Induction Of Systemic Acquired Resistance Research Articles

Cadmium toxicity promotes hormonal imbalance and induces the expression of genes involved in systemic resistances in barley.

Cadmium (Cd) is a widely distributed pollutant that adversely affects plants' metabolism and productivity. Phytohormones play a vital role in the acclimation of plants to metal stress. On the other hand, phytohormones trigger systemic resistances, including systemic acquired resistance (SAR) and induced systemic resistance (ISR), in plants in response to biotic interactions. The present study aimed to investigate the possible induction of SAR and ISR pathways in relation to the hormonal alteration of barley seedlings in response to Cd stress. Barley seedlings were exposed to 1.5mgg-1 Cd in the soil for three days. The nutrient content, oxidative status, phytohormones profile, and expression of genes involved in SAR and ISR pathways of barley seedlings were examined. Cd accumulation resulted in a reduction in the nutrient content of barley seedlings. The specific activity of superoxide dismutase and the hydrogen peroxide content significantly increased in response to Cd toxicity. Abscisic acid, jasmonic acid, and ethylene content increased under Cd exposure. Cd treatment resulted in the upregulation of NPR1, PR3, and PR13 genes in SAR pathways. The transcripts of PAL1 and LOX2.2 genes in the ISR pathway were also significantly increased in response to Cd treatment. These findings suggest that hormonal-activated systemic resistances are involved in the response of barley to Cd stress.

New antimicrobials and plant defense inducers for managing citrus canker disease

For over two decades, Florida citrus growers have been heavily using copper sprays to combat citrus canker (Xanthomonas citri subsp. citri; Xcc), but it raises the risk of developing resistant bacterial strains and excessive accumulation in the soil. Alternative methods are needed to reduce copper dependency and better manage Xcc. Therefore, we screened copper-alternative products against canker on young seedlings in the greenhouse and mature trees in a commercial grove in Florida, USA. In the greenhouse, we evaluated the efficacy of single foliar application of new plant defense inducers (PDI), ‘PDI5’, ‘PDI26’, and ‘PDI31’, and a commercially available systemic acquired resistance inducer, Actigard (drench; 2g/tree), applied two days before injection-infiltration with citrus canker bacterium Xcc (104 CFU/ml), on two-year-old Valencia trees. All three PDIs, sprayed at 500 ppm, as well as Actigard (drench), effectively reduced canker severity on the inoculated leaves in the greenhouse (P ≤0.02). In the grove, we tested new antimicrobials, Mastercop ‘MC’ (21.46% copper sulfate pentahydrate; metallic copper equivalent 5.4%) at concentrations of 1.12 kg/ha, 1.68 kg/ha and 2.24 kg/ha, ‘AM’ at 1.68 kg/ha and 2.24 kg/ha, and a nutrient solution (AGRO-MOS) at 1.12 kg/ha for canker suppression on 4–6-year-old Hamlin trees. Kocide 2000 (growers’ standard control; metallic copper equivalent 30%; 3.92 kg/ha) was used as a control check. Although 2021 was not as conducive for citrus canker due to the relatively dry spring months in the field, our results showed that the six sprays of AM (2.24 kg/ha) or MC (1.68 kg/ha, and 2.24 kg/ha), in 2022, provided excellent control of Xcc, with a significant reduction in disease incidence in leaves and fruits, and disease severity in fruits, similar to Kocide 2000. The results indicate that antimicrobials, AM and MC, and plant defense inducers PDI5, PDI26, and PDI31 can be part of an integrated pest management (IPM) program with copper for managing citrus canker. Reducing the frequency and amount of copper applications can help reduce pesticide and application expenses, lower risks of copper buildup in the soil and toxicity for citrus trees and reduce the risk of the emergence of copper-resistant Xcc strains. Further research on these products is needed to assess their long-term effectiveness and potential environmental risks.

