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.     

Effects of water potential on spore germination and viability of <Emphasis Type="Italic">Fusarium</Emphasis> species

Germination of macroconidia and/or microconidia of 24 strains of Fusarium solani, F. chlamydosporum, F. culmorum, F. equiseti, F. verticillioides, F. sambucinum, F. oxysporum and F. proliferatum isolated from fluvial channels and sea beds of the south-eastern coast of Spain, and three control strains (F. oxysporum isolated from affected cultures) was studied in distilled water in response to a range of water potentials adjusted with NaCl. (0, −13.79, −41.79, −70.37, −99.56 and −144.54 bars). The viability (UFC/ml) of suspensions was also tested in three time periods (0, 24 and 48 h). Conidia always germinated in distilled water. The pattern of conidial germination observed of F. verticilloides, F. oxysporum, F. proliferatum, F. chlamydosporum and F. culmorum was similar. A great diminution of spore germination was found in −13.79 bars solutions. Spore germination percentage for F. solani isolates was maximal at 48 h and −13.79 bars with 21.33% spore germination, 16% higher than germination in distilled water. F. equiseti shows the maximum germination percentage in −144.54 bars solution in 24 h time with 12.36% germination. This results did not agree with those obtained in the viability test were maximum germination was found in distilled water. The viability analysis showed the great capacity of F. verticilloides strains to form viable colonies, even in such extreme conditions as −144.54 bars after 24 h F. proliferatum colony formation was prevented in the range of −70.37 bars. These results show the clear affectation of water potential to conidia germination of Fusaria. The ability of certain species of Fusarium to develop a saprophytic life in the salt water of the Mediterranean Sea could be certain. Successful germination, even under high salty media conditions, suggests that Fusarium spp. could have a competitive advantage over other soil fungi in crops irrigated with saline water. In the specific case of F. solani, water potential of −13.79 bars affected germination positively. It could indicate that F. solani has an special physiological mechanism of survival in low water potential environments.     

Germination of phytopathogenic fungi conidia

The autoregulation of conidium germination in phytopathogenic micromycetes of the genera Fusarium, Botrytis, and Bipolaris was studied. It was shown that Trichoderma longibrachiatum was less competitive than Fusarium oxysporum after their simultaneous inoculation but inhibited the phytopathogen growth in the case of earlier introduction. In the latter case, no autoinhibition of the germination of F. oxysporum conidia occurred; moreover, cooperative effect was observed, i.e., the number of germinated F. oxysporum conidia increased with an increase in their density.     

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.     

Altered growth of Fusarium oxysporum f. sp. chrysanthemi in an in vitro dual culture system with the vesicular arbuscular mycorrhizal fungus Glomus intraradices growing on Daucus carota transformed roots

Vesicular arbuscular mycorrhizal fungi can reduce plant disease symptoms and populations of pathogens through mechanisms that are not well understood. Glomus intraradices was grown on Daucus carota transformed roots in a two-compartment in vitro system. One compartment contained mycorrhizal roots on a complete growth medium, while the other contained a medium lacking sugar on which only mycelial growth was allowed. The direct interaction between G. intraradices and Fusarium oxysporum f. sp. chrysanthemi was studied in the compartment lacking sugar during a 5-day period. G. intraradices hyphal density and spore number were estimated along with F. o. chrysanthemi conidial germination, mycelial growth and sporulation. Five hours after inoculation, germination of F. o. chrysanthemi conidia doubled in the presence of G. intraradices. Radial growth of F. o. chrysanthemi colonies was always slightly but significantly enhanced in the presence of G. intraradices. No correlation was obtained between G. intraradices hyphae or spore densities and F. o. chrysanthemi hyphal growth. Overall sporulation of the 5-day-old F. o. chrysanthemi colonies was not influenced by the presence of G. intraradices. However, significant negative correlations were found between F. o. chrysanthemi conidia production and G. intraradices hyphae or spore concentrations. G. intraradices increased F. o. chrysanthemi conidial germination and slightly stimulated its hyphal growth in dual culture without any root influences. No antibiosis was observed between the fungi. The significance of the results and their potential implication for rhizosphere biology are discussed.     

