Role of silicon in elevating resistance against sheath blight and blast diseases in rice (Oryza sativa L.)

Dual stimuli-responsive prodrug co-delivery nanosystem of salicylic acid and bioavailable silicon for long-term immunity in plant

Plant-induced resistance plays a crucial role in the plant defense system by activating intrinsic immune mechanisms. In this study, a novel amidase- and redox-responsive codelivery nanosystem was developed by covalently linking salicylic acid (SA) to functionalized disulfide-doped mesoporous silica nanoparticles (MSNs-ss-NH2) for the efficient delivery of SA and bioavailable silicon concurrently. Physicochemical characterization confirmed the successful preparation of MSNs-ss-SA, demonstrating its structural integrity and glutathione and amidase responsive degradation mechanism. With a particle size of approximately 90 nm, MSNs-ss-SA could penetrate the stomata of rice leaves, facilitating the efficient intracellular transport of SA and bioavailable silicon. Biological activity assays revealed that MSNs-ss-SA exhibited superior efficacy in inducing resistance to rice sheath blight compared to conventional SA, which was primarily due to its ability to enhance physical barrier formation, strengthen antioxidant defense systems, upregulate the expression of key defense-related genes, and increase chitinase synthesis, collectively triggering both systemic acquired resistance and induced systemic resistance. Most importantly, biological safety assessments confirmed its excellent compatibility with rice plants, aquatic organisms, soil ecosystems, and human cell models. Therefore, the prodrug system of SA and bioavailable silicon shows a significant potential for sustainable agricultural plant disease management.

Discovery of α-Methylene-γ-Butyrolactone Derivatives with Hydrazide Moieties as Novel Fungicidal Agents

To discover novel fungicides with unique structures, a series of α-methylene-γ-butyrolactone derivatives were designed and synthesized by incorporating a flexible amide or hydrazide chain through active substructure splicing and linker modification strategies. Bioassay assessments demonstrated that certain hydrazide-containing compounds have potent fungicidal efficacy. Notably, compound 7IIj exhibited broad-spectrum antifungal activity, with EC50 values as low as 0.179, 0.301, 0.647, 0.549, and 0.789 mg/L against Rhizoctonia solani, Physalospora piricola, Botrytis cinerea, Gaeumanomyces graminis, and Valsa mali, respectively. In vivo experiments confirmed the effective fungicidal activity of compound 7IIj, showing an inhibitory rate of 69.7% against V. mali on apple twigs at 200 mg/L. Additionally, at a concentration of 100 mg/L, compound 7IIj demonstrated significant protective and curative effects against R. solani on rice plants. Research on the mechanism of action revealed that compound 7IIj could disrupt hyphal morphology, induce reactive oxygen species (ROS) accumulation, affect mitochondrial membrane potential (MMP), and interfere with respiratory metabolism by binding to complex II. Molecular docking analysis showed significant interactions of compound 7IIj with TRP 173, TYR 58, and ARG 43 in the succinate dehydrogenase (SDH) binding site, resembling the binding mode of fluxapyroxad. These findings suggest that compound 7IIj holds potential as an SDH inhibitor for agricultural disease control.

Bio-efficacy of Nanosilicon in Regulating Oxidative Activity to Control Rice Seedlings Rot Disease Caused by Burkholderia glumae

Bacterial panicle blight and seedling rot diseases in rice plants (Oryza sativa L.) are caused by the pathogenic bacterial Burkholderia glumae. The nanosilicon treatment is gaining attraction but its effectiveness towards B. glumae infection in rice seedlings through regulating enzymatic activities remains largely unexplored. This study aimed to evaluate the bio-efficacy of nanosilicon in controlling seedling rot disease through regulation of peroxidase and polyphenol oxidase enzymes after challenge infected with B. glumae in rice variety MR297 and PadiU Putra. Nanosilicon was applied as seed priming in germination testing at 0, 300, 600, and 900 ppm on both rice varieties before B. glumae inoculation. Both rice seed varieties primed with nanosilicon at 600 ppm exhibited a significant increase in seedling germination performances over control. The rice seedling of MR297 was more responsive to nanosilicon at 600 ppm with only 17.78% of disease severity index over 26.67% in PadiU Putra and was therefore selected for the enzymatic activity screening. The results showed that the foliar spray of nanosilicon rice plants (MR297) significantly increased both peroxidase (POX) at 24 h and polyphenol oxidase (PPO) at 48 h after B. glumae inoculation with 20.44/min/g and 7.46/g activities, respectively. In addition, the plant growth performances were significantly increased compared with control under the same treatment. This demonstrates nanosilicon's potential to control rice seedling rot disease by regulating POX and PPO activities and hence promote plant growth. The application of nanosilicon is an environmentally friendly approach for controlling B. glumae infection at the early rice growing stage.

