The fraction of acetylation (FA) of chitin is usually
above 0.90, meaning there are few D-glucosamine
(GlcN) units present. Chitin is found as a structural
polymer in fungi, crustaceans, arthropods, insects, and
nematodes (Goody 1990). Chitosan, a linear polymer
made by partial deacetylation of chitin, is a
heteropolymer consisting of N-acetyl-D-glucosamine
(GlcNAc) and D-glucosamine (GlcN) residues (Goody
1990). Chitosan can be hydrolysed into shorter chains to
produce chito-oligosaccharides (CHOS). Both chitosan
and CHOS show little or no toxicity towards mammalian
cells (Jung et al. 1999; Singla and Chawla 2001), are
biodegradable, and may protect plants by direct antimicrobial
activity or by eliciting plant defence mechanisms
(Hadwiger 1979; Hadwiger and Beckman 1980). The
antifungal activity of chitosan is influenced by many
factors, such as its concentration (Palma-Guerrero et al.
2008), degree of polymerization (DP) or molecular
weight (Kendra and Hadwiger 1984), fraction of acetylation
(FA) (Stössel and Leuba 1984), pH, and ionic
strength of the media (Jung et al. 1999; Wang 1992