acibenzolar-S-methyl Research Articles

Efficacy of copper and copper alternatives for management of bacterial spot on tomato under transplant and field production

Bacterial spot of tomatoes (BST) caused by Xanthomonas perforans, is a ubiquitous disease of tomato in field and transplant operations in Florida. For disease management, producers rely heavily on copper or copper-mancozeb sprays, which are often ineffective due to the high prevalence of copper-tolerant Xanthomonas strains. In this study, 19 different chemical agents, biological control agents, plant defense activators, and novel products were evaluated for their ability to manage bacterial spot on tomato seedlings and in the field. Efficacies of single rotations or tank mixes of several compounds were compared to a non-treated control and a copper standard on seedlings. Stand-alone applications of acibenzolar-S-methyl (ASM), copper octanoate, quinoxyfen, oxysilver nitrate, and pentasilver hexaoxoiodate significantly reduced disease compared to inoculated controls. Seedling programs that included either ASM or copper octanoate significantly reduced disease compared to the control. Oxytetracycline and streptomycin were ineffective at reducing disease severity under high disease pressure in seedling trials. Although there were significant differences in disease severity among treatments, there were no significant difference in the overall yield among treatments across field trials. Overall, ASM provided significant disease reduction as a stand-alone or in a program with other compounds in both the greenhouse and field. However, copper octanoate alone or as a tank mixture with other compounds was only effective for seedling production. The use of alternative compounds should improve tomato health, reduce the introduction of disease inoculum into fields, and reduce residual copper in the environment.

Integrated Use of Aureobasidium pullulans Strain CG163 and Acibenzolar-S-Methyl for Management of Bacterial Canker in Kiwifruit.

An isolate of Aureobasidium pullulans (strain = CG163) and the plant defence elicitor acibenzolar-S-methyl (ASM) were investigated for their ability to control leaf spot in kiwifruit caused by Pseudomonas syringae pv. actinidiae biovar 3 (Psa). Clonal Actinidia chinensis var. deliciosa plantlets (‘Hayward’) were treated with ASM, CG163 or ASM + CG163 at seven and one day before inoculation with Psa. ASM (0.2 g/L) was applied either as a root or foliar treatments and CG163 was applied as a foliar spray containing 2 × 107 CFU/mL. Leaf spot incidence was significantly reduced by all treatments compared with the control. The combination of ASM + CG163 had greater efficacy (75%) than either ASM (55%) or CG163 (40%) alone. Moreover, treatment efficacy correlated positively with the expression of defence-related genes: pathogenesis-related protein 1 (PR1), β-1,3-glucosidase, Glucan endo 1,3-β-glucosidase (Gluc_PrimerH) and Class IV chitinase (ClassIV_Chit), with greater gene upregulation in plants treated with ASM + CG163 than by the individual treatments. Pathogen population studies indicated that CG163 had significant suppressive activity against epiphytic populations of Psa. Endophytic populations were reduced by ASM + CG163 but not by the individual treatments, and by 96–144 h after inoculation were significantly lower than the control. Together these data suggest that ASM + CG163 have complementary modes of action that contribute to greater control of leaf spotting than either treatment alone.

Can the inclusion of uniconazole improve the effectiveness of acibenzolar-S-methyl in managing bacterial speck (Pseudomonas syringae pv. tomato) and bacterial spot (Xanthomonas gardneri) in tomato?

There are reports of acibenzolar-S-methyl (ASM) having host fitness costs and variable levels of control of bacterial speck (Pseudomonas syringae pv. tomato) and bacterial spot (Xanthomonas gardneri) in tomato (Solanum lycopersicum). The plant growth regulator uniconazole (UNI) is associated with alleviating abiotic stress symptoms, and was tested as an additive to ASM to see if it would reduce ASM-associated fitness costs and improve the consistency of disease control. Field applied ASM (fASM) plus greenhouse applied UNI (gUNI) was less consistent than fASM alone, as the combination reduced disease incidence in only two of three years versus fASM alone that reduced disease incidence in three of three years. However, fASM alone never increased total yield compared to the non-treated control, whereas fASM+gUNI increased it in one of three years, which was not associated with changes in disease intensity or relative chlorophyll levels. Greenhouse applied ASM (gASM) plus gUNI reduced disease incidence in one of three years, whereas gASM alone was never effective. This is the first report that gASM can result in long term disease control reducing disease severity up to 13 weeks post-application, indicating long-term effects of gASM are possible. The lack of improved consistency for disease control or improved yield with ASM combined with UNI compared to ASM alone indicates that other additives need to be tested. Also, further research is needed to discover why the ASM + UNI combination did provide improvements under certain field conditions.

