Explore the vast range of titles available.

Plant pathogens pose increasing threats to global food security, causing yield losses that exceed 30% in food-deficit regions. Xylella fastidiosa (Xf) represents the major transboundary plant pest and one of the world’s most damaging pathogens in terms of socioeconomic impact. Spectral screening methods are critical to detect non-visual symptoms of early infection and prevent spread. However, the subtle pathogen-induced physiological alterations that are spectrally detectable are entangled with the dynamics of abiotic stresses. Here, using airborne spectroscopy and thermal scanning of areas covering more than one million trees of different species, infections and water stress levels, we reveal the existence of divergent pathogen- and host-specific spectral pathways that can disentangle biotic-induced symptoms. We demonstrate that uncoupling this biotic–abiotic spectral dynamics diminishes the uncertainty in the Xf detection to below 6% across different hosts. Assessing these deviating pathways against another harmful vascular pathogen that produces analogous symptoms, Verticillium dahliae, the divergent routes remained pathogen- and host-specific, revealing detection accuracies exceeding 92% across pathosystems. These urgently needed hyperspectral methods advance early detection of devastating pathogens to reduce the billions in crop losses worldwide.

In autumn 2013, the presence of Xylella fastidiosa , a xylem-limited Gram-negative bacterium, was detected in olive stands of an area of the Ionian coast of the Salento peninsula (Apulia, southern Italy), that were severely affected by a disease denoted olive quick decline syndrome (OQDS). Studies were carried out for determining the involvement of this bacterium in the genesis of OQDS and of the leaf scorching shown by a number of naturally infected plants other than olive. Isolation in axenic culture was attempted and assays were carried out for determining its pathogenicity to olive, oleander and myrtle-leaf milkwort. The bacterium was readily detected by quantitative polymerase chain reaction (qPCR) in all diseased olive trees sampled in different and geographically separated infection foci, and culturing of 51 isolates, each from a distinct OQDS focus, was accomplished. Needle-inoculation experiments under different environmental conditions proved that the Salentinian isolate De Donno belonging to the subspecies pauca is able to multiply and systemically invade artificially inoculated hosts, reproducing symptoms observed in the field. Bacterial colonization occurred in prick-inoculated olives of all tested cultivars. However, the severity of and timing of symptoms appearance differed with the cultivar, confirming their differential reaction.

Plant pathogens cause significant losses to agricultural yields and increasingly threaten food security1, ecosystem integrity and societies in general2,3,4,5. Xylella fastidiosa is one of the most dangerous plant bacteria worldwide, causing several diseases with profound impacts on agriculture and the environment6. Primarily occurring in the Americas, its recent discovery in Asia and Europe demonstrates that X. fastidiosa’s geographic range has broadened considerably, positioning it as a reemerging global threat that has caused socioeconomic and cultural damage7,8. X. fastidiosa can infect more than 350 plant species worldwide9, and early detection is critical for its eradication8. In this article, we show that changes in plant functional traits retrieved from airborne imaging spectroscopy and thermography can reveal X. fastidiosa infection in olive trees before symptoms are visible. We obtained accuracies of disease detection, confirmed by quantitative polymerase chain reaction, exceeding 80% when high-resolution fluorescence quantified by three-dimensional simulations and thermal stress indicators were coupled with photosynthetic traits sensitive to rapid pigment dynamics and degradation. Moreover, we found that the visually asymptomatic trees originally scored as affected by spectral plant-trait alterations, developed X. fastidiosa symptoms at almost double the rate of the asymptomatic trees classified as not affected by remote sensing. We demonstrate that spectral plant-trait alterations caused by X. fastidiosa infection are detectable previsually at the landscape scale, a critical requirement to help eradicate some of the most devastating plant diseases worldwide.

After the first confirmed outbreak of Xylella fastidiosa in the European Union (EU), associated with an olive disease denoted olive quick decline syndrome, mandatory surveys are now carried out in the member States and inspections increased at EU entry points such as ports. Such activities led to the interception of X. fastidiosa -infected coffee plants in consignments originating from Central America. Similarly, the geographic expansion of the olive decline epidemic area of the Apulia region (southern Italy) prompted investigations to identify new host plants. Here we report the interception of three novel bacterial sequence types in Italy, based on multi-locus sequence typing, that cluster with different X. fastidiosa subspecies, illustrating the risk of the introduction of additional pathogen genetic diversity into Europe. In the epidemic area of Apulia, new foci as well as host plant species positive with X. fastidiosa , including cherry, myrtleleaf and rosemary, were found to be all infected with the same sequence type of this bacterium (ST53, or CoDiRO strain). This work highlights the limited knowledge of X. fastidiosa phylogenetic and phenotypic diversity, the risk of novel X. fastidiosa introductions via contaminated plant material, and corroborates other studies indicating that the Apulia epidemic emerged from a single introduction of this pathogen into the region.