Physiological and biochemical responses of <Emphasis Type="Italic">in vitro Fusarium oxysporum</Emphasis> f.sp. <Emphasis Type="Italic">niveum</Emphasis> to benzoic acid

The allelopathic potential of an artificially applied allelochemical, benzoic acid, on in vitro Fusarium oxysporum f.sp. niveum (a soil-borne pathogen causing watermelon wilt) was evaluated. Benzoic acid strongly inhibited its growth, sporulation and conidia germination, whereas it stimulated virulence factors of this pathogen. The biomass was reduced by 83–96 % and the conidia germinating rate and conidia production rate were decreased by 100 % at a concentration of >200 mg/L. However, phytopathogenic enzyme activities and mycotoxin production were stimulated with an increase of 10.2–1250 % for enzyme activities and 610–2630 % for mycotoxin yield.     

Effect of flavonoids on the development of Fusarium oxysporum f. sp. lycopersici

Abstract

In the present study the effect of flavonoid compounds on the germination and fungal growth of the soil-borne tomato pathogen Fusarium oxysporum f. sp. lycopersici was studied. Out of 12 flavonoid compounds only myricetin and luteolin exhibited a low stimulating activity on microconidia germination of Fusarium oxysporum f. sp. lycopersici, whereas the other flavonoids tested were inactive when applied at five different concentrations. In our study the tested flavonoids affect fungal growth differently to microconidia germination. Individual flavonoid concentrations resulted in a small increase of fungal growth, but the lowest flavonoid concentrations showed an inhibiting effect on fungal growth for all flavonoids tested. There is evidence to suggest, that low flavonoid concentrations exhibit slight antimicrobial properties against Fusarium oxysporum f. sp. lycopersici.     

First Report of Stem Canker on Phoenix Tree (Firmiana simplex) Caused by Fusarium oxysporum in China

A stem canker disease was observed on the phoenix trees located in the region of Dezhou, Shandong province. Symptomatic stems were collected and evaluated for the possible casual agent of the disease. A fungus resembling Fusarium sp. was consistently isolated from pieces of symptomatic tissues. The fungus formed abundant aerial mycelium on potato dextrose agar and produced the micro‐ and macro‐conidia on carnation leaf agar. The nucleotide sequences of the internal transcribed spacer of the rDNA from three representative isolates showed 100% identical to those of Fusarium oxysporum isolates deposited in the GenBank database. On the basis of morphological characteristics, pathogenicity test and molecular identification, the causal agent was identified as F. oxysporum. To our knowledge, this is the first report of stem canker on phoenix tree caused by F. oxysporum in China.     

Influence of Plant Root Exudates, Germ Tube Orientation and Passive Conidia Transport on Biological Control of Fusarium Wilt by Strains of Nonpathogenic Fusarium oxysporum

In earlier studies, biological control of Fusarium wilt of cucumber induced by Fusarium oxysporum f. sp. cucumerinum was demonstrated using nonpathogenic strains C5 and C14 of Fusarium oxysporum. Strain C14 induced resistance and competed for infection sites whether roots were wounded or intact, whereas strain C5 required wounds to achieve biocontrol. In the current work, additional attributes involved in enhanced resistance by nonpathogenic biocontrol agents strains to Fusarium wilt of cucumber and pea were further investigated. In pre-penetration assays, pathogenic formae specials exhibited a significantly higher percentage of spore germination in 4-day-old root exudates of cucumber and pea than nonpathogens. Also, strain C5 exhibited the lowest significant reduction in spore germination in contrast to strain C14 or control. One-day-old cucumber roots injected with strain C14 resulted in significant reduction in germ tube orientation towards the root surface, 48–96 h after inoculation with F. o. cucumerinum spores, whereas strain C5 induced significantly lower spore orientation of the pathogen and only at 72 and 96 h after inoculation. In post-penetration tests, passive transport of microconidia of pathogenic and nonpathogens in stems from base to apex were examined when severed plant roots were immersed in spore suspension. In repeated trials, strain C5, F. o. cucumerinum and F. o. pisi were consistently isolated from stem tissues of both cucumber and pea at increasing heights over a 17 days incubation period. Strain C14 however, was recovered at a maximum translocation distance of 4.6 cm at day 6 and later height of isolation significantly declined thereafter to 1.2 cm at day 17. In pea stem, the decline was even less. Significant induction of resistance to challenge inoculation by the pathogen in cucumber occurred 72 and 96 h after pre-inoculation with biocontrol agents. Nonetheless, strain C14 induced protection as early as 48 h and the maximum resistance was reached at 96 h. The presented data confirm the previous findings that attributes important for nonpathogenic fusaria to induce resistant are: rapid spore germination and orientation in response to root exudate; active root penetration and passive conidia transport in stem to initiate defence reaction without pathogenicity and enough lag period between induction and challenge inoculation. Strain C14 possesses all these qualifications and hence its ability to enhance host resistance is superior than strain C5.     

