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.

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The antifungal activity of chitosan, a bioplymer of β-1-4 gluscosamine, against Alternaria alternata, causal agent of black mold of tomato, was investigated. Chitosan was incorporated into potato dextrose broth (PDB) at concentrations of 100, 200, 400, 800, 1600, 3200, and 6400 μg·ml–1, growth and toxin production by the fungus were assessed after a 15-day incubation period. Chitosan significantly affected both growth and toxin production at higher concentrations. However, at lower concentrations, toxin production was affected more than the growth, as evidenced by minimum inhibitory concentrations (MIC) of chitosan derived for toxin production and mycelial growth. Excess sporulation of the fungus was observed in the presence of chitosan, but the spore viability was affected. Chitosan induced aggregation of fungal cells, abnormal shape, excess branching, and hyphal contortion. It also induced leakage of proteins from the fungal cells. The virulence of the toxin in culture filtrate of the fungus from different concentrations of chitosan was assayed by administering on tomato discs. Phospholipid content, electrolyte leakage, xylanase, and pectin methylesterase activity were measured in the culture filtrate administered tomato tissue. Decreased trend in causing electrolyte leakage, phospholipid degradation, and activation of xylanase and pectin methylesterase were observed with increasing concentrations of chitosan. The results showed that chitosan inhibits fungal growth at higher concentrations than toxin production. Further toxin produced at lower concentrations of chitosan was less virulent. Thus chitosan has potential as an antifungal agent.

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