Acibenzolar-S-methyl against Botrytis mold on table grapes in vitro and in vivo

The objective of this work was to investigate the effect of the resistance inducer Acibenzolar-S-methyl (ASM), against Botrytis mold on table grapes in vitro and in vivo. To assess the effect of ASM on mycelial growth Botrytis cinerea, different concentrations (0.125, 0.25, 0.5, 1.0, 2.0 and 3% w:v) were tested. Treatments were set up in triplicate, in a completely randomized experimental design, and replicated twice. Results were expressed in minimum inhibitory concentrations and effective dose per 50% response of mycelial growth. Healthy table grapes (cvs. Italia and Benitaka) were harvested at full ripe to evaluate the ASM 1% effect against gray mold under artificial conditions. Bunches were split into two groups in order to perform two types of experiments (spray or immersion). For both trials, treated bunches were arranged in carton boxes and stored at 2±1 °C, for one month, followed by one week of shelf-life at 22±2 °C. In order to evaluate the ASM effect against gray mold under field conditions, ASM 1% was sprayed on both cultivars one week before harvest. Grapes treated with iprodione 0.2% with three applications during the season were included as a standard chemical control. Bunches were harvested at full ripe, arranged in carton boxes and submitted to a cold storage process as described previously. Results for the in vitro experiments showed that the minimum inhibitory concentration of ASM was achieved by 3% and the ED50 was 0.04%. Under artificial conditions, for both cultivars, the efficacy of ASM was higher when the grapes were immersed than sprayed. A significant difference was observed for ASM as compared with control. Regarding the effect of ASM against gray mold in the field, the incidence of gray mold was recorded for both cultivars. For ‘Italia’ and ‘Benitaka’ grapes, ASM, iprodione and sulfur dioxide pad reduced the incidence of gray mold by 85, 79 and 77%, and by 80.5, 73 and 82%, respectively. As for the physico-chemical berry properties, none of the treatments were significantly different from the control for total soluble solids, titratable acidity and color index. A single ASM treatment applied one week before harvest is effective for controlling gray mold in ‘Italia’ and ‘Benitaka’ table grapes.

Resistance elicitors and defense response enhancers of maize to Spodoptera frugiperda (J.E.Smith) (Lepidoptera: Noctuidae)

The objective of this research was to assess the potential of abiotic compounds as defense response enhancers in maize using enzymatic quantification and their efficiency in reduction of damages caused by S. frugiperda. The experiment was laid out in a randomized complete block design with six treatments and five replications. The treatments were: T1: positive control (distilled water + infestation); T2: negative control (without product application, uninfested); T3: biofertilizer; T4: acibenzolar-S-methyl (ASM); T5: potassium silicate; T6: potassium silicate + ASM. The treatments were applied in V6 stage of maize plants. After five days, the plants were artificially infested with 2nd instar caterpillars of S. frugiperda. Damage assessments were carried out at 4, 8, 16 and 22 days after infestation using a scale of notes. To evaluate the enzymatic activity, one leaf of each plant was removed at 2, 4, 8, 16 and 22 days after infestation. The largest peroxidase activities were observed at two DAI (days after infestation) using the potassium silicate + ASM (2,344.12 UAE.mg-1 of proteína.min-1) treatment, while the larger polyphenol oxidase activity peaks were observed after treatment with ASM at 22 DAI. The application of potassium silicate + ASM in corn plants can promote peroxidase activity. The polyphenol oxidase activity was increased after application of ASM, whereas the presence of the pest (on positive control) could potentially increase the activity of phenylalanine ammonia-lyase. The applications of ASM alone and potassium silicate + ASM contributed to reduction of the foliar damage level caused by S. frugiperda in corn plants.

