Systemic Resistance In Tomato Research Articles

Nano- and Microplastics Increase the Occurrence of Bacterial Wilt in Tomato (Solanum lycopersicum L.).

Concern over nano- and microplastic contamination of terrestrial ecosystems has been increasing. However, little is known about the effect of nano- and microplastics on the response of terrestrial ecosystems already under biotic stress. Here, nano- and microplastics at 150-500 mg·kg-1 were exposed to tomatoes (Solanum lycopersicum L.), and the results demonstrate that the presence of nano- and microplastics increased the occurrence of bacterial wilt caused by Ralstonia solanacearum in tomatoes as a function of contaminant concentration, surface modification, and size. Our work shows that nanoplastics (30 nm, 250 mg·kg-1) increased the disease incidence by 2.19-fold. The disease severities in amino- and carboxyl-modified nanoplastic treatments were 30.4 and 21.7% higher than that in unmodified nanoplastic treatment, respectively. The severity of disease under the influence of different-sized nano- and microplastic treatments followed the order 30 > 100 nm > 1 > 50 μm. Mechanistically, nanoplastics disrupted the structure of the tomato rhizosphere soil bacterial community and suppressed the induced systemic resistance in tomato; nanoplastics in planta decreased the salicylic acid and jasmonic acid content in tomatoes, thus inhibiting systemic acquired resistance; and microplastics increased the soil water retention, leading to increased pathogen abundance in the rhizosphere. Additionally, the leachates from nano- and microplastics had no effect on disease occurrence or the growth of tomatoes. Our findings highlight a potential risk of nano- and microplastic contamination to agriculture sustainability and food security.

Transcriptional analysis reveals induction of systemic resistance in tomato treated with Chlorella microalgae

The application of algae-based products has been reported to promote plant growth and yield of tomato plants, especially by enhancing flowering. However, how microalgae (MA) affect plants at the molecular level remains elusive. The aim of this study was to elucidate the effects of live microalgae application on plant photosynthesis and the transcriptome of the unopened flower buds of tomato plants. Microalgae increased leaf temperature differential in tomato leaves but hardly affected photosynthesis. Contrary to our expectations, RNA-seq data revealed remarkable differential expression of several genes participating in responses to abiotic stresses but only a few genes involved in flowering or pollen/ spore development. Late Embryogenesis Abundant (LEA) proteins (mostly dehydrins), oleosins, ethylene, and abscisic-related genes, and Nascent Polypeptide-Associated Complex (NAC)-domain-containing proteins were upregulated. Genes involved in carbohydrate metabolism were also differentially expressed; glycolysis-related genes were upregulated, while those involved in sugar transport were downregulated. The only upregulated gene implicated in the induction of flowering was Solyc07g006500.3.1 (encoding trehalose-6-phosphate synthase enzyme TPS1). Overall, microalgae treatment led to an empirical upregulation of genes involved in jasmonic acid, abscisic acid, and ethylene pathways which are all essential for abiotic stress response. This study shows that microalgae treatment primed plants by inducing the expression of genes involved in response to abiotic stress, especially cold and water stress, as well as pathogen attack.

Trichoderma pubescens Elicit Induced Systemic Resistance in Tomato Challenged by Rhizoctonia solani.

