Exploration of silicon functions to integrate with biotic stress tolerance and crop improvement

Strategies for Enhancing Plant Immunity and Resilience Using Nanomaterials for Sustainable Agriculture

Research on plant-nanomaterial interactions has greatly advanced over the past decade. One particularly fascinating discovery encompasses the immunomodulatory effects in plants. Due to the low doses needed and the comparatively low toxicity of many nanomaterials, nanoenabled immunomodulation is environmentally and economically promising for agriculture. It may reduce environmental costs associated with excessive use of chemical pesticides and fertilizers, which can lead to soil and water pollution. Furthermore, nanoenabled strategies can enhance plant resilience against various biotic and abiotic stresses, contributing to the sustainability of agricultural ecosystems and the reduction of crop losses due to environmental factors. While nanoparticle immunomodulatory effects are relatively well-known in animals, they are still to be understood in plants. Here, we provide our perspective on the general components of the plant's immune system, including the signaling pathways, networks, and molecules of relevance for plant nanomodulation. We discuss the recent scientific progress in nanoenabled immunomodulation and nanopriming and lay out key avenues to use plant immunomodulation for agriculture. Reactive oxygen species (ROS), the mitogen-activated protein kinase (MAPK) cascade, and the calcium-dependent protein kinase (CDPK or CPK) pathway are of particular interest due to their interconnected function and significance in the response to biotic and abiotic stress. Additionally, we underscore that understanding the plant hormone salicylic acid is vital for nanoenabled applications to induce systemic acquired resistance. It is suggested that a multidisciplinary approach, incorporating environmental impact assessments and focusing on scalability, can expedite the realization of enhanced crop yields through nanotechnology while fostering a healthier environment.

Potassium silicate and vinasse enhance biometric characteristics of perennial sweet pepper (Capsicum annuum) under greenhouse conditions

An effective strategy for enhancing fruit production continuity during extended sweet pepper season involves adopting innovative biostimulants such as potassium silicate (PS) and vinasse. Adjusting PS and vinasse concentrations are crucial for maintaining the balance between vegetative and fruit growth, particularly in sweet pepper with a shallow root system, to sustain fruiting over prolonged season. However, the interaction between PS and vinasse and the underlying physiological mechanisms that extend the sweet pepper season under greenhouse conditions remain unclear. This study aimed to investigate the impact of PS and vinasse treatments on the yield and biochemical constituents of perennial pepper plants cultivated under greenhouse conditions. For two consecutive seasons [2018/2019 and 2019/2020], pepper plants were sprayed with PS (0, 0.5, and 1 g/l) and drenched with vinasse (0, 1, 2, and 3 l/m3). To estimate the impact of PS and vinasse on the growth, yield, and biochemical constituents of pepper plants, fresh and dry biomass, potential fruit yield, and some biochemical constituents were evaluated. Results revealed that PS (0.5 g/l) coupled with vinasse (3 l/m3) generated the most remarkable enhancement, in terms of plant biomass, total leaf area, total yield, and fruit weight during both growing seasons. The implementation of vinasse at 3 l/m3 with PS at 0.5 and 1 g/l demonstrated the most pronounced augmentation in leaf contents (chlorophyll index, nitrogen and potassium), alongside improved fruit quality, including total soluble solid and ascorbic acid contents, of extended sweet pepper season. By implementing the optimal combination of PS and vinasse, growers can significantly enhance the biomass production while maintaining a balance in fruiting, thereby maximizing the prolonged fruit production of superior sweet pepper under greenhouse conditions.

Growth Enhancement and Resistance of Banana Plants to Fusarium Wilt Disease as Affected by Silicate Compounds and Application Frequency

