In recent years, significant advancements in biopolymer-based packaging have emerged as a response to the environmental challenges posed by traditional petroleum-based materials. The drive for sustainable, renewable, and degradable alternatives to fossil-based components in the packaging industry has led to an increased focus on chitosan, the second most abundant biopolymer after cellulose. Chitosan offers intrinsic properties such as biodegradability, biocompatibility, antimicrobial activity, excellent barrier and film-forming capabilities, positioning it as an ideal candidate for food packaging applications. However, limitations including inferior mechanical, thermal, barrier properties, and brittleness compared to conventional plastics have limiting its widespread adoption in the food packaging industry. Chitosan has been extensively utilized in various forms, particularly as nanocomposites incorporating metal nanoparticles, leading to chitosan-based nanocomposite films/coatings that synergistically combine the advantageous properties of both chitosan and metal nanoparticles. Through an in-depth analysis of the current research (primarily the last 5 years), this review delves into the physicochemical, mechanical, sensing, and antimicrobial properties of chitosan nanocomposite as an innovative food packaging material. This review will provide insights into the potential toxicity and environmental impact of nanoparticle migration, as well as the prospects and challenges associated with chitosan-metal/metal oxide nanocomposite films in the development of sustainable packaging solutions.

Imbibing watermelon seeds in 1 mM sodium tetraborate (Na2B4O7) for 24 h systemically protected plants against foliar infection by Stagonosporopsis cucurbitacearum in detached leaves and under greenhouse conditions. The treatment resulted in both a reduction in the overall percentage of leaf infection as well as in the size of lesions. Studies of the mechanisms by which Na2B4O7 protected watermelon showed that there was no direct effect on the S. cucurbitacearum mycelium growth in vitro. On the other hand, plants raised from seeds primed with Na2B4O7 showed a higher frequency of fluorescent epidermal cells compared to the plants treated with water. This indicates that a higher number of cells expressed the hypersensitive response after Na2B4O7 priming. In addition, there was an increase in peroxidase activity and an enhanced accumulation of a 45 kDa acidic peroxidase isoform during the early stages of infection in plants treated with Na2B4O7 compared to plants treated with water and this was positively correlated to the reduction of leaf infection caused by the pathogen. These results indicate that Na2B4O7 is able to induce systemic resistance in watermelon against S. cucurbitacearum by activating the hypersensitive reaction at penetration sites, increasing peroxidase activity and altering the peroxidase isozyme profile. Although each individual response may only have had a minor effect, their combined effects had a reducing effect on the disease.

A variety of secreted effectors are used by fungal pathogens to evade, disrupt, or modify crucial elements of transcription, defense signaling, and metabolic processes to induce resistance against biotic stress in host plant. Induced resistance is a crucial component of managing downy mildew disease in Pennisetum glaucum. However, the underlying mechanisms of effectors and their host targets in biotrophic fungal infections are mainly unknown. In the current study, the effector protein 35983_g from Sclerospora graminicola was treated against the Pennisetum glaucum callus and seedlings of resistant and susceptible variety to downy mildew and compared with the control. Hypersensitivity response (HR), protein-cell wall cross-linking, lignin deposition, hydrogen peroxide (H2O2), phenylalanine-ammonia lyase (PAL) and peroxidase (POX) were evaluated in the both the varieties of Pennisetum glaucum. Experimental data demonstrated that effector protein induced HR, boosted the activity of the enzymes PAL and POX. Additionally, a histochemical examination showed that downy mildew resistant variety treated with effector protein had thicker cell walls due to lignin deposition than untreated cultivar. The identified oomycetes effector protein in this study can be used as a biomarker in breeding programmes to screen pearl millet downy mildew resistant lines across the globe.

