Disease Development Following Infection of Tomato and Basil Foliage by Airborne Conidia of the Soilborne Pathogens Fusarium oxysporum f. sp. radicis-lycopersici and F. oxysporum f. sp. basilici

ABSTRACT Fusarium oxysporum f. sp. radicis-lycopersici, the causal agent of Fusarium crown and root rot of tomato, and F. oxysporum f. sp. basilici, the causal agent of Fusarium wilt in basil, are soilborne pathogens capable of producing conspicuous masses of macroconidia along the stem. The role of the airborne propagules in the epidemics of the disease in tomato plants was studied. In the field, airborne propagules of F. oxysporum f. sp. radicis-lycopersici were trapped with a selective medium and their prevalence was determined. Plants grown in both covered and uncovered pots, detached from the field soil, and exposed to natural aerial inoculum developed typical symptoms (82 to 87% diseased plants). The distribution of inoculum in the growth medium in the pots also indicated the occurrence of foliage infection. In greenhouse, foliage and root inoculations were carried out with both tomato and basil and their respective pathogens. Temperature and duration of high relative humidity affected rate of colonization of tomato, but not of basil, by the respective pathogens. Disease incidence in foliage-inoculated plants reached 75 to 100%. In these plants, downward movement of the pathogens from the foliage to the crown and roots was observed. Wounding enhanced pathogen invasion and establishment in the foliage-inoculated plants. The sporulation of the two pathogens on stems, aerial dissemination, and foliage infection raise the need for foliage protection in addition to soil disinfestation, in the framework of an integrated disease management program.     

Involvement of resistance induction by Penicillum oxalicum in the biocontrol of tomato wilt

Penicillium oxalicum , a biocontrol agent for Fusarium oxysporum f.sp. lycopersici , was tested for its ability to induce resistance against tomato wilt. P. oxalicum and F. oxysporum f.sp. lycopersici were placed at separate sites on tomato plants or in soil, avoiding a direct interaction between the fungi. P. oxalicum induced resistance as expressed by a reduction in disease severity, area under disease progress curve and stunting induced by the pathogen. P. oxalicum colonized the tomato rhizosphere during the experiments but it was not detected inside stems, demonstrating that P. oxalicum and Fusarium oxysporum f.sp. lycopersici remained spatially separated. Biological control was observed both in sensitive and 'resistant' cultivars, indicating the role of a general resistance mechanism. In both cultivars P. oxalicum treatment alone did not produce disease symptoms. Therefore P. oxalicum could be a suitable biocontrol agent in cases of cultivar resistance failure. These results suggest that P. oxalicum can trigger defence mechanisms in the plant.     

Vegetative compatibility of Fusarium oxysporum from sweet basil in Israel

Fusarium wilt and crown rot of sweet basil, caused by Fusarium oxysporum f.sp. basilici (F.o.ba.), is widespread in Israel. Affected plants show a variety of symptoms, including vascular wilt as well as crown rot, and masses of macroconidia on stem surfaces. We used vegetative compatibility to determine whether F.o.ba. isolates associated with various symptoms and sources are genetically related. All 119 isolates previously described as F.o.ba., and 42 additional F. oxysporum isolates which had not been tested for pathogenicity, belonged to a single vegetative compatibility group (VCG). The various symptoms are therefore induced by a single pathogenic form which appears to be a specific clone of F. oxysporum. The isolates of F.o.ba. from Israel were vegetatively compatible with eight isolates of F.o.ba. from Italy and the USA, but not with nonpathogenic isolates of F. oxysporum from basil, or with F.o. lycopersici or F.o. radicis-lycopersici from tomato. We conclude that the population of F.o.ba. in Israel belongs to the common VCG of this pathogen described in the USA, and which includes American and Italian isolates.     