Biochemical insights into basal and induced resistance in cabbage to black rot

AbstractBlack rot, caused by Xanthomonas campestris pv. campestris (Xcc), is the most devastating disease of brassica, but the mechanisms of basal or induced resistance in cabbage remain largely unknown. Here, we performed three experiments to investigate biochemical features associated with cabbage resistance to black rot. In the first experiment, biochemical changes were assessed in plants that were inoculated with a highly (UFPR 5) or a moderately (Xcc 10) aggressive Xcc isolate. In the second experiment, we examined the biochemical responses in two cultivars (Chato de Quintal [CQ] and Louco de Verão [LV], susceptible and moderately resistant to Xcc, respectively). Finally, we examined whether acibenzolar‐S‐methyl (ASM) could induce cabbage resistance to Xcc. Plants inoculated with the Xcc 10 isolate displayed higher activities of superoxide dismutase (SOD), peroxidase (POX) and ascorbate peroxidase (APX), whereas activities of chitinase (CHI), β‐1,3‐glucanase (GLU) and polyphenol oxidase (PPO) as well as the concentrations of hydrogen peroxide (H2O2) and malondialdehyde (MDA) were lower compared to plants inoculated with the UFPR 5 isolate. The resistance of the cultivar LV to Xcc was linked to increases in the activities of CHI, GLU, and PPO and decreases in the activities of SOD, POX and APX as well as in the concentrations of H2O2 and MDA relative to the cultivar CQ. In general, ASM‐sprayed plants displayed higher activities for the enzymes studied, which was associated with decreased disease symptoms and oxidative stress. Taken together, our results demonstrated that high activities of both defence and antioxidant enzymes played a major role in both basal and induced resistance of cabbage to black rot.

Acibenzolar-S-methyl treatment enhances antioxidant ability and phenylpropanoid pathway of blueberries during low temperature storage

Blueberry fruits were immersed in 100 mg/L acibenzolar-S-methyl (ASM) for 10 min and then stored at 4 °C with 40–50% relative humidity (RH) to investigate the changes of anti-oxidative enzyme activity, antioxidants and secondary metabolites in reactive oxygen species metabolism and phenylpropanoid pathway. The results indicated that ASM effectively enhanced the activity of superoxide dismutase, ascorbate peroxidase, catalase and the content of reduced glutathione and ascorbic acid in blueberries but decreased the content of H2O2. The activity of phenylalanine ammonialyase, polyphenol oxidase and the content of lignin, flavonoids, total phenolics and anthocyanin in blueberries were also enhanced by ASM treatment. These results suggest that postharvest ASM treatment could maintain the reactive oxygen species balance and enhance phenylpropanoid pathway to keep antioxidant ability of blueberries during low temperature storage.

Control of pepper bacterial spot and tomato bacterial speck using bactericides in combination with a plant activator

The efficacy of a formulated product of tea tree oil (TTO) and a standard copper based bactericide in combinations with acibenzolar-S-methyl (ASM) for control of bacterial spot of pepper and bacterial speck of tomato was evaluated under controlled conditions. Treatments with copper hydroxide+ASM at both application rates and TTO+ASM showed the best efficacy in control of bacterial spot disease in pepper plants (with respective efficacy values 83.5%, 83.7 % and 86.9%). Similar efficacy was achieved by treatment with copper hydroxide alone (82.2%). On the other hand, the efficacy of TTO, applied alone, was significantly lower at both rates (63.8% and 71.5%) in bacterial spot control in pepper. The same treatments (copper hydroxide +ASM at both application rates and TTO+ASM) were most efficient in suppressing the causal agent of bacterial speck disease in tomato (87%, 82.3% and 81.6%). The efficacy of treatment with the standard bactericide copper hydroxide, applied alone, was significantly lower compared to its combination with ASM (79.1%). Similarly to the bacterial spot experiment, TTO treatments alone showed lower, although satisfactory efficacy at both application rates (66.1% and 68.9%). The results of this study showed that combination of the bioactive compound - ASM with either the standard copper hydroxide bactericide or TTO significantly improved their efficacy in both bacterial spot and speck disease control, and thus implied that combining different biorational compounds, such as essential oils and bioactive products, with standard copper treatments and their inclusion into integrated management programs are of essential importance for the control of bacterial diseases of pepper and tomato.

