La Tour-du-Pin, France
La Tour-du-Pin, France

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Janzac B.,French National Institute for Agricultural Research | Janzac B.,Montpellier SupAgro | Willemsen A.,Polytechnic University of Valencia | Cuevas J.M.,Polytechnic University of Valencia | And 7 more authors.
Plant Pathology | Year: 2015

Potato virus Y (PVY) is a plant virus distributed worldwide that causes damage to several species of the Solanaceae family. It was established long ago that groups of PVY isolates defined by phylogenetic analyses correlate strongly with those demarcated by differential biological properties. Consequently, life-history traits of this viral species can be inferred by phylogenetic analysis. In this study, characteristics of PVY isolates sampled in different tobacco fields in Brazil were analysed and most of the tested Brazilian PVY isolates were assigned to the recently described unconventional serogroup YU. The analysis of molecular diversity of the coat protein (CP) cistron from some YU isolates made it possible (i) to identify specific amino acid residues in the N-terminal of the CP protein and (ii) to assign some YU isolates to a new PVY clade. The symptoms caused by isolates belonging to this new PVY 'Brazilian' clade and their ability to infect selected susceptible hosts led to the conclusion that neither veinal necrosis symptoms expressed on infected tobacco plants nor adaptation to potato or pepper hosts are ancestral characteristics of PVY. These observations suggest that PVY has gained a remarkable new biological property and broadened its host range over time. © 2014 British Society for Plant Pathology.


Janzac B.,University of Rennes 1 | Janzac B.,Institute du Tabac | Janzac B.,Montpellier SupAgro | Tribodet M.,University of Rennes 1 | And 4 more authors.
Plant Disease | Year: 2014

Emergence of viral genotypes can make control strategies based on resistance genes ineffective. A few years after the deployment of tobacco genotypes carrying alleles of the Potato virus Y (PVY) recessive resistance gene va, virulent PVY isolates have been reported, suggesting the low durability of va. To have a broader view of the evolutionary processes involved in PVY adaptation to va, we studied mutational pathways leading to the emergence of PVY resistance-breaking populations. The viral genome-linked protein (VPg) has been described to be potentially involved in va adaptation. Analyses of the VPg sequence of PVY isolates sampled from susceptible and resistant tobacco allowed us to identify mutations in the central part of the VPg. Analysis of the virulence of wild-type isolates with known VPg sequences and of mutated versions of PVY infectious clones allowed us to (i) validate VPg as the PVY virulence factor corresponding to va, (ii) highlight the fact that virulence gain in PVY occurs rapidly and preferentially by substitution at position AA105 in the VPg, and (iii) show that the 101G substitution in the VPg of a PVYC isolate is responsible for cross-virulence toward two resistance sources. Moreover, it appears that the evolutionary pathway of PVY adaptation to va depends on both virus and host genetic backgrounds. © 2014 The American Phytopathological Society.


Lacroix C.,University of Rennes 1 | Lacroix C.,Institute du Tabac | Glais L.,FNPPPT Federation Nationale des Producteurs de Plants de Pomme de Terre | Verrier J.-L.,Institute du Tabac | And 3 more authors.
Plant Pathology | Year: 2011

To investigate the role of environmental conditions on the selection of virulent Potato virus Y (PVY) isolates subject to pressure from the recessive resistance gene va in tobacco, a field survey was performed in Brazil where va-derived genotypes have been recently introduced and now represent less than one-third of cultivated tobacco genotypes. A serological analysis of 397 leaves collected from different Brazilian tobacco-growing areas and mainly from plants with symptoms indicated that 52·4% of samples were infected by at least one of the viral species tested. PVY was present in 72·1% of infected samples. The probability of a plant being infected with PVY was reduced in va hosts. However, the biological characterization of PVY isolates on indicator hosts showed that 20 of the 29 tested isolates were able to overcome the alleles of the va gene. Moreover, the observed biological diversity of isolates was higher in susceptible tobacco genotypes than in va-resistant ones. Comparison of these data with the PVY diversity in French tobacco fields shows that the use of va-derived genotypes in two environments with contrasting climatic conditions, local hosts and cultural contexts, leads to a similar outcome: the prevalence of virulent isolates. These results strongly suggest an important role of the va gene in the modification of PVY populations. © 2011 INRA. Plant Pathology © 2011 BSPP.


