Identifying Fraxinus excelsior tolerant to ash dieback: Visual field monitoring versus a molecular marker

Ash dieback (ADB) caused by the pathogen Hymenoscyphus fraxineus is the cause of massive mortality of Fraxinus spp. in Europe. The aim of this work was to check for the presence of the molecular marker for ADB tolerance in mapped healthy‐looking F. excelsior trees, and to compare its occurrence in trees exhibiting severe ADB symptoms. Monitoring of 135 healthy‐looking F. excelsior on the island of Gotland, Sweden, showed that after 3–4 years 99.3% of these trees had 0%–10% crown damage, thus remaining in a similar health condition as when first mapped. After 5–6 years, 94.7% of these trees had 0%–10% crown damage. Molecular analysis of leaf tissues from 40 of those showed the presence of the molecular marker in 34 (85.0%) trees, while it was absent in 6 (15.0%) trees. Analysis of leaf tissues from 40 severely ADB‐diseased trees showed the presence of the molecular marker in 17 (42.5%) trees, but its absence in 23 (57.5%) trees (p < .0001). The results demonstrated that monitoring of healthy‐looking F. excelsior is a simple and straightforward approach for the selection of presumably ADB‐tolerant ash for future breeding. The cDNA‐based molecular marker revealed moderate capacity on its own to discriminate between presumably ADB‐tolerant and susceptible F. excelsior genotypes.     

Genetic resistance to Hymenoscyphus pseudoalbidus limits fungal growth and symptom occurrence in Fraxinus excelsior

The European common ash (Fraxinus excelsior) is currently threatened by a pathogenic fungus, Hymenoscyphus pseudoalbidus, which seems to enter the trees through the leaves. Continuous assessments of 39 clones in Danish field trials have shown that there are significant differences in the susceptibility of clones to the new disease. Interestingly, clones that showed early leaf senescence in the autumn were in general less susceptible to the disease than late‐senescing clones. Thus, variation in susceptibility could be owing to phenological differences associated with the infection biology. To test whether differences in susceptibility are driven by genetically based factors other than phenology, we compared inoculations with H. pseudoalbidus on four highly susceptible clones with those of four less susceptible clones. Development of necrosis was hereafter followed regularly. The growth of the fungus in the inner bark was further detected with species‐specific PCR primers. The severity of the response to infection shows significant differentiation among clones and significant correlation with clone susceptibility, as assessed from natural infections in field trials. The fungus was detected in tissues immediately surrounding the necrosis but showed some signs of endophytic growth. The results suggest that healthier clones are able to limit the growth and spread of the fungus and thereby minimize the occurrence of symptoms. This gives hope for the future preservation of F. excelsior in Europe through selection and breeding.     

The introduction of Hymenoscyphus fraxineus to Northern Ireland and the subsequent development of ash dieback

Ash dieback caused by Hymenoscyphus fraxineus was first recorded in Northern Ireland (NI) in November 2012. The disease was observed only on recently (<6 years) planted trees. An in-depth case study in 2015 of an ash plantation with severe symptoms indicated that many of the trees were infected at the time of planting. Apothecia were observed developing from pseudosclerotia beneath the epidermis of dead branches still attached to the tree, suggesting a possible mechanism whereby H. fraxineus could be disseminated without leaf or rachises infection. Apothecia also formed on roots, indicating that infections may also occur in the soil. Often young trees were killed by the formation of large basal lesions which did not arise from stem infections higher up. On first detecting the disease on the island of Ireland the Governments of NI and the Republic of Ireland published an “All-Ireland Chalara Control Strategy.” Part of that strategy was a ban on the importation of ash plants from regions where the disease was known to be present, to prevent the introduction of further inoculum, and the implementation of an ‘eradication and containment’ policy with the aim of preventing the establishment and spread of the disease. While these measures may have slowed disease establishment, they were ultimately unsuccessful and by 2018 ash dieback was widespread and established throughout the whole of NI in plantations and in the wider environment.     

