Eco-Friendly Synthesis of Chitosan: Biological Properties and Plant Protection Applications

Plant protection is essential for safeguarding global food security, as plant pathogens and diseases are among the major causes of annual crop losses worldwide. Conventional chemical pesticides have been extensively employed to manage these challenges; however, their intensive and indiscriminate use can pose serious risks to human health, animal welfare, and environmental quality. Therefore, the development of safer, eco-friendly, and sustainable alternatives has become increasingly imperative. In this regard, natural biopolymers have shown promise as candidates for sustainable plant protection strategies. Chitosan (CTS), a natural biopolymer derived primarily from the deacetylation of chitin (CTN) obtained from crustacean shells, insects, and fungal cell walls, has attracted considerable attention due to its remarkable biological properties. However, conventional CTS extraction relies on chemical processes that can negatively affect the environment and human health. Thus, green extraction approaches have attracted considerable interest as simpler, more economical, and environmentally safer methods for biopolymer production. Green-synthesized CTN and its derivative CTS exhibit promising antimicrobial activity against several phytopathogens through dual mechanisms involving direct pathogen inhibition and indirect stimulation of plant immune responses, making them potential alternatives to synthetic agrochemicals. This review provides a comprehensive assessment of the sources, physicochemical characteristics, and green extraction approaches of CTN and CTS, with particular emphasis on their antimicrobial efficacy and applications in sustainable plant protection. Their favorable biocompatibility further broadens their applicability in agricultural, pharmaceutical, and food preservation sectors. Green synthesis approaches represent a significant advancement toward sustainable biopolymer production. Nevertheless, further research is required to optimize extraction processes, enhance bioactive performance, and elucidate mechanisms of action, thereby realizing their potential as multifunctional agents for plant health and broader biotechnological applications.