Effects of timing and method of application of Penicillium oxalicum on efficacy and duration of control of Fusarium wilt of tomato

The effects of timing and method of application of Penicillium oxalicum on the control of fusarium wilt of tomato were investigated. Application of P. oxalicum to tomato seedlings in seedbeds reduced disease caused by Fusarium oxysporum f.sp. lycopersici in a growth chamber by 45–49% and in glasshouse experiments by 22–69%. Disease suppression was maintained for 60–100 days after inoculation with the pathogen in the glasshouse. No disease reduction was observed in tomato plants where P. oxalicum was applied to seeds. Treatment with P. oxalicum did not affect the population of F. oxysporum f.sp. lycopersici in the rhizosphere.     

Induced Resistance by Penicillium oxalicum Against Fusarium oxysporum f. sp. lycopersici: Histological Studies of Infected and Induced Tomato Stems

ABSTRACT Tomato (Lycopersicon esculentum) plants of 'Lorena' were induced with a conidial suspension (10(7) conidia per ml) of Penicillium oxalicum before inoculation with Fusarium oxysporum f. sp. lycopersici, the wilt pathogen. Histological changes occurred in plants under both growth chamber and glasshouse culture conditions and there was a reduction of disease severity. In noninduced plants, the pathogen produced almost a complete loss of cambium (75 to 100% reduction), an increase in the number of bundles, and a decrease in the number of xylem vessels (20% reduction), in which the diameter also was reduced by 20 to 30% in hypocotyls and epicotyls. The percentage of vessels colonized by F. oxysporum f. sp. lycopersici was positively correlated to the area under the disease progress curve (AUDPC). However, plants induced with P. oxalicum showed less disease, did not lose the cambium, had a lower number of bundles, and had less vascular colonization by F. oxysporum f. sp. lycopersici (35 to 99%). These effects also were observed in 'Precodor', which is susceptible to races 1 and 2 of F. oxysporum f. sp. lycopersici, and partially in 'Ramón', which is resistant to both races. Renewed or prolonged cambial activity that led to the formation of additional secondary xylem could be one of the reasons for disease reduction in P. oxalicum-induced tomato plants.     

Suppressive effect of secondary metabolites from Streptomyces plumbeus isolate F31D against Fusarium oxysporum f. sp. lycopersici,the causal agent of Fusarium wilt of tomato

Journal of General Plant Pathology - Fusarium wilt of tomato, a disease caused by the soilborne fungus Fusarium oxysporum f. sp. lycopersici, causes major losses to tomato production. Chemical...     

Race identification of Fusarium oxysporum f. sp. lycopersici isolates obtained from tomato plants in Nova Friburgo,Brazil

European Journal of Plant Pathology - Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici (FOL) is one of the main diseases affecting tomato plants. Three races (races 1, 2 and 3) of the...     

A rapid laboratory method for assessing the biological control potential of Penicillium oxalicum against Fusarium wilt of tomato

A rapid, simple and reliable procedure was developed to evaluate biological control of Fusarium wilt of tomato by Penicillium oxalicum . The method consists in growing tomato plants in flasks with nutrient solution in a growth chamber. Plants were previously treated in the seedbed with a conidial suspension (10⁷ conidia mL⁻¹) of P. oxalicum 7 days before transplanting. Fusarium oxysporum f.sp. lycopersici (race 2) was added to the Hoagland solution just before transplanting. Different concentrations and several isolates of F. oxysporum f.sp. lycopersici were tested. Using this method, plants showed typical symptoms of the disease and the effect of the biocontrol agent was clear. Consumption of nutrient solution was reduced in diseased plants, and this reduction was diminished by treatment with P.oxalicum . Consumption of nutrient solution was correlated with other disease-related parameters (AUDPC, weight of aerial parts, stunting) and was an easy and objective parameter to measure.     

