Induced tolerance of Sclerotium cepivorum to antibiotics in the presence of onion exudates

The onion white rot pathogen Sclerotium cepivorum was cultured on agar media containing 2% malt extract and one of the antifungal antibiotics, endomycin, griseofulvin, venturicidin and cycloheximide at concentrations that reduced but did not prevent growth of mycelium. When onion seeds or agar discs impregnated with diffusates from onion bulbs were placed on the antibiotic media, radial growth of the fungus was greatly increased, and there was a profuse development of aerial mycelium. Gaseous diffusates from onion tissue and from impregnated agar discs were also effective. On the antibiotic media, tomato, cabbage and radish seeds did not stimulate the growth of S. cepivorum and the onion exudates did not stimulate the growth of four other fungi. This and other evidence is considered to show that the stimulation of growth of S. cepivorum was not caused by any direct effect on the antibiotics but by a tolerance of the fungus to them, which was specifically induced by an exudate from its host plant. The phenomenon may be related to the reported reversal by onion extracts of the inhibitory effects of soil mycostasis on germination of sclerotia of the fungus.     

Effect of some antibiotics on Sclerotium cepivorum Berk., the cause of white rot of onion

The effect of some antibiotics onSclerotium cepivorum, the cause of white rot of onion was studied in agar culture and soil. The growth ofS. cepivorum was inhibited in Czapek Dox yeast agar containing 50µg of gliotoxin, viridin, actidione and 100µg of patulin per ml of the medium. Lower concentrations of the antibiotics retarded the growth of the fungus. In soil, patulin had no effect in the control ofS. cepivorum infection of onion seedlings. Concentration of actidione of 5µg/g of soil completely controlled white rot infection but severely stunted the growth of onion seedlings; 40µg/g of actidione killed the seedlings. Despite the importance of actidione as a fungistatic agent its use on onion is limited by its phytotoxicity.     

Root exudates of mycorrhizal tomato plants exhibit a different effect on microconidia germination of Fusarium oxysporum f. sp. lycopersici than root exudates from non-mycorrhizal tomato plants

The effect of root exudates from mycorrhizal and non-mycorrhizal tomato plants on microconidia germination of the tomato pathogen Fusarium oxysporum f. sp. lycopersici was tested. Microconidia germination was enhanced in the presence of root exudates from mycorrhizal tomato plants. The more tomato plants were colonized by the arbuscular mycorrhizal fungus Glomus mosseae, the more microconidia germination was increased, indicating that alterations of the exudation pattern depended on the degree of root AM colonization. Moreover, alterations of the exudation pattern of mycorrhizal plants are not only local, but also systemic. Testing the exudates from plants with a high and a low P level revealed that the alterations of the root exudates from mycorrhizal plants, resulting in a changed effect on microconidia germination, are not due to an improved P status of mycorrhizal plants.     

Effect of root exudates of mycorrhizal tomato plants on microconidia germination of Fusarium oxysporum f. sp. lycopersici

The effect of root exudates from mycorrhizal and non-mycorrhizal tomato plants on microconidia germination of the tomato pathogen Fusarium oxysporum f. sp. lycopersici was tested. Microconidia germination was enhanced in the presence of root exudates from mycorrhizal tomato plants. Tomato plants were colonised by the arbuscular mycorrhizal fungus Glomus fasciculatum, indicating that alterations of the exudation pattern depended on the degree of root AM colonisation. Testing the exudates from plants with a high and a low P level revealed that the alterations of the root exudates from mycorrhizal plants, resulting in a changed effect on microconidia germination, are not due to an improved P status of mycorrhizal plants.     