Endophytic Streptomyces spp . were isolated from pearl millet roots and analyzed for growth characteristics on three different media viz., Streptomyces (S) media, casein starch agar and actinomycetes media. Proteolytic activity of Streptomyces was evaluated by using cell free extracts, 23 isolates were found positive and further tested for their inhibition effects on downy mildew pathogen . Cell-free extract and the mycelial mats were used as seed soaking and seed dressing treatments, respectively. Twenty days old susceptible coleoptile seedlings were artificially inoculated with Sclerospora graminicola pathogen for three consecutive days. The downy mildew suppressing ability (30%) and the disease protection (63%) were observed in Streptomyces spp. Isolates S6-19 and S4-19 offered 63% and 56% disease protection against downy mildew respectively and also promoted the vegetative and reproductive growth of the plant. Thus, endophytic Streptomyces spp . proved as an effective possible biocontrol agent in enhancing the disease resistance.

The fungal symbiosis with the plant root system is importantly recognized as a plant growth promoting fungi (PGPFs), as well as elicitor of plant defence against different biotic and abiotic stress conditions. Thus PGPFs are playing as a key trouper in enhancing agricultural quality and increased crop production and paving a way towards a sustainable agriculture. Due to increased demand of food production, the over and unscientific usage of chemical fertilizers has led to the contamination of soil by organic and inorganic wastes impacting on soil quality, crops quality effecting on export business of agricultural products. The application of microbial based consortium like plant growth promoting fungi is gaining worldwide importance due to their multidimensional activity. These activities are through plant growth promotion, induction of systemic resistance, disease combating and detoxification of organic and inorganic toxic chemicals, a heavy metal tolerance ability. The master key behind these properties exhibited by PGPFs are attributed towards various secretory biomolecules (secondary metabolites or enzymes or metabolites) secreted by the fungi during interaction mechanism. The present review is focused on the multidimensional role PGPFs as elicitors of Induced systemic resistance against phytopathogens as well as heavy metal detoxifier through seed biopriming and biofortification methods. The in-sights on PGPFs and their probable mechanistic nature contributing towards plants to withstand heavy metal stress and stress alleviation by activating of various stress regulatory pathways leading to secretion of low molecular weight compounds like organic compounds, glomalin, hydrophobins, etc,. Thus projecting the importance of PGPFs and further requirement of research in developing PGPFs based molecules and combining with trending Nano technological approaches for enhanced heavy metal stress alleviations in plant and soil as well as establishing a sustainable agriculture.

The present study evaluated the priming efficacy of chitosan and chitosan-derived nanoparticles (CNPs) against bacterial wilt of tomato. In the current study, seed-treated CNPs plus pathogen-inoculated tomato seedlings recorded significant protection of 62 % against pathogen-induced wilt disease and subsequently better growth. The induced resistance was witnessed by a prominent increase in lignin, callose and H2O2 deposition, followed by superoxide radical accumulation in leaves. Additionally, chitosan and CNPs-treated tomato plants recorded a remarkable increase in the upregulation of phenylalanine ammonia-lyase (PAL), peroxidase (POX), polyphenol oxidase (PPO), catalase (CAT) and β-1, 3 glucanase (GLU) in comparison with untreated plants. The chitosan and CNPs-induced antioxidant enzymes were positively correlated with the stimulation of corresponding gene expression in CNPs treated plants related to pathogen-inoculated ones. The results of this study describe that how the application of chitosan and CNPs elicit defense responses at the cellular, biochemical and gene expression in tomato plants against bacterial wilt disease, thereby improve growth and yield.

The increased environmental pollutants due to anthropogenic activities are posing an adverse effects and threat on various biotic forms on the planet. Heavy metals and certain organic pollutants by their toxic persistence in the environment are regarded as significant pollutants worldwide. In recent years, pollutants exist in various forms in the environment are difficult to eliminate by traditional technologies due to various drawbacks. This has lead to shifting of research for the development of cost-effective and efficient technologies for the remediation of environmental pollutants. The adaption of adsorption phenomenon from the traditional technologies with the modification of adsorbents at nanoscale is the trended research for mitigating the environmental pollutants with petite environmental concerns. Over the past decade, the hidden potentials of biological sources for the biofabrication of nanomaterials as bequeathed rapid research for remediating the environmental pollution in a sustainable manner. The biofabricated nanomaterials possess an inimitable phenomenon such as photo and enzymatic catalysis, electrostatic interaction, surface active site interactions, etc., contributing for the detoxification of various pollutants. With this background, the current review highlights the emerging biofabricated nano-based adsorbent materials and their underlying mechanisms addressing the environmental remediation of persistent organic pollutants, heavy metal (loid)s, phytopathogens, special attention to the reduction of pathogen-derived toxins and air pollutants. Each category is illustrated with suitable examples, fundamental mechanism, and graphical representations, along with societal applications. Finally, the future and sustainable development of eco-friendly biofabricated nanomaterial-based adsorbents is discussed.

