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...     

Effects of Varying Environmental Conditions on Biological Control of Fusarium Wilt of Tomato by Nonpathogenic Fusarium spp

ABSTRACT The influence of varying environmental and cropping conditions including temperature, light, soil type, pathogen isolate and race, and cultivar of tomato on biological control of Fusarium wilt of tomato by isolates of nonpathogenic Fusarium oxysporum (CS-20 and CS-24) and F. solani (CS-1) was evaluated in greenhouse and growth chamber experiments. Liquid spore suspensions (10(6)/ml) of the biocontrol isolates were applied to soilless potting mix at the time of tomato seeding, and the seedlings were transplanted into pathogen-infested field soil 2 weeks later. Temperature regimes ranging from 22 to 32 degrees C significantly affected disease development and plant physiological parameters. Biocontrol isolate CS-20 significantly reduced disease at all temperature regimes tested, yielding reductions of disease incidence of 59 to 100% relative to pathogen control treatments. Isolates CS-24 and CS-1 reduced disease incidence in the greenhouse and at high temperatures, but were less effective at the optimum temperature for disease development (27 degrees C). Growing plants under shade (50% of full light) versus full light affected some plant growth parameters, but did not affect the efficacy of biocontrol of any of the three bio-control isolates. Isolate CS-20 effectively reduced disease incidence (56 to 79% reduction) in four different field soils varying in texture (sandy to clayey) and organic matter content (0 to 3.2%). Isolate CS-1 reduced disease in the sandy and loamy soils (49 to 66% reduction), but was not effective in a heavy clay soil. Both CS-1 and CS-20 were equally effective against all three races of the pathogen, as well as multiple isolates of each race (48 to 66% reduction in disease incidence). Both isolates, CS-1 and CS-20, were equally effective in reducing disease incidence (66 to 80% reduction) by pathogenic races 1, 2, and 3 on eight different tomato cultivars containing varying levels of inherent resistance to Fusarium wilt (susceptible, resistant to race 1, or resistant to races 1 and 2). These results demonstrate that both these Fusarium isolates, and particularly CS-20, can effectively reduce Fusarium wilt disease of tomato under a variety of environmental conditions and have potential for further development.     

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.     

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.     

Biological control of Fusarium oxysporum f. sp. lycopersici

Fungi known to produce lytic enzymes were used in an attempt to control wilt of tomato caused by Fusarium oxysporum f. sp. lycopersici (FOL). Some of the fungal species (Penicillium oxalicum, Penicillium purpurogenum and Aspergillus nidulans) damaged hyphae of FOL in vitro and reduced the numbers of microconidia in the soil. Treatments with fungi did not result in a reduction in either chlamydospores of FOL in soil or populations of FOL in the rhizosphere of tomato. P. oxalicum was the most effective agent of biocontrol, and it reduced disease severity in both non-autoclaved (20% decrease) and sterile soil. In sterile soil, P. oxalicum reduced disease with different levels of severity (27% decrease at high levels and 50% decrease at low levels). Disease control by A. nidulans and P purpurogenum was only achieved when disease severity was low in sterile soil (55% and 45%, respectively).     

A fungal elicitor enhances the resistance of tomato fruit to Fusarium oxysporum infection by activating the phenylpropanoid metabolic pathway

Fungi infection in fruits is an important factor in postharvest losses. The effect of a treatment with a fungal elicitor on the response of tomato fruit to Fusarium oxysporum infection and changes in the phenylpropanoid metabolic pathway was studied. Fungal elicitor retarded for 3 days the development of the Fusarium rot development in tomato, at concentration of 2 g?l ^?1 (B2-F treatment). This treatment also induced a 3.11- and 6.03-fold increase of caffeic and chlorogenic acids, respectively, as compared with the control. Furthermore, the flavonoids naringenin-7-O-glucoside, rutin and kaempferol-3-O-glucoside, showed a greater abundance in tomato under the B2-F treatment after 6 days at 20°C. It is concluded that the fungal elicitor reduced the development of Fusarium rot by inducing the biosynthesis of metabolites from the phenylpropanoid metabolic pathway which forms part of the defense response in tomato fruit.     

The occurrence of Fusarium crown and root rot of tomato in Israel

Based upon symptomatology and the results of pathogenicity tests, it has been shown that the Fusarium crown and root rot organism of tomato — previously reported only from North America and Japan — is present in Israel.     