Rhizoctonia solani causes severe diseases in many plant species, particularly root rot in tomato plants. For the first time, Trichoderma pubescens effectively controls R. solani in vitro and in vivo. R. solani strain R11 was identified using the ITS region (OP456527); meanwhile, T. pubescens strain Tp21 was characterized by the ITS region (OP456528) and two genes (tef-1 and rpb2). The antagonistic dual culture method revealed that T. pubescens had a high activity of 76.93% in vitro. A substantial increase in root length, plant height, shoot fresh and dry, and root fresh and dry weight was indicated after applying T. pubescens to tomato plants in vivo. Additionally, it significantly increased the chlorophyll content and total phenolic compounds. The treatment with T. pubescens exhibited a low disease index (DI, 16.00%) without significant differences with Uniform® fungicide at a concentration of 1 ppm (14.67%), while the R. solani-infected plants showed a DI of 78.67%. At 15 days after inoculation, promising increases in the relative expression levels of three defense-related genes (PAL, CHS, and HQT) were observed in all T. pubescens treated plants compared with the non-treated plants. Plants treated with T. pubescens alone showed the highest expression value, with relative transcriptional levels of PAL, CHS, and HQT that were 2.72-, 4.44-, and 3.72-fold higher in comparison with control plants, respectively. The two treatments of T. pubescens exhibited increasing antioxidant enzyme production (POX, SOD, PPO, and CAT), while high MDA and H2O2 levels were observed in the infected plants. The HPLC results of the leaf extract showed a fluctuation in polyphenolic compound content. T. pubescens application alone or for treating plant pathogen infection showed elevated phenolic acids such as chlorogenic and coumaric acids. Therefore, the ability of T. pubescens to inhibit the growth of R. solani, enhance the development of tomato plants, and induce systemic resistance supports the application of T. pubescens as a potential bioagent for managing root rot disease and productivity increase of crops.

Bacillus tequilensis PKDN31 and Bacillus licheniformis PKDL10 –As double headed swords to combat Fusarium oxysporum f. sp. lycopersici induced tomato wilt

Wilt disease, caused by Fusarium oxysporum. f. sp. lycopersici, is a global threat to tomato production that needs to be addressed seriously. The current research envisages the use of two self-compatible Bacillus strains, Bacillus tequilensis PKDN31 and Bacillus licheniformis PKDL10, in a combinatorial approach. The spent supernatant of liquid cultures from strains PKDN31 and PKDL10 showed in vitro antifungal activity against Fusarium sp. attaining an inhibition percentage of 95.33% and 96.54%, respectively. The bacterial isolates lytic activity against Fusarium oxysporum was evaluated by scanning electron microscopic analysis and lytic enzyme production of amylase, lipase, protease and β-1,3 glucanase. Furthermore, PKDN31 and PKDL10 produced siderophores and had root colonizing ability that enhanced the biocontrol efficiency. Combined in vivo inoculation of Bacillus tequilensis PKDN31 and Bacillus licheniformis PKDL10 on tomato seeds revealed that the strains could induce systemic resistance in tomato against Fusarium oxysporum. f. sp. lycopersici by increasing defence enzymes such as β-1,3 glucanase, polyphenol oxidase, peroxidase, phenylalanine ammonia-lyase, chitinase, and total phenol accumulations. Pot culture experiments also proved the biocontrol efficacy of the above dual culture supplementation as this treatment displayed a better growth as well as defense against Fusarium challenge compared to the controls. The obtained results suggest that rhizobacterial isolates could be employed as systemic resistance inducers and biocontrol agents in tomato plants to protect against Fusarium wilt disease.

Systemic Resistance in Tomato Elicited by Some Chemical Inducers Against Root-Knot Nematode, Meloidogyne incognita

Systemic Resistance in Tomato Elicited by Some Chemical Inducers Against Root-Knot Nematode, Meloidogyne incognita

Pseudomonas fluorescens VSMKU3054 mediated induced systemic resistance in tomato against Ralstonia solanacearum

Plant growth-promoting rhizobacteria (PGPR) are potential bio agents for the suppression of various soil-borne diseases in crop plants and considered as viable alternative to chemical pesticides. The selected Pseudomonas fluorescens isolate VSMKU3054 is an effective biological control inoculum for the suppression of wilt disease of tomato incited by Ralstonia solanacearum by inducing plant defense enzymes viz., peroxidase (POX), polyphenol oxidase (PPO), lipoxygenase (LOX), phenylalanine ammonia-lyase (PAL) and total phenol content. The highest level of defense enzymes viz., POX, PAL, PPO, LOX and total phenol contents were observed in tomato seedlings treated with P. fluorescens at 24h, 36h, 36h, 48h and 24h after challenge inoculation of R. solanacearum, respectively. Whereas application of P. fluorescens alone in tomato plants also brought about induction of higher levels of POX, PAL, LOX and total phenol contents, and a moderate level of PPO activity compared to pathogen inoculated plants and control plants. The maximum induction of four prominent PPO isoforms was observed in tomato plants upon the treatment of P. fluorescens VSMKU3054 and challenged with R. solanacearum. Thus, this study showed that induction of defense-related genes by P. fluorescens plays an important role against R. solanacearum.

