Chitosan enhances disease resistance in pearl millet against downy mildew caused by Sclerospora graminicola and defence-related enzyme activation

Chitosan-GSNO Nanoparticles and Silicon Priming Enhance the Germination and Seedling Growth of Soybean (Glycine max L.)

Soybean, a major legume crop, has seen a decline in its production owing to challenges in seed germination and the development of seedlings. Thus, in this study, we systematically investigated the influence of various chitosan-S-nitrosoglutathione (chitosan-GSNO) nanoparticle (0, 25, 50, and 100 µM) and Si (0, 0.5, and 1 mM) priming concentrations on soybean seed germination and seedling growth over five different priming durations (range: 1-5 h at each concentration). Significant differences were observed in all parameters, except seedling diameter, with both treatments. Seed germination was significantly enhanced after 3 h of priming in both treatments. The final germination percentage (FGP), peak germination percentage (PGP), vigor index (VI), seedling biomass (SB), hypocotyl length (HL), and radical length (RL) of 100 μM chitosan-GSNO-nanoparticle-primed seeds increased by 20.3%, 41.3%, 78.9%, 25.2%, 15.7%, and 65.9%, respectively, compared with those of the control; however, the mean germination time (MGT) decreased by 18.43%. Si priming at 0.5 mM increased the FGP, PGP, VI, SB, HL, and RL by 13.9%, 55.17%, 39.2%, 6.5%, 22.5%, and 25.1%, respectively, but reduced the MGT by 12.29% compared with the control treatment. Chitosan-GSNO and Si treatment up-regulated the relative expression of gibberellic acid (GA)-related genes (GmGA3ox3 and GmGA2ox1) and down-regulated that of abscisic acid (ABA)-related genes (GmABA2, GmAAO3, and GmNCED5). Chitosan-GSNO and Si application increased bioactive GA4 levels and simultaneously reduced ABA content. Hence, the use of exogenous chitosan-GSNO nanoparticles and Si as priming agents had a beneficial effect on seed germination and seedling growth because of the up-regulation in the expression of GA and down-regulation in the expression of ABA. Additional research is needed to understand the combined impact of Si and chitosan-GSNO nanoparticles, including their effects on the expression levels of other hormones and genes even in the later growth stage of the crop.

Exogenous priming of chitosan induces resistance in Chinese prickly ash against stem canker caused by Fusarium zanthoxyli

Stem canker is a highly destructive disease that threatens prickly ash plantations in China. This study demonstrated the effective control of stem canker in prickly ash using chitosan priming, reducing lesion areas by 46.77 % to 75.13 % across all chitosan treatments. The mechanisms underlying chitosan-induced systemic acquired resistance (SAR) in prickly ash were further investigated. Chitosan increased H2O2 levels and enhanced peroxidase and catalase enzyme activities. A well-constructed regulatory network depicting the genes involved in the SAR and their corresponding expression levels in prickly ash plants primed with chitosan was established based on transcriptomic analysis. Additionally, 224 ZbWRKYs were identified based on the whole genome of prickly ash, and their phylogenetic evolution, conserved motifs, domains and expression patterns of ZbWRKYs were comprehensively illustrated. The expression of 12 key genes related to the SAR was significantly increased by chitosan, as determined using reverse transcription-quantitative polymerase chain reaction. Furthermore, the activities of defensive enzymes and the accumulation of lignin and flavonoids in prickly ash were significantly enhanced by chitosan treatment. Taken together, this study provides valuable insights into the chitosan-mediated activation of the immune system in prickly ash, offering a promising eco-friendly approach for forest stem canker control.