Spatial distribution and temporal development of fusarium crown and root rot of tomato and pathogen dissemination in field soil

ABSTRACT The spatial distribution and temporal development of tomato crown and root rot, caused by Fusarium oxysporum f. sp. radicis-lycopersici, were studied in naturally infested fields in 1996 and 1997. Disease progression fit a logistic model better than a monomolecular one. Geostatistical analyses and semivariogram calculations revealed that the disease spreads from infected plants to a distance of 1.1 to 4.4 m during the growing season. By using a chlorate-resistant nitrate nonutilizing (nit) mutant of F. oxysporum f. sp. radicis-lycopersici as a "tagged" inoculum, the pathogen was found to spread from one plant to the next via infection of the roots. The pathogen spread to up to four plants (2.0 m) on either side of the inoculated focus plant. Root colonization by the nit mutant showed a decreasing gradient from the site of inoculation to both sides of the inoculated plant. Simulation experiments in the greenhouse further established that this soilborne pathogen can spread from root to root during the growing season. These findings suggest a polycyclic nature of F. oxysporum f. sp. radicis-lycopersici, a deviation from the monocyclic nature of many nonzoosporic soilborne pathogens.     

Inoculum Densities of Fusarium oxysporum f. sp. vasinfectum and Meloidogyne incognita in Relation to the Development of Fusarium Wilt and the Phenology of Cotton Plants (Gossypium hirsutum)

ABSTRACT Development of Fusarium wilt in upland cotton (Gossypium hirsutum) usually requires infections of plants by both Meloidogyne incognita and Fusarium oxysporum f. sp. vasinfectum. In this study, the soil densities of M. incognita and F. oxysporum f. sp. vasinfectum and the incidence of Fusarium wilt in three field sites were determined in 1982-1984. Multiple regression analysis of percent incidence of Fusarium wilt symptoms on population densities of M. incognita and F. oxysporum f. sp. vasinfectum yielded a significant fit (R (2) = 0.64) only on F. oxysporum f. sp. vasinfectum. Significant t-values for slope were also obtained for the interaction of M. incognita and F. oxysporum f. sp. vasinfectum, but densities of M. incognita and F. oxysporum f. sp. vasinfectum were also related on a log(10) scale. The physiological time of appearance of first foliar symptoms of Fusarium wilt, based on a degree-days threshold of 11.9 degrees C (53.5 degrees F), was used as a basis for determining disease progress curves and the phenology of cotton plant growth and development. Effects of Fusarium wilt on plant height and boll set were determined in three successive years. Increases in both of these plant characteristics decreased or stopped before foliar symptoms were apparent. Seed cotton yields of plant cohorts that developed foliar wilt symptoms early in the season (before 2,000 F degree-days) were variable but not much different in these years. This contrasted with cohorts of plants that first showed foliar symptoms late in the season (after 2,400 F degree-days) and cohorts of plants that showed no foliar symptoms of wilt. Regression analyses for 1982-1984 indicated moderate to weak correlations (r = 0.16-0.74) of the time of appearance of the first foliar symptoms and seed cotton yields.     

Differential Colonization of Tomato Roots by Nonpathogenic and Pathogenic Fusarium oxysporum Strains May Influence Fusarium Wilt Control

ABSTRACT Histochemical staining, beta-glucuronidase (GUS) activity, or placing roots on agar were methods used to characterize interactions between the pathogenic fungus, Fusarium oxysporum f. sp. lycopersici, and the nonpathogenic biocontrol F. oxysporum strain 70T01 with respect to colonization behaviors, interaction sites, and population densities on tomato roots. Mycelia of strain 70T01, a genetic transformant expressing stable GUS activity, hygromycin B resistance, and effective disease control, were localized in epidermal and cortex cell layers of tomato roots in a discontinuous and uneven pattern. In contrast, mycelia of F. oxysporum f. sp. lycopersici were found in the vascular bundles. Thus, direct interactions between the two fungi likely happen in the root surface cell layers. Colonization density of strain 70T01 was related to the inoculation density but decreased with distance from the inoculation site. Host defense reactions, including increased cell wall thickness or papilla deposits, were adjacent to 70T01 hyphae. Experiments done in soil showed that strain 70T01 densities in roots were highest at inoculation zones and barely detectable for root segments more than 2 cm away from the inoculation sites. F. oxysporum f. sp. lycopersici densities were lowest at 70T01 inoculation zones and highest (>10 times) where strain 70T01 was not directly applied. Newly elongating roots where strain 70T01 did not reach were available for infection by the pathogen. The higher strain 70T01 density was always found when the plants were simultaneously infected by F. oxysporum f. sp. lycopersici, suggesting that F. oxysporum f. sp. lycopersici has as much influence in predisposing the plant to colonization by strain 70T01 as strain 70T01 has on providing disease protection against the pathogen.     

