Neomyzeten – eine anhaltende Bedrohung für den Schweizer Wald

Abstract

Neomycetes – persistent threats to Swiss forests More than 40 neomycetes pathogenic to woody plant species were introduced to Switzerland during the last 100 years, and the number is increasing exponentially. A few neomycetes are invasive and cause serious diseases on forest and ornamental trees: Cryphonectria parasitica, causal agent of chestnut blight, Hymenoscyphus pseudoalbidus causing ash dieback, Ophiostoma novo-ulmi causing Dutch elm disease and Ceratocystis platani causing canker stain of plane. The causal agents of sudden oak death (Phytophthora ramorum) and collar and root rot of alder (P. alni ssp. alni) have been detected in Switzerland but have not reached epidemic levels. Ceratocystis fagacearum, causal agent of oak wilt, or Leptographium wageneri causing black stain root disease of conifers are absent from Switzerland, but are threats to Swiss forests and measures have been implemented to prevent their introduction. Prevention of threats by fungi which are harmless symbionts in their native range, e.g. endophytic fungi, is more challenging. The only way to avoid the endophyte problem is to grow trees from aseptic seed, saplings or meristem cultures. Additionally, setup of sentinel plantings in as many regions as possible all over the world could serve as early warning systems. To prevent the introduction of wilt and root diseases, only treated wood and treated potting media should be allowed for import. Natural regeneration prevents contamination of forest soils by Phytophthora species originating from nursery plants.