In this case study, the mycelium growth of Sclerospora graminicola in the infected tissues of pearl millet and the process of sporulation and liberation of sporangia and zoospores were observed using four different microscopic techniques. The cotton blue-stained samples observed under light microscope revealed the formation of zoospores with germ tubes, appressoria and initiation of haustorium into the host cells, while the environmental scanning electron microscopy showed the rapid emergence of sporangiophores with dispersed sporangia around the stomata. For fluorescence microscopy, the infected leaf samples were stained with Fluorescent Brightener 28 and Calcofluor White, which react with β-glucans present in the mycelial walls, sporangiophores and sporangia. Calcoflour White was found to be the most suitable for studying the structural morphology of the pathogen. Therefore, samples observed by confocal laser scanning microscopy (CLSM) were pre-treated with Calcofluor White, as well as with Syto-13 that can stain the cell nuclei. Among the four microscopic techniques, CLSM is ideal for observing live host-pathogen interaction and studying the developmental processes of the pathogen in the host tissues. The use of different microscopic bioimaging techniques to study pathogenesis will enhance our understanding of the morphological features and development of the infectious propagules in the host.

Downy mildew caused by Sclerospora graminicola is the most devastating disease in pearl millet which leads to decrease in fodder and grain yield. Application of nanoparticles has become a major thrust for disease management in agriculture. In this study, green synthesized zinc oxide nanoparticles were evaluated for their efficiency to suppress downy mildew. Saponin rich fraction from aqueous extract of Eclipta alba was used to synthesise zinc oxide nanoparticles. The synthesized nanoparticles were characterized using UV spectroscopy, FTIR, SEM, XRD, DLS and EDAX analysis. Under laboratory and greenhouse conditions, seed treatment with synthesized nanoparticles (NP) significantly enhanced pearl millet seed germination, vigor, plant height, fresh and dry weight of seedlings. In inductively coupled plasma mass spectrometry analysis, the zinc content in nanoparticle treated seedlings was found to be higher compared to control seedlings. Sporangicidal assay of ZnO NP showed that 50 ppm of nanoparticle treatment led to plasmolysis and inhibition of spore germination of S. graminicola zoospore. ZnO NP was applied as seed treatment and foliar spray which resulted in 35% reduction in downy mildew incidence in comparison to untreated control. ZnO NP treated seedlings showed high lignification and callose deposition upon downy mildew infection. Analysis of defense enzymes showed that nano particle treatment significantly enhanced the activities of peroxidase, phenylalanine ammonia-lyase, lipoxygenase and polyphenol oxidase in comparison to untreated control. Semi-quantitative RT-PCR analysis revealed differentially expressed transcripts of the defense enzymes where the genes were over expressed in treated seedlings compared to low expression in control. These results indicate that synthesized ZnO NP could promote growth and induce systemic resistance in pearl millet against S. graminicola and can be effectively used to manage downy mildew.