Systemic resistance induction in ‘Ortanique’ tangor

Abstract This study aimed to evaluate the quality of ‘Ortanique’ tangor, in the post-harvest and refrigerated storage after application of pre-harvest resistance inducers, in the 2015 and 2016 crops. The experimental design in the field was in completely randomized blocks, in a single factorial scheme. The treatment factor was composed of the following resistance inducers [without inducer, selenium (Se), silicon (Si), acibenzolar-s-methyl (ASM), methyl jasmonate (MeJa), thiamethoxam (TMT) and imidacloprid (IMI)]. In the laboratory, the design used was the same as that established in the field, but in a two-factorial scheme, where factor A was composed of the same inducers and factor B, for the storage period [zero (fruits that were not submitted to storage) and 30 days (Cold chamber 5±1°C, relative humidity 85 to 95%)], with simulation of the commercialization time (7 days at 20±1°C). The following analysis were performed: coloration (L *, a *, b * and hue), fresh mass loss, rot index, soluble solids (SS), pH, titratable acidity (TA), SS/TA ratio, ascorbic acid, phenolic compounds and antioxidant capacity. The application of resistance inducers reduces the percentage of fresh mass loss and fruit rot after 30 days of refrigerated storage. Inducers keep phenolic compounds and antioxidant capacity, both in pulp and fruit peel, over the storage period. The inducers Si, MeJa and IMI provide phytochemicals improvement, when compared to the control.

Acibenzolar-S-Methyl Reprograms Apple Transcriptome Toward Resistance to Rosy Apple Aphid.

Acibenzolar-S-methyl (ASM) is a chemical compound, which is able to induce resistance in several model and non-model plants, but the end-players of this induced defense remain ill-defined. Here, we test the hypothesis that treatment with ASM can protect apple (Malus × domestica) against the rosy apple aphid (Dysaphis plantaginea) and investigate the defense molecules potentially involved in resistance. We measured aphid life traits and performed behavioral assays to study the effect of ASM on plant resistance against the aphid, and then combined transcriptomic, bioinformatics, metabolic and biochemical analyses to identify the plant compounds involved in resistance. Plants treated with ASM negatively affected several life traits of the aphid and modified its feeding and host seeking behaviors. ASM treatment elicited up-regulation of terpene synthase genes in apple and led to the emission of (E,E)-α-farnesene, a sesquiterpene that was repellent to the aphid. Several genes encoding amaranthin-like lectins were also strongly up-regulated upon treatment and the corresponding proteins accumulated in leaves, petioles and stems. Our results link the production of specific apple proteins and metabolites to the antibiosis and antixenosis effects observed against Dysaphis plantaginea, providing insight into the mechanisms underlying ASM-induced herbivore resistance.

Actinidia-Pseudomonas syringae pv. actinidiae interaction: differentially expressed plant transcripts during infection

Since 2008, kiwifruit bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa) has spread to pandemic scale. In order to elucidate the molecular events of the kiwifruit-Psa interaction, Illumina RNAseq was conducted after Psa inoculation and mock inoculation, on both acibenzolar-S-methyl (ASM) treated and untreated Actinidia chinensis plants. De-novo assembly of the kiwifruit transcriptome revealed 39,607 transcripts. To investigate the transcriptome expression profile during the infection process, hierarchical cluster analysis was performed. During the infection process, about 3000 transcripts were modulated. It was notable that the number of modulated transcripts in infected plants were higher than in ASM-treated infected plants. Furthermore, the RNAseq technology permitted us to identify novel transcripts of unknown function but related to infection and ASM treatment. The analysis revealed that the coordinates of some important gene functional categories change, such as hormonal balance, transcriptional regulation and signalling. Different transcription factors were also linked with signalling and hormonal balance and are involved in the ability of ASM-treated plants to assemble the right defence response against Psa. On the other hand, control plants respond to Psa, but not in an adequate way to counteract the infection. Indeed, several transcripts related to plant signalling and putatively encoding RLK-LRR and PRR proteins were exclusively found under these conditions, while they were absent in ASM-treated plants, highlighting how the response of susceptible plants belongs to a separate cluster from that of ASM-treated plants.

