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The North American gall mite Aceria fraxiniflora was first recorded in Europe in southeast Hungary in 2017. Since then, it has shown a remarkably rapid spread on its host, the also North American green ash (Fraxinus pennsylvanica). By the beginning of 2023 it has been recorded in eight Central-Eastern European countries. In 2022 it was recorded on the other North American ash (Fraxinus Americana) in Zagreb (Croatia) and in Szarvas Arboretum (SE Hungary). Possible reasons and outcomes of this spread are discussed., (© 2023. The Author(s).)

Green ash (Fraxinus pennsylvanica) is the most widely distributed ash tree in North America. Once common, it has experienced high mortality from the non-native invasive emerald ash borer (EAB; Agrilus planipennis). A small percentage of native green ash trees that remain healthy in long-infested areas, termed "lingering ash," display partial resistance to the insect, indicating that breeding and propagating populations with higher resistance to EAB may be possible. To assist in ash breeding, ecology and evolution studies, we report the first chromosome-level assembly from the genus Fraxinus for F. pennsylvanica with over 99% of bases anchored to 23 haploid chromosomes, spanning 757 Mb in total, composed of 49.43% repetitive DNA, and containing 35,470 high-confidence gene models assigned to 22,976 Asterid orthogroups. We also present results of range-wide genetic variation studies, the identification of candidate genes for important traits including potential EAB-resistance genes, and an investigation of comparative genome organization among Asterids based on this reference genome platform. Residual duplicated regions within the genome probably resulting from a recent whole genome duplication event in Oleaceae were visualized in relation to wild olive (Olea europaea var. sylvestris). We used our F. pennsylvanica chromosome assembly to construct reference-guided assemblies of 27 previously sequenced Fraxinus taxa, including F. excelsior. Thus, we present a significant step forward in genomic resources for research and protection of Fraxinus species., (© 2021 The Authors. Molecular Ecology Resources published by John Wiley & Sons Ltd.)

Key Message: The genetic linkage map for green ash (Fraxinus pennsylvanica) contains 1201 DNA markers in 23 linkage groups spanning 2008.87cM. The green ash map shows stronger synteny with coffee than tomato. Green ash (Fraxinus pennsylvanica) is an outcrossing, diploid (2n = 46) hardwood tree species, native to North America. Native ash species in North America are being threatened by the rapid spread of the emerald ash borer (EAB, Agrilus planipennis), an invasive pest from Asia. Green ash, the most widely distributed ash species, is severely affected by EAB infestation, yet few genomic resources for genetic studies and improvement of green ash are available. In this study, a total of 5712 high quality single nucleotide polymorphisms (SNPs) were discovered using a minimum allele frequency of 1% across the entire genome through genotyping-by-sequencing. We also screened hundreds of genomic- and EST-based microsatellite markers (SSRs) from previous de novo assemblies (Staton et al., PLoS ONE 10:e0145031, 2015; Lane et al., BMC Genom 17:702, 2016). A first genetic linkage map of green ash was constructed from 90 individuals in a full-sib family, combining 2719 SNP and 84 SSR segregating markers among the parental maps. The consensus SNP and SSR map contains a total of 1201 markers in 23 linkage groups spanning 2008.87 cM, at an average inter-marker distance of 1.67 cM with a minimum logarithm of odds of 6 and maximum recombination fraction of 0.40. Comparisons of the organization the green ash map with the genomes of asterid species coffee and tomato, and genomes of the rosid species poplar and peach, showed areas of conserved gene order, with overall synteny strongest with coffee.