The expression of the NPR1-dependent defense response pathway genes in Persea americana (Mill.) following infection with Phytophthora cinnamomi

A plant’s defense against pathogens involves an extensive set of phytohormone regulated defense signaling pathways. The salicylic acid (SA)-signaling pathway is one of the most well-studied in plant defense. The bulk of SA-related defense gene expression and the subsequent establishment of systemic acquired resistance (SAR) is dependent on the nonexpressor of pathogenesis-related genes 1 (NPR1). Therefore, understanding the NPR1 pathway and all its associations has the potential to provide valuable insights into defense against pathogens. The causal agent of Phytophthora root rot (PRR), Phytophthora cinnamomi, is of particular importance to the avocado (Persea americana) industry, which encounters considerable economic losses on account of this pathogen each year. Furthermore, P. cinnamomi is a hemibiotrophic pathogen, suggesting that the SA-signaling pathway plays an essential role in the initial defense response. Therefore, the NPR1 pathway which regulates downstream SA-induced gene expression would be instrumental in defense against P. cinnamomi. Thus, we identified 92 NPR1 pathway-associated orthologs from the P. americana West Indian pure accession genome and interrogated their expression following P. cinnamomi inoculation, using RNA-sequencing data. In total, 64 and 51 NPR1 pathway-associated genes were temporally regulated in the partially resistant (Dusa®) and susceptible (R0.12) P. americana rootstocks, respectively. Furthermore, 42 NPR1 pathway-associated genes were differentially regulated when comparing Dusa® to R0.12. Although this study suggests that SAR was established successfully in both rootstocks, the evidence presented indicated that Dusa® suppressed SA-signaling more effectively following the induction of SAR. Additionally, contrary to Dusa®, data from R0.12 suggested a substantial lack of SA- and NPR1-related defense gene expression during some of the earliest time-points following P. cinnamomi inoculation. This study represents the most comprehensive investigation of the SA-induced, NPR1-dependent pathway in P. americana to date. Lastly, this work provides novel insights into the likely mechanisms governing P. cinnamomi resistance in P. americana.

Analysis of the apoplast fluid proteome during the induction of systemic acquired resistance in Arabidopsis thaliana.

Plant-pathogen interactions occur in the apoplast comprising the cell wall matrix and the fluid in the extracellular space outside the plasma membrane. However, little is known regarding the contribution of the apoplastic proteome to systemic acquired resistance (SAR). Specifically, SAR was induced by inoculating plants with Pst DC3000 avrRps4. The apoplast washing fluid (AWF) was collected from the systemic leaves of the SAR-induced or mock-treated plants. A label free quantitative proteomic analysis was performed to identified the proteins related to SAR in AWF. A total of 117 proteins were designated as differentially accumulated proteins (DAPs), including numerous pathogenesis-related proteins, kinases, glycosyl hydrolases, and redox-related proteins. Functional enrichment analyses shown that these DAPs were mainly enriched in carbohydrate metabolic process, cell wall organization, hydrogen peroxide catabolic process, and positive regulation of catalytic activity. Comparative analysis of proteome data indicated that these DAPs were selectively enriched in the apoplast during the induction of SAR. The findings of this study indicate the apoplastic proteome is involved in SAR. The data presented herein may be useful for future investigations on the molecular mechanism mediating the establishment of SAR.

Microbial Filtrates Improved Growth Parameters of In vitro PVX Infected Potato Plantlets

This study focuses on utilizing the phenomenon of systemic acquired resistance (SAR) to control plant viruses and increased growth in vitro. The study demonstrated the induction of SAR in potato plantlets against Potato Virus X by using bacterial culture filtrates invitro. These biotic inducers included Pseudomonas spp. and Bacillus spp. The study observed the occurrence of induced resistance and enhanced growth in potato plantlets treated with culture filtrates containing these microorganisms. This was evident through a reduction in PVX infection, disease severity and associated biochemical changes (such as elevated levels of endogenous salicylic acid, protein content, chlorophyll content, peroxidase and polyphenol oxidase activities), as well as improvements in growth parameters.

