Elm Clones Research Articles

Monitoring of the incidence of Dutch Elm Disease and mortality in experimental plantations of French Ulmus minor clones

The results of 16 experimental plantations of Ulmus minor clones of the French national collection are presented as a complement to a previous work (Collin et al. 2020) on the outcome of the French Programme for the Conservation of Native Elm Genetic Resources. A total of 710 elms from 38 clones were planted in three different regions of France using two types of experimental designs and exposed to natural infection by Dutch Elm Disease (DED). DED infection and subsequent mortality were monitored in rectangular monospecific plantations (“plot-tests”), comprising at least 100 elms (10 clones). Linear plantations of 15 to 36 elms intermixed with other trees and shrubs (“hedge-tests”) investigated the feasibility of using native field elm clones in hedge reconstruction projects. After at least 9 (up to 17) years of experimentation, overall DED infection frequency was 33%, with scores above 63% in the oldest plantation and in two fast-growing tests. The overall mortality in the 232 diseased trees was 21%, reaching 29% in the oldest plantation and 64% in a hedge-test on high quality soil, suggesting a possible effect of the very fast growth of the trees. A few clones showed an interesting lower infection frequency or some ability to recover, whereas some others were found quickly infected in several tests and could serve in future experiments on clone attractiveness for DED vectors. Practical conclusions for genetic resources conservation consist of recommendations for the establishment of conservation plantations using regional clones.

Obtaining Fermentable Sugars from a Highly Productive Elm Clone Using Different Pretreatments

The interest of supplying lignocellulosic materials for producing fermentable sugars has recently emerged in order to diminish the negative environmental effects of fossil fuels. In this study, the Ulmus minor clone Ademuz, characterized for its tolerance to Dutch elm disease and its rapid growth, was evaluated as a source of fermentable sugars. For that, different pretreatments, comprising autohydrolysis, dilute acid hydrolysis, acid catalyzed organosolv, and alkaline extraction, were evaluated at two levels of severity (pretreatment temperatures at 160 °C and 180 °C, except for alkaline extraction at 80 °C and 160 °C); and the resulting pretreated materials were enzymatically hydrolyzed for fermentable sugars production. The major extraction of lignin and hemicellulose was achieved during organosolv (48.9%, lignin; 77.9%, hemicellulose) and acid hydrolysis (39.2%, lignin; 95.0%, hemicellulose) at 180 °C, resulting in the major enzymatic digestibility (67.7%, organosolv; 53.5% acid hydrolysis). Contrarily, under the most favorable conditions for autohydrolysis (180 °C) and alkaline extraction (160 °C), lower extraction of lignin and hemicellulose was produced (4.8%, lignin; 67.2%, hemicellulose, autohydrolysis; 22.6%, lignin; 33.1%, hemicellulose, alkaline extraction), leading to lower enzymatic digestibility (32.1%, autohydrolysis; 39.2%, alkaline extraction). Taking into account the sugars produced during enzymatic hydrolysis of pretreated materials and the solubilized sugars from pretreatment liquors, the highest sugars (glucose and xylose) yield production (28.1%) per gram of biomass from U. minor clone Ademuz was achieved with acid catalyzed organosolv at 180 °C.

Properties versus application requirements of solubilized lignins from an elm clone during different pre-treatments

Kraft pulping, organosolv process and acid hydrolysis were applied on an elm clone. The solubilized lignins were recovered and analyzed. Kraft pulping and acid hydrolysis led to lignins with higher phenolic OH content as result of extensive cleavage of β-O-4′ linkages, as revealed by 13C solid state and 13C−1H heteronuclear single quantum coherence nuclear magnetic resonance. This depolymerization also yielded lower molecular weight lignins inferred by size exclusion chromatography. Contrarily, organosolv process gave rise to a lignin with a more preserved structure, maintaining a large number of β-O-4′ linkages. Consequently, organosolv lignin presented lower phenolic OH content and higher molecular weight. Moreover, the high content of the labile native β-O-4′ linkages in organosolv lignin resulted in a lower thermostability as compared to the kraft and acid lignins. On the other hand, the solubilized lignins from kraft and acid processes displayed an enrichment of S-units, whereas lignin from organosolv process was slightly enriched in G-units, containing all of them different native as well as pre-treatment derived units. These results could help to increase the inventory of lignin sources available for future lignin-based products, for which knowledge of the lignin properties versus application requirements is crucial.

