Olive quick decline syndrome (OQDS) is a severe vascular disease caused by Xylella fastidiosa subsp. pauca (Xfp), a Gram-negative bacterium classified as a quarantine pathogen by the European Union. It was first identified in 2013 in a grove on the Salento peninsula, Apulia region, in southeastern Italy, and rapidly spread northward, infecting approximately 22 million olive plants. Currently, no ‘curative’ interventions are available to control the disease, and preventive strategies may be the only effective solutions for containing OQDS. Management strategies primarily focus on reducing the spread of infection, lowering inoculum pressure, and controlling the vector population to mitigate the negative impact of the disease. Replanting in infected areas is essential, and significant efforts have been made to identify new sources of tolerance or resistance to Xfp in order to restore both the landscape and the olive-growing economy of Apulia. Since the mechanisms governing resistance/tolerance in certain cultivars are still unknown, olive germplasm resources are valuable for studying the plant’s response to the pathogen. The research conducted in this Ph.D. program aims to understand the influence of endogenous factors and cultural practices on the behavior of olive trees toward the disease. Specifically, the research focused on: i) studying the transmission biology of the fastidious bacterium and how it is shaped by insect-plant interactions and vector species-associated factors; ii) investigating the interaction between bacterial endophytes of the genus Methylobacterium and Xfp; iii) characterizing the endophytic fungal populations in olive tree samples, both infected and non-infected with Xfp, including the evaluation of the pathogenic activity of certain fungal species from the genus Pseudophaeomoniella on adult olive plants; and iv) identifying olive trees that survived the bacterial epidemic to detect resistant or tolerant genotypes in the areas that have been infected for the longest time. Finally, this Ph.D. thesis also aimed to investigate the influence of pruning schedules on the behaviour of different olive cultivars. The results demonstrated that periwinkle (Catharanthus roseus (L.) G. Don) can be considered the best model host plant species among those tested for studies on the transmission biology of Xfp ST53 with Philaenus spumarius. Data from EPG-assisted inoculation experiments provided new insights into vector species-related differences in the bacterium’s transmission dynamics. Interestingly, results from the study of the interaction between Methylobacterium spp. and Xfp indicated that the isolates produce ferrioxamine E and ferrichrome, potentially competing with Xfp for iron. Regarding the genus Pseudophaeomoniella, no clear relationship was found between symptom severity induced by Xfp, although the age of the plant appeared to play a crucial role in both internal symptom severity and isolation frequencies. Additionally, new putatively resistant olive genotypes were identified among those that survived the bacterial epidemic. Finally, no strong evidence was found to support that either major or light pruning interventions can reduce bacterial colonization or improve the health status of infected olive trees, even when the vector population is very low.
La sindrome del disseccamento rapido dell’olivo (OQDS) è una grave malattia vascolare causata da Xylella fastidiosa subsp. pauca (Xfp), un batterio Gram-negativo classificato come patogeno da quarantena dall’Unione Europea. È stata identificata per la prima volta nel 2013 in un uliveto nella penisola salentina, nella regione Puglia, nell’Italia sudorientale, e si è rapidamente diffusa verso nord, infettando circa 22 milioni di piante di olivo. Attualmente, non sono disponibili interventi "curativi" per controllare la malattia, e le strategie preventive potrebbero rappresentare l’unica soluzione efficace per contenere l’OQDS. Le strategie di gestione si concentrano principalmente sulla riduzione della diffusione dell’infezione, sull’abbassamento della pressione dell’inoculo e sul controllo della popolazione del vettore, al fine di mitigare l’impatto negativo della malattia. Il reimpianto nelle aree infette è essenziale, e sono stati fatti sforzi significativi per identificare nuove fonti di tolleranza o resistenza a Xfp, al fine di ripristinare sia il paesaggio che il settore olivicolo della Puglia. Poiché i meccanismi che regolano la resistenza/tolleranza in alcune cultivar sono ancora sconosciuti, le risorse genetiche dell’olivo risultano preziose per lo studio della risposta della pianta al patogeno. La ricerca condotta in questo programma di dottorato mira a comprendere l’influenza dei fattori endogeni e delle pratiche colturali sul comportamento degli olivi rispetto alla malattia. In particolare, la ricerca si è concentrata su: i) lo studio della biologia della trasmissione del batterio fastidioso e su come essa venga influenzata dalle interazioni pianta-insetto e dai fattori associati alle specie vettore; ii) l’indagine sull’interazione tra gli endofiti batterici del genere Methylobacterium e Xfp; iii) la caratterizzazione delle popolazioni fungine endofitiche in campioni di olivo, sia infetti che non infetti da Xfp, inclusa la valutazione dell’attività patogenetica di alcune specie fungine del genere Pseudophaeomoniella su piante adulte di olivo; e iv) l’identificazione di olivi che sono