Definition

Chitosan is a linear polysaccharide that can be synthesized by deacetylation of chitin (N-acetyl-glucosamine) present in fungal cell wall, and arthropods’ exoskeleton (figure 1).

Today, a major part of chitosan is produced from marine crustaceans’ waste. Since few years ago, fungal chitosan is also produced by recycling Aspergillus biomass or mushroom waste. In addition to its ecological origin and its affordable prices, chitosan is biodegradable and represents a high level of biocompatibility.

Chitosan (β 1-4 D-glucosamine) is the deacetylated form of chitin (β 1-4 N-acetyl-D-glucosamine)

From technical point of view, the term chitosan is not attributed to a single compound. It is a General Name that covers a variety of commercially available copolymers that are heterogenous in their:

• Degree of deacetylation
• Molecular mass
• Degree of polymerisation
• Acid dissociation constant value (pK_a)

These different characteristics have a strong influence on the physic-chemical properties (including viscosity and solubility), and they have a direct influence on the biological properties of the substance and its effects on plants and animals.

Agricultural application of chitosan

Since late 80’s, many studies have focused on the application of chitosan in different fields of agriculture. Many positive effects have been attributed to chitosan. As such, are plant defense elicitation, root and foliar growth stimulation, fructification, frost, and drought resistance induction. Despite to the growing body of promising empirical data, practical applications of chitosan are very limited. One of the main cause lays in the lack of proper species-specific formulations. As we have mentioned, chitosan is a generic name attributed to a family of copolymers with different Physic-chemical and biological properties. In other words, a chitosan molecule that might activate defence mechanisms of wheat, might be quite ineffective on soybean.

Since 2016, Cibon and our French partner company work in a close collaboration with Bourgogne Franche – Comté University (France) to develop a new generation of agricultural chitosan-based materials. With scientific support of researchers from chemistry school and medical school of the university of Bourgogne Franche – Comté, we have developed CHITOCi  Series product. Using pharmacological techniques (drug delivery, microencapsulation, nano composites, and nano drugs), CHITOCi products are designed to resist to environmental degradation and irrigation. Using the cutting-edge technologies like nano technology, all these products represent a high absorption rate and are highly bioactive. CHITOCi products, are made from nontoxic, biodegradable, and ecological raw materials. As similar products are rare (or even absent) on the market, in the present text, we will frequently refer to these products.

Chitosan as a seed treatment

ISF (International Seed Federation) defines “Seed treatments” are the physical, chemical and /or biological agents and techniques applied on seed to provide protection and improve the establishment of healthy crops”. The germination stage and the first stages of seedling development are the most critical parts of plants life. In fact, many seeds can never finish their germination because of soil- and seedborne pathogens and their inability to uptake micro- or macronutrients or the water, present in the environment.

Chitosan has several properties that represent an interesting seed treatment potential. Some Chitosans with filming properties can provide a coating that insure a physical protection for the seed, increased water retention and chelating effects on macro and micronutrients.

Other chitosans, with high bactericidal and fungicidal activity can provide antipathogenic protection. Riccioni et al. (The use of natural film as seed-coating. In: Proceedings of the Conference “L’agricoltura biologica in risposta alle sfide del futuro: il sostegno della ricerca e dell’innovazione”. Catania, 7–8-nov 2011.) showed that a single treatment of wheat seeds with chitosan could not only render wheat seeds resistant to Fusarium graminearum but it also considerably increased emergence index of treated seeds in comparison to nontreated controls.

Blotter test for seed health analysis after 7 days of incubation at 25°C of durum wheat seeds artificially infected with F. graminearum, one of the causal agents of root and foot rot in cereals. Seeds were then coated with a solution of chitosan and tea tree oil. The chitosan/tea tree oil treatment significantly reduced the fungal infection on seeds (right) compared with the inoculated and not treated seeds (left). Photo from Riccioni L. et al 2011.

Similar results were obtained when we applied our specially designed chitosan-based seed treatment products (CHITOCi SI) on rapeseed that have already been treated with classical techniques (figure 4). The importance of species-specific formulation of chitosan can be seen where another formula, that is designed for other crops, and the commercially available chitosan are not as effective as CHITOCi SI that is specially designed for rapeseed seed treatment.