Fungi in foliage and shoots of Fraxinus excelsior in eastern Ukraine: a first report on Hymenoscyphus pseudoalbidus

In eastern Ukraine, the first symptoms of dieback on common ash (Fraxinus excelsior) were observed in 2010, as sparse flushing of leaves, bark necrosis and wood discoloration of shoots. The aim of this study was to assess possible causal agents of the damage by studying fungal communities in both symptomatic and healthy‐looking shoots, and leaf petioles. Field sampling was carried out in 2010 in Kharkiv and Sumy regions in eastern Ukraine and included 68 segments of symptomatic shoots, 68 segments of healthy‐looking shoots and 240 segments of petioles. DNA isolation from individual segments and direct sequencing of fungal ITS rRNA resulted in 430 fungal sequences representing 29 distinct taxa. Results showed that Hymenoscyphus pseudoalbidus – the primary causal agent of ash dieback in Europe – was present at low proportion (5.6%) in symptomatic shoots. Other more frequently detected fungi were Epicoccum nigrum, Venturia fraxini, Colletotrichum truncatum, Aureobasidium pullulans, Alternaria alternata, Alternaria sp. and Lophiostoma corticola. In conclusion, the study reports on the first incidence of ash decline in the Ukraine and other possible causal agents of damage which may help to evaluate and forecast the future situation with F. excelsior stands in the region.     

Predicting ash dieback severity and environmental suitability for the disease in forest stands

Ash dieback, caused by the ascomycete fungus Hymenoscyphus fraxineus, has been rapidly expanding across Europe during the last two decades, posing a considerable threat to native ash populations. In this study, we applied regression-based models trained by field data, in conjunction with geographic information systems, to produce spatial predictions of ash dieback severity and environmental suitability for the disease in Czech forests. A model of actual ash dieback severity relates disease extent to silvicultural and environmental characteristics of forest stands and their neighbourhood, while a model of environmental suitability for the disease quantifies the relative susceptibility of sites to the disease, independent of the current silvicultural characteristics. The final predictive maps suggested that fertile lowlands and humid areas bordering Poland and Slovakia were the most endangered regions. Areas at the lowest risk of damage were concentrated in dry areas and in highland and mountain areas in the western part of the country, usually with poor soils on acid bedrock. Predictions of actual disease severity are an effective tool for guiding the current management of infested stands whereas predicting environmental suitability is useful for making long-term strategic decisions, e.g. identifying areas where future ash regeneration and cultivation may be unsuccessful.     

Fraxinus nigra (black ash) dieback in Minnesota: Regional variation and potential contributing factors

Extensive tree dieback is a recurrent issue in many regions. Crown dieback of Fraxinus nigra Marsh. (black ash; brown ash) in the northeastern and north central United States is an example. F. nigra is a widely distributed hardwood that is often the dominant species in wetland forests from Manitoba to Newfoundland and West Virginia to Indiana. Widespread crown dieback of F. nigra has been noted in many regions, but there are few quantitative assessments of dieback extent or relationship to potential causes. Most F. nigra dieback episodes are not associated with specific disease or pest agents. Drought, excessive soil moisture, cohort senescense, and road influences, have all been suggested as potential contributing factors. Our objectives were to (1) quantify variable dieback across northern Minnesota, a region described as having extensive dieback, (2) determine the relationship between dieback and site moisture, (3) relate dieback to tree age/size distributions, and (4) assess whether dieback was related to road proximity. Given the increasing threat of Agrilus planipennis (emerald ash borer) in the region, it is important to know the current health status of F. nigra populations before widespread infestation occurs. Many stands in our study exhibited high incidences of crown dieback. However, the incidence of dieback was variable across the region. Spatial variability in dieback was associated with site wetland characteristics; more dieback occurred on jurisdictional wetlands and on sites with a higher wetness index and a deeper depth to a perching layer. Dieback was also positively correlated with mean stand diameter, and tree diameters were generally correlated with age, suggesting that stands with larger and older individuals experienced more dieback. Cohort senescence is a possible explanation for this trend. Finally, dieback occurred with higher frequency nearer to roads. The road influence could be related to hydrological alterations or perhaps toxicity from road deicing salt. The fact that dieback is more severe close to roads may contribute to a general perception that black ash dieback is more severe throughout the region than our study suggests. Collectively, our results indicate that the healthiest F. nigra stands in our study region are likely to be younger and located on relatively drier sites and farther from roads, compared to stands with significant crown dieback.     