Plant pathogenic microbes, the oomycetes, have the remarkable ability to manipulate morphological, physiological, and biochemical processes in their host plants. The special adaptive responses of the oomycetes toward a host enable these pathogens to inflict devastating diseases on food crops with immediate impact on mankind. These manipulations are achieved through a diverse array of pathogenicity factors such as elicitors and effector molecules produced by the conidia/zoospores which have been accepted as the principal dispersive agents of all oomycete pathogens. These molecules can either promote infection or trigger defense responses. The elicitors are molecules which stimulate a defense response in the host plant. Most of them constitute pathogen-associated molecular patterns (PAMPs) since they are structurally conserved and very important product of pathogen life cycle. In order to establish an intimate association with the host plant, the pathogen must suppress immune responses triggered by their own elicitors by secreting effector proteins that can act in many different cellular compartments and alter the host physiological state which supports the colonization. The oomycete pathogen while interacting with the respective host system, both the host and the pathogen, is battling each other for control over the other. During the process, the plant cell membrane receptor or transmembrane pattern recognition receptors (TPRR) recognize the pathogen-associated molecular pattern domain in the apoplast and trigger PAMP-triggered immunity (PTI). The plant-resistant protein recognizes the pathogen effector entering the host cell and elicits effector-triggered immunity (ETI). However, research on oomycetes, especially in Phytophthora, is progressing at an interesting level due to tremendous improvement in host-pathogen interaction at genomic level. A variety of functional assays have been carried out to prove the role of elicitors in pathogen recognition and non-host resistance. These methods have identified important biochemical and molecular intermediates in elicitor-induced signaling responses in the host. Sequence analysis of the elicitor genes from oomycete pathogens shed light on the phylogenetic relationship of the oomycete pathogens and also demonstrates the importance of elicitors for pathogen recognition and development of host defense responses.

In the present study, endophytic fungi were isolated from different parts of pearl millet crop from different regions of Karnataka. Endophytes were screened for diversity in tissue types, plant growth promoting (PGP) traits and downy mildew disease suppression ability in pearl millet. A total of 202 fungal isolates were isolated from leaves, shoot and root regions. The diversity analysis revealed that the plant harbored diverse fungal groups and the dominant fungi varied according to the sampling regions. The isolates were assigned to 29 fungal species based on morphology and molecular characterization using ITS sequence. All the isolates belonged to the phylum Ascomycota. Fusarium species were the most dominant fungi. Out of 29 representative isolates tested for plant growth promoting traits in vitro and in vivo, seven isolates were observed to improve the growth of pearl millet in comparison to control. Among the seven isolates, Fusarium oxysporum, Trichoderma asperellum and Acremonium sp. were found to suppress the downy mildew disease incidence by 36% in greenhouse conditions. The potent isolates were confirmed to behave as endophytes using pathogenicity, SEM and confocal microscopy experiments. This paper underlines the value of the endophytes as untapped suitable source of beneficial microorganisms that can be used to control pathogens in a sustainable way.

Endophytic Trichoderma hamatum UoM 13 isolated from pearl millet roots was evaluated for its efficiency to suppress downy mildew disease. Under laboratory conditions, T. hamatum seed treatment significantly enhanced pearl millet seed germination and seedling vigor. T. hamatum seed treatment resulted in systemic and durable immunity against pearl millet downy mildew disease under greenhouse and field conditions. T. hamatum treated seedlings responded to downy mildew infection with high lignification and callose deposition. Analysis of defense enzymes showed that T. hamatum treatment significantly enhanced the activities of glucanase, peroxidase, phenylalanine ammonia-lyase, and polyphenol oxidase in comparison to untreated control. RT-PCR analysis revealed differentially expressed transcripts of the defense enzymes and PR-proteins in treated, untreated, and checks, wherein PR-1, PR-5, and cell wall defense HRGPs were significantly over expressed in treated seedlings as against their lower expression in controls. T. hamatum treatment significantly stimulated endogenous salicylic acid ( SA) levels and significantly upregulated important SA biosynthesis gene isochorismate synthase. The results indicated that T. hamatum UoM13 treatment induces resistance corresponding to significant over expression of endogenous SA, important defense enzymes, PR-proteins, and HRGPs, suggesting that SA biosynthetic pathway is involved in pearl millet for mounting systemic immunity against downy mildew pathogen.

•We sequenced the downy mildew pathogen, which is one of the most important production constraints for pearl millet.•In a maiden attempt, the whole-genome of Sclerospora graminicola pathotype 1 from India was sequenced and annotated.•The overall genome coverage achieved was 40×.•Estimate genome size of S. graminicola was 299.9Mb.•Out of 65,404 genes that were predicted, a total of 38,120 genes were annotated.