Biorefinery of Lignocellulosic Biomass from an Elm Clone: Production of Fermentable Sugars and Lignin‐Derived Biochar for Energy and Environmental Applications

AbstractValorization of lignocellulosic feedstock from a Dutch elm disease tolerant Ulmus minor clone was studied as a new biomass resource. Herein, fermentable sugars and activated carbons from the side‐stream lignins were produced. For the sugar extraction organosolv and acid hydrolysis pretreatments prior to enzymatic hydrolysis were compared for the first time for this clone prior to enzymatic hydrolysis; organosolv was more efficient for delignification (49 %), while acid hydrolysis was more efficient at eliminating hemicelluloses (95 %). A high final glucose concentration of 22–23.5 g L−1 was obtained after enzymatic hydrolysis suggesting that this clone can be considered a potential source for glucose‐based biofuel production. The side‐stream lignins were converted to microporous biochars of high surface area (1220 m2 g−1) and micropore volume (0.42 cm3 g−1). These biochars exhibited excellent properties as electrodes in supercapacitors with a specific capacitance of 118 F g−1 and a high energy density of 14 Wh kg−1 at 7000 W kg−1, while they were also efficient adsorbents in water remediation of model contaminants.

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

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.

Elm clone identification and the conundrum of the slow spread of Dutch Elm Disease on the Isle of Man

This study was undertaken as part of a review of Ulmus L. for the forthcoming Flora of the Isle of Man. We have adopted molecular and morphological methods to reassess the identity of Ulmus on the Isle of Man and to explore the possibility that past records of English Elm, a single genotype cultivar called U. minor ‘Atinia’, were misidentifications. First, we utilised seven DNA microsatellite markers to test clone identity in a collection of 23 elms from across the Isle of Man. Sixteen samples were matched to a reference sample of Dutch Elm, U. × hollandica ‘Major’, and one sample was matched to a reference sample of English Elm. In parallel, we appraised a method employed to identify English Elm using a leaf shape metric, and found that leaf width divided by length values > 0.69 are indicative of this clone. Both molecular and morphological results in this study highlight that Dutch Elm has been misidentified as English Elm in the past, and that English Elm may in fact be a rare occurrence on the Island....

Genotypic variation in salt tolerance of Ulmus pumila plants obtained by shoot micropropagation

Siberian elm (Ulmus pumila L.) is a tree native to Asia and is widely cultivated in the other parts of the world due to its resistance to drought, temperature extremes, and salinity. In this study, we obtained nine clones of Siberian elm by in vitro shoot propagation of trees varying in growth, morphological characteristics, and salt tolerance in the field to examine traits linked to salt tolerance. The plantlets were subjected for 2 weeks to 0, 0.3, 0.5, 0.7, 0.8, and 0.9 % (w/v) NaCl and to mixture of salts representative of sea water (NaCl, CaCl, K2SO4, MgSO4, and NaHCO3) to examine the effects on growth, tissue concentrations of major osmolytes, proteins, and chlorophyll, as well as activities of the antioxidant enzymes. While higher salt treatment (both NaCl and mixed salt from 0.7 to 0.9 %) concentrations decreased growth rates in all of the studied clones, 0.3 % NaCl treatment resulted in greater shoot growth parameters of the treated plantlets compared with untreated control. In mixed salt treatments, growth parameters, including shoot relative elongation rate (SRGR), branching rate (BR), and length of new shoots (SL), decreased in the examined clones with the exception of clones 51, 105, and 65225, respectively, in which treatment concentrations as high as 0.3 % NaCl had no effect on shoot length. In both NaCl and mixed salt treatments, the antioxidant enzymes (SOD, POD, and CAT) in most of these clones increased at 0.3–0.7 % (or 0.8 %) treatment concentrations and decreased at 0.8–0.9 % salt treatments; malondialdehyde (MDA) content increased with the growing of the salt concentrations; soluble protein and chlorophyll content show a decreased tendency with the raising of the salt concentrations; in most elm clones, sugar and free proline (Pro) content accumulate at 0.3–0.8 % salt treatment decreased in 0.9 % salt treatment. In mixed salt treatment, the superoxide (SOD) shows more activities in most of the clones compared with NaCl treatment. In most clones, chlorophyll concentrations were greater in NaCl compared with mixed salt treatment in 0.8–0.9 % concentrations; the decrease of soluble protein concentrations in the mixed salt was lower compared with NaCl treatment. Using the membership function and cluster analyses, the clones were classified into four distinctly different groups in terms of their salt tolerance. The differences in responses of the examined physiological parameters to salt treatments between these clones with different salt-tolerance capacities point to the importance of osmoregulation and maintenance of antioxidant enzyme activities in salt tolerance of Siberian elm.