Silicon uptake and transport mechanisms in plants: processes, applications and challenges in sustainable plant management

Silicon (Si) is an abundant element in the earth's crust essential for plant growth and development. Recent studies silicon's potential for improving plant resilience to numerous biotic stressors, notably fungal diseases. This review seeks to offer a comprehensive understanding of the processes and advantages of silicon-induced systemic resistance in plants, with a special focus on its interactions with fungal pathogens. Furthermore, we investigate the effect of silicon on plant physiological and biochemical changes, such as enhanced lignification, strengthening of physical barriers, and activation of antioxidant systems. Additionally, we examine the influence of silicon on microbial populations within the rhizosphere and its effects on mycorrhizal associations. Lastly, we discuss the potential applications and challenges of integrating silicon-based strategies in sustainable plant disease management. This review provides valuable insights into using silicon as a novel approach to enhance plant systemic resistance against fungal pathogens, offering prospects for developing eco-friendly and efficient agricultural practices.

Various amino acid substitutions in succinate dehydrogenase complex regulating differential resistance to pydiflumetofen in Magnaporthe oryzae

Rice blast, caused by Magnaporthe oryzae, is a devastating fungal disease worldwide. Pydiflumetofen (Pyd) is a new succinate dehydrogenase inhibitor (SDHI) that exhibited anti-fungal activity against M. oryzae. However, control of rice blast by Pyd and risk of resistance to Pyd are not well studied in this pathogen. The baseline sensitivity of 109 M. oryzae strains to Pyd was determined using mycelial growth rate assay, with EC50 values ranging from 0.291 to 2.1313 μg/mL, and an average EC50 value of 1.1005 ± 0.3727 μg/mL. Totally 28 Pyd-resistant (PydR) mutants with 15 genotypes of point mutations in succinate dehydrogenase (SDH) complex were obtained, and the resistance level could be divided into three categories of very high resistance (VHR), high resistance (HR) and moderate resistance (MR) with the resistance factors (RFs) of >1000, 105.74-986.13 and 81.92-99.48, respectively. Molecular docking revealed that all 15 mutations decreased the binding-force score for the affinity between Pyd and target subunits, which further confirmed that these 15 genotypes of point mutations were responsible for the resistance to Pyd in M. oryzae. There was positive cross resistance between Pyd and other SDHIs, such as fluxapyroxad, penflufen or carboxin, while there was no cross-resistance between Pyd and carbendazim, prochloraz or azoxystrobin in M. oryzae, however, PydR mutants with SdhBP198Q, SdhCL66F or SdhCL66R genotype were still sensitive to the other 3 SDHIs, indicating lack of cross resistance. The results of fitness study revealed that the point mutations in MoSdhB/C/D genes might reduce the hyphae growth and sporulation, but could improve the pathogenicity in M. oryzae. Taken together, the risk of resistance to Pyd might be moderate to high, and it should be used as tank-mixtures with other classes of fungicides to delay resistance development when it is used for the control of rice blast in the field.

Optimizing nutrient transporters to enhance disease resistance in rice

Fertilizers and plant diseases contribute positively and negatively to crop production, respectively. Macro- and micronutrients provided by the soil and fertilizers are transported by various plant nutrient transporters from the soil to the roots and shoots, facilitating growth and development. However, the homeostasis of different nutrients has different effects on plant disease. This review is aimed at providing insights into the interconnected regulation between nutrient homeostasis and immune responses, and it highlights strategies to enhance disease resistance by optimal manipulation of nutrient transporters in rice. First, we highlight the essential roles of six macronutrients (nitrogen, phosphorus, potassium, sulfur, calcium, magnesium) and eight micronutrients (iron, manganese, zinc, copper, boron, molybdenum, silicon, nickel), and summarize the diverse effects of each on rice diseases. We then systematically review the molecular mechanisms of immune responses modulated by nutrient transporters and the genetic regulatory pathways that control the specific nutrient-mediated immune signaling that is regulated by the pathogens and the host plant. Finally, we discuss putative strategies for breeding disease-resistant rice by genetic engineering of nutrient transporters.

