Elicitation Of Resistance Research Articles

Evaluation of lethal and sublethal effects of laminarin on the green peach aphid, Myzus persicae, under extended laboratory conditions

AbstractRecent studies have opened the way for using elicitor‐induced resistance in plants as a method to control arthropod pests. In this study, 1,3‐β‐glucan laminarin, an elicitor of disease resistance in plants, was tested on the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), on peach [Prunus persica (L.) Batsch, Rosaceae] plantlets and evaluated its effects on short‐term mortality and population growth. Laminarin exposure did not affect aphid survival in the short term; however, laminarin‐treated peach plants sustained fewer nymphs and adults in comparison with the control. Aphid populations on plants treated with laminarin declined significantly over the sampling period compared to the control. Moreover, the demographic parameters net reproductive rate (R0), finite rate of increase (λ), and intrinsic rate of increase (rm), all showed decreasing trends in aphid populations reared on laminarin‐treated plants. The decline in aphid populations exposed to laminarin seemed to mainly be linked to reduced adult survival, slower nymph development, and lower nymph survival and only marginally to changes in reproduction outcome. Changes in gene expression causing the final production of defence chemicals by peach plants may contribute to explaining the results. However, potential direct effects of laminarin on M. persicae feeding activity and probing behaviour cannot be ruled out. This study provides evidence that, although laminarin did not display insecticidal activity in the short term, this elicitor caused sublethal effects, significantly reducing aphid populations.

Use of Chemicals and Biological Control Agents as Activators of Plant Defense Against Endoparasitic Sedentary Nematodes.

Full compatible interactions between crop plants and endoparasitic sedentary nematodes (ESNs) lead to severe infestation of the roots and plant growth impairing, as well as to the increase of nematode population in the soil that is a threat for the next planting crop. In the absence of activators, basic plant defense is overcome by nematode secretion of effectorsthat suppress defense gene expression,inhibit ROS generation andtheoxidative burstused byplants to hamper nematode feeding site settlementandlimit its development and reproduction. Activators can be exogenously added as a preventive measure to prime plants and strengthen their defense against ESNs. Activators can be an array of antioxidant compounds or biocontrol agents, such as mutualist microorganisms living in the rhizosphere (biocontrol fungi (BCF), arbuscular mycorrhizal fungi (AMF), plant growth-promoting bacteria (PGPB), etc.). In this chapter, methods are described for usage of both salicylic acid (SA) and its methylated form (Met-SA), and BCF/AMF as elicitors of resistance of vegetable crops against root-knot nematodes (RKNs). The rhizosphere-living BCF/AMF were recovered from commercial formulates pre-incubated in suitable growth media and provided exclusively as soil drench of potted plants. The plant hormones SA and Met-SA were provided to plants as soil drench, foliar spray, and root dip. It is indicated that activators' dosages and plant age are crucial factors in determining the success of a pre-treatment to reduce nematode infection. Therefore, dosages should be expressed as amounts of activators per g of plant weight at treatment. Thresholds exist above which dosages start to work; overdoses were found to be toxic to plants and useless as activators.

Membrane Cascade Fractionation of Tomato Leaf Extracts-Towards Bio-Based Crop Protection.

Promising initial results from the use of membrane-fractionated extracts of tomato leaf as crop protection agents have recently been reported. This paper provides additional evidence from larger scale experiments that identify an efficient pipeline for the separation of tomato leaf extracts to generate a fraction with significant defence elicitor activity. A UF tubular membrane 150 kDa, with an internal diameter of 5 mm, proved appropriate for initial extract clarification, whereas afterwards a UF 10 kDa and three NF membranes (200-800 Da) in sequence were evaluated for the subsequent fractionation of this tomato extract. The compositions of sugars, proteins and total biophenols were changed in these fractions with respect to the initial extract. The initial extract ratio of sugars: proteins: biophenols was 1:0.047:0.052, whereas for the retentate of the 800 Da NF membrane, which has the higher crop protection activity, this ratio was 1:0.06:0.1. In this regard, it appears that the main crop protection effect in this fraction was due to the sugars isolated. It was found that with the appropriate membrane cascade selection (UF 150 kDa, UF 10 kDa and NF 800 Da) it was possible to produce (easily and without the need of additional chemicals) a fraction that has significant activity as an elicitor of disease resistance in tomato, whereas the remaining fractions could be used for other purposes in a biorefinery. This is very promising for the wider application of the proposed approach for the relatively easy formulation of bio-based aqueous streams with bio-pesticide activities.

