Fusarium Oxysporum F. Sp. Radicis-lycopersici Research Articles

Bacillus methylotrophicus DCS1: Production of Different Lipopeptide Families, In Vitro Antifungal Activity and Suppression of Fusarium Wilt in Tomato Plants.

The present work aims to quantitatively and qualitatively monitor the production of lipopeptide mixtures by Bacillus methylotrophicus DCS1 strain in Landy medium and to investigate the antifungal activities of DCS1 strain and its produced lipopeptides. The in vitro activities were tested by the direct confrontation and agar well diffusion methods, while the in vivo study was carried out in order to test the efficiency of DCS1 bacterial suspension in the control of Fusarium wilt in tomato plants. Identification of lipopeptides by mass spectrometry (LC/MSD-TOF) showed that lipopeptide isoforms produced during the first 24h and 48h of fermentation are identical, belonging to bacillomycin D and fengycins A and B homologues with a difference in the yield of production. After 72h of fermentation corresponding to the end of incubation period, B. methylotrophicus DCS1 is able to produce a mixture of surfactin, pumilacidin, iturin A/mycosubtilin, iturin C1, bacillomycin D and fengycins A and B isoforms. The results of in vitro antifungal experiments suggest that B. methylotrophicus DCS1 has a significant potential as a biocontrol agent, owing to lipopeptides produced, endowed with antifungal activity against several phytopathogenic fungi. The curative treatment of tomato plants with DCS1 bacterial suspension was more effective in the protection against Fusarium oxysporum f. sp. radicis-lycopersici (FORL) than the preventive treatment by comparing the average number of leaves remaining healthy after 30days of each treatment and the appearance of tomato plants roots. The results indicate that B. methylotrophicus DCS1 exhibit a significant suppression of Fusarium wilt symptoms in tomato plants comparable to that of commercial fungicides and could be an alternative to chemically synthesized pesticides.

Synergistic effects of Bacillus velezensisSDTB038 and phenamacril on Fusarium crown and root rot of tomato

AbstractFusarium crown and root rot (FCRR) is a damaging ailment that can affect tomato production. It is caused by Fusarium oxysporum f. sp. radicis‐lycopersici (FORL). The use of biological agents, in conjunction with fungicides, has become a practical strategy for combating fungal diseases in crops. Lipopeptide extracts from a potential biocontrol strain of Bacillus velezensis (SDTB038) exhibited an inhibitory effect on the mycelial growth of FORL; the EC50 value was 59.95 mg/L, and at a concentration of 256 mg/L the inhibition rate reached 97.4%. The SDTB038 strain produces metabolites such as protease and siderophores. Additionally, it is capable of forming a biofilm and swimming. Phenamacril, an antifungal agent, also displayed an inhibitory effect on FORL, demonstrating an EC50 value of 1.074 mg/L. The control effects of the combination of Bacillus velezensis SDTB038 and phenamacril against FORL on tomato plants were also studied in the greenhouse. The combination of phenamacril and 108 CFU/mL SDTB038 fermentation broth exhibited a strong synergistic control effect on FORL, of up to 84.0%. The combination also led to a 35.6% increase in tomato yield compared to the control. These results demonstrate that SDTB038 possesses antifungal activity. Moreover, when combined with phenamacril, it exhibits a strong synergistic effect against FORL. This solution proves to be an effective means of controlling FCRR in tomato plants.

Microbial volatile organic compounds 2-heptanol and acetoin control Fusarium crown and root rot of tomato.