Physiological and biochemical differences amongUlmus minorgenotypes showing a gradient of resistance toDutch elm disease

SummaryDutch elm disease (DED) spread across Europe and North America in the 20th century killing most natural elm populations. Today, breeding programmes aim at identifying, propagating and studying elm clones resistant toDED. Here, we have compared the physiology and biochemistry of six genotypes ofUlmus minorof variableDEDresistance. Leaf gas exchange, water potential, stem hydraulic conductivity and biochemical status were studied in 5‐year‐old trees ofAB‐AM2.4, M‐DV2.3, M‐DV2 × M‐CC1.5 and M‐DV1 and 6‐year‐old trees ofVA‐AP38 andBU‐FL7 before and after inoculation withOphiostoma novo‐ulmi. Leaf water potential and net photosynthesis rates declined, while the percentage loss of hydraulic conductivity (PLC) increased after the inoculation in susceptible trees. By the 21st day, leaf predawn and midday water potential, stomatal conductance to water vapour and net photosynthesis rates were lower, andPLCwas higher in trees of susceptible (S) genotypes inoculated with the pathogen than in control trees inoculated with water, whereas no significant treatment effect was observed on these variables in the resistant (R) genotypes. Fourier transform infrared spectroscopy analyses revealed a different biochemical profile for branches of R and S clones. R clones showed higher absorption peaks that could be assigned to phenolic compounds, saturated hydrocarbons, cellulose and hemicellulose than S clones. The differences were more marked at the end of the experiment than at the beginning, suggesting that R and S clones responded differently to the inevitable wounding from inoculation and repeated sampling over the experimental course. We hypothesize that a weak activation of the defence system in response to experimental wounding can contribute to the susceptibility of some genotypes toO. novo‐ulmi. In turn, the decline in shoot hydraulic conductivity and leaf carbon uptake caused by the infection further exacerbates tree susceptibility to the fungus.

Dutch elm disease and elm bark beetles: a century of association

Bark beetles of the genus Scolytus Geoffroy are the main vectors of the fungus Ophiostoma ulmi s.l., which causes the Dutch elm disease. The large and small elm bark beetles - S. scolytus (F.) and S. multistriatus (Marsham), respectively - are the most common and important species spreading the pathogen worldwide. The success of the pathogen-insect interactions is mainly due to the characteristic reproductive behavior of the elm bark beetles, which, however, largely depends on the occurrence of infected trees. During feeding activity on elm twigs, callow adults carrying pathogen conidia on their bodies contaminate healthy trees and facilitate pathogen development and movement within the wood vessels. Infected trees become then suitable for insect breeding in the stem bark. This well-known mutualistic association has devastating consequences for elm survival. Although much is known about insect-pathogen interactions and transmission mechanisms, many topics still deserve additional attention, as, for example, beetle systematic based on new molecular tools and morphological characters; selection of European elm clones based on disease avoidance; consequences of global warming on life-history of the three organisms (fungus-insect-tree) involved in the pathosystem; new problems resulting from the rapid increase of international trade among continents, leading to the accidental introduction of new vector species or new pathogen species or races, or to the introduction of new highly susceptible elm species in gardens and public parks. A holistic approach to tackle the problem is highly recommended, taking into account how these organisms interact with each other and the environment, and how their interactions could be modified in order to face one of the most destructive diseases ever known in plant pathology.

Implementing the dynamic conservation of elm genetic resources in Europe: case studies and perspectives

