Volatile and gaseous metabolites released by germinating seeds of lentil and maize cultivars with different susceptibilities to fusariosis and smut

The effect of volatile and gaseous metabolites released by germinating seeds of lentil cultivars more and less susceptible to fusariosis on the germination of spores ofMucor racemosus, Trichoderma viride, Verticillium dahliae andBotrytis cinerea was found to depend rather on the fungal genus than on the lentil cultivar. However, spores ofFusarium oxysporum reacted more sensitively during germination to the presence of exudates of both cultivars, when the more susceptible lentil displayed a stimulation, the less susceptible one an inhibition of spore germination. The greatest difference in the effect of exudates was observed in the more and less susceptible maize cultivars with respect to the germination of chlamydospores ofUstilago maydis, especially during the first hours of seed germination. Analysis of the exudates of germinating seeds showed the release of a greater amount of ethanol and methanol with acetaldehyde by the more susceptible cultivars of lentil and particularly maize.     

Effect of volatile substances fromOriganum majorana andOcimum basilicum on spore respiration and germination of some soil fungi

Oxygen uptake by the spores ofFusarium moniliforme, F. oxysporum, F. semitectum, F. solani, Mucor racemosus andTrichoderma viride was increased in the presence of volatile substances extracted, fromOriganum majorana andOcimum basilicum. This increase was greater in the presence of volatile substances fromO. basilicum thanO. majorana, except in the case ofF. semitectum where the reverse was true. A drop in the RQ of all the germinating spores was observed in the presence of these substances. Volatile substances fromO. majorana reduced the spore germination ofM. racemosus whereas the spores ofT. viride were stimulated to germinate. Volatile substances fromO. basilicum stimulated the spore germination ofM. racemosus whereasT. viride spores were not affected.     

Effect of volatile and gaseous metabolites of germinating pea seeds on micromycetes

Differences in the effect of volatile and gaseous metabolites of germinating pea seeds on the germination of spores of Mucor racemosus and macroconidia of Fusarium oxysporum are described. Germination of spores of M. racemosus was inhibited by seed metabolites whereas germination of macroconidia of F. oxysporum was stimulated during the first two days and inhibition occurred only after further two days of germination of the seeds. A pronounced inhibition of germination of spores of both micromycetes took place due to absorption of CO2 from volatile and gaseous metabolites. Absorption of some components of seed metabolites in a KMnO4 solution led to a decrease of the inhibitory effect on germination of spores of M. racemosus and stimulatory effect on germination of macroconidia of F. oxysporum.     

Induced resistance to Botrytis cinerea in Capsicum annuum by a Fusarium crude elicitor fraction,free of proteins

Fusarium oxysporum f. sp. lycopersici (FOL) induces resistance in pepper against the airborne pathogen Botrytis cinerea and the soil‐borne pathogen Verticillium dahliae. However, its practical use is limited due to its pathogenicity to other crops. In this study we tested several fractions of a heat‐sterilised crude FOL‐elicitor preparation to protect pepper against B. cinerea and V. dahliae. Only the protein‐free insoluble fraction of the preparation reduced B. cinerea infection. However, none of the fractions reduce V. dahliae symptoms. The insoluble protein‐free fraction induced expression of defence genes in the plant, namely a chitinase (CACHI2), a peroxidase (CAPO1), a sesquiterpene cyclase (CASC1) and a basic PR1 (CABPR1). Even though the CASC1 gene was not induced directly after treatment with the insoluble fraction in the leaves, it was induced after B. cinerea inoculation, showing a priming effect. The insoluble protein‐free FOL‐elicitor protected pepper against the airborne pathogen through a mechanism that involves induced responses in the plant, but different to the living FOL.     

Biological control of a soil-borne pythium infection by seed inoculation

Summary 1. A three-fold effect was produced on white mustard seedlings grown in soil infected withPythium sp. Seed germination, the number of healthy plants which survived and the fresh weight of the shoots were reduced.2. Disease symptoms were controlled to some extent by dusting the seeds with spores of some common soil saprophytes includingTrichoderma viride, Penicillium nigricans, P. jrequentans andP. godlewskii.3. Of three strains ofTrichoderma viride which were tested for antagonism toPythium sp., a gliotoxin-producing strain was more effective in controlling the disease than a viridin-producing strain and an antibiotically inactive strain gave least protection to the seedlings.4. The disease symptoms were less severe in soil treated with acid or calcium hydroxide. Inoculation of the seeds withT. viride gave further control of the disease in soil treated with calcium hydroxide but not in acidified soils. These results are discussed in relation to the production of gliotoxin byT. viride.     

