Chitosan has the ability to prevent infection. Chitosan and its derivatives are safe to use and have been shown to have beneficial effects on plants by inducing both local and systemic defense mechanisms against disease . The accumulation of TMV, the activity of a hydrolase, and the shape of virion particles are all altered by chitosan . To control cucumber mosaic virus (CMV) infection, chitosan can be applied prophylactically to tomato plants or applied after infection has occurred .The degree of inhibition varies with the molecular weight of chitosan , such as potato X virus, tobacco mosaic and necrosis virus, alfalfa mosaic virus, peanut dwarf virus and cucumber mosaic virus . So far, though, no scientific studies have shown for sure that chitosan can stop viruses or viroids from spreading .