The effect of root exudates from two transgenic insect-resistant cotton lines on the growth of Fusarium oxysporum

The attenuation of disease resistance in transgenic insect-resistant cotton has become one of the important factors restricting cotton production in China. Two transgenic insect-resistant cotton lines and their parental conventional cotton lines were used as the testing materials. The effects of root exudates of these cotton lines on the spore germination and mycelial growth of Fusarium oxysporum were studied and the components, contents of amino acids and sugars were determined. The results showed that the resistance of the two insect-resistant cotton lines to F. oxysporum was inferior to the parental lines, and that their root exudates promoted fungal spore germination and mycelial growth. Considerable differences in the components and contents of both, amino acids and sugars were found between the root exudates of transgenic cotton lines and their parental lines, where the disease indices were highly correlated with the total amount of sugars in the root exudates.     

Natural variation of ascospore and conidial germination by Fusarium verticillioides and other Fusarium species

Fusarium verticillioides and other Fusarium species were examined for their spore germination phenotypes. In general, germinating spores of F. verticillioides formed germ tubes that immediately penetrated into agar. Such invasive germination was the predominant growth phenotype among 22 examined field isolates of F. verticillioides from a broad range hosts and locations. However, two of the field isolates were unique in that they formed conidial germ tubes and hyphae that grew along the surface of agar before penetration eventually occurred. Conidia of 22 other Fusarium species were assessed for their germination phenotypes, and only some strains of F. annulatum, F. fujikuroi, F. globosum, F. nygamai, and F. pseudoanthophilum had the surface germination phenotype (21 % of the strains assessed). Sexual crosses and segregation analyses involving one of the F. verticillioides surface germination strains, NRRL 25059, indicated a single locus, designated SIG1 (surface vs. invasive germination), controlled the germ tube growth phenotypes exhibited by both conidia and ascospores. Perfect correlation was observed between an ascospore germination phenotype and the germination phenotype of the conidia produced from the resulting ascospore-derived colony. Recombination data suggested SIG1 was linked (7 % recombination frequency) to FPH1, a recently described locus necessary for enteroblastic conidiogenesis. Corn seedling blight assays indicated surface germinating strains of F. verticillioides were less virulent than invasively germinating strains. Assays also indicated pathogenicity segregated independently of the FPH1 locus. Invasive germination is proposed as the dominant form of spore germination among Fusarium species. Furthermore, conidia were not necessary for corn seedling disease development, but invasive germination may have enhanced the virulence of conidiating strains.     

Selection of antagonistic bacteria isolated from the Physalis peruviana rhizosphere against Fusarium oxysporum

Aims: Cape gooseberries (Physalis peruviana) have become increasingly important in Colombia for both domestic consumption and the international export market. Vascular wilting caused by Fusarium oxysporum is the most damaging disease to P. peruviana crops in Colombia. The control of this pathogen is mainly carried out by chemical and cultural practices, increasing production costs and generating resistance. Therefore, the objectives of this study were to test rhizobacteria isolates from P. peruviana rhizosphere against F. oxysporum under in vitro and in vivo conditions. Methods and Results: Over 120 strains were isolated, and five were selected for their high inhibition of F. oxysporum growth and conidia production under in vitro conditions. These strains inhibited growth by 41–58% and reduced three‐ to fivefold conidia production. In the in vivo assays, all the tested isolates significantly reduced fungal pathogenicity in terms of virulence. Isolate B‐3·4 was the most efficient in delaying the onset of the first symptoms. All isolates were identified as belonging to the genus Pseudomonas except for A‐19 (Bacillus sp.). Conclusions: Our results confirmed that there are prospective rhizobacteria strains that can be used as biological control agents; some of them being able to inhibit in vitro F. oxysporum growth and sporulation. Significance and Impact of the Study: Incorporating these bacteria into biological control strategies for the disease that causes high economical losses in the second most exported fruit from Colombia would result in a reduced impact on environment and economy.     