Genetic variation of Taxus baccata L. populations in the Eastern Alps and its implications for conservation management

Abstract

The English yew (Taxus baccata L.) is an endangered rare tree species in Austria. More than 600 bud samples were collected from seven populations in three regions of the Eastern Alpine mountains for estimating their genetic structures by using isozyme gene markers. Nine gene loci encoding for seven enzyme systems were investigated. The revealed 32 alleles indicate a higher multiplicity of the east alpine gene pool compared with other European regions. English yew showed a high level of genetic variation, with a mean number of alleles per locus (A/L) of 2.7. A total of 76.4% of the loci were polymorphic, the average expected heterozygosity was (H _e) 0.274 and the mean observed heterozygosity (H _o) was 0.238. The relative proportion of genetic differentiation among the regions was found to be 6.2%, the level of gene flow was high (Nm=3.78) and the level of inbreeding (0.130) among the regions was medium. The obligatory out crossing (dioecious plant), the long generation time, the ability to regenerate from stump and the seed dispersal by birds and rodents might contribute to the high level of genetic variation found within the population. The conservation propositions are discussed with respect to the genetic structure and the poor recruitment of this species.     

Genetic variation in survival,growth, and stem form of Pinus leiophylla in Brazil and South Africa and provenance resistance to pitch canker

Pinus leiophylla is a relatively common pine that occurs in the mountains of western and central Mexico. Between 1987 and 1990, Camcore, North Carolina State University, sampled 11 populations and 309 mother trees of the species to determine patterns of genetic variation in survival, growth and stem form. Fifteen provenance/progeny trials were established in southern Brazil and South Africa across a wide range of sites and assessed at 3, 5 and 8 years of age for height, diameter and stem form. Results indicated that average productivity ranged from 5 to 19m³ ha^?1 y^?1 depending on the site and that performance was not as competitive as P. patula (South Africa) and P. taeda (Brazil) controls. Provenances from central Mexico (Michoacán) were statistically better in productivity than those from the southern part of the country (Oaxaca), which in turn were superior to those from the northern part of the country (Durango). However, provenances from northern Mexico exhibited superior survival to seed sources from other locations in Mexico when grown on cold sites (winter minimums –10 to 5°C) in South Africa and superior stem form across all locations. Seedlings from the original 11 provenances were screened for resistance to the pitch canker fungus (PCF; Fusarium circinatum). Results indicated that generally P. leiophylla is as susceptible to PCF as P. patula (stemkill = 85%) with the exception of two fast-growing, moderately resistant populations from Michoacán, La Pinalosa (stemkill = 44%) and Ario de Rosales (stemkill = 73%). The future potential of P. leiophylla might be in hybrid combination with P. patula in the seasonally dry areas of southern Africa where fires are common and pitch canker is a problem.     