Evaluation of systemic acquired resistance inducers for the management of copper and streptomycin resistant strains of Xanthomonas perforans on tomato

Bacterial spot (Xanthomonas spp.) is one of the most detrimental diseases of tomato (Solanum lycopersicum L.) worldwide. Bacterial spot Xanthomonads are either endemic or spread by contaminated seed or transplant material into tomato production areas. Due to limited disease management options, transplant producers rely on copper- and streptomycin-based bactericides that are often ineffective due to the predominance of resistant Xanthomonas strains. In this study, transplant production facilities located across eight counties in western North Carolina were surveyed for bacterial spot symptoms from 2018 to 2019. In total, 29 strains (n = 6 in 2018 and n = 23 in 2019) were isolated and identified as Xanthomonas perforans. All strains were resistant to copper, while only 24% of the strains were resistant to streptomycin. Therefore, the ability of three systemic acquired resistance (SAR) inducers, methyl salicylate, Bacillus mycoides isolate J, and acibenzolar-S-methyl (ASM), alone or in combination with copper or streptomycin were evaluated as potential alternatives to copper-mancozeb (grower standard) to manage bacterial spot under greenhouse and field conditions. Under greenhouse conditions, applications of ASM at 0.4 g/L alone, or in combination with copper or streptomycin, significantly reduced bacterial spot disease severity when compared to the grower standard and nontreated controls (P < 0.05). However, none of the SAR inducers significantly reduced disease severity or improved yield when compared to copper-mancozeb-ASM under field conditions (P < 0.05). This study highlights the potential of using ASM for the management of bacterial spot of tomato transplant production to reduce bacterial spot introduction into the field.

Characterization of Disease Resistance Induced by a Pyrazolecarboxylic Acid Derivative in Arabidopsis thaliana.

Systemic acquired resistance (SAR) is a potent innate immunity system in plants that is induced through the salicylic acid (SA)-mediated signaling pathway. Here, we characterized 3-chloro-1-methyl-1H-pyrazole-5-carboxylic acid (CMPA) as an effective SAR inducer in Arabidopsis. The soil drench application of CMPA enhanced a broad range of disease resistance against the bacterial pathogen Pseudomonas syringae and fungal pathogens Colletotrichum higginsianum and Botrytis cinerea in Arabidopsis, whereas CMPA did not show antibacterial activity. Foliar spraying with CMPA induced the expression of SA-responsible genes such as PR1, PR2 and PR5. The effects of CMPA on resistance against the bacterial pathogen and the expression of PR genes were observed in the SA biosynthesis mutant, however, while they were not observed in the SA-receptor-deficient npr1 mutant. Thus, these findings indicate that CMPA induces SAR by triggering the downstream signaling of SA biosynthesis in the SA-mediated signaling pathway.

The Effect of a New Derivative of Benzothiadiazole on the Reduction of Fusariosis and Increase in Growth and Development of Tulips

The use of inducers of systemic acquired resistance (SAR) is widely described in the literature. Such substances have important advantages over plant protection products (PPPs) and, thus, are often indicated as their alternatives. The main risk indicated in the context of the widespread use of SAR inducers is that of yield reduction that may result from the excessive metabolic imbalance of the treated plant. The general aim of the study presented was to check the effect of using a new active substance, namely N-methoxy-N-methylbenzo(1.2.3)thiadiazole-7-carboxamide (BTHWA), on tulips cultivated in greenhouse conditions. The plant response to BTHWA treatment was also analyzed in terms of the extent to which the growth–immunity phenomena would occur. Surprisingly, the application of BTHWA provided not only efficient protection against fusariosis but also resulted in the stimulation of the growth and development of tomato plants. The results proved very interesting as they stand in contrast to other results on SAR induction. The method of BTHWA application used in this study resulted in SAR induction at a level sufficient to provide effective protection and, at the same time, did not cause disruption to plant metabolism that would result in yield reduction.

N-hydroxypipecolic acid induces systemic acquired resistance and transcriptional reprogramming via TGA transcription factors.

