Activation Of Systemic Resistance Research Articles

Disease-Suppressive Soils Induce Systemic Resistance in Arabidopsis thaliana Against Pseudomonas syringae pv. tomato

Arabidopsis thaliana accession Col-0 seedlings were transferred into an autoclaved soil/sand mixture amended with either 10 or 20% (wt/wt) soil from fields in Washington State that are suppressive to take-all or Rhizoctonia root rot of wheat. Three weeks after transplanting, these plants had population sizes of 2,4-diacetylphloroglucinol (DAPG) or phenazine-1-carboxylic acid (PCA)-producing pseudomonads of greater than 5 × 105 colony forming units per gram fresh weight of root with rhizosphere soil. When the plants were challenge-inoculated with Pseudomonas syringae pv. tomato DC3000, both soils induced systemic resistance in the leaves against bacterial speck to a level similar to that induced by P. simiae WCS417r, P. fluorescens Q2-87 (DAPG+), P. brassicacearum Q8r1-96 and L5.1-96 (both DAPG+), and P. synxantha 2-79 (PCA+). Pasteurization of the soils before adding them into the soil/sand mixture eliminated DAPG- and PCA-producing pseudomonads from the Arabidopsis rhizosphere and significantly reduced induced systemic resistance activity. However, populations of total culturable aerobic bacteria were similar in the rhizosphere of plants grown in soil/sand mixes amended with untreated or pasteurized suppressive soils. This is the first report of induction of systemic resistance in Arabidopsis by take-all and Rhizoctonia-suppressive soils and the ability of PCA-producing P. synxantha 2-79 to induce resistance. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

Effective biological control of chickpea rabies (Ascochyta rabiei) through systemic phytochemical defenses activation by Trichoderma roots colonization: From strain characterization to seed coating

Chickpea (Cicer arietinum) is a legume of great economic and agricultural importance worldwide, whose crop is severely affected by rust or Ascochyta blight, caused by the fungus Ascochyta rabiei. The fungal genus Trichoderma includes several species widely characterized as effective biological control agents against crop pathogens. First, this work characterized several species of the genus Trichoderma as potential biological control agents of A. rabiei directly (in vitro confrontation) or indirectly in chickpea plants (activation of systemic resistance), selecting T. harzianum EN1 as the most efficient strain. Subsequently, different materials were tested as coatings to apply the T. harzianum conidia on chickpea seeds, determining that gum arabic at 1 % concentration was the one that most promoted the germination of conidia and seeds. The third phase of the study was based on the application of the coating and T. harzianum conidia on chickpea seeds and to study plant survival after infection with the pathogen A. rabiei, characterizing root colonization by Trichoderma and systemic hormonal and metabolic changes related to the induction of systemic defenses. The treatment of chickpea seeds with gum arabic and T. harzianum conidia was found to increase Trichoderma-root colonization and to improve plant survival. The induction of systemic ethylene- and melatonin-mediated resistance, which led to the accumulation of nicotinic acid in plant tissues, was considered the cause of such a protection. Therefore, T. harzianum applied as seed coating with gum arabic could be a good biological control strategy against A. rabiei on chickpea, due to the induction of systemic resistance.

Microbial Allies in Agriculture: Harnessing Plant Growth-Promoting Microorganisms as Guardians against Biotic and Abiotic Stresses

Plants face many biological and non-biological challenges throughout their life cycle, from seed to harvest. These challenges have recently increased due to climate changes. Strategies for confronting different types of stresses depend on the type of stress, the cultivated plant, climatic conditions, soil characteristics, water variables, cost, and management system. Chemical methods (fertilizers and pesticides) have been widely used to manage abiotic and biotic stresses, but they raise concerns about environmental contamination, toxic residues, and the development of resistant pathogens. Eco-friendly strategies have recently become one of the most important approaches to obtaining high-quality and quantitative plant-based products. Microbial inoculants, such as plant growth-promoting microorganisms (PGPM), offer a sustainable alternative to chemical methods. PGPM can augment plant growth and nutrition, improve plant tolerance to abiotic stresses, and reduce the growth of certain pathogens. They employ a variety of mechanisms to alleviate stressors and boost plant resilience, including nutrient assimilation, production of metabolites, and activation of systemic resistance. This review aims to elucidate the impact of PGPM, with a particular focus on plant growth-promoting bacteria (PGPB), and their mechanisms of action on plants under varying stressors, while also identifying areas for further research in both PGPB and other non-bacterial organisms.

The Arabidopsis chromatin regulator MOM1 is a negative component of the defense priming induced by AZA, BABA and PIP.

