Elms (Ulmus spp.) were once dominant trees in mixed broadleaf forests of many European territories, mainly distributed near rivers and streams or on floodplains. Since ancient times they have provided important services to humans, and several selected genotypes have been massively propagated and planted. Today elm populations are severely degraded due to the negative impact of human-induced changes in riparian ecosystems and the emergence of the highly aggressive Dutch elm disease pathogens. Despite the death of most large elm specimens, there is no evidence of genetic diversity loss in elm populations, probably due to their ability to resprout after disease. The recovery of elm populations from the remaining diversity should build from genomic tools that facilitate achievement of resistant elm clones. Research works to date have discerned the genetic diversity of elms and are well on the way to deciphering the genetic clues of elm resistance and pathogen virulence, key findings for addressing recovery of elm populations. Several tolerant clones suitable for use in urban and landscape planting have been obtained through traditional species hybridization with Asian elms, and various native clones have been selected and used in pilot forest restoration projects. Successful reintroduction of elms should also rely on a deeper understanding of elm ecology, in particular their resilience to abiotic and biotic disturbances. However, all these efforts would be in vain without the final acceptance of elm reintroduction by the social actors involved, making it necessary to evaluate and publicize the ecosystem services elms can provide for today’s society.

/pdf/breeding-and-scientific-advances-in-the-fight-against-dutch-3ul3qirequ.pdf

Breeding and scientific advances in the fight against Dutch elm disease: Will they allow the use of elms in forest restoration?

Tree species diversity is important to maintain saproxylic beetle diversity in managed forests. Yet, knowledge about the conservational importance of single tree species and implications for forest management and conservation practices are lacking.
We exposed freshly cut branch‐bundles of 42 tree species, representing tree species native and non‐native to Europe, under sun‐exposed and shaded conditions for 1 year. Afterwards, communities of saproxylic beetles were reared ex situ for 2 years. We tested for the impact of tree species and sun exposure on alpha‐, beta‐, and gamma‐diversity as well as composition of saproxylic beetle communities. Furthermore, the number of colonised tree species by each saproxylic beetle species was determined.
Tree species had a lower impact on saproxylic beetle communities compared to sun exposure. The diversity of saproxylic beetles varied strongly among tree species, with highest alpha‐ and gamma‐diversity found in Quercus petraea. Red‐listed saproxylic beetle species occurred ubiquitously among tree species. We found distinct differences in the community composition of broadleaved and coniferous tree species, native and non‐native tree species as well as sun‐exposed and shaded deadwood.
Our study enhances the understanding of the importance of previously understudied and non‐native tree species for the diversity of saproxylic beetles. To improve conservation practices for saproxylic beetles and especially red‐listed species, we suggest a stronger incorporation of tree species diversity and sun exposure of into forest management strategies, including the enrichment of deadwood from native and with a specific focus on locally rare or silviculturally less important tree species.

/pdf/diversity-and-conservation-of-saproxylic-beetles-in-42-47gksv68ar.pdf

Diversity and conservation of saproxylic beetles in 42 European tree species: an experimental approach using early successional stages of branches

Dutch elm disease (DED) is a vascular wilt disease caused by the pathogens Ophiostoma ulmi and Ophiostoma novo-ulmi with multiple ecological phases including pathogenic (xylem), saprotrophic (bark) and vector (beetle flight and beetle feeding wound) phases. Due to the two DED pandemics during the twentieth century the use of elms in landscape and forest restoration has declined significantly. However new initiatives for elm breeding and restoration are now underway in Europe and North America. Here we discuss complexities in the DED ‘system’ that can lead to unintended consequences during elm breeding and some of the wider options for obtaining durability or ‘field resistance’ in released material, including (1) the phenotypic plasticity of disease levels in resistant cultivars infected by O. novo-ulmi; (2) shortcomings in test methods when selecting for resistance; (3) the implications of rapid evolutionary changes in current O. novo-ulmi populations for the choice of pathogen inoculum when screening; (4) the possibility of using active resistance to the pathogen in the beetle feeding wound, and low attractiveness of elm cultivars to feeding beetles, in addition to resistance in the xylem; (5) the risk that genes from susceptible and exotic elms be introgressed into resistant cultivars; (6) risks posed by unintentional changes in the host microbiome; and (7) the biosecurity risks posed by resistant elm deployment. In addition, attention needs to be paid to the disease pressures within which resistant elms will be released. In the future, biotechnology may further enhance our understanding of the various resistance processes in elms and our potential to deploy trees with highly durable resistance in elm restoration. Hopefully the different elm resistance processes will prove to be largely under durable, additive, multigenic control. Elm breeding programmes cannot afford to get into the host–pathogen arms races that characterise some agricultural host–pathogen systems.

