Evaluation of a Peroxyacetic Acid Disinfectant in Hot-water Treatment for the Control of Basal Rot (Fusarium oxysporum f. sp. narcissi) and Stem Nematode (Ditylenchus dipsaci) in Narcissus

Formaldehyde is used routinely in the hot-water treatment (HWT) of narcissus bulbs for the control of stem nematode (Ditylenchus dipsaci) and basal rot (caused by Fusarium oxysporum f.sp. narcissi). Formaldehyde is unpleasant for operators to use, and does not kill all of the thick-walled chlamydospores of F. oxysporum and so less hazardous but more effective materials are being sought. Peroxyacetic acid (as Jet 5, a commercial disinfectant containing 5% peroxyacetic acid) was evaluated in vitro and in a field trial as a possible alternative to formaldehyde. In laboratory studies, peroxyacetic acid (as 1% Jet 5) was as effective as formaldehyde (as 0.5% commercial formalin containing 38 to 40% formaldehyde) in killing free-swimming stem nematodes and nematodes in the wool stage. Peroxyacetic acid (as 0.5% Jet 5) killed F. oxysporum chlamydospores within 1 h, whereas total kill was not achieved with formaldehyde (concentration as above) after 4 h. In a 2 year field trial, there was no evidence of detrimental effects on a healthy narcissus stock due to using peroxyacetic acid. In an infested, diseased stock, bulbs were virtually destroyed by stem nematode within 2 years when HWT was not given. The greatest reduction in nematode symptoms, and the highest bulb yields, were found when formaldehyde or the higher rates of peroxyacetic acid were used in combination with thiabendazole.     

Induction of defence-related enzymes in onion by combined application of fungal and bacterial biocontrol agents against Fusarium oxysporum f. sp. cepae

Basal rot disease of onion is a major problem in different onion growing regions of Tamil Nadu, India. Fungal and bacterial cultures were isolated and tested their efficiency against Fusarium oxysporum f. sp. cepae under in vitro conditions. Effective bacterial and fungal antagonists were tested alone and in combinations for the control of F. oxysporum f. sp. cepae in glasshouse experiments. Defence-related enzymes such as peroxidase, polyphenol oxidase and phenylalanine ammonia-lyase were induced and accumulated in onion treated with fungal and bacterial antagonists. Defence-related enzymes were significantly higher in onion pretreated with consortial formulation of Pf12 + Pf27 + TH3 at 5 days after the challenge inoculation with F. oxysporum f. sp. cepae and gave resistance to onion against basal rot disease.     

Production of Pectic Enzymes by Fusarium oxysporum f. sp. cepae and its Involvement in Onion Bulb Rot

Fusarium oxysporum f. sp. cepae produced an exo-polygalacturonase (exo-PG) and endopectin-trans-eliminase (endo-PTE) in a mineral medium supplemented with a restricted supply of either D-galacturonic acid or onion cell walls. These enzymes were also extracted from infected onion tissue, but only endo-PTE caused tissue maceration and cell death. The patterns of host tissue colonization and pectic enzyme production were followed during bulb rot development. Stem plates were invaded within two weeks of inoculation. The pathogen then remained confined to the stem plates for several weeks or months, before spreading to the outer fleshy scales to initiate a basal rot. In most cases the inner leaf sheaths containing the lateral bud remained healthy. Exo-PG activity m stem plate tissue was greatest at two weeks after inoculation, then it declined. Endo-PTE was not detected in newly invaded stem plate tissue, but was recovered from infected stem plates before decay and from the bases of bulb scales and leaf sheaths at the onset of bulb rot. There was no pectic enzyme activity in uninvaded onion tissue. Spread of the fungus and pectic enzyme production in two Caledon Globe genotypes susceptible or tolerant to F. oxysporum f. sp. cepae were similar, but the onset of bulb rot in tolerant genotypes was considerably delayed.     

