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Chitosan polymer sizes effective in inducing phytoalexin accumulation and fungal suppression are verified with synthesized oligomers.

Biologically derived chitosan has been reported to induce pisatin and disease resistance response proteins in pea tissue and also to inhibit the germination and growth of some fungal pathogens. Stereo-controlled synthesis of chitosan tetramer, hexamer, and octamer allowed the precise verification of oligomer size required for biological activity. The octameric oligomer optimally induced pisatin accumulation and inhibited fungal growth, verifying previous results obtained with column-purified oligomers derived from crab shells.