Effect of dsRNA-containing and dsRNA-free hypovirulent isolates of Fusarium oxysporum on severity of Fusarium seedling disease of soybean in naturally infested soil

In the sandy soils of eastern Virginia, soybean seedlings are colonized by hypovirulent and virulent isolates of Fusarium oxysporum and F. solani. Our objectives were to determine if prior inoculation of soybean seeds with hypovirulent F. oxysporum isolates reduced severity of seedling disease in naturally infested soil, and to determine if there was an association between the presence of dsRNA mycovirus and hypovirulence in isolates of F. oxysporum and F. solani from soybean plants. The presence of dsRNA was not associated with hypovirulence in F. oxysporum since some hypovirulent isolates contained dsRNA while other hypovirulent isolates did not. Furthermore, of six dsRNA-containing F. oxysporum isolates, three were hypovirulent and three were virulent. Four segments of dsRNA, with sizes of 4.0, 3.1, 2.7 and 2.2 kb were detected in extracts of all six F. oxysporum isolates. No hypovirulent or dsRNA-containing of F. solani isolates were found. Prior inoculation of cv. Essex soybean seeds with conidia of dsRNA-free hypovirulent F. oxysporum isolates significantly (P < 0.05) reduced disease severity on cotyledons and hypocotyls, and increased the rate of seedling emergence in field soil, compared to control plants. No significant (P > 0.05) differences were found between dsRNA-containing and dsRNA-free hypovirulent F. oxysporum isolates in their effects on reducing disease severity. Hypovirulent isolates that colonize soybean tissues may play a role in reducing Fusarium seedling disease of soybean in natural soils.     

香蕉上的镰孢菌种类及其系统发育关系(英文)

镰孢菌属真菌是香蕉上的重要病原菌,主要引起香蕉枯萎病以及香蕉冠腐病,在我国已明确引起香蕉枯萎病的病原为尖孢镰孢古巴专化型 Fusarium oxysporum f. sp. cubense(FOC)1号和4号生理小种,但是引起香蕉冠腐病的镰孢菌种类还未明确。为了解香蕉上镰孢菌在种间及种内水平上的多样性,2008–2011 年间作者从华南地区不同的水果市场及香蕉果园采集香蕉样品90份,分离得到143株镰孢菌。通过形态学观察及基于 EF-1α基因的系统进化分析鉴定出10种镰孢菌,即F. oxysporum、F. solani、F. camptoceras、F. pallidoroseum、F. stiloides、F. chlamydosporum、F.verticillioides、F. proliferatum、F. concentricum、F. sacchari,以及藤仓赤霉复合种(Gibberella fujikuroi species complex,GFC)中 3 个未定名的类群。轮纹镰孢 F. concentricum 及甘蔗镰孢 F.sacchari 是香蕉果实中最常见种,前菌为我国首次报道,后菌是首次报道与香蕉有关。对从香蕉上分离的藤仓赤霉复合种(GFC)及尖孢镰孢复合种(FOSC)的EF-1α序列进行了系统发育分析,其GFC中的27个菌株组成的单系群可分为7个不同的亚群,分别为 F.verticillioides、F. proliferatum、F. concentricum、F. sacchari 以及3个没有描述过的菌系 Fusarium sp. 1、Fusarium sp.2和 Fusarium sp.3;FOSC中的50个菌株形成2大分枝共12个谱系,分离自我国华南地区的21株尖孢镰孢形成7个谱系,其中 13株已知的香蕉枯萎病病原菌分布在3个谱系中,我国大陆的香蕉枯萎病病原菌菌株与来源于台湾地区及东南亚的菌株亲缘关系较近,FOC1号生理小种的遗传分化大于4号生理小种,FOC 1号生理小种与分离自香蕉果实上的尖孢镰孢菌的亲缘关系比与FOC 4号生理小种的亲缘关系更近。研究结果表明,我国香蕉上存在着丰富的镰孢菌种类,而且种内遗传多样性丰富。     

我国部分地区蔬菜镰孢菌的分离及鉴定

对采自我国6省18市（县）的蔬菜根茎样本进行了组织分离和形态学鉴定,共鉴定出镰孢菌10个种.其中尖镰孢（Fusarium oxysporum）为优势茵,占镰孢菌总量的73.42％,其他种类的镰孢菌为锐顶镰孢(F.acuminatum)、弯角镰孢（F.camptoceras）、蓝色镰孢（F.coeruleunm）、木贼镰...     