The amendment of soils with silicate (Si) compounds is essential to promote growth performance and control Fusarium wilt disease in bananas. Two successive greenhouse trials were conducted at the experimental farm of the University of Putra Malaysia. The treatments were arranged in split plots using a randomized complete block design (RCBD) with four replicates to investigate the effects of Si compounds and application frequency on controlling FOC. Si compounds were used at a constant concentration of 0.1%: T0 (control), T1 (13% SiO2:20% K2O), T2 (26.6% SiO2:13.4% K2O) and T3 (36.2% SiO2:17% Na2O). There were three application frequencies by day intervals (DI): 0DI (without any application), 7DI (12× within 12 weeks after transplanting (WAT)), 15DI (6× within 12 WAT) and 30DI (3× within 12 WAT). From these findings, we observed that the photosynthesis rate started to increase from 10.6 to 19.4 µmol CO2 m-2s-1, when the total chlorophyll content started to increase from 3.85 to 7.61 mgcm-2. The transpiration rate started to increase from a value of 1.94 to 4.31 mmol H2O m-2s-1, when the stomata conductance started to increase from 0.237 to 0.958 mmol m-2s-1. The proline content started to increase from 22.89 to 55.07 µmg-1, when the relative water content started to increase from 42.92 to 83.57%.

Role of boron and its interaction with other elements in plants

Boron (B) is an essential microelement for plants, and its deficiency can lead to impaired development and function. Around 50% of arable land in the world is acidic, and low pH in the soil solution decreases availability of several essential mineral elements, including B, magnesium (Mg), calcium (Ca), and potassium (K). Plants take up soil B in the form of boric acid (H3BO3) in acidic soil or tetrahydroxy borate [B(OH)4]- at neutral or alkaline pH. Boron can participate directly or indirectly in plant metabolism, including in the synthesis of the cell wall and plasma membrane, in carbohydrate and protein metabolism, and in the formation of ribonucleic acid (RNA). In addition, B interacts with other nutrients such as Ca, nitrogen (N), phosphorus (P), K, and zinc (Zn). In this review, we discuss the mechanisms of B uptake, absorption, and accumulation and its interactions with other elements, and how it contributes to the adaptation of plants to different environmental conditions. We also discuss potential B-mediated networks at the physiological and molecular levels involved in plant growth and development.

Incorporation of zinc sulfide nanoparticles, Acinetobacter pittii and Bacillus velezensis to improve tomato plant growth, biochemical attributes and resistance against Rhizoctoniasolani

Green nanobiotechnology and beneficial bacterial strains as biofertilizers are crucial in agriculture to achieve food security. Both these strategies have been individually studied in improving plant resistance against phytopathogens along with enhancing plant productivity. Therefore, objective of this study was to explore the eco-friendly and cost-effective approach of utilizing plant growth promoting and disease suppressing bacterial strains and nanoparticles, individually as well as in combination, as bio-stimulants to improve plant growth, antioxidant defense system, nutrition and yield of tomato. A pot experiment was conducted to investigate the zinc sulfide nanoparticles (ZnS NPs) synthesized by using Jacaranda mimosifolia flower extracts (JFE), Acinetobacter pittii and Bacillus velezensis either individually or in combinations to check their potential against Rhizoctonia solani in tomato to suppress root rot infection and improve growth and yield. Among all the combinations the JFE-ZnS NPs + B. velezensis compared to untreated infected plants showed minimum disease incidence and maximum significant protection (66%) against R. solani instigated root rot that was followed by JFE-ZnS NPs + A. pittii and individual application of JFE-ZnS NPs by 58%. The same treatment showed maximum significant increase in plant fresh and dry biomass. B. velezensis significantly increased the photosynthetic pigments when applied individually. However, JFE-ZnS NPs alone and in mixed treatments with B. velezensis efficiently improved total soluble protein, sugar and phenolic contents. The same interactive application of JFE-ZnS NPs + B. velezensis improved the tomato plant nutrition (silicon (Si), magnesium (Mg), calcium (Ca) and potassium (K)) and redox quenching status by improving the activity of antioxidant defense enzymes. Overall, the interactive use of JFE-ZnS NPs with A. pittii and B. velezensis very appropriately prepared the host plant to fight against the negative effects of root rot pathogen in tomato. Advancements in interactively investigating the nanoparticles with beneficial plant growth promoting bacterial strains importantly can contribute in resolving the challenges of food security. According to our information, this is a pioneer report for implying JFE-ZnS NPs in synergism with A. pittii and B. velezensis to hinder the root rot in tomatoes.

