Control of Fusarium wilt of tomato caused by Fusarium oxysporum f. sp. lycopersici using leaf extract of Piper betle L.: a preliminary study

Defense Mechanisms Induced by Celery Seed Essential Oil against Powdery Mildew Incited by Podosphaera fusca in Cucumber

This study aimed to evaluate the effectiveness of essential oil extracted from celery (Apium graveolens) seeds (CSEO) for the control of powdery mildew of cucumber (Cucumis sativus) incited by Podosphaera fusca and to investigate the metabolic and genetic defense mechanisms triggered by the treatment with this essential oil in cucumber seedlings. The main compounds in the CSEO as determined by gas chromatography-mass spectrometry (GC-MS) analysis were d-limonene, 3-butyl phthalide, β-selinene, and mandelic acid. The treatment with CSEO led to an increase in the content of both chlorophyll and phenolic/flavonoid compounds in cucumber leaves. In greenhouse tests, the application of CSEO reduced by 60% the disease severity on leaves of cucumber plants and stimulated the activity of defense-related enzymes such as β-1,3-glucanase, chitinase, phenylalanine ammonia-lyase, peroxidase, and polyphenol oxidase. Moreover, treatment with CSEO induced overexpression of β-1,3-glucanase, chitinase, and phenylalanine ammonia-lyase genes. A highly significant correlation was found between the β-1,3-glucanase, chitinase, and phenylalanine ammonia-lyase enzymatic activities and the relative expression of the corresponding encoding genes in both inoculated and non-inoculated cucumber seedlings treated with the essential oil. Overall, this study showed that CSEO is a promising eco-friendly candidate fungicide that can be exploited to control cucumber powdery mildew.

In Vitro Antibacterial Activity and Mode of Action of Piper betle Extracts against Soft Rot Disease-Causing Bacteria

Soft rot disease affects a range of crops in the field and also during transit and storage, resulting in significant yield losses and negative economic impacts. This study evaluated the in vitro antibacterial activities and mode of action of Piper betle extracts against the soft rot disease-causing bacteria, Erwinia caratovora subsp. caratovora (ECC). Dried leaves of P. betle were extracted with water, ethanol, and hexane solvents and evaluated for their antibacterial activity. The results showed the highest antibacterial activity against ECC in the ethanol extract, followed by hexane and water extracts with minimum inhibitory concentration (MIC) 1.562, 6.25, and more than 12.50 mg/mL, respectively. The time-kill assay indicated a bactericidal mode of action. ECC growth was destroyed within 6 and 8 hours after treatment with the ethanol extract at 4-fold MIC and 2-fold MIC, respectively. The ethanol extract of P. betle showed promising activity against ECC, with the potential for further development as a novel alternative treatment to control phytobacteria.

In vitro screening and in silico prediction of antifungal metabolites from rhizobacterium Achromobacter kerstersii JKP9

The main objective of this study was to identify the antifungal metabolites from Achromobacter kerstersii JKP9, a rhizosphere bacterium isolated from tomato cultivations, inhibiting the melanin biosynthetic pathways in vascular wilt pathogen Fusarium oxysporum f. sp. lycopersici (Fol). To achieve this objective, all the rhizobacterial morphotypes were screened for plant-growth-promoting and antagonistic activities. Ethyl acetate extract of Achromobacter kerstersii JKP9 was purified in HPLC and predicted for antifungals in GC-MS equipped with Wiley library. After identification, molecular docking of useful ligands with modeled Short-chain Dehydrogenase/ Reductase (SDR) of Fol (Locus: FOXG_00472). Results were indicated that the potential strain Achromobacter kerstersii JKP9 exclusively secreted five pyrrole analogs notable for their antifungal role with no extracellular antifungal enzyme production as seen in other rhizobacterial isolates. In silico docking studies identified, Pyrrolo[1, 2-a]pyrazine-1,4-dione, hexahydro- as effective for SDR in Fol. From these results, we conclude that bacterial pyrroles can be used as an effective fungicide to control Fusarium wilt in tomatoes. In the future, these pyrrole derivatives can directly be employed as eco-friendly fungicides or may be used as antifungal supplements in agrochemical products for the sustainable production of tomatoes.

Exploring the efficacy of antagonistic rhizobacteria as native biocontrol agents against tomato plant diseases

As the environmental and health concerns alert the necessity to move towards a sustainable agriculture system, biological approach using indigenous plant growth-promoting rhizobacteria (PGPR) gains a strong impetus in the field of plant disease control. In this context, the present review article addresses the usage of rhizospheric antagonistic bacteria as a suitable alternative to control tomato fungal diseases namely Fusarium wilt and early blight disease. Biological control has been considered to be an eco-friendly, safe and effective method for disease management. The inherent traits of PGPR to antagonize a pathogen through various mechanisms has been investigated extensively to utilize them as potent biocontrol agents (BCA). Hence, the article provides a detailed account on different biocontrol mechanisms displayed by BCA. It is also suggested that the use of bacterial consortium ensures consistent performance by BCA in field conditions. Likewise, this review also deals with the opportunities and obstacles faced during commercialization of these antagonistic bacteria as biocontrol agents in the market.

