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

**Soumia El boumlasy 1,2,†, Federico La Spada 2,†, Nunzio Tuccitto 3,4, Giovanni Marletta 3,4, Carlos Luz Mínguez 5, Giuseppe Meca 5, Ermes Ivan Rovetto 2, Antonella Pane 2, Abderrahmane Debdoubi <sup>1</sup> and Santa Olga Cacciola 2,\***


**Abstract:** (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, EtOAcextract, 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.

**Keywords:** metabolites; phenolic compounds; inhibitory effect; citrus; apple; HPLC-ESI-MS-TOF; post-harvest diseases; mal secco disease; MIC; MFC