Some microbial volatile organic compounds (mVOCs) can act as antagonistic weapons against plant pathogens, but little information is available on the contribution of individual mVOC to biocontrol and how they interact with plant pathogens. In this study, the Bacillus subtilis strain N-18 isolated from the rhizosphere of healthy plants grown in areas where Fusarium crown and root rot (FCRR) of tomatooccurs could reduce the 30% of the incidence of FCRR. Moreover, the volatile organic compounds (VOCs) produced by N-18 had inhibitory effects on Fusarium oxysporum f. sp. radicis-lycopersici (FORL). The identification of VOCs of N-18 was analyzed by the solid-phase microextraction coupled to gas chromatography-mass spectrometry.Meanwhile, we conducted sensitivity tests with these potential active ingredients and found that the volatile substances acetoin and 2-heptanol can reduce the 41.33% and 35% of the incidence of FCRR in tomato plants. In addition, the potential target protein of acetoin, found in the cheminformatics and bioinformatics database, was F. oxysporum of hypothetical protein AU210_012600 (FUSOX). Molecular docking results further predicted that acetoin interacts with FUSOX protein. These results reveal the VOCs of N-18 and their active ingredients in response to FORL and provide a basis for further research on regulating and controlling FCRR.

Diagnosis of Induced Resistance State in Tomato Using Artificial Neural Network Models Based on Supervised Self-Organizing Maps and Fluorescence Kinetics.

The aim of this study was to develop three supervised self-organizing map (SOM) models for the automatic recognition of a systemic resistance state in plants after application of a resistance inducer. The pathosystem Fusarium oxysporum f. sp. radicis-lycopersici (FORL) + tomato was used. The inorganic, defense inducer, Acibenzolar-S-methyl (benzo-[1,2,3]-thiadiazole-7-carbothioic acid-S-methyl ester, ASM), reported to induce expression of defense genes in tomato, was applied to activate the defense mechanisms in the plant. A handheld fluorometer, FluorPen FP 100-MAX-LM by SCI, was used to assess the fluorescence kinetics response of the induced resistance in tomato plants. To achieve recognition of resistance induction, three models of supervised SOMs, namely SKN, XY-F, and CPANN, were used to classify fluorescence kinetics data, in order to determine the induced resistance condition in tomato plants. To achieve this, a parameterization of fluorescence kinetics curves was developed corresponding to fluorometer variables of the Kautsky Curves. SKN was the best supervised SOM, achieving 97.22% to 100% accuracy. Gene expression data were used to confirm the accuracy of the supervised SOMs.

Transcriptome Analysis Reveals the Response Mechanism of Frl-Mediated Resistance to Fusarium oxysporum f. sp. radicis-lycopersici (FORL) Infection in Tomato.

Tomato Fusarium crown and root rot (FCRR) is an extremely destructive soil-borne disease. To date, studies have shown that only plants with tomato mosaic virus (TMV) resistance exhibit similar resistance to tomato Fusarium oxysporum f. sp. radicis-lycopersici (FORL) and have identified a single relevant gene, Frl, in Peruvian tomato. Due to the relative lack of research on FCRR disease-resistance genes in China and elsewhere, transcriptome data for FORL-resistant (cv. ‘19912’) and FORL-susceptible (cv. ‘Moneymaker’) tomato cultivars were analysed for the first time in this study. The number of differentially expressed genes (DEGs) was higher in Moneymaker than in 19912, and 189 DEGs in the ‘plant–pathogen interaction’ pathway were subjected to GO and KEGG enrichment analyses. MAPK and WRKY genes were enriched in major metabolic pathways related to plant disease resistance; thus, we focused on these two gene families. In the early stage of tomato infection, the content of JA and SA increased, but the change in JA was more obvious. Fourteen genes were selected for confirmation of their differential expression levels by qRT-PCR. This study provides a series of novel disease resistance resources for tomato breeding and genetic resources for screening and cloning FORL resistance genes.

