Systemic Resistance In Tomato Plants Research Articles

Interspecific plant interaction via root exudates structures the disease suppressiveness of rhizosphere microbiomes

Terrestrial plants can affect the growth and health of adjacent plants via interspecific interaction. Here, we studied the mechanism by which plant root exudates affect the recruitment of the rhizosphere microbiome in adjacent plants—with implications for plant protection—using a tomato (Solanum lycopersicum)–potatoonion (Allium cepa var. agrogatum) intercropping system. First, we showed that the intercropping system results in a disease-suppressive rhizosphere microbiome that protects tomato plants against Verticillium wilt disease caused by the soilborne pathogen Verticillium dahliae. Second, 16S rRNA gene sequencing revealed that intercropping with potatoonion altered the composition of the tomato rhizosphere microbiome by promoting the colonization of specific Bacillus sp. This taxon was isolated and shown to inhibit V. dahliae growth and induce systemic resistance in tomato plants. Third, a belowground segregation experiment found that root exudates mediated the interspecific interaction between potatoonion and tomato. Moreover, experiments using split-root tomato plants found that root exudates from potatoonion, especially taxifolin—a flavonoid compound—stimulate tomato plants to recruit plant-beneficial bacteria, such as Bacillus sp. Lastly, ultra-high-pressure liquid chromatography–mass spectrometry analysis found that taxifolin alters tomato root exudate chemistry; thus, this compound acts indirectly in modulating root colonization by Bacillus sp. Our results revealed that this intercropping system can improve tomato plant fitness by changing rhizosphere microbiome recruitment via the use of signaling chemicals released by root exudates of potatoonion. This study revealed a novel mechanism by which interspecific plant interaction modulates the establishment of a disease-suppressive microbiome, thus opening up new avenues of research for precision plant microbiome manipulations.

Phenol and antioxidant enzymatic activity in root knot nematode, Meloidogyne incognita infected tomato plants treated with chitosan nanoparticles

Root knot nematode, Meloidogyne spp. causes severe yield losses in vegetable crops. Chitosan is one of the most abundant biopolymer available worldwide next to cellulose. It is known to have anti-nemic, anti-fungal and anti- bacterial properties. Application of chitosan induces systemic resistance in tomato plants against pathogens by increasing phenolic content and antioxidant enzymes viz., Polyphenol oxidase, Superoxide dismutase and phytoalexins. A study was conducted to study the phenol content and activity of antioxidant enzymes, polyphenol oxidase and peroxidase activities in root knot nematode infected tomato plants treated with chiotsan nanoparticles. The antioxidant enzymatic activities were recorded after 25th day of nematode inoculation. It was observed that the phenolic content increased due to the application of chitosan nanoparticle in nematode infected plants (174.32 µg/g of root) compared to 160.37 µg/g of root in untreated plants. Similarly the peroxidase and polyphenol oxidase activity also increased in chitosan nanoparticle treated nematode infected plants. The study revealed that chitosan nano particles protect plants from root knot nematode infection by increasing the phenol content, peroxidase and polyphenol oxidase activity and induce systemic resistance against nemayodes.

Foliar Applications of Bacillus subtilis HA1 Culture Filtrate Enhance Tomato Growth and Induce Systemic Resistance against Tobacco mosaic virus Infection