Trichoderma spp. are well known biocontrol agents used against phytopathogens. In the present work Trichoderma- mediated Selenium nanoparticles (SeNPs) were synthesized and extent of downy mildew (DM) disease control in pearl millet (PM) was studied. Six species of Trichoderma namely, T . asperellum , T . harzianum , T . atroviride , T . virens , T . longibrachiatum and T . brevicompactum were evaluated in the form of culture filtrate (CF), cell lysate (CL) and crude cell wall (CW) to synthesize SeNPs. All these components produced SeNPs, but CF was significant than CL and CW. The size of SeNPs ranged from 49.5 to 312.5 nm with zeta potential of +3.3 mv to −200 mv. The nanoparticles suppressed the growth, sporulation and zoospore viability of Sclerospora graminicola and these biological activities were inversely proportional to the size of SeNPs. Under greenhouse conditions, application of SeNPs and T . asperellum together enhanced the early plant growth and suppressed DM incidence as compared to their individual application. This study demonstrated the ability of Trichogenic-SeNPs to suppress growth and proliferation of S . graminicola , the incitant of DM of PM and their activity is inversely proportional to size of nanoparticles.

In recent years, diverse physiological functions of various sugars are the subject of investigations. Their roles in signal transduction in plant responses to adverse biotic and abiotic stress conditions have become apparent, and growing scientific evidence has indicated that disaccharides like sucrose and trehalose mediate plant defense responses in similar way as those induced by elicitors against the pathogens. Trehalose is a well-known metabolic osmoregulator, stress-protectant and non-reducing disaccharide existing in a variety of organisms, including fungi, bacteria, and plants. Commercially procured trehalose was applied to seeds of susceptible pearl millet (Pennisetum glaucum) cultivar “HB3,” and tested for its ability to reduce downy mildew disease incidence by induction of resistance. Seed treatment with trehalose at 200 mM for 9 h recorded 70.25% downy mildew disease protection, followed by those with 100 and 50 mM trehalose which offered 64.35 and 52.55% defense, respectively, under greenhouse conditions. Furthermore, under field conditions treatment with 200 mM trehalose for 9 h recorded 67.25% downy mildew disease protection, and reduced the disease severity to 32.75% when compared with untreated control which displayed 90% of disease severity. Trehalose did not affect either sporangial formation or zoospore release from sporangia, indicating that the reduction in disease incidence was not due to direct inhibition but rather through induction of resistance responses in the host. Additionally, trehalose was shown to enhance the levels of polyphenol oxidase, phenylalanine ammonia lyase, and peroxidase, which are known as markers of both biotic and abiotic stress responses. Our study shows that osmoregulators like trehalose could be used to protect plants against pathogen attacks by seed treatment, thus offering dual benefits of biotic and abiotic stress tolerance.

Native endophytic actinomycetes isolated from pearl millet roots were examined for their efficacy to protect pearl millet against downy mildew. Nineteen of 39 isolates were found to be proteolytic, of which 7 strains could directly suppress the sporangium formation of Sclerospora graminicola, the pearl millet downy mildew pathogen. Thus, mycelial suspensions containing either spores or cell-free extract of these 7 isolates were used for seed-coating and -soaking treatments to test for their induction of downy mildew resistance. Results indicated that seed-coating overall provided better protection to downy mildew than seed-soaking. In both treatments, the tested isolates demonstrated differential abilities in downy mildew disease protection, with Streptomyces griseus SJ_UOM-07-09 and Streptosporangium roseum SJ_UOM-18-09 showing the highest protection rates. Additionally, the levels of disease protection conferred by the actinomycetes were just slightly lower than that of the systemic fungicide Apron, suggesting their effectiveness. Further studies revealed that the more rapid root colonization by SJ_UOM-18-09 resulted in faster and higher induced resistance in comparison with SJ_UOM-07-09 under greenhouse conditions, indicating that SJ_UOM-18-09 was superior than SJ_UOM-07-09 in inducing resistance. Results from this study provide comprehensive information on biocontrol functions of SJ_UOM- 18-09 with great potential to control downy mildew disease in pearl millet.

