A single gene in Fusarium oxysporum limits host range

Fusarium oxysoporum f. sp. radicis-cucumerinum (Forc) is able to cause disease in cucumber, melon, and watermelon, while F. oxysporum f. sp. melonis (Fom) can only infect melon plants. Earlier research showed that mobile chromosomes in Forc and Fom determine the difference in host range between Forc and Fom. By closely comparing these pathogenicity chromosomes combined with RNA-sequencing data, we selected 11 candidate genes that we tested for involvement in the difference in host range between Forc and Fom. One of these candidates is a putative effector gene on the Fom pathogenicity chromosome that has nonidentical homologs on the Forc pathogenicity chromosome. Four independent Forc transformants with this gene from Fom showed strongly reduced or no pathogenicity towards cucumber, while retaining pathogenicity towards melon and watermelon. This suggests that the protein encoded by this gene is recognized by an immune receptor in cucumber plants. This is the first time that a single gene has been demonstrated to determine a difference in host specificity between formae speciales of F. oxysporum.     

Radiometric assessment of tillage and seed treatment effect on soybean root rot caused by Fusarium spp. in central Minnesota

Soybean root rot, caused primarily by Fusarium solani f. sp. phaseoli in a complex with F. oxysporum and Rhizoctonia solani, has become an increasing problem for soybeans, dry beans, and other rotation crops in central Minnesota due to soil conditions associated with reduced tillage. This study was conducted, in two field sites in central Minnesota located near Staples and Verndale, to develop methods for nondestructive assessment of root rot severity using plant radiometric properties. Soybean canopy reflectance was measured with a hand-held multi-spectral radiometer. Prior to the radiometer measurements, attempts were made to create differing root rot situations with moldboard or chisel tillage, and with or without a biological seed treatment. Root rot severity was estimated using a visual disease severity scale. Colony-forming units (CFU) were determined to estimate soil populations of pathogenic F. solani and F. oxysporum. Results from the Verndale site consistently showed significant treatment effects in the measured canopy radiometric parameters, and in the visual disease rating and yield (significant for seed treatment). Values of a simple ratio vegetation index from this site exhibited negative relationships with disease rating and F. oxysporum CFU, and a positive linear relationship with yield. Treatment effects were generally not significant at the Staples site because of low initial F. oxysporum populations. The results indicate that remote sensing is potentially a rapid, nondestructive means for assessment of root rot diseases in soybean.     

Molecular characterization of pathogenic Fusarium species in cucurbit plants from Kermanshah province, Iran

Fusarium is one of the important phytopathogenic genera of microfungi causing serious losses on cucurbit plants in Kermanshah province, the largest area of cucurbits plantation in Iran. Therefore, the objectives in this study were to isolate and identify disease-causing Fusarium spp. from infected cucurbit plants, to ascertain their pathogenicity, and to determine their phylogenetic relationships. A total of 100 Fusarium isolates were obtained from diseased cucurbit plants collected from fields in different geographic regions in Kermanshah province, Iran. According to morphological characters, all isolates were identified as Fusarium oxysporum, Fusarium proliferatum, Fusarium equiseti, Fusarium semitectum and Fusarium solani. All isolates of the five Fusarium spp. were evaluated for their pathogenicity on healthy cucumber (Cucumis sativus) and honeydew melon (Cucumis melo) seedlings in the glasshouse. F. oxysporum caused damping-off in 20–35 days on both cucurbit seedlings tested. Typical stem rot symptoms were observed within 15 days after inoculation with F. solani on both seedlings. Based on the internal transcribed spacer (ITS) regions of ribosomal DNA (rDNA) restriction fragment length polymorphism (RFLP) analysis, the five Fusarium species were divided into two major groups. In particular, isolates belonging to the F. solani species complex (FSSC) were separated into two RFLP types. Grouping among Fusarium strains derived from restriction analysis was in agreement with criteria used in morphological classification. Therefore, the PCR-ITS-RFLP method provides a simple and rapid procedure for the differentiation of Fusarium strains at species level. This is the first report on identification and pathogenicity of major plant pathogenic Fusarium spp. causing root and stem rot on cucurbits in Iran.     

