The key pathways for synthesizing nanoparticles are physical and chemical, usually expensive and possibly hazardous to the environment. In the recent past, the evaluation of green chemistry or biological techniques for synthesizing metal nanoparticles from plant extracts has drawn the attention of many researchers. The literature on the green production of nanoparticles using various metals (i.e., gold, silver, zinc, titanium and palladium) and plant extracts is discussed in this study. The generalized mechanism of nanoparticle synthesis involves reduction, stabilization, nucleation, aggregation and capping, followed by characterization. During biosynthesis, major difficulties often faced in maintaining the structure, size and yield of particles can be solved by monitoring the development parameters such as temperature, pH and reaction period. To establish a widely accepted approach, researchers must first explore the actual process underlying the plant-assisted synthesis of a metal nanoparticle and its action on others. The green synthesis of NPs is gaining attention owing to its facilitation of the development of alternative, sustainable, safer, less toxic and environment-friendly approaches. Thus, green nanotechnology using plant extract opens up new possibilities for the synthesis of novel nanoparticles with the desirable characteristics required for developing biosensors, biomedicine, cosmetics and nano-biotechnology, and in electrochemical, catalytic, antibacterial, electronics, sensing and other applications.

Exploration of nanoparticles (NPs) for various biological and environmental applications has become one of the most important attributes of nanotechnology. Due to remarkable physicochemical properties, silver nanoparticles (AgNPs) are the most explored and used NPs in wide-ranging applications. Also, they have proven to be of high commercial use since they possess great chemical stability, conductivity, catalytic activity, and antimicrobial potential. Though several methods including chemical and physical methods have been devised, biological approaches using organisms such as bacteria, fungi, and plants have emerged as economical, safe, and effective alternatives for the biosynthesis of AgNPs. Recent studies highlight the potential of AgNPs in modern agricultural practices to control the growth and spread of infectious pathogenic microorganisms since the introduction of AgNPs effectively reduces plant diseases caused by a spectrum of bacteria and fungi. In this review, we highlight the biosynthesis of AgNPs and discuss their applications in plant disease management with recent examples. It is proposed that AgNPs are prospective NPs for the successful inhibition of pathogen growth and plant disease management. This review gives a better understanding of new biological approaches for AgNP synthesis and modes of their optimized applications that could contribute to sustainable agriculture.

This review deals with the mechanism of antagonistic action of bacterial and fungal biocontrol agents such as the production of antibiotics, siderophores, enzyme secretion, competition for nutrition, plant growth promotion by rhizosphere microorganism. The utilisation of synthetic pesticides has been the predominant control processor for diseases brought about by phytopathogenic microorganisms. Notwithstanding, their open and improper application in intensive agriculture has realised issues that have prompted ecological contamination, considerable residues in agricultural products and phytopathogen resistance. They are likewise disrupting the quantity of beneficial microorganism which is available in the soil and capable of expanding soil fertility. Along these lines, there is a need to look through the option of synthetic pesticides that are safe, environmental and monetarily feasible to confront this problem. Biocontrol agent’s utilisation is the best alternative method to control the different kinds of diseases, such as nematode infestation, fungal pathogen and bacterial pathogen. Nowadays, biocontrol agents assume a significant role in the field of agriculture. It is a financially savvy, environment-friendly and inhibits the advancement of pathogenic microorganism sustainably. This review emphasises the role of biocontrol agents against different pathogenic microorganisms and their significance potentiality to improve plant growth and enhance defence system of plants.

