Is there evidence for post‐epidemic attenuation in the Dutch elm disease pathogenOphiostoma novo‐ulmi?

Abstract

The first pandemic of Dutch elm disease (DED) in Europe and North America caused by the introduced Ophiostoma ulmi began in the early 1900s but declined unexpectedly in Europe from the 1930s onwards after killing 30–40% of the elms. Later a second pandemic caused by the much more aggressive Ophiostoma novo‐ulmi spread across the same areas and by 1990 most of Britain's c. 30 million mature elms had died. During the second pandemic, O. novo‐ulmi acquired debilitating viruses and changed from being largely clonal to highly heterogeneous through horizontal transfer of novel, sometimes deleterious, genes from O. ulmi. In the post‐epidemic period a new disease dynamic has emerged, with millions of small recruitment elms repeatedly attacked by sequential cycles of disease. This study investigated the possibility of pathogenic attenuation in O. novo‐ulmi as the epidemic has progressed. Isolates collected from the three original outbreak areas in Britain in 1982–3 (early post‐epidemic period) and 2011 (advanced post‐epidemic) were compared for two fitness components: pathogenic aggressiveness and in vitro growth rate. Mean aggressiveness of the 2011 isolates to clonal English elm (Ulmus procera) proved not to differ significantly from that of the 1982 isolates, either overall or within each outbreak area. Similarly, the mean growth rates of the 1982 and 2011 samples showed no differences. The implications of these findings are discussed in relation to the future of the current DED pandemic in Europe, the decline of the first pandemic, and the difficulty of drawing parallels between different tree–pathogen systems.

Ophiostomatoid fungi associated with pine bark beetles and infested pines in south-eastern Australia, including Graphilbum ipis-grandicollis sp. nov.

“…Fungi within Ophiostomatales and Microascales are best known for their associations with arthropod vectors and include examples of some of the most devastating fungalinsect symbioses known to plant pathologists over the past century (Fisher et al 2012;Wingfield et al 2017b;Brasier and Webber 2019). Notable examples include the Dutch elm disease pathogens, Ophiostoma ulmi and O. novo-ulmi (Santini and Faccoli 2015;Brasier and Webber 2019), the laurel wilt pathogen Raffaelea lauricola (Harrington et al 2008) as well as the numerous pathogens belonging to Ceratocystis which cause tree mortality in natural and agricultural ecosystems (Roux et al 2007;Wingfield et al 2017b;Tsopelas et al 2017). In a recent review on novel associations for members of Ophiostomatales and Microascales, Wingfield et al (2017b) highlight the numerous biological and anthropogenic factors that influence the dispersal of these fungi and their vectors globally; a major feature of the ever-increasing threat these fungi pose to global biosecurity.…”

“…Fungi within Ophios to matales and Microascales are best known for their associations with arthropod vectors and include examples of some of the most devastating fungal-insect symbioses known to plant pathologists over the past century (Fisher et al 2012 ; Wingfield et al 2017b ; Brasier and Webber 2019 ). Notable examples include the Dutch elm disease pathogens, Ophiostoma ulmi and O. novo-ulmi (Santini and Faccoli 2015 ; Brasier and Webber 2019 ), the laurel wilt pathogen Raffaelea lauricola (Harrington et al 2008 ) as well as the numerous pathogens belonging to Ceratocystis which cause tree mortality in natural and agricultural ecosystems (Roux et al 2007 ; Wingfield et al 2017b ; Tsopelas et al 2017 ).…”

Emergence and diversification of a highly invasive chestnut pathogen lineage across southeastern Europe

“…Introgression from closely related species can also reintroduce a missing mating type. O. novo-ulmi acquired the missing mating type from O. ulmi ( Brasier and Webber, 2019 ; Paoletti et al, 2006 ). Although switches in reproductive modes can be a key factor for invasion success ( Philibert et al, 2011 ), mechanisms underlying such switches remain poorly understood ( Billiard et al, 2012 ).…”

Comparing environmental impacts of alien plants, insects and pathogens in protected riparian forests

“…have died (Alford and Backhaus 2005;Brunet et al 2013). Breeding of several resistant clones and reintroduction of resistant native elms mitigated the threat of extinction (Brasier and Webber 2019;Jürisoo et al 2019;Martín et al 2019). Another invasive ascomycete fungus, Hymenoscyphus fraxineus, of the high-ranked alien species, causes ash die-back, a lethal disease of ash trees (Fraxinus spp.)…”