Microorganisms represent a rich source of biologically active substances including antifungal compounds that can potentially be used as alternative methods to control fungal plant diseases. In the present study, a number of bacterial strains producing and releasing antifungal compounds were identified from natural forest soils and utilized to obtain antifungal preparations. Selected bacteria were associated to 4 different 16S genotypes clustering within the genus Pseudomonas spp. Alcoholic extracts from these bacteria proved a significant antifungal activity by inhibiting the mycelial growth of typical postharvest pathogens including Botrytis cinerea, Penicillium digitatum, Penicillium italicum, Penicillium expansum, Monilinia fructicola, and Colletrotrichum acutatum. The same extracts were particularly effective in reducing the incidence of rots on different artificially inoculated fruits such as citrus, apricots, sweet cherries, table grape, and tomatoes. On tangerines, the selected extracts also showed a curative activity since treatments made 24 h after the inoculations of P. digitatum reduced rots, suggesting the possible control of already established infections. In addition to the direct antifungal activity, the induction of resistance in treated host tissues was also demonstrated. In fact, on apricots inoculated with M. fructicola and on table grape and tomatoes inoculated with B. cinerea a significant reduction of rots was achieved without a direct contact between extracts and pathogens. Furthermore, these extracts proved effective under semi-commercial conditions by reducing natural rots on sweet cherries subjected to cold storage and shelf-life. In field conditions, the most effective extract significantly reduced the incidence and severity of grape powdery mildew. According to metabolomics analyses, 521 target features were detected within the extracts of 3 selected bacteria. Although most of them were not annotated, some common Pseudomonas membrane structural lipids as well as natural products such as phenazine and orfamide analogs, known to have some antimicrobial and antifungal activity, were identified. Additional investigations are needed to correlate the composition of extracts with their biological activity, to identify putative active ingredients and ascertain their safety for humans’ health and the environment. However, currently available data shows important features including: i) a high efficacy under different conditions and against a broad range of diseases, ii) complex mechanisms of action that include a direct antimicrobial activity and the induction of resistance in treated host tissues, and iii) the possible control of already established infection (curative action). Furthermore, selected bacteria can be easily grown with simple and cheap culturing media and their extracts are active at a very low concentration, suggesting the possible development cost effective formulations, able to compete with traditional chemical compounds.

I microrganismi rappresentano una ricca fonte di sostanze biologicamente attive, compresi i composti antifungini che possono essere potenzialmente utilizzati come metodi alternativi per controllare le malattie fungine delle piante. Nel presente studio, un certo numero di ceppi batterici che producono e rilasciano composti antifungini è stato identificato da terreni forestali naturali e utilizzati per ottenere preparati antifungini. I batteri selezionati sono stati associati a 4 diversi genotipi 16S che si raggruppano all'interno del genere Pseudomonas spp. Gli estratti alcolici di questi batteri hanno dimostrato una significativa attività antifungina inibendo la crescita miceliare dei tipici patogeni post-raccolta tra cui Botrytis cinerea, Penicillium digitatum, Penicillium italicum, Penicillium expansum, Monilinia fructicola, e Colletrotrichum acutatum. Gli stessi estratti sono stati particolarmente efficaci nel ridurre l'incidenza dei marciumi su diversi frutti inoculati artificialmente come agrumi, albicocche, ciliegie dolci, uva da tavola e pomodori. Sui mandarini, gli estratti selezionati hanno mostrato anche un'attività curativa poiché i trattamenti effettuati 24 ore dopo l'inoculazione di P. digitatum hanno ridotto le marcescenze, suggerendo il possibile controllo delle infezioni già stabilite. Oltre all'attività antifungina diretta, è stata dimostrata anche l'induzione di resistenza nei tessuti dell'ospite trattati. Infatti, su albicocche inoculate con M. fructicola e su uva da tavola e pomodori inoculati con B. cinerea si è ottenuta una riduzione significativa dei marciumi senza un contatto diretto tra estratti e patogeni. Inoltre, questi estratti si sono dimostrati efficaci in condizioni semi-commerciali, riducendo i marciumi naturali su ciliegie dolci sottoposte a frigoconservazione e a shelf life. In condizioni di campo, l'estratto più efficace ha ridotto significativamente l'incidenza e la gravità dell'oidio dell'uva. Secondo le analisi metabolomiche, sono state rilevate 521 caratteristiche target negli estratti di 3 batteri selezionati. Anche se la maggior parte di esse non sono state annotate, sono stati identificati alcuni lipidi strutturali comuni della membrana di Pseudomonas e prodotti naturali come gli analoghi della fenazina e dell'orfamide, noti per avere una certa attività antimicrobica e antifungina. Ulteriori indagini sono necessarie per correlare la composizione degli estratti con la loro attività biologica, per identificare i principi attivi putativi e accertare la loro sicurezza per la salute umana e l'ambiente. Tuttavia, i dati attualmente disponibili mostrano importanti caratteristiche tra cui: i) un'elevata efficacia in diverse condizioni e contro un'ampia gamma di malattie, ii) complessi meccanismi d'azione che includono un'attività antimicrobica diretta e l'induzione di resistenza nei tessuti dell'ospite trattato, e iii) il possibile controllo dell'infezione già stabilita (azione curativa). Inoltre, i batteri selezionati possono essere facilmente coltivati con mezzi di coltura semplici ed economici e i loro estratti sono attivi ad una concentrazione molto bassa, suggerendo il possibile sviluppo di formulazioni economiche, in grado di competere con i composti chimici tradizionali.

