Microdochium nivale (Fr.) Samuels & Hallett and Microdochium majus (Wollenw.) Glynn & S.G. Edwards are sister species that cause diseases on grasses and cereals at low temperatures. The DNA sequences of RPB2 (RNA polymerase II), -tubulin, EF-1␣ (elongation factor), and ITS (rDNA internal transcribed spacer) from these groups were analysed to compare the extent of differences between these species, among isolates from Europe compared with those from North America, and among isolates of M. nivale originally collected from Agrostis spp. compared with isolates from wheat (Triticum aestivum). All of the regions studied except for ITS resolved M. nivale and M. majus isolates into separate clades. The RPB2 sequences also resolved both the North American and European M. majus isolates and M. nivale isolates from either turfgrasses or wheat into separate clades. These results support the recent elevation of M. nivale and M.majus to sister species and also provide some support for the assertion that there may be host-specific differences among M. nivale, which has a wider host range than M. majus. Résumé: Le Microdochium nivale (Fr.) Samuels & Hallett et le Microdochium majus (Wollenw.) Glynn & S.G. Edwards constituent deux plantes soeurs causant des maladies chez les herbacées et les céréales à basse température. Afin de comparer l'étendue des différences entre ces deux espèces, les auteurs ont analysé la séquence ADN du RBP2 (polymérase de l'ARN II), la -tubuline, le EF-1␣ (facteur d'élongation) et l'ITS (espaceur interne transcrit du rADN) chez ces groupes, entre isolats d'Europe comparés à ceux de l'Amérique du Nord; également entre des isolats du M. nivale originalement récoltés d'Agrostis spp. comparativement à des isolats provenant du blé. (Triticum aestivum). Toutes les régions étudiées, sauf pour l'ITS, regroupent les isolats de M. nivale et du M. majus dans des clades séparés. Les séquences RBP2 distinguent également les isolats du M. majus européens et nord-américains et les isolats du M. nivale provenant soit d'herbacées ou de blé dans des clades distincts. Ces résultats supportent l'élévation récente du M. nivale et du M. majus en espèces soeurs, et fournit également un certain support à l'affirmation qu'il pourrait exister des différences spécifiques à l'hôte parmi les M. nivale ayant un nombre d'hôtes plus large que le M. majus. [Traduit par la Rédaction]Mots-clés : Microdochium nivale, Microdochium majus, maladie des plantes, moisissure nivéale rose, plaque de Fusarium, plaque de Microdochium.
Slime flux involves exudations from wounds or cracks of trees resulting in light or dark streaks down the trunk and the viscous exudates may be thick enough to form a layer on the bark (Sinclair and Lyon 2005). Slime flux may be considered an aesthetic and sometimes an odiferous nuisance, but does not harm the tree. The exudates result from a bacterial presence inside the tree called wetwood, which is described as waterlogged wood tissue, with alkaline pH levels and a microfauna of bacteria (Sinclair and Lyon 2005). Wetwood is considered a natural occurrence, and is not considered detrimental to tree health, although its presence decreases the value of lumber because the waterlogged tissue takes longer to dry and may dry unevenly leading to checking (Sinclair and Lyon 2005). Only when wetwood occurs in the outer living sapwood is it considered pathogenic (Murdoch and Campana 1983).
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