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Effect of chitosan on Xanthomonas pathogens.
Institute of Biotechnology, Zhejiang University, China
summary
The antibacterial activity and mechanism of two chitosans with different molecular weights were investigated against 12 strains of Xanthomonas isolated from poinsettia. The results showed that the two chitosans significantly inhibited bacterial growth based on OD (Optical Density). Transmission electron microscopy revealed that chitosan caused changes in protoplast (cells with their cell walls removed) concentration and surface morphology, with some cells' membranes and cell walls severely distorted and destroyed. It was confirmed that the two chitosans removed biofilm* (bacterial membrane) masses. This study revealed that biofilm and cell membrane play important roles in the antibacterial mechanism of chitosan.
*Biofilm: A bacterial membrane is a structure formed by microorganisms.
Diseases caused by Xanthomonas bacteria
Peach bacterial hole disease, citrus canker disease, grape bacterial spot disease, mango canker disease
Black rot of cruciferous plants, such as cabbage black rot, broccoli black rot, and radish black rot
Rice bacterial leaf blight, Chinese cabbage black rot, carrot bacterial spot, soybean leaf burn, etc.
Efficacy of low-level copper and chitosan in combination to control late blight of potato
Department of Plant Pathology, Washington State University, USA (2006)
summary
Organic growers control potato late blight, caused by Phytophthora infestans (Mont.) de Bary, with natural copper compounds such as copper sulfate pentahydrate (CuSO4·5H2O), copper oxide, or copper hydroxide. However, recent environmental concerns about copper residues from the USDA National Organic Program indicate the need to reduce copper use to control late blight.
The study described the use of low levels of copper sulfate pentahydrate in combination with chitosan (as a spreading agent) for disease control, and reported that analysis of excised leaves showed that copper levels 40 times lower than the recommended amount were effective in suppressing late blight and preventing the leaf yellowing that is often associated with copper-based fungicides, compared to commercial fungicides that contain copper hydroxide as the active ingredient.

Chitosan approved for use in organic farming in EU
2017.1
In January 2017, the European Commission's Department of Agriculture and Rural Development approved chitosan as a Basic Substance (natural substances) that can be used in organic farming .
"Basic Substances" are defined in Article 2 of EC Regulation No 178/2002 as foodstuffs, which are of animal or plant origin and are intended for human consumption. They do not contain animal feed, medicines, cosmetics, tobacco, residues or contaminants. In Article 23 of EC Regulation No 1107/2009, "Basic Substances " are defined as plant active substances that do not have the genetic ability to cause endocrine disruption, neurotoxicity or immunotoxicity. They are not plant protection agents (pesticides) but are used to protect plants."
Chitosan meets this definition, and with strong requests from Germany and France, it has now been approved for use in organic farming. *The purpose of its use is to prevent mold and bacteria. Please see our blog for more details.

Spray chitosan promptly after typhoons, wind damage, hail damage, etc.
It is known that chitosan has the ability to repair wounds in plants. When exposed to strong winds such as typhoons, the leaves and stems of plants develop numerous visible and invisible fine wounds, which increase the likelihood of disease infection from the wounds. If it takes a long time for the wounds to heal, the plant will lose nutrients and moisture, and various risks such as the outbreak of disease will arise. Prompt spraying of chitosan is effective in repairing wounds and restoring plant immunity.
Expected effects of chitosan spraying
① Activity of lytic enzymes such as chitinase and glucanase to prevent pathogenic infections. ② Promotion of wound repair and lignin synthesis through callus (undifferentiated cells) formation by phenylalanine ammonia lyase (PAL) activity (strengthening of fiber).
③ Promotion of lignin synthesis through peroxidase activity ④ Induction of antibacterial substances phytoalexins within cells ⑤ Induction of plant hormones ethylene and jasmonic acid, and improvement of resistance to disease infection (including bactericidal and antibacterial effects)
⑥Improved photosynthetic capacity due to cell division activity (increase in chlorophyll a₊b)
7. Reduces withering caused by salt damage (Chitosan-chlorine chelate bond)
Please feel free to use this as a reference.

Drug resistance spreads
2017.2.26
As drug resistance, which makes drugs ineffective against humans, livestock, and plants, has become an international issue, countries committed to working together to combat drug-resistant bacteria at the 2016 G7 Ise-Shima Summit. In addition, a 2016 survey by the Ministry of Agriculture, Forestry and Fisheries called for greater vigilance in the use of drugs, stating that the incidence of drug-resistant pests in domestic agricultural products has more than doubled in three years.
As drug resistance spreads worldwide, the fact that chitosan, which increases resistance to pathogenic microorganisms, has been approved for use in organic farming in 27 EU countries is likely related to this background. There are high hopes that it will also be approved in Japan, which also recognizes organic equivalence.