Overall, proper application of chitosan, with a correct formulation and good quality, can ameliorate:

• The seed germination index
• The mean germination time and flowering time
• Plant growth (e.g. shoot height, root length, and seedling, vegetative growth vigor)
• Biomass increase
• Lower chance of being infected by fungi in comparison with the untreated seeds.

CHITOCi S products have been tested for different crops with a great success. As such are, rapeseed, sunflower, maize, soybean, lettuce, beans, wheat, barely and tomato.

Chitosan as a defense elicitor

One of the most important effects of chitosan on plants is to elicit plants’ innate resistance against infection (fungal, bacterial and to some extent viral) and infestation (insects). It has been showed that chitosan can cross the tegument and interact with plant cells and influence cellular metabolism (figure 5). The exact mechanism of its action is still ambiguous, but it is well demonstrated that chitosan strongly stimulates production of PR’s (Pathogen related proteins) and Phytoalexins.

Figure 5- Although the exact mechanism of chitosan defense elicitation of plants is not still clear, several studies showed that chitosan treatment activates the fabrication of defense proteins (PR’s or pathogen related proteins), Phytoalexins, and a huge increase in deposition of callose and lignin into plant cell wall which increases plant vigor and physical resistance. Figure shows the two main proposed mechanisms.

In a recent study, we have measured the impact of CHITOCi formulations on plants innate defense against rapeseed flea beetle (Phyllotretta sp.). Results showed that seed treatment, followed by foliar application of chitosan can reduce the number of damaged leaves up to 80% without application of any other treatment

Amongst CHITOCi series range, CHITOCi SA, Salicylic Acid, encapsulated by chitosan and/or Nano chitosan, can stimulate strong and rapid defense reactions even in small doses. These products can be applied in preventive and curative applications. CHITOCi Phi|SA is our strongest antifungal product.

Chitosan as a nano vehicle – nano chelate

Unlike chitin, chitosan is soluble in acidic conditions and is one of the rare polycationic polymers. This means that chitosan will absorb negatively charged particles, like bacteria, fungi, algae etc. On the other hand, the amine group of chitosan, has a strong affinity for metals

In pharmaceutical industry, chitosan has long been applied as a nano drug delivery vehicle. Recently, Chitosan nano particles are used to vehicular zinc, copper, phosphide, salicylic acid, and many other molecules into the plant organism. Chitosan nano vehicle can not only transfer targeted molecules into the plant organism, but it also provides a strong protection against environmental UV and protects the molecules from being washed away by water. Additionally, chitosan tends to attach targeted molecules to hydrophobic surface of leaves

Physical, and chemical properties of chitosan can highly influence its affinity for metals. In other words, the ability of chitosan to absorb metals depends to its type, molecular weight and other factors. Here again an exact formulation can highly affect the efficiency of the product.

Many studies have tried to apply chitosan nanocomposites for chelating metals for agricultural applications. Unfortunately, chitosan nanoparticles tend to agglomerate and the application of chitosan as an agricultural chelator, synthesized with common techniques, is not possible. Recently, we have developed CHITOCi Phi|Cu, CHITOCi Zn, CHITOCi Fe, and CHITOCi Nano. These are highly stable metal chelates and/or nano complexes which bring essential micronutrients to the culture. Moreover, these molecules are more effective than similar products as they preserve the metals for a long period and in the same time release the complexed molecules steadily, over time.

Figure 8- Chitosan as a nano chelating agent can reduce the application dose and increase the efficiency of the metal or desired molecules.

Chitosan for soil amendment

In addition to its direct physical and physiological impacts on plants, chitosan can also improve soil biological conditions as a soil amendment. Two mechanisms are proposed: whether chitinolytic microorganisms, which can hydrolyse the chitinous hyphae of pathogenic fungi, increased their numbers and/or activities secondary responders to the added chitosan have a detrimental activity against pathogens.

CHITOCi AGUA is designed for soil amendment. It can be diluted in irrigation water and has a strong biostimulating imapcts. Triales with vine showed that CHITOCi AGUA treatment induce formation of leaves and root and can stimulate an antifrost defence. CHITOCi SA can also be applied on vine for frost and cold shock protection.