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Source activity and sink strength are important aspects to measure growth and yield in wheat. Despite zinc's extended functions in the amendment of plant metabolic activities, critical research findings are missing on mapping the elusive interplays of slow-release zinc (Zn) application from nanoparticles (NPs) in crop plants. The present study reports that slow-releasing Zn application through Zn-chitosan NPs bestows myriad effects on source activity and sink strength in wheat plants. Herein, effects of foliar application of Zn-chitosan NPs (0.04-0.16%; w/v) at booting stage of wheat crop were evaluated to quantify the source sink potential compared to ZnSO4. Zn-chitosan NPs endowed elevated source activity by up-regulating cellular redox homeostasis by improving the antioxidant status, cellular stability and higher photosynthesis. Cognately, in the field experiment, NPs (0.08-0.16%, w/v) significantly spurred sink strength by up-regulating starch biosynthesis enzymes viz. sucrose synthase (SUS), invertase (INV), ADP-glucose pyrophosphorylase (AGPase), soluble starch synthase (SSS) and accumulated more starch in developing wheat grains. Concomitantly, higher spike lengths without awns, significantly higher number of grains/spike, test weight (24% more than ZnSO4 treatment), yield (21% more than ZnSO4 treatment), biological yield and harvest index quantified the higher sink size to further validate the better sink strength in slow-release Zn application via chitosan NPs.

Sustained source-activity is imperative for vigor plant growth and yield. In present study, physio-biochemical responses of wheat plant contributing to source-activity were measured after application of salicylic acid-chitosan nanoparticles (SA-CS NPs). SA-CS NPs slowly release SA for sustained availability to plant. In seedling bioassay, as compared with salicylic acid (SA), SA-CS NPs incurred up to ~1.5 folds increased activities of seed reserve food remobilizing enzymes for substantial mobilization of reserve food to growing seedlings and enhanced seedling vigor index (SVI) by 1.6 folds. At booting stage, foliar application of SA-CS NPs (0.01-0.08%; w/v) enhanced the activities of superoxide dismutase (1.94 folds), catalase (1.33 folds), peroxidase (1.99 folds) and polyphenol oxidase (1.04 folds) in flag leaf. SA-CS NPs further contrived cellular homeostasis by comforting reactive oxygen species (ROS), malondialdehyde (MDA) and proline contents in flag leaf. SA-CS NPs (0.08%; w/v) significantly increased chlorophylls (a-b) contents (1.46 folds), spike length without awns, spike lets per spike and grain weight per pot as compared with SA. Study categorically explicates that slow release of SA from SA-CS NPs could exert significant effect on source-activity by maneuvering various physio-biochemical responses of wheat plant.

We, herein, report the effect of chitosan nanofertilizer comprising of copper (Cu) and salicylic acid (SA) on source activity in maize. Seed treatment and foliar application of chitosan nanofertilizer significantly up-regulated the source activity in developing maize plants. Seed treatment with nanofertilizer induced 1.6 folds higher seedling vigour index, 1.7-3.0 folds higher activities of reserve food mobilizing enzymes in seedlings as compared with control. Foliar application of nanofertilizer (0.01-0.16%) statistically significantly increased the activities of antioxidant enzymes (1.06-1.91 folds), reduced malondialdehyde content and enhanced chlorophyll contents (2 folds) in leaves. Application of nanofertilizer remarkably induced sucrose translocation (2.5-3.5 folds) in internodes which gives subtle clue of higher remobilization of nutrients towards growing cob. The elusive bioactivities of nanofertilizer can be attributed to slow release and synergistic effects of Cu and SA. We claim that chitosan nanofertilizer has immense potential to promote source activity in maize for higher crop yield.

Global agriculture is urgently seeking ways to mitigate the detrimental effects of conventional chemical fertilizers on the environment. Biodegradable, eco-friendly, renewable energy-sourced next-generation fertilizers could be an answer, allowing for improved nutrient use efficiency and a lower environmental footprint. During the last decade, agricultural research on chitosan nanomaterials (NMs) has expanded, demonstrating their usefulness in enhancing agricultural output not only as plant immune boosters but also via slow, controlled and target delivery of nutrients to plants. Chitosan NMs natively act as an abundant nutrient source of C (54.4-47.9 wt%), O (42.3-30.19 wt%), N (7.6-5.8 wt%), and P (6.1-3.4 wt%) to plants. Moreover, chitosan NMs can further functionalized by more nutrients payloads through its functional groups. The current review investigates the technical features of chitosan NMs as prospective next-generation fertilizers based on rationales. The review offers crucial insights into future directions, sources, production capacity of chitosan-based next-generation nanofertilizers for industrial-scale manufacturing.

The excessive and irrational use of synthetic fungicides has perturbed us with irrevocable soil-water-air contaminations, development of resistance in microbes, and disturbing biosphere. Thus, search for biodegradable/ecofriendly materials has emerged as the main goal to replace/reduce the synthetic fungicides in agriculture for crop protection. Under this scenario, nanobiotechnology seems to be a boon for the synthesis of ecofriendly, biocompatible, and safe fungicides which will not only improve the soil health and the defense system of plants but also help in obtaining healthy food for the continuously growing population. Among the available biomaterials/biopolymers, chitosan is being explored as new generation smart material to be used in agriculture especially for plant protection. This chapter describes various chitosan-based nanomaterials (NMs) which have been used from laboratory to field for control of fungal disease in crops.