Abstract: Many European countries have undertaken the static preservation of native elm genotypes in clone collections maintained ex situ. Less development has been devoted to the dynamic conservation of elm populations in situ. Case studies of elm conservation in France are given here as an illustration of methods employed at country level. We also briefly review the process used by the “European Forest Genetic Resources Programme” (EUFORGEN) to monitor elm dynamic conservation in a pan-European perspective. Dynamic conservation methods were promoted by EUFORGEN through leaflets, strategies, Technical Guidelines and the geo-referenced database EUFGIS on Dynamic Conservation Units (DCUs). Because the network of DCUs needs to be representative of the partitioning of adaptive diversity across the species distribution range, a GIS-aided approach has been developed to position DCUs in environmental zones and identify conservation gaps. The two DCUs of European white elm (Ulmus laevis Pall.) selected in riparian forests of two different climatic zones of France show that management oriented toward habitat protection is compatible with dynamic conservation, and that the species can still be conserved in situ in spite of Dutch Elm Disease (DED). Collaboration with habitat conservationists enabled the monitoring of losses to DED and the assessment of within-population diversity for flowering phenology. Collaboration with forest geneticists revealed that the diversity of the Garonne population was low, but that it contained rare DNA variants and adaptive traits. Since 1987, experimental restoration of countryside hedges has been carried out, using field elm clones (U. minor Mill.) selected from the French national collection and tested for lower susceptibility to the agent of DED in artificial inoculation tests. Such plantations can be viewed as a very dynamic form of conservation if they permit the local gene pool to be reinforced with trees able to reach sexual maturity and exchange pollen with elms in the neighborhood, hence contributing new genotypes that will be submitted to natural selection and provide fuel for ongoing adaptation processes. Initiatives assembling a large consortium of stakeholders, including habitat conservationists and hedge re-constructors, are needed to trigger new conservation projects.

Growth of Ulmus glabra Huds. grafts in the clone archive in Bielsk Forest District

Abstract Vegetative progeny were obtained from 46 elms (Ulmus glabra Huds.) by grafting. These grafted trees were planted in 2009 in a clone archive in forest plot 264j in the Bielsk Forest District. After one year of growth, elm clone survival ranged from 38% to 100% (89% on average). Although all clones were of similar age and were grown under similar conditions, their average height was highly variable and ranged from 99.0 cm (clone no. 9473z) to 186.6 cm (clone no. 9645z), while average root collar diameter ranged from 8.4 mm (clone no. 9473z) to 18.0 mm (clone no. 9645z). There were large differences crown architectural among the different clones, and variation in average shape of the crown was high (from 2.6 in clone no. 9655 to 3.8 in clone no. 9446z). Index breeding values determined on the standardized data for height, root collar diameter, crown shape and survival, ranged from -0.71 (clone no. 9473z) to 0.61 (clone no. 9645z). Clones from Czerwony Dwór reached a better breeding value (0.17) than clones from Gołdap (-0.0266), and variation in their average breeding values was high (0.197).

Genotype × environment interaction and growth stability of several elm clones resistant to Dutch elm disease

Conventionally hybrid elm clones obtained within breeding programs for Dutch elm disease (DED) resistance were selected to meet requirements for use as ornamentals. However, it has been long and commonly observed that these clones may show hybrid vigour and enhanced growth. Nowadays DED resistant hybrid elm clones, which have been released to the market or are under evaluation for an upcoming release, are numerous enough to be considered for timber production or short rotation coppice (SRC). But experimental testing of the growth performances of these clones in different environments is still lacking. In this paper, growth and stability of performance of 24 DED resistant hybrid elm clones planted at three experimental sites with contrasting environmental conditions in Italy were studied. Height and diameter were measured yearly from 2001 to 2009, and the mean yearly increments after plant establishment were calculated. The study revealed a general good growth performance of the majority of the clones with mean height increments above 1 m/year, and an excellent growth performance of some genotypes. Analysis of variance showed significant effects of clone, site and clone × site interaction, for both height and diameter increments. Stability analysis of diameter and height increments was performed by using two parametric (CV% and W 2) and two non-parametric (Hühn's S i (1) and S i (2)) indexes. According to all indexes, two clones showed superior and stable growth. These clones may be suitable for planting in a range of environments. In addition, several other clones had high growth in general or at a particular site. The results support our belief that these elm clones could be successfully used for timber and biomass production, and provide new knowledge for an informed choice of the most suitable genotypes.

