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Progress on Understanding and Management of Xylella fastidiosa Infections

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A special issue of Pathogens (ISSN 2076-0817).

Deadline for manuscript submissions: closed (15 November 2021) | Viewed by 23712

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Special Issue Editors

Dr. Stefania Loreti

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Guest Editor

Research Centre for Plant Protection and Certification, Council for Agricultural Research and Economics (CREA), 00156 Rome, Italy
Interests: phytopathogenic bacteria; bacterial diseases; detection and identification; characterization of bacterial populations; resistance induction
Special Issues, Collections and Topics in MDPI journals

Dr. Marco Scortichini

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Council for Agricultural Research and Economics-Research Centre for Olive, Fruit and Citrus Crops, Via di Fioranello, 52, I-00134 Roma, Italy
Interests: detection; host–plant interaction; taxonomy; field control strategies
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Xylella fastidiosa (XF) is a Gram-negative plant pathogenic bacteria with a broad range of crop, urban shade, and forest plant hosts. Symptoms caused by XF are not specific and, despite often being similar to those caused by water stress, may vary depending on the host plant–XF strain combination. Many hosts are symptomless; however, infection with some species causes rapid death, making this pathogen very difficult to manage. XF is a xylem-limited bacterium that is transmitted by xylem-sap-feeding insects. Since the beginning of the last century, it has been endemic to North, Central, and South America, where it causes, among other things, Pierce’s disease on grapevine and Citrus variegated chlorosis on Citrus spp.. It was recently introduced into southern Italy (the Apulia region), where it led to major damage to olive crops, and was also found in some European countries on several plant species.

Given the serious phytosanitary emergency that arose in the European Union during the last decade and despite the extensive study carried out, more effort has to be made to study several aspects of this dangerous bacterial pathogen. For the forthcoming Special Issue of Pathogens, we invite you to submit original research articles, reviews, and short notes describing advances in our understanding of biology, epidemiology, population genetics, interactions of different strains/subspecies with their hosts and vectors, molecular mechanisms, and genetic aspects of bacteria–host–vector interactions as well as in strategies for disease management, early detection and identification, and disease risk assessment.

Dr. Stefania Loreti
Dr. Marco Scortichini
Guest Editors

Manuscript Submission Information

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Keywords

epidemiology
host–plant interaction
insect vectors
detection
field control
disease risk assessment

Published Papers (6 papers)

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Research

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15 pages, 7904 KiB

Open AccessArticle

Neofusicoccum mediterraneum Is Involved in a Twig and Branch Dieback of Olive Trees Observed in Salento (Apulia, Italy)

by Angela Brunetti, Antonio Matere, Valentina Lumia, Vittorio Pasciuta, Valeria Fusco, Domenico Sansone, Paolo Marangi, Nicola Cristella, Francesco Faggioli, Marco Scortichini and Massimo Pilotti

Pathogens 2022, 11(1), 53; https://0-doi-org.brum.beds.ac.uk/10.3390/pathogens11010053 - 02 Jan 2022

Cited by 8 | Viewed by 4531

Abstract

Olive trees are infected and damaged by Botryosphaeriaceae fungi in various countries. The botryosphaeriaceous fungus Neofusicoccum mediterraneum is highly aggressive and is a major concern for olive groves in Spain and California (USA), where it causes ‘branch and twig dieback’ characterized by wood discoloration, bark canker, and canopy blight. During surveys of olive groves in Apulia (southern Italy), we noticed that—in some areas—trees were heavily affected by severe branch and twig dieback. In addition, chlorosis and the appearance of red-bronze patches on the leaf preceded the wilting of the foliage, with necrotic leaves persisting on the twigs. Given the severity of the manifestation in zones also subject to olive quick decline syndrome (OQDS) caused by Xylella fastidiosa subsp. pauca, we investigated the etiology and provide indications for differentiating the symptoms from OQDS. Isolation from diseased wood samples revealed a mycete, which was morphologically and molecularly identified as N. mediterraneum. The pathogenicity tests clearly showed that this fungus is able to cause the natural symptoms. Therefore, also considering the low number of tested samples, N. mediterraneum is a potential causal agent of the observed disease. Specifically, inoculation of the twigs caused complete wilting in two to three weeks, while inoculation at the base of the stem caused severe girdling wedge-shaped cankers. The growth rate of the fungus in in vitro tests was progressively higher from 10 to 30 °C, failing to grow at higher temperatures, but keeping its viability even after prolonged exposure at 50 °C. The capacity of the isolate to produce catenulate chlamydospores, which is novel for the species, highlights the possibility of a new morphological strain within N. mediterraneum. Further investigations are ongoing to verify whether additional fungal species are involved in this symptomatology. Full article