Haradamyces foliicola anam. gen. et sp. nov., a cause of zonate leaf blight disease in Cornus florida in Japan

A fungus causing zonate leaf blight diseases in various evergreen and deciduous woody plant species in Japan was characterized by a discoid multicellular propagule arising from a hyaline sclerotium-like structure in the leaf tissue and dark-coloured microconidia produced enteroblastically from the terminal cells on the surface of the discoid propagules. Myrioconium-like microconidiophores also producing microconidia were occasionally produced in culture. No teleomorphic characteristics were observed on the fungus. Molecular analysis based on the partial nu-rDNA sequence data revealed that the fungus was phylogenetically related to the Sclerotiniaceae, Leotiomycetes, and Ascomycota. Because the morphology and sequence data of this fungus does not coincide with those of any known anamorphic fungi, Haradamyces foliicola is proposed here as a new anamorphic genus and species for this fungus.     

Biological control of white rot of onion

Summary Interactions of 123 isolates of fungi, 17 of bacteria and 22 of actinomycetes, respectively, withSclerotium cepivorum were studied in agar culture. They were grouped into 4 different types of reactions. Amongst themTrichoderma viride, Fusarium graminearum, Coniothyrium minitans andGliocladium roseum inhibited the growth ofS. cepivorum and later grew over its colony.T. viride showed a characteristic coiling around the hyphae ofS. cepivorum. T. viride andF. graminearum prevented the development of sclerotia.C. minitans was found to parasitize the sclerotia ofS. cepivorum and produced its pycnidia within them.Aleurisma carnis, Cladosporium elatum, Penicillium expansum, P. nigricans, P. notatum, P. piscarium, P. puberulum, P. rolfsii, P. urticae, P. variabile, Tilachlidium humicola andHelminthosporium sp. inhibited the growth ofS. cepivorum at a distance. Eleven isolates of bacteria and 3 ofStreptomyces sp. showed pronounced antagonistic properties againstS. cepivorum.Experiments were carried out to study the effects on white rot development in soil of organisms selected from agar plate tests. None of the antagonistic micro organisms had any deleterious effects on onion growth. Of the organisms testedP. nigricans gave the best results in controlling white rot infection.This work was carried out at the Department of Botany, The University, Birmingham, England. I wish to thank Prof.C. J. Hickman for his invaluable advice and encouragement.     

Microconidia germination of the tomato pathogen Fusarium oxysporum in the presence of root exudates

Abstract

In this study we assessed microconidia germination of the tomato pathogens F. oxysporum f. sp. lycopersici (Fol) and F. oxysporum f. sp. radicis-lycopersici (Forl) in the presence of root exudates. Tomato root exudates stimulated microconidia germination and the level of stimulation was affected by plant age. Treatment of root exudates with insoluble polyvinylpolypyrrolidone, which binds phenolic compounds, indicated that tomato root exudates contain phenolic compounds inhibitory to F. oxysporum microconidia germination. Our study indicates that tomato root exudates similarly stimulate microconidia germination of both Fol and Forl. However, individual F. oxysporum strains differ in the degree of germination response to the root exudates. Furthermore, root exudates from non-host plants also contain compounds that stimulate microconidia germination of Fol. In general, the effects of root exudates from non-host plants did not differ considerably from those of tomato. The ability of phenolic compounds to inhibit germination of Fol seems not to be plant-specific.     

The effect of species of Allium on soil bacteria in relation to germination of sclerotia of Sclerotium cepivorum Berk

Extracts made from Allium species were shown to exhibit marked antibiotic properties in a variety of tests. However, no evidence was obtained to suggest that intact Allium seedlings exude antibiotic compounds in sufficient quantity to cause inhibition of bacteria in the soil or in assay tests in the laboratory. Germination of sclerotia of Sclerotium cepivorum was induced by Allium extracts which were too dilute to cause antibiotic responses in laboratory tests using a number of bacteria. Synthetic methyl-methanethiolsulphinate had little effect on germination of sclerotia. The specific reversal, by Allium species and their extracts, of the mycostatic effect of unsterile soil on sclerotia of S. cepivorum does not appear to be due to antibiotic effects.     