Genetic variation in height growth curves observed in three clonal tests of sugi (Cryptomeria japonica D. Don) in Kyushu

Genetic variation in the height growth curves was investigated by analyzing data from three clonal trials of sugi (Crytomeria japonica D. Don) in Kyushu. Average height of twelve clones measured at each of five years until 30 years of age were fitted to the Chapman-Richards function with two parameters model. Clonal variation in the two parameters (an upper asymptote and a rate of growth parameter) was statistically significant across the tests, indicating that height growth pattern is under genetic control. The type of growth curve was clearly classified with the two parameters and agreed with the empirical classifications of the growth habit of local varieties. The rate of growth parameter was correlated with total height up to 20 years of age, while the upper asymptote was correlated only with the last ten years’ increment from 21 to 30 years where the clonal repeatability was decreasing. This indicates that a clonal selection for long rotation management system would not be reliable unless the height is measured accurately with more advanced devices or it is adjusted by the current increment of diameter.     

Genetic control of fiber properties and growth in triploid hybrid clones of Populus tomentosa

To better understand the genetic control of fiber properties (fiber length [FL], fiber width [FW] and coarseness [C]) and growth traits (tree height [H], diameter at breast height [DBH] and stem volume [SV]) in triploid hybrid clones of Populus tomentosa carr., genetic relationships among selected fiber properties with growth traits were examined in five-year-old clonal field trials located in Yanzhou, Gaotang and Xiangfen, China. In total, 180 trees from 10 clones were sampled from the three sites. The site had a moderate effect on FW, C and tree growth, and a highly significant (P<0.001) effect on FL and fiber length/width (FL/W). Clonal effects were also significant (P<0.05) for all studied traits except for the DBH and SV. Clone×site interactions were significant for all studied traits (except for FL). The estimated repeatability of clonal mean for FL (0.91) was higher than for FW (0.88), C (0.77), FL/W (0.74), H (0.62), DBH (0.61) and SV (0.55). Intersite genetic correlation estimates indicated that fiber properties were more stable than growth traits. Positively insignificant genetic correlation estimates between FL and growth trait and negatively insignificant genetic correlation estimates between C and growth traits were observed. This suggests that in the triploid hybrid poplar, clones selection for growth traits will not result in a significant increase or reduction in the fiber properties.     

山苍子家系幼林生长性状遗传变异及稳定性分析

[目的]对山苍子不同家系幼林生长性状进行遗传变异及稳定性分析,为山苍子优良家系选择及推广提供参考。[方法]以13个半同胞山苍子家系为材料,采用随机区组设计,分别在重庆万州、湖北京山和福建清流3个试验点营建家系试验林。对23年生山苍子幼林的树高和地径性状进行测定和多点联合分析,并采用AMMI模型对山苍子各家系的生长稳定性进行评价。[结果](1)山苍子家系的树高和地径在家系和地点效应上均达到显著(0. 01 P0. 05)或极显著(P 0. 01)水平,地径的家系和地点交互作用达到显著水平(0. 01 P 0. 05); 3个试验点树高和地径的表型变异系数为20. 98%～29. 27%,遗传变异系数为0. 62%～20. 35%,其中,地径的表型和遗传变异系数普遍大于树高;树高的家系遗传力为0. 003～0. 578,地径的家系遗传力为0. 455～ 0. 806。(2)综合双标图和稳定性参数得出:家系JY2和GX4地径表现较好且稳定性较高。[结论]山苍子家系的树高和地径在家系和地点间的差异均达到极显著水平(P 0. 01),存在丰富的遗传变异。在家系水平上,树高受低等到中等强度的遗传控制,地径受中等到高等强度的遗传控制。各家系在福建清流试点生长表现最好,湖北京山试点居次,重庆万州试点最差,其中家系JY2和GX4在3个试验点地径均表现较好且稳定性较高。     

Early growth and survival of Eucalyptus pellita provenances in a range of tropical environments,compared with E. grandis,E. urophylla and Acacia mangium