Biological control of Fusarium wilt of tomato with <Emphasis Type="Italic">Fusarium equiseti</Emphasis> GF191 in both rock wool and soil systems

The plant growth-promoting fungus (PGPF) Fusarium equiseti GF191 was tested for its ability to control Fusarium wilt of tomato (FWT) caused by Fusarium oxysporum f. sp. lycopersici (FOL) in both a hydroponic rock wool and soil system. F. equiseti effectively controlled FWT, with protective effects based on disease severity of 66.7–88.6% in four experiments. The numbers of colony-forming units of FOL per gram fresh weight of stems were significantly reduced (P < 0.05) in plants treated with F. equiseti. Stem extracts from F. equiseti-treated and pathogen-challenged plants significantly inhibited the germination and germ-tube length of FOL microconidia and the production of FOL budding-cells. Tomatine content in tomato stems treated with F. equiseti was significantly increased compared with the non-treated control.     

Genetic Diversity of Fusarium oxysporum Populations Isolated from Tomato Plants in Tunisia

Fusarium crown and root rot of tomato (Lycopersicon esculentum) caused by Fusarium oxysporum f. sp. radicis‐lycopersici is a new devastative disease of tomato greenhouse crops in Tunisia. Nothing is known neither about the population of this pathogen in this region, nor about the population of F. oxysporum f. sp. lycopersici the causal agent of Fusarium wilt of tomato. In order to examine the genetic relatedness among the F. oxysporum isolates by intergenic spacer restriction fragment length polymorphism (IGS‐RFLP) analysis and to elucidate the origin of the formae specialesradicis‐lycopersici in Tunisia by looking for genetic similarity of Tunisians isolates with isolates from a foreign source, the genetic diversity among F. oxysporum f. sp. radicis‐lycopersici and F. oxysporum f. sp. lycopersici populations was investigated. A total of 62 isolates of F. oxysporum, obtained from symptomless tomato plants, were characterized using IGS typing and pathogenicity tests on tomato plants. All Fusarium isolates were highly pathogenic on tomato. Fusarium oxysporum f. sp. radicis‐lycopersici isolates were separated into five IGS types. From the 53 F. oxysporum f. sp. radicis‐lycopersici isolates, 34 isolates have the same IGS types (IGS type 25), and the remaining 19 isolates were distributed into four IGS types. However, the only nine isolates of F. oxysporum f. sp. lycopersici have six different IGS types. This difference of diversity between the two formae speciales suggests that F. oxysporum f. sp. radicis‐lycopersici isolates have a foreign origin and may have been accidentally introduced into Tunisia.     

Hot-water treatment of seed as a method for decreasing the incidence of certain cotton and flax seedling diseases

Improved pathogen-free seed germination and better seedling growth were obtained by hot-water treatments at 60 °C for 10 min of seed of the cotton varieties Karnak and Ashmouni, and at 45 °C for 5 min of seed of the flax varieties Giza 4 and Baladi. These treatments also reduced pre- and post-emergence losses due to Rhizoctonia solani and Fusarium oxysporum f.sp. vasinfectum in cotton, and to F. oxysporum f.sp. lini in flax, and resulted in better growth of the surviving plants.     