Bacterial extracts as natural preparations to control fungal plant diseases / Librizzi, Valentina Tindara. - (2022 May 02).

Bacterial extracts as natural preparations to control fungal plant diseases

LIBRIZZI, Valentina Tindara
2022-05-02

Abstract

Microorganisms represent a rich source of biologically active substances including antifungal compounds that can potentially be used as alternative methods to control fungal plant diseases. In the present study, a number of bacterial strains producing and releasing antifungal compounds were identified from natural forest soils and utilized to obtain antifungal preparations. Selected bacteria were associated to 4 different 16S genotypes clustering within the genus Pseudomonas spp. Alcoholic extracts from these bacteria proved a significant antifungal activity by inhibiting the mycelial growth of typical postharvest pathogens including Botrytis cinerea, Penicillium digitatum, Penicillium italicum, Penicillium expansum, Monilinia fructicola, and Colletrotrichum acutatum. The same extracts were particularly effective in reducing the incidence of rots on different artificially inoculated fruits such as citrus, apricots, sweet cherries, table grape, and tomatoes. On tangerines, the selected extracts also showed a curative activity since treatments made 24 h after the inoculations of P. digitatum reduced rots, suggesting the possible control of already established infections. In addition to the direct antifungal activity, the induction of resistance in treated host tissues was also demonstrated. In fact, on apricots inoculated with M. fructicola and on table grape and tomatoes inoculated with B. cinerea a significant reduction of rots was achieved without a direct contact between extracts and pathogens. Furthermore, these extracts proved effective under semi-commercial conditions by reducing natural rots on sweet cherries subjected to cold storage and shelf-life. In field conditions, the most effective extract significantly reduced the incidence and severity of grape powdery mildew. According to metabolomics analyses, 521 target features were detected within the extracts of 3 selected bacteria. Although most of them were not annotated, some common Pseudomonas membrane structural lipids as well as natural products such as phenazine and orfamide analogs, known to have some antimicrobial and antifungal activity, were identified. Additional investigations are needed to correlate the composition of extracts with their biological activity, to identify putative active ingredients and ascertain their safety for humans’ health and the environment. However, currently available data shows important features including: i) a high efficacy under different conditions and against a broad range of diseases, ii) complex mechanisms of action that include a direct antimicrobial activity and the induction of resistance in treated host tissues, and iii) the possible control of already established infection (curative action). Furthermore, selected bacteria can be easily grown with simple and cheap culturing media and their extracts are active at a very low concentration, suggesting the possible development cost effective formulations, able to compete with traditional chemical compounds.
2-mag-2022
Settore AGR/12 - PATOLOGIA VEGETALE
SCHENA, Leonardo
POIANA, MARCO
Doctoral Thesis
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.12318/129686
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