Mycorrhizal colonization and Streptomyces viridosporus HH1 synergistically up-regulate the polyphenol biosynthesis genes in wheat against stripe rust.

BACKGROUND: Stripe rust is considered one of the most devastating diseases of wheat all over the world, resulting in a high loss in its production. In this study, time-course changes in expression of the polyphenol biosynthesis pathways genes in wheat against stripe rust were investigated. The defense mechanisms triggered by mycorrhizal colonization and/or spraying with Streptomyces viridosporus HH1 against this disease were also investigated. RESULTS: Results obtained revealed that C3H, which is considered the key gene in lignin biosynthesis, was the most expressed gene. Furthermore, most of the chlorogenic acid and flavonoid biosynthesis genes were also overexpressed. Volcano plots of the studied genes reveal that the dual treatment led to a high significant overexpression of 10 out of the 13 studied genes. Heatmap of these genes showed that the most frequent expressed gene in response to all applied treatments along the study period was DFR, the key gene in the biosynthesis of anthocyanidins. Gene co-expression network of the studied genes showed that HQT was the most central gene with respect to the other genes, followed by AN2 and DFR, respectively. Accumulation of different flavonoids and phenolic acids were detected in response to the dual treatment, in particular, cinnamic acid, coumarin, and esculetin, which recorded the highest elevation level recording 1000, 488.23, and 329.5% respectively. Furthermore, results from the greenhouse experiment showed that application of the dual treatment led to an 82.8% reduction in the disease severity, compared with the control treatment. CONCLUSIONS: We can conclude that the biosynthesis of lignin, chlorogenic acid, and flavonoids contributed to the synergistic triggering effect of the dual treatment on wheat resistance to stripe rust.

Biocontrol potential of the endophytic Epicoccum nigrum HE20 against stripe rust of wheat.

Biological control using endophytic microorganisms represents an eco-friendly and effective alternative to the health-hazardous chemical fungicides used to control devastating plant diseases such as stripe rust in wheat. In this study, the inhibitory potential of the endophytic Epicoccum nigrum HE20, isolated from a healthy wheat plant, was screened against uredospores germination in vitro. A high suppression (96%) in the germination of the uredospores was recorded. GC-MS analysis of the culture filtrate of E. nigrum HE20 showed a production of various secondary metabolites with an antifungal background such as butyric acid, α-linolenic acid, hexanoic acid, lactic acid, 10,12-Tricosadiynoic acid, and pentadecanoic acid. Results from the greenhouse experiment revealed that the application of E. nigrum HE20 suspension led to a reduction in the disease severity by 87.5%, compared with the untreated-infected plants. Real-time PCR results exhibited an overexpression in three defensive genes (JERF3, GLU, and PR1) in the infected wheat plants, in response to the application of E. nigrum HE20, recorded 8-, 15.8-, and 3.5-fold, respectively. In addition, an increment in the phenolic content, activity of POD, PPO, and CAT, and a reduction in the lipid peroxidation were recorded due to the endophyte application. Transmission electron microscopic observations indicated mitigation of the pathogen in wheat cells after the treatment with E. nigrum HE20 metabolite. Furthermore, a growth-promoting effect was also observed due to E. nigrum HE20 application, as well as an increment in the total photosynthetic pigments in wheat leaves. Based on these results, it can be concluded that E. nigrum HE20 is a probable efficient bioagent against stripe rust in wheat. However, its field evaluation is highly necessary in the future studies.

Synergism between Streptomyces viridosporus HH1 and Rhizophagus irregularis Effectively Induces Defense Responses to Fusarium Wilt of Pea and Improves Plant Growth and Yield.