Chitosan as a potential natural compound to manage plant diseases

The necessity for non-chemical approaches has grown as awareness of the dangers posed by pesticides has spread. Chitosan, due to its biocompatibility, biodegradability, and bioactivity is one the effective choice in phytopathology. Chitosan is a biopolymer that reduces plant diseases through two main mechanisms: (1) Direct antimicrobial function against pathogens, including plasma membrane damage mechanisms, interactions with DNA and RNA (electrostatic interactions), metal chelating capacity, and deposition onto the microbial surface, (2) Induction of plant defense responses resulting from downstream signalling, transcription factor activation, gene transcription and finally cellular activation after recognition and binding of chitin and chitosan by cell surface receptors. This biopolymer have potential with capability to combating fungi, bacteria, and viruses phythopathogens. Chitosan is synthesized by deacetylating chitin. The degree of deacetylation and molecular weight of chitosan are variable and have been mentioned as important structural parameters in chitosan's biological properties. Chitosan with a higher degree of deacetylation (>70 %) has better biological properties. Many crops able to withstand pre- and post-harvest illnesses better after receiving chitosan as a seed treatment, soil amendment, or foliar spray. This review discussed the properties and use of chitosan and focuses on its application as a plant resistance inducer against pathogens.

Transcriptomic and Metabolomic Analysis Reveal Possible Molecular Mechanisms Regulating Tea Plant Growth Elicited by Chitosan Oligosaccharide

Chitosan oligosaccharide (COS) plays an important role in the growth and development of tea plants. However, responses in tea plants trigged by COS have not been thoroughly investigated. In this study, we integrated transcriptomics and metabolomics analysis to understand the mechanisms of chitosan-induced tea quality improvement and growth promotion. The combined analysis revealed an obvious link between the flourishing development of the tea plant and the presence of COS. It obviously regulated the growth and development of the tea and the metabolomic process. The chlorophyll, soluble sugar, and amino acid content in the tea leaves was increased. The phytohormones, carbohydrates, and amino acid levels were zoomed-in in both transcript and metabolomics analyses compared to the control. The expression of the genes related to phytohormones transduction, carbon fixation, and amino acid metabolism during the growth and development of tea plants were significantly upregulated. Our findings indicated that alerted transcriptomic and metabolic responses occurring with the application of COS could cause efficiency in substrates in pivotal pathways and hence, elicited plant growth.

Priming seeds for the future: Plant immune memory and application in crop protection

Plants have evolved adaptive strategies to cope with pathogen infections that seriously threaten plant viability and crop productivity. Upon the perception of invading pathogens, the plant immune system is primed, establishing an immune memory that allows primed plants to respond more efficiently to the upcoming pathogen attacks. Physiological, transcriptional, metabolic, and epigenetic changes are induced during defense priming, which is essential to the establishment and maintenance of plant immune memory. As an environmental-friendly technique in crop protection, seed priming could effectively induce plant immune memory. In this review, we highlighted the recent advances in the establishment and maintenance mechanisms of plant defense priming and the immune memory associated, and discussed strategies and challenges in exploiting seed priming on crops to enhance disease resistance.

Use of Chitosan and Other Natural Compounds Alone or in Different Strategies with Copper Hydroxide for Control of Grapevine Downy Mildew

Grapevine downy mildew (GDM) is one of the most serious diseases of grapevines. Limitations to the use of copper-based products in organic agriculture according to the European Union (EU) regulation EU/2002/473 and the later EU Commission implementing regulation 2018/1981 have promoted a search for alternatives. This 5-year field trial evaluated the effectiveness of several strategies against GDM using different chitosan-based formulations and application rates in comparison with other natural compounds applied individually or with copper hydroxide. Trials were performed in commercial vineyards with different environmental conditions and grapevine cultivars. For the natural compounds applied as individual treatments, a 0.5%/0.8% chitosan formulation provided the best protection against GDM; the other compounds and formulations were less effective. When copper hydroxide use was halved by combining it with the natural compounds according to three different strategies, the GDM incidence, severity, and McKinney index were reduced, particularly for copper hydroxide applied in combination with the 0.5%/0.8% chitosan formulation. The 0.5%/0.8% chitosan formulation alone and with copper hydroxide provided good protection against GDM during both high-pressure and low-pressure disease seasons. Therefore, chitosan represents a good alternative to copper formulations for the control of GDM and both organic and integrated disease management.