Genome-Wide Identification and Functions against Tomato Spotted Wilt Tospovirus of PR-10 in Solanum lycopersicum.

Tomato spotted wilt virus impacts negatively on a wide range of economically important plants, especially tomatoes. When plants facing any pathogen attack or infection, increase the transcription level of plant genes that are produced pathogenesis-related (PR) proteins. The aim of this study is a genome-wide identification of PR-10 superfamily and comparative analysis of PR-10 and Sw-5b gene functions against tomato responses to biotic stress (TSWV) to systemic resistance in tomato. Forty-five candidate genes were identified, with a length of 64–210 amino acid residues and a molecular weight of 7.6–24.4 kDa. The PR-10 gene was found on ten of the twelve chromosomes, and it was determined through a genetic ontology that they were involved in six biological processes and molecular activities, and nine cellular components. Analysis of the transcription level of PR-10 family members showed that the PR-10 gene (Solyc09g090980) has high expression levels in some parts of the tomato plant. PR-10 and Sw-5b gene transcription and activity in tomato leaves were strongly induced by TSWV infection, whereas H8 plants having the highest significantly upregulated expression of PR-10 and Sw-5b gene after the inoculation of TSWV, and TSWV inoculated in M82 plants showed significantly upregulated expression of PR-10 gene comparatively lower than H8 plants. There was no significant expression of Sw-5b gene of TSWV inoculated in M82 plants and then showed highly significant correlations between PR-10 and Sw-5b genes at different time points in H8 plants showed significant correlations compared to M82 plants after the inoculation of TSWV; a heat map showed that these two genes may also participate in regulating the defense response after the inoculation of TSWV in tomato.

Evaluation of the Effectiveness of Soil Streptomyces Isolates for Induction of Plant Resistance Against Tomato mosaic virus (ToMV).

The ability of various Streptomyces isolates obtained from soil to induce systemic resistance in tomato (Solanum lycopersicum cv. Supra) plant against Tomato mosaic virus (ToMV) was characterized in current study. Importantly, of nine Streptomyces isolates tested herein, the culture filtrate (CF) of one isolate, designated as Streptomyces ovatisporus LC597360, was the most effective. It exhibited 93.9% biocontrol efficacy and induced a significant decrease (17.6 ± 0.8%) of symptoms severity compared with infected control plants. These finding were confirmed using I-ELISA showing that ToMV concentration was significantly reduced in plants treated with S. ovatisporus LC597360 CF as compared with plants inoculated with ToMV. Moreover, treatment with CF of S. ovatisporus LC597360 not only increased activity of defense-related enzymes such as ascorbate oxidase, catalase, peroxidase, and polyphenol oxidase, but also induced plant growth promotion. The present study is the first one that demonstrates the potential of S. ovatisporus LC597360 in biocontrol of ToMV and investigated its antiviral mechanisms.

Nematicidal Volatiles from Bacillus atrophaeus GBSC56 Promote Growth and Stimulate Induced Systemic Resistance in Tomato against Meloidogyne incognita.

Bacillus volatiles to control plant nematodes is a topic of great interest among researchers due to its safe and environmentally friendly nature. Bacillus strain GBSC56 isolated from the Tibet region of China showed high nematicidal activity against M. incognita, with 90% mortality as compared with control in a partition plate experiment. Pure volatiles produced by GBSC56 were identified through gas chromatography and mass spectrometry (GC-MS). Among 10 volatile organic compounds (VOCs), 3 volatiles, i.e., dimethyl disulfide (DMDS), methyl isovalerate (MIV), and 2-undecanone (2-UD) showed strong nematicidal activity with a mortality rate of 87%, 83%, and 80%, respectively, against M. incognita. The VOCs induced severe oxidative stress in nematodes, which caused rapid death. Moreover, in the presence of volatiles, the activity of antioxidant enzymes, i.e., SOD, CAT, POD, and APX, was observed to be enhanced in M. incognita-infested roots, which might reduce the adverse effect of oxidative stress-induced after infection. Moreover, genes responsible for plant growth promotion SlCKX1, SlIAA1, and Exp18 showed an upsurge in expression, while AC01 was downregulated in infested plants. Furthermore, the defense-related genes (PR1, PR5, and SlLOX1) in infested tomato plants were upregulated after treatment with MIV and 2-UD. These findings suggest that GBSC56 possesses excellent biocontrol potential against M. incognita. Furthermore, the study provides new insight into the mechanism by which GBSC56 nematicidal volatiles regulate antioxidant enzymes, the key genes involved in plant growth promotion, and the defense mechanism M. incognita-infested tomato plants use to efficiently manage root-knot disease.