Comparison of the hydrolysis of polyethylene terephthalate fibers by a hydrolase from Fusarium oxysporum LCH I and Fusarium solani f. sp. pisi

The hydrolysis of polyethylene terephthalate (PET) fibers by two fungal hydrolases was investigated. The hydrolase from a newly isolated Fusarium oxysporum strain (LCH 1) was more efficient in releasing terephthalic acid from PET fibers compared to the enzyme from F. solani f. sp. pisi DSM 62420 when equal amounts of p-nitrophenyl butyrate-hydrolyzing activity were employed. PET fabrics treated under the same conditions with the enzyme from F. oxysporum LCH 1 also showed a considerably higher increase in hydrophilicity compared to fabrics treated with the enzyme from F. solani f. sp. pisi DSM 62420.     

sti35, a stress-responsive gene in Fusarium spp.

A stress-induced mRNA was identified in the phytopathogenic fungus Fusarium oxysporum f. sp. cucumerinum. Treatment of the fungus with ethanol resulted in the induction of a major mRNA species encoding a protein of approximate Mr 37,000. A full-length cDNA clone of the induced message was obtained. RNA blot analysis indicated that the mRNA was induced by various other stresses, including treatment with copper(II) chloride and heat (37 degrees C). However, it was not greatly induced by treatment with phaseollinisoflavan, an antifungal isoflavonoid produced by Phaseolus vulgaris (French bean). In contrast, phaseollinisoflavan induced the homologous mRNA in the related bean pathogen Fusarium solani f. sp. phaseoli. A genomic clone of the F. solani f. sp. phaseoli gene was obtained, and both this and the cDNA clone from F. oxysporum f. sp. cucumerinum were sequenced. The latter indicated an open reading frame of 320 codons encoding a 34,556-dalton polypeptide. The corresponding reading frame in F. solani f. sp. phaseoli was 324 codons, 89% identical to the F. oxysporum f. sp. cucumerium sequence, and was interrupted by a short intron. The gene was designated sti35 (stress-inducible mRNA). Although computer homology searches were negative, the cloned gene was observed to cross-hybridize to DNAs of other filamentous fungi, Saccharomyces cerevisiae, and soybean. Thus, sti35 appears to be a common gene among a variety of eucaryotes.     

河北省苹果园根际土壤中疑似致病镰孢菌种类

为了解引起河北省苹果再植病害的病原菌,在河北省10个地区苹果园中采集土壤样品,在实验室进行病原菌的诱集分离培养,根据形态和分子特征对主要病原菌进行种类鉴定。结果表明,在分离得到的293株真菌中,有116株镰孢菌,为分离频率最高的真菌。在形态学鉴定的基础上,对供试镰孢菌进行了分子鉴定。在基于核糖体基因内转录间隔区（rDNA-ITS）序列与翻译延长因子1α（EF-1α）序列片段构建的系统发育树中,代表菌株分别与GenBank登记的所属菌株聚于同一群。研究结果明确了河北省苹果再植病害的疑似致病镰孢菌,包括：尖孢镰孢Fusarium oxysporum、木贼镰孢F. equiseti、锐顶镰孢F. acuminatum、层出镰孢F. proliferatum和茄腐镰孢F. solani。     

Induced Resistance in Cucumbers against Fusarium oxysporum f. sp. cucumerinum and Rhizoctonia solani AG2–2 by Infection of the Cotyledons

Localized infection in cucumber cotyledons with Colletotrichum lagenarium induced resistance against infection after challenge inoculation with Rhizoctonia solani AG2–2 and Fusarium oxysporum f. sp. cucumerinum in the roots. The plants were unprotected in soil that was infested heavily with R. solani or in contact with the mycelium, and induced resistance was not observed. Wounding of the root also negated the effect of induced resistance to F. oxysporum .     