The Potential of Using Chitosan on Cereal Crops in the Face of Climate Change

This review presents the main findings from measurements carried out on cereals using chitosan, its derivatives, and nanoparticles. Research into the use of chitosan in agriculture is growing in popularity. Since 2000, 188 original scientific articles indexed in Web of Science, Scopus, and Google Scholar databases have been published on this topic. These have focused mainly on wheat (34.3%), maize (26.3%), and rice (24.2%). It was shown that research on other cereals such as millets and sorghum is scarce and should be expanded to better understand the impact of chitosan use. This review demonstrates that this chitosan is highly effective against the most dangerous diseases and pathogens for cereals. Furthermore, it also contributes to improving yield and chlorophyll content, as well as some plant growth parameters. Additionally, it induces excellent resistance to drought, salt, and low temperature stress and reduces their negative impact on cereals. However, further studies are needed to demonstrate the full field efficacy of chitosan.

Effect of Ginkgo biloba seed exopleura extract and chitosan coating on the postharvest quality of ginkgo seed

BACKGROUND

The effects of Ginkgo biloba seed exopleura extract (GSEE) and chitosan (CH) coating on the preservation of ginkgo seeds were investigated.

RESULTS

Results showed that CH could alleviate the decay rate, and that CH combined with GSEE (CH-GSEE) treatment further inhibited the development of seed decay due to the additional antifungal activity of GSEE. The nutrient contents, including water, starch and soluble protein, were maintained by both CH-GSEE and CH treatments. CH-GSEE treatment led to better restriction on oxidative stress by decreasing superoxide anion production rate, membrane permeability, malondialdehyde content, respiration rate and ethylene production rate. The antioxidant enzyme activities of peroxidase, superoxide dismutase and catalase in ginkgo seeds were maintained by treatment with CH-GSEE at a higher level. These results were consistent with the enhanced visual appearance, qualities and storability of the CH-GSEE-treated seeds. Principal component analysis provided a global view of the internal relations of the ginkgo seeds with different treatments.

CONCLUSIONS

The postharvest qualities of CH-GSEE-treated seeds were better than those of other treatment groups. Therefore, CH-GSEE is an effective and alternative way for inhibiting decay, maintaining quality and extending the postharvest life of ginkgo seeds. © 2018 Society of Chemical Industry.

Effects of chitosan nanoparticles on seed germination and seedling growth of wheat (Triticum aestivum L.)

To investigate the effect and mechanism of chitosan nanoparticles (CSNPs) on the germination and seedling growth of wheat (Triticum aestivum L.), we conducted systematic research on the impact of different concentrations (1-100 μg/mL) of CSNPs and chitosan (CS). The result of energy-dispersive spectroscopy (EDS) and confocal laser scanning microscopy (CLSM) showed that adsorption of CSNPs on the surface of wheat seeds was higher than that of CS. CSNPs had growth promoting effect at a lower concentration (5 μg/mL) compared with CS (50 μg/mL). In addition, the application of 5 μg/mL CSNPs induced the auxin-related gene expression, accelerated indole-3-acetic acid (IAA) biosynthesis and transport, and reduced IAA oxidase activity resulting in the increase of IAA concentration in wheat shoots and roots. The results suggest that CSNPs have positive effect on seed germination and seedling growth of wheat at a lower concentration than CS due to higher adsorption on the surface of wheat seeds.