Induction of Systemic Resistance in Tomato (Solanum lycopersicom L.) Against Damping-off Disease by Using a Mixture of Mycorrhizae

Khrieba, M.I., M.F. Azmeh, W. Chouman, I. Ghazal, and A.K. Ali. 2021. Induction of Systemic Resistance in Tomato (Solanum lycopersicom L.) Against Damping-off Disease by Using a Mixture of Mycorrhizae. Arab Journal of Plant Protection, 39(1): 61-68. The effect of vesicular-arbuscular mycorrhiza (VAM) in improving the activity of the enzyme peroxidase and its role in controlling tomato damping-off caused by Pythium ultimum was studied in a pot experiment during the 2013 growing season. Five treatments were compared with a non-treated control (C): in treatment 1, soil was infested only with Pythium (Py), in treatment 2, soil was infested with mycorrhiza only (My), in treatment 3 soil was infested with Pythium and mycorrhiza at sowing (My+Py), in treatment 4, soil was infested with Pythium and two weeks after sowing with Mycorrhiza (Py-My) and in treatment 5, soil was infested with mycorrhiza and two weeks after sowing with Pythium (My-Py). The results showed that peroxidase concentration in plant tissues 14 days after seed germination in the My treatment (361.91 μmole/mg) significantly exceeded the other treatments. In the treatment where mycorrhiza was added before the pathogen 67 Arab J. Pl. Prot. Vol. 39, No. 1 (2021) peroxidase activity reached 183.73 μmole/mg, which was 41% significantly higher than the My+Py treatment in which the pathogen and mycorrhizal inoculant were added together at sowing (108.27 μmole/mg). The peroxidase concentration increased significantly 28 days after seed germination in the My treatment (687.52 μmole/mg) as compared with the Py treatment (10.52 μmole/mg). Results also showed that in the treatment My-Py, where the mycorrhyzal inoculum was added before the pathogen, peroxidase activity (458.27 μmole/mg) was significantly higher than in the treatment Py+My, when the pathogen was added simultaneously with the vesicular-arbuscular mycorrhizal inoculum (98.67 μmole/mg). Furthermore, results showed that 35 days after seed germination, the enzyme concentration was significantly higher in the My-Py treatment (763.39 μmole/mg) as compared with My+Py treatment (143.5 μmole/mg). Keywords: Vesicular-arbuscular mycorrhiza, VAM, Pythium ultimum, peroxidase, tomato, Syrian coast, induced resistance.

Induction of Systemic Resistance in Tomato by some Abiotic Com-pounds Against Meloidogyne javanica

The comparative of some abiotic compounds (Ascorbic acid, Citric acid, DL-Aspartic acid, Indole-3Acetic acid, Indole-3Butyric acid, DL-leucine, Gibberllic acid, L-Arginine and Sulfosalicylic acid), as resistance inducing for managing Meloidogyne javanica infecting tomato (Super strain B Australian cv.) was studied under greenhouse conditions. The results showed that all tested compounds reduced all nematode parameters compared with untreated control. Application of Citric acid caused a superior effect in the reduction percentage of J2 in soil (95.2%) followed by L-arginine (92.9%) and then Gibberllic acid (92.2%). Also, DL-Aspartic acid gave the highest effect in the reduction percentage of root galls (95.6%) followed by Citric acid and then L-Arginine acid as following (94.3% and 93.02%) respectively compared with untreated control. The treatments of L-arginine followed by Gibberllic acid were recorded the best in plant growth response of tomato plants compared with the untreated control. Tested abiotic agent inducers activators had the potential to suppress M. javanica infection through the stimulation of tomato tolerance. Most of the treatments showed a significant reduction in the percentage values of total and non-reducing sugars comparing with infected and healthy control, while Sulfosalicylic acid and L-arginine recorded high amounts in total and non-reducing sugars. On the other hand, Dl-Aspartic acid, Indol-3Acetic acid and Citric acid showed a high percentage of total phenols comparing with untreated control. Among all treatments, only Dl-leucine showed a significant increment in proline comparing with untreated control and healthy control. The level of Polyphenol oxidase and peroxidase activity increased in the treated plants compared with untreated plants.

