Fusarium udum as a mycoparasite ofMortierella subtilissima

Summary Fusarium udum was found to be a mycoparasite ofMortierella subtilissima which is a new record. Formation of chlamydospores byF. udum insideM. subtilissima was observed as a result of mycoparasitism.     

Mycoparsitic behaviour ofFusarium oxysporum Schlechtendahl towardsAspergillus luchuensis Inui

Summary Mycoparasitic behaviour ofFusarium oxysporum Schlechtendahl towardsAspergillus luchuensis Inui was studiedin vitro. Growth of the hyphae ofF. oxysporum inside the hyphae and conidiophores ofA. luchuensis and formation of resting bodies ofF. oxysporum in conidiophores and hyphae ofA. luchuensis were observed. Bursting of the host hypha attacked by the parasitic hyphae was also noticed.     

Fungistatic activity of different Indian soils againstFusarium udum Butler

Summary The fungistatic activity of different Indian soils againstF. udum, causing wilt disease of pigeon-pea, has been assessed in relation to soil pH and organic matter. Correlation co-efficient between soil characteristics and fungistasis has been calculated to evaluate relationship. High fungistatic activity was exhibited generally by the soils having low pH but high organic matter. The soils exhibiting high fungistatic activity againstF. udum have low incidence of wilt disease of pigeon-pea. There was no definite correlation between volatile and non-volatile fungistasis and, therefore, the origins of volatile and non-volatile fungistasis are different. In the usual biological limit pH had insignificant impact on fungistasis.     

Studies on antagonism betweenFusarium udum Butler and root region microflora of pigeon-pea

Antagonism betweenFusarium udum Butler causing wilt of pigeon-pea (Cajanus cajan (L.) Millsp.) and the saprophytic microflora of the root region of the host was studied with reference to colony interaction, hyphal interference, volatile and non-volatile metabolites and staling growth products. Studies were extended to screen potential antagonists against the wilt pathogen in soil. Aspergillus flavus, A. niger, A. terreus, Penicillium citrinum andMicromonospora globosa (an actinomycete) were antagonistic againstF. udum, whereas the pathogen parasitized and killedAspergillus luchuensis, Cunninghamella echinulata, Curvularia lunata, Mortierella subtilissima andSyncephalastrum racemosum. The pattern of growth of microorganisms on nutrient agar staled by rhizosphere soil inocula of healthy or wilted pigeon-pea plants was found to be different.F. udum colonized and grew on nutrient agar staled by the rhizosphere inoculum of the wilted plants upto 120h of incubation. However, it could not colonise and grow on the nutrient agar staled by rhizosphere microflora of healthy plants after 48h of incubation because of the presence of antagonists likeA. niger, A. flavus, A. terreus and a few species ofPenicillium in the soil inoculum. When pure cultures in soil ofF. udum was mixed with those of antagonists in different ratios,A. niger, A. flavus andM. globosa significantly suppressed the population ofF. udum, whereasA. terreus markedly reduced the population. When inoculated in soil, the antagonists exhibited a high fungistatic activity againstF. udum.     

Biodegradation of mango kernel by Syncephalastrum racemosum and its biological control

Poor germination of mango seed due to fungal decay is a common problem in mango nurseries. The main causal fungus behind this problem is a black spore producing fungus, Syncephalastrum racemosum. This fungus exhibited high amylolytic activity and hence utilised the starch present in mango kernel for its own growth, thereby resulting in the death of emerging radical and plumule, which ultimately causes the death of emerging seedlings. A simple biocontrol device has been worked out by modifying the storage conditions of the mango seeds from aerobic to facultative. This change resulted in yeast growth on the pulp sticking to the mango seed, which in turn produced alcohol and prevented the growth of this fungus. The germination of such seeds has been found to be about 85–90%.     

Tolerance to higher temperature byAspergillus nidulans and its possible implication in biological control of wilt disease of pigeon-pea

Summary During the course of studies on the ecology ofFusarium udum Butler, the incitant of wilt disease of pigeon-pea (Cajanus cajan (L.) Millsp.),Aspergillus nidulans was found to tolerate higher temperatures of summer, and other species includingF. udum were suppressed in field soil. The population ofA. nidulans increased in the soil incubated at 40±2°C at pH6 and 7 while the population ofF. udum was highly suppressed. The wilt disease of pigeon-pea was significantly suppressed at 38±2°C in the soil having a mixture of the inocula ofF. udum andA. nidulans whereas at lower temperature (25±2°C) no significant impact ofA. nidulans on the disease was found. On the basis of this study an integrated use of higher temperature, alkaline pH andA. nidulans has been suggested for biological control of wilt disease of pigeon-pea.     

