First European Report of a Leaf Spot on Common Ragweed (<i>Ambrosia artemisiifolia</i>) Caused by a <i>Phoma</i> sp.
Notice bibliographique
Résumé
Common ragweed, native to North America, has recently become invasive in some parts of Europe. In Hungary, it has become the most widespread agricultural weed species and the most important producer of allergenic pollen since the 1990s. During surveys for its fungal plant pathogens to be evaluated as potential biological control agents (1), ragweed plants exhibiting necrotic spots on the leaves and stems were repeatedly found in Heves and Vas counties in Hungary in September 2004 and 2006. Numerous globose and ostiolate pycnidia, 68 to 115 μm in diameter, containing hyaline, unicellular conidia, 3 to 8 μm long, were found in necrotic tissues. On the basis of these characteristics, the fungus was identified as a Phoma sp., and 21 isolates were obtained on Czapek-Dox medium supplemented with 2% malt and 0.5% tetracycline in 2004 and 2006. Two well-sporulating isolates, designated Ph-5 and Ph-17, were selected for further studies. DNA was extracted from mycelium with a Qiagen DNeasy Plant Kit (Hilden, Germany) and the rDNA internal transcribed spacer (ITS) sequences were amplified and determined as described by Szentiványi et al. (2). The ITS sequences were identical in these two isolates and were 97 to 98% similar to those of Didymella bryoniae (anamorph Phoma cucurbitacearum), a pathogen of cucurbits, and also to those of other Phoma spp. No ITS sequences identical to those determined in Phoma isolates Ph-5 and Ph-17 were found in GenBank. Sequence data were deposited in GenBank (No. FJ794609). To test the pathogenicity of Ph-17 grown on Czapek-Dox medium with 2% malt, a 2 to 6 × 105 conidia/ml aqueous suspension was used to inoculate 2-month-old potted ragweed plants and 1-month-old cucumber cv. Rajnai fürtös, bottle gourd (Lagenaria leucantha) cv. Minibottle, and watermelon (Citrullus lanatus) cv. Sugar Baby, which were all grown from seeds in a greenhouse. Plants were kept in transparent plastic chambers for 6 weeks. Five pots with one to three plants each were used for each plant species tested and the experiment was carried out twice. Noninoculated plants, two pots with one to three individuals for each species kept in the same way, served as controls. Necrotic spots with pycnidia developed on 38 to 47% of the leaves of all inoculated ragweed plants 18 to 25 days after inoculation, whereas all the cucurbitaceous plants tested, as well as the control ragweed plants, did not develop disease symptoms. Although the Phoma isolate Ph-17 was, based on ITS sequence data, closely related to D. bryoniae, it was not pathogenic to cucurbits. The pathogen was reisolated from two diseased ragweed plants. Several Phoma spp. strains were isolated from Ambrosia artemisiifolia in the United States and Canada (3,4), but to our knowledge, none were isolated outside North America. One of the strains has already been used as a potential biological control agent of ragweed in Canada, but then lost its virulence in culture (3). The biocontrol potential of the Hungarian Phoma sp. isolate Ph-17 against A. artemisiifolia is currently being investigated. To our knowledge, this is the first report of a Phoma sp. on A. artemisiifolia in Europe. References: (1) L. Kiss. Biocontrol Sci. Technol. 17:535, 2007. (2) O. Szentiványi et al. Mycol. Res. 109:429, 2005. (3) M. P. Teshler et al. Ambrosia artemisiifolia L., Common Ragweed (Asteraceae) in: Biological Control Programmes in Canada, 1981-2000. CABI, Wallingford, UK, 2002. (4) L. Zhou et al. Mycologia 97:612, 2005.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,001 | 0,001 |
| Communication savante | 0,001 | 0,001 |
| Science ouverte | 0,000 | 0,001 |
| Intégrité de la recherche | 0,002 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,003 | 0,001 |
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 source (Gemma direct ou Codex distillé), 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 ».