Plasmopara viticola
(Berk. et Curt.) Berl. and de Toni, the agent of downy mildew, is one of the most important pathogens of European grapevine (
Vitis vinifera
L.). Extensive evaluation of ...cultivated grapevine germplasm has highlighted the existence of resistant phenotypes in the Georgian (Southern Caucasus) germplasm. Resistance is shown as a reduction in disease severity. Unraveling the genetic architecture of grapevine response to
P. viticola
infection is crucial to develop resistant varieties and reduce the impact of disease management. The aim of this work was to apply a genome-wide association (GWA) approach to a panel of Georgian-derived accessions phenotyped for
P. viticola
susceptibility and genotyped with Vitis18kSNP chip array. GWA identified three highly significant novel loci on chromosomes 14 (
Rpv29
), 3 (
Rpv30
) and 16 (
Rpv31
) associated with a low level of pathogen sporulation.
Rpv29
,
Rpv30
, and
Rpv31
loci appeared to be associated with plant defense genes against biotic stresses, such as genes involved in pathogen recognition and signal transduction. This study provides the first evidence of resistant loci against
P. viticola
in
V. vinifera
germplasm, and identifies potential target genes for breeding
P. viticola
resistant grapevine cultivars.
Endophytic plant-growth-promoting bacteria (ePGPB) are interesting tools for pest management strategies. However, the molecular interactions underlying specific biocontrol effects, particularly ...against phytopathogenic viruses, remain unexplored. Herein, we investigated the antiviral effects and triggers of induced systemic resistance mediated by four ePGPB (
strain R8,
strain R16,
strain 255-7, and
strain 260-02) against four viruses (Cymbidium Ring Spot Virus-CymRSV; Cucumber Mosaic Virus-CMV; Potato Virus X-PVX; and Potato Virus Y-PVY) on
plants under controlled conditions and compared them with a chitosan-based resistance inducer product. Our studies indicated that ePGPB- and chitosan-treated plants presented well-defined biocontrol efficacy against CymRSV and CMV, unlike PVX and PVY. They exhibited significant reductions in symptom severity while promoting plant height compared to nontreated, virus-infected controls. However, these phenotypic traits showed no association with relative virus quantification. Moreover, the tested defense-related genes (
(
),
(
), and
(
)) implied the involvement of a salicylic-acid-related defense pathway triggered by
gene upregulation.
Downy mildew, caused by the oomycete
Plasmopara viticola
, is one of the diseases causing the most severe economic losses to grapevine (
Vitis vinifera
) production. To date, the application of ...fungicides is the most efficient method to control the pathogen and the implementation of novel and sustainable disease control methods is a major challenge. RNA interference (RNAi) represents a novel biotechnological tool with a great potential for controlling fungal pathogens. Recently, a candidate susceptibility gene (
VviLBDIf7
) to downy mildew has been identified in
V. vinifera
. In this work, the efficacy of RNAi triggered by exogenous double-stranded RNA (dsRNA) in controlling
P. viticola
infections has been assessed in a highly susceptible grapevine cultivar (Pinot noir) by knocking down
VviLBDIf7
gene. The effects of dsRNA treatment on this target gene were assessed by evaluating gene expression, disease severity, and development of vegetative and reproductive structures of
P. viticola
in the leaf tissues. Furthermore, the effects of dsRNA treatment on off-target (
EF1α
,
GAPDH
,
PEPC
, and
PEPCK
) and jasmonic acid metabolism (
COI1
) genes have been evaluated. Exogenous application of dsRNA led to significant reductions both in
VviLBDIf7
gene expression, 5 days after the treatment, and in the disease severity when artificial inoculation was carried out 7 days after dsRNA treatments. The pathogen showed clear alterations to both vegetative (hyphae and haustoria) and reproductive structures (sporangiophores) that resulted in stunted growth and reduced sporulation. Treatment with dsRNA showed signatures of systemic activity and no deleterious off-target effects. These results demonstrated the potential of RNAi for silencing susceptibility factors in grapevine as a sustainable strategy for pathogen control, underlying the possibility to adopt this promising biotechnological tool in disease management strategies.
Flavescence dorée (FD) is the most important phytoplasma-associated disease of the grapevine yellows complex in Europe. Recent studies highlighted a great genetic diversity within FD phytoplasma ...(FDp) strains and demonstrated that their diffusion is not related exclusively to the pathosystem including Vitis vinifera L. and Scaphoideus titanus but involves additional vectors and reservoir plants. This study aimed to investigate FD epidemiology in north-western Italy, with a particular focus on FDp hosts. During field surveys, leaf samples were collected from symptomatic grapevines and other symptomless plant species, and insects were collected within and around vineyards. Phytoplasmas belonging to the ribosomal group 16SrV were detected and typed using nested-PCR-based amplification and nucleotide sequence analyses of the map gene. All symptomatic grapevines were found to be infected by the FDp genotype M54, prevalent in S. titanus and also identified in other known and newly reported hosts. Interestingly, other FDp strains (M38, M50, M51, M121) and FDp-related strains (M39, M43, M48), never detected in grapevines, were largely identified in several known and newly reported host plants and insects including S. titanus. Such evidence confirmed the complexity of FD ecology, expanding the knowledge on the range of FDp host plants putatively involved in the disease spread.