Microconidia germination of the tomato pathogen Fusarium oxysporum in the presence of root exudates

Abstract

In this study we assessed microconidia germination of the tomato pathogens F. oxysporum f. sp. lycopersici (Fol) and F. oxysporum f. sp. radicis-lycopersici (Forl) in the presence of root exudates. Tomato root exudates stimulated microconidia germination and the level of stimulation was affected by plant age. Treatment of root exudates with insoluble polyvinylpolypyrrolidone, which binds phenolic compounds, indicated that tomato root exudates contain phenolic compounds inhibitory to F. oxysporum microconidia germination. Our study indicates that tomato root exudates similarly stimulate microconidia germination of both Fol and Forl. However, individual F. oxysporum strains differ in the degree of germination response to the root exudates. Furthermore, root exudates from non-host plants also contain compounds that stimulate microconidia germination of Fol. In general, the effects of root exudates from non-host plants did not differ considerably from those of tomato. The ability of phenolic compounds to inhibit germination of Fol seems not to be plant-specific.     

Presence of Fusarium oxysporum f. sp. melonis Race 1 in Soils Cultivated with Melon in the State of Colima (Mexico)

During years 2001, 2002 and 2003 the gravity of the Fusarium wilt in 1000 hectares of melon culture was evaluated in Colima (Mexico). In spite of the soil disinfections with methyl bromide, the losses could reach 25% of the final production. The analysis of 4 soil samples from the fields with ill plants, in a selective medium for Fusarium, allowed to detect the presence of F. oxysporum. By means of the presented technique “soil phytopathometry”, 31 isolates of F. oxysporum f. sp. melonis were obtained from the soil samples. The isolates were inoculated on melon plants to evaluate their pathogenicity. The 31 isolates inoculated, produced the symptoms of chlorosis and wilting, in melon cultivars that allowed us to affirm that all isolates were race 1 of F. oxysporum f. sp. melonis. Being this the first news of the presence of F. oxysporum f. sp. melonis in the state of Colima (Mexico).     

The effect of volatile and gaseous metabolites of swelling seeds on germination of fungal spores

Effects of volatile and gaseous metabolites of swelling seeds of pea, bean, wheat, corn, cucumber, tomato, lentil, carrot, red pepper and lettuce on germination of spores of five genera of fungi were found to depend rather on the fungal than on the plant genus. Germination of spores ofBotrytis cinerea, Mucor racemosus andTrichoderma viride was most severely inhibited. Spores ofVerticillium dahliae were less sensitive and germination of spores ofFusarium oxysporum was inhibited only in two cases. On the other hand, exudates of pea and bean stimulated germination of spores ofFusarium oxysporum. Also spores ofTrichoderma viride germinated better in an atmosphere enriched with exuded metabolites of swelling lettuce seeds. When carbon dioxide produced by the swelling seeds was absorbed in potassium hydroxide, spores ofTrichoderma viride andVerticillium dahliae did not germinate at all, the inhibitory effects of volatile and gaseous exudates on germination of spores ofMucor racemosus were accentuated, and also the percentage of germinated spores ofFusarium oxysporum decreased. Germination of spores ofBotrytis cinerea was not influenced. Absorption of volatile and gaseous metabolites in a solution of potassium permanganate decreased in most cases their inhibitory effects, particularly inBotrytis cinerea.     

Fungitoxic activity of fruit extracts of Syzygium cumini (L.) Skeels against plant pathogenic fungi Alternaria alternata and Fusarium oxysporum

This study was aimed to evaluate the effectiveness of the aqueous and ethanolic extracts of fruits of Syzygium cumini, against the mycelial growth of Alternaria alternata and Fusarium oxysporum. The results showed that ethanolic extract at the concentrations of 7.5 and 9?mg/ml completely inhibited the mycelial growth of A. alternata and F. oxysporum, respectively. While the aqueous extract at a highest tested concentration (37.5?mg/ml) exhibited only 27.86 and 37.23% inhibition of mycelial growth of A. alternata and F. oxysporum, respectively. The spore germination assay also showed the complete inhibition of spore germination of A. alternata and F. oxysporum by ethanolic extract at 50 and 60?mg/ml concentrations, respectively. Minimum inhibitory concentration was recorded as 0.039 and 0.156?mg/ml in ethanolic extract and 20 and 6.25?mg/ml in aqueous extract against A. alternata and F. oxysporum, respectively. Phytochemical analysis also showed the presence of high amount of phenolics, tannins, flavonoids, alkaloids and saponins.