Copper-Catalyzed Synthesis of S-S Bond-Containing Silanols from SCBs and Trisulfide-1,1-dioxides

In this work, an efficient method for the copper-catalyzed ring-opening hydrolysis of silacyclobutanes to silanols was developed. This strategy has the advantages of friendly reaction conditions, simple operation, and good functional group compatibility. No additional additives are required in the reaction, and the S-S bond can also be introduced into the organosilanol compounds in one step. Furthermore, the success at the gram scale demonstrates the great potential of the developed protocol for practical industrial applications.

Chitosan/silica: A hybrid formulation to mitigate phytopathogens

Long-term and indiscriminate use of synthetic pesticides to mitigate plant pathogens have created serious issues of water health, soil contamination, non-target organisms, resistant species, and unpredictable environmental and human health hazards. These constraints have forced scientists to develop alternative plant disease management strategies to reduce synthetic chemical' dependency. During the last 20 years, biological agents and resistance elicitors have been the most important used alternatives. Silica-based materials/chitosan with a dual mode of action have been proposed as promising alternatives to prevent plant diseases through direct and indirect mechanisms. Moreover, the combined application of nano-silica and chitosan, due to their controllable morphology, high loading capacity, low toxicity, and efficient encapsulation, act as suitable carriers for biological agents, pesticides, and essential oils, making them proper candidates for mitigation of phytopathogens. Based on this potential, this literature study reviewed the silica and chitosan properties and their function in the plant. It also assessed their role in the fighting against soil and aerial phytopathogens, directly and indirectly, as novel hybrid formulations in future managing platforms.

Silicon and soil microorganisms improve rhizospheric soil health with bacterial community, plant growth, performance and yield

The interaction of silicon and soil microorganisms stimulates crop enhancement to ensure sustainable agriculture. Silicon may potentially increase nutrient availability in rhizosphere with improved plants' growth, development as it does not produce phytotoxicity. The rhizospheric microbiome accommodates a variety of microbial species that live in a small area of soil directly associated with the hidden half plants' system. Plant growth-promoting rhizobacteria (PGPR) play a major role in plant development in response to adverse climatic conditions. PGPRs may enhance the growth, quality, productivity in variety of crops, and mitigate abiotic stresses by reprogramming stress-induced physiological variations in plants via different mechanisms, such as synthesis of indole-3-acetic acid, 1-aminocyclopropane-1-carboxylate deaminase, exopolysaccharides, volatile organic compounds, atmospheric nitrogen fixation, and phosphate solubilization. Our article eye upon interactions of silicon and plant microbes which seems to be an opportunity for sustainable agriculture for series of crops and cropping systems in years to come, essential to safeguard the food security for masses.

Influence of nanosilicon on drought tolerance in plants: An overview

Insufficient availability of water is a major global challenge that plants face and that can cause substantial losses in plant productivity and quality, followed by complete crop failure. Thus, it becomes imperative to improve crop cultivation/production in unsuitable agricultural fields and integrate modern agri-techniques and nanoparticles (NPs)-based approaches to extend appropriate aid to plants to handle adverse environmental variables. Nowadays, NPs are commonly used with biological systems because of their specific physicochemical characteristics, viz., size/dimension, density, and surface properties. The foliar/soil application of nanosilicon (nSi) has been shown to have a positive impact on plants through the regulation of physiological and biochemical responses and the synthesis of specific metabolites. Reactive oxygen species (ROS) are produced in plants in response to drought/water scarcity, which may enhance the ability for adaptation in plants/crops to withstand adverse surroundings. The functions of ROS influenced by nSi and water stress have been assessed widely. However, detailed information about their association with plants and stress is yet to be explored. Our review presents an update on recent developments regarding nSi and water stress in combination with ROS accumulation for sustainable agriculture and an eco-friendly environment.

