Chitosan treatment (2-8 mg/mL) of wheat seeds significantly improved seed germination to recommended seed certification standards (>85%) and vigor at concentrations >4 mg/mL, in two cultivars of spring wheat (Norseman and Max), by controlling seed-borne Fusarium graminearum infection. The germination was <80% in the control and >85% in benomyl- and chitosan-treated seeds. Seed-borne F. graminearum was reduced to >50% at higher chitosan treatments compared to the control. Synthesis of phenolic acids was stimulated in primary leaves following chitosan treatment, and levels of these phenolic acids, especially ferulic acid, increased significantly with increasing chitosan concentration. Lignin content of primary leaves also showed a similar pattern. The synthesis of precursors of lignin such as p-coumaric, ferulic, and sinapic acids and phenolic acids having antimicrobial activity such as benzoic, p-coumaric, caffeic, protocatechuic, chlorogenic, ferulic, and gallic acids was also stimulated by chitosan treatment. The induction of phenolic acids and lignin was significantly lower in cv. Max compared to Norseman. Chitosan also inhibited fungal transmission to the primary roots of germinating seedlings. Results suggest that chitosan controlled seed-borne F. graminearum infection and increased the resistance in seedlings by stimulating the accumulation of phenolics and lignin. Thus, chitosan has a potential for improvement of seed quality and enhancement of crop yields as well as increased value of stored grains for food and feed.

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Stem scar application of chitosan inhibited growth and production of pathogenic factors by blackmold rot [Alternaria alternata (Fr.:Fr.) Keissl.] in challenged tomato (Lycopersicon esculentum Mill.) fruit stored at 20 °C for 28 days. Blackmold lesions were visible within 4 days of inoculation in control fruit, compared with >7 days in chitosantreated fruit. Macerating enzyme activity (polygalacturonase, pectate lyase, and cellulase) in the tissue in the vicinity of the lesions was <50% in chitosan-treated fruit compared with control fruit. Chitosan also inhibited production of oxalic and fumaric acids (chelating agents) and host-specific toxins such as alternariol and alternariol monomethylether by the fungus. The pH of the infected tissue decreased from 4.7 to 4.0 in the control fruit, the optimum for polygalacturonase activity, while the pH of chitosan-treated fruit remained at 4.6. In addition, chitosan also induced production of rishitin (a phytoalexin) in tomato tissue. Such chitosan-pathogen-host interactions may be exploited in the control of postharvest pathogens of fresh fruit and vegetables.