The application of microbial products as natural biocontrol agents for inducing systemic resistance against plant viral infections represents a promising strategy for sustainable and eco-friendly agricultural applications. Under greenhouse conditions, the efficacy of the culture filtrate of Bacillus subtilis strain HA1 (Acc# OM286889) for protecting tomato plants from Tobacco mosaic virus (TMV) infection was assessed. The results showed that the dual foliar application of this culture filtrate (HA1-CF) 24 h before and 24 h after TMV inoculation was the most effective treatment for enhancing tomato plant development, with substantial improvements in shoot and root parameters. Furthermore, compared to non-treated plants, HA1-CF-treated tomato had a significant increase in total phenolic and flavonoid contents of up to 27% and 50%, respectively. In addition, a considerable increase in the activities of reactive oxygen species scavenging enzymes (PPO, SOD, and POX) and a significant decrease in non-enzymatic oxidative stress markers (H2O2 and MDA) were reported. In comparison to untreated control plants, all HA1-CF-treated plants showed a significant reduction in TMV accumulation in systemically infected tomato leaves, up to a 91% reduction at 15 dpi. The qRT-PCR results confirmed that HA1-CF stimulated the transcription of several defense-related tomato genes (PR-1, PAL, CHS, and HQT), pointing to their potential role in induced resistance against TMV. GC–MS analysis showed that phenol, 2,4-bis (1,1-dimethylethyl)-, Pyrrolo [1,2-a] pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl)- and eicosane are the primary ingredient compounds in the HA1-CF ethyl acetate extract, suggesting that these molecules take part in stimulating induced systemic resistance in tomato plants. Our results imply that HA1-CF is a potential resistance inducer to control plant viral infections, a plant growth promoter, and a source of bioactive compounds for sustainable disease management.

Induction of Systemic Resistance in Tomato Plants Against Tomato yellow leaf curl virus in Protected Cultivation Using a Local Bacterial Isolate of Bacillus subtilis

Ghanem, H.M., E.H. Akel, Q.A. Al-Rhayeh and I.D. Ismail. 2021. Induction of Systemic Resistance in Tomato Plants Against Tomato yellow leaf curl virus in Protected Cultivation Using a Local Bacterial Isolate of Bacillus subtilis. Arab Journal of Plant Protection, 39(4): 289-295. https://doi.org/10.22268/AJPP-039.4.289295 This study was conducted at the Agricultural Scientific Research Center in Lattakia Governorate in a plastic house during the 2020/2021 growing season to evaluate the efficiency of the native bacterial isolate B.Ra.217 of Bacillus subtilis, in reducing infection of tomato plants with Tomato yellow leaf curl virus (TYLCV), by treating tomato seeds and later watering the seedlings with a suspension of the tested bacteria at a concentration of 1x109 /ml, and then measuring incidence (%) and severity of virus infection, and estimating peroxidase enzyme activity. The results showed that 30 days after inoculation with tomato leaf curl virus, a decrease in virus infection rate and severity in virus-infected and bacteria-treated plants compared with virus-infected and untreated control plants was observed. The reduction in disease incidence and severity of infection reached 26.67% and 34.28%, respectively, with significant differences between the treatments. In addition, the activity of peroxidase enzyme 7 days after infection with the virus showed an increase in plants treated with bacteria only (0.1342 μmol/mg) and those treated with bacteria and virus-infected (0.0913 μmol/mg), compared with the healthy control plants (0.0958 μmol/mg), and virus-infected and untreated with bacteria (0.0570 µmol/mg). The results also showed 15 days after infection that the enzyme activity was higher in plants treated with bacteria only (0.1592 µmol/mg) compared with the healthy control (0.1415 µmol/mg) with significant differences, and also the differences were significant with the untreated infected plants (0.1002 µmol/mg), and with inoculated and treated plants (0.1372 µmol/mg). Thus, this bacterial isolate may have an important applied role in enhancing tomato plant resistance to the virus and consequently reducing its damage. Keywords: Bacillus subtilis B.Ra.217, TYLCV, peroxidase, incidence, severity of infestation, tomato plant

Mechanical strengthening and metabolic re-modulations are involved in protection against Fusarium wilt of tomato by B. subtilis IAGS174