Methyl salicylate and methyl jasmonate induce resistance to Alternaria tenuissima by regulating the phenylpropane metabolism pathway of winter jujube

The black rot disease of winter jujube causes considerable losses to the jujube industry in Xinjiang. Methyl salicylate (MeSA) and methyl jasmonate (MeJA) are elicitors of plant disease resistance; therefore, the inhibitory effects of 1 mmol/L MeSA and 0.1 mmol/L MeJA on the black rot disease of winter jujube caused by Alternaria tenuissima were investigated herein. Both MeSA and MeJA reduced the fruit decay index, and the effect of MeJA was superior. MeSA and MeJA enhanced the activities of enzymes related to phenylpropane metabolism and pathogenesis-related proteins, and the expression of their corresponding genes. MeSA and MeJA increased the accumulation of phenylpropane metabolites, containing the lignin, total phenol, and total flavonoid contents. These findings indicated that MeSA and MeJA may enhance the resistance of winter jujube to A. tenuissima by enhancing the phenylpropane metabolism pathway and the activity of pathogenesis-related proteins.

Bacillus lipopeptide-mediated biocontrol of peanut stem rot caused by Athelia rolfsii.

Peanut (Arachis hypogaea L.) is a widespread oilseed crop of high agricultural importance in tropical and subtropical areas. It plays a major role in the food supply in the Democratic Republic of Congo (DRC). However, one major constraint in the production of this plant is the stem rot (white mold or southern blight) disease caused by Athelia rolfsii which is so far controlled mainly using chemicals. Considering the harmful effect of chemical pesticides, the implementation of eco-friendly alternatives such as biological control is required for disease management in a more sustainable agriculture in the DRC as in the other developing countries concerned. Bacillus velezensis is among the rhizobacteria best described for its plant protective effect notably due to the production of a wide range of bioactive secondary metabolites. In this work, we wanted to evaluate the potential of B. velezensis strain GA1 at reducing A. rolfsii infection and to unravel the molecular basis of the protective effect. Upon growth under the nutritional conditions dictated by peanut root exudation, the bacterium efficiently produces the three types of lipopeptides surfactin, iturin and fengycin known for their antagonistic activities against a wide range of fungal phytopathogens. By testing a range of GA1 mutants specifically repressed in the production of those metabolites, we point out an important role for iturin and another unidentified compound in the antagonistic activity against the pathogen. Biocontrol experiments performed in greenhouse further revealed the efficacy of B. velezensis to reduce peanut disease caused by A. rolfsii both via direct antagonism against the fungus and by stimulating systemic resistance in the host plant. As treatment with pure surfactin yielded a similar level of protection, we postulate that this lipopeptide acts as main elicitor of peanut resistance against A. rolfsii infection.

Formulation-based antagonistic endophyte Amycolatopsis sp. SND-1 triggers defense response in Vigna radiata (L.) R. Wilczek. (Mung bean) against Cercospora leaf spot disease.