Survival of Sclerotium cepivorum Sclerotia and Fusarium oxysporum Chlamydospores in Soil Amended with Cruciferous Residues

The use of cruciferous plant residues to reduce the amount of sclerotia of Sclerotium cepivorum and chlamydospores of Fusarium oxysporum f. sp. lycopersici in soil was investigated. Air‐dried and crushed mustard (Brassica juncea) added to the soil effectively reduced the viability of fungal propagules. Consequently, the reduction of white rot of onion, caused by S. cepivorum and wild of tomato caused by F. oxysporum was observed. The addition of rapeseed (Brassica. napus cv. Bolko and B. napus cv. Gorczanski) residues to soil also resulted in a significant decrease of number of S. cepivorum sclerotia but the effect on F. oxysporum chlamydospores was variable. Introduction of the plant material increased the total number of bacteria, spore‐forming bacteria, fluorescent pseudomonads, actinomycetes, and fungi in soil. One year after the soil amendment, the amount of sporeforming bacteria in treatments with cruciferous residues was higher as compared to the control soil without plant residues. The possible contribution of the decomposition of plant residues and soil micro‐organisms to the reduction of the pathogens population is discussed.     

Interaction between Fusarium oxysporum F. vasinfectum and Cephalosporium maydis on cotton and maize

The interaction between Fusarium oxysporum (cause of cotton wilt) and Cephalosporium maydis (cause of maize late-wilt) on cotton roots is associated with an appreciable decrease in the severity of the cotton wilt disease. Reduction in infection is more pronounced when the latter fungus precedes the former in the soil than when they are inoculated simultaneously. C. maydis exerts little or no such effect when it follows F. oxysporum in the soil. C. maydis grows on the surface of cotton roots near growing points as a root-surface inhabitant. Dark red lesions are produced but these disappear, as does the fungus, when the root becomes hardened either naturally or in response to the growth of the fungus on the surface. The presence of the fungus is associated with increased production of root laterals. Cotton plants, including those which may appear healthy, show only mild internal symptoms of Fusarium infection when grown in soil inoculated with the two fungi, suggesting that the decreased severity of wilt is largely due to increased tolerance of the plants to infection with the disease as a result of increased number of root laterals. It is also possible that cotton roots with C. maydis on their surface become less suitable for the progress of F. oxysporum. F. oxysporum produces in culture a metabolite inhibitory to C. maydis. This may partly account for the little effect that the latter fungus exerts on the severity of wilt when it follows F. oxysporum in the soil. It appears that the interaction between F. oxysporum and C. maydis does not affect the pathogenicity of the latter fungus to maize.     

Studies on a species of Monosporascus isolated from triticum

Hyphal parasitic behaviour of Fusarium oxysporum on Rhizoctonia solani and consecutive changes during this phenomenon have been investigated and studied. The hyphal parasitism was very commonly recorded between the test fungi. During the course of parasitism coiling, penetration, lysis and formation of chlamydospores by F. oxysporum on R. solani were observed. R. solani is a new host record for the mycoparasite F. oxysporum.     

A rapid serological test for detecting Fusarium oxysporum f.sp. narcissi in Narcissus

Polyclonal antiserum was elicited against a strain of Fusarium oxysporum f.sp. narcissi (GCRI80/26) and a specific and sensitive enzyme-linked immunosorbent assay developed. Antiserum raised to cell wall fractions gave better recognition than that to cytoplasmic fractions. Recognition was equally good in artificially and naturally infected bulbs. Little cross-reactivity in bulb tissue was shown by three other bulb-rotting fungi. Nine isolates of F. oxysporum f.sp. narcissi from a wide geographic area gave similar results in an indirect ELISA of mycelial extracts, although some cross-reactivity was observed with two other Fusarium spp. Four Fusarium spp. and four other fungi showed little cross-reactivity. Ten days after inoculation the pathogen was readily detected in the base plate area of three Narcissus cultivars and points remote from the inoculation site in the most susceptible cultivar. A direct correlation was observed between positive results in the enzyme-linked immunosorbent assay and recovery of the pathogen on selective medium.     

