First Report of Pear Decline Caused by ‘<i>Candidatus</i> Phytoplasma pyri’ in Ontario, Canada
Notice bibliographique
Résumé
Pear decline (PD) is a serious disease of pear (Pyrus communis L.) caused by 'Candidatus Phytoplasma pyri', which belongs to the subgroup 16SrX-C of the apple proliferation (AP) group of phytoplasmas (3). Pear seedlings from the Agriculture and Agri-Food Canada (AAFC) pear breeding program, which have been selected for advanced test and grower trials, are routinely submitted to the Canadian Food Inspection Agency (CFIA) Sidney Laboratory (formerly, CFIA Centre for Plant Health, Saanichton, BC) for virus testing at the same time that propagation is initiated to produce trees for further evaluations. In early 2007, the CFIA reported that samples of two seedling selections submitted in 2005 tested positive for phytoplasmas by a nested PCR assay with phytoplasma universal primers P1/P7 (1), followed by phytoplasma universal primers fU5/rU3 (2) and real time PCR with universal phytoplasma primers developed by the CFIA-Sidney (personal communication). Phytoplasmas present in both selections were subsequently identified as 'Ca. P. pyri' strains by nested PCR with the P1/P7 primers followed by PD/peach yellow leaf roll (PYLR)-specific primers fPD/rPDS (2,4). These were the first PD-positive results from many samples submitted over the years for testing. Following PD-positive diagnoses for the seedling trees, others propagated from these seedling trees were removed from the nursery. When tested by PD-specific nested PCR (P1/P7 then fPD/rPDS), one selection had 39 of 79 nursery trees (49%) that were PD positive, while the other selection had 27 of 96 trees (28%) testing as PD positive. PCR amplification of DNA isolated from leaves of six of the propagated trees, with primer pair fPD/rPDS, yielded an ~1,400-bp product that was sequenced. A consensus sequence of 1,313 bp (GenBank Accession No. GU565959) was subjected to a nucleotide BLAST search of the NCBI database and showed 100% nt identity with sequences of phytoplasmas PD1 (AJ542543) and PYLR (Y16394). Subsequently, the PD-positive results from leaf, dormant shoot, and root tissues from the original seedling trees were confirmed by PD-specific nested PCR. On the original seedling trees, visible symptoms typical of PD, especially premature leaf coloration, were observed in late summer 2008 and samples taken of green and red leaves were subjected to PD-specific PCR. Red leaves were PD-positive, while green leaves were mostly PD-negative. Pear leaves, dormant shoots, and roots collected from research and commercial orchards in southern Ontario in 2007 and 2008 were subjected to PD-specific nested PCR (P1/P7 then fPD/rPDS), AP-specific nested PCR (P1/P7 then fO1/rO1) (2), as well as the universal phytoplasma nested PCR (P1/P7 then fU5/rU3), resulting in the identification of PD-positive trees of several cultivars. The sequence of the 1,057-bp amplicon from accession PYR0190 (selection HW615), with AP-specific primers fO1/rO1, was deposited in GenBank (GU475131). Although there have been no previous reports of PD in Ontario, Canada, it would appear that PD has been present for some time based on the number and distribution (both geographic and cultivar) of positive samples. References: (1) S. Deng and C. Hiruki. J. Microbiol. Methods 14:53, 1991. (2) K.-H. Lorenz et al. Phytopathology 85:771, 1995. (3) E. Seemüller et al. J. Plant Pathol. 80:3, 1998. (4) C. D. Smart et al. Appl. Environ. Microbiol. 62:2988, 1996.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».