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.

Bacillus firmus Strain I-1582, a Nematode Antagonist by Itself and Through the Plant.

Bacillus firmus I-1582 is approved in Europe for the management of Meloidogyne on vegetable crops. However, little information about its modes of action and temperature requirements is available, despite the effect of these parameters in its efficacy. The cardinal temperatures for bacterial growth and biofilm formation were determined. The bacteria was transformed with GFP to study its effect on nematode eggs and root colonization of tomato (Solanum lycopersicum) and cucumber (Cucumis sativus) by laser-scanning confocal microscopy. Induction of plant resistance was determined in split-root experiments and the dynamic regulation of genes related to jasmonic acid (JA) and salicylic acid (SA) by RT-qPCR at three different times after nematode inoculation. The bacteria was able to grow and form biofilms between 15 and 45°C; it degraded egg-shells and colonized eggs; it colonized tomato roots more extensively than cucumber roots; it induced systemic resistance in tomato, but not in cucumber; SA and JA related genes were primed at different times after nematode inoculation in tomato, but only the SA-related gene was up-regulated at 7 days after nematode inoculation in cucumber. In conclusion, B. firmus I-1582 is active at a wide range of temperatures; its optimal growth temperature is 35°C; it is able to degrade Meloidogyne eggs, and to colonize plant roots, inducing systemic resistance in a plant dependent species manner.

Amelioration of systemic resistance in tomato against root rotting fungi by the endophytic Trichoderma species

Amelioration of systemic resistance in tomato against root rotting fungi by the endophytic Trichoderma species

Commercial Formulates of Trichoderma Induce Systemic Plant Resistance to Meloidogyne incognita in Tomato and the Effect Is Additive to That of the Mi-1.2 Resistance Gene.

Meloidogyne is the most damaging plant parasitic nematode genus affecting vegetable crops worldwide. The induction of plant defense mechanisms against Meloidogyne in tomato by some Trichoderma spp. strains has been proven in pot experiments, but there is no information for tomato bearing the Mi-1.2 resistance gene or for other important fruiting vegetable crops. Moreover, Trichoderma is mostly applied for managing fungal plant pathogens, but there is little information on its effect on nematode-antagonistic fungi naturally occurring in soils. Thus, several experiments were conducted to determine (i) the ability of two commercial formulates of Trichoderma asperellum (T34) and Trichoderma harzianum (T22) to induce systemic resistance in tomato and cucumber against an avirulent Meloidogyne incognita population in split-root experiments; (ii) the effect of combining T34 with tomato carrying the Mi-1.2 resistance gene to an avirulent M. incognita population in sterilized soil; and (iii) the effect of combining T34 with tomato carrying the Mi-1.2 resistance gene to a virulent M. incognita population in two suppressive soils in which Pochonia chlamydosporia is naturally present, and the effect of T34 on the level of P. chlamydosporia egg parasitism. Both Trichoderma formulates induced resistance to M. incognita in tomato but not in cucumber. In tomato, the number of egg masses and eggs per plant were reduced by 71 and 54% by T34, respectively. T22 reduced 48% of the number of eggs per plant but not the number of egg masses. T34 reduced the number of eggs per plant of the virulent M. incognita population in both resistant and susceptible tomato cultivars irrespective of the suppressive soil, and its effect was additive with the Mi-1.2 resistance gene. The percentage of fungal egg parasitism by P. chlamydosporia was not affected by the isolate T34 of T. asperellum.

