flavus and A. parasiticus was delayed in the early stage of the incubation time, although they completely germinated at 27 h. In contrast, spore germination of F. verticillioides was inhibited 87.7% up to 96 h. The lengths and diameters of hyphae, and spore diameters of the three fungi, were significantly smaller in comparison with those of the controls, and several morphological alterations were observed. Concerning aflatoxin B₁ and fumonisin B₁, fraction F6-1 did not show any inhibition effect at the concentration used. Fraction F6-1 was able to significantly inhibit the development of the three fungi, mainly F. verticillioides. The strong inhibitory effect of F6-1 on hyphae and spores suggests that it interacted with the fungi cell walls, which caused severe deformities. Nevertheless, this fraction was unable in inhibiting mycotoxin production from the three fungi at the concentration tested.     

Interaction between the Ectomycorrhizal Fungus Paxillus involutus, Damping-off Fungi and Pinus resinosa Seedlings

Paxillus involutus, an ectomycorrhizal fungus, had an inhibitory effect on the root pathogenic fungus Fusarium moniliforme and two isolates of F. oxysporum when grown in paired cultures on modified Melin Norkrans’ medium. In contrast, one isolate of F. oxysporum was not inhibited and another damping-off fungus, Cylindrocarpon destructans inhibited growth of Pax. involutus in similar paried cultures. Survival of Pinus resinosa (red pine) seedlings was increased significantly when they were grown in vitro concomitantly with either Pax. involutus and F. moniliforme or Pax. involutus and the three isolates of F. oxysporum, compared with seedlings inoculated with either F. moniliforme or F. oxysporum isolates alone. pax. involutus showed no protective effect against C. destructans. The number of colony forming units of Fusarium spp. was reduced significantly in the root extract and rhizosphere substrate of P. resinosa seedlings inoculated with Pax. involutus. Spore germination of Fusarium spp. was reduced significantly when treated with culture filtrate of Pax. involutus and root extract of P. resinosa seedlings inoculated with Pax. involutus. Neither colony forming units nor spore germination of C. destructans was affected either by culture filtrate of Pax. involutus or root extract of P. resinosa seedlings inoculated with Pax. involutus.