By 2050, population growth and climate change will lead to increased demand for food and water. Nanoparticles (NPs), an advanced technology, can be applied to many areas of agriculture, including crop protection and growth enhancement, to build sustainable agricultural production. Ionic gelation method is a synthesis of microparticles or NPs, based on an electrostatic interaction between opposite charge types that contains at least one polymer under mechanical stirring conditions. NPs, which are commonly based on chitosan (CS), have been applied to many agricultural fields, including nanopesticides, nanofertilizers, and nanoherbicides. The CS-NP or CS-NPs-loaded active ingredients (Cu, saponin, harpin, Zn, hexaconazole, salicylic acid (SA), NPK, thiamine, silicon, and silver (Ag)) are effective in controlling plant diseases and enhancing plant growth, depending on the concentration and application method by direct and indirect mechanisms, and have attracted much attention in the last five years. Many crops have been evaluated in in vivo or in greenhouse conditions but only maize (CS-NP-loaded Cu, Zn, SA, and silicon) and soybean (CS-NP-loaded Cu) were tested for manage post flowering stalk rot, Curvularia leaf spot, and bacterial pustule disease in field condition. Since 2019, five of eight studies have been performed in field conditions that have shown interest in CS-NPs synthesized by the ionic gelation method. In this review, we summarized the current state of research and provided a forward-looking view of the use of CS-NPs in plant disease management.

Leaf spot is one of the most important cassava diseases. Nanotechnology can be applied to control diseases and improve plant growth. This study was performed to prepare chitosan (CS) nanoparticle (NP)-loaded salicylic acid (SA) or silver (Ag) by the ionic gelation method, and to evaluate their effectiveness on reducing leaf spot disease and enhancing the growth of cassava plants. The CS (0.4 or 0.5%) and Pentasodium triphosphate (0.2 or 0.5%) were mixed with SA varying at 0.05, 0.1, or 0.2% or silver nitrate varying at 1, 2, or 3 mM to prepare three formulations of CS-NP-loaded SA named N1, N2, and N3 or CS-NP-loaded Ag named N4, N5, and N6. The results showed that the six formulations were not toxic to cassava leaves up to 800 ppm. The CS-NP-loaded SA (N3) and CS-NP-loaded Ag (N6) were more effective than the remaining formulations in reducing the disease severity and the disease index of leaf spot. Furthermore, N3 at 400 ppm and N6 at 200, 400, and 800 ppm could reduce disease severity (68.9–73.6% or 37.0–37.7%, depending on the time of treatment and the pathogen density) and enhance plant growth more than or equal to commercial fungicide or nano-fungicide products under net-house conditions. The study indicates the potential to use CS-NP-loaded SA or Ag as elicitors to manage cassava leaf spot disease.

This study focuses on a commercial plant elicitor based on chitooligosaccharides (BIG^®), which aids in rice plant growth and disease resistance to bacterial leaf blight (BLB). When the pathogen (Xoo) vigorously attacks rice that has suffered yield losses, it can cause damage in up to 20% of the plant. Furthermore, Xoo is a seed-borne pathogen that can survive in rice seeds for an extended period. In this study, when rice seeds were soaked and sprayed with BIG^®, there was a significant increase in shoot and root length, as well as plant biomass. Furthermore, BIG^®-treated rice plants showed a significant reduction in BLB severity of more than 33%. Synchrotron radiation-based Fourier transform infrared (SR-FTIR) analysis was used to characterize BIG^®’s mechanism in the chemical structure of rice leaves. The SR-FTIR results at 1650, 1735, and 1114 cm⁻¹ indicated changes in biochemical components such as pectins, lignins, proteins, and celluloses. These findings demonstrated that commercial BIG^® not only increased rice growth but also induced resistance to BLB. The drug’s target enzyme, Xoo 1075 from Xanthomonas oryzae (PDB ID: 5CY8), was analyzed for its interactions with polymer ingredients, specifically chitooligosaccharides, to gain molecular insights down to the atomic level. The results are intriguing, with a strong binding of the chitooligosaccharide polymer with the drug target, revealing 10 hydrogen bonds between the protein and polymer. Overall, the computational analysis supported the experimentally demonstrated strong binding of chitooligosaccharides to the drug target.