Changes in the sucrose metabolism in apple fruit following postharvest acibenzolar-S-methyl treatment.

Apple (cv. Ralls) fruit were treated with 0.1 g L-1 acibenzolar-S-methyl (ASM) for 10 min to evaluate the changes in enzyme activity and gene expression in the sucrose metabolism during storage at 20 °C with 30%-40% relative humidity. The results showed that sucrose phosphate synthase (SPS) and sucrose synthase synthesis (SS-s) activity was enhanced by ASM in apple fruit during the entire storage period. Sucrose synthase-cleavage (SS-c) and neutral invertase (NI) activity was suppressed by ASM treatment but acid invertase (AI) activity was increased in the middle period after ASM treatment. Acibenzolar-S-methyl treatment also significantly inhibited SPS and NI gene expression in apple fruit during storage. However, SS gene expression increased in the ASM-treated apple fruit. High levels of expression of the fructokinase (FK) and hexokinase (HK) genes were observed during the middle storage period in the ASM-treated fruit. Taken together, these results suggest that ASM delays the senescence of apple fruit by regulating the sugar metabolism. © 2018 Society of Chemical Industry.

Systemic resistance inducer acibenzolar-S-methyl (ASM) and its microencapsulated formulations: their long-lasting control efficacy against cucumber diseases and mitigation of phytotoxicity.

The development of fungicide resistance by pathogens is a major limiting factor for the control of plant diseases. To combat resistance development, the use of broad-spectrum but nonfungitoxic resistance inducers such as acibenzolar-S-methyl (ASM) is a promising approach because the orchestrated mechanisms underlying systemic acquired resistance induced by ASM are less likely to be overcome easily by pathogens. However, phytotoxicity is the main limiting factor of ASM. ASM was highly active at inducing systemic resistance against powdery and downy mildews, the two major cucumber diseases. Based on the duration of the control, ASM effectiveness against these diseases was maintained well in plastic greenhouses and the number of sprays could be reduced. Control efficacy after seed treatment with ASM and the applications of microencapsulated ASM was also high against mildews in pots as well as in greenhouse experiments, with no problematic phytotoxicity. The use of ASM is a potential integrated pest management-based tactic to control cucumber powdery and downy mildews because its long-lasting efficacy allows the application of typical fungicides to be reduced. The risk for resistance development in mildew pathogens will also be reduced. ASM seed treatment as well as soil amendment with microencapsulated ASM is effective in lowering the risk for the phytotoxicity of this compound. © 2018 Society of Chemical Industry.

Antimicrobial activity of Agaricus brasiliensis on Plasmopara viticola and its effect on the induction of resistance to the control of downy mildew on ‘Isabel Precoce’

ABSTRACT: Agaricus brasiliensis include bioactive compounds that can act as antibiotics, bacteriostatic, fungistatic and nematostatic substances. In this sense, this study aimed to evaluate the effect of a single application of aqueous mycelial suspension (AMS) of A. brasiliensis in control of downy mildew (Plasmopara viticola) and resistance induction in ‘Isabel Precoce’ grapevines under greenhouse conditions. Treatments consisted of three doses of 1%, 5%, 10%, 15% and 20% AMS A. brasiliensis, as well as treatment with acibenzolar-S-methyl (ASM). The variables analyzed were: sporangiospore germination, disease severity, represented by the area under the disease progress curve (AUDPC), catalase enzyme activity, peroxidase and polyphenol. The 10%, 15% and 20% doses of AMS caused approximately 80% reduction in germination of P. viticola sporangiospores. The treatments did not show significant effects in reducing both the AUDPC of mildew and polyphenol oxidase enzyme activity. The A. brasiliensis aqueous mycelial suspension showed a fungitoxic effect on the germination of sporangiopores; however, it was not enough to reduce the severity of mildew in the ‘Isabel Precoce’ grapevines, even when acting on the catalase and peroxidase enzymes. Thus, experiments should be performed to verify the viability of the reproductive structures of the pathogen externalized in the vines when treated with A. brasiliensis AMS.