/pdf/complexities-underlying-the-breeding-and-deployment-of-dutch-1cnxxdv3o6.pdf

Complexities underlying the breeding and deployment of Dutch elm disease resistant elms

European white elm (Ulmus laevis Pallas) populations are scarce, small and fragmented in the Iberian Peninsula. Due to these characteristics the indigenous status of the species in the region has been questioned, whilst the species’ role in Iberian riparian forest ecology has been neglected. Herein we review past studies regarding this species’ distribution and ecology in the Iberian Peninsula, with special emphasis on the establishment of conservation priorities. We first present a collection of palaeogeographic, historic and genetic data suggesting that the Iberian Peninsula was a glacial refuge for U. laevis. Secondly, we analyse U. laevis distribution in relation to soil physico- chemical properties and water availability in Spain. Following this, we focus on the reproductive biology of the species, and investigate the effect of masting and empty seed production on predation and regeneration establishment. Finally, based on this knowledge, we propose conservation policies for U. laevis in the Iberian Peninsula.

https://iforest.sisef.org/pdf/?id=ifor1201-008

Ulmus laevis in the Iberian Peninsula: a review of its ecology and conservation

Potential Dutch elm disease vector beetle species were caught with pheromone bottle traps and handpicked in 2019: in total, seven species and 261 specimens were collected. The most common was Scolytus triarmatus, but by percent, the incidence of Ophiostoma novo-ulmi was highest in Scolytus scolytus, followed by Xyleborinus saxesenii and S. triarmatus. We analysed the beetles' DNA using PacBio sequencing to determine vector beetles of Ophiostoma novo-ulmi. Ophiostoma novo-ulmi was found on six out of seven analysed beetle species: Scolytus scolytus, S. triarmatus, S. multistriatus, S. laevis, Xyleborinus saxesenii and Xyleborus dispar. The last two beetles were detected as vectors for Ophiostoma novo-ulmi for the first time. Previous knowledge on the spread of beetles is discussed.

Vectors of Dutch Elm Disease in Northern Europe.

Se estudio la respuesta de alimentacion de S. scolytus a extractos del floema de ramillas de olmo en bioensayos de laboratorio. Se muestrearon en primavera ramillas de olmo de uno a cuatro anos de edad y su floema fue extraido independientemente con metanol o con una mezcla de eter de petroleo y eter dietilico (1:1). Los extractos del floema se evaluaron en un bioensayo de doble eleccion consistente en dos discos de poliuretano dispuestos en una placa Petri de 10 cm de diametro. Se aplicaron los extractos a los discos y se midio la superficie de disco comida por diez adultos recien emergidos de S. scolytus durante 24 h. Se ensayaron diez U. minor, dos U. laevis, seis U. glabra, tres hibridos holandeses (europeo x asiatico) y un U. pumila en diversas comparaciones. Los discos con extractos de ambos U. laevis fueron significativamente menos comidos que aquellos con los de U. pumila o de U. minor. Igualmente, los extractos de todos los U. glabra recibieron menor alimentacion que aquellos de U. minor. Por el contrario, S. scolytus no mostro preferencias entre los extractos de U. minor y de U. pumila, e igualmente, entre los de U. minor y los de hibridos holandeses. Nuevamente, los escolitidos prefirieron alimentarse menos de los extractos de U. laevis que de los hibridos holandeses. Se encontraron diferencias intraespecificas significativas en U. minor. Uno de los clones de U. minor resulto menos preferido cuando se le comparo con otros cuatro arboles. Los extractos de un U. minor moribundo recibieron mayor alimentacion que los de un arbol sano. Se realizaron comparaciones entre los extractos del floema de ramillas de 2 a 4 anos de edad y de ramillas del ano en curso de un mismo arbol. En uno de cuatro U. minor ensayados se observo una preferencia significativa por los extractos de las ramillas mas viejas.

Feeding responses by Scolytus scolytus to twig bark extracts from elms

In order to better understand the chemical factors involved in the host feeding selectivity by Scolytus, components were extracted from elm bark and studied. Sampled trees were located in an elm stand that survived the Dutch twig elm disease pandemia, and from elm clones from throughout the Iberian Peninsula. The main samples studied were from Ulmus minor, and the other samples from U. pumila, U. laevis and several hybrids. The main compounds in the extracts obtained from current-year twigs were aliphatic hydrocarbons (particularly heptacosane and nonacosane) and from 2- to 4-year-old stems were triterpenes. Three of the triterpenes were identified for the first time in Ulmus (lupenol, alnulin, and ilexol) and two in Ulmaceae (moretenol and betulin). Differences occurred in the compounds isolated from U. minor from the two locations, and between species.

Elm bark components and their potential influence on bark beetle feeding

PAJARES J. A., J. J. DIEZ, S. GARCIA, C. GARCIA-VALLEJO, D. MARTIN. 2004. Elm bark beetle preferences among extracts from different elm species. Bol. San. Veg. Plagas, 30: 229-238 Feeding preferences by the elm bark beetle Scolytus scolytus among bark extracts from different elm species were studied. Bark extracts from twigs sampled in spring were obtained using methanol or a mixture of diethyl ether : petroleum ether (1:1) as solvents. Feeding responses by freshly emerged S. scolytus adults were tested in a two-choice bioassay, comparing the areas eaten from discs treated with extracts from different species. Four U. minor, six U. glabra, four I7. laevis, one U. pumila and two Dutch hybrid trees were assayed in several comparisons. Discs treated with extracts from t/. glabra resulted significantly less fed than those with U. minor extracts. Similarly, extracts from U. laevis were less preferred than those from the field elm. It seemed that U. glabra was less accepted than U. laevis when these two species were compared. No significant differences were observed in feeding responses between U. minor and U. pumila or Dutch hybrids, but these two later were preferred to U. laevis by the beetles. Possible implications of these results in the screening of field elms unsuitable to the elm bark beetle vectors of Dutch elm disease are discussed.

Preferencias de alimentación de los escolítidos del olmo frente a extractos de distintas especies de olmos

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Feeding responses by Scolytus scolytus to twig bark extracts from elms

Elm bark components and their potential influence on bark beetle feeding

Preferencias de alimentación de los escolítidos del olmo frente a extractos de distintas especies de olmos