Pathogenicity of Fusarium oxysporum to Easter lily, narcissus and gladiolus

Isolates of Fusarium oxysporum from roots, bulbs and stems of Easter lilies (Lilium longiflorum) differed widely in pathogenicity and also, apparently, in tissue specificity. Virulent isolates caused a typical basal rot and root rot (but not a wilt) in which the mycelium advanced intercellularly through the scales and basal plates. Mildly pathogenic isolates became established in mature or senescent outer scales, at first producing only superficial effects, but further growth of mycelium occurred as the outer scales died and sometimes continued until the dead tissues were permeated and chlamydospores were formed. The underlying scales were then colonized. The modes of pathogenicity and survival in Easter lily were compared with those of the F. oxysporum formae causing bulb rots of gladiolus and narcissus. It is suggested that advance of hyphae by penetration between the cells of the vascular parenchyma, which is common in isolates causing rots in bulbs and corms, represents a stage in the evolution of the truly vascular habit among fusaria.     

Fungus gnats vector Fusarium oxysporum f.sp. radicislycopersici1

Fungus gnat adults transported Fusarium oxysporum f.sp. radicis-lycopersici from Petri dish culture and infected host plants to the roots and hypocotyls of healthy tomato and bean plants. The source of the fungus did not affect the ability of fungus gnats to transport the fungus to healthy hosts. The presence of fungus gnat larvae in media in which young tomato plants were grown did not increase the incidence of plant infection by the pathogen. Fungus gnat adults appear to aid in the dissemination of F. oxysporum f.sp. radicis-lycopersici.     

Detection of cross-reactive antigens shared byFusarium oxysporum andGlycine max by indirect ELISA and their cellular location in root tissues

Pathogenicity test ofFusarium oxysporum on ten cultivars of soybean revealed Soymax and Punjab-1 to be most resistant while JS-2 and UPSM-19 were most susceptible. Antigens were prepared from the roots of all the ten varieties of soybean and the mycelium ofF. oxysporum. Polyclonal antisera were raised against the mycelial suspension ofF. oxysporum and the root antigen of the susceptible cultivar UPSM-19. Cross reactive antigens shared by the host and the pathogen were detected first by immunodiffusion. The immunoglobulin fraction of the antiserum was purified by ammonium sulfate precipitation and DEAE-Sephadex column chromatography. The immunoglobulin fractions were used for detection of cross-reactive antigens by enzyme-linked immunosorbent assay. In enzyme-linked immunosorbent assay, antigens of susceptible cultivars showed higher absorbance values when tested against the purified anti-F. oxysporum antiserum. Antiserum produced against UPSM-19 showed cross-reactivity with the antigens of other cultivars. Indirect staining of antibodies using fluorescein isothiocyanate indicated that in cross-sections of roots of susceptible cultivar (UPSM-19) cross-reactive antigens were concentrated around xylem elements, endodermis and epidermal cells, while in the resistant variety, fluorescence was concentrated mainly around epidermal cells and distributed in the cortical tissues. CRAs were also present in microconidia, macroconidia and chlamydospores of the fungus.     

Comparison of two fatty acid analysis protocols to characterize and differentiate Fusarium oxysporum f. sp. lycopersici and F. oxysporum f. sp. radicis-lycopersici

The utility of fatty acid methyl ester (FAME) profiles for characterization and differentiation of isolates of Fusarium oxysporum f. sp. lycopersici and F. oxysporum f. sp. radicis-lycopersici was investigated. Two fatty acid analysis protocols of the normal (MIDI) and a modified MIDI method were used for their utility. Only the modified MIDI method allowed a clear differentiation between F. oxysporum f. sp. lycopersici and F. oxysporum f. sp. radicislycopersici. FAME profiles using the modified MIDI method gave the most consistent and reproducible analyzed fatty acid data. Evaluation of the FAME profiles based on cluster analysis and principal-component analysis revealed that FAME profiles from tested isolates were correlated with the same vegetative compatibility groups (VCGs) compared to the same races in F. oxysporum f. sp. lycopersici. Results indicated that FAME profiles could be an additional tool useful for characterizing isolates and forma species of F. oxysporum obtained from tomato.     