Downy mildew caused by Sclerospora graminicola is a devastating disease of pearl millet. Based on candidate gene approach, a set of 22 resistance gene analogues were identified. The clone RGPM 301 (AY117410) containing a partial sequence shared 83% similarity to rice R-proteins. A full-length R-gene RGA RGPM 301 of 3552 bp with 2979 bp open reading frame encoding 992 amino acids was isolated by the degenerate primers and rapid amplification of cDNA ends polymerase chain reaction (RACE-PCR) approach. It had a molecular mass of 113.96 kDa and isoelectric point (pI) of 8.71. The sequence alignment and phylogenetic analysis grouped it to a non-TIR NBS LRR group. The quantitative real-time PCR (qRT-PCR) analysis revealed higher accumulation of the transcripts following inoculation with S. graminicola in the resistant cultivar (IP18296) compared to susceptible cultivar (7042S). Further, significant induction in the transcript levels were observed when treated with abiotic elicitor β-aminobutyric acid (BABA) and biotic elicitor Pseudomonas fluorescens. Exogenous application of phytohormones jasmonic acid or salicylic acid also up-regulated the expression levels of RGA RGPM 301. The treatment of cultivar IP18296 with mitogen-activated protein kinase (MPK) inhibitors (PD98059 and U0126) suppressed the levels of RGA RGPM 301. A 3.5 kb RGA RGPM 301 which is a non-TIR NBS-LRR protein was isolated from pearl millet and its up-regulation during downy mildew interaction was demonstrated by qRT-PCR. These studies indicate a role for this RGA in pearl millet downy mildew interaction.

Pearl millet (Pennisetum glaucum) stands sixth among the most important cereal crops grown in the semi-arid and arid regions of the world. The downy mildew disease caused by Sclerospora graminicola, an oomycete pathogen, has been recognized as a major biotic constraint in pearl millet production. On the other hand, basidiomycetes are known to produce a large number of antimicrobial metabolites, providing a good source of anti-oomycete agrochemicals. Here, we report the discovery and efficacy of a compound, named G_app7, purified from Ganoderma applanatum on inhibition of growth and development of S. graminicola, as well as the effects of seed treatment with G_app7 on protection of pearl millet from downy mildew. G_app7 consistently demonstrated remarkable effects against S. graminicola by recording significant inhibition of sporangium formation (41.4%), zoospore release (77.5%) and zoospore motility (91%). Analyses of G_app7 compound using two-dimensional nuclear magnetic resonance spectroscopy and liquid chromatography-mass spectrometry revealed its close resemblance to metominostrobin, a derivative of strobilurin group of fungicides. Furthermore, the G_app7 was shown to stably maintain the inhibitory effects at different temperatures between 25 and 80 °C. In addition, the anti-oomycete activity of G_app7 was fairly stable for a period of at least 12 months at 4 °C and was only completely lost after being autoclaved. Seed treatment with G_app7 resulted in a significant increase in disease protection (63%) under greenhouse conditions compared with water control. The identification and isolation of this novel and functional anti-oomycete compound from G. applanatum provide a considerable agrochemical importance for plant protection against downy mildew in an environmentally safe and economical manner.

Plants are hosts to a diverse group of pathogens belonging to different kingdoms of life.In absence of active immune system, plants have evolved several layers of defense to combat individual pathogen strain and evolving pathogen populations.Management of various plant pathogen infections necessitates the use of multiple resistance (R) genes, which requires efficient and accurate practices for identification, isolation and characterization of R genes.This knowledge helps to probe R gene(s) in a host plant and sort out their functional redundancy and specificity.Pearl millet [Pennisetum glaucum (L.) R. Br.] is highly nutritive, summer-annual forage crop, drought tolerant cereal, staple food crop of the semi-arid tropics but is highly susceptible to the downy mildew disease caused by oomycetous Sclerospora graminicola (Sacc.)schroet.Earlier studies have identified several resistance gene analogues (RGAs) in pearl millet which may be involved in resistance against downy mildew.Of these, a clone RGPM213 was shown to encode resistant protein having serine threonine kinase domain and its transcript was upregulated following S. graminicola infection and β-amino butyric acid an abiotic inducer treatment.Here we have shown the accumulation of transcripts of RGPM 213 in pearl millet during treatment with Chitosan, a chitin derivative, a known inducer of plant defense which is completely safe, characterized by unique properties, like bioactivity and biocompatibility.