三江平原地区大豆根腐病病株上镰孢菌的分离鉴定

为了明确引起三江平原地区大豆根腐病的镰孢菌(Fusarium)种类及优势种群,对该地区大豆根腐病样本进行了采集。通过组织分离和形态学鉴定,共鉴定出6种镰孢菌,分别为木贼镰孢(F.equiseti)、尖孢镰孢(F.oxysporum)、芬芳镰孢(F.redolens)、半裸镰孢(F.semitectum)、腐皮镰孢(F.solani)和拟轮枝镰孢(F.verticillioides)。其中尖孢镰孢(F.oxysporum)的分离频率最高,达16.67%。对6种镰孢菌的形态学特征进行了描述。     

两种秸秆醋液对尖孢镰刀菌和立枯丝核菌的抑菌作用

本研究以玉米秸秆醋液、水稻秸秆醋液为供试材料,研究不同稀释度的秸秆醋液对尖孢镰刀菌(Fusarium oxysporum)和立枯丝核菌(Rhizoctonia solani)的抑制作用,测定其可溶性蛋白和可溶性糖。结果表明,50倍稀释液对2种病原菌的抑制率为100%,即2种病原菌在50倍稀释处理的秸秆醋液中不能生长。玉米秸秆醋液对尖孢镰刀菌中可溶性蛋白的影响不显著,对立枯丝核菌中可溶性蛋白的影响表现为先升高后降低。水稻秸秆醋液对尖孢镰刀菌中可溶性蛋白的影响是先升高后降低,对立枯丝核菌中可溶性蛋白的影响是逐渐累积。高浓度的水稻秸秆醋液可提高2种菌体内可溶性糖含量,100倍稀释的玉米秸秆醋液可提高尖孢镰刀菌体内的可溶糖含量,玉米秸秆醋液对立枯丝核菌的可溶性糖含量基本不会产生影响。本研究为秸秆醋液在农业生产上的推广应用等提供科学依据。     

我国东北地区玉米穗腐镰孢菌的种类及其分离频率

从辽宁、吉林、黑龙江三省采集的43份玉米病穗上共分离获得327株镰孢菌,根据形态特征鉴定属于7个种,其分离频率分别为半裸镰孢菌(Fusarium semitecturrt)37.77%,尖孢镰孢菌(F.oxysporum)3.51%,拟轮枝镰孢菌(F.verticillioides)3.57%,克鲁克威尔镰孢菌(F.c...     

Morphological and Molecular Characterization of Fusarium solani Isolates

Fusarium solani is a species complex (FSSC) containing isolates that cause diseases in important crops such as root and fruit rot of Cucurbita spp., root and stem rot of pea, sudden death syndrome of soybean, foot rot of bean and dry rot of potato tubers during storage. Based on host range tests, F. solani were subdivided into different formae specialis (f. sp.) and varieties, while DNA sequences of 28S rDNA, internally transcribed spacers (ITS) rDNA and elongation factor (EF-1α) distinguished the ' F. solani complex' in 50 subspecific lineages. In this study we characterized, by cultural, morphological and molecular criteria, 34 isolates of F. solani obtained from potato, other crops and soil. The 34 isolates in the FSSC showed wide variability for their cultural, morphological and molecular traits. The wide variability observed with amplified fragment-length polymorphism (AFLP) and mini-microsatellite analyses is in agreement with the polymorphism observed, in a previous study, within FSSC. Nine of 34 isolates in the FSSC, classified as F. solani var. coeruleum , were morphologically distinguishable from the other F. solani isolates but they were distributed in different clusters; moreover, the nine isolates showed instability of the coeruleum pigmentation of the colonies, supporting the ambiguity of the taxa of this variety of F. solani. Using sequence data from ITS plus 5.8S rDNA region, the isolates were classified into different clades. In particular eight isolates were classified into a well-supported clade including F. solani f. sp . pisi , nine into a clade including only isolates of F. solani f. sp . radicicola and four into a clade including F. solani f. sp . cucurbitae , but this classification could not be used if is not in agreement with host specificity. Two of the nine F. solani var. coeruleum isolates were phylogenetically distinct from all the other FSSC strains.     

