Genetic diversity of poplar leaf rust populations in the north-central United States

نویسنده

  • W. Chen
چکیده

Uredinia of poplar leaf rust, Melampsora medusae Thüm f.sp. deltoides, appeared in late July 1998, June 1999, and August 2000 in a cottonwood (Populus deltoides Bartr.) stand in Ames, Iowa. Seedlings of the alternate host (eastern larch, Larix laricina (Du Roi) K. Koch) set out at the site in spring 2000 formed aecia 3 months before uredinia appeared. Using three PCR-based microsatellite markers, the aecial population was genetically diverse and in Hardy–Weinberg equilibrium, typical of a population that had gone through sexual reproduction. Uredinia populations in 1998–2000 had lower levels of gene diversities (from 0.58 to 0.71) and were not in Hardy–Weinberg equilibrium. Of nine populations in Minnesota, Iowa, and Missouri during the early stage of the 1999 epidemic, the two populations with the highest gene diversity, the highest level of heterozygosity, and the greatest number of unique genotypes were within the natural geographic range of larch. However, the southernmost population in Missouri was also in Hardy– Weinberg equilibrium. Epidemics started sooner in Iowa than in Minnesota, which contradicts the hypothesis that epidemics begin in northern regions where the alternate hosts naturally overlap. Epidemics appeared to commence independently in the various locations, perhaps focused around areas where ornamental larch is in proximity to P. deltoides. Résumé : Les urédosores de la rouille des feuilles du peuplier, causée par Melampsora medusae Thüm f. sp. deltoides, sont apparus respectivement à la fin de juillet 1998, en juin 1999 et en août 2000 dans un peuplement de peuplier deltoïde (Populus deltoides Bartr.) à Ames, en Iowa. Des semis de l’hôte alterne, le mélèze laricin (Larix laricina (Du Roi) K. Koch), installés sur le site au printemps 2000 ont formé des écies 3 mois avant l’apparition des urédosores. Selon trois marqueurs microsatellites obtenus par PCR, la population d’écies était génétiquement diversifiée et en équilibre de Hardy–Weinberg, typique d’une population issue de la reproduction sexuée. Les populations d’urédosores de 1998 à 2000 avaient un degré de diversité génétique plus faible (de 0,58 à 0,71) et n’étaient pas en équilibre Hardy– Weinberg. Des neuf populations du Minnesota, de l’Iowa et du Missouri au début de l’épidémie de 1999, les deux populations avec la plus grande diversité génétique, le degré le plus élevé d’hétérozygotie et le plus grand nombre de génotypes uniques étaient dans l’aire de répartition naturelle du mélèze. Cependant, la population la plus méridionale au Missouri était également en équilibre Hardy–Weinberg. L’épidémie a commencé plus tôt en Iowa et au Minnesota, ce qui contredit l’hypothèse selon laquelle les épidémies débutent dans les régions plus au nord où les hôtes alternes se recoupent naturellement. Les épidémies ont semblé débuter indépendamment les unes des autres dans les différents endroits, peut-être concentrées dans les endroits où le mélèze ornemental côtoie P. deltoides. [Traduit par la Rédaction] Chen and Harrington 2057

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تاریخ انتشار 2006