In agriculture, search for biopolymer derived materials are in high demand to replace the synthetic agrochemicals. In the present investigation, the efficacy of Cu-chitosan nanoparticles (NPs) to boost defense responses against Curvularia leaf spot (CLS) disease of maize and plant growth promotry activity were evaluated. Cu-chitosan NPs treated plants showed significant defense response through higher activities of antioxidant (superoxide dismutase and peroxidase) and defense enzymes (polyphenol oxidase and phenylalanine ammonia-lyase). Significant control of CLS disease of maize was recorded at 0.04 to 0.16% of Cu-chitosan NPs treatments in pot and 0.12 to 0.16% of NPs treatments in field condition. Further, NPs treatments exhibited growth promotry effect in terms of plant height, stem diameter, root length, root number and chlorophyll content in pot experiments. In field experiment, plant height, ear length, ear weight/plot, grain yield/plot and 100 grain weight were enhanced in NPs treatments. Disease control and enhancement of plant growth was further enlightened through Cu release profile of Cu-chitosan NPs. This is an important development in agriculture nanomaterial research where biodegradable Cu-chitosan NPs are better compatible with biological control as NPs “mimic” the natural elicitation of the plant defense and antioxidant system for disease protection and sustainable growth.

Food crop seedlings often have susceptibility to various abiotic and biotic stresses. Therefore, in the present study, we investigated the impact of Cu-chitosan nanoparticles (NPs) on physiological and biochemical changes during maize seedling growth. Higher values of percent germination, shoot and root length, root number, seedling length, fresh and dry weight, and seed vigor index were obtained at 0.04-0.12% concentrations of Cu-chitosan NPs as compared to water, CuSO4, and bulk chitosan treatments. Cu-chitosan NPs at the same concentrations induced the activities of α-amylase and protease enzymes and also increased the total protein content in germinating seeds. The increased activities of α-amylase and protease enzymes corroborated with decreased content of starch and protein, respectively, in the germinating seeds. Cu-chitosan NPs at 0.16% and CuSO4 at 0.01% concentrations showed inhibitory effect on seedling growth. The observed results on seedling growth could be explained by the toxicity of excess Cu and growth promotory effect of Cu-chitosan NPs. Physiological and biochemical studies suggest that Cu-chitosan NPs enhance the seedling growth of maize by mobilizing the reserved food, primarily starch, through the higher activity of α-amylase.

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An antibacterial and plant growth promoting nanoemulsion was formulated using thymol, an essential oil component of plant and Quillaja saponin, a glycoside surfactant of Quillaja tree. The emulsion was prepared by a sonication method. Fifty minutes of sonication delivered a long term stable thymol nanoemulsion which was characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), cryogenic-field emission scanning electron microscopy (Cryo-FESEM) and fourier transform infra-red (FTIR) spectroscopy. Creaming index, pH and dilution stability were also studied for deliberation of its practical applications. The nanoemulsion (0.01–0.06%, v/v) showed substantial in vitro growth inhibition of Xanthomonas axonopodis pv. glycine of soybean (6.7-0.0 log CFU/ml). In pot experiments, seed treatment and foliar application of the nanoemulsion (0.03–0.06%, v/v) significantly lowered the disease severity (DS) (33.3–3.3%) and increased percent efficacy of disease control (PEDC) (54.9–95.4%) of bacterial pustule in soybean caused by X. axonopodis pv. glycine. Subsequently, significant enhancements of plant growth were also recorded in plants treated with thymol nanoemulsion. This is the first report of a thymol based nanoemulsion obtained using Quillaja saponin as a surfactant. Our study claims that nano scale thymol could be a potential antimicrobial and plant growth promoting agent for agriculture.

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