In the present work, Amycolatopsissp. SND-1 (SND-1) was isolated fromCleome chellidoniiLinn. (C. chellidonii) was performed as biocontrol and resistance elicitor inVigna radiata(L.) R. Wilczek (mung bean) plants against Cercospora leaf spot causing pathogenCercospora canescens(C.canescens). The SND-1 isolate showed 74% of inhibition againstC. canescensin dual culture and GC-MS analysis revealed the presence of antifungal compounds. Molecular characterization through 16S rRNA showed that the isolated SND-1 belongs to Amycolatopsis sp. Thein vitroplant growth trials exhibited production of indole acetic acid, gibberellic acid, cytokinin, ammonia, hydrogen cyanide, and siderophore and phosphate solubilization. In vivostudy with talcum formulation of SND-1 revealed a significant increase in plant root length, shoots length, root and shoot fresh weight, and reduced the disease severity in treated mung bean plants. Triggering of resistance by SND-1 formulation was studied by histochemical depositions and biochemical defense enzymes that resulted in the acceleration in defense response in comparison with control plants. The bioactive endophyticAmycolatopsissp. SND-1 enhanced the defense againstC. canescensinfection; hence, it can be used as a biological control agent in mung bean cultivars.

Antifungal mechanisms of γ-aminobutyric acid against the postharvest pathogen Alternaria alternata

γ-Aminobutyric acid (GABA) is a plant resistance elicitor essential in preventing and controlling postharvest disease in fruits and vegetables. However, limited information is available involving the inhibitory effect of exogenous GABA on postharvest pathogens. This study found that GABA inhibited the postharvest pathogenic fungus, Alternaria alternata (A. alternata). Transcriptome analysis revealed that the genes related to sporulation, toxin synthesis, and cell wall degradation enzymes are downregulated in A. alternata after GABA treatment. Moreover, the effect of GABA on A. alternata was verified using electron microscopy and by determining the activity of the cell wall degradation enzyme. These findings provided information about the underlying antifungal mechanism about GABA against A. alternata and suggested that GABA could be a potential alternative for controlling A. alternata in fruit and vegetable preservation.

Role of Some Essential Plant Oils, Fungicides and Inducer Resistance Elicitors on The Management of Cucumber Downy Mildew

Role of Some Essential Plant Oils, Fungicides and Inducer Resistance Elicitors on The Management of Cucumber Downy Mildew

Chitin-induced systemic disease resistance in rice requires both OsCERK1 and OsCEBiP and is mediated via perturbation of cell-wall biogenesis in leaves.

Chitin is a well-known elicitor of disease resistance and its recognition by plants is crucial to perceive fungal infections. Chitin can induce both a local immune response and a systemic disease resistance when provided as a supplement in soils. Unlike local immune responses, it is poorly explored how chitin-induced systemic disease resistance is developed. In this study, we report the systemic induction of disease resistance against the fungal pathogen Bipolaris oryzae by chitin supplementation of soils in rice. The transcriptome analysis uncovered genes related to cell-wall biogenesis, cytokinin signaling, regulation of phosphorylation, and defence priming in the development of chitin-induced systemic response. Alterations of cell-wall composition were observed in leaves of rice plants grown in chitin-supplemented soils, and the disease resistance against B. oryzae was increased in rice leaves treated with a cellulose biosynthesis inhibitor. The disruption of genes for lysin motif (LysM)-containing chitin receptors, OsCERK1 (Chitin elicitor receptor kinase 1) and OsCEBiP (Chitin elicitor-binding protein), compromised chitin-induced systemic disease resistance against B. oryzae and differential expression of chitin-induced genes found in wild-type rice plants. These findings suggest that chitin-induced systemic disease resistance in rice is caused by a perturbation of cell-wall biogenesis in leaves through long-distance signalling after local recognition of chitins by OsCERK1 and OsCEBiP.

Mechanisms and technology of marine oligosaccharides to control postharvest disease of fruits

Fruit and vegetable postharvest diseases wreak havoc on food supply and the market economy. Meanwhile, the frequent use of synthetic fungicides poses a threat to the environment and public health. Marine oligosaccharides can act as an elicitor of postharvest disease resistance in fruits and also show broad-spectrum antimicrobial activity. Therefore, this review focuses on the mechanism and technology of marine oligosaccharides for postharvest disease control and compares them to horticulture studies to highlight the limitations of existing research and the prospects for future study. It is critical to developing marine oligosaccharides-based products for postharvest disease control.