A stable inhibitor of spore germination produced by fungi

Summary The level of inhibition of germination of spores added to cell-free culture filtrates of Fusarium oxysporum Schlecht. ex Fr. declines with time. This decline can be accounted for by the decreasing levels of volatile sporostatic factors and a stable vacuolation factor produced by F. oxysporum. After the disappearance of the volatile sporostatic factors, a stable principle is recognised in the culture filtrate by a persistent level of inhibition of spore germination which is not completely alleviated by the addition of nutrients. A stable inhibitor of spore germination has been isolated and characterised as nonanoic acid, and evidence is presented that this compound is widely produced among fungi and can inhibit the germination of spores of many fungal species. The contribution of nonanoic acid to sporostasis in cultures of F. oxysporum is assessed.     

Effect of rhizosphere fungi on seed germination

Summary The effect of culture filtrates of some common rhizosphere fungi on the seed germination ofDichanthium annulatum, Bothriochloa pertusa andSetaria glauca was studied. Surface sterilized seeds were soaked in the fungal culture filtrates for 24 hours and after several washings in distilled water transferred to moist filter paper in Petri dishes and the percentage germination recorded. No significant inhibition or stimulation of germination was noticed in any of the treatments. The only exception wasTrichoderma viride which inhibited the germination ofD. annulatum seeds to some extent.     

Colonization ofRetama raetam seeds by fungi and their significance in seed germination

Examination by scanning electron microscopy and incubation on potato-dextrose agar medium showed that dry seeds ofRetama raetam were externally free of fungi. When planted in sandy loam soil, the seeds become colonized with eleven soil-borne fungal species. The fungi were isolated on cellulose agar, pectin agar and lignin agar media.Aspergillus flavus, A. niger, A. fumigatus, Penicillium capsolatum andFusarium oxysporum had broad occurrence and were recovered on all the three media. The production of hydrolytic enzymes by the isolated fungi depends on the substrate and species.Penicillium capsolatum, P. spinulosum andA. niger had wide enzymatic amplitude and they were able to produce cellulolytic, pectolytic and lignolytic activities on corresponding substrates as well as on seed-coat-containing media. The lignolytic activities of the isolated species exceptChaetomium bostrychodes andTrichoderma viride were enhanced by applying the seed-coat materials as C- source rather than lignin. SoakingR. raetam seeds in culture filtrates of most of the fungi grown on seed-coat-supplemented media induced a pronounced and distinct stimulating effect on seed germination. The most effective filtrates were those ofP. capsolatum, P. spinulosum andSporotrichum pulverulentum.     

Anti-Fungal Sesquiterpenoid from the Root Exudate of Solanum abutiloides

The Solanum abutiloides plant is highly resistant to soil-borne pathogens such as Fusarium oxysporum f. sp. melongenae, Verticillium dahliae, and Ralstonia solanacearum. This species is utilized as a mating source of resistant cultivars and is also used as a rootstock. The root exudate of Solanum abutiloides was extracted from a soil system composed of charcoal and vermiculite. Anti-fungal activity was found in the extract, and an active ingredient was isolated. The chemical structure of the active compound was determined to be 3-β-acetoxysolavetivone, a new sesquiterpenoid. The anti-fungal activity of 3-β-acetoxysolavetivone examined by the inhibition of spore germination of Fusarium oxysporum was close to that of lubimin, and higher than that of solavetivone.     

Antagonistic activity and hyphal interactions of Trichoderma spp. against Fusarium proliferatum and F. oxysporum in vitro

Trichoderma is a well-known antagonist against soilborne plant pathogens. However, the species and even various isolates have different biocontrol potential. To evaluate the antagonistic activities of Trichoderma harzianum, T. harzianum strain T100 (T100), T. viride and T. haematum against Fusarium oxysporum and F. proliferatum, we used dual culture and productions of volatile and non-volatile metabolites in three different phases in vitro. An analysis of the data in dual culture tests represented T. viride, T. haematum and T100 as effective antagonists of Fusarium while T100 was the only fungus being able to lyse the confronting mycelia. Similar results were obtained in the volatile metabolites tests also. In contrast with the two previous tests, the non-volatile metabolites produced by T. harzianum inhibited Fusarium mycelial growth the most, and T100 acted moderately. It was also clearly showed that the antagonistic effect of Trichoderma spp. was more on F. proliferatum than on F. oxysporum. Finally, because Trichoderma spp. was most effective in the second phase, we recommend to use T100 against F. proliferatum at the initial stages of infection as its mycoparasitism on F. oxysporum was observed microscopically through forming apressoria structures without any coiling around the pathogen.     

