Induced Resistance of Acibenzolar-S-methyl (CGA 245704) to Cucumber and Japanese Pear Diseases

Antifungal activity of the novel compound acibenzolar-S-methyl (CGA245704: benzo[1,2,3]thiadiazole-7-carbothioic acid S-methyl ester) was examined in vitro. No remarkable activity was observed on mycelial growth and conidial germination of almost all fungi tested. Only melon isolates of Didymella bryoniae were sensitive to this compound. On potted plants, acibenzolar-S-methyl showed control efficacy on anthracnose and scab of cucumber and rust of Japanese pear but not on Fusarium wilt of cucumber. In field trials, the occurrence of both rust and scab on Japanese pear was suppressed with this compound. Based on these experiments, it was suggested that acibenzolar-S-methyl induced resistance to some but not all diseases on cucumber and Japanese pear. Induction of disease resistance in cucumber was rapidly triggered after treatment with acibenzolar-S-methyl.     

Induction of systemic resistance toColletotrichum falcatum in sugarcane by a synthetic signal molecule, acibenzolar-S-Methyl(CGA-245704)

The effect of a novel synthetic signal molecule, acibenzolar-S-methyl (CGA-245704; benzo [1,2,3] thiadiazole-7-carbothioic acid S-methyl ester), in inducing resistance in sugarcane against red rot disease caused by the fungusColletotrichum falcatum Went was studied. Application of CGA-245704 as a soil drench or along with marcotting rooting mixture induced resistance in sugarcane to challenge inoculation withC. falcatum. When the pathogen was inoculated by the plug method, it caused discoloration in the untreated control stalk tissues; however, in the stalk tissues pretreated with acibenzolar-S-methyl, pathogen colonization was considerably reduced. When the pathogen was inoculated by nodal swabbing, its penetration was arrested in the sensitized stalk tissues. An induced systemic resistance effect was found to persist up to 30 days in the pretreated cut canes. Increased phenolic content and accumulation of pathogenesis-related (PR) proteins,viz., chitinase, β-1,3-glucanase and thaumatin-like protein (PR-5), were observed in sugarcane plants treated with acibenzolar-S-methyl.     

Effects of Plant Defence Activators on Anthracnose Disease of Cashew

The plant defence activators acibenzolar-S-methyl (Benzo[1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester, ASM), 2,6-dichloro-isonicotinic acid (DCINA), salicylic acid (SA), and dibasic potassium phosphate (K₂HPO₄) were tested for their ability to protect cashew (Anacardium occidentale) seeds and leaves from anthracnose disease caused by Colletotrichum gloeosporioides. No inhibition of the early stages of pathogen development was caused by concentrations equal to or lower than 1.1mM a.i. ASM, 1.2mM a.i. DCINA, 5mM SA and 50mM K₂HPO₄. Maximum reduction of the disease in detached leaves, without phytotoxic effects, was obtained with 0.07mM a.i. ASM and DCINA, 5mM SA, and 50mM K₂HPO₄, with a time interval of at least 72h between application of the activator and inoculation with the pathogen. On attached leaves, foliar sprays were slightly more efficient than soil drench treatments, with 5mM SA being the most effective treatment, while 50mM SA as well as 0.3mM a.i. ASM and DCINA caused phytotoxic effects. In field-grown plants, protection was conferred by a soil drench of concentrations as low as 12.6M a.i. ASM and DCINA and 2.6mM SA. These concentrations were not phytotoxic suggesting that plant defence activators have potential for control of anthracnose disease in the field.     

Induction of systemic resistance to <Emphasis Type="Italic">Exobasidium vexans</Emphasis> in tea through SAR elicitors

The effect of two chemical elicitors (acibenzolar-S-methyl benzo-[1,2,3]- thiadiazole-7-carboxylic acid S-methyl ester [Boost 500SC]) and salicylic acid in inducing resistance in tea plants against blister blight disease caused by Exobasidium vexans Massee, was studied. Treatments with elicitors resulted in reduced severity of blister blight disease in nursery plants on challenge with the pathogen. There was a significant increase in the activities of defense enzymes like phenylalanine ammonia lyase, peroxidase and β-1,3-glucanase on elicitor treatments in tea leaves challenged with the pathogen than on unchallenged leaves. Acibenzolar-S-methyl (ASM) at 0.14% registered the lowest disease severity (25.2%), whereas treatments with salicylic acid were inferior. Under field conditions, the application of ASM at 0.14% resulted in disease protection of 25%. When ASM was applied in alternate rounds with a standard fungicide, the disease protection improved to 46.8%. The importance of incorporating ASM as a component in integrated disease management and also its importance in organic tea cultivation is discussed.     