Deciphering the role of Trichoderma sp. bioactives in combating the wilt causing cell wall degrading enzyme polygalacturonase produced by Fusarium oxysporum: An in-silico approach

The cell wall degrading enzymes polygalacturonase (PG) secreted by Fusarium oxysporum f. sp. radicis-lycopersici (FOL) is testified to trigger Fusarium crown and root rot disease in tomato crops; instigated due to the degradation of the pectin. Trichoderma sp. is documented as a potential biocontrol agent playing a pivotal role in plant health and disease management. An in-silico approach employing homology modelling, molecular docking, molecular dynamics (MD) simulation and MMPBSA was employed to assess the prospective role of bioactives produced by Trichoderma sp. in combating the PG2 enzyme. The studies revealed that amongst the wide range of bioactives screened, Trichodermamide B produced by T. harzianum and Viridin, Virone, and Trichosetin produced by T. virens emerged as the potential inhibitors of the PG2. Docking results revealed that the complexes possessed most stable energy for Trichodermamide B (−8.1 kcal/mol) followed by Viridin (−7.7 kcal/mol), Virone (−7.1 kcal/mol), and Trichosetin (−7 kcal/mol), respectively. Interaction studies of FOL with T. virens and T. harzianum reported an inhibition of 83.33% and 75.87%, respectively. The structural rigidity and stability of the docked complex was confirmed through MD simulations evaluated across multiple descriptors from the simulation trajectories. Further, MMPBSA analysis validated the results that binding of the enzyme to the screened ligands was spontaneous. The study unravels new insights on the versatile potential of Trichoderma sp. Bioactives as a prospective agent for the inhibition of cell-wall degrading enzymes secreted by phytopathogens. The proposed study can be implemented for design of bioformulations that serve the role of biopesticide, promising a sustainable alternate to chemical-based products.

Determination of The Response of Wild and Cultivated Tomato Genotypes to Some Disease and Pests by Molecular Markers

Fusarium oxysporum f. sp. lycopersici, Verticillium spp., and nematodes, as well as virus diseases that negatively affect production with limited chemical control cause significant losses in greenhouse tomato cultivation. The practical and effective side of controlling diseases is genetic control by breeding. Using a genomic approach for plant breeding is a more sustainable and effective way to control disease and pests. The development of the resistant line is improved by conventional breeding methods that can be conducted over a long period. However, molecular markers make these processes considerably shorter with identifying resistant individuals. In this study, 14 wild and 188 cultivated tomato genotypes have been tested against Fusarium oxysporum f. sp. radicis-lycopersici (FORL), Meloidogyne spp. (root-knot nematodes), Tomato spotted wilt virus (TSWV), Tomato mosaic virus (ToMV), Tomato yellow leaf curl virus (TYLCV) and Verticillum dahliae Kleb. (Ve) diseases and pests with using MAS (Marker- Assisted Selection) technique. According to these results, it has been determined that the selected markers can be used effectively in breeding studies to determine the diseases mentioned above.

In Vitro Screening of New Biological Limiters against Some of the Main Soil-Borne Phytopathogens

This study explored the role of Aphanocladium album (strain MX95), Pleurotus ostreatus (strain ALPO) and Pleurotus eryngii (strain AL142PE) as potential biological limiters. MX95, ALPO and AL142PE were screened under laboratory studies against Phytophthora nicotianae (PN), Fusarium oxysporum f. sp. radicis-lycopersici (FORL), Fusarium oxysporum f. sp. lycopersici (FOL), Fusarium solani (FS), Sclerotinia minor (SM), Sclerotinia sclerotiorum (SS), Athelia (Sclerotium) rolfsii (AR) and Verticillium dahliae (VD). The radial growth inhibition and the over-growth of potential antagonists on the target organisms were used to assess the interactions in the in vitro dual culture plate assay. The antagonistic ability of each challenge isolate was evaluated by calculating an index of the antagonism (AI) based on the interaction type in the dual cultures. MX95, reducing the growth of SS (20%) and FS (40%), displayed deadlock at mycelial contact against FOL and FORL, deadlock at distance versus VD and completely over-grew PN and SM. ALPO reduced (43 to 88%) the mycelial growth of tested pathogens except FORL and replaced PN and VD. AL142PE reducing (53 to 67%) SS, VD, FS and FOL mycelial growth and completely over-grew PN. AR showed combative ability against all the experienced biological limiters. Based on the results of the AI values, MX95 (AI = 16.5) was considered an active antagonist, while ALPO (AI = 11.5) and AL142PE (AI = 12.0) were moderately active antagonists. Strains MX95, ALPO and AL142PE were suitable as environment-friendly potential biocontrol agents to manage some of the main soil-borne agents of foot, root, soft rot and wilt diseases. These results are the first step in the assessment of the potential capacity of these organisms as biological limiters. Nevertheless, additional experiments should be performed for the translation to the field conditions in plant protection against soil-borne plant pathogens. In particular, the optimisation of dose and application time validation should be performed for a solid conclusion about the competitive ability of MX95, ALPO and AL142PE and the usefulness of potential biological limiters.