Organic matter in the pest and plant disease control: a meta-analysis

BackgroundPesticides have become a central public health problem and a source of environmental contamination. The use of organic matter is an important strategy to reduce synthetic agrochemicals, improve soil conditions, and increase nutrient uptake by plants. Organic matter can also induce plant resistance against biotic stress in some circumstances. However, the results reported for different types of organic matter applications are often very different form each other, thus making difficult their interpretation and hindering and discouraging their use as valuable alternative. Identifying the main factors involved in the efficacy of these sustainable methodologies and the associated research gaps is important to increase the efficiency of organic matter and reduce the use of pesticides.Materials and methodsWe performed a comprehensive meta-analysis of the current recent scientific literature on the use of organic matter as control method for pest and disease, using data reduction techniques, such as principal component analysis. We found 695 articles listing the keywords in the databases between 2010 and 2021 and selected 42 that met inclusion criteria.ResultsIn general, all organic matter reported showed a high inhibition of pests and diseases. Control effectiveness was close to 75% for fungal diseases and 67% for the pest control. The source of organic matter most frequently reported was the vermicompost. However, humic substances showed the greatest effectiveness of 74% when compared to both fungal and bacterial disease control. The concentration of humic substances ranged from 1 to 500 mg L−1, with the highest concentrations used in case of soil application.ConclusionsThe study demonstrated the potential role of organic matter as a resistance elicitor in plants, thus allowing a partial/total reduction of pesticides in crops. Despite the efficiency reported in the works, the mechanisms of induction of pest and disease control remains poorly studied.Graphical

(1→3)-α-D-glucooligosaccharides as Elicitors Influencing the Activity of Plant Resistance Pathways in Wheat Tissues

Laetiporus sulphureus (Bull.: Fr.) Murrill is an arboreal species of the large-fruited Basidiomycota fungus from the Polyporales, family Laetiporaceae. The cell wall of this fungus is the source of many bioactive polymer compounds, including (1→3)-α-D-glucans. (1→3)-α-D-glucans can be hydrolyzed to shorter compounds, (1→3)-α-D-glucooligosaccharides (GOS), with different degrees of polymerization (DP). The use of GOS obtained from L. sulphureus (1→3)-α-D-glucans, as an elicitor of plant resistance, may be important for biological protection used in sustainable agriculture. In the presented study, GOS influenced the activity of antioxidant enzymes (Catalase−CAT, Ascorbate Peroxidase−APX, Guaiacol Peroxidase−GPX, and Superoxide Dismutase−SOD), lignin and flavonoids producing phenylpropanoids pathways (Phenylalanine Ammonia-Lyase−PAL and Tyrosine Ammonia-Lyase−TAL), and pathogen-related proteins (with Glucanase−GLUC and Chitinase−CHIT activity) in wheat (Triticum aestivum L.) seedling tissues. Other than that, the application of GOS increased the fresh weight of wheat stems and roots by 1.5–2-times, compared to the water control. The GOS at a concentration of 0.05% most strongly increased the activity of APX and GPX, where a 2-fold (up to 6000 U) and a 3-fold (up to 180 U) increase in enzymatic activity in wheat stems was observed, compared to the control. Simultaneously, 0.1% GOS significantly increased the activity of PAL (80 U in stems and 50 U in roots) and TAL (60 U in stems and 50 U in roots), where a 4–5-fold increase in enzymatic activity was observed, both in comparison to the water control and commercial elicitors (chitosan−CHI and laminarin−LAM). No effect of GOS on GLUC activity was observed, but a 1.5–2-fold increase in CHIT activity in plant tissues was noted. The complexity of the influence of GOS on the level of marker enzymes indicates the potential of their application in agriculture. This work is the first report of the successful use of (1→3)-α-D-glucooligosaccharides as an elicitor inducing resistance in the cereal plant (wheat).