Cyanobacteria mediated plant growth promotion and bioprotection against Fusarium wilt in tomato

Cyanobacteria - phytopathogenic fungi - tomato plant interactions were evaluated for developing suitable biological options for combating biotic stress (Fusarium wilt) and enhancing plant vigour. Preliminary evaluation was undertaken on the fungicidal and hydrolytic enzyme activity of the cyanobacterial strains (Anabaena variabilis RPAN59, A. laxa RPAN8) under optimized environmental/nutritional conditions, followed by amendment in compost-vermiculite. Such formulations were tested against Fusarium wilt challenged tomato plants, and the Anabaena spp. (RPAN59/8) amended composts significantly reduced mortality in fungi challenged treatments, besides fungal load in soil. Cyanobacteria amended composts also led to an enhancement in soil organic C, nitrogen fixation, besides significant improvement in growth, yield, fruit quality parameters, N, P and Zn content. The tripartite interactions also enhanced the activity of defence and pathogenesis related enzymes in tomato plants. A positive correlation (r?=?0.729 to 0.828) between P content and pathogenesis/defense enzyme activity revealed their role in enhancing the resistance of the plant through improved nutrient uptake. Light and scanning electron microscopy (SEM) revealed cyanobacterial colonization, which positively correlated with reduced fungal populations. The reduced disease severity coupled with improved plant growth/ yields, elicited by cyanobacterial treatments, illustrated the utility of such novel formulations in integrated pest and nutrient management strategies for Fusarium wilt challenged tomato crop.     

Pathological evaluation of host-specific AAL-toxins and fumonisin mycotoxins produced by Alternaria and Fusarium species

Host-specific AAL-toxins and mycotoxin fumonisins are structurally related and were originally isolated from the tomato pathotype of Alternaria alternata and from Fusarium verticillioides, respectively. Previous reports on the production of fumonisin derivatives by the tomato pathotype suggested a possible involvement in the pathogenicity of the pathogen. Here, we have evaluated the role of fumonisin in A. alternata–tomato interactions. The results indicate that highly pathogenic isolates of A. alternata tomato pathotype produce AAL-toxin as the sole toxin, strongly implicating it as a pathogenicity factor. The related compound, fumonisin, is also toxigenic and has infection-inducing activity on susceptible tomato plants.     

Biological Control Efficiency of Fusarium Wilt of Tomato by Nonpathogenic Fusarium oxysporum Fo-B2 in Different Environments

ABSTRACT Efficiency of nonpathogenic Fusarium oxysporum Fo-B2 for the biological control of Fusarium wilt of tomato, caused by F. oxysporum f. sp. lycopersici CU1, was examined in different environments: a growth chamber with sterile soil-less medium, a greenhouse with fumigated or nonfumigated soil, and nonfumigated field plots. Inoculation of Fo-B2 onto tomato roots significantly reduced the severity of disease, but the efficiency of disease suppression decreased as the experimental environment became less controlled. Relationships between the recovery of Fo-B2 from hypocotyls and the disease severity indicated that the biocontrol agent was most effective when it colonized vascular tissues intensively. Moreover, the degree of Fo-B2 colonization was greatly reduced when the seedlings were grown in nonfumigated soil. Dose-response models (negative exponential, hyperbolic saturation, and logistic) were fit to observed data collected over a range of inoculum densities of the pathogen and the antagonist; the logistic model provided the best fit in all environments. The ratios of an 50% effective dose parameter for Fo-B2 to that of CU1 increased as the environment became less controlled, suggesting that environmentally related efficiency reduction impacted the antagonist more than the pathogen. The results suggest that indigenous soil microbes were a primary factor negatively influencing the efficiency of Fo-B2. Therefore, early establishment of the antagonist in a noncompetitive environment prior to outplanting could improve the efficacy of biological control.     