N-hydroxypipecolic acid (NHP) accumulates in pathogen-inoculated and distant leaves of the Arabidopsis shoot and induces systemic acquired resistance (SAR) in dependence of the salicylic acid (SA) receptor NPR1. We report here that SAR triggered by exogenous NHP treatment requires the function of the transcription factors TGA2/5/6 in addition to NPR1, and is further positively affected by TGA1/4. Consistently, a tga2/5/6 triple knockout mutant is fully impaired in NHP-induced SAR gene expression, while a tga1/4 double mutant shows an attenuated, partial transcriptional response to NHP. Moreover, tga2/5/6 and tga1/4 exhibited fully and strongly impaired pathogen-triggered SAR, respectively, while SA-induced resistance was more moderately compromised in both lines. At the same time, tga2/5/6 was not and tga1/4 only partially impaired in the accumulation of NHP and SA at sites of bacterial attack. Strikingly, SAR gene expression in the systemic tissue induced by local bacterial inoculation or locally applied NHP fully required functional TGA2/5/6 and largely depended on TGA1/4 factors. The systemic accumulation of NHP and SA was attenuated but not abolished in the SAR-compromised and transcriptionally blocked tga mutants, suggesting their transport from inoculated to systemic tissue. Our results indicate the existence of a critical TGA- and NPR1-dependent transcriptional module that mediates the induction of SAR and systemic defence gene expression by NHP.

Synthesis, Fungicidal Activity and Plant Protective Properties of 1,2,3-Thiadiazole and Isothiazole-Based N-acyl-N-arylalaninates.

The addition of active groups of known fungicides, or systemic acquired resistance inducers, into novel compound molecules to search for potential antifungal compounds is a popular and effective strategy. In this work, a new series of N-acyl-N-arylalanines was developed and synthesized, in which 1,2,3-thiadiazol-5-ylcarbonyl or 3,4-dichloroisothiazol-5-ylcarbonyl (fragments from synthetic plant resistance activators tiadinil and isotianil, respectively) and a fragment of N-arylalanine, the toxophoric group of acylalanine fungicides. Several new synthesized compounds have shown moderate antifungal activity against fungi in vitro, such as B. cinerea, R. solani and S. sclerotiorum. In vivo tests against A. brassicicola showed that compound 1d was 92% effective at a concentration of 200 µg/mL, similar to level of tiadinil, a known inducer of systemic resistance. Thus, 1d could be considered a new candidate fungicide for further detailed study. The present results will advance research and influence the search for more promising fungicides for disease control in agriculture.

New plant resistance inducers based on polyamines

Abstract The novel and revolutionary approach to plant protection presented in this work, based on the preparation of bifunctional salts of a plant resistance inducer combined with a polyamine cation, may become a potential solution in the future for reducing the effects of abiotic and biotic stresses to which the plant is exposed. This study presents the synthesis, physical properties, phytotoxicity, and systemic acquired resistance (SAR) induction efficacy of new salts composed of the anion of plant resistance inducers and N,N,N,N′,N′,N′-hexamethylpropane-1,3-diammonium cation (5 salts), N,N,N,N′,N′,N′-hexamethyl-butane-1,4-diammonium cation (5 salts), spermidine salicylate, and spermine salicylate. SAR induction efficiency tests were performed on tobacco, Nicotiana tabacum var. Xanthi, infected with the tobacco mosaic virus.

A New Benzothiadiazole Derivative with Systemic Acquired Resistance Activity in the Protection of Zucchini (Cucurbita pepo convar. giromontiina) against Viral and Fungal Pathogens