Germination of sclerotia of Sclerotium cepivorum Berk. under aseptic conditions

The response of sclerotia of Sclerotium cepivorum to a number of plant extracts and nutrient solutions was tested, aseptically, on agars, silica gels, filter paper discs, and on columns of soil. There was no specific response of sclerotia to extracts of Allium species in any of these experiments, whereas in unsterile soil consistently high levels of germination were obtained only with Allium extracts. It was shown that sclerotia are subject to the mycostatic influence of unsterile soil. With S. cepivorum soil mycostasis appears to be specifically reversed by Allium species or by water extracts made from them.     

A NEW FUNGUS ON CYPERUS IRIA

Thind , K. S., and G. S. Rawla . (Panjab U., Chandigarh, India.) A new fungus on Cyperus iria. Amer. Jour. Bot. 48(10): 859–862. Illus. 1961—Duosporium cyperi gen. et sp. nov., collected on Cyperus iria Linn., is characterized by the production of 2 types of conidia, macroconidia and microconidia. The macroconidia are straight, cylindrical, triseptate, with their middle cells dark brown, long, thick-walled, and end cells much paler or subhyaline, short, thin-walled, the middle and the end cells being equally wide. The microconidia are nonseptate, spherical, dark brown, prominently verrucose, and produced apically on the conidiophores like the macroconidia; occasionally also formed as secondary conidia on germinating 3-septate macroconidia in culture. The formation of 2 distinct types of conidia in Duosporium and the features of its macroconidia characteristically differentiate it from its close relative Helminthosporium, although Duosporium. cyperi is not unique among fungi in producing 2 types of conidia.     

Survival of Sclerotium cepivorum Sclerotia and Fusarium oxysporum Chlamydospores in Soil Amended with Cruciferous Residues

The use of cruciferous plant residues to reduce the amount of sclerotia of Sclerotium cepivorum and chlamydospores of Fusarium oxysporum f. sp. lycopersici in soil was investigated. Air‐dried and crushed mustard (Brassica juncea) added to the soil effectively reduced the viability of fungal propagules. Consequently, the reduction of white rot of onion, caused by S. cepivorum and wild of tomato caused by F. oxysporum was observed. The addition of rapeseed (Brassica. napus cv. Bolko and B. napus cv. Gorczanski) residues to soil also resulted in a significant decrease of number of S. cepivorum sclerotia but the effect on F. oxysporum chlamydospores was variable. Introduction of the plant material increased the total number of bacteria, spore‐forming bacteria, fluorescent pseudomonads, actinomycetes, and fungi in soil. One year after the soil amendment, the amount of sporeforming bacteria in treatments with cruciferous residues was higher as compared to the control soil without plant residues. The possible contribution of the decomposition of plant residues and soil micro‐organisms to the reduction of the pathogens population is discussed.     

Redheadia quercus gen. et sp. nov., the teleomorph of Mycopappus quercus, the frosty mildew fungus in Quercus acutissima

The teleomorph of Mycopappus quercus causing frosty mildew in Quercus acutissima is described as a new genus and species, Redheadia quercus, in the Sclerotiniaceae. Apothecia sprout from sclerotia on the fallen infected leaves kept for 10 months at 5°C and subsequent incubation at 15°C under diffused room light. Typical zonate lesions and multicellular propagules of M. quercus are produced on Q. acutissima, by mycelial inoculation using an isolate from a single ascospore, confirming the teleomorph–anamorphic connection. No significant differences are observed between cultured colonies of isolates from the ascospore and those from the propagule. Sclerotia and microconidia of the fungus are produced on culture media.     

Environmental factors and growth of Histoplasma capsulatum in soil

Summary Environmental factors influencing the growth ofHistoplasma capsulatum in soil have been studied. The role of temperature and moisture in the growth of the fungus was found to be critical. The fungus can tolerate very low temperatures, if the soil moisture content is high, but cannot withstand temperatures of 40° C or above for an extended period.Dry, sterile chicken manure and an extract of unsterile chicken manure showed an inhibitory effect on the growth of the fungus. However, the relationship between bird manure andH. capsulatum has not been satisfactorily clarified.Morphological studies ofH. capsulatum in soil showed that the fungus grows within the upper two inches of the soil and a majority of sporulation occurs within the upper one-half inch of soil. Morphological studies of the fungus, in the presence of chicken manure and chicken manure extract, showed an increased number of macroconidia and microconidia and decreased mycelial production.The growth ofH. capsulatum in soil is markedly affected by soil pH above 10 and below 5. No growth was observed on soil cultures outside these values. There was no definite pH range within these values in which the fungus grew more abundantly.     

