S14 - Session O2 - Chitosan, a complex substance but with great potential for global IPM and for reducing farmers dependence on synthetic fungicides

Authors: Emmanuel Pajot *

Chitosan is a natural polysaccharide resulting from the deacetylation of chitin, the second most abundant polysaccharide on earth. Today, its production is mainly based on the recycling of crustacean shells, but it can also be obtained from insects or fungi. The terms chitin and chitosan refer to any polysaccharide composed of a succession of two "glucose" units: N-acetyl-glucosamine and N-glucosamine. The only criteria for differentiating them is the proportion of each of the units in the polymer: if N-glucosamine is the majority, it is chitin, whereas if it is the minority, it is chitosan. Thus, each « chitosan » is unique and its performance for a given function is governed by three major factors: the size or degree of polymerisation of the chitosan molecules, the proportion of each of the two glucose units (degree of acetylation or deacetylation) and their linkage pattern (acetylation pattern). Due to its numerous biological properties, its absence of toxicity and its biodegradability, chitosan is now used in various fields of application such as nutraceuticals, water treatment and plant protection. The interest of chitosan in agriculture has been known for decades and a considerable number of scientific papers deal with the influence of the previously described parameters on its performance. For example, small chitosan oligomers will have a better plant eliciting effect due to their small size allowing them to reach molecular receptors more easily. Polymers, on the other hand, will be responsible for bacterial and fungistatic activity thanks to their ability to interact ionically with the microorganisms cell wall and their film-forming effect. Recently, new research has revealed new parameters influencing the biological effectiveness of a chitosan-based product, in particular the interaction that can exist between certain polymers and oligomers. In-depth knowledge on the chitosan characterisation, their evaluation and a high level of control of the production process will enable this active ingredient to contribute to the sustainability of technicals production scheme by reducing the use of synthetic fungicides. Thanks in particular to recent regulatory changes at the global level, major crops such as cocoa, vegetables and fruits, but also cereals, are already benefiting from this natural, non-toxic and biodegradable substance with very favourable results.