Optimization of chitosan nanoparticle synthesis and its potential application as germination elicitor of Oryza sativa L

The worldwide rice production has been dwindling due to biotic and abiotic causes. Chitosan is a proven biofunctional material that induces many biological responses in plants. However, the growth and yield increasing properties of chitosan nanoparticles (ChNP) on rice crop are not well understood. In the present work, effect of ChNP on germination of rice has been studied. Seed toxicity of ChNP was also analyzed to ensure the safety of ChNP application. The toxicity study was done according to EPA guidelines and ChNP was found to be non-toxic. Rice seeds were treated with ChNP at different concentrations for different time periods and kept for germination. Upon complete germination, the seedlings were sown in seed trays and growth was evaluated at 21 days after sowing. All treatments showed better results than the untreated control. Treatment T₂₂ (1 mg/ml ChNP for 120 mins) gave the highest growth rates. Therefore we could deduce that ability of ChNP to elicit growth was associated with the concentration of ChNP and soaking time. The shelf life of ChNP was studied over a period of one year by analyzing the germination eliciting capacity on rice seeds. ChNP was found to effective for seven months when stored under room temperature.

Chitosan-induced immunity in Camellia sinensis (L.) O. Kuntze against blister blight disease is mediated by nitric-oxide

Blister blight disease, caused by an obligate biotrophic fungal pathogen, Exobasidium vexans Massee is posing a serious threat for tea cultivation in Asia. As the use of chemical pesticides on tea leaves substantially increases the toxic risks of tea consumption, serious attempts are being made to control such pathogens by boosting the intrinsic natural defense responses against invading pathogens in tea plants. In this study, the nature and durability of resistance offered by chitosan and the possible mechanism of chitosan-induced defense induction in Camellia sinensis (L.) O. Kuntze plants against blister blight disease were investigated. Foliar application of 0.01% chitosan solution at 15 days interval not only reduced the blister blight incidence for two seasons, but also maintained the induced expressions of different defense related enzymes and total phenol content compared to the control. Defense responses induced by chitosan were found to be down regulated under nitric oxide (NO) deficient conditions in vivo, indicating that the observed chitosan-induced resistance is probably activated via NO signaling. Such role of NO in host defense response was further established by application of the NO donor, sodium nitroprusside (SNP), which produced similar defense responses accomplished through chitosan treatment. Taken together, our results suggest that increased production of NO in chitosan-treated tea plants may play a critical role in triggering the innate defense responses effective against plant pathogens, including that causing the blister blight disease.

Impact of Alternative Fungicides on Grape Downy Mildew Control and Vine Growth and Development

Grapevine downy mildew (GDM) is one of the most serious diseases of grapevines. With limitations in the use of copper-based products imposed for organic agriculture by the European Union, research for alternatives is encouraged. The aim of this research was to follow a 2-year trial to evaluate the control of GDM using some alternative compounds, and to determine their effects on shoot growth, plant photosynthesis, and grape quality and quantity. Under low disease pressure, Bordeaux mixture, copper hydroxide, laminarin combined with low copper, and 0.5 and 0.8% chitosan had the lowest GDM incidence, reduced on leaves by 96, 95, 75, 56, and 81%, respectively, compared with the untreated control in the last survey. With high disease pressure, Bordeaux mixture, laminarin combined with Saccharomyces extracts, and 0.5 and 0.8% chitosan had the lowest GDM incidence, reduced on grape by 86, 37, 66, and 75%, respectively, compared with the untreated control in the survey of mid-July. Chitosan at 0.8% lowered net photosynthesis, due to reduced stomatal conductance, leaf area, and dry weight, with no negative effects observed on the quantity of the grape berries and the quality parameters of their juice. Among the alternatives to copper, chitosan provided the best GDM protection and reduced the vigor of the vegetation, inducing physiological changes without negative effects on grape production.

Chitosan-induced antiviral activity and innate immunity in plants

Immunity represents a trait common to all living organisms, and animals and plants share some similarities. Therefore, in susceptible host plants, complex defence machinery may be stimulated by elicitors. Among these, chitosan deserves particular attention because of its proved efficacy. This survey deals with the antiviral activity of chitosan, focusing on its perception by the plant cell and mechanism of action. Emphasis has been paid to benefits and limitations of this strategy in crop protection, as well as to the potential of chitosan as a promising agent in virus disease control.