Potential of silicon-rich biochar (Sichar) amendment to control crop pests and pathogens in agroecosystems: A review

We reviewed the potential of silicon (Si)-rich biochars (sichars) as crop amendments for pest and pathogen control. The main pathosystems that emerged from our systematic literature search were bacterial wilt on solanaceous crops (mainly tomato, pepper, tobacco and eggplant), piercing-sucking hemipteran pests and soil-borne fungi on gramineous crops (mainly rice and wheat), and parasitic nematodes on other crops. The major pest and pathogen mitigation pathways identified were: i) Si-based physical barriers; ii) Induction of plant defenses; iii) Enhancement of plant-beneficial/pathogen-antagonistic soil microflora in the case of root nematodes; iv) Alteration of soil physical-chemical properties resulting in Eh-pH conditions unfavorable to root nematodes; v) Alteration of soil physical-chemical properties resulting in Eh-pH, bulk density and/or water holding capacity favorable to plant growth and resulting tolerance to necrotrophic pathogens; vi) Increased Si uptake resulting in reduced plant quality, owing to reduced nitrogen intake towards some hemi-biotrophic pests or pathogens. Our review highlighted synergies between pathways and tradeoffs between others, depending, inter alia, on: i) crop type (notably whether Si-accumulating or not); ii) pest/pathogen type (e.g. below-ground/root-damaging vs above-ground/aerial part-damaging; "biotrophic" vs "necrotrophic" sensu lato, and corresponding systemic resistance pathways; thriving Eh-pH spectrum; etc.); iii) soil type. Our review also stressed the need for further research on: i) the contribution of Si and other physical-chemical characteristics of biochars (including potential antagonistic effects); ii) the pyrolysis process to a) optimize Si availability in the soil and its uptake by the crop and b) to minimize formation of harmful compounds e.g. cristobalite; iii) on the optimal form of biochar, e.g. Si-nano particles on the surface of the biochar, micron-sized biochar-based compound fertilizer vs larger biochar porous matrices.

Chemopriming for induction of disease resistance against pathogens in rice

Rice is an important grain crop of Asian population. Different fungal, bacterial and viral pathogens cause large reduction in rice grain production. Use of chemical pesticides, to provide protection against pathogens, has become incomplete due to pathogens resistance and is cause of environmental concerns. Therefore, induction of resistance in rice against pathogens via biopriming and chemopriming with safe and novel agents has emerged on a global level as ecofriendly alternatives that provide protection against broad spectrum of rice pathogens without any significant yield penalty. In the past three decades, a number of chemicals such as silicon, salicylic acid, vitamins, plant extract, phytohormones, nutrients etc. have been used to induce defense against bacterial, fungal and viral rice pathogens. From the detailed analysis of abiotic agents used, it has been observed that silicon and salicylic acid are two potential chemicals for inducing resistance against fungal and bacterial diseases in rice, respectively. However, an inclusive evaluation of the potential of different abiotic agents to induce resistance against rice pathogens is lacking due to which the studies on induction of defense against rice pathogens via chemopriming has become disproportionate and discontinuous. The present review deals with a comprehensive analysis of different abiotic agents used to induce defense against rice pathogens, their mode of application, mechanism of defense induction and the effect of defense induction on grain yield. It also provides an account of unexplored areas, which might be taken into attention to efficiently manage rice diseases. DATA AVAILABILITY STATEMENT: Data sharing not applicable to this article as no datasets were generated or analysed during the current study.

Lanthanum Silicate Nanomaterials Enhance Sheath Blight Resistance in Rice: Mechanisms of Action and Soil Health Evaluation