In silico Prediction, Characterization, Molecular Docking, and Dynamic Studies on Fungal SDRs as Novel Targets for Searching Potential Fungicides Against Fusarium Wilt in Tomato

Vascular wilt of tomato caused by Fusarium oxysporum f.sp. lycopersici (FOL) is one of the most devastating diseases, that delimits the tomato production worldwide. Fungal short-chain dehydrogenases/reductases (SDRs) are NADP(H) dependent oxidoreductases, having shared motifs and common functional mechanism, have been demonstrated as biochemical targets for commercial fungicides. The 1,3,6,8 tetra hydroxynaphthalene reductase (T4HNR) protein, a member of SDRs family, catalyzes the naphthol reduction reaction in fungal melanin biosynthesis. We retrieved an orthologous member of T4HNR, (complexed with NADP(H) and pyroquilon from Magnaporthe grisea) in the FOL (namely; FOXG_04696) based on homology search, percent identity and sequence similarity (93% query cover; 49% identity). The hypothetical protein FOXG_04696 (T4HNR like) had conserved T-G-X-X-X-G-X-G motif (cofactor binding site) at N-terminus, similar to M. grisea (1JA9) and Y-X-X-X-K motif, as a part of the active site, bearing homologies with two fungal keto reductases T4HNR (M. grisea) and 17-β-hydroxysteroid dehydrogenase from Curvularia lunata (teleomorph: Cochliobolus lunatus PDB ID: 3IS3). The catalytic tetrad of T4HNR was replaced with ASN¹¹⁵, SER¹⁴¹, TYR¹⁵⁴, and LYS¹⁵⁸ in the FOXG_04696. The structural alignment and superposition of FOXG_04696 over the template proteins (3IS3 and 1JA9) revealed minimum RMSD deviations of the C alpha atomic coordinates, and therefore, had structural conservation. The best protein model (FOXG_04696) was docked with 37 fungicides, to evaluate their binding affinities. The Glide XP and YASARA docked complexes showed discrepancies in results, for scoring and ranking the binding affinities of fungicides. The docked complexes were further refined and rescored from their docked poses through 50 ns long MD simulations, and binding free energies (ΔG_bind) calculations, using MM/GBSA analysis, revealed Oxathiapiprolin and Famoxadone as better fungicides among the selected one. However, Famoxadone had better interaction of the docked residues, with best protein ligand contacts, minimum RMSD (high accuracy of the docking pose) and RMSF (structural integrity and conformational flexibility of docking) at the specified docking site. The Famoxadone was found to be acceptable based on in silico toxicity and in vitro growth inhibition assessment. We conclude that the FOXG_04696, could be employed as a novel candidate protein, for structure-based design, and screening of target fungicides against the FOL pathogen.

Identification and characterization of Fusarium sp. using ITS and RAPD causing fusarium wilt of tomato isolated from Assam, North East India

Fusarium oxysporum which causes wilt is a serious pathogen. Fusarium isolates were isolated from Assam located in North East region of India. Morphological identification of Fusarium isolates was done using conidial and hyphal structures. Molecular identification of Fusarium isolates was done by amplifying the internal transcribed spacer (ITS) region of the conserved ribosomal DNA using primers ITS1 and ITS4. All the ITS sequences were compared for gaps and similarity. Further, characterization of random amplified polymorphic DNA (RAPD) was carried out using 40 primers. 15 primers that gave reproducible results were selected. RAPD was used to observe the relatedness among these isolates. Thus, it was concluded that molecular profiling using ITS is an indispensable method for identification studies.

Antifungal activity of some botanical extracts on Fusarium oxysporum

The present paper describes the antifungal activity of some plant extracts on the development of Fusarium oxysporum f.sp. lycopersici. The best extracts were selected to be tested as a phytofungicide to control crop diseases, with the ultimate goal of developing a green alternative to synthetic fungicides. Using the conidia germination assay, of the 24 plant extracts tested, 15 reduced conidia germination and 6 completely inhibited germination. Extracts of Rivina humulis, Brassica carinata, Brunfelsia calyicina, Salvia guaranitica and Punica granatum showed good antifungal activity. The relationship between total phenolic content (TPC) in each plant extract tested and the percentage of mycelial growth inhibition showed a significant correlation (R2 = 0.69), while no correlation was found between total flavonoid content (TFC) and percentage mycelial growth inhibition. Among all extracts tested, Punica granatum and Salvia guaranitica showed the best inhibitory effect against Fusarium oxysporum f.sp. lycopersici . Our results indicate that plant extracts with a good antifungal activity generally had a high level of total polyphenolic content and titratable acidity, and low values of pH.