125 research outputs found
Olive quick decline and Xylella fastidiosa in Southern Italy: the state of the art
The identification in 2013 of an outbreak of Xylella fastidiosa (Xf) in olive groves in the Salento peninsula
(southern Italy) resulted in a plant health emergency of unprecedented proportions for the EU. Infected
olive trees show extensive desiccation of the canopy and severe quick decline symptoms. In the outbreak
area, the bacterium was found to be efficiently spread by the meadow spittlebug Philaenus spumarius,
abundant on the olive canopies during the dry season. The initial demarcated foci rapidly expanded over
the past 4 years, establishing a new demarcation line distant 80 km from the first reported outbreak;
while few species were found infected in 2013 the currently known susceptible hosts reached the number
of ca. 30 different plant species. Phytosanitary measures to combat the spread and mitigate the impact
of the bacterial infections, included restrictions for the new plantations, for the movement of propagating
materials and removal of infected trees. The severe damage suffered by the infected olive trees combined
with the imposed phytosanitary restrictions determined severe economic and social impacts in the local
community, raising major concerns against the application of the containment measures and determining
the failure to implement timely, effective and coordinated preventive measures. Due to the novelty of
the Xylellaâassociated disease in olives and in general the fact that Xf is conquering new geographical
area, like the EU territories, the EU Commission mobilized dedicated resources to build EU research
actions to fulfil research gaps for this emerging pathogen threatening the entire EU territory. Between
2015 and 2016, two relevant research projects in the framework of the H2020 programs have been
funded: the project "Pest Organisms Threatening Europe" (POnTE) and the project "Xylella Fastidiosa
Active Containment Through a multidisciplinaryâOriented Research Strategy" (XFâACTORS) the latter
targeting exclusively Xf. From the intense research activity developed in the past three years some major
results have been already achieved, providing data on the genetic and biological properties of the
population of the bacterium, the range of hosts, the identification and biology of the vector, the
identification of olive cultivars with promising traits of resistance
The endophytic microbiome of X. fastidiosa susceptible and resistant olives
A multi-factorial strategy is required to co-exist with X. fastidiosa infections, which are
devastating olive trees in the southern area of Apulia (Italy). Observations in the outbreak area can
provide information on potential approaches for containment. Olive cvs Leccino and FS17 show
lessened symptoms and host lower bacterial populations (1,2) than cvs Ogliarola salentina, Cellina di
Nardò and Kalamata. We are evaluating whether microbial communities inhabiting the xylem vessels
of olive cvs showing different susceptibilities to X. fastidiosa -infection play a role in resistance. To
explore these endophytic microbiomes, a whole-metagenome shotgun analysis is currently ongoing. X.
fastidiosa -infected and healthy olive plants of the cultivars FS17, Leccino and Kalamata, were
selected from the same plot to limit the influence of diverse soil composition and crop management.
Shotgun sequencing of DNA extracted from the xylem tissues will be used to investigate the
microbiome community by bio-informatic analysis. Moreover, efforts to isolate culturable
microorganisms to be used in antagonistic assays against X. fastidiosa, will be performed.
Concurrently, the X. fastidiosa-biocontrol potency of Paraburkholderia phytofirmans PsJN strain,
whose beneficial effects in the reduction of symptoms in Pierceâs Disease (3) have been recently
described, are under evaluation. We are testing the ability of P. phytofirmans to colonise xylem
vessels and interact with X. fastidiosa in tobacco and olive
First Report of âCandidatusLiberibacter asiaticusâ Associated with Huanglongbing in Sweet Orange in Ethiopia
Huanglongbing (HLB) is a serious disease of citrus worldwide. Three different âCandidatus Liberibacterâ species are associated with HLB: âCa. Liberibacter asiaticusâ, âCa. L. africanusâ, and âCa. L. americanusâ (1). âCa. L. africanusâ and its vector, Trioza erytreae, are both heat sensitive, and when present, occur in citrus when temperatures remain below 30 to 32°C. In Africa, âCa. L. africanusâ and T. erytreae have been reported in South Africa, Zimbabwe, Malawi, Burundi, Kenya, Somalia, Ethiopia, Cameroon, and Madagascar (1). Inspection of citrus trees in orchards and budwood sources in nurseries located in the warmer citrus-growing areas of Tigray and North Wollo in northern Ethiopia revealed nearly 100 trees with symptoms of leaf yellowing with a blotchy mottle pattern, dead branches, and decreased fruit quality and yield. Two symptomatic sweet orange budwood trees and three symptomatic orchard plants were sampled in April 2009, along with three healthy-looking sweet orange plants. DNA was extracted from 200 mg of desiccated leaf midribs using the CTAB method (4) and subjected to conventional PCR using the primer pairs A2/J5 (2) and OI2/23S1 (3) that amplify the ribosomal protein gene in the rplKAJL-rpoBC operon and the 16S/23S ribosomal intergenic regions, respectively, of âCa. L. africanusâ and âCa. L. asiaticusâ. Positive PCR reactions were obtained for all five symptomatic samples with both primer pairs. PCR amplicons of 703 bp (A2/J5) and 892 bp (OI2/23S) recovered from two of these samples were purified, cloned, and sequenced. BLAST analysis revealed that the nucleotide sequences we obtained for the ribosomal protein (GenBank Accessions Nos. GQ890155 and GQ890156) shared 100% identity with each other and 99% identity with sequences of âCa. L. asiaticusâ from Brazil (DQ471904), Indonesia (AB480161), China (DQ157277), and Florida (CP001677). Similarly, the 16S/23S ribosomal intergenic sequences (GU296538 and GU296539) shared 100% identity with each other and 99% identity with homologous âCa. L. asiaticusâ sequences from Brazil (DQ471903), Indonesia (AB480102), China (DQ778016), and Florida (CP001677) and contained two tRNA genes as occurs in âCa. L. asiaticusâ but not in âCa. L. africanusâ (3). To our knowledge, this is the first report of âCa. L. asiaticusâ in Africa. The presence of âCa. L. asiaticusâ is a threat for warmer citrus-growing areas of Africa that are less favorable for âCa. L. africanusâ and T. erytreae. In areas where âCa. L. asiaticusâ was confirmed, symptomatic trees must be promptly eradicated and surveys to determine spread of the disease and its vectors are necessary