Formation of antigenic extracellular polysaccharides by selected strains ofMucor spp.,Rhizopus spp.,Rhizomucor spp.,Absidia corymbifera andSyncephalastrum racemosum

In this study, polyclonal IgG antibodies raised against extracellular polysaccharides (EPS) ofMucor racemosus were characterised as almost specific for moulds belonging to the order of Mucorales. Cross-reactivity in the ELISA could be observed only towards the yeastPichia membranaefaciens. EPS were isolated from various cultures ofM. hiemalis growing on six different carbon sources and two nitrogen sources, with ratios varying from 0.13 to 0.44 relative to the amount of biomass. Other strains includingMucor spp.,Rhizopus spp.,Rhizomucor spp.,Absidia corymbifera andSyncephalastrum racemosum also excreted EPS, with ratios varying from 0.05 to 0.23. In all cases, the excreted EPS had similar antigenic properties as determined by ELISA. No enzymatic degradation of the antigenic parts of the polysaccharides could be observed upon prolonged incubation. Considering that all tested strains formed similar amounts of antigenic EPS there might be scope for the specific detection of biomass of Mucoralean moulds using ELISA techniques for example in food.     

Lysis of mycelium ofFusarium oxysporum f. sp.udum in soil amended with organic matters

Summary Autoclaved or natural field soil amended with 0.1 to 5.0 per cent (W/W) of margosa cake, rice husk and sawdust with or without supplemental nitrogen were tested for lytic activity and bacterial numbers. Generally, non-amended autoclaved soil caused little or no lysis of mycelium ofF. oxysporum f. sp.udum; non-amended natural soil caused more lysis. Amendment of soil with margosa cake, rice husk or saw-dust with or without supplemental nitrogen greatly enhanced its lytic effect on the fungus. The degree of lysis depended on the dosage of amendment used and the stage of its decomposition in the soil. The extent of lysis increased as the bacterial population increased. Amongst bacteria,Bacillus subtilis was very common in most lytic zones.     

Isolation of beauvericin as an insect toxin from Fusarium semitectum and Fusarium moniliforme var. subglutinans

Nonpolar methylene chloride-soluble extracts from the mycelia of Fusarium semitectum and Fusarium moniliforme var. subglutinans were toxic to Colorado potato beetles. The major toxic metabolite was isolated and found to be the cyclodepsipeptide, beauvericin. This is the first report of the isolation of beauvericin from the genus Fusarium.     

A new fumonisin from solid cultures of Fusarium moniliforme

A new fumonisin has been isolated from Fusarium moniliforme isolate MRC826 grown on corn. It was shown by NMR and mass spectrometry to be an isomer of fumonisin B₂ that has free hydroxyl groups at C-3 and C-10 instead of the normal C-3 and C-5. This new fumonisin was detected in cultures of most isolates of F. moniliforme that were examined and was usually present at concentrations similar to those of fumonisin B₂. Two isolates of F. moniliforme that produce significantly higher levels of this new isomer were identified.Abbreviations ELEM equine leukoencephalomalacia Mention of companies or products by name does not imply their endorsement by the US Department of Agriculture over others not cited.     

Biosynthesis of labeled fumonisins in liquid cultures of Fusarium moniliforme

Fumonisins were readily produced in cultures of Fusarium moniliforme using a defined liquid medium. Addition of 200 mg of d₃-methyl L-methionine to 100-ml cultures of F. moniliforme gave increased overall yields and high levels of deuterium (²H) incorporation into fumonisin B₁. Approximately 90% of the resulting fumonisin B₁ contained 6 deuterium atoms, while 9% of the product contained 3 deuterium atoms. Deuterium was shown to be incorporated exclusively in the methyl groups of the fumonisin backbone. The addition of as little as 5 mg of labeled methionine stimulated fumonisin production, but only about 5% of the fumonisin produced contained 3 deuterium atoms.Abbreviations ELEM equine leukoencephalomalacia Mention of companies or products by name does not imply their endorsement by the US Department of Agriculture over others not cited.     

