After cellulose, which is found in woody plants, chitin is the most common biopolymer on earth. It can be found in the skeletons of crustaceans and lobsters, but also in the cell wall of fungi, the cell wall of nematode eggs, the skin of insects, etc. Chitin is completely degradable to carbon dioxide, water and nitrogen compounds and is therefore a 100% biological product.
Studies since the 1960s have shown that the product has a positive effect on the disease resistance of crops. The reason that chitin is not widely used in agriculture and horticulture is due to the fact that up to 10 tonnes per hectare had to be applied to see any effect. This became far too expensive in practice.
It was later discovered that chitin can be converted to chitosan by deacetylation or with the help of enzymes.
Chitosan is a much faster acting substance than the raw chitin and is much easier to apply in practice. Whereas with chitin, 10 tonnes per hectare were needed to see an effect, with 10 litres of chitosan hydrochlorid, 4 crop sprays per hectare can be made.
Mode of Action
Chitosan works in the plant in a number of ways:
- Scientific research has shown that chitosan has a direct microbial toxic effect on pathogens such as fungi and bacteria. As a result, the cell nucleus of these pathogens is destroyed by chitosan, preventing them from multiplying.
- Chitosan also has a plant strengthening function (and works as a so-called elicitor). When chitosan is sprayed onto a leaf, the plant reacts by producing enzymes and proteins that the plant naturally makes to protect itself against fungal and bacterial attack. As a result, the plant is already ready to protect itself if it is attacked by fungi or bacteria.
- Scientific research has shown that after treatment with chitosan, the plant produces more chlorophyll, which promotes photosynthesis. On the one hand, this can lead to a higher yield per hectare, but on the other hand, the plant is also more vital to defend itself when attacked by pathogens.
- When chitosan comes into contact with the soil, certain bacteria that live on chitin multiply very strongly. When these bacteria have used up the chitin from the chitosan, they look for other sources of chitin in the soil. They find it in the cell wall of pathogenic fungi or in the cell wall of eggs laid by nematodes.
In this way, a protective layer of bacteria is formed around the plant roots, preventing pathogens from infecting the plant roots.
- The formation of symbiotic relationships such as mycorrhizal connections is also stimulated. This improves the plant’s ability to extract nutrients and moisture from the soil and enables it to better survive dry conditions.
For a schematic representation of the effect of chitosan in the plant, see the figure below (source: Asian Journal of Pathology, 2017):
Chitosan hydrochlorid can be applied in two ways: as a crop spray or as a coating on potato tubers or seeds, or a combination of both. Scientific studies show the following:
- Leaf mass increases;
- Increased chlorophyll content in the leaf, which promotes photosynthesis;
- Wounds close more quickly due to the formation of epithelium (this reduces the chance of Stemphylium infestation, for example)
- In dry conditions, stomata stay closed longer, which means the plant uses the available water more efficiently.
Soil treatment / coating of seeds or tubers
- The microbial community around the roots of the plant changes in favour of good fungi (mycorrhiza) and bacteria, so that harmful fungi, bacteria and nematodes in the direct vicinity of the plant roots are combated (effect of the enzyme chitinase, among others);
- The growth of the root system is stimulated;
- The osmotic pressure in the root cells changes, allowing them to better absorb water and nutrients from the soil;
- The germination of treated seed and seedlings increases (hydrolytic enzymes accelerate the release of starch and proteins, which are necessary for growth).