The four plants pathogens, Botrytis cinerea, Phytophthora cinnamomi, Cryphonectria parasitica and Heterobasidion annosum are responsible for several diseases affecting different plant species in Portugal, such as pines (H. annosum), chestnuts (P. cinnamomi and C. parasitica) and eucalyptus (B. cinerea). These pathogens incurs in large economic losses, and ultimately causes the death of these plants. The use of biopolymers as antimicrobial agents, such as chitosan (derived from chitin), is increasing, in order to reduce the negative impact of conventional chemical treatments on the environment, avoiding health risks. Therefore, eco-friendly polymers were produced through (1) N-acetylation with addition of acetic anhydride and (2) hydrogen peroxide of chitosan samples, obtained from two different sources: shrimp (commercial chitosan) and swimming crab bycatch specie Polybius henslowii. The chemical structure and molecular weight of the prepared chitosan derivatives, water soluble chitosan (WSC) and chitooligosaccharides (COS), was confirmed by Fourier Transform Infrared (FT-IR) and Gel Permeation Chromatography (GPC) and their antifungal activity evaluated against Botrytis cinerea, Phytophthora cinnamomi, Cryphonectria parasitica and Heterobasidion annosum. The concentration range varied from 0.0125 to 0.1 mg/mL and inhibition percentages were determined by differences in radial growth on the agar plates for all species. Although not all species tested exhibited equal vulnerability towards the concentrations range, antifungal activity of chitosan samples proved to be dependent, increasing the inhibitory capacity with lower concentrations. The results obtained support the use of chitosan fromPolybius henslowii when compared with commercial chitosan with shrimp towards antifungal approaches, suggesting that chitin producers can rely on this crab waste as a raw material for chitin extraction, adding value to this bycatch specie. Financial support was obtained from European Fisheries Fund – Axis 4 managed by Fishery Local Action Group Oeste-Portugal.