Origin of Race 3 of Fusarium oxysporum f. sp. lycopersici at a Single Site in California

ABSTRACT Thirty-nine isolates of Fusarium oxysporum were collected from tomato plants displaying wilt symptoms in a field in California 2 years after F. oxysporum f. sp. lycopersici race 3 was first observed at that location. These and other isolates of F. oxysporum f. sp. lycopersici were characterized by pathogenicity, race, and vegetative compatibility group (VCG). Of the 39 California isolates, 22 were in VCG 0030, 11 in VCG 0031, and six in the newly described VCG 0035. Among the isolates in VCG 0030, 13 were race 3, and nine were race 2. Of the isolates in VCG 0031, seven were race 2, one was race 1, and three were nonpathogenic to tomato. All six isolates in VCG 0035 were race 2. Restriction fragment length polymorphisms (RFLPs) and sequencing of the intergenic spacer (IGS) region of rDNA identified five IGS RFLP haplotypes, which coincided with VCGs, among 60 isolates of F. oxysporum from tomato. Five race 3 isolates from California were of the same genomic DNA RFLP haplotype as a race 2 isolate from the same location, and all 13 race 3 isolates clustered together into a subgroup in the neighbor joining tree. Collective evidence suggests that race 3 in California originated from the local race 2 population.     

番茄枯萎病和青枯病拮抗细菌的筛选、评价与鉴定

从宁夏银川、江苏沭阳和福建厦门的番茄、辣椒、西瓜等作物根际土壤中,分离纯化获得367株细菌菌株。以番茄枯萎病菌Fusarium oxysporum f.sp.lycopersici和番茄青枯病菌Ralstonia solanacearum为靶标菌,从367株菌株中筛选出对两种病菌皆具有很强拮抗作用的菌株22株。拮抗细菌抑菌物质的研究结果表明：22株拮抗细菌均能分泌蛋白酶;不能分泌几丁质酶;3株细菌能分泌纤维素酶;3株细菌能分泌嗜铁素。盆栽试验结果表明：拮抗细菌PTS-394对番茄枯萎病和青枯病的防效最高,分别为77.4%和80%;菌株H-70、L-1和SJ-280对番茄枯萎病和青枯病的防效均大于60%。对上述4株拮抗细菌进行16S rRNA种属鉴定,均为枯草芽孢杆菌Bacillus subtilis。     

Effects of soil application of fly ash on the fusarial wilt on tomato cultivars

A study was carried out in microplots to evaluate the effect of fly ash on the plant growth and yield of tomato cultivars, Pusa Ruby, Pusa Early Dwarf and New Uday, and on wilt disease caused by Fusarium oxysporum f.sp. lycopersici . Fly ash was applied to soil by broadcast or in rows at the rate of 1, 2, 3 and 4 kg ash m-2 in place of inorganic fertilizers. In control plots, NPK (about 40 : 20 : 20 kg acre-1) and compost were added in place of fly ash. Ash application greatly increased the soil contents of P, K, B, Ca, Mg, Mn, Zn, carbonates, bicarbonates and sulphates. Plants grown in the ash-treated plots, especially at 3 or 4 kg dose, showed luxuriant growth and greener foliage, and plant growth and yield of the three cultivars were significantly increased in comparison with the plants grown in plots without fly ash. The wilt fungus, F. oxysporum f.sp. lycopersici at the inoculum level of 2 g plant-1 caused significant suppression of growth and yield in all three cultivars. Application of fly ash, however, checked the suppressive effect of the fungus, leading to a significant increase in the considered variables compared with the inoculated control. Soil population of the fungus (colony-forming units g soil-1) gradually decreased with an increase in ash dose. Row application was found to be relatively more effective in enhancing the yield of tomato cultivars and suppressing the wilt disease. The greatest increase in the yield of fungus inoculated and uninoculated plants due to broadcast or row application at 3 or 4 kg ash m-2 was recorded in tomato cv. Pusa Ruby (39 - 61 and 9 - 24%), followed by Pusa Early Dwarf (31 - 61 and 17 - 34%) and New Uday (21 - 35 and 4 - 22%).     