Management Fusarium wilt on melon and watermelon by Penicillium oxalicum

The potential of the biological control fungus Penicillium oxalicum to suppress wilt caused by Fusarium oxysporum f. sp. melonis and F. oxysporum f. sp. niveum on melon and watermelon, respectively, was tested under different growth conditions. The area under disease progress curve of F. oxysporum f. sp. melonis infected melon plants was significantly reduced in growth chamber and field experiments. In glasshouse experiments, it was necessary to apply P. oxalicum and dazomet in order to reduce Fusarium wilt severity in melons caused by F. oxysporum f. sp. melonis. For watermelons, we found that P. oxalicum alone reduced the area under the disease progress curve by 58% in the growth chamber experiments and 54% in the glasshouse experiments. From these results, we suggested that P. oxalicum may be effective for the management of Fusarium wilt in melon and watermelon plants.     

林下参内生球毛壳菌FS-01对人参病原真菌的抑制作用

为探究林下参内生真菌球毛壳菌(Chaetomium globosum) FS-01菌株对人参病原菌的抑菌作用,该研究在实验室条件下,测定了FS-01菌株菌丝、发酵液和孢子悬浮液对人参黑斑病菌(Alternaria panax)、人参菌核病菌(Sclerotinia schinseng)、人参灰霉病菌(Botrytis cinerea)、人参立枯病菌(Rhizoctonia solani)、人参根腐病菌(Fusarium solani) 5种人参病原菌的抑制作用。结果表明:内生真菌球毛壳菌FS-01对5种病原菌均有抑制作用,其中,对人参黑斑病菌的抑制作用最高,为30.80%,其次是人参立枯病菌、人参菌核病菌、人参根腐病菌和人参灰霉病菌;发酵液抑菌实验结果表明,在加入内生真菌球毛壳菌FS-01菌株发酵液的PDA培养基上,对人参灰霉病菌的抑制作用最高,为82.09%,其次是人参菌核病菌、人参黑斑病菌、人参立枯病菌和人参根腐病菌;孢子抑菌实验结果表明,在加入内生真菌球毛壳菌FS-01菌株孢子悬浮液的PDA培养基上,对人参黑斑病菌的抑制作用最高,为83.72%,其次是人参灰霉病菌、人参立枯病菌、...     

Decomposition of cellulose strips in relation to climate,litterfall nitrogen,phosphorus and C/N ratio in natural boreal forests

Isolates of Alternaria alternata, Botrytis cinerea, Fusarium oxysporum, Penicillium sp., Rhizoctonia solani, Stemphylium sp., Thielaviopsis basicola, and Verticillium dahliae were cultured on potato–dextrose agar (PDA), barley-sand and alfalfa-sand substrates in petri-dish or in column microcosms. N-mineralization by fungi and fungal-feeding nematodes in combination or fungi alone was assessed. Numbers of Aphelenchus avenae or Aphelenchoides composticola supported by the fungi were measured every 7 days. Times for full colonization of the substrates by fungi ranged from 5 to 15 days. Rhizoctonia solani and B. cinerea on PDA supported the largest A. avenae and A. composticola populations, respectively. Penicillium sp. was a nonhost for A. composticola and A. avenae. Rhizoctonia solani, B. cinerea, V. dahliae, and F. oxysporum supported significantly more nematodes than the other four fungal species. The ranked order of fungi based on the amount of N mineralized in columns free of nematodes was A. alternata (with a rate of 0.052 μg N/g-sand per day), Stemphylium sp., V. dahliae, T. basicola, B. cinerea, F. oxysporum, R. solani, and Penicillium sp. (with a rate of 0.0045 μg N/g-sand perday). The presence of A. avenae resulted in significant increases in mineral N, compared to nematode-free columns colonized by F. oxysporum, R. solani, and T. basicola alone. The presence of A. composticola resulted in significant increases in mineral N, compared to nematode-free columns colonized by A. alternata, B. cinerea, F. oxysporum, and R. solani alone. There was more mineral N incolumns in the presence of A. composticola than A. avenae in most cases. This revised version was published online in August 2006 with corrections to the Cover Date.     