Variability in Indian Isolates of Arthrobotrys dactyloides Drechsler: A Nematode-Trapping Fungus

Five isolates of Arthrobotrys dactyloides (A, B, C, D, and E) were isolated from different locations of India. Their variability in relation to morphology, radial growth, and nematode capturing or trap-forming ability was observed. All of the five isolates produced two-celled slender conidia, whereas wider two- and three-celled conidia were produced by isolates A, C, D, and E only. The wider two- and three-celled conidia were not observed in cultures of isolate B. The isolate B produced macroconidia as well as microconidia. The microconidia were produced on separate conidiophores of smaller size. Macroconidia and microconidia were never produced on the same conidiophore, but the two types of conidiophores were produced on same or different hyphae. Similar to macroconidia, the microconidia also produced constricting rings of smaller size in presence of Meloidogyne graminicola. The constricting rings formed on microconidia did not capture second-stage juveniles of M. graminicola because of their smaller size. Among all the isolates, isolate B showed slow growth and higher nematode-capturing ability or trap-forming ability.     

Aloe-emodin-mediated antimicrobial photodynamic therapy against dermatophytosis caused by Trichophyton rubrum

Trichophyton rubrum is responsible for the majority of dermatophytosis. Current systemic and topical antifungals against dermatophytosis are often tedious and sometimes unsatisfactory. Antimicrobial photodynamic therapy (aPDT) is a non-invasive alternative suitable for the treatment of superficial fungal infections. This work investigated the photodynamic inactivation efficacy and effects of aloe-emodin (AE), a natural photosensitizer (PS) against T. rubrum microconidia in vitro, and evaluated the treatment effects of AE-mediated aPDT for T. rubrum-caused tinea corporis in vivo and tinea unguium ex vivo. The photodynamic antimicrobial efficacy of AE on T. rubrum microconidia was evaluated by MTT assay. The inhibition effect of AE-mediated aPDT on growth of T. rubrum was studied. Intracellular location of AE, damage induced by AE-mediated aPDT on cellular structure and surface of microconidia and generation of intracellular ROS were investigated by microscopy and flow cytometry. The therapeutic effects of AE-mediated aPDT against dermatophytosis were assessed in T. rubrum-caused tinea corporis guinea pig model and tinea unguium ex vivo model. AE-mediated aPDT effectively inactivated T. rubrum microconidia in a light energy dose-dependent manner and exhibited strong inhibitory effect on growth of T. rubrum. Microscope images indicated that AE is mainly targeted to the organelles and caused damage to the cytoplasm of microconidia after irradiation through generation of abundant intracellular ROS. AE-mediated aPDT demonstrated effective therapeutic effects for T. rubrum-caused tinea corporis on guinea pig model and tinea unguium in ex vivo model. The results obtained suggest that AE is a potential PS for the photodynamic treatment of dermatophytosis caused by T. rubrum, but its permeability in skin and nails needs to be improved.     

Biological control of Fusarium wilt of tomato with <Emphasis Type="Italic">Fusarium equiseti</Emphasis> GF191 in both rock wool and soil systems

The plant growth-promoting fungus (PGPF) Fusarium equiseti GF191 was tested for its ability to control Fusarium wilt of tomato (FWT) caused by Fusarium oxysporum f. sp. lycopersici (FOL) in both a hydroponic rock wool and soil system. F. equiseti effectively controlled FWT, with protective effects based on disease severity of 66.7–88.6% in four experiments. The numbers of colony-forming units of FOL per gram fresh weight of stems were significantly reduced (P < 0.05) in plants treated with F. equiseti. Stem extracts from F. equiseti-treated and pathogen-challenged plants significantly inhibited the germination and germ-tube length of FOL microconidia and the production of FOL budding-cells. Tomatine content in tomato stems treated with F. equiseti was significantly increased compared with the non-treated control.     