The ability of plant resistance inducers to provide protection against viral diseases is one of their main advantages over conventional pesticides. In the case of viral diseases that cannot be controlled directly with pesticides, insecticides are used to control the vectors of viruses. However, the effectiveness of such treatments is strictly dependent on the time of application. The plant response to the application of systemic acquired resistance (SAR) inducers, as a result of the stimulating action of these substances, does not depend on the time of application as it triggers the plant's natural defence mechanism. The best-recognised substance showing SAR inducer activity is acibenzolar-S-methyl ester (ASM, BTH). As its activity against different plant pathogens of crops has been well documented, the current research is concentrated on the search for novel substances of the type. The tested substance, N-methoxy-N-methylbenzo(1,2,3)thiadiazole-7-carboxamide (BTHWA), is an amide derivative of benzothiadiazole, showing plant resistance-inducing activity. This article presents the activity of BTHWA that has led to increased resistance of zucchini (Cucurbita pepo convar. giromontiina) towards viral infections. In addition, since the occurrence of the fungal pathogen, powdery mildew, was also observed during the two-year field experiments, the activity of BTHWA related to the reduction of infection with this fungus was also investigated. The substance was applied in two different variants either four or eight times, over the whole vegetation season. Surprisingly, the variant of four applications performed at the beginning of the vegetation season proved more effective in protection against viruses and fungus. A possible explanation may be the occurrence of the growth-immunity trade-off phenomenon that is known in the literature. Disturbance in plant metabolism resulting from eight applications may lead to lower yields of plants treated with SAR inducers. Perhaps such overstimulation of the plants we treated eight times may not have brought the optimum increase in plant resistance.

Protein glycosylation changes during systemic acquired resistance in Arabidopsis thaliana

N-glycosylation, an important post-translational modification of proteins in all eukaryotes, has been clearly shown to be involved in numerous diseases in mammalian systems. In contrast, little is known regarding the role of protein N-glycosylation in plant defensive responses to pathogen infection. We identified, for the first time, glycoproteins related to systemic acquired resistance (SAR) in an Arabidopsis thaliana model, using a glycoproteomics platform based on high-resolution mass spectrometry. 407 glycosylation sites corresponding to 378 glycopeptides and 273 unique glycoproteins were identified. 65 significantly changed glycoproteins with 80 N-glycosylation sites were detected in systemic leaves of SAR-induced plants, including numerous GDSL-like lipases, thioglucoside glucohydrolases, kinases, and glycosidases. Functional enrichment analysis revealed that significantly changed glycoproteins were involved mainly in N-glycan biosynthesis and degradation, phenylpropanoid biosynthesis, cutin and wax biosynthesis, and plant-pathogen interactions. Comparative analysis of glycoproteomics and proteomics data indicated that glycoproteomics analysis is an efficient method for screening proteins associated with SAR. The present findings clarify glycosylation status and sites of A. thaliana proteins, and will facilitate further research on roles of glycoproteins in SAR induction.

Strigolactones Modulate Salicylic Acid-Mediated Disease Resistance in Arabidopsis thaliana.

Strigolactones are low-molecular-weight phytohormones that play several roles in plants, such as regulation of shoot branching and interactions with arbuscular mycorrhizal fungi and parasitic weeds. Recently, strigolactones have been shown to be involved in plant responses to abiotic and biotic stress conditions. Herein, we analyzed the effects of strigolactones on systemic acquired resistance induced through salicylic acid-mediated signaling. We observed that the systemic acquired resistance inducer enhanced disease resistance in strigolactone-signaling and biosynthesis-deficient mutants. However, the amount of endogenous salicylic acid and the expression levels of salicylic acid-responsive genes were lower in strigolactone signaling-deficient max2 mutants than in wildtype plants. In both the wildtype and strigolactone biosynthesis-deficient mutants, the strigolactone analog GR24 enhanced disease resistance, whereas treatment with a strigolactone biosynthesis inhibitor suppressed disease resistance in the wildtype. Before inoculation of wildtype plants with pathogenic bacteria, treatment with GR24 did not induce defense-related genes; however, salicylic acid-responsive defense genes were rapidly induced after pathogenic infection. These findings suggest that strigolactones have a priming effect on Arabidopsis thaliana by inducing salicylic acid-mediated disease resistance.

Impact of Foliar Application of Acibenzolar-S-Methyl on Rose Rosette Disease and Rose Plant Quality.