Expression of Dm-AMP1 in rice confers resistance to Magnaporthe oryzae and Rhizoctonia solani

Magnaporthe oryzae and Rhizoctonia solani, are among the most important pathogens of rice, severely limiting its productivity. Dm-AMP1, an antifungal plant defensin from Dahlia merckii, was expressed in rice (Oryza sativa L. sp. indica cv. Pusa basmati 1) using Agrobacterium tumefaciens-mediated transformation. Expression levels of Dm-AMP1 ranged from 0.43% to 0.57% of total soluble protein in transgenic plants. It was observed that constitutive expression of Dm-AMP1 suppresses the growth of M. oryzae and R. solani by 84% and 72%, respectively. Transgenic expression of Dm-AMP1 was not accompanied by an induction of pathogenesis-related (PR) gene expression, indicating that the expression of DmAMP1 directly inhibits the pathogen. The results of in vitro, in planta and microscopic analyses suggest that Dm-AMP1 expression has the potential to provide broad-spectrum disease resistance in rice.     

Effect of solarization of soil within plastic bags on root rot of gerbera (Gerbera jamesonii L.)

Solarization of soil, (potting mix = coarse sand:Eucalyptus marginata fines = 1∶1) infested with 3 fungi pathogenic to gerbera (Phytophthora cryptogea, Fusarium oxysporum andRhizoctonia solani), for 3 to 4 weeks within transparent polyethylene bags controlled root rot of gerbera. Solarization for 2 weeks however, was less effective. All plants grown in the infested potting mix which had been kept in shade for 2, 3 or 4 weeks were severely attacked. Solarization of soil within plastic bags for 4 weeks also increased availability of nutrients such as NH₄ ⁺-N, PO₄ ⁻ and K⁺ in comparison to bagged soil kept in the shade for the same period.     

Biological Control of Stem Canker and Black Scurf on Potato by Date Palm Compost and its Associated Fungi

The suppressive effects of two different types of date palm composts and some of their indigenous microorganisms were evaluated in vitro and on potato plants inoculated with Rhizoctonia solani. Fungi isolated from composts screened against R. solani by dual cultural assays on PDA showed a significant inhibition of pathogen mycelium growth as compared with untreated control. The type of hyphal interactions between R. solani and each tested antagonist was observed by light microscopy. Microscopic observations carried out at the confrontation zone of both agents showed different mechanisms of actions: mycelia lyses, mycoparasitism and/or formation of mycelia cords via anatomosis between mycelia filaments. Unsterilized and sterilized compost extracts were tested for efficacy against R. solani using agar‐well diffusion method or by pouring the extracts on PDA. Two sterilization methods were used: a filtration through a microfilter of 0.22 microns or autoclaving. Results showed that compost extract lost its activity after heating or filtration, confirming that chemical factors in compost had no direct inhibiting effect on the pathogen. The suppressiveness of composts was mainly due to their biotic component. Series of greenhouse trials showed that black scurf and stem canker incidence and severity were significantly reduced in peat–sand amended with compost compared with the untreated control. However, the potential suppressive effect of cattle manure and date palm compost (CMC) was higher than sheep manure and date palm compost (SMC). On potato seed tubers pre‐inoculated with the selected fungal isolates from compost, there was variability in the reduction of disease severity among treatments. Plant growth was unaffected by the application of fungal antagonists or by CMC amendment; however, an increase in the total yield was observed by the SMC potting mix compared with untreated control.     