Suppression of Sclerotinia sclerotiorum by the Induction of Systemic Resistance and Regulation of Antioxidant Pathways in Tomato Using Fengycin Produced by Bacillus amyloliquefaciens FZB42.

Lipopeptides from Bacillus species exhibit promising biological control activity against plant pathogens. This study aimed to explore the potential of purified fengycin to induce systemic resistance in tomato against Sclerotinia sclerotiorum. Bacillus amyloliquefaciens FZB42, its mutant AK1S, and their corresponding metabolites showed in vitro inhibition of S. sclerotiorum mycelium. Fengycin derived from an AK1S mutant was purified and identified through HPLC and MALDI-TOF-MS, respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed structural deformities in the fungal mycelium. Moreover, fengycin induced the accumulation of reactive oxygen species (ROS) in S. sclerotiorum mycelium and downregulated the expression of ROS-scavenging genes viz., superoxide dismutase (SsSOD1), peroxidase (SsPO), and catalase (SsCAT1) compared to the untreated control. Furthermore, the lesion size was dramatically reduced in fengycin-treated tomato plants compared to plants infected with S. sclerotiorum only in a greenhouse experiment. Additionally, the transcriptional regulation of defense-related genes GST, SOD, PAL, HMGR, and MPK3 showed the highest upsurge in expression at 48 h post-inoculation (hpi). However, their expression was subsequently decreased at 96 hpi in fengycin + S. sclerotiorum treatment compared to the plants treated with fengycin only. Conversely, the expression of PPO increased in a linear manner up to 96 hpi.

Induction of systemic resistance in tomato against broomrape (Phelipanche aegyptiaca)

AbstractRhizosphere dwelling bacteria can increase plant resistance to biotic and abiotic stresses, and they promote plant growth through various mechanisms. In this study, three bioassays were conducted including the following: (a) screening for effective bacterial isolates in the suppression of broomrape, (b) evaluating induced systemic resistance against broomrape and (c) comparing the selected bacterium isolate with plant chemical inducers. Fifteen plant growth‐promoting rhizobacteria (PGPR) were examined to assess their biocontrol potential against Egyptian broomrape (Phelipanche aegyptiaca). Ten isolates significantly reduced the broomrape biomass compared to the control. The Lysinibacillus boronitolerans B124 reduced the dry weight of broomrape plants from 2.15 g in control to 0.45 g. Bacillus megaterium B6 was the best isolate in reducing the number of broomrape tubercles. In addition, the activity of three selected bacterial isolates was investigated in induced systemic resistance to broomrape by split‐root method. The Bacillus pumilus INR7 reduced the number of visible broomrape tubercles by 90%, and B. megaterium B71 and L. boronitolerans B124 were the next two in rank. Compared with the control, L. boronitolerans B124 reduced the dry weight of broomrape from 1.49 g in control to 0.39 g. In a subsequent experiment, L. boronitolerans B124 was evaluated along with some resistance‐inducing volatile compounds. Lysinibacillus boronitolerans B124 decreased the number of broomrapes by 87% on average, while the lowest dry weight of broomrape was observed in methyl jasmonate treatment. In conclusion, PGPR have considerable potential to be used in the integrated management of broomrape. It is also possible to use a mixture of rhizobacteria and defence inducers, such as biogenic volatiles as a promising approach in the management of this noxious parasitic weed.

Bacillus halotolerans strain LYSX1-induced systemic resistance against the root-knot nematode Meloidogyne javanica in tomato