Fusarium wilt is a detrimental disease of pea crop, resulting in severe damage and a reduction in its yield. Developing synergistically enhanced bioagents for disease management and growth promotion is pivotal for food safety, security, and sustainability. In this study, biocontrol potential of treating pea plants with Streptomycesviridosporus HH1 and/or their colonization with Rhizophagusirregularis against infection with Fusarium wilt was investigated. Impacts on the expression profiles of defense-related genes, biochemical, and ultrastructural levels, as well as the growth and yield of pea plants in response to these treatments, were also investigated. Data obtained indicated the antifungal activity of S. viridosporus HH1 against F. oxysporum f.sp. pisi in vitro. Furthermore, the GC-MS analysis revealed production of different bioactive compounds by S. viridosporus HH1, including 2,3-butanediol, thioglycolic acid, and phthalic acid. The results from the greenhouse experiment exhibited a synergistic biocontrol activity, resulting in a 77% reduction in disease severity in pea plants treated with S. viridosporus HH1 and colonized with R. irregularis. In this regard, this dual treatment overexpressed the responsive factor JERF3 (5.6-fold) and the defense-related genes ß-1,3-glucanase (8.2-fold) and the pathogenesis-related protein 1 (14.5-fold), enhanced the total phenolic content (99.5%), induced the antioxidant activity of peroxidase (64.3%) and polyphenol oxidase (31.6%) enzymes in pea plants, reduced the antioxidant stress, and improved their hypersensitivity at the ultrastructural level in response to the Fusarium wilt pathogen. Moreover, a synergistic growth-promoting effect was also recorded in pea plants in response to this dual treatment. In this regard, due to this dual treatment, elevated levels of photosynthetic pigments and improved growth parameters were observed in pea leaves, leading to an increment in the yield (113%). In addition, application of S. viridosporus enhanced the colonization levels with R. irregularis in pea roots. Based on the obtained data, we can conclude that treating pea plants with S. viridosporus HH1 and colonization with R. irregularis have synergistic biocontrol activity and growth-promoting effects on pea plants against Fusarium wilt. Despite its eco-safety and effectiveness, a field evaluation of this treatment before a use recommendation is quite necessary.

Magnesium carbonate elicits defense-related genes in King Ruby grapevines against downy mildew and improves its growth, yield, and berries quality.

Downy mildew, caused by Plasmopara viticola (Berk. and M. A. Curtis) Berl. and De Toni, is a serious disease of grapevines in general and King Ruby seedless cultivar in particular, affecting their growth and yield. Magnesium carbonate (MgCO3) is an antitranspirant, which induces stomatal closing and enhances plant growth and physiology. In this study, effect of foliar application of MgCO3 at 1 and 3% on plant resistance, growth, yield and physiology of grapevines (cv. King Ruby seedless) infected with downy mildew was investigated under field conditions. The obtained results showed that foliar application of MgCO3 at 3% led to upregulation of the transcription factor JERF3 (9.6-fold), and the defense-related genes GLU (6.3-fold), POD (8.7-fold), PR1 (9.6-fold), and CHI II (8.6-fold). In addition, this treatment led to a reduction in the disease severity (78%), and an increment in the yield per grapevine (20%). Furthermore, biochemical properties of berries, total contents of the photosynthetic pigments, phenolic compounds, and activities of the antioxidant enzymes peroxidase and polyphenol oxidase also enhanced. In contrast, lipid peroxidation, and H2O2 content in grapevines leaves reduced in response to MgCO3 spraying. Light microscope observations revealed that average number of closed stomata increased and the average stomatal pore area decreased in grapevines leaves as a result to MgCO3 spraying. Based on these results, we can conclude that spraying with MgCO3 at 3% has effective roles in inducing the plant resistance against downy mildew, and improving the growth and yield of grapevines.

Ascophyllum nodosum Extract and Mycorrhizal Colonization Synergistically Trigger Immune Responses in Pea Plants against Rhizoctonia Root Rot, and Enhance Plant Growth and Productivity.

Rhizoctonia root rot is one of the most destructive diseases affecting pea crops, resulting in up to 75% loss. In this study, the biocontrol activity of seaweed (Ascophyllum nodosum) extract at 1, 2, and 3% and/or mycorrhization of pea roots was investigated against Rhizoctonia root rot under greenhouse conditions. In addition, their effects on the transcriptional, physiological, ultrastructural, and growth status of pea plants were also studied. The results showed that the mycorrhizal colonization of pea roots and the application of the seaweed extract at 3% synergistically overexpressed the responsive factor (JERF3) recording 18.2-fold, and the defense-related genes peroxidase (23.2-fold) and chitinase II (31.8-fold). In addition, this treatment improved the activity of the antioxidant enzymes POD and PPO, increased the phenolic content in pea roots, and triggered multiple hypersensitivity reactions at the ultrastructural level of the cell, leading to a 73.1% reduction in disease severity. Moreover, a synergistic growth-promoting effect on pea plants was also observed. The photosynthetic pigments in pea leaves were enhanced in response to this dual treatment, which significantly improved their yield (24 g/plant). The inducing effect of mycorrhizal colonization on plant resistance and growth has been extensively studied. However, developing improved and synergistically acting biological agents for plant disease control and growth promotion as alternatives to the chemical fungicides is crucial for safety and food security. Based on these results, it can be concluded that the mycorrhizal colonization of pea roots and soaking their seeds in the A. nodosum extract at 3% have a promising and improved biocontrol activity against R. solani, and a growth-promoting effect on pea plants. However, field applications should be evaluated prior to any use recommendations.