Effect of Smut Infection on the Photosynthetic Physiological Characteristics and Related Defense Enzymes of Sugarcane

Pathogen infection seriously affects plant development and crop productivity, sometimes causing total crop failure. In this study, artificial stab inoculation was used to inoculate sugarcane smut. The changes in leaf gas exchange, chlorophyll fluorescence variables, and related defense enzyme activities were measured in sugarcane cultivar ROC22 after pathogen infection. The results showed that the net photosynthetic rate (Pn), stomatal conductance (gs), and transpiration rate (Tr) downregulated in the first three days after smut infection and upregulated on the fourth day; intercellular CO₂ concentration (Ci) increased in the first three days of smut infection and reduced on the fourth day. The chlorophyll fluorescence parameters, i.e., Fo, Fm, Fv/Fm, Fs, and Fv′/Fm′ decreased at the initial stage of pathogen infection but increased rapidly up to 3 days after smut infection. It can be seen that sugarcane seedlings showed a positive response to pathogen infection. The correlation coefficient relationship between Pn, gs, and Tr reached above 0.800, showing a significant correlation; Ci was positively correlated with Fv′/Fm′ and ΦPSII, reaching above 0.800 and showing a significant correlation; Fo positively correlated with Fv/Fm, Fs, and ETR; Fv /Fm was positively correlated with Fv′/Fm′; Fs significantly correlated with Fv′/Fm′; and Fv′/Fm′ positively correlated with ΦPSII. After inoculation with smut, the related defense enzymes, i.e., POD, SOD, PPO, and PAL, were increased and upregulated; photosynthetic parameters can be associated with an increase in enzymatic activities. The results of this study will help to further study of the response mechanism to smut in the sugarcane growing period and provide a theoretical reference for sugarcane resistance to smut breeding.

Alleviation of Ammonium Toxicity in Salvia splendens ‘Vista Red’ with Silicon Supplementation

Ammonium (NH₄⁺) toxicity seriously hampers the yield and quality of salvia plants because most varieties or sub-species are highly sensitive to NH₄⁺. Silicon (Si) is an alternative that is used to minimize these disturbances and maintain better growth under NH₄⁺ toxicity. Nevertheless, the mitigatory effects of Si on NH₄⁺-stressed salvia are unknown. Therefore, this study was carried out to determine how Si assists to alleviate the NH₄⁺ toxicity degree in salvia. To this end, salvia plants were cultivated in a controlled environment supplied with a constant N (nitrogen) level (13 meq·L⁻¹) in the form of three NH₄⁺:NO₃⁻ ratios (0:100, 50:50, 100:0), each with (1.0 meq·L⁻¹) or without Si. Physiological disorders and typical NH₄⁺ toxicity symptoms, as well as interrupted photosynthesis, were observed in the 100% NH₄⁺-treated plants. Furthermore, cation uptake inhibition and oxidative damage were also imposed by the 100% NH₄⁺ supply. In contrast, in the presence of Si, the NH₄⁺ toxicity degree was attenuated and plant growth was ensured. Accordingly, the NH₄⁺ toxicity appearance ratio decreased significantly. Furthermore, Si-treated plants showed an ameliorated photosynthetic ability, elevated internal K and Ca levels, and enhanced antioxidative capacity, as reflected by improved major antioxidant enzyme activities, as well as diminished accumulation of ROS (reactive oxygen species) and MDA (malondialdehyde). Our findings enlightened the agronomic importance of additional Si to nutrient solutions, especially pertaining to bedding plants at risk of NH₄⁺ toxicity.

Changes to the Bacterial Microbiome in the Rhizosphere and Root Endosphere of Persea americana (Avocado) Treated With Organic Mulch and a Silicate-Based Mulch or Phosphite, and Infested With Phytophthora cinnamomi

Plant growth and responses of the microbial profile of the rhizosphere soil and root endosphere were investigated for avocado plants infested or not infested with Phytophthora cinnamomi and the changes were compared in plants grown with various soil additives or by spraying plants with phosphite. Soil treatments were organic mulches or silica-based mineral mulch. Reduction of root growth and visible root damage was least in the infested plants treated with phosphite or mineral mulch applied to the soil. Rhizosphere soils and root endospheres were analyzed for bacterial communities using metabarcoding. Bacterial abundance and diversity were reduced in infested rhizospheres and root endospheres. The presence or absence of mineral mulch resulted in greater diversity and larger differences in rhizosphere community composition between infested and non-infested pots than any other treatment. Some rhizosphere bacterial groups, especially Actinobacteria and Proteobacteria, had significantly higher relative abundance in the presence of Phytophthora. The bacterial communities of root endospheres were lower in abundance than rhizosphere communities and not affected by soil treatments or phosphite but increased in abundance after infection with P. cinnamomi. These findings suggested that the addition of silicate-based mineral mulch protects against Phytophthora root rot, which may be partly mediated through changes in rhizosphere bacterial community composition. However, the changes to the microbiome induced by spraying plants with phosphite are different from those resulting from the application of mineral mulch to the soil.