The present study was to investigate the application and mechanism of salicylic acid (SA) as SA-Ricemate for the control of leaf blight disease using a Synchrotron Radiation-based Fourier-Transform Infra-Red (SR-FTIR) microspectroscopy and docking studies. After treating rice plants cv. KDML 105 with SA-Ricemate, the leaves were inoculated with Xanthomonas oryzae pv. oryzae, the causal agent of leaf blight, and disease severity were assessed. The leaves were also used to detect changes in endogenous SA content. The results indicated that SA-Ricemate, as an activated compound, reduced disease severity by 60% at three weeks post-inoculation and increased endogenous content by 50%. The SR-FTIR analysis of changes in the mesophyll of leaves (treated and untreated) showed that the groups of lipids, pectins, and proteins amide I and amide II occurred at higher values, and polysaccharides were shown at lower values in treated compared to untreated. Besides, docking studies were used to model a three-dimensional structure for Pathogenesis-related (PR1b) protein and further identify its interaction with SA. The results showed that ASP28, ARG31, LEU32, GLN97, and ALA93 are important residues that have strong hydrogen bonds with SA. The docking results showed that SA has a good interaction, confirming its role in expression.

Cassava root rot disease caused by the fungal pathogens Fusarium solani and Lasiodiplodia theobromae produces severe damages on cassava production. This research was conducted to produce and assess silver nanoparticles (AgNPs) synthesized by Trichoderma harzianum for reducing root rot disease. The results revealed that using the supernatants of T. harzianum on a silver nitrate solution changed it to reddish color at 48 h, indicating the formation of AgNPs. Further characterization was identified using dynamic light scattering (DLS) and scanning electron microscope (SEM). DLS supported that the Z-average size is at 39.79 nm and the mean zeta potential is at − 36.5 mV. SEM revealed the formation of monodispersed spherical shape with a diameter between 60–75 nm. The antibacterial action of AgNPs as an antifungal agent was demonstrated by an observed decrease in the size of the fungal colonies using an increasing concentration of AgNPs until the complete inhibition growth of L. theobromae and F. solani at > 58 µg mL⁻¹ and at ≥ 50 µg mL⁻¹, respectively. At in vitro conditions, the applied AgNPs caused a decrease in the percentage of healthy aerial hyphae of L. theobromae (32.5%) and of F. solani (70.0%) compared to control (100%). The SR-FTIR spectra showed the highest peaks in the first region (3000–2800 cm⁻¹) associated with lipids and fatty acids located at 2962, 2927, and 2854 cm⁻¹ in the AgNPs treated samples. The second region (1700–1450 cm⁻¹) consisting of proteins and peptides revealed the highest peaks at 1658, 1641, and 1548 cm⁻¹ in the AgNPs treated samples. The third region (1300–900 cm⁻¹), which involves nucleic acid, phospholipids, polysaccharides, and carbohydrates, revealed the highest peaks at 1155, 1079, and 1027 cm⁻¹ in the readings from the untreated samples. Finally, the observed root rot severity on cassava roots treated with AgNPs (1.75 ± 0.50) was significantly lower than the control samples (5.00 ± 0.00).

Biotic elicitors, including Trichoderma and Bacillus can improve plant growth and disease resistance. Current research evaluated the efficacy of 14 Bacillus subtilis strains, Trichoderma viride, Trichoderma harzianum, Trichoderma sp. on enhancing growth and managing anthracnose in scallion. The inhibition efficiency of Bacillus and Trichoderma on Colletotrichum growth was assessed in vitro. Besides, effective biotic treatments against anthracnose were evaluated at net house conditions. Then, defence mechanisms including endogenous SA accumulation, production of phenolic compounds, catalase, peroxidase, phenylalanine ammonia-lyase and b-1,3-glucanase were revealed. The results showed that four biotic elicitors, including B. subtilis strains CaSUT008-2, D604, SUNB1 and T. harzianum showed high antagonistic activity against in vitro growth of Colletotrichum colonies at 41-77 %. At 28 days after planting, scallion plants treated with B. subtilis strain CaSUT008-2 and SUNB1 gained stem length at 15.35-15.79 cm. These four biotic treatments had low disease severity in net-house conditions at 25.00-50.00 %. On mechanisms of anthracnose resistance, at 24 hours after inoculation (HAI), scallion plants treated with T. harzianum and B. subtilis strain CaSUT008-2 showed high content of salicylic acid at 2.17-2.20 µg/g fresh weight. At 48 HAI, scallion plants induced by B. subtilis strain SUNB1 increased phenolic compounds at 42.65 µg gallic acid/mg dry mass. Moreover, four biotic elicitors enhanced activities of catalase, peroxidase, phenylalanine ammonia-lyase and b-1,3-glucanase in treated scallion plants. This study suggests that B. subtilis strain CaSUT008-2 and SUNB1, T. harzianum stimulated growth, helped scallion plants against anthracnose disease. The combined Trichoderma-bacteria bio-inoculants may be a good strategy to develop biocontrol agent and plant growth promoter within green and sustainable production of scallion.