Immunity elicitors for induced resistance against the downy mildew pathogen in pearl millet

Pearl millet (Pennisetum glaucum (L.) R. Br.) is a globally important cereal whose production is severely constrained by downy mildew caused by Sclerospora graminicola (Sacc.). In this study, immunity eliciting properties of 3,5-dichloroanthranilic acid (DCA), Cell Wall Glucan (CWG), Lipopolysaccharide (LPS), and Glycinebetaine (GB) was deciphered through enzymatic and protein studies based on elicitor treatment activated defense mechanisms. Glycinebetaine, LPS, CWS and DCA elicited enzyme activities and gene expression of the defense enzymes, such as β-1,3-glucanase, phenylalanine ammonia lyase (PAL), peroxidase (POX), polyphenol oxidase (PPO), lipoxygenase (LOX) and defense protein hydroxyproline-rich glycoproteins (HRGPs). However, the speed and the extent of elicitation differed. High levels of enzyme activities and gene expression in elicitor-treated P. glaucum positively correlated with the increased downy mildew resistance. A very rapid and large changes in elicitor-treated seedlings, in contrast to the delayed, smaller changes in the untreated susceptible control seedlings suggests that the rate and magnitude of defense gene expression are important for effective manifestation of defense against pathogen. As compared to other elicitors and control, GB promoted increase in enzyme activities and gene expression, implicating that GB is a promising elicitor of downy mildew resistance in P. glaucum.

Extracellular DNA as an elicitor of broad-spectrum resistance in Arabidopsis thaliana

Like in mammals, the plant immune system has evolved to perceive damage. Damaged-associated molecular patterns (DAMPs) are endogenous signals generated in wounded or infected tissue after pathogen or insect attack. Although extracellular DNA (eDNA) is a DAMP signal that induces immune responses, plant responses after eDNA perception remain largely unknown. Here, we report that signaling defenses but not direct defense responses are induced after eDNA applications enhancing broad-range plant protection. A screening of defense signaling and hormone biosynthesis marker genes revealed that OXI1, CML37 and MPK3 are relevant eDNA-Induced Resistance markers (eDNA-IR). Additionally, we observed that eDNA from several Arabidopsis ecotypes and other phylogenetically distant plants such as citrus, bean and, more surprisingly, a monocotyledonous plant such as maize upregulates eDNA-IR marker genes. Using 3,3′-Diaminobenzidine (DAB) and aniline blue staining methods, we observed that H2O2 but not callose was strongly accumulated following self-eDNA treatments. Finally, eDNA resulted in effective induced resistance in Arabidopsis against the pathogens Hyaloperonospora arabidopsidis, Pseudomonas syringae, and Botrytis cinerea and against aphid infestation, reducing the number of nymphs and moving forms. Hence, the unspecificity of DNA origin and the wide range of insects to which eDNA can protect opens many questions about the mechanisms behind eDNA-IR.

Actividad peroxidasa y concentración de proteínas en Phaseolus vulgaris l. tratado con preparaciones homeopáticas

The objective of this work was to evaluate peroxidase activity and protein concentration in the defence system expression of common bean Phaseolus vulgaris L., submitted to different potencies of homeopathic preparations. The treatments were composed by: Arsenicum album, Staphisagria, Silicea and Sulphur, in the 6, 12 and 18 CH potencies, compared to the controls. The bean seeds were sown in pots which were kept in a greenhouse and the treatments were applied to them at 1% in distilled water since the sowing day, with intervals of 15 days until the R7 stage. The first evaluation was performed at 15 e 60 days after sowing, after artificial mechanical damage. Protein concentration and the activity of guaiacol peroxidase (POD) and ascorbate peroxidase (APX) enzymes were determined. Differences between treatments and controls were estimated by Glass Delta effect size analysis. Staphisagria 12CH induced greater increase in protein concentration on bean leaves. The Induction on APX and POD activities were observed in leaves treated with Sulphur in all tested potencies. The Glass Delta effect showed undulatory behaviour, sometimes acting positively, sometimes negatively, throughout all evaluations. Homeopathic preparations have the potential to induce biochemical defence mechanisms in beans, acting as resistance elicitors.