Extract of Hedera helix induces resistance on apple rootstock M26 similar to Acibenzolar-S-methyl against Fire Blight (Erwinia amylovora)

The potential of acibenzolar-S-methyl (Benzo [1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester, ASM; Bion 50 WG) and of an extract of Hedera helix, to protect M26 apple rootstocks against fire blight was determined under controlled conditions. Marked differences were observed in the rate and extent of multiplication as well as in pathogen cell viability between control and ASM and H. helix-treated rootstocks. Although the pathogen multiplied abundantly in the plant tissue of water-treated rootstocks and showed severe damage, ASM and the plant extract of H. helix applied prior to inoculation with the causal agent of fire blight, E. amylovora (strain 7/74), suppressed disease development and bacterial multiplication. Physiological observations of ASM and plant extract-treated rootstocks indicated that restriction of pathogen colonization in plant tissue was correlated with a pronounced increase of peroxidase (POX) and chitinase activity. Furthermore, physiological changes caused by these treatments in host cells were characterized by POX labeling methods with SDS-Page electrophoresis. Differences in expression of the POX and protein bands were observed in tissues of plants treated with different inducers. POX activity was determined by the presence of three strong bands in plant extract-treated leaves, two strong bands and one very weak band of about 20.1 and 43 kDa were visible in ASM-treated leaves. Evidence is provided that ASM, as well as extract of H. helix are equally capable of inducing of resistance responses in M26 apple rootstock, which result in an increased resistance to E. amylovora—the fire blight pathogen. These findings demonstrate that both treatments have the ability to induce the activation of defense genes leading to the accumulation of structural and biochemical activities at strategic sites, and these can be associated with induction of resistance against fire-blight.     

Mechanisms of Phosphate-induced Disease Resistance in Cucumber

Certain phosphate salts are known inducers of systemic acquired resistance (SAR). In the present study, a local spray application of dipotassium hydrogenphosphate (K₂HPO₄) was effective in inducing a high level of systemic protection in cucumber plants against anthracnose caused by Colletotrichum lagenarium. Resistance induction by K₂HPO₄ was associated with localized cell death in cucumber leaves treated with the phosphate salt. The cell death observed, subsequently resulted in the appearance of macroscopically visible, necrotic spots. Appearing lesions resembled those provoked by tobacco necrosis virus (TNV) during a hypersensitive response (HR) that leads to pathogen-induced activation of SAR. Phosphate-mediated cell death was preceeded by a rapid generation of superoxide and hydrogen peroxide. As a further consequence of phosphate application, a local and systemic increase in free and conjugated salicylic acid (SA) levels was detected. The phosphate-induced responses were also identified with a similar time range in cucumber leaves that had been pre-inoculated with TNV. In contrast, none of these responses was triggered by application of the commercial plant activator benzo[1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester (BTH), which nevertheless was highly effective in inducing SAR in cucumber against anthracnose. In conclusion, the chemical SAR inducer K₂HPO₄ and the biological inducer TNV share some common early steps in signal transduction leading to SAR in cucumber, which differ from those involved in BTH-mediated SAR.     

Increasing control reliability of <Emphasis Type="Italic">Orobanche cumana </Emphasis>through integration of a biocontrol agent with a resistance-inducing chemical

Fusarium oxysporum Schlecht. f.sp. orthoceras (Appel & Wollenw.) Bilai is a potential biocontrol agent against the root-parasitic weed Orobanche cumana. In pot experiments with different sunflower cultivars, the application of F. oxysporum was combined with a treatment of BTH (Benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester), a product known to induce resistance against O. cumana in sunflower. The combined treatments resulted in highly reliable control and sometimes in increased control level compared to the Fusarium treatment alone. In laboratory experiments, no enhancing effect of BTH on virulence and growth of the fungus was observed. Future experiments should further investigate the basic mechanisms of the effect achieved by combining the two control strategies as well as the transfer of this innovative control approach into field experiments.     