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。     

解淀粉芽胞杆菌B1619防控设施番茄枯萎病田间使用技术研究与示范

解淀粉芽胞杆菌B1619能够有效防控设施番茄枯萎病,研究菌株B1619田间高效使用技术对保证生防效果至关重要。本文对菌株B1619在接种番茄枯萎菌的病土中的定殖规律,菌株B1619水分散粒剂在田间的撒施方式和使用剂量,菌株B1619水分散粒剂对番茄枯萎病的田间防治效果进行了试验。结果表明,解淀粉芽胞杆菌B1619可以在接种枯萎菌的病土中稳定定殖并维持一定数量,在21 d时仍然有5.9×10~4 cfu/g土的种群数量。田间穴施和灌根的撒施方式防治效果明显好于蘸根和拌土,田间使用剂量应≥6 g/株。2年4地的田间药效试验结果表明,当田间撒施方式为穴施,田间使用剂量为32 kg/667 m~2时,菌株B1619水分散粒剂对番茄枯萎病的防治效果达到65.1%~85.2%,显著高于化学药剂百菌清。示范推广试验证明,菌株B1619水分散粒剂对番茄枯萎病的田间防治效果达到85%~90%。     

Loss of Avirulence and Reduced Pathogenicity of a Gamma-Irradiated Mutant of Fusarium oxysporum f. sp. lycopersici

ABSTRACT The tomato Fusarium resistance gene I-2 confers resistance to F. oxy-sporum f. sp. lycopersici race 2, which expresses the corresponding aviru-lence gene avrI-2. To elucidate the molecular basis of this gene-for-gene interaction, we initiated a search for the avrI-2 gene. Gamma irradiation mutagenesis, using (137)Cs, was performed to generate an avrI-2 mutant of F. oxysporum f. sp. lycopersici. To this end, a race 2 isolate was first transformed with a phleomycine resistance gene and a GUS marker gene in order to distinguish mutants from contaminating isolates. A total of 21,712 mutagenized colonies was tested for loss of avirulence on I-2-containing tomato seedlings. One mutant was selected that showed the expected loss of avirulence but, surprisingly, also showed reduced pathogenicity toward susceptible tomato plants. DNA analysis was subsequently used to visualize genomic changes in the mutant. Southern analysis on contour-clamped homogeneous electrophoretic field blots demonstrated a translocation of a 3.75-Mb chromosome in the mutant. Random amplified polymorphic DNA and amplified fragment length polymorphism analysis identified at least nine polymorphisms between the wild-type and mutant isolates. Most of these polymorphisms appeared as extra fragments in the mutant and contained repetitive DNA sequences.     

Germination of Fusarium oxysporum in root exudates from tomato plants challenged with different Fusarium oxysporum strains

The response of microconidia from pathogenic and non-pathogenic Fusarium oxysporum to root exudates from tomato plants inoculated with different pathogenic and non-pathogenic F. oxysporum strains was studied. Root exudates from non-inoculated tomatoes highly stimulated the microconidial germination of the two tomato pathogens, F. oxysporum f.sp. lycopersici strain Fol 007 and F. oxysporum f.sp. radicis-lycopersici strain Forl 101587. In root exudates from tomato plants challenged with the pathogen Fol 007 the microconidial germination of Fol 007 was increased, whereas in root exudates from plants challenged with Forl 101587 the microconidial germination of Fol 007 was reduced. Root exudates of tomato plants challenged with the non-pathogenic unspecific F. oxysporum strain Fo 135 and the biocontrol strain Fo 47 clearly reduced microconidial germination of the pathogenic strain Forl 101587. Moreover, the microconidial germination rate of the biocontrol strain Fo 47 was increased in the presence of root exudates of tomato plants challenged with the tomato wilt pathogen Fol 007. These results indicate that pathogenic and non-pathogenic F. oxysporum strains alter the root exudation of tomato plants differently and consequently the fungal propagation of pathogenic and non-pathogenic F. oxysporum strains in the rhizosphere is affected differently.     

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.     

荧光假单胞菌PEF-5#18防控番茄枯萎病的定殖机理

通过电转法成功将EGFP表达质粒p EGFP20转入对番茄枯萎病具有优良防病效果的荧光假单胞菌PEF-5#18体内,并研究了该生防菌在番茄根际土壤与植株根、茎内部组织的定殖情况。结果表明,处理25 d后,标记型与野生型生防菌处理均能有效控制番茄枯萎病害并增加植株鲜、干重量。与病原菌阳性对照相比,野生型菌株的防治效果为76.92%,鲜重增加194.10%,干重增加564.71%;接种后的PEF-5#18能良好定殖于番茄根际土壤并扩展进入植物根茎内部生长,其分布数量呈现出根际土壤(1.05×106 CFU/g)根(6.75×104 CFU/g)茎(1.25×102 CFU/g);与病原菌阳性对照相比,接种PEF-5#18对番茄根际土壤的可培养细菌总数影响差异不显著,但可显著提高根(增幅为8.42%)、茎(增幅为14.78%)内的可培养细菌总数以及根际土壤pH(增幅为1.61%);接种PEF-5#18能显著降低根际土壤与根、茎内病原菌侵染数量;激光共聚焦镜检发现,接种25 d后,PEF-5#18能大量分布于番茄根系表面、根内木质部、根内皮层细胞、根内细胞间隙、茎内维管及其周围细胞。     