In the current study, foliar spray with lanthanum (La) based nanomaterials (La10Si6O27 nanorods, La10Si6O27 nanoparticle, La(OH)3 nanorods, and La2O3 nanoparticle) suppressed the occurrence of sheath blight (Rhizoctonia solani) in rice. The beneficial effects were morphology-, composition-, and concentration-dependent. Foliar application of La10Si6O27 nanorods (100 mg/L) yielded the greatest disease suppression, significantly decreasing the disease severity by 62.4% compared with infected controls; this level of control was 2.7-fold greater than the commercially available pesticide (Thifluzamide). The order of efficacy was as follows: La10Si6O27 nanorods > La10Si6O27 nanoparticle > La(OH)3 nanorods > La2O3 nanoparticle. Mechanistically, (1) La10Si6O27 nanorods had greater bioavailability, slower dissolution, and simultaneous Si nutrient benefits; (2) transcriptomic and metabolomic analyses revealed that La10Si6O27 nanorods simultaneously strengthened rice systemic acquired resistance, physical barrier formation, and antioxidative systems. Additionally, La10Si6O27 nanorods improved rice yield by 35.4% and promoted the nutritional quality of the seeds as compared with the Thifluzamide treatment. A two-year La10Si6O27 nanorod exposure had no effect on soil health based on the evaluated chemical, physical, and biological soil properties. These findings demonstrate that La based nanomaterials can serve as an effective and sustainable strategy to safeguard crops and highlight the importance of nanomaterial composition and morphology in terms of optimizing benefit.

Elevated CO2 and temperature under future climate change increase severity of rice sheath blight

Sheath blight (ShB), caused by Rhizoctonia solani, is one of the major threats to rice (Oryza sativa L.) production. However, it is not clear how the risk of rice ShB will respond to elevated CO₂ and temperature under future climate change. Here, we conducted, field experiments of inoculated R. solani under combinations of two CO₂ levels (ambient and enriched up to 590 μmol mol^-1) and two temperature levels (ambient and increased by 2.0°C) in temperature by free-air CO₂ enrichment (T-FACE) system for two cultivars (a susceptible cultivar, Lemont and a resistant cultivar, YSBR1). Results indicate that for the inoculation of plants with R. solani, the vertical length of ShB lesions for cv. Lemont was significantly longer than that for cv. YSBR1 under four CO₂ and temperature treatments. The vertical length of ShB lesions was significantly increased by elevated temperature, but not by elevated CO₂, for both cultivars. The vertical length of ShB lesions under the combination of elevated CO₂ and elevated temperature was increased by 21-38% for cv. Lemont and by -1-6% for cv. YSBR1. A significant increase in MDA level was related to a significant increase in the vertical length of ShB lesions under the combination of elevated CO₂ and elevated temperature. Elevated CO₂ could not compensate for the negative effect of elevated temperature on yield of both cultivars under future climate change. Rice yield and biomass were further decreased by 2.0-2.5% and 2.9-4.2% by an increase in the severity of ShB under the combination of elevated CO₂ and elevated temperature. Thus, reasonable agronomic management practices are required to improve both resistance to ShB disease and grain yield for rice under future climate change.

Silicon inhibits gummosis by promoting polyamine synthesis and repressing ethylene biosynthesis in peach

Silicon is a beneficial element for plant growth, as well as for improving plant resistance to multiple biotic and abiotic stresses. Gummosis is a common harmful disease in peach and is induced by many factors. However, the effect of silicon on gummosis of peach has not been determined yet. In this study, we reported that application of silicon significantly reduced gummosis by regulating biosynthesis of ethylene and polyamines in peach. Ethylene promoted the development of gummosis by inducing the expression of genes encoding cell wall degrading enzymes. While application of different types of polyamines, including spermidine and spermine, dramatically inhibited the occurrence of gummosis. Moreover, polyamines inhibited the ethylene biosynthesis by down-regulating expression of ethylene biosynthetic gene PpACS1 (1-aminocyclopropane -1-carboxylic acid synthase), as well as the enzymatic activity of ACS. We further found that application of silicon significantly restricted the development of gummosis in peach. Exogenous silicon dramatically inhibited expression of PpACS1 and the enzymatic activity of its product to reduce ethylene biosynthesis. Simultaneously, the activity of S-adenosylmethionine decarboxylase, a key enzyme in ployamines biosynthesis, was increased by 9.85% under silicon treatment, resulting in elevated accumulation of polyamines. Thus, our data proved that application of silicon restricted gummosis development by activating ployamines biosynthesis and inhibiting ethylene synthesis in peach.

