Chitin Oligosaccharide and Chitosan Oligosaccharide: Two Similar but Different Plant Elicitors

Natural resources have been traditionally used in agriculture by humans. For example, crab and shrimp shell powder has been applied to control crop disease and improve soil fertility (Ha and Huang, 2007). On the other hand, chitin is an important structural component in fungal cell walls and can be degraded by plant chitinases to eradicate fungal infection (Grover, 2012). Plant cells can recognize chitin and chitin-derived molecules to elicit immune response. Since the 1980s, chitin and its deacetylation product chitosan have been used for crop farming as biopesticides, biofertilizers, seed coating formulation, and agricultural film (El Hadrami et al., 2010; Hadwiger, 2013; Trouvelot et al., 2014). In order to overcome the poor solubility obstacle to chitin and chitosan application, soluble chitin oligosaccharides (CTOS) and chitosan oligosaccharides (CSOS) are prepared from these polysaccharides. The effects of CTOS and CSOS on crop disease control were validated by several researches (Yin et al., 2010). Several biopesticides or biofertilizers have been developed based on these two oligosaccharides. However, the quantity and quality of the research on CTOS is much better than that on CSOS. Some papers even claimed that CSOS had no effect on plant disease control (Vander et al., 1998). However, based on the previous works (Cabrera et al., 2006;Maksimov et al., 2011; Guo et al., 2012), just like CTOS, CSOS are potent pathogen-associated molecular patterns (PAMP).