Different Patterns of Host Genes are Induced in Rice by Pseudomonas syringae, a Biological Inducer of Resistance, and the Chemical Inducer Benzothiadiazole (BTH)

Rice seedlings treated with the synthetic compound benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH) acquired resistance to subsequent attack by the rice blast fungus Magnaporthe grisea (Hebert) Barr. BTH (trade name Bion) has been released to the market as a plant protecting agent for rice. Here, we analysed the pattern of expressed genes in rice plants treated with BTH, and compared this pattern with those induced by the formerly discovered resistance inducer 2,6-dichloroisonicotinic acid (INA) and by Pseudomonas syringae pv. syringae, a non-host pathogen inducing a hypersensitive response. Both INA and BTH induced similar patterns of genes, suggesting that these compounds are functional analogues. In contrast, the patterns induced by the chemical inducers and by P. syringae were clearly dissimilar.     

Suppressive effect of abscisic acid on systemic acquired resistance in tobacco plants

Recent studies have indicated that the phytohormone abscisic acid (ABA), induced in response to a variety of environmental stresses, plays an important role in modulating diverse plant–pathogen interactions. In Arabidopsis thaliana, we previously clarified that ABA suppressed the induction of systemic acquired resistance (SAR), a plant defense system induced by pathogen infection through salicylic acid (SA) accumulation. We investigated the generality of this suppressive effect by ABA on SAR using tobacco plants. For SAR induction, we used 1,2-benzisothiazole-3(2H)-one 1,1-dioxide (BIT) and benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH) that activate upstream and downstream of SA in the SAR signaling pathway, respectively. Wild-type tobacco plants treated with BIT or BTH exhibited enhanced disease resistance against Tobacco mosaic virus (TMV) and tobacco wildfire bacterium, Pseudomonas syringae pv. tabaci (Pst), however, which was suppressed by pretreatment of plants with ABA. Pretreatment with ABA also suppressed the expression of SAR-marker genes by BIT and BTH, indicating that ABA suppressed the induction of SAR. ABA suppressed BTH-induced disease resistance and pathogenesis-related (PR) gene expression in NahG-transgenic plants that are unable to accumulate SA. The accumulation of SA in wild-type plants after BIT treatment was also suppressed by pretreatment with ABA. These data suggest that ABA suppresses both upstream and downstream of SA in the SAR signaling pathway in tobacco.     

Induction of systemic resistance to<Emphasis Type="Italic">Colletotrichum lindemuthianum</Emphasis> in bean by a benzothiadiazole derivative and rhizobacteria

Plants have developed mechanisms to resist secondary infection upon inoculation with a necrotizing pathogen, chemical treatment as well as treatment with some non-pathogenic microorganisms such as rhizosphere bacteria. This phenomenon has been variously described as induced systemic resistance (ISR) or systemic acquired resistance. In the present study, the chemical benzo(1,2,3)thiadiazole-7-carbothioic acid-S-methyl ester (BTH, acibenzolar-S-methyl), and the rhizobacteriaPseudomonas aeruginosa KMPCH andP. fluorescens WCS417 were tested for their ability to induce resistance toColletotrichum lindemuthianum in susceptible and moderately resistant bean plants (Phaseolus vulgaris L.). BTH induced local and systemic resistance when bean leaves were immersed in 10⁻³ to 10⁻⁷ M BTH 3 days before the challenge inoculation. At a high concentration (10⁻³ M), BTH induced resistance of the same order as resistance induced by the pathogenC. lindemuthianum, although at this high concentration BTH appeared to be phytotoxic. Soil and seed treatment with 1 mg kg⁻¹ BTH protected beans against anthracnose. BTH-mediated induced resistance was effective in susceptible and moderately resistant plants.P. aeruginosa KMPCH induced resistance in bean againstC. lindemuthianum only in a moderately resistant interaction. KMPCH-567, a salicylic acid mutant of KMPCH, failed to induce resistance, indicating that salicylic acid is important for KMPCH to induce resistance in the bean—C. lindemuthianum system.P.fluorescens WCS417 could induce resistance toC. lindemuthianum in a susceptible and in moderately resistant interactions. http://www.phytoparasitica.org posting Jan. 16, 2002.     