An ultrastructural study of tomato roots inoculated with pathogenic and non-pathogenic necrotrophic fungi and a saprophytic fungus

Tomato cultivar Moneymaker was independently inoculated with Alternaria alternata, Cunninghamella elegans, Fusarium culmorum, F. oxysporum f.sp. lycopersici, F. oxysporum f.sp. pisi and Stromatinia gladioli and analysed ultrastructurally. The extent and amount of superficial fungal growth on tomato roots was similar but C. elegans , a saprophyte, was exceptional in that hyphae were not closely appressed to plant surfaces and did not adhere to plant cell walls.
In general, the type of plant responses to fungal colonization and infection were similar in all of the interactions studied, with the exception of C. elegans which did not infect tomato root tissue. The failure to penetrate tomato roots by C. elegans may have been associated with the lack of hyphal adhesion to plant cell walls. Migration of cytoplasm and wall apposition/penetration papilla formation were regularly observed in tomato root tissue beneath appressed hyphae and at sites of fungal infection. Specific cellular reactions in the exodermis, namely the formation of wall 'inclusions' and appearance of 'sensitive' cells, indicated that exodermal cells were particularly responsive to fungal challenge.
Fusarium oxysporum f.sp. lycopersici , a pathogen of tomato, invaded tomato root tissue more extensively than the other fungi inoculated onto tomato roots. Infection of tomato by the other fungi studied was variable, and the extent and success of fungal invasion was tentatively associated with their necrotrophic capability and typical host range.     

Fusarium confers protection against several mycelial pathogens of pepper plants

Inoculation of nonhost pepper ( Capsicum annuum ) plants with the tomato wilt pathogen, Fusarium oxysporum f.sp. lycopersici (FOL), caused no symptoms and the fungus was not recovered from any part of the plant. FOL, however, partially protected pepper plants from subsequent infection with Phytophthora capsici , Verticillium dahliae or Botrytis cinerea by significantly reducing the percentage of diseased plants and the appearance and intensity of symptoms. FOL did not inhibit the mycelial growth of these pathogens in vitro . The protection induced by FOL against Botrytis was inhibited by 1-methylcyclopropene (MCP), an inhibitor of ethylene perception, suggesting the involvement of this hormone in the signalling of FOL-induced resistance. The activities of β-1,3-glucanase and peroxidase 48 h after FOL induction were similar to those in control plants. Chitinase activity, however, was higher in the stems of plants inoculated with FOL. A study of the levels of phenolic compounds revealed that cell-wall-bound phenolics were more abundant in plants treated with FOL, especially in stems, while soluble phenolic contents did not differ.     

Treatment with the Mycoparasite Pythium oligandrum Triggers Induction of Defense-Related Reactions in Tomato Roots When Challenged with Fusarium oxysporum f. sp. radicis-lycopersici