ABSTRACT Rhizospheric bacteria may induce resistance to plant diseases. However, the underlying plant resistance mechanisms are unclear. We demonstrated the potential ability of the rhizobacterial strain Bacillus subtilis IAGS174 to elicit systemic resistance in tomato plants against Fusarium wilt pathogens. Comparative biochemical, histological, and molecular analyses were conducted to screen the differential responses between non-inoculated and B. subtilis IAGS174-inoculated tomato plants followed by pathogen challenge. B. subtilis IAGS174 had a significant inhibitory effect on disease development and reduced the disease index. B. subtilis IAGS174-primed plants exhibited significantly improved synthesis of total phenolics, flavonoids, and plant defense enzymes. Furthermore, priming increased the production of physical defense barriers including lignin. Additionally, RT-qPCR analysis revealed that disease resistance in bacteria-treated tomato plants was associated with increased expression levels of lignin-related and phenylpropanoid biosynthetic genes. Our findings support a positive role of B. subtilis IAGS174 in triggering immunity of tomato plants against a soil-borne disease.

Molecular insights into biochar-mediated plant growth promotion and systemic resistance in tomato against Fusarium crown and root rot disease

Molecular mechanisms associated with biochar-elicited suppression of soilborne plant diseases and improved plant performance are not well understood. A stem base inoculation approach was used to explore the ability of biochar to induce systemic resistance in tomato plants against crown rot caused by a soilborne pathogen, Fusarium oxysporum f. sp. radicis lycopersici. RNA-seq transcriptome profiling of tomato, and experiments with jasmonic and salycilic acid deficient tomato mutants, were performed to elucidate the in planta molecular mechanisms involved in induced resistance. Biochar (produced from greenhouse plant wastes) was found to mediate systemic resistance against Fusarium crown rot and to simultaneously improve tomato plant growth and physiological parameters by up to 63%. Transcriptomic analysis (RNA-seq) of tomato demonstrated that biochar had a priming effect on gene expression and upregulated the pathways and genes associated with plant defense and growth such as jasmonic acid, brassinosteroids, cytokinins, auxin and synthesis of flavonoid, phenylpropanoids and cell wall. In contrast, biosynthesis and signaling of the salicylic acid pathway was downregulated. Upregulation of genes and pathways involved in plant defense and plant growth may partially explain the significant disease suppression and improvement in plant performance observed in the presence of biochar.

Exploring the Extracellular Macromolecular Composition of Crude Extracts of Penicillium rubens Strain 212 for Elucidation Its Mode of Action as a Biocontrol Agent

Penicillium rubens strain 212 (PO212) acts as an inducer of systemic resistance in tomato plants. The effect of crude extracellular extracts of PO212 on the soil-borne pathogen Fusarium oxysporum f. sp. lycopersici has been evaluated. Evidence of the involvement of soluble, thermo-labile, and proteinase-inactivated macromolecules present in PO212 crude extracts in the control of Fusarium vascular disease in tomato plants was found. Proteomic techniques and the availability of the access to the PO212 genome database have allowed the identification of glycosyl hydrolases, oxidases, and peptidases in these extracellular extracts. Furthermore, a bioassay-guided fractionation of PO212 crude extracellular extracts using an integrated membrane/solid phase extraction process was set up. This method enabled the separation of a PO212 crude extracellular extract of seven days of growth into four fractions of different molecular sizes and polarities: high molecular mass protein fraction >5 kDa, middle molecular mass protein fraction 5–1 kDa, low molecular mass metabolite fraction, and nutrients from culture medium (mainly glucose and minerals). The high and middle molecular mass protein fractions retained disease control activity in a way similar to that of the control extracts. Proteomic techniques have allowed the identification of nine putatively secreted proteins in the high molecular mass protein fraction matching those identified in the total crude extracts. Therefore, these enzymes are considered to be potentially responsible of the crude extracellular extract-induced resistance in tomato plants against F. oxysporum f. sp. lycopersici. Further studies are required to establish which of the identified proteins participate in the PO212’s action mode as a biocontrol agent.

