The interest for the search of new active compounds for controlling plant pathogenic bacteria is a big challenge in a modern trend concerning plant protection since against these pathogens there is a lack of effective control means. In particular, against Xylella fastidiosa pauca, the causal agent of the Olive Quick Decline Syndrome (OQDS), whose first outbreak in Europe occurred in 2013 on the olive trees of the Salento Peninsula, there is an urgent need to find effective control measures. Against this bacterium, quarantine and sanitation measures, control of insect vectors as well as political actions are not able to arrest the spread of the disease(Morelli et al., 2021). Therefore, it is important to find a strategy to control the pathogen and to save the olive-growing heritage. In this work, new bioactive and sustainable substances were evaluated and selected for their antimicrobial activity against X. fastidiosa pauca as well as other plant pathogenic bacteria. In the first part of the research, selected products were tested against 13 widespread and important phytopathogenic bacteria determining the minimum inhibitory concentration (MIC) of each product against each bacterium. Many of the tested products evidenced a strong antibacterial activity against most of the tested phytopathogenic bacteria, and the activity was often similar and sometimes even better than standard antibiotics used as control. The second part of the work focused on the evaluation of the selected products against X. fastidiosa subsp. pauca (Xfp), strain ST53 responsible of OQDS. Starting from previous experiments, in vitro assays were assessed to evaluate bactericidal activity against Xfp by the time-kill assay. Furthermore, experiments on pot grown olive plants kept in green-house conditions were carried out to evaluate the capability of the most promising compounds to control the disease caused by Xfp. Most of the tested products showed bactericidal effect on the bacterium in vitro and in planta experiments, some of them applied by foliar treatments were able to significantly reduce the presence of Xfp symptoms. In addition, on treated plants a significant reduction of the bacterial population was observed at the end of the experiments compared to the starting conditions. However, once the treatments were stopped, the plants underwent a rapid decay that led to their death. Collectively, results of experiments reported in the present thesis are positive and attested the large spectrum capability of most of the tested compounds to inhibit the growth of different species of widespread and dangerous phytopathogenic bacteria, even including different strains and subspecies of X. fastidiosa (Xf). Since most of the tested products are systemic or cytotropic, they are very interesting being able to directly inhibit endophytic bacteria, such as Xf which colonizes the vascular tissues of host plants, as well as inducing defence responses in plant. Further experiments in vivo, on pot grown plants or rather in the field are necessary to confirm the positive result obtained in the present research.
L’interesse per la ricerca di nuove sostanze attive utilizzabili per il controllo dei batteri fitopatogeni è una delle più grandi sfide che riguardano le tendenze moderne in materia di protezione delle piante giacché contro questi agenti patogeni mancano mezzi di controllo efficaci. In particolare, contro Xylella fastidiosa pauca, l'agente causale del disseccamento rapido dell’olivo (OQDS), il cui primo focolaio in Europa si è verificato nel 2013 sugli ulivi della Penisola Salentina, è urgente trovare misure di controllo efficaci. Le misure di quarantena e sanificazione, il controllo degli insetti vettori insieme alle azioni politiche non sono state in grado di arrestare la diffusione del batterio e dei suoi insetti vettori. In questo scenario risulta oggi importante trovare una strategia per controllare il patogeno e salvare il patrimonio olivicolo. Nel presente lavoro nuove sostanze bioattive e sostenibili sono state valutate e selezionate per la loro attività antimicrobica contro X. fastidiosa pauca e altri batteri patogeni delle piante. Nella prima parte della ricerca, i prodotti selezionati sono stati saggiati contro 13 dei più importanti e diffusi batteri fitopatogeni, determinando la concentrazione minima inibitoria (MIC) per ciascun batterio e per ciascun prodotto. Molti dei prodotti testati hanno evidenziato una forte attività antibatterica contro la maggior parte dei batteri fitopatogeni, mostrando un’attività simile e talvolta anche migliore rispetto agli antibiotici usati come controllo. La seconda parte dell'attività si è concentrata sulla valutazione dei prodotti selezionati nei confronti di X. fastidiosa subsp. pauca (Xfp). A partire dai precedenti esperimenti, i prodotti sono stati saggiati in vitro per valutare l'attività battericida contro Xfp utilizzando il time-kill assay. Successivi