Septoria Leaf Speck, a New Disease of Sunflower, Caused by Septoria helianthina sp. nov.

Many strains of a pathogenic fungus were isolated from diseased sunflower leaf tissue. According to their characteristics they belonged to the genus Septoria . Leaf speck symptoms, characteristic for spontaneous infection, were also reproduced by artificial inoculation of sunflower plants in the greenhouse.
Comparing the morphological, cultural and pathogenic properties of the isolated fungus with other sunflower pathogens, it was indicated that the strains, originating from diseased sunflower leaves represented a new, so far not described species. Therefore, for the causal agent of this disease, the name Septoria helianthina Petrov & Arsenijevic was suggested.     

环境因子对一种病原真菌(Amoeboaphelidium sp.)感染微藻细胞能力的影响

油球藻(Graesiella sp.WBG-1)是一株适合于开放池规模化培养的产油微藻,在室外规模培养过程中常因一种病原真菌(Amoeboaphelidium sp.)的污染严重影响其生长和油脂积累,甚至导致培养失败。本文利用MTT染色法借助光学显微镜对被病原真菌感染的油球藻细胞计数并统计感染率,设置不同温度、光照强度、p H以及通气量等培养条件,研究环境因子对病原真菌感染能力的影响。结果表明:MTT染色法简单易行,可用于油球藻规模培养中病原真菌的检测;温度、光照强度、通气量和p H值均能够显著影响病原真菌的感染能力,高温、高光照强度、弱酸性环境和藻液静止等培养条件不利于病原真菌对油球藻的感染;在温度30℃、光强140μmol·m~(-2)·s~(-1)、通气量1.0 L·min~(-1)和p H 9.0±0.5的培养条件下成功建立了病原真菌感染油球藻的连续传代培养。本研究在实验室内模拟油球藻规模培养中被病原真菌感染的全过程,为深入研究该病原真菌对微藻细胞的感染行为及其感染机制提供了平台。     

Two linear plasmids in mitochondria of Fusarium solani f. sp. cucurbitae

Two linear plasmid-like DNAs designated pFSC1 (9.2 kbp) and pFSC2 (8.3 kbp) were found in an isolate of the plant pathogenic fungus Fusarium solani f. sp. cucurbitae race 1. The plasmids were maternally inherited and copurified with mitochondrial DNA obtained from a mitochondria-enriched cell fraction suggesting that they are located in mitochondria. The plasmids did not share extensive sequence similarity. No homology was detected between either plasmid and the nuclear or mitochondrial genome when cloned plasmids were used as probes in Southern hybridization analyses. The fungus was cured of plasmids by ethidium bromide treatment. Compared to the plasmid-containing isolate, plasmid-cured derivatives had reduced pathogenicity on a susceptible plant host, Cucurbita maxima "Pink Banana."     

Ustilago maydis, the delightful blight.

Recent studies of the corn smut fungus life cycle and its regulation by two mating type loci and other genes provide a cornucopia of challenges in cell biology, genetics and protein structure. The fungus can exist in two states: nonpathogenic and pathogenic. The change from one state to the other is accompanied by a change in morphology (yeast-like to filamentous) and growth properties (saprophytic to parasitic).     

Analysis of Genetic Diversity of Fusarium oxysporum f. sp. phaseoli Isolates, Pathogenic and Non-pathogenic to Common Bean (Phaseolus vulgaris L.)

Twenty isolates of Fusarium oxysporum from Brazil, pathogenic and non‐pathogenic to common bean, were analysed using random amplified polymorphic DNA (RAPDs) to study the genetic diversity. RAPD analysis using 23 oligonucleotides resulted in the amplification of 229 polymorphic and 7 monomorphic DNA fragments ranging from 234 to 2590 bp. High genetic variability was observed among the isolates, with the distances varying between 8% and 76% among pathogenic, 2% and 63% among the non‐pathogenic and 45% and 76% between pathogenic and non‐pathogenic isolates. The analysis of genetic distance data showed that the pathogenic isolates tended to group in one group and the non‐pathogenic in another. The genetic distance values of 30% among the pathogenic isolates in cluster A are compatible with the genetic distance values observed within the physiological races, but the distance values among the pathogenic isolates in clusters B and G are not compatible with the distance values observed within the race. Although our results are preliminary, it was not possible to exclude the existence of more than one race of this fungus in Brazil.     

Interactions between clay minerals and siderophores affect the respiration of Histoplasma capsulatum.