Induction of Systemic Resistance in Tomato Plants against Root-Knot Nematode, Meloidogyne incognita (Passe-Muraille) with β, Amino Butyric Acid

In this study, the efficiency of β amino butyric acid (BABA) on induction of resistance against root-knot nematode (Meloidogyne incognita, PM) infection of tomato plants were evaluated. The effects of treatments were estimated by counting the number of galls, egg masses / root system and juvenile per 250 g soil. In addition, tomato plants growth parameters were estimated. Results showed that the plants which sprayed with BABA at 32 and 16 Mm gave the highest reduction in gall numbers, egg masses formation and juveniles, ( 57.87- 55.85, 60-59.48 and 49.8- 47.25 % respectively). Concerning the soil drench of BABA with 32 and 16 Mm the highest reduction in gall numbers, egg masses formation and juveniles were recorded ( 61.92- 60.05, 63.99-61.85 and 55.65- 53.38 % respectively). Treatments as well enhance both fresh and dry shoot and root system compared with inoculated control. Also, results showed that application of BABA interior to nematode inoculation were outstanding in inducing acquired resistance for M. incognita than application at the same time or next nematode infection.

Phenylacetic Acid Is ISR Determinant Produced by Bacillus fortis IAGS162, Which Involves Extensive Re-modulation in Metabolomics of Tomato to Protect against Fusarium Wilt.

Bacillus fortis IAGS162 has been previously shown to induce systemic resistance in tomato plants against Fusarium wilt disease. In the first phase of current study, the ISR determinant was isolated from extracellular metabolites of this bacterium. ISR bioassays combined with solvent extraction, column chromatography and GC/MS analysis proved that phenylacetic acid (PAA) was the potential ISR determinant that significantly ameliorated Fusarium wilt disease of tomato at concentrations of 0.1 and 1 mM. In the second phase, the biochemical basis of the induced systemic resistance (ISR) under influence of PAA was elucidated by performing non-targeted whole metabolomics through GC/MS analysis. Tomato plants were treated with PAA and fungal pathogen in various combinations. Exposure to PAA and subsequent pathogen challenge extensively re-modulated tomato metabolic networks along with defense related pathways. In addition, various phenylpropanoid precursors were significantly up-regulated in treatments receiving PAA. This work suggests that ISR elicitor released from B. fortis IAGS162 contributes to resistance against fungal pathogens through dynamic reprogramming of plant pathways that are functionally correlated with defense responses.

Magnesium oxide nanoparticles induce systemic resistance in tomato against bacterial wilt disease

Bacterial wilt is a serious problem affecting many important food crops. Recent studies have indicated that treatment with biotic or abiotic stress factors may increase the resistance of plants to bacterial infection. This study investigated the effects of magnesium oxide nanoparticles (MgO NP) on disease resistance in tomato plants against Ralstonia solanacearum, as well as its antibacterial activity. The roots of tomato seedlings were inoculated with R. solanacearum and then immediately treated with MgO NP; the treated plants showed very little inhibition of bacterial wilt. In contrast, when roots were drenched with a MgO NP suspension prior to inoculation with the pathogen, the incidence of disease was significantly reduced. Rapid generation of reactive oxygen species such as O2−˙ radicals was observed in tomato roots treated with MgO NP. Further O2−˙ was rapidly generated when tomato plant extracts or polyphenols were added to the MgO NP suspension, suggesting that the generation of O2−˙ in tomato roots might be due to a reaction between MgO NP and polyphenols present in the roots. Salicylic acid‐inducible PR1, jasmonic acid‐inducible LoxA, ethylene‐inducible Osm, and systemic resistance‐related GluA were up‐regulated in both the roots and hypocotyls of tomato plants after treatment of the plant roots with MgO NP. Histochemical analyses showed that β‐1,3‐glucanase and tyloses accumulated in the xylem and apoplast of pith tissues of the hypocotyls after MgO NP treatment. These results indicate that MgO NP induces systemic resistance in tomato plants against R. solanacearum.