(This article belongs to the Special Issue Progress on Understanding and Management of Xylella fastidiosa Infections)

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14 pages, 2109 KiB

Open AccessArticle

Phenotypic and Phylogenetic Characterization of Cu Homeostasis among Xylella fastidiosa Strains

by Qing Ge, Ranlin Liu, Paul A. Cobine, Neha Potnis and Leonardo De La Fuente

Pathogens 2021, 10(4), 495; https://0-doi-org.brum.beds.ac.uk/10.3390/pathogens10040495 - 20 Apr 2021

Cited by 3 | Viewed by 1950

Abstract

Xylella fastidiosa is a bacterial pathogen causing severe diseases and asymptomatic colonization in more than 600 plants worldwide. Copper (Cu) is a widely used antimicrobial treatment for various plant diseases, including those affecting X. fastidiosa hosts. Cu homeostasis among X. fastidiosa strains from different geographical locations and host species has not been characterized. Here, we assessed minimum inhibitory concentration (MIC) of Cu for 54 X. fastidiosa strains. We observed strain-level variation in MIC values within each subspecies. We hypothesized that these differences could be explained by sequence variation in Cu homeostasis genes. Phylogenies based on copA, copB, copL, and cutC were created using 74 genomes (including 43 strains used in vitro) of X. fastidiosa, showing that the phylogenetic clustering of Cu homeostasis associated with clustering was based on core genome phylogenies, rather than on pattern of MIC. No association was found among Cu MIC, subspecies classification, and host and location of isolation, probably due to uneven and limited group of strains whose genomes are available. Further analysis focused on a subgroup of isolates from Georgia’s vineyards that shared similar Cu-related phenotypes. Further research is needed to better understand the distribution of Cu homeostasis for this pathogen. Full article

(This article belongs to the Special Issue Progress on Understanding and Management of Xylella fastidiosa Infections)

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21 pages, 5954 KiB

Open AccessArticle

Further In Vitro Assessment and Mid-Term Evaluation of Control Strategy of Xylella fastidiosa subsp. pauca in Olive Groves of Salento (Apulia, Italy)

by Giuseppe Tatulli, Vanessa Modesti, Nicoletta Pucci, Valeria Scala, Alessia L’Aurora, Simone Lucchesi, Manuel Salustri, Marco Scortichini and Stefania Loreti

Pathogens 2021, 10(1), 85; https://0-doi-org.brum.beds.ac.uk/10.3390/pathogens10010085 - 19 Jan 2021

Cited by 18 | Viewed by 4704

Abstract

During recent years; Xylella fastidiosa subsp. pauca (Xfp) has spread in Salento causing relevant damage to the olive groves. Measures to contain the spreading of the pathogen include the monitoring of the areas bordering the so-called “infected” zone and the tree eradication in case of positive detection. In order to provide a control strategy aimed to maintain the tree productivity in the infected areas, we further evaluated the in vitro and in planta mid-term effectiveness of a zinc-copper-citric acid biocomplex. The compound showed an in vitro bactericidal activity and inhibited the biofilm formation in representative strains of X. fastidiosa subspecies, including Xfp isolated in Apulia from olive trees. The field mid-term evaluation of the control strategy assessed by quantitative real-time PCR in 41 trees of two olive groves of the “infected” area revealed a low concentration of Xfp over the seasons upon the regular spraying of the biocomplex over 3 or 4 consecutive years. In particular, the bacterial concentration lowered in July and October with respect to March, after six consecutive treatments. The trend was not affected by the cultivar and it was similar either in the Xfp-sensitive cultivars Ogliarola salentina and Cellina di Nardò or in the Xfp-resistant Leccino. Moreover, the scoring of the number of wilted twigs over the seasons confirmed the trend. The efficacy of the treatment in the management of olive groves subjected to a high pathogen pressure is highlighted by the yielded a good oil production Full article

(This article belongs to the Special Issue Progress on Understanding and Management of Xylella fastidiosa Infections)

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17 pages, 1315 KiB

Open AccessArticle

Orthology-Based Estimate of the Contribution of Horizontal Gene Transfer from Distantly Related Bacteria to the Intraspecific Diversity and Differentiation of Xylella fastidiosa

by Giuseppe Firrao, Marco Scortichini and Laura Pagliari

Pathogens 2021, 10(1), 46; https://0-doi-org.brum.beds.ac.uk/10.3390/pathogens10010046 - 07 Jan 2021

