Diversity, migration routes, and worldwide population genetic structure of Lecanosticta acicola, the causal agent of brown spot needle blight

Abstract

Lecanosticta acicola is a pine needle pathogen causing brown spot needle blight that results in premature needle shedding with considerable damage described in North America, Europe, and Asia. Microsatellite and mating type markers were used to study the population genetics, migration history, and reproduction mode of the pathogen,

The Increasing Threat to European Forests from the Invasive Foliar Pine Pathogen, Lecanosticta Acicola

“…Population studies illustrate the wide dissemination of the northern and southern lineages from North America into Europe (Janoušek et al, 2014(Janoušek et al, , 2016Sadiković et al, 2019a;Laas et al, 2022) and Asia (Huang et al, 1995;Laas et al, 2022). Microsatellite and TEF1 markers demonstrate the southern USA lineage is present in southwest France, Portugal and Spain, close to the first finding of the pathogen in Europe (Janoušek et al, 2016;Laas et al, 2022). It is also present in Colombia in South America, where it may have been introduced on exotic Pinus seedlings used for timber plantations (Janoušek et al, 2016).…”

“…Lecanosticta acicola is the most widely studied species to date, and three lineages have been described based on the Translation Elongation 1-α gene region (TEF1), microsatellite and RAPD markers, together with observations of cultural morphology (Huang et al, 1995;Janoušek et al, 2016;van der Nest et al, 2019b). The northern lineage occurs in northern USA, Canada and Europe, the southern lineage is dominant in southern USA and has spread to Europe, and a third lineage occurs in Mexico and to date, appears not to have spread from this region (van der Nest et al, 2019b;Laas et al, 2022). The third lineage is the most diverse, probably constituting one or more distinct cryptic species, and Mexico may be the centre of origin of L. acicola (Huang et al, 1995;Janoušek et al, 2016;van der Nest et al, 2019b).…”

“…The Croatian population has not spread north to neighbouring Slovenia (Sadiković et al, 2019a), but the population appears to share common origin in North America with the populations in western Asia (Turkey, Georgia, South Russia) (Laas et al, 2022). Northern European populations originate from North America via the Central European population (Laas et al, 2022). These recent analyses defined northern and southern lineages of L. acicola using molecular methods, but differences in cultural morphology and behaviour in vitro, and pathogenicity in planta between isolates from southern and northern states of the USA had been apparent from the 1970s.…”

“…Both southern and northern lineages co-occur in France, and both mating types are found in Estonia, Lithuania, Poland, Germany, France, Ireland, Switzerland, Austria, Slovenia and Spain (Laas et al, 2022). Molecular analysis also suggested ongoing sexual recombination in Europe (Janoušek et al, 2016;Laas et al, 2022), even before it was confirmed in 2020 with the discovery of the sexual stage of L. acicola on P. radiata D. Don in Spain (Mesanza et al, 2021a). Like Dothistroma species, the sexual ascospores have far greater potential for long distance winddriven dissemination than the splash-dispersed asexual conidia.…”

“…Since the 1990s, Lecanosticta acicola (Thümen) Sydow, a foliar pathogen found predominantly on Pinus spp., has been expanding its range globally and increasing in impact. In the past ten years the area of forest affected by this pathogen within Europe and neighbouring countries has increased markedly (Adamson et al, 2018;Mullett et al, 2018;van der Nest et al, 2019a;Oskay et al, 2020;Laas et al, 2022). There are concerns that the pathogen could become severely damaging, both economically and environmentally, following a similar pattern to Dothistroma spp.…”