Chitosan as Source for Pesticide Formulations

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 LMWCh-mediated 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

Swaposin domain of potato aspartic protease (StAsp-PSI) exerts antimicrobial activity on plant and human pathogens

Plant-specific insert domain (PSI) is a region of approximately 100 amino acid residues present in most plant aspartic protease (AP) precursors. PSI is not a true saposin domain; it is the exchange of the N- and C-terminal portions of the saposin like domain. Hence, PSI is called a swaposin domain. Here, we report the cloned, heterologous expression and purification of PSI from StAsp 1 (Solanum tuberosum aspartic protease 1), called StAsp-PSI. Results obtained here show that StAsp-PSI is able to kill spores of two potato pathogens in a dose-dependent manner without any deleterious effect on plant cells. As reported for StAPs (S. tuberosum aspartic proteases), the StAsp-PSI ability to kill microbial pathogens is dependent on the direct interaction of the protein with the microbial cell wall/or membrane, leading to increased permeability and lysis. Additionally, we demonstrated that, like proteins of the SAPLIP family, StAsp-PSI and StAPs are cytotoxic to Gram-negative and Gram-positive bacteria in a dose dependent manner. The amino acid residues conserved in SP_B (pulmonary surfactant protein B) and StAsp-PSI could explain the cytotoxic activity exerted by StAsp-PSI and StAPs against Gram-positive bacteria. These results and data previously reported suggest that the presence of the PSI domain in mature StAPs could be related to their antimicrobial activit