The mitochondrial genome of Fusarium oxysporum

Physical and genetic maps have been constructed for mtDNA from strains of the fungus Fusarium oxysporum representing three pathogenically specialized forms. All three mtDNA maps are circular. Their sizes are 45 kb for F. oxysporum f.sp. raphani and 52 kb for both F. oxysporum f.sp. conglutinans and F. oxysporum f.sp. matthioli. The genetic loci for cytochrome b, the mitochondrial 25S ribosomal RNA and cytochrome oxidase subunit II, have been identified and are similarly arranged on the three genomes.     

牛蒡根际土壤致害菌Fusarium solani分离鉴定

目的：探索牛蒡根际镰刀菌与牛蒡之间的相互关系。方法：从全国30个地区采集牛蒡根际土壤样品,进行了根际土壤真菌数量和群落的生态学研究,测定镰刀菌发酵液对牛蒡幼苗和牛蒡子萌发的影响,并对其中毒性最强的两株镰刀菌F130和F131进行了形态学和分子生物学的鉴定。结果：镰刀菌为牛蒡根际的最优势类群,贡献率为34.297%,其次为木霉,贡献率为22.519%;绝大多数镰刀菌对牛蒡有明显的毒性作用,其中F130和F131被鉴定为Fusarium solani。结论：Fusarium solani是牛蒡根际土壤中的致害菌。     

傣药植物内生真菌的抑菌活性评价及发酵条件探索

从云南傣药植物中分离到180株内生真菌,选用9种培养基进行发酵。利用茄腐镰刀菌、尖孢镰刀菌、立枯丝核菌、玉米小斑病、稻梨孢菌等5种植物病原菌作为指示菌株,结合TLC检测对其发酵粗提物进行活性评价和化学多样性分析,以期寻找到具有开发潜力的活性菌株。研究结果表明活性菌株为36株,其中有7株菌活性好且产物多样性丰富。     

Effect of ultraviolet-induced mutants of Trichoderma harzianum with altered antibiotic production on selected pathogens in vitro

Mutants of Trichoderma harzianum with altered antibiotic production were isolated using ultraviolet light mutagenesis. These included strains whose activity in a Fusarium oxysporum spore germination assay was greater than twice that of the parental strain and one that had no detectable antifungal activity. Characterisation of extracellular metabolites of these strains using thin-layer chromatography and gas-liquid chromatography showed that the strains with high activity produced only elevated levels of a 6-n-pentyl pyrone, the antibiotic produced by the parental strain, but two new antifungal compounds. One of these has been identified as an isonitrile antibiotic. The nature of the interactions of the mutants with Fusarium oxysporum, Rhizoctonia solani, and Pythium ultimum was examined in an in vitro dual-plating assay using two media. High antibiotic production by two T. harzianum strains, BC10 and BC63, did increase inhibition of hyphal growth of R. solani and P. ultimum, but there was no correlation between increased antibiotic production and colonisation ability. In some cases the increased antibiotic levels appeared to impede colonisation of F. oxysporum and R. solani by the mutants. Slow growth rate also affected colonising ability. The types of interactions showed great variability depending on the nature of the T. harzianum isolate and on the test fungus.     

Antifungal activity and enhancement of plant growth by Bacillus cereus grown on shellfish chitin wastes

Bacillus cereus QQ308 produced antifungal hydrolytic enzymes, comprising chitinase, chitosanase and protease, when grown in a medium containing shrimp and crab shell powder (SCSP) produced from marine waste. The growth of the plant-pathogenic fungi Fusarium oxysporum, Fusarium solani, and Pythium ultimum were considerably affected by the presence of the QQ308 culture supernatant. The supernatant inhibited spore germination and germ tube elongation of F. oxysporum, F. solani, and P. ultimum. The increase in the growth time of the fungal culture was associated with a gradual decrease in inhibition. Besides antifungal activity, QQ308 enhanced growth of Chinese cabbage. These characteristics were unique among known strains of B. cereus. To our knowledge, this is the first report on the antifungal and Chinese cabbage growth enhancing compounds produced by B. cereus.     