In plants, the establishment of broad and long-lasting immunity is based on programs that control systemic resistance and immunological memory or "priming". Despite not showing activated defenses, a primed plant induces a more efficient response to recurrent infections. Priming might involve chromatin modifications that allow a faster/stronger activation of defense genes. The Arabidopsis chromatin regulator "Morpheus Molecule 1" (MOM1) has been recently suggested as a priming factor affecting the expression of immune receptor genes. Here, we show that mom1 mutants exacerbate the root growth inhibition response triggered by the key defense priming inducers azelaic acid (AZA), β-aminobutyric acid (BABA) and pipecolic acid (PIP). Conversely, mom1 mutants complemented with a minimal version of MOM1 (miniMOM1 plants) are insensitive. Moreover, miniMOM1 is unable to induce systemic resistance against Pseudomonas sp. in response to these inducers. Importantly, AZA, BABA and PIP treatments reduce the MOM1 expression, but not miniMOM1 transcript levels, in systemic tissues. Consistently, several MOM1-regulated immune receptor genes are upregulated during the activation of systemic resistance in WT plants, while this effect is not observed in miniMOM1. Taken together, our results position MOM1 as a chromatin factor that negatively regulates the defense priming induced by AZA, BABA and PIP.

The Innate Immune Signaling System as a Regulator of Disease Resistance and Induced Systemic Resistance Activity AgainstVerticillium dahliae

In the last decades, the plant innate immune responses against pathogens have been extensively studied, while biocontrol interactions between soilborne fungal pathogens and their hosts have received much less attention. Treatment of Arabidopsis thaliana with the nonpathogenic bacterium Paenibacillus alvei K165 was shown previously to protect against Verticillium dahliae by triggering induced systemic resistance (ISR). In the present study, we evaluated the involvement of the innate immune response in the K165-mediated protection of Arabidopsis against V. dahliae. Tests with Arabidopsis mutants impaired in several regulators of the early steps of the innate immune responses, including fls2, efr-1, bak1-4, mpk3, mpk6, wrky22, and wrky29 showed that FLS2 and WRKY22 have a central role in the K165-triggered ISR, while EFR1, MPK3, and MPK6 are possible susceptibility factors for V. dahliae and bak1 shows a tolerance phenomenon. The resistance induced by strain K165 is dependent on both salicylate and jasmonate-dependent defense pathways, as evidenced by an increased transient accumulation of PR1 and PDF1.2 transcripts in the aerial parts of infected plants treated with strain K165.

Identification and Characterization of Novel Biocontrol Bacterial Strains

Because bacterial isolates from only a few genera have been developed commercially as biopesticides, discovery and characterization of novel bacterial strains will be a key to market expansion. Our previous screen using plant bioassays identified 24 novel biocontrol isolates representing 12 different genera. In this study, we characterized the 3 isolates showing the best biocontrol activities. The isolates were Pantoea dispersa WCU35, Proteus myxofaciens WCU244, and Exiguobacterium acetylicum WCU292 based on 16S rRNA sequence analysis. The isolates showed differential production of extracellular enzymes, antimicrobial activity against various fungal or bacterial plant pathogens, and induced systemic resistance activity against tomato gray mold disease caused by Botrytis cinerea. E. acetylicum WCU292 lacked strong in vitro antimicrobial activity against plant pathogens, but induced systemic resistance against tomato gray mold disease. These results confirm that the trait of biological control is found in a wide variety of bacterial genera.

Activation of Systemic Resistance to Magnaporthe oryzae in Rice by Substances Produced by Fusarium solani Isolated from Soil

Of 70 micro-organisms (fungi, bacteria and actinomycetes) isolated from soil using vegetable tissue baits, 16 produced substances in culture fluids capable of preventing the development of blast caused by Magnaporthe oryzae on rice leaves with little or no inhibitory effect on the conidial germination of the pathogen. Isolate KS-F14, which secreted substances capable of activating resistance in untreated leaves, was selected and identified as Fusarium solani. The resistance-inducing substances were effective at pH values ranging from 5 to 10 and were stable under high temperatures, maintaining approximately the same level of activity even after autoclaving for 20 min. After application, the activated resistance in rice leaves persisted for 14 days. The polar solvent extracts of freeze-dried KS-F14 secretions were effective in activating resistance against M. oryzae in rice plants. The non-polar solvent extracts were also effective, albeit not as effective as the polar solvent extracts, indicating that although the majority of the secreted resistance-inducing compounds are hydrophilic, some of the compounds are hydrophobic. Treating secretions with cation or anion exchange resins only partially reduced their resistance-inducing ability, suggesting that the resistance-inducing components include both charged and non-charged compounds. The resistance-inducing compounds produced by F. solani have the potential to be developed into a commercial product for the control of rice blast and possibly other plant diseases.