Searching ISR determinant/s from Bacillus subtilis IAGS174 against Fusarium wilt of tomato

Bacillus subtilis IAGS174 has been previously shown to induce systemic resistance in tomato plants against Fusarium wilt disease. In the present investigation, the resistance-inducing determinant was isolated from cell-free culture filtrates (CFCF) of this bacterium. For this purpose, CFCF was extracted by a series of organic solvents, and the fraction that showed induced systemic resistance (ISR) activity was further partitioned into sub-fractions by column chromatography by using a stepwise elution method. Gas chromatography/mass spectrometry analysis identified four compounds in the ISR-active sub-fraction viz. eugenol, 3-methoxy butyl acetate, pentachloroaniline and phthalic acid methyl ester (PAME). Subsequent bioassays proved that PAME is the potential ISR determinant that significantly ameliorated Fusarium wilt disease of tomato at concentrations of 0.01 and 0.1 mM. Furthermore, compared to the respective controls, tomato plants treated with PAME showed increased activities of defense-related enzymes such as phenylalanine ammonia-lyase, polyphenol oxidase, and peroxidase. Our research indicates that B. subtilis IAGS174 has great potential for use as a biological control agent, and PAME is the ISR determinant secreted by this bacterium into the rhizosphere. This determinant can effectively trigger defense responses in tomato plants.

Light-induced systemic resistance in tomato plants against root-knot nematode Meloidogyne incognita

Plant immunity and defense responses are putatively stimulated by the quality of light spectra. To determine whether aerial light quality can modify the resistance of tomato plants to root pests, in this study, tomato plants inoculated with Meloidogyne incognita were exposed to purple, blue, green, yellow and red light from light-emitting photodiodes at 20 µmol m−2 s−1 photosynthetic photon flux density at the level of the canopy during night for 4 weeks and the number of nematode galls (incidence), plant growth, and defense responses were investigated. Among the studied light treatments, only the nightly red (R) light treatment reduced the number of nematode galls in the roots; this was associated with a 7.9-fold increase in the expression of PROTEINASE INHIBITOR PROTEIN 1 gene, a 17.4-fold increase in the transcript of PATHOGENESIS-RELATED CLASS 1 (PR1) gene, and a 25.4 % increase in the salicylic acid (SA) content in the roots. Furthermore, nightly R light treatment significantly recovered nematode-induced decreases in the light saturated rate of CO2 assimilation and plant fresh weight; however, the other light treatments did not have similar effects. These results indicate that the exposure of the shoot to R light at night induces systemic resistance in tomato plants against root knot nematodes in the roots, which is partly dependent on the jasmonic acid and SA defence pathways. Our study also suggests that exposure to R light at night could be a potential approach to control the nematode infestation in tomato which is particularly feasible for greenhouse production.

Pseudomonas fluorescens mediated suppression of Meloidogyne incognita infection of cowpea and tomato

Plant growth-promoting rhizobacterium, Pseudomonas fluorescens strain BICC602 suppresses root-knot nematode (Meloidogyne incognita) by enhancing defence mechanism leading to induced systemic resistance in cowpea (Vigna unguiculata) cv. L.Walp. and tomato (Solanum lycopersicum) cv. Pusa Ruby. In cowpea, the soil treatment proved more effective than foliar spray on root galling and eggs in roots. However, which factors are necessary in the induction of resistance response in plants against nematodes by BICC602 is not yet known. Salicylic acid (SA) production by some bacteria acts as endogenous signal for the activation of certain plant defence responses. In a split-root trial with tomato as a host plant and M. incognita as challenging parasite, BICC602 induces systemic resistance in tomato plants. Based on the results, it is assumed that P. fluorescens-induced resistance against M. incognita in cowpea and tomato is made either through SA-dependent or SA-independent transduction pathway.