Seed treatments to control seedborne fungal pathogens of vegetable crops

Vegetable crops are frequently infected by fungal pathogens, which can include seedborne fungi. In such cases, the pathogen is already present within or on the seed surface, and can thus cause seed rot and seedling damping-off. Treatment of vegetable seeds has been shown to prevent plant disease epidemics caused by seedborne fungal pathogens. Furthermore, seed treatments can be useful in reducing the amounts of pesticides required to manage a disease, because effective seed treatments can eliminate the need for foliar application of fungicides later in the season. Although the application of fungicides is almost always effective, their non-target environmental impact and the development of pathogen resistance have led to the search for alternative methods, especially in the past few years. Physical treatments that have already been used in the past and treatments with biopesticides, such as plant extracts, natural compounds and biocontrol agents, have proved to be effective in controlling seedborne pathogens. These have been applied alone or in combination, and they are widely used owing to their broad spectrum in terms of disease control and production yield. In this review, the effectiveness of different seed treatments against the main seedborne pathogens of some important vegetable crops is critically discussed.

Involvement of mitogen-activated protein kinase signalling in pearl millet-downy mildew interaction

Mitogen-activated protein kinase (MAPK) cascade-mediated signalling is essential in the establishment of resistance towards pathogens. The present study compared MAPK activities in a compatible and incompatible interaction between pearl millet [Pennisetum glaucum (L.) R. Br.] and downy mildew pathogen Sclerospora graminicola. Differential expression was observed with rapid and increased activation of MAPKs, PgMPK1 (48kDa) and PgMPK2 (44kDa), in the incompatible interaction; with a weak activity of only PgMPK1 in the compatible interaction. Immunoblot analysis showed PgMPK1 and PgMPK2 to be orthologs of salicylic acid-induced protein kinase and wound-induced protein kinase, respectively. Immunocytochemical analysis revealed pathogen-induced accumulation and nuclear localisation of PgMPKs only in the incompatible interaction with highest signals in the vascular tissues. Maximum PgMPKs activation correlated with the activation of several defence-related enzymes. In addition, inhibition of MAPK-activation by kinase cascade inhibitors correlated with the suppression of defence-related enzyme activities and pathogen-induced H2O2 accumulation. Treatment of pearl millet seedlings with abiotic and biotic elicitors led to a strong early induction of only PgMPK1. β-Amino butyric acid and H2O2 were found to be best activators of PgMPK1. These results suggest that in pearl millet MAPK signalling is involved in mediating several defence mechanisms in response to pathogen infection.

Biotechnological approaches for field applications of chitooligosaccharides (COS) to induce innate immunity in plants

Plants have evolved mechanisms to recognize a wide range of pathogen-derived molecules and to express induced resistance against pathogen attack. Exploitation of induced resistance, by application of novel bioactive elicitors, is an attractive alternative for crop protection. Chitooligosaccharide (COS) elicitors, released during plant fungal interactions, induce plant defenses upon recognition. Detailed analyses of structure/function relationships of bioactive chitosans as well as recent progress towards understanding the mechanism of COS sensing in plants through the identification and characterization of their cognate receptors have generated fresh impetus for approaches that would induce innate immunity in plants. These progresses combined with the application of chitin/chitosan/COS in disease management are reviewed here. In considering the field application of COS, however, efficient and large-scale production of desired COS is a challenging task. The available methods, including chemical or enzymatic hydrolysis and chemical or biotechnological synthesis to produce COS, are also reviewed.

Antibacterial activity of two chitosan solutions and their effect on rice bacterial leaf blight and leaf streak

BACKGROUND

Bacterial leaf blight and leaf streak are the two most damaging bacterial diseases of rice. However, few bactericidal chemicals are available for controlling both diseases. The antibacterial properties of two kinds of chitosan with different molecular weights and degrees of N-deacetylation and their effect on rice bacterial leaf blight and leaf streak were evaluated.