Protection of Fusarium and Verticillium Propagules from Selected Biocides Following Ingestion by Pristionchus lheritieri

Spores of Fusarium oxysporum f. lycopersici or Verticillium dahliae (potato strain) ingested by Pristionchus Iheritieri (a saprozoic nematode) survived exposure to otherwise lethal solutions of free chlorine, thiabendazole or the methyl ester of l-butylcarbamoyl-2-bendimidazole carbamic acid. Viability of mechanically-freed or defecated spores were the same.     

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.     

Trichoderma viride as a mycoparasite ofAspergillus spp.

Summary Trichoderma viride was found to be parasitic on three species of Aspergillus. The mycoparasitism was characterized by frequent coiling, penetration and hyphal growth of the parasite inside the conidiophores of Aspergillus. The volatile and non-volatile metabolites ofT. viride, more or less, inhibited radial growth of all the testAspergillus spp.     

Growth and conidiation ofTrichoderma viride are affected by non-steroidal antiinflammatory agents

Nonsteroid antiinflammatory agents (NSAIA's) (inhibitors of cyclooxygenase and lipoxygenase) of several structural series inhibited growth ofTrichoderma viride. The most potent growth inhibitors were indomethacin and its derivative repanidal which inhibited in the range of 0.1 mmol/L. The weakest inhibitors were acetylosalicylic acid and lysine salicylate which exerted only a weak effect at concentrations above 1 mmol/L. The inhibition of growth was accompanied by a stimulation of conidiation in the dark. A light pulse increased the efficiency of these drugs to stimulate the conidiation.Saccharomyces cerevisiae was as sensitive to NSAIA's asT. viride whileBotrytis cinerea was less sensitive. The results indicate that arachidonate metabolism may play a role in the growth of fungi and may participate also in the process of conidiation.     

A non-cyclic baboon θ-defensin derivative exhibiting antimicrobial activity against the phytopathogen Verticillium dahliae

θ-Defensins are the only natural cyclic proteins found in primates. They have strong antimicrobial activity related to their trisulfide ladders and macrocyclic conformation. A non-cyclic baboon θ-defensin (BTD) was synthesized by substituting valine with phenylalanine at position 17, at the C-terminal end of the BTD; this was termed “BTD-S.” The antimicrobial activities of this synthetic peptide were investigated against Escherichia coli and two cotton phytopathogens: Verticillium dahliae and Fusarium oxysporum. The minimum inhibitory concentration (MIC) of BTD-S for E. coli was 10 μg/mL and for V. dahliae was 5 μg/mL, significantly lower than that for F. oxysporum (40.0 μg/mL). A time course analysis of fungal cultures indicated that the growth of V. dahliae was completely inhibited after 96 h of BTD-S treatment. Furthermore, hemolysis assays revealed that BTD-S was not toxic to mammalian cells as it could not induce lysis of sheep red blood cells even at ten times the MIC (50 μg/mL). Scanning electron microscopy and double-stained (calcofluor white and propidium iodide binding) fluorescence microscopy showed that exposure of spores of V. dahliae to BTD-S either disabled normal germination or disintegrated the spores. The size of cells exposed to BTD-S was significantly reduced compared with controls, and their number increased in a dose-dependent curve when measured by flow cytometry. These findings suggest that BTD-S has great potential to inhibit the growth of V. dahliae and can be utilized as an effective remedy to control economic losses caused by Verticillium wilt in the development of wilt-resistant cotton.     

Direct effect of biocontrol agents on wilt and root-rot diseases of sesame

In Egypt, sesame cultivation is subject to attack by wilt and root-rot diseases caused by Fusarium oxysporum f.sp. sesami (Zap) Cast. and Macrophomina phaseolina (Maubl) Ashby causing losses in quality and quantity of sesame seed yield. Bacillus subtilis and Trichoderma viride isolates which were isolated from sesame rhizosphere were the most effective to antagonise fungal pathogens, causing high reduction of hyphal fungal growth. Trichoderma viride was found to be mycoparasitic on Fusarium oxysporum f.sp. sesami and M. phaseolina causing morphological atternation of fungal cells and sclerotial formation. In general, Bacillus subtilis, T. viride, avirulent Fusarium oxysporum isolate and Glomus spp. (Amycorrhizae) significantly reduced wilt and root-rot incidence of sesame plants at artificially infested potted soil by each one or two pathogens. Data obtained indicate that Glomus spp significantly reduced wilt and disease severity development on sesame plants followed by T. viride. Meanwhile, avirulent Fusarium oxysporum isolate followed by Glomus spp. were effective against root-rot disease incidence caused by M. phaseolina. Glomus spp. followed by B. subtilis significantly reduced wilt and root-rot disease of sesame plants. All biotic agents significantly reduced F. oxysporum f.sp. sesami and M. phaseolina counts in sesame rhizosphere at the lowest level. Glomus spp. and the avirulent isolate of F. oxysporum eliminated M. phaseolina in sesame rhizosphere. Meanwhile T. viride was the best agent at reducing F. oxysporum at a lower level than other treatments. Application of VA mycorrhizae (Glomus spp.) in fields naturally infested by pathogens significantly reduced wilt and root-rot incidence and it significantly colonised sesame root systems and rhizospheres compared to untreated sesame transplantings.     