Bud dormancy release in elm (Ulmus spp.) clones--a case study of photoperiod and temperature responses

Dormancy release as influenced by duration of outdoor winter chilling in Florence (Italy) was studied under different photoperiodic and temperature treatments in collected twigs of two European (Ulmus glabra Huds. and Ulmus minor Mill.) and four Asian (Ulmus pumila L., Ulmus parvifolia Jacq., Ulmus macrocarpa Hance and Ulmus villosa Brandis) elm clones. Photoperiod had no effect on dormancy release, and there was no evidence that photoperiod affected bud burst during quiescence in the studied elm clones. Thermal time (day degrees >0 degrees C) to bud burst decreased in all the clones with increasing outdoor chilling. Although all the clones exhibited a rather weak dormancy, they significantly differed from each other. Dormancy was released earlier in the Asian than in the European clones, and the clones could be ranked from the U. pumila clone (very weak and short dormancy) to the U. minor clone (relatively stronger and longer dormancy), the other clones being intermediate. In all the clones except U. minor, the observed decrement in thermal time to bud burst was efficiently explained as an inverse exponential function of the number of chill days < or =5 degrees C received outdoor in autumn and winter. Endodormancy, as measured by the single-node cuttings test, was weak and short in all the clones. The latter result suggests that correlative inhibitions were largely responsible for preventing bud burst during winter in these elm clones.

Susceptibility of native French elm clones to Ophiostoma novo-ulmi

Plus de 200 clones d'ormes indigenes en Europe (U. minor, U. glabra et leurs hybrides et U. laevis) ont ete inocules avec Ophiostoma novo-ulmi en comparaison avec quelques cultivars sur deux sites et au cours de six series d'inoculations. Le pourcentage de fletrissement ou de defeuillaison a ete estime l'annee de l'inoculation, et la guerison ou la mortalite ulterieures ont aussi ete notees. Des comparaisons multiples indiquent que les resultats sont reproductibles. L'effet espece est generalement significatif, U. glabra etant l'espece indigene la plus sensible. L'effet clone est toujours tres significatif et une large gamme de comportement est mise en evidence, notamment chez U. minor. U. laevis revele des clones a forte mortalite alors que d'autres presentent de bonnes facultes de recuperation. Du fait de l'effet clone, il est possible au sein de chaque espece de distinguer des clones de bon comportement. Celui-ci se traduit notamment par des guerisons completes en deuxieme annee apres l'inoculation. La frequence de ces clones ne semble pas liee a l'espece ni a l'origine geographique. Ces clones indigenes n'offrent cependant pas le niveau de resistance des meilleurs cultivars ('Sapporo Autumn Gold'® et 'LUTECE® Nanguen') et de ce fait leur culture en plantation monospecifique ou monoclonale ne peut etre recommandee. Ils pourraient toutefois etre utilises avec prudence dans des plantations multispecifiques, notamment pour la reconstitution de haies, voire integres dans un programme d'amelioration.

Influence of Plant Age on Symptom Development in Ulmus minor Following Inoculation by Ophiostoma novo-ulmi.

In American and European breeding programs, numerous elm trees from many species (Ulmus spp.) and hybrids have been inoculated annually with the fungus Ophiostoma novo-ulmi (the Dutch elm disease pathogen) in screening tests for resistance. Because trees were inoculated at different ages, it appeared necessary to study the influence of host age on the symptoms shown. Four Ulmus minor trees and one U. minor × U. pumila tree were cloned annually from 1994 to 1999. The replicates obtained (usually n = 6) were inoculated on 17 May 2000 with an O. novoulmi strain. At the end of the season, 2-year-old U. minor trees showed average wilting of 8 ± 3% (ES), significantly less than that of 3-year-old trees (34 ± 5%) (P ≤ 0.01). Elms that were 4, 5, 6, and 7 years old showed wilting values of around 50%. A positive relationship between the symptoms shown and the diameter of the elm xylem vessels was observed, and the implications for elm resistance and breeding are discussed. Breeders and pathologists should use trees of the same age and physiological phase when determining the relative resistance among elm clones. It is concluded that under the growing conditions of this experiment, the optimal age for U. minor screening was 4-year-old plants.

Variation among Italian and French elm clones in their response to Ophiostoma novo‐ulmi inoculation

SummaryIn 1995 a clone bank of elms from across Italy was created at Antella (Florence, I) under a European Union project. In 1998 an experimental planting of some clones from this source was established in Antella together with material from a similar clone bank in France and two reference clones: Commelin (relatively susceptible) and Lobel (relatively resistant). In May 2001, the elms were inoculated with Ophiostoma novo‐ulmi and disease development was assessed throughout that summer and the next. Significant differences in susceptibility were found between taxonomic groups, with putative natural hybrids between Ulmus minor and Ulmus pumila being the most resistant and Ulmus glabra the most susceptible. Significant differences were also found within U. minor, some clones being as resistant as Lobel. For U. minor, a statistically significant relation was found with latitude, southerly clones showing less disease than more northerly ones. Relationships were also found between disease severity and times to bud burst, these relationships applying both to the different taxonomic groups and within U. minor. Relationships between growth increment and disease severity were inconsistent. These results are discussed in relation to the intrinsic genetically‐controlled differences that exist between elms and to differences in susceptibility that occur as the growing season proceeds and as a consequence of environmental influences.