RESULTS

Results showed that the two kinds of chitosan solution possess a strong antibacterial activity against both rice bacterial pathogens and significantly reduced disease incidence and severity by comparison with the control under greenhouse conditions. However, the interaction between chitosan and rice pathogens was affected by the type and concentration of chitosan, the bacterial species and the contact time between chitosan and bacteria. The direct antibacterial activity of chitosan may be attributed to both membrane lysis and the destruction of biofilm. In addition, both chitosan solutions significantly increased the activities of phenylalanine ammonia lyase, peroxidase and polyphenol oxidase in rice seedlings following inoculation of two rice pathogens by comparison with the control.

CONCLUSION

The role of chitosan in protection of rice against bacterial pathogens has been shown to involve direct antibacterial activity and indirect induced resistance.

A Biopolymer Chitosan and Its Derivatives as Promising Antimicrobial Agents against Plant Pathogens and Their Applications in Crop Protection

Recently, much attention has been paid to chitosan as a potential polysaccharide resource. Although several efforts have been reported to prepare functional derivatives of chitosan by chemical modifications, few attained their antimicrobial activity against plant pathogens. The present paper aims to present an overview of the antimicrobial effects, mechanisms, and applications of a biopolymer chitosan and its derivatives in crop protection. In addition, this paper takes a closer look at the physiochemical properties and chemical modifications of chitosan molecule. The recent growth in this field and the latest research papers published will be introduced and discussed.

Nitric oxide is involved in chitosan-induced systemic resistance in pearl millet against downy mildew disease

BACKGROUND

The nature and durability of resistance offered by chitosan and the involvement of nitric oxide (NO) in chitosan-induced defence reactions in pearl millet against downy mildew disease were investigated.

RESULTS

It had previously been reported that chitosan seed priming protected pearl millet plants against downy mildew disease. Further elucidation of the mechanism of resistance showed that chitosan seed priming protects the plants systemically. A minimum 4 day time gap is required between the chitosan treatment and pathogen inoculation for maximum resistance development, and it was found to be durable. Chitosan seed priming elevated NO accumulation in pearl millet seedlings, beginning from 2 h post-inoculation, and it was found to be involved in the activation of early defence reactions such as hypersensitive reaction, callose deposition and PR-1 protein expression. Pretreatment with NO scavenger C-PTIO and nitric oxide synthase (NOS) inhibitor L-NAME before pathogen inoculation reduced the disease-protecting ability of chitosan, and defence reactions were also downregulated, which indicated a possible role for NO in chitosan-induced resistance.

CONCLUSION

Protection offered by chitosan against pearl millet downy mildew disease is systemic in nature and durable. Chitosan-induced resistance is activated via NO signalling, as defence reactions induced by chitosan were downregulated under NO deficient conditions.

Salicylic acid confers resistance to a biotrophic rust pathogen, Puccinia substriata, in pearl millet (Pennisetum glaucum)

Studies were undertaken to assess the induction of defence response pathways in pearl millet (Pennisetum glaucum) in response to infection with the leaf rust fungus Puccinia substriata. Pretreatment of pearl millet with salicylic acid (SA) conferred resistance to a virulent isolate of the rust fungus, whereas methyl jasmonate (MeJA) did not significantly reduce infection levels. These results suggest that the SA defence pathway is involved in rust resistance. In order to identify pearl millet genes that are specifically regulated in response to SA and not MeJA, and thus could play a role in resistance to P. substriata, gene expression profiling was performed. Substantial overlap in gene expression responses between the treatments was observed, with MeJA and SA treatments exhibiting 17% co-regulated transcripts. However, 34% of transcripts were differentially expressed in response to SA treatment, but not in response to MeJA treatment. SA-responsive transcripts represented genes involved in SA metabolism, defence response, signal transduction, protection from oxidative stress and photosynthesis. The expression profiles of pearl millet plants after treatment with SA or MeJA were more similar to one another than to the response during a compatible infection with P. substriata. However, some SA-responsive genes were repressed during P. substriata infection, indicating possible manipulation of host responses by the pathogen.