Effects of Nitrogen and Phosphorus Regulation on Plant Type, Population Ecology and Sheath Blight of Hybrid Rice

(1) Background: Sheath blight is one of the most economically significant rice diseases worldwide. A study was conducted in order to find the relationship and impact of the amount of nitrogen (N) and phosphorus (P) application on the hybrid rice population microclimate and the severity of sheath blight. (2) Methods: Four N and four P application levels were used to determine their impact on plant type, temperature, and humidity variation in different positions of population and the severity of sheath blight in the later stage. (3) Results: We found that N and P application levels could affect the plant type and change the population temperature and humidity by increasing the leaf length and leaf angle. (4) Conclusions: N application had a more significant (p < 0.05) impact on the plant type. High N application caused decreased temperature (hybrid rice population), while increased humidity (especially the population base layer at grain filling stage) resulted in severe sheath blight. High P application had similar impacts; however, P application increased material and nitrogen transport in plants and reduced the severity of sheath blight.

Advances in Understanding Silicon Transporters and the Benefits to Silicon-Associated Disease Resistance in Plants

Silicon (Si) is the second most abundant element after oxygen in the earth’s crust and soil. It is available for plant growth and development, and it is considered as quasi-essential for plant growth. The uptake and transport of Si is mediated by Si transporters. With the study of the molecular mechanism of Si uptake and transport in higher plants, different proteins and coding genes with different characteristics have been identified in numerous plants. Therefore, the accumulation, uptake and transport mechanisms of Si in various plants appear to be quite different. Many studies have reported that Si is beneficial for plant survival when challenged by disease, and it can also enhance plant resistance to pathogens, even at low Si accumulation levels. In this review, we discuss the distribution of Si in plants, as well as Si uptake, transport and accumulation, with a focus on recent advances in the study of Si transporters in different plants and the beneficial roles of Si in disease resistance. Finally, the application prospects are reviewed, leading to an exploration of the benefits of Si uptake for plant resistance against pathogens.

A Novel Guanine Elicitor Stimulates Immunity in Arabidopsis and Rice by Ethylene and Jasmonic Acid Signaling Pathways

Rice sheath blight (ShB) caused by Rhizoctonia solani is one of the most destructive diseases in rice. Fungicides are widely used to control ShB in agriculture. However, decades of excessive traditional fungicide use have led to environmental pollution and increased pathogen resistance. Generally, plant elicitors are regarded as environmentally friendly biological pesticides that enhance plant disease resistance by triggering plant immunity. Previously, we identified that the plant immune inducer ZhiNengCong (ZNC), a crude extract of the endophyte, has high activity and a strong ability to protect plants against pathogens. Here, we further found that guanine, which had a significant effect on inducing plant resistance to pathogens, might be an active component of ZNC. In our study, guanine activated bursts of reactive oxygen species, callose deposition and mitogen-activated protein kinase phosphorylation. Moreover, guanine-induced plant resistance to pathogens depends on ethylene and jasmonic acid but is independent of the salicylic acid signaling pathway. Most importantly, guanine functions as a new plant elicitor with broad-spectrum resistance to activate plant immunity, providing an efficient and environmentally friendly biological elicitor for bacterial and fungal disease biocontrol.

Exploration of silicate solubilizing bacteria for sustainable agriculture and silicon biogeochemical cycle

Silicon (Si), a quasi-essential element for plants, is abundant in the soil typically as insoluble silicate forms. However, plants can uptake Si only in the soluble form of monosilicic acid. Production of monosilicic acid by rock-weathering mostly depends on temperature, pH, redox-potential, water-content, and microbial activities. In the present review, approaches involved in the efficient exploration of silicate solubilizing bacteria (SSB), its potential applications, and available technological advances are discussed. Present understanding of Si uptake, deposition, and subsequent benefits to plants has also been discussed. In agricultural soils, pH is found to be one of the most critical factors deciding silicate solubilization and the formation of different Si compounds. Numerous studies have predicted the role of Indole-3-Acetic Acid (IAA) and organic acids produced by SSB in silicate solubilization. In this regard, approaches for the isolation and characterization of SSB, quantification of IAA, and subsequent Si solubilization mechanisms are addressed. Phylogenetic evaluation of previously reported SSB showed a highly diverse origin which provides an opportunity to study different mechanisms involved in Si solubilization. Soil biochemistry in concern of silicon availability, microbial activity and silicon mediated changes in plant physiology are addressed. In addition, SSB's role in Si-biogeochemical cycling is summarized. The information presented here will be helpful to explore the potential of SSB more efficiently to promote sustainable agriculture.