Induce resistance in tomato plants against Tomato Mosaic Virus (ToMV) by Pseudomonas fluorescens

s fluorescens This study was conducted to evaluate the ability of Pseudomona to induce systemic resistance in tomato plants against Tomato mosaic virus (ToMV) infection.Tomato seeds were surface sterilized by sodium hypochlorite (1%).Twenty seeds were soaked in Pseudomonas fluorescens suspension at 5 × 109 CFU/ml for 24 hrs anthor 20 seeds were soaked in( KB)broth for 24 hrs.The treated seeds were sown in plastic pots with 15× 10cm dimension (sterilized with ethanol )containing steril mix soil (2seeds /pot).Also non treated seeds were sown in the same soil for foliage spraying with bacterial suspension. The pots were maintained in muslin protected cages under green house condition.The plants were ToMV- inoculated at 2 primary leaves. The virus multiplication was followed by formation of local lesions on Nicotiana glutinosa .Reuslts showed that treated seeds with bacterial suspension at 5× 109 CFU/ml inhibited ToMVmultiplication by 90.30 %after 15 day of virus inoculation,2 spots were appeared on half leaf Nicotiana glutinosa inoculated by extract from treated plants compared with 26 spots on the half leaf inoculated by extract from infected plants.Similar results were obtained when the plants foliage was sprayed by the bacterial suspension (88.8%inhibition)at 5× 108CFU/ml.

Induced systemic resistance in tomato plants against Fusarium oxysporum f.sp. lycopersici by different kinds of compost

Fusarium wilt caused by Fusarium oxysporium f. sp lycopersici is the most serious diseases attacking tomato plants. The objectives of the study were to determine the effects of three types of compost as resistance inducers in tomato plants against F. oxysporium f.sp. lycopersici and to provide new strategies to control the wilt disease of tomatoes. The results demonstrate that different types and rates of compost resulted in significant decreases in percentages of infection and disease severity, compared with those of the control. Compost 2 rate 2 gave the highest reduction of disease by 73.3%, while compost 3. rate 3 gave the highest of disease severity by 78.4% whereas, treatment with the fungicide Topsin M resulted in the lowest reduction, by 46.6 and 45.4%, respectively. Compost 2 rate 2 proved to be the superior treatment as it increased total phenols by 57.9% relative to the untreated control. Compost 1 rate 2 was the best treatment and increased total chlorophyll and carotenoids (5.8 and 4 mg, respectively) in fresh leaves relative to the control. Different types and rates of compost significantly increased the activity of tyrosine ammonia lyase (TAL), peroxidase (POX), polyphenol oxidase (PPO), alkaline phosphatase (ALP) and acid phosphatase (ACP) as defense enzymes against pathogen. These results suggest that broad bean straw compost at rate 10 ton/feddan might have contributed to restriction of invasion of F. oxysporium f.sp.lycopersici in tomato plants, since they are safe, low cost and effective against the disease. Key words: Fusarium oxysporum f.sp. lycopersici, composts, tomato plants, induced resistance, fungicide, fusarium wilt.

Growth promotion and induction of resistance in tomato plant against Xanthomonas euvesicatoria and Alternaria solani by Trichoderma spp.

In tomato crop, the induction of resistance emerges as an important alternative for achieving the reduction of chemicals in disease control. This study aimed to evaluate the ability of 28 Trichoderma isolates to promote the growth of tomato seedlings and to induce systemic resistance (ISR) against Xanthomonas euvesicatoria and Alternaria solani, the causal agents of bacterial spot and early blight, respectively. Twelve isolates promoted the increase of plant dry matter mass (DMM) above 100%, showing the great potential of these strains. All isolates were able to colonize the root system of tomato plants. The plant growth-promoting isolates were further evaluated for potential elicitation of ISR. Treatment of the soil with all Trichoderma isolates provided protection in tomato plants from 24.13 to 95.94% against X. euvesicatoria and 30.69 to 95.23% against A. solani. The most efficient isolates in reducing the severity of bacterial spot and early blight were the isolates IB 28/07, IB 30/07, IB 37/01 and IB 28/07, IB 30/07 and IB 42/03, respectively. The effect of different time intervals between Trichoderma application and inoculation with pathogens in inducing systemic resistance in tomato plants was evaluated for the isolate IB 28/07. IB 28/07 conferred protection against both diseases at all time intervals, confirming the ability of the isolate to reduce the severity of these diseases up to 21 days after treatment of tomato plants. In vitro assays revealed that all isolates of Trichoderma were able to degrade cellulose. Only the isolate IB 34/08 showed antagonistic activity against X. euvesicatoria and none caused reduction in the in vitro mycelial growth of A. solani. Trichoderma isolates were identified at species level by DNA sequencing.