Chlorophyll fluorescence for quantification of fungal foliar infection and assessment of the effectiveness of an induced systemic resistance activator

Chlorophyll fluorescence imaging was used to follow infections of Nicotiana benthamiana with the hemibiotrophic fungus, Colletotrichum orbiculare. Based on Fv/Fm images, infected leaves were divided into: healthy tissue with values similar to non-inoculated leaves; water-soaked/necrotic tissue with values near zero; and non-necrotic disease-affected tissue with intermediate values, which preceded or surrounded water-soaked/necrotic tissue. Quantification of Fv/Fm images showed that there were no changes until late in the biotrophic phase when spots of intermediate Fv/Fm appeared in visibly normal tissue. Those became water-soaked approx. 24 h later and then turned necrotic. Later in the necrotrophic phase, there was a rapid increase in affected and necrotic tissue followed by a slower increase as necrotic areas merged. Treatment with the induced systemic resistance activator, 2R, 3R-butanediol, delayed affected and necrotic tissue development by approx. 24 h. Also, the halo of affected tissue was narrower indicating that plant cells retained a higher photosystem II efficiency longer prior to death. While chlorophyll fluorescence imaging can reveal much about the physiology of infected plants, this study demonstrates that it is also a practical tool for quantifying hemibiotrophic fungal infections, including affected tissue that is appears normal visually but is damaged by infection.

GDSL lipase‐like 1 regulates systemic resistance associated with ethylene signaling in Arabidopsis

Systemic resistance is induced by necrotizing pathogenic microbes and non-pathogenic rhizobacteria and confers protection against a broad range of pathogens. Here we show that Arabidopsis GDSL LIPASE-LIKE 1 (GLIP1) plays an important role in plant immunity, eliciting both local and systemic resistance in plants. GLIP1 functions independently of salicylic acid but requires ethylene signaling. Enhancement of GLIP1 expression in plants increases resistance to pathogens including Alternaria brassicicola, Erwinia carotovora and Pseudomonas syringae, and limits their growth at the infection site. Furthermore, local treatment with GLIP1 proteins is sufficient for the activation of systemic resistance, inducing both resistance gene expression and pathogen resistance in systemic leaves. The PDF1.2-inducing activity accumulates in petiole exudates in a GLIP1-dependent manner and is fractionated in the size range of less than 10 kDa as determined by size exclusion chromatography. Our results demonstrate that GLIP1-elicited systemic resistance is dependent on ethylene signaling and provide evidence that GLIP1 may mediate the production of a systemic signaling molecule(s).

Benzo-thiadiazole-7-carbothioic AcidS-methyl Ester does not protect Melon Fruits againstFusarium pallidoroseumInfection but Induces Defence Responses in Melon Seedlings

The present study investigated the potential of benzo-thiadiazole-7-carbothioic acid S-methyl ester (BTH) to protect postharvest melons var. ‘Orange Flesh’ from the fruit rot caused by Fusarium pallidoroseum. It was noticed that melon fruits immersed in BTH and postinoculated with the fungus presented the same pattern of disease incidence/severity and activity of the defence-related enzymes superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, phenylalanine ammonia-lyase, and β-1,3-glucanase of controls, indicating that BTH was ineffective in protecting melons from the fruit rot disease. However, the preflowering application of BTH in melon seedlings induced stunted growth, probably related to enhanced lignification which is related to the plant cell wall reinforcement and increase of resistance against invading pathogens, and alterations of the activity of the studied defence-related enzymes in comparison with controls, suggesting that this strategy could probably be effective for the control of the postharvest rot of melon fruits through activation of systemic resistance.

Plant Growth–Promoting Methylobacterium Induces Defense Responses in Groundnut (Arachis hypogaea L.) Compared with Rot Pathogens

This study, framed in two different phases, studied the plant-growth promotion and the induction of systemic resistance in groundnut by Methylobacterium. Seed imbibition with Methylobacterium sp. increased germination by 19.5% compared with controls. Combined inoculation of Methylobacterium sp. with Rhizobium sp. also significantly increased plant growth, nodulation, and yield attributes in groundnut compared with individual inoculation of Rhizobium sp. Methylobacterium sp. challenge-inoculated with Aspergillus niger/Sclerotium rolfsii in groundnut significantly enhanced germination percentage and seedling vigour and showed increased phenylalanine ammonia lyase (PAL), beta-1,3-glucanase, and peroxidase (PO) activities. Under pot-culture conditions, in Methylobacterium sp. seed-treated groundnut plants challenge-inoculated with A. niger/S. rolfsii through foliar sprays on day 30, the activities of enzymes PO, PAL, and beta-1,3-glucanase increased constantly from 24 to 72 hours, after which decreased activity was noted. Five isozymes of polyphenol oxidase and PO could be detected in Methylobacterium-treated plants challenged with A. niger/S. rolfsii. Induced systemic resistance activity in groundnut against rot pathogens in response to methylotrophic bacteria suggests the possibility that pink-pigmented facultative methylotrophic bacteria might be used as a means of biologic disease control.