Evaluation of the leaf juice of some higher plants for their toxicity against soil borne pathogens

Out of the leaf juices of eighteen plant species screened, only Eupatorium cannabinum exhibited complete toxicity against Pythium debaryanum, Fusarium oxysporum, Rhizoctonia solani and Sclerotium rolfsii. Shade drying of the leaves had no adverse effect, while oven drying produced an adverse effect on the fungitoxicity of the leaves of E. cannabinum. The crude leaf juice of E. cannabinum successfully inhibited damping-off (Fusarium oxysporum) infection of Pisum sativum seedlings.     

Colonization of cucumber plants by the biocontrol fungus Clonostachys rosea f. catenulata

Clonostachys rosea f. catenulata (Gliocladium catenulatum) strain J1446 (formulated as Prestop WP) suppressed Fusarium root and stem rot caused by Fusarium oxysporum f. sp. radicis-cucumerinum (Forc) on cucumber plants grown hydroponically in rockwool medium. Sixty days following application at seeding, the biocontrol agent had proliferated through the rockwool blocks and was present on cucumber roots and the crown region of the stem at populations >1 × 10⁵ CFU/g fresh weight. Scanning electron micrographs showed that C. rosea had rapidly colonized the root surface and was associated with root hairs and epidermal cell junctions. Following transformation of the fungus with Agrobacterium tumefaciens strain AGL-1 containing the hygromycin resistance (hph) and β-glucuronidase (uidA) genes, blue-stained mycelia could be seen growing on the surface and within epidermal and cortical cells of roots, stems and shoots 3 weeks after treatment. Quantification of GUS activity by fluorometric assays showed that fungal biomass was highest in the roots and crown area, while the extent of colonization of upper stems and true leaves was variable. Higher population levels resulted following application to rockwool blocks compared to seed treatment. Application of C. rosea preceding inoculation with Forc significantly reduced pathogen populations on roots compared to plants inoculated with Forc alone. Colonization of infection sites in the root zone reduced pathogen development and disease incidence. Densities of the biocontrol agent appeared to increase in the presence of the pathogen.     

Stress-induced expression of cucumber chitinase and <Emphasis Type="Italic">Nicotiana plumbaginifolia</Emphasis><Emphasis Type="Italic">β</Emphasis>-1,3-glucanase genes in transgenic potato plants

The genes encoding for a cucumber class III chitinase and Nicotiana plumbaginifolia class I glucanase were co-introduced into Slovak potato (Solanum tuberosum L.) cultivar ETA using Agrobacterium tumefaciens. Expression of both genes was driven by wound-inducible polyubiquitin promoter isolated from Slovak potato breeding line 116/86. Analyses showed inducible, peel-specific expression of both transgenes under stress conditions. The effect of transgene expression on fungal susceptibility of transformants was evaluated in vitro and in vivo. Experiments with crude protein extracts isolated from transgenic microtubers showed growth inhibition of Rhizoctonia solani hyphae in the range from 7.3 to 14.2%. In contrast, experiments performed in growth chamber conditions revealed that the polyubiquitin promoter driven transgene expression did not ensure any obvious increase of transgenic potato resistance against Rhizoctonia solani.     

Prevalence of wilt-root rot and their associated pathogens at reproductive phase in lentil

A survey of 116 districts of nine lentil growing states covering 603 farmers' fields revealed a range of 0.7–9.3% mean plant mortality at reproductive stages in different lentil growing states of the country. The overall mean mortality was 6.3%. The main pathogens found associated with plant mortality at this stage were Fusarium oxysporum f. sp. lentis (62.0%), Rhizoctonia bataticola (25.2%) and Sclerotium rolfsii (9.8%). The minor involvement of 1.8% was that of F. solani, F. chlamydosporum. F. equisetii, and R. solani. For the first time a national scenario of lentil wilt-root rot incidence at the crucial reproductive stage and their associated pathogens is reported here.     