Endophytic Bacteria Induce Growth Promotion and Wilt Disease Suppression in Oilseed Rape and Tomato

To determine whether bacteria isolated from within plant tissue can have plant growth-promotion potential and provide biological control against soilborne diseases, seeds and young plants of oilseed rape (Brassica napus L. cv. Casino) and tomato (Lycopersicon lycopersicum L. cv. Dansk export) were inoculated with individual bacterial isolates or mixtures of bacteria that originated from symptomless oilseed rape, wild and cultivated. They were isolated after surface sterilization of living roots and stems. The effects of these isolates on plant growth and soilborne diseases for oilseed rape and tomato were evaluated in greenhouse experiments. We found isolates that not only significantly improved seed germination, seedling length, and plant growth of oilseed rape and tomato but also, when used for seed treatment, significantly reduced disease symptoms caused by their vascular wilt pathogens Verticillium dahliae Kleb and Fusarium oxysporum f. sp. lycopersici (Sacc.), respectively.     

Fusarium lateritium Nees ex Link as a Parasite and Host in Interfungal Hyphal Interactions

In dual cultures Fusarium lateritium Nees ex Link coiled, penetrated and destroyed young actively growing hyphae of Botrytis cinerea Pers., Cytospora rubescens Fr., Eutypa armeniacae Hansf. et Carter, Sphaeropsis malorum Peck, Rhizoctonia solani Kühn, Trichoderma koningii Oud. (Tk-1) and Trichoderma hamatum (Bon.) Bain. (Tha-2), and conidiophores and conidia of Botrytis cinerea Pers. The isolates of Trichoderma koningii Oud. (Tk-3) and Trichoderma pseudokoningii Rifai (Tp-1) parasited and destroyed the hyphae of Fusarium lateritium. There was no hyphal interaction between Fusarium lateritium and an isolate of Trichoderma longibrachiatum Rifai. Hyphal, interactions occurred mostly on the aerial hyphae of test fungi which grew over the inhibition zone formed between the colonies of Fusarium lateritium and the test fungus, and contacted the hyphae of Fusarium lateritium. Details of dual culture studies are given.     

Studies on some fungi isolated from the rhizosphere of tomato plants and the consequent prospect for the control of Verticillium wilt

Summary Biological control of Verticillium wilt disease with antagonistic micro-organisms was studied. Antagonism of some fungi, isolated from tomato rhizosphere, toVerticillium albo-atrum R & B. was observedin vitro. A clearly defined zone, in which the growth of the pathogen was inhibited, was observed withPenicillium spp. (includingPenicillium chrysogenum Thom) andFusarium culmorum (S.G. Sm) Sacc., whileTrichoderma viride pers. ex Fries,Gliocladium spp. andPenicillium vermiculatum Dangeard, suppressed the growth ofV. albo-atrum by penetrating, and overgrowing it. OnlyT. viride andP. vermiculatum culture filtrate added to the Dox's agar, reduced the radial growth ofV. alboatrum. Root-dip application of culture filtrates ofT. viride andP. chrysogenum was found to be most effective in controlling the disease, followed by other species ofPenicillium andGliocladium spp. WhileFusarium culmorum provided no control. Improvement of plant height and vigour with a better yield due to culture filtrate treatment occurred. Root-dip application of antagonistic fungal propagules (T. viride, P. chrysogenum) to tomato seedlings was also very effective in controlling wilt in tomato plants grown inV. albo-atrum infested soil. Dedicated to the memory of the late Prof. Ivor Isaac with whom I had the pleasure of working     

Verticillium dahliae (Kleb.) Infecting Pumpkin Seed

This study investigated the natural occurrence of Verticillium dahliae (Kleb.) infection in pumpkin (Cucurbita pepo L.) seed. The mean incidence of infection was found to be 21.0%. Isolates recovered from seeds were pathogenic to pumpkin (cultivar ‘Jamaican squash’). Surface sterilization by immersion in 0.6% sodium hypochlorite for 20 min eradicated V. dahliae from infected pumpkin seeds without affecting germinability. Plating of seed components revealed that the fungus was present in the seed coat but not in the embryo or cotyledons. In a growing‐on test, 25% of 6‐week‐old plants grown from untreated seeds were infected. Germination and production of normal seedlings were unaffected by V. dahliae infection of seeds. Verticillium dahliae in pumpkin seed was found to be external and transmissible to plants. The findings of this study are important in devising disease control strategies.