A benzothiadiazole applied to foliage reduces development and egg deposition by Meloidogyne spp. in glasshouse-grown grapevine roots

Foliar application of a benzothiadiazole (BTH), as Bion WG50 (50 mg active ingredient/mL), to glasshouse-grown Cabernet Sauvignon grapevines caused a significant reduction in egg deposition by root-knot nematodes in 10-week-old plants. No change in the number of nematodes in roots of treated grapevines was observed 3 days after inoculation, but fewer mature nematodes were recorded after a further 18 days. BTH was not toxic to the juvenile nematodes in vitro. The activity of β-1,3-glucanase increased in the leaves of BTH-treated grapevines at 7 and 28 days, and increased slightly and transiently in the roots at 5 days after foliar application. The results are interpreted as indicating the activation of systemic resistance to nematode development in the roots.

Activation of PR-1a Promoter by Rhizobacteria That Induce Systemic Resistance in Tobacco against Pseudomonas syringae pv. tabaci

Investigations were conducted to determine whether induction of PR-1a gene promoter was correlated with systemic resistance, induced by rhizobacteria, against wildfire disease of tobacco. Ten different strains of plant growth-promoting rhizobacteria (PGPR), including the species Bacillus pumilus, Serratia marcescens, Pseudomonas fluorescens, P. putida, Curtobacterium flaccumfaciens, and Bukholderia gladioli, were tested. Induction of PR-1a gene activity was assessed using transgenic tobacco plants expressing the β-glucuronidase (GUS) gene fused to the PR-1a gene promoter. In a microtiter plate assay, GUS activity was significantly enhanced, compared to that of water-treated controls by salicylic acid (SA), four PGPR strains with known induced systemic resistance activity, and one endophytic bacterium previously shown to lack induced systemic resistance activity in cucumber. No enhanced GUS activity was noted with three control bacteria (two plant-associated strains and Escherichia coli strain HB-101). In a separate assay, infiltration of greenhouse-grown tobacco leaves with these same bacteria resulted in significant increases in GUS activity compared to that of the water-treated control, for all strains which induced GUS activity in the microtiter plate assay. The two plant-associated bacterial controls did not affect GUS activity. Treatment of tobacco with SA and all bacterial strains which enhanced GUS activity in the microtiter and leaf assays led to reduced symptoms of wildfire disease caused by Pseudomonas syringae pv. tabaci in the greenhouse, whereas none of the three control bacterial strains significantly affected disease. These results support the conclusion that induction of PR-1a promoter activity and PGPR-mediated induced systemic disease resistance are linked events for the PGPR strains studied.

Mixtures of Plant Growth-Promoting Rhizobacteria Enhance Biological Control of Multiple Cucumber Pathogens

ABSTRACT Plant growth-promoting rhizobacteria (PGPR) strains INR7 (Bacillus pumilus), GB03 (Bacillus subtilis), and ME1 (Curtobacterium flaccumfaciens) were tested singly and in combinations for biological control against multiple cucumber pathogens. Investigations under greenhouse conditions were conducted with three cucumber pathogens-Colletotrichum orbiculare (causing anthracnose), Pseudomonas syringae pv. lachrymans (causing angular leaf spot), and Erwinia tracheiphila(causing cucurbit wilt disease)-inoculated singly and in all possible combinations. There was a general trend across all experiments toward greater suppression and enhanced consistency against multiple cucumber pathogens using strain mixtures. The same three PGPR strains were evaluated as seed treatments in two field trials over two seasons, and two strains, IN26 (Burkholderia gladioli) and INR7 also were tested as foliar sprays in one of the trials. In the field trials, the efficacy of induced systemic resistance activity was determined against introduced cucumber pathogens naturally spread within plots through placement of infected plants into the field to provide the pathogen inoculum. PGPR-mediated disease suppression was observed against angular leaf spot in 1996 and against a mixed infection of angular leaf spot and anthracnose in 1997. The three-way mixture of PGPR strains (INR7 plus ME1 plus GB03) as a seed treatment showed intensive plant growth promotion and disease reduction to a level statistically equivalent to the synthetic elicitor Actigard applied as a spray.