Overexpression of Lectin Receptor-Like Kinase 1 in Tomato Confers Resistance to Fusarium oxysporum f. sp. Radicis-Lycopersici.

The disease Fusarium crown and root rot (FCRR), caused mainly by Fusarium oxysporum f. sp. radicis-lycopersici (FORL), seriously affects commercial tomato [Solanum lycopersicum (Sl)] yields. However, the genes that offer resistance to FORL are limited and the mechanism of resistance to FCRR is poorly understood. Lectin receptor-like kinases (LecRKs) play critical roles in defensive responses and immunity in many plant species; however, whether specific LecRKs are involved in the response of tomato plants to FORL is unclear. Here, we report that the expression of SlLecRK1/Solyc09g011070.1 was obviously induced by the infection of FORL. Biochemical and cell biological data revealed that SlLecRK1 is an active kinase that is located at the cell membrane, while real-time quantitative PCR data suggested that SlLecRK1 is mainly expressed in stems and roots. Genetic studies showed that overexpression of SlLecRK1 significantly improved the resistance of tomato plants to FORL but did not cause visible changes in plant growth and development compared with wild-type control plants. RNA-Seq data suggested that the positive effects of SlLecRK1 on the resistance of tomato plants to FORL occur mainly by triggering the expression of ethylene-responsive transcription factor (ERF) genes. Together, our findings not only identify a new target for the development of FCRR-resistant tomato varieties, they also demonstrate a molecular mechanism linking SlLecRK1 and ERFs in regulating the immune responses of tomato plants to FORL.

Biocontrol of Soil-Borne Pathogens of Solanum lycopersicum L. and Daucuscarota L. by Plant Growth-Promoting Actinomycetes: In Vitro and In Planta Antagonistic Activity.

Biotic stress caused by pathogenic microorganisms leads to damage in crops. Tomato and carrot are among the most important vegetables cultivated worldwide. These plants are attacked by several pathogens, affecting their growth and productivity. Fourteen plant growth-promoting actinomycetes (PGPA) were screened for their in vitro biocontrol activity against Solanum lycopersicum and Daucus carota microbial phytopathogens. Their antifungal activity was evaluated against Fusarium oxysporum f. sp. radicis-lycopersici (FORL) and Rhizoctonia solani (RHS). Antibacterial activity was evaluated against Pseudomonas syringae, Pseudomonas corrugata, Pseudomonas syringae pv. actinidiae, and Pectobacterium carotovorum subsp. carotovorum. Strains that showed good in vitro results were further investigated in vitro (cell-free supernatants activity, scanning electron microscope observations of fungal inhibition). The consortium of the most active PGPA was then utilized as biocontrol agents in planta experiments on S. lycopersicum and D. carota. The Streptomyces albidoflavus H12 and Nocardiopsis aegyptica H14 strains showed the best in vitro biocontrol activities. The diffusible and volatile compounds and cell-free supernatants of these strains showed both antifungal (in vitro inhibition up to 85%, hyphal desegregation and fungicidal properties) and antibacterial activity (in vitro inhibition >25 mm and bactericidal properties). Their consortium was also able to counteract the infection symptoms of microbial phytopathogens during in planta experiments, improving plant status. The results obtained highlight the efficacy of the selected actinomycetes strains as biocontrol agents of S. lycopersicum and D. carota.