Impact of Application of Abscisic Acid, Benzothiadiazole and Chitosan on Berry Quality Characteristics and Plant Associated Microbial Communities of Vitis vinifera L var. Mouhtaro Plants

The phenolic profile of the grape berries is a key quality factor for the red grapevine varieties and several techniques have been applied to improve it. An innovative technique is the application of resistance elicitors and phytohormones. In the present study, leaves and berries of a Greek red indigenous variety (Mouhtaro) sprayed with two elicitors, benzothiadiazole and chitosan and a plant hormone abscisic acid, during veraison. Physicochemical and phenolic characteristics of the berries and microbial communities of rhizosphere, phyllosphere and carposphere were analyzed at harvest. Differences in the microbial communities on different plant compartments were observed after the application of the plant activators. Chitosan treatment increased the abundance of the beneficial lactic acid bacteria, while the abscisic acid treatment decreased the presence of spoilage fungi on the carposphere. Treatments differentiate total phenolics, anthocyanins and in the chemical characteristics of grape must with chitosan treated grapes had increased anthocyanins and skin-derived phenolics that correlated positively with the microbial taxa that was discriminant by LefSe analysis. This research provides an overview of the effect of plant activators on the microbial ecology and grape quality of the Greek variety Mouhtaro and presents the potential of new and innovative approaches in the field of sustainable viticulture.

BTH Treatment Delays the Senescence of Postharvest Pitaya Fruit in Relation to Enhancing Antioxidant System and Phenylpropanoid Pathway.

The plant resistance elicitor Benzo (1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) can enhance disease resistance of harvested fruit. Nonetheless, it is still unknown whether BTH plays a role in regulating fruit senescence. In this study, exogenous BTH treatment efficiently delayed the senescence of postharvest pitaya fruit with lower lipid peroxidation level. Furthermore, BTH-treated fruit exhibited lower hydrogen peroxide (H2O2) content, higher contents of reduced ascorbic acid (AsA) and reduced glutathione (GSH) levels and higher ratios of reduced to oxidized glutathione (GSH/GSSG) and ascorbic acid (AsA/DHA), as well as higher activities of ROS scavenging enzymes, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD) and glutathione reductase (GR) in comparison with control fruit. Moreover, BTH treatment enhanced the activities of phenylpropanoid pathway-related enzymes, including cinnamate-4-hydroxylase (C4H), phenylalanine ammonia-lyase (PAL) and 4-coumarate/coenzyme A ligase (4CL) and the levels of phenolics, flavonoids and lignin. In addition, BTH treatment upregulated the expression of HuSOD1/3/4, HuCAT2, HuAPX1/2 and HuPOD1/2/4 genes. These results suggested that application of BTH delayed the senescence of harvested pitaya fruit in relation to enhanced antioxidant system and phenylpropanoid pathway.

Expresión de genes antioxidantes y contenido de clorofila y almidón en árboles de limón Persa (Citrus latifolia Tanaka Ex Q. Jiménez) con HLB bajo la aplicación de elicitores de resistencia

Persian lime is economically important for Mexico. However, the disease known as Huanglongbing (HLB) causes chlorosis symptoms in the foliage that affect the growth and decreases the yield of the trees. The expression of chlorosis symptoms is associated with starch accumulation and inhibition of antioxidant activity. The objective of the present work was to determine the effect of the application of three resistance elicitors on the expression of three antioxidant genes and on starch and chlorophyll content in Persian lime trees with HLB. Salicylic acid (SA), jasmonic acid (JA) or gamma-aminobutyric acid (GABA) were applied every eight days for nine weeks using a completely randomized design and a one-way ANOVA was performed for the analysis. Expression of APX, CAT and SOD genes was quantified at week nine at four different times. Starch and total chlorophyll content was estimated every three weeks by spectrophotometric methods. The application of the elicitors significantly increased the expression of the three genes, with SA and GABA generating the greatest increase at different times of application. No difference was found in starch and total chlorophyll content at most of the times evaluated. The use of resistance elicitors is promising in the management of HLB in plots already infected, seeking to extend the productive life of the orchards and thus counteract the economic losses caused by HLB.