Microbial metabolism and detoxification of 7,12-dimethylbenz[a]anthracene

Summary Six strains of fungi grown on Sabouraud dextrose broth in the presence of 7,12-dimethylbenz[a]anthracene (DMBA) were surveyed for their ability to metabolize DMBA. Experiments with [¹⁴C]DMBA indicated that the extent of formation of organic-soluble metabolites ranged from 6 to 28% after 5 days of incubation, depending on the organism tested. The yields of water-soluble metabolites also varied, and ranged from 1 to 33% after 5 days.Cunninghamella elegans ATCC 36112 andSyncephalastrum racemosum UT-70 exhibited the highest DMBA-metabolizing activity among the organisms surveyed.S. racemosum metabolized DMBA primarily to 7-hydroxymethyl-12-methylbenz[a]anthracene (7-OHM-12-MBA)_ and 7,12-dihydroxymethylbenz[a]anthracene (7,12-diOHMBA). Minor metabolites included 7-OHM-12-MBA-trans-5,6-, 8,9- and 10,11-dihydrodiols, and glucuronide and sulfate conjugates of phenolic derivatives of DMBA. In contrast, the major DMBA metabolites produced byC. elegans were water-soluble. The predominant organic-soluble metabolites produced byC. elegans included 7-OHM-12-MBA-trans-5,6-, 8,9- and 10,11-dihydrodiols. DMBA-trans-3,4-dihydrodiol was also detected. Circular dichroism spectral analysis revealed that the major enantiomer of the 7-OHM-12-MBA-trans-8,9-dihydrodiol formed by each organism has anS,S absolute configuration, while the major enantiomers of the 5,6-, 10,11- and 3,4-dihydrodiols had anR,R configuration. The mutagenic activity of extracts fromS. racemosum exposed to DMBA were determined inSalmonella typhimurium TA98. The mutagenicity of DMBA decreased by 36% over a period of 5 days as 33% of the compound was metabolized. Comparison of these results with previously reported results in mammalian systems suggests that there are similarities and differences between the fungal and mammalian oxidation of DMBA and that the overall balance of fungal metabolism is towards a detoxification rather than a bioactivation pathway.     

Production of Fusarium solani f. sp. pisi cutinase in Fusarium venenatum A3/5

Fusarium venenatum A3/5 was transformed using the Aspergillus niger expression plasmid, pIGF, in which the coding sequence for the F. solani f. sp. pisi cutinase gene had been inserted in frame, with a KEX2 cleavage site, with the truncated A. niger glucoamylase gene under control of the A. niger glucoamylase promoter. The transformant produced up to 21 U cutinase l⁻¹ in minimal medium containing glucose or starch as the primary carbon source. Glucoamylase (165 U l⁻¹ or 8 mg l⁻¹) was also produced. Both the transformant and the parent strain produced cutinase in medium containing cutin.     

Chlamydosporol,a new metabolite from Fusarium chlamydosporum

Extracts of rice on which an isolate of Fusarium chlamydosporum had been cultured were toxic to brine shrimps. The toxic fraction was purified by flash chromatography to give two compounds which were identified by UV, IR, NMR and mass spectroscopy at the 6 and 6 isomers of 5-hydroxy-4-methoxy-6, 8a-dimethyl-6,7-dihydro-2H,8aH-pyrano[2,3-b]pyran-2-one. These lactones for which the name chlamydosporol is proposed have not been reported previously. When tested in brine shrimp and HeLa cell assays, the LC₅₀ concentration for a mixture of the isomers was approximately 400 g/ml in both systems.     

Natural occurrence of fumonisins and their correlation to Fusarium contamination in commercial corn hybrids growth in Argentina

Fifty commercial corn hybrids with different endosperm characteristics, vegetative cycle length and cross class grown in the same geographical area (Cordoba Province, Argentina) were analysed for fumonisin accumulation. All hybrids analysed showed fumonisin B₁ and B₂ contamination ranging from 185 to 27,050 ng/g for FB₁ and from 40 to 9950 ng/g for FB₂. Although most of the hybrids analysed had flint-type endosperm, two hybrids with dent-type endosperm (e.g. Prozea 10 and AX 746) showed the highest level of fumonisin (37,000 ng/g) and more FB₂ than FB₁ (FB₂/FB₁ ratio 2.42), respectively. There was no correlation between fumonisin concentration and length of the vegetative cycle. Among 18 hybrids examined for Fusarium species contamination there was also no correlation between fumonisin contamination and the level of infection with Fusarium species (Section Liseola). Eighteen hybrids showed fumonisin levels lower than 1000 ng/g. This result suggests that there is some possibility of selecting hybrids resistant or less susceptible to fumonisin and Fusarium contamination.     

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.     