Abiotic Compounds as Inducers of Resistance to Fusarium Wilt in Tomatoes

To study the effects of resistance inducers used to control fusarium wilt in tomatoes due to the fungus Fusarium oxysporum Schlecht f. sp. lycopersici, we evaluated the effects of ASM (acibenzolar-S-methyl), Agro-Mos, chitosan, Biopirol and neem oil on F. oxysporum f. sp. lycopersici mycelial growth and sporulation and systemic resistance in tomatoes. In vitro experiments comprised evaluations of the products’ effects on the mycelial growth and sporulation of the PDA (potato dextrose agar) growth medium-cultured pathogen. In vivo experiments included product application to tomato plants of the Santa Cruz cultivar that were grown for 25 days on autoclaved soil, followed by determinations of disease severity and peroxidase, polyphenol oxidase and Beta-1,3-glucanase enzyme activity levels, which are related to the process of resistance induction. Pathogen inoculation occurred after 5 days at a concentration of 106 conidia/mL. We evaluated the disease according to a rating scale. Enzymatic activity was determined according to specific protocols. Neem oil controlled pathogen mycelial growth and sporulation, while ASM influenced sporulation. The products reduced the severity of wilt in the plants. We highlight neem oil, Agro-Mos and Biopirol due to their ability to induce significant peroxidase, polyphenol oxidase and Beta-1,3-glucanase expression, respectively.

<b>‘Navelina’ oranges submitted to pre-harvest resistance inducers

The objective of this study was to evaluate the physical-chemical characteristics, rot index and bioactive compounds of ‘Navelina’ oranges under postharvest refrigerated storage conditions after pre-harvest resistance induction in crops from 2015 and 2016. The field experimental design was completely randomized blocks. The treatment factors were composed of the following resistance inducers: noresistance inducer (control), selenium (Se), silicon (Si), acibenzolar-s-methyl (ASM), methyl jasmonate (MeJa), thiamethoxam (TMT) and imidacloprid (IMI). In the laboratory, the experimental design was the same as that in the field, but it used a two-factor scheme instead of a unifactorial scheme. In the two-factor scheme, factor A was composed of the abovementioned resistance inducers, and factor B was composed of the refrigerated storage periods (zero and 30 days). The analyses investigated the coloration, fresh mass loss, rot index, soluble solids, pH, titratable acidity, SS/TA ratio, ascorbic acid, total phenolic compounds and antioxidant capacity of the oranges. The application of pre-harvest resistance inducers was efficient in maintaining the physical-chemical characteristics of the ‘Navelina’ oranges in postharvest, increasing their bioactive compounds in comparison to the control. The resistance inducers Se, Si, MeJa, and IMI reduced rot rates, while ASM and MeJa prevented fresh fruit mass loss.

Postharvest longevity of 'BRS Vitória' seedless grapes subjected to cold storage and acibenzolar-S-methyl application

Abstract: The objective of this work was to evaluate cold storage periods and postharvest longevity of the seedless table grape 'BRS Vitória' subjected to the application of the disease-resistance inducer acibenzolar-S-methyl (ASM). Bunches were treated or not with 1% ASM, placed individually in plastic clamshell trays and stored in a cold chamber at 2±1ºC, at a high relative humidity, for three periods (30, 45, and 60 days), followed by a 5-day period of shelf life in plastic clamshells, at 22±2ºC. After each storage period, gray mold (Botrytis cinerea) incidence was evaluated, and the physicochemical analysis was performed. A completely randomized design, with four replicates, was used in two 2x3 factorial arrangements: one evaluating ASM application and cold storage periods; and another, ASM and cold storage + shelf-life periods. ASM did not change the physicochemical characteristics of the bunches, and the incidence of gray mold was lower than 1% in all treatments. Water loss from bunches increased with storage periods. Even without ASM application, 'BRS Vitória' grape can preserve its postharvest quality for up to 60 days of cold storage, plus five days of shelf life in plastic clamshells.

