Inhibitory Activity of Shrimp Waste Extracts on Fungal and Oomycete Plant Pathogens.

(1) Background: This study was aimed at determining the in vitro inhibitory effect of new natural substances obtained by minimal processing from shrimp wastes on fungi and oomycetes in the genera Alternaria , Colletotrichum , Fusarium , Penicillium , Plenodomus and Phytophthora ; the effectiveness of the substance with the highest in vitro activity in preventing citrus and apple fruit rot incited by P. digitatum and P. expansum , respectively, was also evaluated. (2) Methods: The four tested substances, water-extract, EtOAc-extract, MetOH-extract and nitric-extract, were analyzed by HPLC-ESI-MS-TOF; in vitro preliminary tests were carried out to determine the minimal inhibitory/fungicidal concentrations (MIC and MFC, respectively) of the raw dry powder, EtOAc-extract, MetOH-extract and nitric-extract for each pathogen. (3) Results: in the agar-diffusion-assay, nitric-extract showed an inhibitory effect on all pathogens, at all concentrations tested (100, 75, 50 and 25%); the maximum activity was on Plenodomus tracheiphilus , C. gloeosporioides and Ph. nicotianae ; the diameters of inhibition halos were directly proportional to the extract concentration; values of MIC and MFC of this extract for all pathogens ranged from 2 to 3.5%; the highest concentrations (50 to 100%) tested in vivo were effective in preventing citrus and apple fruit molds. (4) Conclusions: This study contributes to the search for natural and ecofriendly substances for the control of pre- and post-harvest plant pathogens.