The reduction in the respiration of Histoplasma capsulatum in broth culture caused by montmorillonite appeared to be the result, in part, of the interference by the clay with the iron nutrition of the fungus. This interference was apparently the result of the adsorption by the clay of the iron-transporting siderophore (deferricoprogen B) produced by the fungus, as the reduction in respiration was partially alleviated by the addition of foreign siderophores. Neither kaolinite nor attapulgite (palygorskite) appeared to adsorb significant amounts of the siderophores, probably because of the low cation exchange capacity and specific surface area of kaolinite and the inaccessibility of adsorption sites in the fibrous attapulgite. These observations, in addition to the adhesion of montmorillonite to the hyphae, suggest mechanisms that may explain the discrete geographic distribution of this fungus, which is pathogenic to humans and which has been isolated essentially only from soils that do not contain montmorillonite.     

An inhibitor-resistant histone deacetylase in the plant pathogenic fungus Cochliobolus carbonum.

We have partially purified and characterized histone deacetylases of the plant pathogenic fungus Cochliobolus carbonum. Depending on growth conditions, this fungus produces HC-toxin, a specific histone deacetylase inhibitor. Purified enzymes were analyzed by immunoblotting, by immunoprecipitation, and for toxin sensitivity. The results demonstrate the existence of at least two distinct histone deacetylase activities. A high molecular weight complex (430,000) is sensitive to HC-toxin and trichostatin A and shows immunoreactivity with an antibody against Cochliobolus HDC2, an enzyme homologous to yeast RPD3. The second activity, a 60,000 molecular weight protein, which is resistant even to high concentrations of well-known deacetylase inhibitors, such as HC-toxin and trichostatin A, is not recognized by antibodies against Cochliobolus HDC1 (homologous to yeast HOS2) or HDC2 and represents a different and/or modified histone deacetylase which is enzymatically active in its monomeric form. This enzyme activity is not present in the related filamentous fungus Aspergillus nidulans. Furthermore, in vivo treatment of Cochliobolus mycelia with trichostatin A and analysis of HDACs during the transition from non-toxin-producing to toxin-producing stages support an HC-toxin-dependent enzyme activity profile.     

In planta production of indole-3-acetic acid by Colletotrichum gloeosporioides f. sp. aeschynomene

The plant pathogenic fungus Colletotrichum gloeosporioides f. sp. aeschynomene utilizes external tryptophan to produce indole-3-acetic acid (IAA) through the intermediate indole-3-acetamide (IAM). We studied the effects of tryptophan, IAA, and IAM on IAA biosynthesis in fungal axenic cultures and on in planta IAA production by the fungus. IAA biosynthesis was strictly dependent on external tryptophan and was enhanced by tryptophan and IAM. The fungus produced IAM and IAA in planta during the biotrophic and necrotrophic phases of infection. The amounts of IAA produced per fungal biomass were highest during the biotrophic phase. IAA production by this plant pathogen might be important during early stages of plant colonization.     

Production of phleichrome by Cladosporium phlei as stimulated by diketopiperadines of Epichloe typhina

Epichloe typhina is an endophytic fungus, while Cladosporium phlei is a pathogenic fungus of the timothy plant (Phleum pretense L.). We found two activities in the culture filtrate of E. typhina: one stimulated the pathogenic fungus, C. phlei, to produce phleichrome and the other inhibited its growth. The active ingredients that stimulated the production of phleichrome and inhibited the growth of C. phlei were isolated and characterized. The isolated compounds were identified as cyclo-(L-Pro-L-Leu) and cyclo-(L-Pro-L-Phe), which were stimulatory compounds, and p-hydroxybenzaldehyde, which was the growth inhibitory compound, based on an analysis of their spectral data. Of the two stimulatory compounds, cyclo-(L-Pro-L-Phe) showed higher activity. However, when 500 microg of cyclo-(L-Pro-L-Phe) was spotted on the TLC plate for bio-autography, a growth inhibitory zone was identified in the central red region, which contained phleichrome. On the other hand, phleichrome showed antifungal activity against E. typhina in the light, so it is assumed that there might be antagonism between the endophytic fungus, E. typhina, and the pathogenic fungus, C. phlei.     