Establishment of an experimental field to explore the differential olive cultivar response to Xylella fastidiosa infection
While different sources of natural resistance to Xylella fastidiosa (Xf) have been described in grapevines and citrus, lack of consolidated information exists on the wide panel of cultivars characterizing the vast olive germplasm. Preliminary observations on few cultivars, support the evidence that differential cultivar responses to Xf infections may exist. To explore the response of a larger panel of cultivars, in April 2015, an experimental olive plot, located within the Xf-heavily affected olive groves, was established in the Apulia Region (Italy). Twenty-four trees for each of the ten different cultivars were planted in randomized blocks. Each tree was caged with 15-20 specimens of Philaenus spumarius collected from the neighboring infected olive groves. Upon removing the cages, the trees are then continuously exposed to the natural vector populations occurring in the area. Nine and 12-months after planting, the trees were sampled, tested for Xf and inspected for symptoms. The first data confirmed the infectivity of the vector populations occurring in the Apulian contaminated area and the Xf susceptibility of the olive cultivars tested. Almost 50% of the trees tested positive, with an infection incidence ranging from 25% (Leccino) to 78% (Koroneiki). Symptoms of shoot dieback started to appear 1-year after planting, limitedly on few replicates of Cellina di Nardò. In April 2016, the number of cultivars has been increased up to 30. Periodical surveys for symptoms and quantitative analyses to monitor the differential bacterial titer and expression of target genes involved in the host response, are underway
Complete Genome Sequence of the Olive-Infecting Strain Xylella fastidiosa subsp. pauca De Donno
We report here the complete and annotated genome sequence of the
plant-pathogenic bacterium Xylella fastidiosa subsp. pauca strain De Donno. This strain was recovered from an olive tree severely affected by olive quick decline syndrome (OQDS), a devastating olive disease associated with X. fastidiosa infections in susceptible olive cultivars
Characterization of Citrus tristeza virus isolates recovered in Syria and Apulia (southern Italy) using different molecular tools
Citrus tristeza virus (CTV) is the causal agent of the most important virus disease of citrus. CTV isolates differing in biological and molecular characteristics have been reported worldwide. Recently, CTV was detected in Syria in citrus groves from two Governorates (Lattakia and Tartous) and several CTV outbreaks have been reported in Apulia (southern Italy) since 2003. To molecularly characterize the CTV populations spreading in Syria and Italy, a number of isolates from each region was selected and examined by different molecular approaches including: Multiple Molecular Markers analysis (MMM), real time RT-(q)PCR, single strand conformation polymorphism (SSCP) of the major coat protein (CP) gene (P25), and sequence analysis of the CP (P25), P18, P20 and RdRp genes. SSCP analysis of CP25 yielded two distinct simple patterns among the Syrian isolates and three different patterns in the Italian isolates. Based on MMM analysis, all Syrian CTV isolates were categorized as VT-like genotype, whereas the Italian isolates reacted only with the markers specific for the T30 genotype. These findings were also confirmed by RT-qPCR and by sequencing analysis of four genomic regions. The Italian isolates had nucleotide identities which varied: from 99.5 to 99.8 for the CP gene; from 97.4% to 98.3% for the P18 gene; from 98.6% to 99.8% for the P20 and from 97.8% to 99.1% for the partial RdRp sequenced. High sequence identity was found for all genomic regions analyzed between the Syrian isolates (from 98.9% to 99.6%). These results show that the CTV populations spreading in Apulia and Syria are associated with different genotypes, indicating different potential impacts on the citrus trees in the field. Since in both areas the introduction of the virus is relatively recent, infected plants resulted to contain a single and common genotype, suggesting that CTV is spreading from the first outbreaks by aphids or local movement of autochthonous infected plant material
First international proficiency testing for laboratory performance on Xylella fastidiosa detection
A proficiency test (PT) to evaluate the performance of laboratories involved in molecular
and serological detection of X. fastidiosa was carried out in early 2017; 35 laboratories from EU/non-
EU Countries tested 4 different methods to purify DNA, conventional and qPCR assays, and 2 ELISA
tests. The number of resultant positive agreement/negative agreement/positive deviation/negative
deviation was used to determine the laboratory performance (i.e. accuracy 100%). The overall results
showed that all laboratories were able to correctly diagnose X. fastidiosa in the blind samples containing the highest X. fastidiosa concentrations, whereas the performance of several laboratories
was negatively affected by the lack of detection in the samples with the lowest concentrations, both
through molecular and serological tests. Accuracy level of 100% (laboratory conformed to the PT) was
successfully recovered in the majority of the laboratories performing qPCR and PCR assays on DNA
purified using at least 2 of the 4 tested protocols. The use of automated platform ensured higher
laboratory performance. As expected, results of the ELISA tests generated lower performance values
in the majority of the laboratories, due to the lack of detection of positive samples containing the
lowest the bacterial concentration. This study provides a good overview on the laboratory
performance for the diagnostics currently used in the EPPO countries and indicate useful
improvements that laboratories can adopt to achieve a better performance
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