Late blight and wilt caused by the oomycete, Phytophthora infestans, and the fungus, Fusarium solani f. sp. eumartii, respectively, are severe diseases in Solanaceae crops worldwide. Although traditional approaches to control plant diseases have mainly relied on toxic chemical compounds, current studies are focused to identify more sustainable options. Finding alternatives, a low molecular weight chitosan (LMWCh) obtained from biomass of Argentine Sea's crustaceans was assayed. In an attempt to characterize the action of LMWCh alone or in combination with the synthetic fungicide Mancozeb, the antimicrobial properties of LMWCh were assayed. In a side-by-side comparison with the SYTOX Green nucleic acid stain and the nitric oxide-specific probe, diaminofluorescein-FM diacetate (DAF-FM DA), yielded a similar tendency, revealing LMWChmediated cell death. The efficacy of LMWCh, Mancozeb, and the mixture LMWCh-Mancozeb was in turn tested. A synergistic effect in the reduction of F. eumartii spore germination was measured in the presence of subinhibitory dosis of 0.025 mg ml −1 LMWCh and 0.008 mg ml −1 Mancozeb. This mixture was efficient to increase the effectiveness of the single treatments in protecting against biotic stress judged by a drastic reduction of lesion area in P. infestans-inoculated tissues and activation of the potato defense responses.