G6PDH regulated NADPH production and reactive oxygen species metabolism to enhance disease resistance against blue mold in apple fruit by acibenzolar-S-methyl

Apple fruit were treated with 100 mg L−1 acibenzolar-S-methyl (ASM) and 100 μM dehydroepiandrosterone (DHEA) to investigate its effect on the lesion development inoculated with Penicillium expansum. Effects of ASM on the glucose-6-phosphate dehydrogenase (G6PDH) activity, nicotinamide ademine dinucleotidephosphate (NADPH) production, and reactive oxygen species (ROS) metabolism in apple fruit were also studied. The results indicated that ASM treatment decreased the lesion development of blue mold in apple fruit. ASM treatment enhanced the content of H2O2, the activities of NADPH oxidase (NOX), superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and peroxidase (POD) in apple fruit. ASM treatment increased the gene expression of SOD, APX, DHAR as well as ascorbic acid (AsA) and reduced glutathione (GSH) content whereas it inhibited MDHAR expressions. The result also indicated that ASM treatment significantly inhibited CAT activity in apple fruit. In addition, the higher activity of G6PDH and content of NADPH was observed in ASM-treated apple fruit. In contrast, lesion diameter in ASM + DHEA-treated apple fruit developed more quickly than the control fruit. Also, the accumulation of H2O2, NADPH, AsA and GSH were reduced by DHEA treatment while inhibiting the activities of NOX, SOD, POD, APX, GR, MDHAR and G6PDH. Gene expressions of SOD, APX and DHAR were also inhibited by DHEA treatment. These results suggest that G6PDH played a crucial role in ROS metabolism and NADPH production in apple fruit to enhance resistance against P. expansum.

Identification of rhizobacteria that increase yield and plant tolerance to angular leaf spot disease in cucumber

The biological control of angular leaf spot disease (ALS) of cucumbers (Cucumis sativus), caused by Pseudomonas syringae pv. lachrymans (Psl), using promising rhizobacteria (RB) and to compare RB efficacy to that of acibenzolar-S-methyl (ASM) was investigated. Effects of ASM and RB isolate Pseudomonas putida AA11/1 that was isolated from the healthy cucumber root surface on disease severity and plant growth were evaluated using ALS-susceptible and tolerant cucumber cultivars in a growth chamber and a soilless growing system. ASM and AA11/1 significantly reduced average disease severity of ALS by 69 and 34% in the susceptible cultivar and 92 and 21% in the tolerant cultivar, respectively. ASM treatment significantly reduced Psl populations, but AA11/1 did not inhibit Psl growth in either cultivar. In the soilless system, disease severity was limited by either ASM or AA11/1, whereas only AA11/1 treatments significantly increased cucumber yield by 68 and 33% in the susceptible and tolerant cultivar, respectively.

Two invasive herbivores on a shared host: patterns and consequences of phytohormone induction.

Herbivore-induced changes in host quality mediate indirect interactions between herbivores. The nature of these indirect interactions can vary depending on the identity of herbivores involved, species-specific induction of defense-signaling pathways, and sequence of attack. However, our understanding of the role of these signaling pathways in the success of multiple exotic herbivores is less known. Eastern hemlock (Tsuga canadensis) is attacked by two invasive herbivores [elongate hemlock scale (EHS; Fiorinia externa) and hemlock woolly adelgid (HWA; Adelges tsugae)] throughout much of its range, but prior attack by EHS is known to deter HWA. The potential role of phytohormones in this interaction is poorly understood. We measured endogenous levels of phytohormones in eastern hemlock in response to attack by these invasive herbivores. We also used exogenous application of methyl jasmonate (MJ) and acibenzolar-S-methyl (ASM), a salicylic acid (SA) pathway elicitor, to test the hypothesis that defense-signaling phytohormones typically induced by herbivores could deter HWA. Resistance to adelgid attack was assessed using a behavioral assay. Adelgid feeding significantly elevated both abscisic acid (ABA) and SA in local tissues, while EHS feeding had no detectable effect on either phytohormone. HWA progrediens and sistens crawlers preferred to settle on ASM-treated foliage. In contrast, HWA crawlers actively avoided settlement on MJ-treated foliage. We suggest that induction of ABA- and SA-signaling pathways, in concert with defense-signaling interference, may aid HWA invasion success, and that defense-signaling interference, induced by exotic competitors, may mediate resistance of native hosts.