Screening European Elms for Resistance to Ophiostoma novo-ulmi

Abstract Resistance breeding of the native elms against Dutch elm disease, caused by the fungus Ophiostoma novo-ulmi Brasier, is a major objective in Europe for the conservation of this tree species. More than 2,500 cuttings of 324 elm clones (Ulmus minor Miller, U. glabra Huds., U. laevis Pall., U. pumila L., U. minor x U. glabra, and U. minor x U. pumila) from eight European countries, planted in several randomized two-block designed plots were inoculated with various O. novo-ulmi strains. Crown wilting and dieback were recorded during the first year after inoculation. The wilting of the control trees varied among the plots, making the results difficult to compare, but analysis of variance (ANOVA) within each plot showed significant differences in disease severity among the clones tested, allowing study of the variation of the response among elm taxa. Results showed that 19 European inoculated clones recovered from O. novo-ulmi attack, giving hope for the reestablishment of native elms in countryside hedges and forests. FOR. SCI. 51(2):134–141.

Evaluation of 19 American Elm Clones for Tolerance to Dutch Elm Disease

Abstract Rooted stem cuttings of 19 American elm (Ulmus americana L.) cultivars and selections, and rooted cuttings of two non-American elm selections, U. carpinifolia Gleditsch 51 and 970 (U. glabra Huds. x (U. wallichiana Planch. x U. carpinifolia)), along with a group of American elm seedlings, were planted in a randomized block design. When the trees were nine years old, they were inoculated with a mixed spore suspension of Ophiostoma ulmi (Buisman) C. Nannf. and Ophiostoma novo-ulmi Brasier, the causal fungi for Dutch elm disease (DED). Analyses of variance showed highly significant variation among clones in foliar symptoms 4 weeks after inoculation and in crown dieback one and two years after inoculation. After two years, 13 of the American clones showed significantly less dieback than the American elm seedlings, and 18 American clones showed significantly less injury than a randomly chosen, unselected American elm clone, 57845. The American clones with the most DED-tolerance were cultivars ‘Valley Forge,’ ‘Princeton,’ ‘Delaware,’ and ‘New Harmony,’ and selections N3487, R18-2, 290, 190, and GDH. The non-American selections 51 and 970 also exhibited high levels of disease tolerance. Most susceptible were American clones 57845, ‘Augustine,’ Crandall, W590, and the American elm seedlings. The most disease-tolerant American elm selections identified in this study are being evaluated further for possible naming and release to the nursery industry.

Evaluation of Elm Clones for Tolerance to Dutch Elm Disease

Rooted cuttings of ten hybrid elm (Ulmus) clones, including one named 'Patriot', and all derived from various crosses of 'Homestead', 'Prospector', 'Urban', and Selection 970, were established along with a randomly selected American elm clones and three disease-tolerant cultivars ('Frontier', 'Homestead', and 'Prospector') in a replicated field plot. When the rooted cuttings were 3 years old, they were inoculated with a mixed spore suspension of Ophiostoma novo-ulmi and O. ulmi, the fungi that cause Dutch elm disease. Analyses of variance and regression showed significant variation among clones in crown dieback, survival, and height growth over a 7-year time period following inoculation. The American elm clone and selection 15-87 (an 'Urban' x 'Prospector' clone) showed the most crown dieback and lowest survival rate and were among the slowest in growth rate, 7 years after inoculation. Selections and cultivars showing the least dieback and highest survival were most hybrids from parentages of 'Urban' x 'Prospector', those from 'Homestead' x 'Prospector', and 'Homestead' x 970; and cultivars 'Patriot', 'Homestead', and 'Prospector'. Many of the same disease-tolerant clones and cultivars also showed the greatest height growth after inoculation. Significant variation in disease symptoms occurred among clones from the 'Urban' x 'Prospector' cross. Results of this study emphasize the importance of selection and testing of specific clones within full-sib families.

Elm bark components and their potential influence on bark beetle feeding

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.