Silica Nanoparticles as a Probable Anti-Oomycete Compound Against Downy Mildew, and Yield and Quality Enhancer in Grapevines: Field Evaluation, Molecular, Physiological, Ultrastructural, and Toxicity Investigations.

Downy mildew is the most destructive disease of grapevines in the regions of relatively warm and humid climate causing up to 50% yield losses. Application of silicon- (Si-) based products have been extensively studied against various oomycete, fungal, bacterial, and viral plant diseases, but studies on Si application in their nanosize are limited. In this study, the field application of silica nanoparticles (SiNPs) on Thompson Seedless grapevines (H4 strain) infected with downy mildew was evaluated. In addition, molecular, physiological, ultrastructural, and toxicity investigations were also conducted. The obtained results revealed that spraying of grapevines with SiNPs at 150 ppm significantly overexpressed the transcription factor jasmonate and ethylene-responsive factor 3 recording 8.7-fold, and the defense-related genes ß-1,3-glucanase (11-fold), peroxidase (10.7-fold) pathogenesis-related-protein 1 (10.6-fold), and chitinase (6.5-fold). Moreover, a reduction up to 81.5% in the disease severity was achieved in response to this treatment. Shoot length and yield per grapevine were considerably enhanced recording up to 26.3 and 23.7% increase, respectively. The berries quality was also improved. Furthermore, this treatment led to an enhancement in the photosynthetic pigments, induction of phenolic and ascorbic acid contents, an increase in the activity of peroxidase and polyphenol oxidase enzymes, and a reduction in the cellular electrolyte leakage, lipid peroxidation, and H2O2 content. Scanning electron microscopy observations showed an increase up to 86.6% in the number of closed stomata and a reduction up to 55% in the average stomatal pore area in response to this treatment. Observations of the transmission electron microscopy showed ultrastructural alterations in the cells of a grapevine leaf due to the infection with downy mildew, including plasmolysis and disruption of the cellular components, abnormal chloroplasts, and thickening of the cell wall and cell membrane. These abnormal alterations were reduced in response to SiNPs spray. In contrast, this study also showed that this treatment had considerable cytotoxic and genotoxic effects at this direct dose/concentration. So, additional investigations to determine the SiNPs residue in the produced edible plant parts are urgently needed. In addition, the pre-harvest interval, toxicity index, and risk assessment should be evaluated before any recommendation for use.

Synergistic effect of growth-promoting microorganisms on bio-control of Fusarium oxysporum f. sp. pisi, growth, yield, physiological and anatomical characteristics of pea plants.

Fusarium root rot caused by Fusarium oxysporum is an aggressive disease-causing damping-off, root rot, and vascular wilt in all peas growing fields. The disease can cause 100% yield losses under favorable conditions. The present study aims to control Fusarium root rot using Trichoderma harzianum, Pseudomonas fluorescens, and arbuscular mycorrhizal fungi, singly or in combinations. The results showed that all treatments significantly enhanced not only the plant growth, total phenol, activities of antioxidant enzymes, but also, the yield and seed quality. Several changes in the anatomical, physiological, and characteristics of the treated plants were also recorded. Compared to the untreated control treatment, under greenhouse conditions, the maximum reduction of the disease severity (80%) was achieved by the synergistic triple treatment consists of arbuscular mycorrhizal fungi, Trichoderma harzianum, and Pseudomonas fluorescens, as they gave the best growth and yield parameters. The same combination showed the highest activity of the antioxidant enzyme peroxidase (57.1%), as well as the highest total phenol content (117.7%), over the control. The synergistic triple increased the contents of protein (64.6%), total soluble sugars (48.5%), and total carbohydrate (24.8%) in seeds of pea compared with the control. The synergistic triple treatment led to an increase in the thickness of the root section (25%), the thickness of the cortex (24.8%), the thickness of the vascular cylinder (31.5%), and the diameter of the xylem vessels (81.5%) of the root. Based on their efficiency and eco-safety, this synergistic triple might be very effective for controlling root rot disease of pea caused by F. oxysporum, as well as improve the growth, yield, and seed quality.