Sporulation of Fusarium oxysporum f. sp. lycopersici on Stem Surfaces of Tomato Plants and Aerial Dissemination of Inoculum

ABSTRACT Plants exhibiting symptoms of wilt and xylem discoloration typical of Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici were observed in greenhouses of cherry tomatoes at various sites in Israel. However, the lower stems of some of these plants were covered with a pink layer of macroconidia of F. oxysporum. This sign resembles the sporulating layer on stems of tomato plants infected with F. oxysporum f. sp. radicis-lycopersici, which causes the crown and root rot disease. Monoconidial isolates of F. oxysporum from diseased plants were assigned to vegetative compatibility group 0030 of F. oxysporum f. sp. lycopersici and identified as belonging to race 1 of F. oxysporum f. sp. lycopersici. The possibility of coinfection with F. oxysporum f. sp. lycopersici and F. oxysporum f. sp. radicis-lycopersici was excluded by testing several macroconidia from each plant. Airborne propagules of F. oxysporum f. sp. lycopersici were trapped on selective medium in greenhouses in which plants with a sporulating layer had been growing. Sporulation on stems was reproduced by inoculating tomato plants with races 1 and 2 of F. oxysporum f. sp. lycopersici. This phenomenon has not been reported previously with F. oxysporum f. sp. lycopersici and might be connected to specific environmental conditions, e.g., high humidity. The sporulation of F. oxysporum f. sp. lycopersici on plant stems and the resultant aerial dissemination of macroconidia may have serious epidemiological consequences. Sanitation of the greenhouse structure, as part of a holistic disease management approach, is necessary to ensure effective disease control.     

Effect of ammonium/nitrate ratio in nutrient solution on control of Fusarium wilt of tomato by Trichoderma asperellum T34

The behaviour of Fusarium oxysporum f.sp. lycopersici (Fol) and the effectiveness of the microbial control agent Trichoderma asperellum strain T34 were examined in hydroponically grown tomato plants under five ammonium/nitrate ratios. The results showed that disease severity was reduced by the action of T34 under increasing concentrations of ammonia. Furthermore, rhizosphere F. oxysporum populations decreased with T34 application. The presence of T34 augmented leaf nitrogen concentration in treatments infested with Fol. In addition, T34 application reduced iron concentration in tomato leaves at high ammonium/nitrate ratios and reduced the severity of Fusarium wilt at high iron and nitrogen leaf concentrations.     

Carnation Fusarium wilt suppression in four composts

Fusarium wilt is now a major disease of carnation crops worldwide. Methyl bromide, which is used to remedy it, is environmentally unsafe. An alternative approach integrated into biological control is to grow crops in suppressive media. Suppressiveness of seven plant growth media to Fusarium oxysporum f. sp. dianthi was evaluated in bioassays with carnation (Dianthus cariophyllus) cv. Medea. These media were: (1) grape marc compost, (2) cork compost, (3) olive oil husk + cotton gin trash composted and mixed with rice husk, (4) spent mushroom compost mixed with peat, (5) coir fibre, (6) light peat and (7) vermiculite. In order to look for carnation Fusarium wilt suppressiveness indicators, growth medium pH and β-glucosidase activity were evaluated. Furthermore, F. oxysporum populations were measured in plant growth media at the beginning and end of bioassays. The compost media showed a range of suppressiveness in comparison with peat. Grape marc compost was the most effective plant growth medium in suppressing carnation Fusarium wilt. On the other hand coir fibre, peat and vermiculite were conducive for this disease. β-glucosidase activity and pH were positively correlated with disease severity as in other reports for tomato. Therefore, these two parameters are good indicators for carnation Fusarium wilt suppressiveness, and possibly for other F. oxysporum pathosystems. All composts showed similar F. oxysporum populations at the end of the bioassays to peat and vermiculite.