籽用美洲南瓜叶片对白粉病菌的抗逆生理响应

以籽用美洲南瓜(Cucurbita pepo L.)白粉病抗病品系F2和感病品系M3为试材,在人工气候箱内接种白粉病生理小种2US孢子悬浮液,考察在接种白粉病菌后南瓜幼苗植株与白粉病菌的互作、叶片活性氧代谢及保护酶活性的变化,探讨南瓜抵御白粉病的生理机制。结果表明：(1)与感病品系M3相比,接种白粉病菌后,抗病品系F2叶片上病原菌发育缓慢,较难侵染叶片。(2)抗病品系F2在感病初期叶片H₂O₂、O₂^-·含量迅速升高后逐渐下降,而感病品系在感病初期H₂O₂、O₂^-·含量上升缓慢,在达最大值后始终保持较高水平,且感病品系叶片MDA含量始终高于抗病品系;组织化学染色分析发现,抗病品系叶片着色比感病品系快,之后着色面积有所减少并趋于较低水平。(3)抗病品系F2和感病品系M3叶片抗氧化酶CAT、SOD、POD活性及PAL、PPO活性在接种白粉病菌后均显著增加,但抗病品系的活性及其增幅均高于感病品系。研究发现,籽用美洲南瓜抗病品系叶片上白粉病菌发育缓慢,较难受到侵染,生成菌丝体后叶片上粉状斑点较小;抗病品系在被白粉病菌侵染初期依靠活性氧的增加抵御病原菌的入侵,随着活性氧含量增加抗病品系通过迅速增加自身抗氧化酶活性来防止氧化胁迫;与感病品系相比,抗病品系在受病原菌侵染后能迅速增加PAL、PPO活性以抵御病原菌侵染。     

In Planta Production of Indole-3-Acetic Acid by Colletotrichum gloeosporioides f. sp. aeschynomene

The plant pathogenic fungus Colletotrichum gloeosporioides f. sp. aeschynomene utilizes external tryptophan to produce indole-3-acetic acid (IAA) through the intermediate indole-3-acetamide (IAM). We studied the effects of tryptophan, IAA, and IAM on IAA biosynthesis in fungal axenic cultures and on in planta IAA production by the fungus. IAA biosynthesis was strictly dependent on external tryptophan and was enhanced by tryptophan and IAM. The fungus produced IAM and IAA in planta during the biotrophic and necrotrophic phases of infection. The amounts of IAA produced per fungal biomass were highest during the biotrophic phase. IAA production by this plant pathogen might be important during early stages of plant colonization.     

The effects of insect pathogenic soil fungi and ectomycorrhizal inoculation of birch seedlings on the survival of Otiorhynchus larvae

• 1 Weevil larvae of the genus Otiorhynchus are a serious problem in agriculture and forestry, causing damage to a wide range of plant species, primarily by larval feeding on roots. Otiorhynchus larvae are a serious pest in forest plantations in Iceland, causing 10–20% mortality of newly‐planted seedlings.
• 2 We studied the effects of soil fungi on the survival of Otiorhynchus sulcatus larvae. The larvae were introduced into pots with birch seedlings grown in: (i) nursery peat; (ii) nursery peat inoculated with three different species of ectomycorrhizal fungi; (iii) nursery peat inoculated with insect pathogenic fungi; (iv) nursery peat inoculated with ectomycorrhizal fungi and insect pathogenic fungi; and (v) nursery peat inoculated with natural forest soil from Icelandic birch woodland.
• 3 Larval survival was negatively affected by inoculation of: (i) the ectomycorrhizal fungus Laccaria laccata; (ii) the ectomycorrhizal fungus Cenococcum geophylum; (iii) the insect pathogenic fungus Metarhizium anisopliae; and (iv) forest soil. Inoculation with the ectomycorrhizal fungus Phialophora finlandia did not have any significant effect on larval survival. No significant synergistic effect was found between insect pathogenic and ectomycorrhizal fungi.
• 4 It is concluded that ectomycorrhizal and insect pathogenic fungi have a significant potential in biological control of Otiorhynchus larvae in afforestation areas in Iceland. Further studies are needed to establish the effect of these fungi in the field and to analyse how mycorrhizal fungi affect root‐feeding larvae.