Effects of Commercial and Indigenous Microorganisms on Fusarium Wilt Development in Chickpea

The purpose of this research was to determine whetherBacillus subtilis,nonpathogenicFusarium oxysporum,and/orTrichoderma harzianum,applied alone or in combination to chickpea (Cicer arietinumL.) cultivars ‘ICCV 4’ and ‘PV 61’ differing in their levels of resistance to Fusarium wilt, could effectively suppress disease caused by the highly virulent race 5 ofFusarium oxysporumf. sp.ciceris.Seeds of both cultivars were sown in soil amended with the three microbial antagonists, alone or in combination, and 7 days later seedlings were transplanted into soil infested with the pathogen. All three antagonistic microorganisms effectively colonized the roots of both chickpea cultivars, whether alone or in combination, and significantly suppressed Fusarium wilt development. In comparison with the control, the incubation period for the disease was delayed on average about 3 days and the final disease severity index and standardized area under the disease progress curve were reduced significantly between 14 and 33% and 16 and 42%, respectively, by all three microbial antagonists. Final disease incidence only was reduced byB. subtilis(18–25%) or nonpathogenicF. oxysporum(18%). The extent of disease suppression was higher and more consistent in ‘PV 61’ than in ‘ICCV 4’ whether colonized byB. subtilis,nonpathogenicF. oxysporum,orT. harzianum.The combination ofB. subtilis+T. harzianumwas effective in suppressing Fusarium wilt development but it did not differ significantly from treatments with either of these antagonists alone. In contrast, the combination ofB. subtilis+ nonpathogenicF. oxysporumtreatment was not effective but either antagonist alone significantly reduced disease development.     

产胞外多糖菌株的分离鉴定及其功能研究

微生物产生的胞外多糖(exopolysaccharides, EPS)可促进大粒径土壤团聚体形成,高产EPS的菌株在土壤改良、促进作物生长方面具有较好的应用前景。【目的】从土壤样品中筛选高产胞外多糖的细菌,研究其在土壤改良、环境适应性、广谱抗病等方面的功能,为制备土壤改良型功能菌剂提供候选菌株。【方法】采用蒽酮硫酸法测定菌株胞外多糖的产量,通过形态学观察、生理生化试验及16S rRNA基因序列测定确定其分类地位,结合土壤培养试验研究菌株对土壤团聚体形成的影响。【结果】获得3株胞外多糖产量大于500 mg/L的细菌,经鉴定A-5为地衣芽孢杆菌(Bacillus licheniformis),XJ-3为萎缩芽孢杆菌(Bacillus atrophaeus),KW3-10为耐盐芽孢杆菌(Bacillus halotolerans)。菌株A-5、XJ-3、KW3-10处理后,土壤大团聚体(>0.25 mm)含量较对照分别提高了4.07、2.14和3.16倍。3株菌株对疮痂链霉菌(Streptomyces scabies)、尖孢镰刀菌(Fusarium oxysporum)、茄链格孢菌(Alternaria solani)和立枯丝核菌(Rhizoctonia solani)等多种植物病原菌具有明显的抑制效果,可耐受pH为5-9和NaCl含量1%‒9%的盐碱环境,促进植物生长,其中KW3-10的代谢产物中IAA含量为25.58 mg/L。【结论】菌株A-5、XJ-3、KW3-10可显著促进土壤团粒结构形成,具有较好的广谱抗病性和促生长特性,可作为高效复合功能菌剂的候选菌株。     

Interaction of Fusarium Oxysporum f.sp. Cubense with Pseudomonas Fluorescens Precolonized to Banana Roots

Effect of precolonization of banana cv Neeypovan roots with Pseudomonas fluorescens on infection with Fusarium oxysporum f.sp. cubense was studied. Under in vitro conditions Pseudomonas fluorescens clearly inhibited Fusarium oxysporum f.sp. cubense. Fluorescein isothiocyanate-tagged antibodies raised in a rabbit system for Pseudomonas fluorescens and Fusarium oxysporum f.sp. cubense separately were used to study the spread of both organisms in banana root. It was observed that precolonization with Pseudomonas fluorescens could reduce Fusarium oxysporum f.sp. cubense colonization by 72%, and also correlated with a number of structural changes in the cortical cells, mainly with densely stained amorphous material and polymorphic wall thickenings as revealed by light and electron microscopic studies. Massive depositions of unusual structures at sites of fungal entry was also noticed, which clearly indicated that bacterized root cells were signalled to mobilize a number of defence structures for preventing the spread of pathogen in the tissue. This revised version was published online in July 2006 with corrections to the Cover Date.     