Benzothiadiazole Activates Resistance in Sunflower (Helianthus annuus) to the Root-Parasitic Weed Orobanche cuman

ABSTRACT The study was conducted to evaluate the potential of induced resistance to infestation of sunflower (Helianthus annuus L.) by the parasitic weed Orobanche cumana Wallr. Treatment of sunflower seeds with 40 ppm of benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH) for 36 h completely prevented infection in root chambers. In pot studies using 2.86 x 10(-4) g of Orobanche seeds per gram of soil as inoculum, the total number of O. cumana shoots was reduced by 84 and 95% in the 60-ppm BTH treatment in the first and second trial, respectively. Evaluation of the disease incidences revealed that attachment of O. cumana at the sunflower root and the stage of early penetration was reduced in the BTH-treated plants. Chemical analysis of root extracts revealed synthesis of the phytoalexin scopoletin and of hydrogen peroxide in the BTH-treated sunflower roots, but no increase in lignification. Western blot analysis demonstrated accumulation of the pathogenesis-related protein chitinase in roots and stems of induced resistant plants. These results show that the phenomenon of induced resistance is not restricted to viral, bacterial, and fungal disease and demonstrate the great potential of this protection strategy as an effective component of future plant production systems.     

Menadione sodium bisulphite: a novel plant defence activator which enhances local and systemic resistance to infection by Leptosphaeria maculans in oilseed rape

Pretreatment of the first true leaves of oilseed rape plants ( Brassica napus cv. Bristol) with menadione sodium bisulphite (MSB) locally and systemically induced resistance, as shown by reduced lesion size and number, to infection by the fungal pathogen Leptosphaeria maculans , the causal agent of stem canker. Using a known systemic activator of salicylic acid-dependent PR-1 induction, acibenzolar- S -methyl (BTH; S -methylbenzo[1,2,3]thiadiazole-7-carbothiate) as a comparison, real-time PCR expression analysis of genes encoding a pathogenesis-related protein 1 ( PR-1 ) and an ascorbate peroxidase ( APX ) demonstrated a systemic enhancement of APX expression in MSB-pretreated plants, with no effect on PR-1 expression, suggesting augmented reactive oxygen species production in MSB-pretreated plants. The results demonstrate MSB to be an effective resistance activator in oilseed rape, and potentially useful for the control of stem canker.     

Induction of defence-related enzymes and resistance by the plant activator acibenzolar-S-methyl in tomato seedlings against bacterial canker caused by Clavibacter michiganensis ssp. michiganensis

Using tomato seedlings, the plant defence activator acibenzolar-S-methyl (benzo-[1,2,3]-thiadiazole-7-carbothioic acid-S-methyl ester, ASM; Bion 50 WG) was assayed for its ability to induce resistance against Clavibacter michiganensis ssp. michiganensis , the causal agent of bacterial canker of tomato. In ASM-pretreated plants, reduction in disease severity (up to 76·3%) was correlated with lower bacterial growth (up to 68·2% lower) during the time course of infection. To understand the possible mechanism of action of ASM, alterations in the activities of peroxidase (POX) and chitinase were assessed as markers of resistance. The enhanced resistance of ASM-treated plants was associated with significant increases in the activities of POX and chitinase     

Effects of acibenzolar-s-methyl and ethirimol on the composition of a laboratory population of barley powdery mildew