esperimenti sono stati condotti su piante di olivo in vaso mantenute in serra in condizioni controllate per valutare la capacità dei prodotti più promettenti di contrastare Xfp. La maggior parte dei prodotti saggiati ha mostrato un elevato effetto battericida in vitro e nelle prove in planta, alcuni prodotti somministrati per via fogliare hanno significativamente ridotto la presenza i sintomi sulle piante trattate. Inoltre, alla fine degli esperimenti, sulle piante trattate, è stata anche osservata una significativa riduzione della popolazione batterica rispetto alle condizioni di partenza. Tuttavia, a seguito dell’interruzione dei trattamenti, le piante hanno subito un rapido decadimento arrivando successivamente a morte. Nel complesso, i risultati ottenuti nella presente ricerca sono positivi e attestano l’elevata efficacia e l’ampio spettro di attività della maggior parte dei prodotti saggiati, in quanto capaci di inibire la crescita di diverse specie di batteri fitopatogeni, ivi inclusi diversi ceppi e sottospecie di X. fastidiosa (Xf). Essendo la maggior parte dei prodotti testati sistemici o citotropici, essi risultano molto interessanti in quanto oltre ad una inibizione diretta dei patogeni batterici, tali prodotti possono indurre risposte di difesa nella pianta e controllare anche batteri endofiti, come ad esempio Xf, che colonizzano i tessuti vascolari delle piante ospiti. Ulteriori esperimenti in vivo, su piante in vaso o meglio in campo saranno necessari per confermare i risultati positivi ottenuti nella presente ricerca.
Selection, evaluation and characterization of bioactive compounds for their activity against Xylella fastidiosa and other phytopathogenic bacteria
DEL GROSSO, Carmine
2022-09-26
Abstract
The interest for the search of new active compounds for controlling plant pathogenic bacteria is a big challenge in a modern trend concerning plant protection since against these pathogens there is a lack of effective control means. In particular, against Xylella fastidiosa pauca, the causal agent of the Olive Quick Decline Syndrome (OQDS), whose first outbreak in Europe occurred in 2013 on the olive trees of the Salento Peninsula, there is an urgent need to find effective control measures. Against this bacterium, quarantine and sanitation measures, control of insect vectors as well as political actions are not able to arrest the spread of the disease(Morelli et al., 2021). Therefore, it is important to find a strategy to control the pathogen and to save the olive-growing heritage. In this work, new bioactive and sustainable substances were evaluated and selected for their antimicrobial activity against X. fastidiosa pauca as well as other plant pathogenic bacteria. In the first part of the research, selected products were tested against 13 widespread and important phytopathogenic bacteria determining the minimum inhibitory concentration (MIC) of each product against each bacterium. Many of the tested products evidenced a strong antibacterial activity against most of the tested phytopathogenic bacteria, and the activity was often similar and sometimes even better than standard antibiotics used as control. The second part of the work focused on the evaluation of the selected products against X. fastidiosa subsp. pauca (Xfp), strain ST53 responsible of OQDS. Starting from previous experiments, in vitro assays were assessed to evaluate bactericidal activity against Xfp by the time-kill assay. Furthermore, experiments on pot grown olive plants kept in green-house conditions were carried out to evaluate the capability of the most promising compounds to control the disease caused by Xfp. Most of the tested products showed bactericidal effect on the bacterium in vitro and in planta experiments, some of them applied by foliar treatments were able to significantly reduce the presence of Xfp symptoms. In addition, on treated plants a significant reduction of the bacterial population was observed at the end of the experiments compared to the starting conditions. However, once the treatments were stopped, the plants underwent a rapid decay that led to their death. Collectively, results of experiments reported in the present thesis are positive and attested the large spectrum capability of most of the tested compounds to inhibit the growth of different species of widespread and dangerous phytopathogenic bacteria, even including different strains and subspecies of X. fastidiosa (Xf). Since most of the tested products are systemic or cytotropic, they are very interesting being able to directly inhibit endophytic bacteria, such as Xf which colonizes the vascular tissues of host plants, as well as inducing defence responses in plant. Further experiments in vivo, on pot grown plants or rather in the field are necessary to confirm the positive result obtained in the present research.File | Dimensione | Formato | |
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