Potential antifungal effects of silver nanoparticles (AgNPs) of different sizes against phytopathogenic Fusarium oxysporum f. sp. radicis-lycopersici (FORL) strains

Fusarium species are the primary fungal pathogen affecting agricultural foodstuffs both in crop yield and economic loss. Due to these problems, control of phytopathogenic fungi has become one of the critical problems around the World. Nanotechnology is a new technology with potential in many fields, including agriculture. This study focused on determining potential effects of silver nanoparticles (AgNPs) with different nanosizes (3, 5, 8 and 10 nm) and at different concentrations (12.5–100 ppm) against phytopathogenic Fusarium oxysporum f. sp. radicis-lycopersici (FORL) strains. The maximum antifungal activity was achieved by decreasing nanosize and increasing concentration of AgNPs. Mycelium growth abilities were decreased about 50%, 75% and 90% by AgNPs treatment with 3 nm sizes at 25 ppm, 37.5 ppm and 50 ppm concentrations, respectively. The productivity of fungal biomass in the liquid growth media was found to be too limited at the 25–37.5 ppm of AgNPs concentrations with all sizes. In addition, both septation number and dimensions of micro- and macroconidia were found to be gradually decreased with the application of silver nanoparticles. This work showed that the low concentration of AgNPs could be used as potential antifungal agents and applied for control of phytopathogens.

In vitro activity of Lavandula dentata essential oil against Fusarium oxysporum f. sp. radicis-lycopersici in Algeria

This work was inspired by the growing international interest in the study of natural products of plant origin with bioactive properties that can replace synthetic chemical pesticides in the control of pathogens. The aim of this study was to explore the in vitro activity of Lanvandula dentata L. essential oil (EO) on Fusarium oxysporum f. sp. radicis-lycopersici (FORL), a dangerous fungal plant pathogen, causal agent of tomato crown and root rot. Initially, we proceeded to identify the forma specialis of two strains of F. oxysporum by PCR based on the differences in the genes responsible for the synthesis of endo-polygalacturonases (pg1) and exo-polygalacturonases (pgx4) and then tested the activity of the EO on these strains by the direct contact method at different concentrations. The results showed that increasing the concentration of EO had a significant inhibitory effect, with a minimum inhibition rate of 49.3±2.2 % and 21.8±4.2 for the strains IB19501 and IB19502 respectively at the 0.25 μL/mL concentration and reaching 100±0.0 at the 1 μL/mL concentration for both strains. The data of this study reveal an important anti-fungal activity of the EO of L. dentata, these effects further validate the interest of our study and the traditional use of this plant, while indicating the possibilities of its potential use as a natural alternative to pesticides for the control of pathogenic fungi and thus preserve human health and the environment.

Ability of endophytic fungi associated with Withania somnifera L. to control Fusarium Crown and Root Rot and to promote growth in tomato

Fusarium crown and root rot (FCRR), caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL), is a soilborne tomato disease of increased importance worldwide. In this study, Withania somnifera was used as a potential source of biological control and growth-promoting agents. Seven fungal isolates naturally associated with W. somnifera were able to colonize tomato seedlings. They were applied as conidial suspensions or a cell-free culture filtrate. All isolates enhanced treated tomato growth parameters by 21.5-90.3% over FORL-free control and by 27.6-93.5% over pathogen-inoculated control. All tested isolates significantly decreased by 28.5-86.4% disease severity over FORL-inoculated control. The highest disease suppression, by 86.4-92.8% over control and by 81.3-88.8% over hymexazol-treated control, was achieved by the I6 isolate. FORL radial growth was suppressed by 58.5-82.3% versus control when dual cultured with tested isolates and by 61.8-83.2% using their cell-free culture filtrates. The most active agent was identified as Fusarium sp. I6 (MG835371), which displayed chitinolytic, proteolytic, and amylase activities. This has been the first report on the potential use of fungi naturally associated with W. somnifera for FCRR suppression and for tomato growth promotion. Further investigations are required in regard to mechanisms of action involved in disease suppression and plant growth promotion.