This study was conducted on tomato (Solanum lycopersicum cv. K-21) to investigate the bioprotective nature of Pseudomonas fluorescens and its interactive effects with Meloidogyne incognita in terms of growth biomarkers, changes in biochemical attributes and modulation in antioxidant enzymes of the tomato plant. In this study, we grew tomato plants with M. incognita and P. fluorescens in separate pots, simultaneously and sequentially (15 days prior or post) after 15 days of seed sowing. The sequential inoculation of Mi15→Pf maximally increased the root-knot index and decreased the nematode population. It was also noted that inoculation suppressed the plant growth biomarkers in comparison to control. However, maximum suppression in nematode reproduction and increment in growth and physiological attributes were observed when P. fluorescens was applied 15 days prior to the nematode (Pf15→Mi) as compared to control. All the treatments showed an increase in antioxidant enzymes. Expression of phenol content and defensive enzymes such as peroxidase (POX) and superoxide dismutase (SOD) increased, in contrast to a significant reduction in malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents when compared with the untreated inoculated plants. However, the highest levels of POX and SOD, and a lowest of phenol, MDA and H₂O₂ were displayed in the treatment Pf15→Mi, followed by Mi+Pf and Mi15→Pf.

This investigation presents a novel finding showing the effect of culture filtrates (CFs) of macrofungi, Ganoderma lucidum, against Meloidogyne incognita evaluated in vitro and in planta. To determine the nematicidal activity, juveniles of M. incognita were exposed to Ganoderma CFs of three different ages (Two, four and eight weeks old) of pileus and stipe at different concentrations, i.e., 100%, 50%, 10% and 1% for different time intervals (12, 24, 48 and 72 h). Ganoderma species were examined morphologically based on external appearance and analytically using SEM. The ethanolic samples of basidiocarp were prepared and analyzed for in vitro nematicidal assay and different bioactive compounds. The in vitro experiment results revealed that among all three ages of pileus and stipe, two-week-old pileus and stipe exhibited great nematotoxic potency and caused 83.8% and 73.8% juveniles’ mortality at 100% concentration after 72 h of exposure time, respectively. Similarly, the two-week-old pileus and stipe showed the highest egg hatching inhibition of 89.2% and 81.0% at the 100% concentration after five days. The eight-week-old pileus and stipe were not more effective than the two- and four-week-old pileus and stipe. The metabolites were characterized using GC-MS, including sugar alcohol, steroids, silanes, glucosides, pyrones, ester, oleic acid, phthalic acid, linoleic acid, palmitates and ketones. The in planta study conducted in the greenhouse demonstrated that the root dip treatment for 30 min with Ganoderma CFs curtailed the infection level of M. incognita and promoted the eggplant plant growth. The maximum percent increase in plant length, plant fresh weight, plant dry weight, total chlorophyll, carotenoids and yield/plant was obtained at 100% conc. of fungus CFs, whereas a reduction was observed in nematode infestation parameters. It was concluded from the study that Ganoderma CFs can be explored as an effective and eco-friendly antinemic biocontrol agent in fields infected with root-knot nematodes.

Root-knot nematode, Meloidogyne incognita (Kofoid and White) is one of most damaging pathogen of vegetables, including carrot (Daucus carota L.). We evaluated nematicidal potential of chitosan in combination with chopped leaves of Argemone mexicana L., Achyranthes aspera L., and Ricinus communis L. against infestation caused by M. incognita on carrot under both in vitro and in vivo. Infectious stage (J2s) and egg masses of M. incognita were exposed to different concentrations (2500, 2000, 1500, 1000, and 500 ppm) of chitosan and botanical extracts separately. Maximum mortality of J2s and the highest inhibition in egg hatching was observed at 2500 ppm of chitosan after 36 h and days incubation period, respectively and minimum found in 500 ppm of A. aspera after 12 h of incubation period. Furthermore, pots treated with 1 g chitosan and 30 g of freshly chopped leaves of all three tested botanicals significantly reduced pathological parameters and improved growth and photosynthetic attributes of carrot. In combination with botanicals, chitosan showed a synergistic effect against M. incognita on carrot as compared to chitosan alone. This study proves that chitosan's bio-efficacy, combined with selected three botanicals, could be utilised to manage M. incognita on the carrot as a potential sustainable treatment.