Drenched Silicon Suppresses Disease and Insect Pests in Coffee Plant Grown in Controlled Environment by Improving Physiology and Upregulating Defense Genes

Plant disease and insect pests are major limiting factors that reduce crop production worldwide. The ornamental indoor cultivation cash crop dwarf coffee Punica arabica ‘Pacas’ is also troubled by these issues. Silicon (Si) is one of the most abundant elements in the lithosphere and positively impacts plant health by effectively mitigating biotic and abiotic stresses. Several studies have shown that Si activates plant defense systems, although the specific nature of the involvement of Si in biochemical processes that lead to resistance is unclear. In our study, Si significantly promoted the growth and development of dwarf coffee seedlings grown in plant growth chambers. More than that, through natural infection, Si suppressed disease and insect pests by improving physiology (e.g., the strong development of the internal structures of roots, stems, and leaves; higher photosynthetic efficiency; more abundant organic matter accumulation; the promotion of root activity; the efficient absorption and transfer of mineral elements; and various activated enzymes) and up-regulating defense genes (CaERFTF11 and CaERF13). Overall, in agriculture, Si may potentially contribute to global food security and safety by assisting in the creation of enhanced crop types with optimal production as well by mitigating plant disease and insect pests. In this sense, Si is a sustainable alternative in agricultural production.

The Current State of Knowledge about Essential Oil Fumigation for Quality of Crops during Postharvest

Prolonging crops’ shelf-life while retaining their high quality is a major issue related to postharvest management. During storage, fruits and vegetables are exposed to microbial attacks, which may cause spoilage. Crop deterioration causes the loss of physical properties and drops in quality and nutritional value. Hence, new techniques to improve the resistance of food products are being explored. One promising technique is fumigation. Essential oils and their constituents, due to their antimicrobial properties, are likely to be used as fumigants, as they are highly volatile, effective in low concentrations, biodegradable, and safe. Papers indicate that some of them can improve their quality by increasing the content of antioxidants. This comprehensive review aims to present the current state of knowledge about the influence of essential oil fumigation on crop quality. It covers antioxidant capacity, the content of some bioactive compounds, physicochemical properties, decay properties, and sensory attributes of fruits and vegetables treated with essential oil vapors. The review indicates that this technique might be an interesting field for further exploration due to the promising results presented in the studies. Moreover, the review presents major objectives for current studies and indicates a lack of recent papers in this field.

Influence of Silicon on Biocontrol Strategies to Manage Biotic Stress for Crop Protection, Performance, and Improvement

Silicon (Si) has never been acknowledged as a vital nutrient though it confers a crucial role in a variety of plants. Si may usually be expressed more clearly in Si-accumulating plants subjected to biotic stress. It safeguards several plant species from disease. It is considered as a common element in the lithosphere of up to 30% of soils, with most minerals and rocks containing silicon, and is classified as a "significant non-essential" element for plants. Plant roots absorb Si, which is subsequently transferred to the aboveground parts through transpiration stream. The soluble Si in cytosol activates metabolic processes that create jasmonic acid and herbivore-induced organic compounds in plants to extend their defense against biotic stressors. The soluble Si in the plant tissues also attracts natural predators and parasitoids during pest infestation to boost biological control, and it acts as a natural insect repellent. However, so far scientists, policymakers, and farmers have paid little attention to its usage as a pesticide. The recent developments in the era of genomics and metabolomics have opened a new window of knowledge in designing molecular strategies integrated with the role of Si in stress mitigation in plants. Accordingly, the present review summarizes the current status of Si-mediated plant defense against insect, fungal, and bacterial attacks. It was noted that the Si-application quenches biotic stress on a long-term basis, which could be beneficial for ecologically integrated strategy instead of using pesticides in the near future for crop improvement and to enhance productivity.