A Fusarium solani endophyte vs fungicides: Compatibility in a Fusarium oxysporum f.sp. radicis-lycopersici – tomato pathosystem

The potential of FsK, a non-pathogenic endophytic Fusarium solani strain, to be utilized as a biocontrol agent in combination with nine selected fungicides registered in tomato crops in Greece was evaluated. In vitro fungitoxicity tests revealed that FsK was insensitive to doses exceeding 100 μg/mL of thiophanate-methyl, fenhexamid, cyprodinil, boscalid and mancozeb. On the contrary, prochloraz, fludioxonil, pyraclostrobin and difenoconazole were most toxic to FsK. None of the later fungicides affected conidial production in an adverse way. Drenching of tomato plants with the above fungicides at recommended doses did not significantly affect colonization of tomato roots by FsK as revealed by in vitro isolation and Real Time PCR quantification. The disease suppressive ability of FsK against Fusarium oxysporum f.sp.radicis lycopersici (FORL) was not adversely affected by the post-inoculation application of commercial formulations of fludioxonil (Switch) and pyraclostrobin (Comet) at the recommended doses. Even more, the Comet–FsK combination resulted in enhanced disease suppression compared to either of the two treatments applied individually. In conclusion, not only biocontrol agent FsK is suitable for use in tomato integrated disease management programs that include all tested fungicides but also, some FsK –fungicide combinations can have additive effect against FORL disease incidence.

Identifying molecular markers suitable for Frl selection in tomato breeding

Modern plant breeding heavily relies on the use of molecular markers. In recent years, next generation sequencing (NGS) emerged as a powerful technology to discover DNA sequence polymorphisms and generate molecular markers very rapidly and cost effectively, accelerating the plant breeding programmes. A single dominant locus, Frl, in tomato provides resistance to the fungal pathogen Fusarium oxysporum f. sp. radicis-lycopersici (FORL), causative agent of Fusarium crown and root rot. In this study, we describe the generation of molecular markers associated with the Frl locus. An F2 mapping population between an FORL resistant and a susceptible cultivar was generated. NGS technology was then used to sequence the genomes of a susceptible and a resistant parent as well the genomes of bulked resistant and susceptible F2 lines. We zoomed into the Frl locus and mapped the locus to a 900 kb interval on chromosome 9. Polymorphic single-nucleotide polymorphisms (SNPs) within the interval were identified and markers co-segregating with the resistant phenotype were generated. Some of these markers were tested successfully with commercial tomato varieties indicating that they can be used for marker-assisted selection in large-scale breeding programmes.

Management of Fusarium Crown and Root Rot of tomato by Solanum linnaeanum L. extracts

Abstract Leaf, stem and fruit aqueous extracts of Solanum linnaeanum were tested for their ability to suppress Fusarium Crown and Root Rot (FCRR) in tomato caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL) and to enhance tomato growth. Leaf extract used at 30% (w/v) was the most effective in reducing disease severity by 92.3% and the extent of vascular browning by 97.56% compared to FORL-inoculated and untreated control. A significant enhancement of growth parameters was recorded on tomato cv. Rio Grande seedlings inoculated with or without FORL. A significant improvement of seed germination was noted. FORL mycelial growth, assessed using the poisoned food technique, varied depending on plant organs, extracts, and concentrations used. Butanolic extracts were the most active, leading to 60.81% decrease in FORL mycelial growth. The high performance liquid chromatography (HPLC) analysis of butanolic extract revealed the presence of thirteen phenolic compounds including seven acids such as protocatechuic acid, salicylic acid, syringic acid, 3.4-dimethoxybenzoic acid, two stilbenes (resveratrol and isorhamnetin 3 O rutinoside) and four flavonoids such as catechol, epigallocatechine, rutin and rutin trihydrate which was the major compound (15.82%). Thus, S. linnaeanum can be explored as a potential source of antifungal and bio-fertilizing compounds.

