The complex world of polysaccharides edited by Desiree Nedra Karunaratne

 

Is Chitosan a New Panacea? Areas of Application 

 

27 

chitosan are phytoalexines, pathogenesis related proteins (PR), protein inhibitors, chitinases 

and glucanases, as well as Reactive Oxygen Species (ROS) and hydrogen peroxide 

generation [224]. This is because chitosan interacts with cellular DNA generating multiple 

biochemical reactions in the plant, generating a rapid response in the plant against 

pathogens attack. For this reason, chitosan has been considered as an elicitor, namely a 

defense mechanism activator in plants, generating a process at cellular level in which plant 

cells get and transduce biological signals in order to activate defense responses [225]. There 

are some specific elicitor-binding proteins which act like physiological receptors in signal 

transduction cascades, varying their specificity depending on the studied system, which 

allows researchers to find the molecular bases that origin the signal interchanges between 

host plants and microbial pathogens [225-227]. 

Not only at biochemical level but also at microbiological level, chitosan is effective on 

plant protection. It has been found that application of chitosan in plants by the ways 

mentioned in sections above reduces visibly the damages caused in the plants by 

pathogenic fungi because of the antibiotic nature of chitosan [215, 218]. Because of being 

a polysaccharide, chitosan acts as a bioremediator molecule that stimulates the activity of 

beneficial microorganisms in the soil such as Bacillus, fluorescent, Pseudomonas, 

Actinomycetes, Mycorrhiza and Rhizobacteria [228-233], which alter the microbial 

equilibrium in the rhizosphere disadvantaging plant pathogens, making them able to 

compete through mechanisms such as parasitism, antibiosis, and induced resistance 

[234,235]. 

44. Bioinsecticide 

Chitosan research has been focused principally in controlling bacterial and fungal burden; 

nevertheless there are some investigations about the use of chitosan as bioinseciticide. One 

of the first findings was that chitosan is active against some insects like lepidopterous and 

homopterous, with a mortality of 80%, and this percentage increases when increasing oligo-

chitosan concentration too [236]. 

Not only chitosan, but also its derivates (as N-acetyl (NAC) and N-benzyl (NBC) 

chitosan derivatives) had shown significant insecticidal activities superior to those of 

chitosan itself, particularly against species like Spodoptera littoralis, an important 

destructive pest of subtropical and tropical agriculture in northern Europe, affecting 

cotton, vegetable and ornamental crops [237]. Some other insects have been successfully 

attacked by chitosan derivates, like Helicoverpa armigera (H¨ubn), Plutella xylostella (L), 

Aphis gossypii (Glover), Metopolophium dirhodum (Walker), Hyalopterus pruni 

(Geoffroy), Rhopalosiphum padi L, Sitobium avenae (Fabricius) and Myzus persicae 

(Sulzer) [238]. 

Active chitinases from chitosan are relevant enzymes for biopesticide control mechanisms, 

being the hydrolysis of chitin-containing media a common practice to evaluate the efficiency 

of bioinsecticide organisms. It has been considered to add chitin derivatives to formulations 

---

 

The Complex World of Polysaccharides 

 

28 

containing these microorganisms to increase biopesticide effectiveness, to provide a 

favorable developmental environment and resistance against adverse conditions [239]. New 

chitosan derivatives with insecticidal or fungicidal properties may thus serve as good 

alternatives for broad-spectrum and highly persistent pesticides because they are non-toxic 

to vertebrates and humans, and have a biodegradable matrix. 

45. Biopesticide 

Tricoderma sp. and Bacilus sp. are microorganisms which often increase chitin and chitosan 

production, enhancing its efficiency to control pathogenic microorganisms and pests [238]. 

Native populations of biocontrol microorganisms became increased by adding chitin in soils 

infected with pathogenic agents. Thereafter, these endogenous control strains can be 

isolated, cultured and potentially used as biological controls. It has also been demonstrated 

a significant increase in chitinolytic microorganisms even in very infertile soils like in dunes, 

improving soil microbiota and its properties [239, 241].  

46. Bionematicide 

Nematodes proliferation can be controlled when chitosan is applied in soil, because 

chitinolytic microorganisms proliferate destroying nematode eggs and degrading the chitin-

containing cuticle of young nematodes [240]. Because of the high content of nitrogen in 

chitosan and chitin molecules, concentrations of ammonia emissions increase turning toxic 

to nematodes which principally affect plant roots and shoots [239, 243].  

Further research is still required to find more applications of chitosan in agriculture, but 

nowadays this polymer means to be a cheap and easy material to deal with crop problems 

pre-harvest, harvest and post-harvest level. 

47. Conclusions 

Scientific databases reveal thousands of articles and patents related to chitin, chitosan and 

its derivatives and increasingly opens up new possibilities to produce new derivatives as 

well as new applications. 

The answer to the question if the chitosan is a “new panacea”, is given by the multiple 

applications for this new biopolymer and its predecessor, the chitin. Two hundred years 

have passed since its discovery and this biopolymer has shown unique qualities that many 

other polymers do not have, as it can be applied in different areas like in the agricultural 

and medical field or in related areas such as pharmacy and biomedical. 

As seen in this chapter, chitosan’s behavior in different applications within diverse areas, is 

governed by its molecular weight, degree of deacetylation, degree of polymerization and 

source of obtention. Twenty years ago the articles published did not provide data on the 

characterization of material but today most papers focus on the properties of the polymer 

before the application. 

---