     

Differential expression of genes involved in entomopathogenicity of the fungi Metarhizium anisopliae var. anisopliae and M. anisopliae var. acridum (Clavicipitaceae)

Expression analysis of the genes involved in germination, conidiogenisis and pathogenesis of Metarhizium anisopliae during its saprophytic and pathogenic life stages can help plan strategies to increase its efficacy as a biological control agent. We quantified relative expression levels of the nitrogen response regulator gene (nrr1) and a G-protein regulator of genes involved in conidiogenesis (cag8), using an RT-qPCR assay. Comparisons were made between M. anisopliae var. anisopliae and M. anisopliae var. acridum during germination and conidiogenesis and at different stages of pathogenesis. The cag8 gene was repressed during germination and induced during conidial development and the pathogenic phase, and the nrr1 gene was induced during germination, conidiogenesis and the pathogenic phase. Both genes were more expressed in M. anisopliae var. anisopliae, demonstrating that different varieties of M. anisopliae differ in activation of genes linked to virulence for certain environments and hosts. This suggests that differences among these varieties in the ability to adapt could be attributed not only to specific genomic regions and genes, but also to differential gene expression in this fungus, modulating its ability to respond to environmental stimuli.     

Apical meristems of tomato roots and their modifications induced by arbuscular mycorrhizal and soilborne pathogenic fungi

Functional morphological patterns in root apices of tomato ( Lycopersicon esculentum ) dependent on growth, ageing and infection by the arbuscular mycorrhizal (AM) fungus Glomus mosseae and/or by the soilborne pathogenic fungus Phytophthora nicotianae var parasitica ( P. parasitica ) were studied. Uninfected root apices were characterized by closed, tri-layered meristems with nonreticulate nuclei; however, some apices of each treatment lost their meristematic nature, stopped growing and differentiated, becoming 'parenchymatized'. The pathogenic fungus reduced the apex diameter and the number of mitotically active and viable apices inducing plasmolysis, cell and nucleus degeneration, and necrosis. The AM fungus, on the other hand, produced an increase in apex size and reduced the percentage of necrosis both in uninfected roots and in roots infected by P. parasitica . Thus, the AM fungus protected the apices from the pathogenic infection, allowing normal root growth. Furthermore, larger apices, which produce thicker roots, might indirectly contribute to plant protection. Increased volumes of colonizable tissues favour the spreading of the symbiont, and P. parasitica hyphae are always excluded from arbuscule-containing cells.     

Cell-cell recognition of host surfaces by pathogens. The adsorption of maize (Zea mays) root mucilage by surfaces of pathogenic fungi.

The adsorption of radioactive mucilage by pathogenic fungi was shown to be dependent upon time, the composition of mucilage, the type of fungal surface (conidia, hyphae, hyphal apices), fungal species, pH and bivalent cations. All fungal adhesins were inactivated by either proteinase or polysaccharase treatments. Adsorption was not inhibited by the numberous mono-, di- and oligo-saccharides that were tested individually, but it was inhibited absolutely by several polysaccharides. This suggested that adsorption of mucilage by pathogens involved conformational and ionic interactions between plant and fungal polymers but not fungal lectins bound to sugar residues of mucilage. Several fractionation schemes showed that pathogens bound only the most acidic of the variety of polymers that comprise mucilage. There was not any absolute distinction between ability to bind radioactive mucilage and type of pathogen or non-pathogen. However, there were notable differences in characteristics of adsorption between two types of pathogen. Differences were revealed by comparison of the adsorption capacities of conidia and germinant conidia and chromatography of radioactive mucilage on germinant conidia. An ectotrophic root-infecting fungus (a highly specialized pathogen) bound a greater proportion of mucilage than did a vascular-wilt fungus (of catholic host and tissue range) with more than one class of site for adsorption. In contrast with the vascular-wilt fungus, sites for adsorption on the specialized pathogen were present solely on surfaces formed by germination.     

Reaction of soybean callus to culture filtrates of Phialophora gregata

Soybean [Glycine max (L.) Merr.] calli derived from susceptible and resistant soybean genotypes were exposed to the culture filtrates of pathogenic and non-pathogenic isolates of Phialophora gregata (Allington and Chamberlain) W. Gams. The rate of browning, growth and viability (measured by 2,3,5-triphenyltetrazolium chloride reduction) of the callus were determined after various exposure times to the fungus culture filtrates. Callus from susceptible Century, Cumberland, Corsoy 79, Harosoy and Clark 63 were sensitive to the culture filtrates of pathogenic isolates of P. gregata. Callus from Plant Introductions 437833 and 84946-2, when treated with fungal culture filtrates, did not develop browning and callus growth and cell viability were not decreased compared to untreated controls. Culture filtrates from non-pathogenic isolates of the fungus did not affect the growth of susceptible and resistant callus. Tobacco (Nicotiana tabacum L.) callus was not sensitive to the culture filtrate of a P. gregata isolate pathogenic to soybean. The fungal culture filtrate, based on limited evaluation, appears to be selective towards soybean callus. Based on this initial work, it appears that soybean callus bioassays have utility for evaluating soybean for resistance to P. gregata as well as assessing pathogenicity of fungus isolates.     