Immobilization and deactivation of pathogenic enzymes and toxic metabolites by biochar: A possible mechanism involved in soilborne disease suppression

Adding biochar to soil and soilless media can help protect plants against diseases caused by soilborne pathogens. There are a number of direct and indirect mechanisms that are potentially responsible for this effect. This study tested the hypothesis that biochar adsorption and consequent deactivation of cell wall degrading enzymes (CWDEs) and toxic metabolites produced by soilborne pathogens can help defend plant roots against pathogen attack. The specific objectives were to: (i) quantify adsorption and inactivation of model extracellular pathogenic enzymes (polygalacturonase and cellulase) by 4 model biochars; and (ii) determine the effect of biochar adsorption of CWDEs and toxic metabolites produced by Fusarium oxysporum f. sp. radicis lycopersici (FORL) on the severity of disease symptoms in tomato seedlings. All the enzyme adsorption isotherms were strongly non-linear and well-described by the Langmuir model. Maximum adsorption capacity (Qm) was generally greater for polygalacturonase than cellulase on a given biochar, and reached as high as 448 g polygalacturonase per kg biochar. There was no straightforward relationship between biochar adsorption capacity and its surface area or any other biochar characteristics. The adsorbed enzymes were 100% immobilized by the biochars, and the immobilized enzymes were revealed to be substantially deactivated. Activity of immobilized polygalacturonase ranged from 16 to 30% on the four biochars, and activity of immobilized cellulase ranged from 5 to 9%. There were no significant relationships between deactivation extent and any determined biochar physical and chemical characteristic or substrate/product adsorption characteristics. In the tomato seedling bioassay, the adsorption of FORL-produced enzymes and toxic metabolites led to substantially lessened disease-like symptom severity. Thus, the hypothesis was successfully confirmed. We anticipate that adsorption/deactivation of virulence factors by biochar is part of the puzzle responsible for biochar's varied impacts on severity of soilborne disease, but not the only part. This is because most biochar dose-disease resistance curves are non-monotonic, and reveal best results at some interim biochar dose. This would not be the case if only adsorption/deactivation was important, since in that event, increasing biochar dose would increasingly remove virulence factors from near the plant roots.

English

Fusarium crown and root rot (FCRR) is a serious tomato disease in Tunisia which is difficult to control due to its soilborne nature and to the luck of genetic resistance. In the current study, native Solanum linnaeanum was explored as potential source of effective fungal agents for disease biocontrol. Eight fungal isolates, recovered from S. linnaeanum plants growing in the Tunisian Centre-East and shown able to colonize roots, crowns and stems of tomato (Solanum lycopersicum L.) seedlings, were tested for their ability to inhibit Fusarium oxysporum f. sp. radicis-lycopersici (FORL), the causal agent of this disease, and to promote plant growth. Tomato seedlings inoculated or not with FORL and treated using tested fungal isolates, exhibited significant increments in their growth parameters. Tested as conidial suspensions or cell-free culture filtrates, I74 and I92 isolates were the most active leading to 92.8% decrease in FCRR severity and 89.3 to 95.2% lowered vascular browning extent as compared to FORL-inoculated and untreated controls. These two isolates were microscopically and macroscopically described and identified using rDNA sequencing gene as being Penicillium crustosum I74 (MF188258) and Fusarium proliferatum I92 (MF188256). Pathogen mycelial growth was inhibited by 29.4 to 78.1% using their conidial suspensions and by 67.5 to 82% with their cell-free culture filtrates. P. crustosum I74 and F. proliferatum I92 showed chitinolytic, proteolytic and amylase activities. Only I92 isolate exhibited a lipolytic activity. Our study clearly demonstrated that I74 and I92 isolates were promising candidates for suppressing FCRR severity and promoting tomato growth. Further investigations are required for elucidating their mechanisms of action involved in disease suppression and plant growth promotion. Key words: Antifungal activity, associated fungi, Fusarium oxysporum f. sp. radicis-lycopersici, Solanum linnaeanum, tomato growth.