The 2016 discovery of Emerald Ash Borer ( Agrilus planipennis; EAB ) in Nebraska warranted an assessment of the physical conditions of ash trees ( Fraxinus spp. ) across the state. Here we present a dataset of current physical conditions and spatial location of 30 Green Ash ( Fraxinus pennsylvanica ) throughout riparian woodlands along the Platte River in southcentral Nebraska. Ten Green Ash were assessed along transect lines through three riparian woodlands. Physical indicators of EAB infection and morphometric characteristics were recorded at each tree including diameter at breast height (DBH), estimated age, canopy condition rating scale (CCRS), borer holes, woodpecker holes, serpentine gallery, epicormic shoots, basal shoots, and bark splitting to document the health and condition of local Green Ash. We recorded variables of crown class category (CCC), crown ratio, and Green Ash seedling and sapling numbers within 6 m of the measured tree to document current canopy cover and regenerative potential of Green Ash within each woodland. Metric summaries are provided looking at each woodland individually and at the woodlands combined.

Monitoring the health and condition of wetlands using biological assessments can serve as an effective tool for environmental managers to better evaluate and monitor the status and trends of their wetland ecosystems. Woody species can be used as conspicuous biological assessment tools due to their direct response to environmental change, such as hydrologic alteration. The purpose of this study is to use field-measured morphological measurement indices to develop and optimize tree growth parameters and growth curves using multi-model combination approach to improve tree biomass estimations. Field morphological investigations were conducted for two common wetland tree species in Texas. A range of morphological characteristics including leaf area index, height, and biomass was measured for black willow (Salix nigra Marsh) and green ash (Fraxinus pennsylvanica) sampled from 15 sites in a wetland near Cameron, Texas. The measured morphological parameters were used to optimize tree growth and development with the ALMANAC model. The developed tree growth parameters and growth curves were subsequently used in the APEX model to simulate tree biomass at the catchment scale. Both models accurately simulated biomass of trees growing in the wetland. This accurate biomass prediction will be useful to advance science to better monitor and assess wetland health on a large scale (e.g. national or global).

Emerald ash borer (Agrilus planipennis Fairmaire) is an invasive primary pest of North American ash (Fraxinus spp.) trees. Blue ash (F. quadrangulata) is less susceptible to emerald ash borer infestations in the forest than other species of North American ash. Whereas other studies have examined adult host preferences, we compared the capacity of emerald ash borer larvae reared from emerald ash borer eggs in the field and in the laboratory to survive and grow in blue ash and the more susceptible green ash (F. pennsylvanica). Emerald ash borer larval survivorship was the same on both ash species. Mortality due to wound periderm formation was only observed in living field grown trees, but was low (<4%) in both green and blue ash. No difference in larval mortality in the absence of natural enemies suggests that both green and blue ash can support the development of emerald ash borer. Larvae reared from eggs on blue ash were smaller than on green ash growing in the field and also in bolts that were infested under laboratory conditions. In a laboratory study, parasitism rates of confined Tetrastichus planipennisi were similar on emerald ash borer larvae reared in blue and green ash bolts, as were fitness measures of the parasitoid including brood size, sex ratio, and adult female size. Thus, we postulate that emerald ash borer larvae infesting blue ash could support populations of T. planipennisi and serve as a potential reservoir for this introduced natural enemy after most of the other native ash trees have been killed., (© The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Protection of green ash trees (Fraxinus pennsylvanica Marshall) from the emerald ash borer (EAB), Agrilus planipennis Fairmaire, by soil applications of neonicotinoids (imidacloprid, clothianidin, and dinotefuran) was tested at five locations between 2005 and 2013. Application rate and spring versus fall application dates were evaluated in tests with neighborhood street trees and in one plantation of 65 ash trees. Insecticide treatments of ash trees at all five sites were initiated as the leading edge of the EAB invasion began to kill the first ash trees at each location. Trees were treated and evaluated at each site for 4 to 7 yr. Spring applications of imidacloprid were more efficacious than fall applications. Application rates of 0.8 g a.i./cm dbh or greater per year gave a higher level of protection and were more consistent than rates of 0.56 g a.i./cm dbh per year or less. The number of years between the first observation of canopy loss due to EAB and death of most of the control trees varied from three to seven years among test sites, depending on how many non-treated ash trees were nearby., (© The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)