Antimicrobial activity of plant extracts and induction of systemic resistance in tomato plants by mixtures of PGPR strains and Zimmu leaf extract against Alternaria solani

Extracts from 20 non-host plant species were tested for their ability to inhibit the mycelial growth of Alternaria solani, the causal agent of early blight disease of tomato. In vitro studies indicated that leaf extract of Zimmu ( Allium cepa L. x Allium sativum L.) demonstrated the highest inhibition of mycelial growth (87%) of A. solani. Known biocontrol agents Pseudomonas fluorescens (Pf1 and Py15) and Bacillus subtilis (Bs16) were also tested alone, together, and in conjunction with the most effective plant extract, Zimmu, in both in vitro and in vivo experiments for control of A. solani. All isolates were compatible with each other and with Zimmu leaf extract. Among the various bioformulations tested as seed treatment and foliar application, the talc-based formulation of Pf1 + Py15 + Bs16 + Zimmu was superior in reducing the early blight disease incidence when compared to other treatments. Further, induction of defense enzymes, such as peroxidase (PO) and polyphenol oxidase (PPO) phenylalanine ammonia-lyase (PAL), chitinase and β-1,3-glucanase and accumulation of phenolics were studied. The enzyme accumulation was greater in Pf1 + Py15 + Bs16 + Zimmu treated plants compared to control. The study revealed the probable influence of plant growth promotion and induced systemic resistance (ISR) in enhancing the disease resistance in tomato plants against early blight disease by Zimmu based PGPR mixture.

Rhizobacterial induction of systemic resistance in tomato plants: non-specific protection and increase in enzyme activities

Abstract Rhizobacteria B101R, B212R, and A068R, selected as inducers of systemic resistance against Pseudomonas syringae pv. tomato, were tested individually for biological control of multiple pathogens causing foliar diseases in tomato plants. Greenhouse bioassays were carried with five pathogens—Alternaria solani (early blight), Corynespora cassiicola (foliar blight), Oidium lycopersici (powdery mildew), Stemphilium solani (leaf spot), and Xanthomonas campestris pv. vesicatoria (bacterial spot). The level of control achieved by each rhizobacterium varied with the pathosystem studied. Isolate B101R afforded reduced disease intensity in terms of average number of leaf lesions as compared to the treatment control, protection against A. solani, S. solani, and O. lycopersici. Lipoxygenase, phenylalanine amonia-lyase, and peroxidase activities were estimated spectrophotometrically in extracts of plants grown from seeds that were microbiolized with rhizobacterium B101R, and inoculated with P. syringae pv. tomato. Increases in peroxidase and lipoxygenase activities were detected in foliar extracts from plants whose seeds had been microbiolized, while no increase in phenylalanine amonia-lyase activity was observed.

Induced Systemic Resistance in Tomato Plants against Phytophthora infestans

AbstractInfection of lower leaves of tomato plants with Phytophthora infestans followed by a period unfavourable to disease development increased the general resistance of the plants against the pathogen. Induced resistance to a second infection of upper leaves was expressed in the development of necrotic lesions that were sharply defined and reduced in size. Sporulation of the pathogen was suppressed. Lesions on unprotected plants expanded with a sporulating zone passing gradually to the healthy tissue under the same conditions. Induced resistance delayed and reduced penetration of the pathogen into the epidermis and subsequent colonisation of the mesophyll by formation of papillae in epidermal cells and hypersensitive‐like reactions of penetrated, mesophyll cells.