Recently obtained molecular and biological information has prompted the revision of the taxonomic structure of the family Closteroviridae. In particular, mealybug-transmitted species have been separated from the genus Closterovirus and accommodated in a new genus named Ampelovirus (from ampelos, Greek for grapevine). Thus, the family now comprises three genera. Their major properties are (i) Closterovirus: type species Beet yellows virus, genome monopartite, 15.5-19.3 kb in size, a 22-25 kDa major coat protein (CP), the gene encoding the divergent CP analogue (CPd) upstream of the CP cistron, transmission by aphids, a membership of 8 definitive and 4 tentative species; (ii) Ampelo-virus: type species Grapevine leafroll virus 3, genome monopartite 16.9-19.5 kb in size, a 35-37 kDa major CP, a CPd cistron generally located downstream of the CP gene, transmission by pseudococcid and coccid mealybugs, a membership of 6 definitive and 5 tentative species; (iii) Crinivirus: type species Lettuce infectious yellows virus, genome essentially bipartite 15.3-19 kb in size, a 28-33 kDa CP, a CPd cistron downstream of the CP gene, transmission by whiteflies (Bemisia, Trialeurodes), a membership of 7 definitive and 3 tentative species. There are five unassigned species in the family.

In previous surveys for the presence of Plum pox virus (PPV) in Albania, PPV-M prevailed largely whereas PPV-D and PPV-Rec were less represented. Natural mixed infections of strains M and D were also found, more frequently than expected in varietal collections (Stamo and Myrta, 2006). In spring 2011, a new field survey was carried out to collect representative PPV isolates from different areas of the country and evaluate their diversity. A total of 11 PPV isolates were recovered from symptomatic plants in 10 orchards located at Kavajë, Elbasan, Pogradec and Korçë. Samples were tested by DASI-ELISA using the monoclonal antibodies 5B (universal), 4DG5 (PPV-D specific) and AL (PPV-M specific), and two highly informative genome portions (P3-6K1 and NIb- CP) were sequenced to check for the presence of PPV-M, PPV-D PPV-Rec and other strains. Five of the tested Albanian isolates proved to be PPV-M, four were PPV-Rec, one was PPV-D and one PPV-T. Further comparative sequence analysis of the entire CP gene demonstrated that the isolate Al-08pl (from an European plum tree) diverged from the cluster of PPV-M isolates and was 99% identical to PPV-T (Serce et al., 2009). To our knowledge, this is the first report of PPV-T in Albania. To assess the importance of this new PPV strain in Albania, further work is needed. An interesting output of this study, is the fact that in a small collection of Albanian PPV isolates the biodiversity of this virus is very high (4 different strains in 11 isolates). This can be interpreted either as an indication of a long history of PPV presence in the country or as the consequence of frequent introduction events from outside.

Xylella fastidiosa (Xf) is a xylem-inhabiting, vector-transmitted bacterium and the agent of a variety of diseases in a broad range of plant hosts. A destructive Xf outbreak has recently emerged in some olive groves of the province of Lecce (south-eastern Italy), caused by a strain (called CoDiRO from the Italian for Rapid desiccation complex of olive) of Xf subsp. pauca, a pathogen known to infect coffee and citrus in South America. Taking into account that this is the first confirmed record of the presence of Xf in the European Union (EU) territory and fairing its possible spread from the affected site, the EU has issued the Commission Implementing Decision L 45/29-31 (February 24, 2014), which prohibits the transfer from the province of Lecce of all plant genera and species not listed in the Annex I of the cited Decision. A survey was therefore initiated to verify the health status of a number of ornamental and forestry plants growing mostly in nurseries, but also in public and private gardens, which are or can be naturally exposed to high inoculum pressure. Samples collected from 207 conifers, 105 members of the family Arecaceae, Musaceae and Cycadaceae, and 208 succulent plants (totalling 520) were comparatively examined by serological (DAS-ELISA) and molecular (PCR) methods. None of the tested plant species proved to be infected, providing a strong indication that they may not be susceptible to field infection by the Xf subsp. pauca strain currently present in the province of Lecce.

A virus with filamentous particles ca. 700 nm long, denoted Fig latent virus 1 (FLV-1) is widespread in Apulian (southern Italy) fig orchards, in trees showing or not mosaic symptoms and in symptomless seedlings. This virus was transmitted by sap inoculation to a very restricted range of herbaceous hosts without inducing apparent symptoms. It was successfully purified from root tissues of infected figs. A virus-specific antiserum raised in rabbits, proved useful for its detection in fig leaf dips by immunosorbent electron microscopy. The cytology of infected cells was little affected. Bundles of filamentous particles were observed in the cytoplasma of parenchyma cells of infected fig trees and seedlings. The viral genome is a single-stranded positive-sense RNA with an estimated size of ca. 8,000 nt, 6,620 of which have been sequenced, starting from the polyadenylated 3' terminus. Genomic RNA consists of four open reading frames encoding, in the 5' → 3' direction, the replication-associated proteins (ORF 1), a 43 kDa putative movement protein (ORF 2), the 46 kDa coat protein (ORF 3), and a 12 kDa protein with nucleic acid binding properties. The viral genome structure and organization resembles that of members of the genus Trichovirus, family Flexiviridae and, indeed, FLV-1 clusters with trichoviruses in phylogenetic trees constructed with coat protein sequences. However, a distinct difference with all members of the genus rests with the size of the coat protein subunits (46 versus 22-27 kDa) and the presence of ORF 4, which is present only in three tentative species of this genus.