Suppressing Fusarium Crown and Root Rot infections and enhancing the growth of tomato plants by Lycium arabicum Schweinf. Ex Boiss. extracts

Leaf, stem and fruit extracts of a wild medicinal plant, Lycium arabicum, were assessed for their ability to promote tomato growth and to suppress Fusarium Crown and Root Rot (FCRR), a damaging tomato soilborne disease in Tunisia, caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL). Aqueous and organic extracts (at 1, 2, 3 and 4% (v/v)) were screened in vitro for their antifungal activity. Disease severity was decreased significantly 60days after inoculation. Leaf (LC2) and fruit (FC2) aqueous extracts used at 30% (w/v) were the most effective in inducing 84.6 and 61.5% reduction of leaf damage severity and 84.9 and 82.9% decrease in the vascular browning extent, respectively, as compared to FORL-inoculated and untreated control. A significant improvement in growth of treated and FORL-inoculated tomato plants cv. Rio Grande was found. LC2-based treatment was the most effective in increasing growth by 65–70% relative to control. Moreover, tested on FORL-free plants, all L. arabicum aqueous extracts had significantly enhanced growth compared to the control. Root length and aerial part height were improved by 46–60%, root and aerial part fresh weight were enhanced by 23–60.8% and 22.2–64.9%, respectively, and tomato stem diameter was increased by 19.1%. In vitro, the extracts antifungal activity, screened using the poisoned food technique, varied significantly depending on plant organs, concentrations tested and organic solvent used for extraction. All aqueous extracts inhibited FORL radial growth where percentage inhibition reached 33.5, 24.4 and 30.3%, as compared to control, by leaf, stem and fruit extracts at 4%, respectively. Butanolic leaf extract at 4%, was the most active, inducing 41.4% reduction in FORL mycelial growth. L. arabicum leaf aqueous extract was the most efficient for disease severity suppression and tomato growth promotion. Thus, this wild plant could be explored as a potential source of antifungal and biofertilizing compounds.

Antifungal activity of aqueous and organic extracts from Withania somnifera L. against Fusarium oxysporum f. sp. radicis-lycopersici

The aim of this study was to evaluate the in vitro antifungal activity of aqueous and organic extracts from native Withania somnifera L. leaves, stems, and fruits against Fusarium oxysporum f. sp. radicis-lycopersici (FORL), the causal agent of Fusarium Crown and Root Rot disease in tomato. Aqueous and organic extracts (used at 1, 2, 3 and 4%) were added to molten Potato Dextrose Agar (PDA) medium. After pathogen challenge, cultures were incubated at 25°C for 5 days. All extracts tested, whatever the concentrations used, showed a strong antifungal activity toward targeted pathogen. FORL response to the different extracts assessed using the poisoned food technique, varied depending on plant organs, concentrations tested and organic solvent used for extraction. For aqueous extracts, fruit extract used at 2% exhibited the highest antifungal potential where FORL growth was decreased by 56.27%, relative to the untreated control, compared to 52 and 45.34% achieved using stem and leaf extracts at 3%, respectively. The highest antifungal activity of organic extracts was registred at the highest concentration used (4%). FORL was found to be more sensitive to fruit extracts than those from leaves and stems. Among the three organic extracts tested, butanolic fractions were the most active against FORL growth. The highest antifungal potential expressed by 62.03% decrease in pathogen radial growth was displayed by butanolic stem extracts applied at 4%. These results indicate that native W. somnifera plants may be exploited as potential source of allelochemicals biologically active against FORL.