Sphaeropsidins D and E, two other pimarane diterpenes, produced in vitro by the plant pathogenic fungus Sphaeropsis sapinea f. sp. cupressi

Two pimarane diterpenes structurally related to sphaeropsidins were isolated from the liquid culture of Sphaeropsis sapinea f. sp. cupressi, a plant pathogenic fungus causing a form of canker disease of Italian cypress (Cupressus sempervirens L.). The two metabolites, characterised by spectroscopic methods, were named sphaeropsidins D (0.40 mg l(-1)) and E (0.16 mg l(-1)). The same fungus produced sphaeropsidins A, B and C, sphaeropsidone and episphaeropsidone, which proved to be phytotoxic to cypress, and chlorosphaeropsidone and epichlorosphaeropsidone showing no phytotoxicity. Sphaeropsidin D assayed at 0.1 mg ml(-1) on severed cypress twigs caused leaf browning and necrosis on Cupressus macrocarpa, but no symptoms were observed on C. sempervirens and C. arizonica. Symptoms appeared in a period of time (6 days after toxin-treatment) shorter than that for sphaeropsidin A. Sphaeropsidin E assayed at 0.2 mg ml(-1) did not produce any symptom on the same cypress species tested with sphaeropsidin D.     

Detoxification of terpinolene by plant pathogenic fungus Botrytis cinerea

Detoxification of an antifungal monoterpene terpinolene (1) by the plant pathogenic fungus Botrytis cinerea afforded hydroxlyated metabolites 2,3-dihydro-3beta,6beta-dihydroxy-terpinolene (2) (39%) and 2,3-dihydro-1alpha,3alpha-dihydroxy-terpinolene (3) (20%), respectively. Terpinolene showed good levels of antifungal activity while both the metabolites were inactive against another plant pathogenic fungus Cladosporium herbarun.     

银杏内生真菌No.1028的培养条件及其代谢产物对作物真菌病害的抑制作用

通过大量筛选从银杏茎中分离到一株内生真菌(编号为No.1028),其代谢产物对重要作物真菌病害病原菌具有明显的抑制作用。结果表明:离体条件下内生真菌发酵液对番茄早疫病菌、黄瓜枯萎病菌、菜豆炭疽病菌、葡萄炭疽病菌、水稻纹枯病菌、黄瓜立枯病菌均有较强的抑制作用,对上述不同病原菌的抑制率分别为:66.7%、48.3%、64.6%、36.5%、57.1%和23%。同时也研究了不同碳源、氮源、无机离子对内生真菌No.1028生物学特性和生长的影响。结果发现玉米粉、黄豆饼粉比较适合其生长和抑菌代谢产物的合成,Na+对抑菌代谢产物的合成有较明显的促进作用。     

Specific interactions between arbuscular mycorrhizal fungi and plant growth-promoting bacteria: as revealed by different combinations

The interactions between two plant growth-promoting rhizobacteria (PGPR, Pseudomonas fluorescens SBW25 and Paenibacillus brasilensis PB177), two arbuscular mycorrhizal (AM) fungi (Glomus mosseae and Glomus intraradices) and one pathogenic fungus (Microdochium nivale) were investigated on winter wheat (Triticum aestivum cultivar Tarso) in a greenhouse trial. PB177, but not SBW25, had strong inhibitory effects on M. nivale in dual culture plate assays. The results from the greenhouse experiment show very specific interactions; for example, the two AM fungi react differently when interacting with the same bacteria on plants. Glomus intraradices (single inoculation or together with SBW25) increased plant dry weight on M. nivale-infested plants, suggesting that the pathogenic fungus is counteracted by G. intraradices, but PB177 inhibited this positive effect. This is an example of two completely different reactions between the same AM fungus and two species of bacteria, previously known to enhance plant growth and inhibit pathogens. When searching for plant growth-promoting microorganisms, it is therefore important to test for the most suitable combination of plant, bacteria and fungi in order to achieve satisfactory plant growth benefits.