Antifungal activity of Bacillus sp. isolated from compost

Four strains ofBacillus isolated from lupine compost exhibited an antifungal activity against six plant fungal pathogens (Rhizoctonia solani, Bipolaris sorokiniana, Sclerotinia sclerotiorum, Trichothecium roseum, Fusarium solani, Fusarium oxysporum). It was significantly influenced by the composition of the cultivation media.     

Control of blast and sheath blight diseases of rice using antifungal metabolites produced by Streptomyces sp. PM5

Two antifungal aliphatic compounds, SPM5C-1 and SPM5C-2 with a lactone and ketone carbonyl unit, respectively obtained from Streptomyces sp. PM5 were evaluated under in vitro and in vivo conditions against major rice pathogens, Pyricularia oryzae and Rhizoctonia solani. These compounds were dissolved in distilled water/medium to get the required concentrations. The well diffusion bioassay indicated that the of SPM5C-1 remarkably inhibited the mycelial growth of P. oryzae and R. solani in comparison to SPM5C-2. Though SPM5C-2 showed low antifungal activity against P. oryzae, it was not active against R. solani. Further, SPM5C-1 completely inhibited the growth of P. oryzae and R. solani at concentrations of 25, 50, 75 and 100 μg/ml. Greenhouse experiments revealed that spraying of SPM5C-1 at 500 μg/ml on rice significantly decreased blast and sheath blight development by 76.1% and 82.3%, respectively, as compared to the control with a corresponding increase in rice grain yield.     

Effect of the high polycyclic aromatic hydrocarbon, benzo[a]pyrene, on the lipid content of Fusarium solani

The purpose of the present paper was to study the effect of the high polycyclic aromatic hydrocarbon (PAH), benzo[a]pyrene, on the lipid [fatty acid (FA) and sterol] composition and content of the fungi Fusarium solani and F. oxysporum, respectively recognized as good and poor PAH degraders. The major FAs and the major sterol that characterized the tested Fusarium strains were C16:0, C18:1, C18:2, and ergosterol. Lipid profiles of F. solani remained unchanged with the addition of benzo[a]pyrene in the culture media at all concentrations and duration of treatment. However, in the presence of benzo[a]pyrene, significant decreases in FA content, which reached 18 % in young cultures and 28 % in mature colonies, were registered. Similarly, the sterol content of F. solani was reduced by 27 % in the presence of benzo[a]pyrene. In contrast, no modification in lipid profile and lipid content were observed with F. oxysporum, a strain recognized as a low benzo[a]pyrene degrader.     

Cross-pathogenicity between Formae Speciales of Fusarium oxysporum, the Pathogens of Cucumber and Melon

The population structure of Fusarium oxysporum f. sp. cucumerinum was studied using the vegetative compatibility grouping (VCG) approach. All 37 of the examined isolates from Israel were assigned to VCG 0180, the major VCG found in North America and the Mediterranean region. Approximately two‐thirds of the tested isolates were pathogenic to both cucumber and melon, but cumulatively they were more aggressive on cucumber, their major host, than on melon. Disease symptoms on melon plants were less destructive and often expressed as growth retardation. Melon cultivars differing in Fom genes for resistance to F. oxysporum f. sp. melonis were inoculated with three isolates of F. oxysporum f. sp. cucumerinum. Results showed that Fom genes do not confer resistance to F. oxysporum f. sp. cucumerinum, although different horticultural types may respond differently to this pathogen. The reciprocal inoculation of F. oxysporum f. sp. melonis on cucumber, using four physiological races, did not result in disease symptoms or growth retardation. It is concluded that cucumerinum and melonis should remain two distinct formae speciales.