Lacroix C.,Agrocampus Ouest | Lacroix C.,Institute du Tabac | Glais L.,FNPPPT Federation Nationale des Producteurs de Plants de Pomme de Terre | Verrier J.-L.,Institute du Tabac | Jacquot E.,Agrocampus Ouest
European Journal of Plant Pathology | Year: 2011

Control strategies developed for plant viral diseases through breeding programs can be impaired by adaptive response of pathogens. A few years after the deployment in France of improved tobacco genotypes introgressed with alleles of the Potato virus Y (PVY) recessive resistance gene va, necrotic symptoms associated with PVY infection have been reported on these cultivars. Due to the lack of efficient alternative methods to control PVY, the va resistance sources have to be managed according to viral parameters, such as the dynamic of emergence of virulent variants. The effects of va alleles on the evolution of PVY was tested in experimental conditions using a PVY infectious clone and two couples of resistant tobacco near isogenic lines BVA/Bva0 and FVA/Fva2 both allelic for the va gene. Infection efficiencies data showed that a single passage on Fva2 line led to the selection of virulent viral populations able to overcome both va0 and va2 alleles. Sequence analyses of va2 derived PVY variants revealed that the acquisition of the capacity to overcome va2 resistance is associated with single point mutations at two different nucleotide positions in the central part of the VPg. The described PVY adaptation process to overcome resistance mediated by different va alleles should be considered for the future development of durable and integrated strategies of management of PVY infections in tobacco crops. © 2011 KNPV.


Amelot N.,Toulouse 1 University Capitole | Dorlhac de Borne F.,Institute du Tabac | San Clemente H.,Toulouse 1 University Capitole | Mazars C.,Toulouse 1 University Capitole | And 2 more authors.
Cell Calcium | Year: 2012

Cryptogein is a proteinaceous elicitor secreted by the oomycete Phytophthora cryptogea, which induces a hypersensitive response in tobacco plants. We have previously reported that in tobacco BY-2 cells treated with cryptogein, most of the genes of the phenylpropanoid pathway were upregulated and cell wall-bound phenolics accumulated. Both events were Ca 2+ dependent. In this study, we designed a microarray covering a large proportion of the tobacco genome and monitored gene expression in cryptogein-elicited BY-2 cells to get a more complete view of the transcriptome changes and to assess their Ca 2+ dependence. The predominant functional gene categories affected by cryptogein included stress- and disease-related proteins, phenylpropanoid pathway, signaling components, transcription factors and cell wall reinforcement. Among the 3819 unigenes whose expression changed more than fourfold, 90% were Ca 2+ dependent, as determined by their sensitivity to lanthanum chloride. The most Ca 2+-dependent transcripts upregulated by cryptogein were involved in defense responses or the oxylipin pathway. This genome-wide study strongly supports the importance of Ca 2+-dependent transcriptional regulation of regulatory and defense-related genes contributing to cryptogein responses in tobacco. © 2011 Elsevier Ltd.


Lacroix C.,Agrocampus Ouest | Lacroix C.,Institute du Tabac | Glais L.,FNPPPT Federation Nationale des Producteurs de Plants de Pomme de Terre | Kerlan C.,Agrocampus Ouest | And 2 more authors.
Plant Pathology | Year: 2010

Improved tobacco cultivars introgressed with alleles of the recessive resistance va gene have been widely deployed in France to limit agronomical consequences associated with Potato virus Y (PVY) infections. Unfortunately, necrotic symptoms associated with PVY have been reported on these cultivars suggesting that PVY is able to overcome the resistance. A field survey was performed in France in 2007 to (i) estimate the prevalence of PVY in tobacco plants showing symptoms and (ii) characterize PVY isolates present in susceptible and va-derived tobacco cultivars. A serological typing procedure, applied to 556 leaves collected from different French tobacco growing areas, was performed using polyclonal antisera raised against different viral species including PVY. Viral species were detected in 80·8% of leaves and PVY was present in 83·5% of infected samples. However, statistical analysis confirmed that the probability of a tobacco plant being infected with PVY is reduced in va hosts. Eighty-six PVY isolates were mechanically inoculated on one susceptible and three va-derived tobacco cultivars used as indicator hosts to define virulence of these isolates against alleles 0, 1 and 2 of the va gene. Both qualitative and quantitative analyses showed that 55 PVY isolates were able to overcome the three va alleles. Moreover, the monitored biological diversity of PVY isolates was higher in the susceptible tobacco hosts than in the va-derived ones. This study helps to understand consequences of the deployment of the va gene in tobacco on diversity and virulence of PVY isolates. © 2010 The Authors. Plant Pathology © 2010 BSPP.

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