ABSTRACT The influence exerted by the mycoparasite Pythium oligandrum in triggering plant defense reactions was investigated using an experimental system in which tomato plants were infected with the crown and root rot pathogen Fusarium oxysporum f. sp. radicis-lycopersici. To assess the antagonistic potential of P. oligandrum against F. oxysporum f. sp. radicis-lycopersici, the interaction between the two fungi was studied by scanning and transmission electron microscopy (SEM and TEM, respectively). SEM investigations of the interaction region between the fungi demonstrated that collapse and loss of turgor of F. oxysporum f. sp. radicis-lycopersici hyphae began soon after close contact was established with P. oligandrum. Ultrastructural observations confirmed that intimate contact between hyphae of P. oligandrum and cells of the pathogen resulted in a series of disturbances, including generalized disorganization of the host cytoplasm, retraction of the plasmalemma, and, finally, complete loss of the protoplasm. Cytochemical labeling of chitin with wheat germ agglutinin (WGA)/ovomucoid-gold complex showed that, except in the area of hyphal penetration, the chitin component of the host cell walls was structurally preserved at a time when the host cytoplasm had undergone complete disorganization. Interestingly, the same antagonistic process was observed in planta. The specific labeling patterns obtained with the exoglucanase-gold and WGA-ovomucoid-gold complexes confirmed that P. oligandrum successfully penetrated invading cells of the pathogen without causing substantial cell wall alterations, shown by the intense labeling of chitin. Cytological investigations of samples from P. oligandrum-inoculated tomato roots revealed that the fungus was able to colonize root tissues without inducing extensive cell damage. However, there was a novel finding concerning the structural alteration of the invading hyphae, evidenced by the frequent occurrence of empty fungal shells in root tissues. Pythium ingress in root tissues was associated with host metabolic changes, culminating in the elaboration of structural barriers at sites of potential fungal penetration. Striking differences in the extent of F. oxysporum f. sp. radicis-lycopersici colonization were observed between P. oligandrum-inoculated and control tomato plants. In control roots, the pathogen multiplied abundantly through much of the tissues, whereas in P. oligandrum-colonized roots pathogen growth was restricted to the outermost root tissues. This restricted pattern of pathogen colonization was accompanied by deposition of newly formed barriers beyond the infection sites. These host reactions appeared to be amplified compared to those seen in nonchallenged P. oligandrum-infected plants. Most hyphae of the pathogen that penetrated the epidermis exhibited considerable changes. Wall appositions contained large amounts of callose, in addition to be infiltrated with phenolic compounds. The labeling pattern obtained with gold-complexed laccase showed that phenolics were widely distributed in Fusarium-challenged P. oligandrum-inoculated tomato roots. Such compounds accumulated in the host cell walls and intercellular spaces. The wall-bound chitin component in Fusarium hyphae colonizing P. oligandrum-inoculated roots was preserved at a time when hyphae had undergone substantial degradation. These observations provide the first convincing evidence that P. oligandrum has the potential to induce plant defense reactions in addition to acting as a mycoparasite.     

Fusarium crown and root rot of tomatoes in the UK

Fusarium crown and root rot caused by Fusarium oxysporum f. sp. radicis-lycopersici was found in the UK in 1988 and 1989 mainly in rockwool-grown tomato crops. Up to 14% of plants were affected in individual crops. In experiments, leaf and stem symptoms did not appear until the time of first fruit harvest even when the plants were inoculated at planting, first flowers or fruit set. Conidial inoculum at 10⁶ spores/plant applied at seed sowing killed 70–83% of tomato seedlings, whereas similar levels of inoculum applied to young plants caused root and basal stem decay, and eventually death but only after fruit harvest began. Disease incidence and symptom severity increased with inoculum concentration. Experimentally, the disease was more severe in peat- or compost-grown plants than in rockwool. Disease spread was only a few centimetres in 50 days in experimental rockwool-grown plants. All tomato cultivars tested were highly susceptible. Prochloraz-Mn was highly effective against the pathogen in vitro and controlled the disease in the glasshouse, but only when applied preventively. Non-pathogenic Fusarium oxysporum isolates and Trichoderma harzianum also reduced FCRR disease levels.     

The infestation of tomato seed by Fusarium oxysporum f.sp. radicis-lycopersici

The infestation of seed by Fusarium oxysporum f.sp. radicis-lycopersici occurred at rates of 0-1 to 0-01 % in fruit on stem-infected plants. Direct infection of fruit in the flower or young developing fruit stage resulted in a grayish-brown lesion on the stylar end of the fruit or mummification. F. oxysporum f.sp. radicis-lycopersici was isolated from all seeds in such fruit. Picked fruit inoculated on the stem scar also became infected but 96 h after inoculation of the fruit, the seed was not infested or infected. The contact of clean seed with hands that had previously handled F. oxysporum f.sp. radicis-lycoperisid-infesied sawdust resulted in a high level of seed infestation. The fungus survived on seed sent across Canada and stored for up to 12 weeks. Treatment with NaOCl or 0·1 N HCl did not completely disinfest infested seed.