Rose rosette disease (RRD) caused by rose rosette emaravirus (RRV) is a major issue in the U.S. rose industry with no effective method for its management. This study evaluated the effect of foliar application of acibenzolar-S-methyl (ASM), a plant systemic acquired resistance inducer, in reducing RRD disease severity on Rosa species cv. Radtkopink ('Pink Double Knock Out') under greenhouse conditions, and the effect of ASM on plant growth under commercial nursery production conditions. ASM at 50- or 100-mg/liter concentrations at weekly intervals significantly reduced RRD severity compared with the untreated control in two of the three greenhouse trials (P < 0.05). The plants in these trials were subsequently pruned and observed for symptoms, which further indicated that application of ASM at 50- or 100-mg/liter concentrations lowered disease severity compared with the untreated control (P < 0.05) in these two trials. Plants treated with ASM at 50- or 100-mg/liter concentrations had delayed incidence of RRD compared with the nontreated controls. Plants treated with ASM at the 50- or 100-mg/liter rate in all three trials either did not have RRV present or the virus was present in fewer leaf samples than untreated controls as indicated by quantitative reverse transcription PCR analysis. Overall, plants treated with ASM at the 50-mg/liter concentration had 36 to 43% reduced RRD incidence compared with the water control. The treatment of two cultivars of rose, 'Radtkopink' and 'Meijocos' ('Pink Drift'), with weekly foliar applications of ASM at the three rates (0.5, 0.75, and 1.0 oz/A) indicated that ASM had no negative effect on flowering or plant growth at even the highest rate of application.

Identification of chlorpromazine hydrochloride role as a new systemic acquired resistance inducer against Magnaporthe oryzae in rice

Chlorpromazine HCL is considered an active ingredient for psychopharmacological agents for humans, the current study was undertaken to determine the ability of chlorpromazine HCL to induce systemic acquired resistance (SAR) in rice plants, to protect rice from blast disease caused by Magnaporthe oryzae. Chlorpromazine HCL was used at different concentrations; 10, 25, 50, 125, 250, 500, 1000 and 2000 mg/L under laboratory and greenhouse conditions. The results showed that chlorpromazine HCL was effective on fungus radial growth on high concentrations of more than 250 mg/L in vitro. Under greenhouse condition, resistance response was significantly improved with low and high concentrations. The potential inducer concentration was 250 mg/L which reached 18.4% of disease severity. The gene expression for chlorpromazine HCL treatment induces some of the indicators for salicylic acid (SA) pathway such as OsWRKY45 and OsNPR1 which recorded 15.14 and 17.79 fold changes, respectively after 24 h of inoculation, and jasmonic acid (JA) pathway such as AOS2, JAMYB and PBZ1 (OsPR10) which recorded 11.27, 10.57 and 13.51 fold changes, respectively, after 24 h of inoculation. The results suggest that chlorpromazine HCL induces SAR in rice against blast disease which could be related to SA and JA defense pathways.

Synthesis, characterization and biological activity of bifunctional ionic liquids based on dodine ion.

Development of new plant protection strategies has become an urgent matter in modern agriculture, in view of the evidently proved negative effect of currently used active ingredients of pesticides. In recent years, much effort has been made to eliminate the use of pesticides established to be toxic to pollinators. In this study, we present a group of new bifunctional ionic liquids based on dodine (N-dodecylguanidine) cation whose physical and biological properties have been modified relative to those of the commercially available N-dodecylguanidine acetate. The decreased level of residue of active substances in plant tissues reduces their availability to pollinators, which increases the safety of their use. Moreover, lower environmental impact in combination with high antifungal activity and an additional biological function, that is the systemic acquired resistance induction, are in line with the goals of sustainable agriculture. The presented approach shows the possibility of derivatization of commonly used fungicide into the form of bifunctional salts whose physical and biological properties can be easily modified. The paper reports successful design and synthesis of new sustainable and green chemicals for the modern agriculture, being less toxic to the environment and human health but still effective against pathogens. © 2021 Society of Chemical Industry.

Transcriptomic Analysis of Wheat Seedling Responses to the Systemic Acquired Resistance Inducer N-Hydroxypipecolic Acid.