Biocontrol of onion white rot by application of Trichoderma species formulated on wheat bran powder

In vitro, Trichoderma album, Trichoderma harzianum, Trichoderma koningii, Trichoderma viride and Trichoderma virens showed antagonistic effect against the most pathogenic isolate (Sc2) of Sclerotium cepivorum, the cause of onion white rot disease. Five Trichoderma preparations of each Trichoderma sp. were prepared on wheat bran powder to be used for controlling white rot disease of onion. Greenhouse and field experiments followed the same trend where T. harzianum and T. koningii were the most effective in reducing the incidence and severity of white rot disease compared with the control. Trichoderma species preparations caused promotion to vegetative parameters of onion plants in pots and increase bulb productivity in filed. In this regard, T. harzianum and T. koningii were the most effective. A positive correlation was found between the biocontrol activity of Trichoderma species preparations and enhancement of peroxidase, polyphenoloxidase and chitinase enzymes in onion plants to resist infection with S. cepivorum.     

Effect of flavonoids on the development of Fusarium oxysporum f. sp. lycopersici

Abstract

In the present study the effect of flavonoid compounds on the germination and fungal growth of the soil-borne tomato pathogen Fusarium oxysporum f. sp. lycopersici was studied. Out of 12 flavonoid compounds only myricetin and luteolin exhibited a low stimulating activity on microconidia germination of Fusarium oxysporum f. sp. lycopersici, whereas the other flavonoids tested were inactive when applied at five different concentrations. In our study the tested flavonoids affect fungal growth differently to microconidia germination. Individual flavonoid concentrations resulted in a small increase of fungal growth, but the lowest flavonoid concentrations showed an inhibiting effect on fungal growth for all flavonoids tested. There is evidence to suggest, that low flavonoid concentrations exhibit slight antimicrobial properties against Fusarium oxysporum f. sp. lycopersici.     

Fungi isolated from Sclerotia ofSclerotium cepivorum and from soil and their effects upon the pathogen

Summary Data are presented on the antagonistic effects of the fungi isolated from sclerotia ofSclerotium cepivorum and from nonrhizosphere soil taken from around the roots of infected onions upon mycelial growth and sclerotial germination ofS. cepivorum. Most of the isolated fungi especiallyPenicillium species were antagonistic to mycelial growth. Sclerotial germination was slightly inhibited by diffusates of these fungal isolates. Testing the antifungal effect of someAllium extracts against the fungal isolates by the inhibition zone method showed that garlic extract has the greatest antifungal effects and onion extract is the least potent. However, spore germination tests indicated that onion extract completely inhibits the spore germination of all test fungi. The role of host-plant extracts in stimulating sclerotial germination is discussed.     

Production of Microconidia by Cercospora henningsii Allesch, Cause of Brown Leaf Spot of Cassava (Manihot esculenta Crantz) and Tree Cassava (Manihot glaziovii Muell.-Arg.)

Sporulation ofCercospora henningsii Allesch has been examinedunder various relative humidities, and in the presence of freewater in lesions on leaves of cassava and tree cassava. Matureconidia of the fungus on both cassava and tree cassava do notgerminate in lesions but accumulate, and under the optimum conditionsof 25–32 °C and in the presence of free water, theybud and fragment into numerous microconidia. Microconidia arecylindrical, mostly one-celled, and measure 7.5–17.5x3.7–7.5µm. Production of microconidia significantly decreasesas relative humidity decreases. Microconidia readily germinateby means of a germ tube at 100% relative humidity on both surfacesof host leaf and on glass slides. Some germ tubes form appressoriaand symptoms appear on cassava leaves inoculated with microconidia.The results are discussed in relation to possible modes of dispersalof the spores and control of the disease. Free water; sporulation; budding; microconidia