Frequency and diversity of Fusarium spp. colonizing roots of Egyptian cottons

Abstract

Fusarium species are known to play a role in several diseases of cotton including the seedling disease complex, wilt, and boll rot. Therefore, a mycoflora study was conducted in 1998 in order to identify Fusarium species found in association with cotton roots. A total of 109 samples of cotton seedlings infected with post-emergence damping-off or rotted roots of adult plants were obtained from different cotton-growing areas in Egypt. Forty-six isolates were recovered and were identified as follows: F. oxysporum (28 isolates), F. moniliforme (9), F. solani (6), F. avenaceum (2), F. chlamydosporum (1). F. oxysporum, F. moniliforme and F. solani, the dominant species, accounted for 60.9%, 19.6% and 13% of the total isolates, respectively in 1998. F. oxysporum showed the highest isolation frequency in Beharia and Minufiya while F. moniliforme showed the most isolation frequency in Minufiya and Gharbiya. F. oxysporum was one of the major taxa of the Fusarium assemblage from Giza 70. F. oxysporum showed the most frequently isolated fungus in May while F. moniliforme and F. solani were the most frequently isolated fungi in August. Isolation frequency of Fusarium spp. during July and August was significantly greater than that of April or June. This implies that cotton roots are subjected more to colonization by Fusarium spp. as plants mature. Regarding pathogenicity, of the 46 isolates of Fusarium spp. tested under greenhouse conditions, 38 isolates (82.4%) were pathogenic to seedlings of Giza 89. This study indicates that F. oxysporum and F. moniliforme are important pathogens in the etiology of cotton damping-off in Egypt.     

Effect of Placement and Sequence of Inoculation with Fusarium oxysporum on its Interaction with Meloidogyne arenaria on Subterranean Clover

The effect of the placement of inoculum of Fusarium oxysporum at two soil depths, and the sequences of inoculations with Meloidogyne arenaria and Fusarium oxysporum on root growth and development of root disease in Trifolium subterraneum L. (subterranean clover) were investigated. The timing of infection and the proximity of root tips of the host root system to infection by M. arenaria and F. oxysporum appeared to be the major determining factors of root growth and of disease development in plants exposed to the pathogens. Immediate contact of roots with F. oxysporum (where the fungus was placed at seed level of 10 mm depth) appeared to result in more severe effects on roots in the presence of the nematode than later infection by the fungus placed at 30 mm depth. The production of galls by the nematode and early infection by F. oxysporum at 10 mm depth resulted in a severe inhibition of root growth, particularly of the lateral roots. But no such growth inhibition was evident when F. oxysporum and M. arenaria were introduced together at the lower depth of 30 mm. The lowest density of M. arenaria inoculum was sufficient to cause severe root rot if F. oxysporum was present at the host seed level. With the fungus at 30 mm depth, however, the expression of root rot appeared to be influenced by the inoculum level of the nematode. In sequential inoculation with F. oxysporum or M. arenaria, the organism added 2 weeks later had little or no effect on root development. The first organism (M. arenaria or F. oxysporum) to infect the germinated seedlings was the main cause of root growth inhibition. The organism that came into contact with the roots 2 weeks later had little or no effect on the roots. Concurrent infection by F. oxysporum and M. arenaria resulted in less M. arenaria gall production on the tap root system than those added with the nematode alone or in advance of the fungus.     