The fungal pathogen Fusarium graminearum can cause destructive diseases on wheat, such as Fusarium head blight and Fusarium crown rot. However, a solution is still unavailable. Recently, N-hydroxypipecolic acid (NHP) was identified as a potent signaling molecule that is capable of inducing systemic acquired resistance to bacterial, oomycete, and fungal infection in several plant species. However, it is not clear whether NHP works in wheat to resist F. graminearum infection or how NHP affects wheat gene expression. In this report, we showed that pretreatment with NHP moderately increased wheat seedling resistance to F. graminearum. Using RNA sequencing, we found that 17% of wheat-expressed genes were significantly affected by NHP treatment. The genes encoding nucleotide-binding leucine-rich repeat immune receptors were significantly overrepresented in the group of genes upregulated by NHP treatment, while the genes encoding receptor-like kinases were not. Our results suggested that NHP treatment sensitizes a subset of the immune surveillance system in wheat seedlings, thereby facilitating wheat defense against F. graminearum infection.

Evaluation of the control effect of SAR inducers against citrus Huanglongbing applied by foliar spray, soil drench or trunk injection

Huanglongbing (HLB) or greening disease, associated with the bacterial pathogen Candidatus Liberibacter asiaticus (Las), is currently the most devastating citrus disease worldwide and no cure is available. Inducers of systemic acquired resistance (SAR) are effective and sustainable to combat various plant diseases. In this study, the SAR inducers acibenzolar-S-methyl (ASM), imidacloprid (IMI), 2,6-dichloroisonicotinic acid (INA), and salicylic acid (SA), applied individually by foliar spray, soil drench or trunk injection at various rates and frequencies, were evaluated for control of HLB in a 3-year field trial with mature Hamlin sweet orange trees in central Florida, USA in the 2016, 2017, and 2018 crop seasons. Six foliar sprays, six soil applications, and three trunk injections of ASM, IMI, INA, or SA per year were conducted with the untreated as a negative control. HLB disease severity, Las titers, pre-harvest fruit drop, yield and fruit quality were investigated for the treatments. By the end of the 2018 season, all trunk injection treatments at 0.25 g/tree and foliar sprays of INA or SA (but not ASM or IMI) at 0.5 g/tree significantly reduced disease severity, Las population, and fruit drop, and increased fruit yield; whereas all foliar spray treatments at 0.25 g/tree, trunk injection treatments at 0.125 g/tree, and soil drench treatments at 0.25 or 0.5 g/tree did not provide effective control of HLB. Additionally, all trunk injection treatments at 0.25 g/tree had shown a significant decrease in fruit drop and increase of fruit yield starting from 2016 after 1 year of applications, whereas foliar sprays of INA or SA at 0.5 g/tree exhibited similar effects at 2018 after 3 years of applications. None of the SAR inducer treatments had significant effect on fruit quality. Economic analysis suggested that the trunk injection treatments at 0.25 g/tree might produce financial benefits. Overall, this study presents useful information for management of citrus HLB with SAR inducers.

Recombinant Protein Foliar Application Activates Systemic Acquired Resistance and Increases Tolerance against Papaya Dieback Disease

Similar to animals, plants possess ‘immune memory’ in response to invading pathogens that lead to enhanced defense reaction following pathogen exposure. Systemic acquired resistance (SAR) is a well-characterized type of plant immunity and is associated with coordinated expression of a set of pathogenesis-related (PR) genes and proteins also known as SAR markers. Induction of SAR in plants was shown to be initiated by group of chemicals and biological compounds known as SAR inducers that can be used for the management of important plant diseases. Elucidation and characterization of potential SAR inducers as potential elicitors that can protect papaya from the papaya dieback disease pathogen were carried out using HRPX protein, which was produced as a recombinant protein in an Escherichia coli system. Disease severity analysis in a glasshouse experiment indicated lower disease infection rates in the HRPX-treated plants than in water-treated plants. Selected SAR-associated defense gene expression was also shown to increase in treated plants, via quantitative real-time PCR analysis, confirming enhanced disease response through SAR activation. In this report, the selected recombinant protein was shown to activate the SAR mechanism in papaya for increased tolerance against papaya dieback disease, which was proven via physiological and molecular analysis.