Transmission of Fusarium boothii mycovirus via protoplast fusion causes hypovirulence in other phytopathogenic fungi

There is increasing concern regarding the use of fungicides to control plant diseases, whereby interest has increased in the biological control of phytopathogenic fungi by the application of hypovirulent mycoviruses as a possible alternative to fungicides. Transmission of hypovirulence-associated double-stranded RNA (dsRNA) viruses between mycelia, however, is prevented by the vegetative incompatibility barrier that often exists between different species or strains of filamentous fungi. We determined whether protoplast fusion could be used to transmit FgV1-DK21 virus, which is associated with hypovirulence on F. boothii (formerly F. graminearum strain DK21), to F. graminearum, F. asiaticum, F. oxysporum f. sp. lycopersici, and Cryphonectria parasitica. Relative to virus-free strains, the FgV1-DK21 recipient strains had reduced growth rates, altered pigmentation, and reduced virulence. These results indicate that protoplast fusion can be used to introduce FgV1-DK21 dsRNA into other Fusarium species and into C. parasitica and that FgV1-DK21 can be used as a hypovirulence factor and thus as a biological control agent.     

A PCR-denaturing gradient gel electrophoresis approach to assess Fusarium diversity in asparagus

In North America, asparagus (Asparagus officinalis) production suffers from a crown and root rot disease mainly caused by Fusarium oxysporum f. sp. asparagi and F. proliferatum. Many other Fusarium species are also found in asparagus fields, whereas accurate detection and identification of these organisms, especially when processing numerous samples, is usually difficult and time consuming. In this study, a PCR-denaturing gradient gel electrophoresis (DGGE) method was developed to assess Fusarium species diversity in asparagus plant samples. Fusarium-specific PCR primers targeting a partial region of the translation elongation factor-1 alpha (EF-1 alpha) gene were designed, and their specificity was tested against genomic DNA extracted from a large collection of closely and distantly related organisms isolated from multiple environments. Amplicons of 450 bp were obtained from all Fusarium isolates, while no PCR product was obtained from non-Fusarium organisms. The ability of DGGE to discriminate between Fusarium taxa was tested over 19 different Fusarium species represented by 39 isolates, including most species previously reported from asparagus fields worldwide. The technique was effective to visually discriminate between the majority of Fusarium species and/or isolates tested in pure culture, while a further sequencing step permitted to distinguish between the few species showing similar migration patterns. Total genomic DNA was extracted from field-grown asparagus plants naturally infested with different Fusarium species, submitted to PCR amplification, DGGE analysis and sequencing. The two to four bands observed for each plant sample were all affiliated with F. oxysporum, F. proliferatum or F. solani, clearly supporting the reliability, sensitivity and specificity of this approach for the study of Fusarium diversity from asparagus plants samples.     

Non-pathogenic Fusarium solani represses the biosynthesis of nematicidal compounds in vitro and reduces the biocontrol of Meloidogyne javanica by Pseudomonas fluorescens in tomato

AIMS: The aim of the present investigation was to determine the influence of various Fusarium solani strains on the production of nematicidal agent(s) in vitro and biocontrol of Meloidogyne javanica in tomato by Pseudomonas fluorescens strains CHA0 and CHA0/pME3424. METHODS AND RESULTS: Culture filtrates (CF) of P. fluorescens strain CHA0 and its diacetylphloroglucinol-overproducing derivative CHA0/pME3424 caused substantial mortality of M. javanica juveniles in vitro. Bacterial growth medium amended with the growth medium of F. solani repressed the nematicidal activity of the bacteria. Methanol extract of F. solani CF resulting from Czapek's Dox liquid (CDL) medium without zinc amendment repressed the nematicidal activity of the bacteria while the CF obtained from CDL medium amended with zinc did not. Conidial suspension of F. solani strain Fs5 (repressor strain for the biosynthesis of nematicidal compounds in P. fluorescens) reduced biocontrol potential of the bacterial inoculants against M. javanica in tomato while strain Fs3 (non-repressor) did not. CONCLUSIONS: Fusarium solani strains with increased nematicidal activity repress the biosynthesis of nematicidal compounds by P. fluorescens strains in vitro and greatly alter its biocontrol efficacy against root-knot nematode under natural conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: Fusarium solani strains are distributed worldwide and found in almost all the agricultural fields which suggest that some mycotoxin-producing strains will also be found in almost any soil sample taken. Besides the suppressive effect of these metabolite-producing strains on the production of nematicidal compound(s) critical in biocontrol, F. solani strains may also affect the performance of mycotoxin-sensitive biocontrol bacteria effective against plant-parasitic nematodes.