Downy and powdery mildews are major grapevine diseases. In organic viticulture, a few fungicides with protectant activities (copper and sulphur in particular) can be used, and their preventative ...application frequently leads to unneeded spraying. The adoption of an epidemiological disease forecasting model could optimise the timing of treatments and achieve a good level of disease protection. In this study, the effectiveness of the EPI (Etat Potentiel d'Infection) model in predicting infection risk for downy and powdery mildews was evaluated in nine organic vineyards located in Panzano in Chianti (FI), over a 2-year period (2020-2021). The reliability of the EPI model was investigated by comparing the disease intensities, the number of fungicide sprayings, the quantities of the fungicides (kg/ha), and the costs of the treatment achieved, with or without the use of the model, in a vineyard. The results obtained over two seasons indicated that, in most cases, the use of the EPI model accurately signalled the infection risk and allowed for a reduction in the frequency and cost of spraying, particularly for powdery mildew control (-40% sprayings, -20% costs compared to the farmer's schedule), without compromising crop protection. The use of the EPI model can, therefore, contribute to more-sustainable disease management in organic viticulture.
Mgaloblishvili, a
cultivar, exhibits unique resistance traits against
, the downy mildew agent. This offers the unique opportunity of exploring the molecular responses in compatible and incompatible ...plant-pathogen interaction. In this study, whole transcriptomes of Mgaloblishvili, Pinot noir (a
susceptible cultivar), and Bianca (a resistant hybrid) leaves, inoculated and non-inoculated with the pathogen
were used to identify
effector-encoding genes and plant susceptibility/resistance genes. Multiple effector-encoding genes were identified in
transcriptome, with remarkable expression differences in relation to the inoculated grapevine cultivar. Intriguingly, five apoplastic effectors specifically associated with resistance in
. Gene coexpression network analysis identified specific modules and metabolic changes occurring during infection in the three grapevine cultivars. Analysis of these data allowed, for the first time, the detection in
of a putative
susceptibility gene, encoding a LOB domain-containing protein. Finally, the de novo assembly of Mgaloblishvili, Pinot noir, and Bianca transcriptomes and their comparison highlighted novel candidate genes that might be at the basis of the resistant phenotype. These results open the way to functional analysis studies and to new perspectives in molecular breeding of grapevine for resistance to
.
Rapid and sensitive assays for the identification of plant pathogens are necessary for the effective management of crop diseases. The main limitation of current diagnostic testing is the inability to ...combine broad and sensitive pathogen detection with the identification of key strains, pathovars, and subspecies. Such discrimination is necessary for quarantine pathogens, whose management is strictly dependent on genotype identification. To address these needs, we have established and evaluated a novel all-in-one diagnostic assay based on nanopore sequencing for the detection and simultaneous characterization of quarantine pathogens, using
as a case study. The assay proved to be at least as sensitive as standard diagnostic tests and the quantitative results agreed closely with qPCR-based analysis. The same sequencing results also allowed discrimination between subspecies when present either individually or in combination. Pathogen detection and typing were achieved within 13 min of sequencing owing to the use of an internal control that allowed to stop sequencing when sufficient data had accumulated. These advantages, combined with the use of portable equipment, will facilitate the development of next-generation diagnostic assays for the efficient monitoring of other plant pathogens.
Summary
‘Candidatus Liberibacter spp.’ cause serious plant diseases. ‘Candidatus Liberibacter asiaticus’, ‘Ca. L. americanus’ and ‘Ca. L. africanus’ are the aetiological agents of citrus greening ...(Huanglongbing) in Asia, America and Africa. ‘Candidatus Liberibacter solanacearum’ causes diseases in Solanaceae in America and New Zealand. All four species are vectored by psyllid insects of different genera. Here, we show that the pear psyllid pest Cacopsylla pyri (L.) hosts a novel liberibacter species that we named ‘Ca. Liberibacter europaeus’. It can bloom to high titres in the psyllid host, with more than 109 16S rRNA gene copies per individual. Fluorescent in situ hybridization experiments showed that ‘Ca. L. europaeus’ is present in the host midgut lumen, salivary glands and Malpighian tubules. ‘Candidatus L. europaeus’ has a relatively high prevalence (> 51%) in C. pyri from different areas in the Piedmont and Valle d'Aosta regions in Italy and can be transmitted to pear plants in experimental transmission trials. However, even though high titres of the bacterium (more than 108 16S rRNA gene copies g−1 of pear plant tissue) could be detected, in the pear tissues no specific disease symptoms could be observed in the infected plants over a 6‐month period. Despite liberibacters representing potential quarantine organisms, ‘Ca. L. europaeus’, first described in Italy and Europe, apparently behaves as an endophyte rather than a pathogen.
"Bois noir" disease associated with '
Phytoplasma solani' seriously compromises the production and survival of grapevines (
L.) in Europe. Understanding the plant response to phytoplasmas should help ...to improve disease control strategies. Using a combined metabolomic and transcriptomic analysis, this work, therefore, investigated the phytoplasma-grapevine interaction in red cultivar Sangiovese in a vineyard over four seasonal growth stages (from late spring to late summer), comparing leaves from healthy and infected grapevines (symptomatic and symptomless). We found an accumulation of both conjugate and free salicylic acids (SAs) in the leaves of '
. P. solani'-positive plants from early stages of infection, when plants are still asymptomatic. A strong accumulation of gentisic acid (GA) associated with symptoms progression was found for the first time. A detailed analysis of phenylpropanoids revealed a significant accumulation of hydroxycinnamic acids, flavonols, flavan 3-ols, and anthocyanin cyanidin 3-
-glucoside, which are extensively studied due to their involvement in the plant response to various pathogens. Metabolomic data corroborated by gene expression analysis indicated that phenylpropanoid biosynthetic and salicylic acid-responsive genes were upregulated in '
. P. solani-positive plants compared to -negative ones during the observed period.
PDF