Cited by 5 | Viewed by 2457

Abstract

Xylella fastidiosa is a xylem-limited bacterium phylogenetically related to the xanthomonads, with an unusually large and diversified range of plant hosts. To ascertain the origin of its peculiarities, its pan-genome was scanned to identify the genes that are not coherent with its phylogenetic position within the order Xanthomonadales. The results of the analysis revealed that a large fraction of the genes of the Xylella pan-genome have no ortholog or close paralog in the order Xanthomonadales. For a significant part of the genes, the closest homologue was found in bacteria belonging to distantly related taxonomic groups, most frequently in the Betaproteobacteria. Other species, such as Xanthomonas vasicola and Xanthomonas albilineans which were investigated for comparison, did not show a similar genetic contribution from distant branches of the prokaryotic tree of life. This finding indicates that the process of acquisition of DNA from the environment is still a relevant component of Xylella fastidiosa evolution. Although the ability of Xylella fastidiosa strains to recombine among themselves is well known, the results of the pan-genome analyses stressed the additional relevance of environmental DNA in shaping their genomes, with potential consequences on their phytopathological features. Full article

(This article belongs to the Special Issue Progress on Understanding and Management of Xylella fastidiosa Infections)

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Review

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25 pages, 5632 KiB

Open AccessReview

Aphrophoridae Role in Xylella fastidiosa subsp. pauca ST53 Invasion in Southern Italy

by Ugo Picciotti, Nada Lahbib, Valdete Sefa, Francesco Porcelli and Francesca Garganese

Pathogens 2021, 10(8), 1035; https://0-doi-org.brum.beds.ac.uk/10.3390/pathogens10081035 - 16 Aug 2021

Cited by 12 | Viewed by 4001

Abstract

The Philaenus spumarius L. (Hemiptera Aphrophoridae) is a xylem-sap feeder vector that acquires Xylella fastidiosa subsp. pauca ST53 during feeding on infected plants. The bacterium is the plant pathogen responsible for olive quick decline syndrome that has decimated olive trees in Southern Italy. Damage originates mainly from the insect vector attitude that multiplies the pathogen potentialities propagating Xf in time and space. The principal action to manage insect-borne pathogens and to contain the disease spread consists in vector and transmission control. The analysis of an innovative and sustainable integrated pest management quantitative strategy that targets the vector and the infection by combining chemical and physical control means demonstrates that it is possible to stop the Xylella invasion. This review updates the available topics addressing vectors’ identification, bionomics, infection management, and induced disease by Xylella invasion to discuss major available tools to mitigate the damage consequent to the disease. Full article

(This article belongs to the Special Issue Progress on Understanding and Management of Xylella fastidiosa Infections)

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22 pages, 7948 KiB

Open AccessReview

Progress towards Sustainable Control of Xylella fastidiosa subsp. pauca in Olive Groves of Salento (Apulia, Italy)

by Marco Scortichini, Stefania Loreti, Nicoletta Pucci, Valeria Scala, Giuseppe Tatulli, Dimitri Verweire, Michael Oehl, Urs Widmer, Josep Massana Codina, Peter Hertl, Gianluigi Cesari, Monica De Caroli, Federica Angilè, Danilo Migoni, Laura Del Coco, Chiara Roberta Girelli, Giuseppe Dalessandro and Francesco Paolo Fanizzi

Pathogens 2021, 10(6), 668; https://0-doi-org.brum.beds.ac.uk/10.3390/pathogens10060668 - 29 May 2021

Cited by 20 | Viewed by 4217

Abstract

Xylella fastidiosa subsp. pauca is the causal agent of “olive quick decline syndrome” in Salento (Apulia, Italy). On April 2015, we started interdisciplinary studies to provide a sustainable control strategy for this pathogen that threatens the multi-millennial olive agroecosystem of Salento. Confocal laser scanning microscopy and fluorescence quantification showed that a zinc-copper-citric acid biocomplex—Dentamet^®—reached the olive xylem tissue either after the spraying of the canopy or injection into the trunk, demonstrating its effective systemicity. The biocomplex showed in vitro bactericidal activity towards all X. fastidiosa subspecies. A mid-term evaluation of the control strategy performed in some olive groves of Salento indicated that this biocomplex significantly reduced both the symptoms and X. f. subsp. pauca cell concentration within the leaves of the local cultivars Ogliarola salentina and Cellina di Nardò. The treated trees started again to yield. A ¹H-NMR metabolomic approach revealed, upon the treatments, a consistent increase in malic acid and γ-aminobutyrate for Ogliarola salentina and Cellina di Nardò trees, respectively. A novel endotherapy technique allowed injection of Dentamet^® at low pressure directly into the vascular system of the tree and is currently under study for the promotion of resprouting in severely attacked trees. There are currently more than 700 ha of olive groves in Salento where this strategy is being applied to control X. f. subsp. pauca. These results collectively demonstrate an efficient, simple, low-cost, and environmentally sustainable strategy to control this pathogen in Salento. Full article

(This article belongs to the Special Issue Progress on Understanding and Management of Xylella fastidiosa Infections)

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