ABSTRACT To assemble a laboratory population of Blumeria graminis f. sp. hordei for a competition experiment, controlled crosses were performed among 30 parent isolates, which were characterized by their pathotype (i.e., the phenotype observed on a differential set containing lines including host resistance alleles) and their response to the fungicides ethirimol and triadimenol. Variability in the response to the chemical inducer of host-resistance acibenzolar-S-methyl (BTH: benzo[1,2,3]thiadiazole-7carbothioic acid-S-methyl ester) was introduced by using isolates collected in fields repeatedly treated with this chemical. Based on their pathotype and response to ethirimol, 137 isolates recovered from the crosses were chosen to assemble a laboratory population. This protocol produced variability in the laboratory population for traits chosen only in the parents (triadimenol) or both in the parents and the progenies (ethirimol). It was therefore postulated that the variability in the response to BTH, if present in the parents, was also present in the laboratory population. No association between these traits was observed. The effect of BTH on the evolution of the laboratory population was compared with the effect of the fungicide ethirimol. The laboratory population was exposed to selection pressures and its evolution was followed over 10 generations. Ethirimol treatments always induced a decrease in sensitivity, whereas no consistent trend was observed for sensitivity to triadimenol (not selected). This result indicates that the application of ethirimol induced a selection pressure. For BTH, (toxicological) sensitivity tests have not detected any consistent evolution, but pathotype diversity indicated that in cases when BTH was applied with ethirimol, BTH induced a further selection pressure in addition to that of ethirimol.     

Plant Resistance Genes: Their Structure, Function and Evolution

Plants have developed efficient mechanisms to avoid infection or to mount responses that render them resistant upon attack by a pathogen. One of the best-studied defence mechanisms is based on gene-for-gene resistance through which plants, harbouring specific resistance (R) genes, specifically recognise pathogens carrying matching avirulence (Avr) genes. Here a review of the R genes that have been cloned is given. Although in most cases it is not clear how R gene encoded proteins initiate pathways leading to disease resistance, we will show that there are clear parallels with disease prevention in animal systems. Furthermore, some evolutionary mechanisms acting on R genes to create novel recognitional specificities will be discussed.     

Allylamine antimycotics: Recent trends in structure—activity relationships and syntheses

Methods developed for the synthesis of terbinafine-related allylamine antimycotics are reviewed. The synthesis of the en-yne side chains were generally accomplished by means of organometallic reactions. The use of Pd⁰-catalysed coupling reactions allowed easy access to derivatives bearing sensitive side-chain substituents. As examples, four metabolites of terbinafine were prepared via this procedure. Investigations with the carbon analogue of terbinafine revealed that, within the allylamine antimycotics, the nitrogen appears to be necessary for penetration by the drug into the fungal cell. Replacement of the naphthalene moiety of terbinafine by optionally substituted benzo[b]thiophenes led to a number of derivatives with high antifungal activity. A series of benzo[b]thienyl compounds with the side chain at position 7 and different substituents at position 3 showed significantly increased activity against Candida albicans in vitro. In particular, the 3-chloro derivative with the allylamine side chain at position 7(SDZ 87–469) proved to be the most potent allylamine antimycotic reported to this date. Two novel types of lead structures, the homopropargylamines and the benzylamines show very high activity in vitro.     

The effect of potential resistance inducers on development of <Emphasis Type="Italic">Microdochium majus</Emphasis> and <Emphasis Type="Italic">Fusarium culmorum</Emphasis> in winter wheat

The effect of potential resistance inducing chemicals on disease development of Fusarium head blight was studied in winter wheat (Triticum aestivum L.). As a pre-screening test, the effect of different treatments on development of Microdochium majus (syn. Microdochium nivale var. majus) was studied in detached leaves. Based on these tests, DL-3-aminobutyric acid, Bion (benzo-(1,2,3) thiadiazole-7-carbothioic acid S-methyl ester), and a foliar fertilizer containing potassium phosphite were selected for further studies. Greenhouse-grown winter wheat was sprayed with aqueous solutions of the potential resistance inducers 7 days prior to Fusarium culmorum point inoculation of the heads. Disease development was registered as number of bleached spikelets per inoculated spike. Spraying plants with the foliar fertilizer reduced the disease severity of F. culmorum by up to 40%. A reduced disease development of M. majus was also observed in detached leaves pre-treated with the foliar fertilizer. When the foliar fertilizer was added to the growth medium, a reduced in vitro growth of M. majus and F. culmorum was observed, indicating that the effect on disease development is at least partly due to a fungistatic effect. No significant reduction in disease development was observed in wheat pre-treated with DL-3-aminobutyric acid or Bion, although these compounds tended to reduce disease development, especially when applied in combination with other potential resistance inducers. We conclude that spraying winter wheat with a solution containing potassium phosphite can reduce development of M. majus and F. culmorum.     