sopravvissuti all’epidemia batterica per individuare genotipi resistenti o tolleranti nelle aree infette da più tempo. Infine, questa tesi di dottorato ha anche avviato indagini sull’influenza dei regimi di potatura sul comportamento di diverse varietà di olivo I risultati hanno dimostrato che la pervinca (Catharanthus roseus (L.) G. Don) può essere considerata la migliore specie di pianta ospite modello tra quelle testate per studi sulla biologia della trasmissione di Xfp ST53 con Philaenus spumarius. I dati ottenuti dagli esperimenti di inoculazione assistiti da EPG hanno fornito nuove informazioni sulle differenze nella dinamica di trasmissione del batterio legate al vettore. Interessante è stato il risultato dello studio sull’interazione tra Methylobacterium spp. e Xfp, che ha indicato come gli isolati producano ferrioxamina E e ferricromo, potendo quindi potenzialmente competere con Xfp per il ferro. Per quanto riguarda il genere Pseudophaeomoniella, non è stata trovata una chiara relazione tra la gravità dei sintomi indotti da Xfp e la presenza del patogeno, sebbene l’età della pianta sembri svolgere un ruolo cruciale sia nella gravità dei sintomi interni che nelle frequenze di isolamento. Inoltre, sono stati identificati nuovi genotipi di olivo potenzialmente resistenti tra quelli che sono sopravvissuti all’epidemia batterica. Infine, non è stata trovata alcuna prova convincente a supporto del fatto che interventi di potatura pesante o leggera possano ridurre la colonizzazione batterica o migliorare lo stato sanitario degli olivi infetti, anche quando la popolazione del vettore è molto bassa.
Comportamento di Olea europaea nei confronti di Xylella fastidiosa subsp. pauca ST53: influenza delle pratiche culturali e dei fattori endogeni
CARLUCCI, MARIANGELA
2025
Abstract
Olive quick decline syndrome (OQDS) is a severe vascular disease caused by Xylella fastidiosa subsp. pauca (Xfp), a Gram-negative bacterium classified as a quarantine pathogen by the European Union. It was first identified in 2013 in a grove on the Salento peninsula, Apulia region, in southeastern Italy, and rapidly spread northward, infecting approximately 22 million olive plants. Currently, no ‘curative’ interventions are available to control the disease, and preventive strategies may be the only effective solutions for containing OQDS. Management strategies primarily focus on reducing the spread of infection, lowering inoculum pressure, and controlling the vector population to mitigate the negative impact of the disease. Replanting in infected areas is essential, and significant efforts have been made to identify new sources of tolerance or resistance to Xfp in order to restore both the landscape and the olive-growing economy of Apulia. Since the mechanisms governing resistance/tolerance in certain cultivars are still unknown, olive germplasm resources are valuable for studying the plant’s response to the pathogen. The research conducted in this Ph.D. program aims to understand the influence of endogenous factors and cultural practices on the behavior of olive trees toward the disease. Specifically, the research focused on: i) studying the transmission biology of the fastidious bacterium and how it is shaped by insect-plant interactions and vector species-associated factors; ii) investigating the interaction between bacterial endophytes of the genus Methylobacterium and Xfp; iii) characterizing the endophytic fungal populations in olive tree samples, both infected and non-infected with Xfp, including the evaluation of the pathogenic activity of certain fungal species from the genus Pseudophaeomoniella on adult olive plants; and iv) identifying olive trees that survived the bacterial epidemic to detect resistant or tolerant genotypes in the areas that have been infected for the longest time. Finally, this Ph.D. thesis also aimed to investigate the influence of pruning schedules on the behaviour of different olive cultivars. The results demonstrated that periwinkle (Catharanthus roseus (L.) G. Don) can be considered the best model host plant species among those tested for studies on the transmission biology of Xfp ST53 with Philaenus spumarius. Data from EPG-assisted inoculation experiments provided new insights into vector species-related differences in the bacterium’s transmission dynamics. Interestingly, results from the study of the interaction between Methylobacterium spp. and Xfp indicated that the isolates produce ferrioxamine E and ferrichrome, potentially competing with Xfp for iron. Regarding the genus Pseudophaeomoniella, no clear relationship was found between symptom severity induced by Xfp, although the age of the plant appeared to play a crucial role in both internal symptom severity and isolation frequencies. Additionally, new putatively resistant olive genotypes were identified among those that survived the bacterial epidemic. Finally, no strong evidence was found to support that either major or light pruning interventions can reduce bacterial colonization or improve the health status of infected olive trees, even when the vector population is very low.File | Dimensione | Formato | |
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16_12_24Tesi Carlucci (1)_pdfA-signed_1.pdf
embargo fino al 18/02/2026
Dimensione
4.55 MB
Formato
Adobe PDF
|
4.55 MB | Adobe PDF |
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https://hdl.handle.net/20.500.14242/210879
URN:NBN:IT:UNIBA-210879