Influence of pea-root exudates on germination of conidia and chlamydospores of physiologic races of Fusarium oxysporum f. pisi

Sterile root exudates from wilt susceptible and wilt resistant pea cultivars showed no differential effects on spore germination of Fusarium oxysporum Schl. f.pisi (Linf.) Snyd. & Hans, races 1 and 2 which could be correlated with the pathogenicity of a particular isolate to a given cultivar. Uniformly high percentages of germination were obtained with conidia of the two races in aseptic shake culture with exudates collected from resistant or susceptible plants of various ages. Chlamydospores of the two races incubated with exudates under sterile conditions germinated to uniformly high levels irrespective of exudate origin. Conidia and chlamydospores of Fusarium solani (Mart.) Sacc. f. pisi (Jones) Snyd. & Hans., used for comparative purposes, also germinated to high levels in the presence of exudate solutions of all cultivars. Non-specific germination of the two races of F. oxysporum f. pisi occurred in soil when the exudates were supplied to populations of chlamydospores via diffusion units. Germination was lower than that recorded under sterile conditions and was rapidly followed by germling lysis.     

Bulb and Root Rot in Lily (Lilium longiflorum) and Onion (Allium cepa) in Israel

In the past 10 years, there has been a substantial increase in reports, from growers and extension personnel, on bulb and root rots in lily (Lilium longiflorum) in Israel. Rot in these plants, when grown as cut flowers, caused serious economic damage expressed in reduction in yield and quality. In lily, the fungal pathogens involved in the rot were characterized as binucleate Rhizoctonia AG‐A, Rhizoctonia solani, Pythium oligandrum, Fusarium proliferatum (white and purple isolates) and F. oxysporum, using morphological and molecular criteria. These fungi were the prevalent pathogens in diseased plants collected from commercial greenhouses. Pathogenicity trials were conducted on lily bulbs and onion seedlings under controlled conditions in a greenhouse to complete Koch's postulates. Disease symptoms on lily were most severe in treatments inoculated with binucleate Rhizoctonia AG‐A, P. oligandrum and F. proliferatum. Plant height was lower in the above treatments compared with the control plants. The least aggressive fungus was R. solani. In artificial inoculations of onion, seedling survival was significantly affected by all fungi. The most pathogenic fungus was F. proliferatum w and the least were isolates of F. oxysporum (II and III). All fungi were successfully re‐isolated from the inoculated plants.     

Influence of the ectomycorrhizal fungus <Emphasis Type="Italic">Laccaria laccata</Emphasis> on pre-emergence,post-emergence and late damping-off by <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> and <Emphasis Type="Italic">F. verticillioides</Emphasis> on Stone pine seedlings

In greenhouse experiments, the ectomycorrhizal fungus Laccaria laccata was evaluated for biological control of preemergence, post-emergence and late damping-off of Pinus pinea caused by Fusarium verticillioides and F. oxysporum. In pre-emergence damping-off assays, preinoculation with Laccaria laccata did not significantly improve germination of seeds and no statistical significant differences were found in Fusarium treatments when compared with controls. At 18 weeks after sowing, inoculation with L. laccata reduced the incidence of post-emergence damping-off but differences were significant only in F. oxysporum treatments. Pinus pinea transplanted plants were used in late damping off assays, and only F. oxysporum produced significant damage. Inoculation with L. laccata did not attenuate significantly the virulence of F. oxysporum. However, the percentage of mycorrhization did not reached significant level, so the amount of mycorrhizal fungus was insufficient for effective protection. Although very low percentages of mycorrhization were recorded in all mycorrhized treatments, and Fusarium occurrence significantly reduced mycorrhization, those levels have been efficient to reduce damage in F. oxysporum post-emergence damping-off assays. In short, pre-emergence damping-off was not found; only F. oxysporum produced significant damage on P. pinea seedlings and L. laccata reduced damage when the percentage of mycorrhization reached a significant level. These results have been compared with previous work on P. sylvestris inoculated with the same mycorrhizae isolate and Fusarium pathogens.     