Biochemical basis of systemic acquired resistance induced by different Systemic Acquired Resistance (SAR) elicitors in Brassica cultivars challenge inoculated with downy mildew pathogen

In India, Brassica is attacked by many bacterial, fungal and viral pathogens causing various diseases among which, downy mildew caused by Hyaloperonospora brassicae, an oomycete is the most severe one. The present investigation was conducted to reduce fungicide load on Brassica by testing an alternate method of disease control. Different Systemic Acquired Resistance (SAR) compounds were tested as foliar sprays like Salicylic acid, Jasmonic acid and Bion (Benzothiadiazole-BTH) for inducing resistance in different genotypes of Raya (Brassica juncea) against downy mildew pathogen. Protein content in plants ranged between 43.5 to 57.7 mg/g fresh weight compared to 37.2 mg/g fresh weight in control. Induction of proteins and defense related enzymes was systemic in nature. The SAR compounds also surged the levels of defense related proteins, i.e. Polyphenol oxidase (PPO), Phenylalanine ammonia lyase (PAL) and pathogenesis related Pr- proteins i.e. ?-1,3 glucanase, Peroxidase (POD), from 21 to 130 per cent indicating induction of resistance. Protein profiling of treated Brassica plants was also done electrophoreticaly, which further confirmed the induction of pathogenesis-related proteins ranging from 15- 75 kDa along with some other proteins. Salicylic acid @ 500µM showed best results with 71.27 per cent disease control followed by Jasmonic acid with 69.6 per cent; whereas both, Bion and ?eta amino butyric acid gave almost 63 per cent disease control as compared to control plants. Integration of disease tolerance in Brassica varieties/genotypes combined with prophylactic spray of salicylic acid proved to be very economical for managing downy mildew disease.

Comparative Effectiveness of Potential Elicitors of Soybean Plant Resistance Against Spodoptera Littoralis and Their Effects on Secondary Metabolites and Antioxidant Defense System

Cotton leaf worm (Spodoptera littoralis) is considered one of the most destructive agricultural pests in Egypt. It is overcome by the producer by using chemical pesticides, but that leads to the appearance of new generations and causes environmental pollution. So in the present investigation six soybean genotypes (Giza-82, Giza 22, Giza 83, Giza 21, Giza 35 and Giza 111) were planted under natural infection with cotton leaf worm. The effect of two elicitors, methyl jasmonate (20 µM MeJA) and sodium nitroprusside (500 µM SNP) on the six soybean genotypes was studied to enhance the ability of the susceptible genotypes to resist cotton leaf worm. Results showed that Giza 35 and Giza 111 showed tolerance performance under natural infection compared to Giza 22 and Giza 82 as sensitive ones, while Giza 83 and Giza 21 showed moderate tolerance. Treatments with MeJA and SNP positively affected contents of secondary metabolites (phenol, flavonoid and tannin), non-enzymatic antioxidants (anthocyanin, tocopherol and ascorbic acid) and enzymatic antioxidants (catalase, peroxidase, polyphenol oxidase and Guaiacol peroxidase) in shoots of all soybean genotypes. Treatment with MeJA was found to be more effective than SNP and enhanced the resistance of the susceptible genotypes. In conclusion, treatment of soybean plants with MeJA and SNP would be effective enhancing the ability of these plants to resists cotton leaf worm infection and increased secondary metabolites and antioxidants responsible for plant defense.