Induced plant defences in biological control of arthropod pests: a double‐edged sword

Biological control is an important ecosystem service delivered by natural enemies. Together with breeding for plant defence, it constitutes one of the most promising alternatives to pesticides for controlling herbivores in sustainable crop production. Especially induced plant defences may be promising targets in plant breeding for resistance against arthropod pests. Because they are activated upon herbivore damage, costs are only incurred when defence is needed. Moreover, they can be more specific than constitutive defences. Nevertheless, inducible defence traits that are harming plant pest organisms may interfere with biological control agents, such as predators and parasitoids. Despite the vast fundamental knowledge on plant defence mechanisms and their effects on natural enemies, our understanding of the feasibility of combining biological control with induced plant defence in practice is relatively poor. In this review, we focus on arthropod pest control and present the most important features of biological control with natural enemies and of induced plant defence. Furthermore, we show potential synergies and conflicts among them and, finally, identify gaps and list opportunities for their combined use in crop protection. We suggest that breeders should focus on inducible resistance traits that are compatible with the natural enemies of arthropod pests, specifically traits that help communities of natural enemies to build up. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Bioluminescence reporter assay system to monitor Arabidopsis MPK3 gene expression in response to infection by Botrytis cinerea

The Arabidopsis MPK3 gene product participates in disease resistance mediated by the MAP kinase cascade. The expression of the MPK3 gene is induced by pathogen inoculation and treatment with chemicals such as salicylic acid (SA) and methyl jasmonate (JA), but the detailed expression pattern of the MPK3 gene has been largely unknown. To investigate MPK3 gene expression in response to disease stress, we fused the MPK3 promoter to the firefly luciferase gene to create a real-time monitoring system for regulated gene expression in planta. The results of an in vivo reporter assay using transgenic Arabidopsis plants harboring MPK3::Fluc showed that the MPK3 promoter activity was induced by treatment with chemicals such as SA and benzo(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), that induce defense gene expression. Inoculation with the fungal pathogen Botrytis cinerea resulted in systemic induction of MPK3::Fluc.     

Effect of Trichoderma viride pre-inoculation in pine species with different levels of susceptibility to Fusarium circinatum: physiological and hormonal responses

Pine pitch canker (PPC), caused by Fusarium circinatum, affects Pinus species worldwide. Although no effective solutions have yet been found to control it, there is a growing interest in using biological control agents (BCA) such as Trichoderma to avoid the application of chemical-based products. Using species with an increasing level of susceptibility to PPC (Pinus pinea, Pinus pinaster and Pinus radiata), this study aimed to evaluate the effect of Trichoderma viride pre-inoculation on disease development, assessing several physiological and hormonal parameters. A 2-week period elapsed between T. viride and F. circinatum inoculation. Sampling for each species was performed independently when at least 50% of the plants of one of the inoculated groups developed disease symptoms. Fusarium circinatum infection reduced water status and photosynthesis, but increased proline, abscisic acid and jasmonic acid concentrations in plants of P. radiata and P. pinaster with symptoms; while in P. pinea water relations were maintained and anthocyanin accumulation occurred in the presence of F. circinatum. In P. radiata, T. viride pre-inoculation accelerated disease progression, with some PPC-induced responses augmented (decreased water potential and photosynthesis; increased substomatal CO₂ concentration) and novel changes not found in seedlings inoculated exclusively with F. circinatum (increased electrolyte leakage and salicylic acid; decreased relative water content). This suggests that T. viride may be initially recognized as an invading organism, subverting the plant defence mechanisms for successful root colonization. If seedlings are not allowed to recover from this state, pathogen infection may thus be facilitated, highlighting the importance of application timing in BCA strategies.