Galleria mellonella as model host for the trans-kingdom pathogen Fusarium oxysporum

Fusarium oxysporum, the causal agent of vascular wilt disease, affects a wide range of plant species and can produce disseminated infections in humans. F. oxysporum f. sp. lycopersici isolate FGSC 9935 causes disease both on tomato plants and immunodepressed mice, making it an ideal model for the comparative analysis of fungal virulence on plant and animal hosts. Here we tested the ability of FGSC 9935 to cause disease in the greater wax moth Galleria mellonella, an invertebrate model host that is widely used for the study of microbial human pathogens. Injection of living but not of heat-killed microconidia into the hemocoel of G. mellonella larvae resulted in dose-dependent killing both at 30 °C and at 37 °C. Fluorescence microscopy of larvae inoculated with a F. oxysporum transformant expressing GFP revealed hyphal proliferation within the hemocoel, interaction with G. mellonella hemocytes, and colonization of the killed insects by the fungus. Fungal gene knockout mutants previously tested in the tomato and immunodepressed mouse systems displayed a good correlation in virulence between the Galleria and the mouse model. Thus, Galleria represents a useful non-vertebrate infection model for studying virulence mechanisms of F. oxysporum on animal hosts.     

Growth substrates control the ability of Fusarium oxysporum to solubilize low-rank coal

The ability of the fungus Fusarium oxysporum to solubilize lignite was found to depend on the presence of a specific carbon source. When grown on glucose or another carbohydrate, the fungus is unable to solubilize coal but it produces the red dye bikaverin. In the coal-solubilizing state, which can be induced by cultivation in the presence of glutamate or gluconate, the fungus does not produce bikaverin. The presence or absence of the pigment can therefore be taken as an indicator of the ability of the fungus to solubilize coal. Addition of extracted and purified bikaverin to F. oxysporum growing on glutamate or gluconate inhibits coal solubilization. Hence, F. oxysporum offers a suitable system for investigating the mechanism of microbial coal degradation by comparing the two growth-substrate-controlled physiological states.     

Dismutation and cross-dismutation of aldehydes, and alcohol: aldehyde oxidoreduction by resting-cells of Pseudomonas putida F61-a

Pseudomonas putida F61-a defective in formaldehyde dehydrogenase was derived from the parent strain (F61). The bacterial strain grown on a nutrient broth supplemented with 1% glucose exhibited high formaldehyde dismutase activity. The dismutation and cross-dismutation of aldehydes occurred stoichiometrically in the resting-cells reaction. Many kinds of aliphatic and aromatic aldehydes that are scarcely soluble in water were utilized in these reactions as well as soluble ones. Formaldehyde at an extremely high concentration (0.5 M) was almost completely converted to equimolar amounts of methanol and formic acid by the resting-cells, which could be used three times without a loss of activity. The cross-dismutation between acrolein and formaldehyde occurred efficiently in the resting-cells reaction with 0.1 M each substrate. The alcohol: aldehyde oxidoreduction of the short-chain substrates was also shown by the resting-cells of a mutant (M6) unable to grow on n-propanol.     

Further Investigation of the Specificity of Interactions Between Wild Lactuca spp. and Bremia lactucae Isolates from Lactuca serriola

Callus cultures derived from isogenic lines of the tomato cultivars Moneymaker and Craigella, resistant or susceptible to F. oxysporum f. sp. lycopersici, were inoculated with Fusarium oxysporum f. sp. lycopersici race 1. Fungal growth was restricted on callus derived from resistant plants, after inoculation with a conidial suspension, whereas callus derived from susceptible plants was totally overgrown by the fungus within 7 days. The concentration of the phytoalexin rishitin was significantly higher in the callus culture derived from a resistant tomato line compared with the callus culture from a susceptible line, 2 and 3 days after inoculation with mycelium. The results of the experiments were compared with experiments with whole plants. Rishitin production as well as growth of the fungus was comparable with responses in plant-fungus interaction. Therefore callus culture may be useful in studying the interaction between tomato plants and race 1 of F. oxysporum f. sp. lycopersici.