New monoterpene glycosides and phenolic compounds from Distylium racemosum and their inhibitory activity against ribonuclease H

Two new monoterpene glycosides, distyloside A-B (1-2), and a new megastigmane glucoside, iso-dihydrodendranthemoside A (3) were isolated from twigs and leaves of Distylium racemosum, along with five known phenolic compounds (4-8). The structures were established via spectroscopic techniques and chemical transformations, and the absolute stereochemistry of 3 was determined by Mosher’s esterification. A homogeneous fluorescence resonance energy transfer (FRET) quenching assay was used to determine the inhibitory activity of isolates (1-8) on the ribonuclease H enzymes from HIV-1, 2, human, and Escherichia coli. Among them, 6″-O-galloylsalidroside (6) showed potent inhibitory effects with an IC₅₀ value of 3.5 μM on HIV-2, and 1.7 μM on human RNase H, respectively.     

A model wheat cultivar for transformation to improve resistance to Fusarium Head Blight

Fusarium head blight (FHB), caused primarily by Fusarium graminearum, is a major disease problem in wheat (Triticum aestivum). Genetic engineering holds significant potential to enhance FHB resistance in wheat. Due to the requirement of screening for FHB resistance on flowers at anthesis, the number of screens carried out in a year is limited. Our objective was to evaluate the feasibility of using the rapid-maturing dwarf wheat cultivar Apogee as an alternative genotype for transgenic FHB resistance research. Our transformation efficiency (number of transgenic plants/number of embryos) for Apogee was 1.33%. Apogee was also found to exhibit high FHB susceptibility and reached anthesis within 4 weeks. Interestingly, microsatellite marker haplotype analysis of the chromosome 3BS FHB resistant quantitative trait locus (QTL) region indicated that this region maybe deleted in Apogee. Our results indicate that Apogee is particularly well suited for accelerating transgenic FHB resistance research and transgenic wheat research in general. C.A. Mackintosh and D.F. Garvin contributed equally to the article and should be considered co-first authors     

Fusarium root rot of coneflower seedlings and integrated control using <Emphasis Type="Italic">Trichoderma</Emphasis> and fungicides

Fusarium root rot (Fusarium spp.) is one of the most important seedling diseases of coneflower (Echinacea spp.) in Alberta greenhouses. Effects of microbial antagonists (Trichoderma spp.) and fungicides, including difenoconazole, fludioxonil, and a mixture of fludioxonil, metalaxyl and difenoconazole, on the management of this disease, were investigated in Alberta. Twenty Trichoderma isolates demonstrated antagonistic activity to Fusarium in agar plate bioassays, with inhibition rates ranging from 44 to 65%. Some Trichoderma isolates significantly ( p < 0.05) reduced disease incidence and severity on seedlings in greenhouse experiments. An in vitro bioassay indicated that difenoconazole and the mixture equally inhibited the growth of both Fusarium and Trichoderma, but, while fludioxonil strongly inhibited the growth of Fusarium, it had little effect on Trichoderma, according to the dose--response models developed ( p < 0.01, R²= 0.902-0.998). Two Trichoderma isolates, T1 and T13 were applied singly or in combination with a low rate of fludioxonil in greenhouse evaluations. The results suggested that fludioxonil and Trichoderma could be integrated into a disease management program for fusarium root rot in coneflower.     

Overexpression of defense response genes in transgenic wheat enhances resistance to Fusarium head blight

Fusarium head blight (FHB) of wheat, caused by Fusarium graminearum and other Fusarium species, is a major disease problem for wheat production worldwide. To combat this problem, large-scale breeding efforts have been established. Although progress has been made through standard breeding approaches, the level of resistance attained is insufficient to withstand epidemic conditions. Genetic engineering provides an alternative approach to enhance the level of resistance. Many defense response genes are induced in wheat during F. graminearum infection and may play a role in reducing FHB. The objectives of this study were (1) to develop transgenic wheat overexpressing the defense response genes α-1-purothionin, thaumatin-like protein 1 (tlp-1), and β-1,3-glucanase; and (2) to test the resultant transgenic wheat lines against F. graminearum infection under greenhouse and field conditions. Using the wheat cultivar Bobwhite, we developed one, two, and four lines carrying the α-1-purothionin, tlp-1, and β-1,3-glucanase transgenes, respectively, that had statistically significant reductions in FHB severity in greenhouse evaluations. We tested these seven transgenic lines under field conditions for percent FHB disease severity, deoxynivalenol (DON) mycotoxin accumulation, and percent visually scabby kernels (VSK). Six of the seven lines differed from the nontransgenic parental Bobwhite line for at least one of the disease traits. A β-1,3-glucanase transgenic line had enhanced resistance, showing lower FHB severity, DON concentration, and percent VSK compared to Bobwhite. Taken together, the results showed that overexpression of defense response genes in wheat could enhance the FHB resistance in both greenhouse and field conditions.