PurposeDetermination of the nematicidal potential and mode of action of bacteria isolated from tobacco rhizosphere soil against the root-knot nematode Meloidogyne javanica in tomato plants.MethodsAntagonistic bacteria were isolated from rhizosphere soil of tobacco infested with root-knot nematodes. Culture filtrate was used to examine nematicidal activity and ovicidal action of bacterial strains. Biocontrol of M. javanica and growth of treated tomato plants were assessed in pot experiments. To clarify whether secondary metabolites of bacteria in tomato roots induced systemic resistance to M. javanica, bacterial culture supernatants and second-stage juvenile nematodes were applied to spatially separated tomato roots using a split-root system. Bacterial strains were identified by 16S rDNA and gyrB gene sequencing and phylogenetic analysis.ResultsOf the 15 bacterial strains isolated, four (LYSX1, LYSX2, LYSX3, and LYSX4) demonstrated nematicidal activity against second-stage juveniles of M. javanica, and strain LYSX1 showed the greatest antagonistic activity; there was dose-dependent variability in nematicidal activity and inhibition of egg mass hatching by strain LYSX1. In vivo application of LYSX1 to tomato seedlings decreased the number of egg masses and galls and increased the root and shoot fresh weight. Treatment of half of the split-root system with LYSX1 reduced nematode penetration to the other half by 41.64%. Strain LYSX1 was identified as Bacillus halotolerans.ConclusionBacillus halotolerans LYSX1 is a potential microbe for the sustainable biocontrol of root-knot nematodes through induced systemic resistance in tomato.

Bacillus amyloliquefaciens Ba13 induces plant systemic resistance and improves rhizosphere microecology against tomato yellow leaf curl virus disease

The control effect of Bacillus against tomato yellow leaf curl virus (TYLCV) disease has not been reported. It is not clear whether adjustment of the rhizosphere microbial community structure by beneficial microbes applied as biocontrol agents is related to their role in increasing resistance of plants to viral diseases. Therefore, the objective of this study was to investigate the control effect and mechanism of Bacillus amyloliquefaciens Ba13 against TYLCV disease. Two treatments including control and Ba13 treatment followed by natural infection with whiteflies were conducted. We measured plant growth, physiological parameters, disease severity, and leaf virus quantity and also assayed resistance-related gene expression, defense enzyme activity, and rhizosphere microbial community structure. Strain Ba13 lowered the infection rate, disease severity, and leaf virus quantity in tomato plants, with the control rate of 48–52%. Root development and shoot biomass markedly improved in tomato following Ba13 treatment. Ba13 elevated expression of pathogenesis-related PR1, PR2, and PR3 genes, and enhanced activities of phenylalanine ammonia lyase, polyphenol oxidase, peroxidase, β-1,3 glucanase, and chitinase in tomato leaves. Cultivation-dependent microbiological analysis showed that Ba13 increased the bacteria-to-fungi ratio and the number of beneficial microbes while decreasing the number of pathogenic fungi in the rhizosphere. Further analysis revealed the potential of a dominant rhizosphere bacterium, B. velezensis B3, to promote plant growth and improve systemic resistance in tomato. B. amyloliquefaciens Ba13 can enhance plant resistance against TYLCV disease through direct induction of systemic resistance and also by increasing the number of beneficial microbes in the rhizosphere, thereby achieving control of TYLCV disease.

Induction of systemic resistance in tomato against Botrytis cinerea by N-decanoyl-homoserine lactone via jasmonic acid signaling

N-decanoyl-homoserine lactone activates plant systemic resistance against Botrytis cinerea in tomato plants, which is largely dependent on jasmonic acid biosynthesis and signal transduction pathways. Rhizosphere bacteria secrete N-acylated-homoserine lactones (AHLs), a type of specialized quorum-sensing signal molecule, to coordinate their population density during communication with their eukaryotic hosts. AHLs behave as low molecular weight ligands that are sensed by plants and promote the host's resistance against foliar pathogens. In this study, we report on N-decanoyl-homoserine lactone (DHL), which is a type of AHL that induces systemic immunity in tomato plants and protects the host organism against the necrotrophic fungus Botrytis cinerea. Upon DHL treatment, tomato endogenous jasmonic acid (JA) biosynthesis (rather than salicylic acid biosynthesis) and signal transduction were significantly activated. Strikingly, the DHL-induced systemic resistance against B. cinerea was blocked in the tomato JA biosynthesis mutant spr2 and JA signaling gene-silenced plants. Our findings highlight the role of DHL in systemic resistance against economically important necrotrophic pathogens and suggest that DHL-induced immunity against B. cinerea is largely dependent on the JA signaling pathway. Manipulation of DHL-induced resistance is an attractive disease management strategy that could potentially be used to enhance disease resistance in diverse plant species.