Provenance/family trials of Eucalyptus pellita F. Muell were established at three seasonally-dry tropical sites in northern Australia (two in north Queensland and one on Melville Island in the Northern Territory), and at Luasong, a tropical site with year-round high rainfall and humidity in Sabah, Malaysia. After 2–3 years, it was clear that New Guinea provenances outperformed Queensland provenances in their survival, growth and form, and in their crown health, in the humid tropical environment of Luasong. New Guinea provenances were also clearly superior to Queensland provenances in their growth and form at Melville Island, but less clearly so at Cardwell, Queensland. Among Queensland provenances, Helenvale and Kuranda were superior to the more northerly Cape York provenances, Tozers Gap and Lankelly Creek, while there was little difference between the two New Guinea provenances tested, Bupul-Muting (Irian Jaya) and Keru (Papua New Guinea). Significant differences in growth traits, form and survival were demonstrated between families within provenances. In a species/provenance trial at Luasong, E. pellita displayed better growth and survival than tropical provenances of E. grandis and E. urophylla, but was inferior in growth and crown health to Acacia mangium.     

Genetic variation in growth and wood-quality traits of Corymbia citriodora subsp. variegata across three sites in south-east Queensland,Australia

Ten growth or wood-quality traits were assessed in three nearby Corymbia citriodora subsp. variegata (CCV) open-pollinated family-within-provenance trials (18 provenances represented by a total of 374 families) to provide information for the development of a breeding program targeting both pulp and solid-wood products. Growth traits (diameter at breast high over bark [DBH], height and conical volume) were assessed at 3 and 7 years of age. Wood-quality traits (density [DEN], Kraft pulp yield [KPY], modulus of elasticity [MoE] and microfibril angle [MfA]) were predicted using near-infrared spectroscopy on wood samples collected from these trials when aged between 10 and 12 years. The high average KPY, DEN and MoE, and low average MfA observed indicates CCV is very suitable for both pulp and timber products. All traits were under moderate to strong genetic control. In across- trials analyses, high (>0.4) heritability estimates were observed for height, DEN, MoE and MfA, while moderate heritability estimates (0.24 to 0.34) were observed for DBH, volume and KPY. Most traits showed very low levels of genotype × site interaction. Estimated age–age genetic correlations for growth traits were strong at both the family (0.97) and provenance (0.99) levels. Relationships among traits (additive genetic correlation estimates) were favourable, with strong and positive estimates between growth traits (0.84 to 0.98), moderate and positive values between growth and wood-quality traits (0.32 to 0.68), moderate and positive between KPY and MoE (0.64), and high and positive between DEN and MoE (0.82). However, negative (but favourable) correlations were detected between MfA and all other evaluated traits (?0.31 to ?0.96). The genetic correlation between the same trait expressed on two different sites, at family level, ranged from 0.24 to 0.42 for growth traits, and from 0.29 to 0.53 for wood traits. Therefore simultaneous genetic improvement of growth and wood property traits in CCV for the target environment in south-east Queensland should be possible, given the moderate to high estimates of heritability and favourable correlations amongst all traits studied, unless genotype × site interactions are greater than was evident.     

Variation,inheritance and correlation of growth characteristics of <Emphasis Type="Italic">Populus deltoides</Emphasis> Bartr. at various ages in the central-plain region of Punjab,India

The growth performance of twenty poplar(Populus deltoides Bartr.) clones,planted in the central-plain region of Punjab in north-western India,was evaluated using a randomized block design with three replications and plot size of four plants.Significant differences among clones were observed for diameter at breast height(DBH),height and volume per tree at age five,six and eight years.Clone L-48/89 recorded significantly superior volume than the control(G-48) at all ages,with superiority of 51.4,43.9 and 48.5 per cent at age five,six and eight years,respectively.The phenotypic and genotypic coefficients of variation were the highest for volume(26.55-34.66% and 15.84-26.00%) and the minimum for tree height(8.43-12.13% and 4.71-7.59%).The broad sense heritability was relatively higher for DBH(0.42-0.55) and genetic advance as per cent of mean was highest for volume(19.48-40.18).All genetic parameters increased with age.All traits showed significant positive correlation with each other.     

Effects of brassinolide on the survival,growth and drought resistance of <Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> seedlings under water-stress

We conducted field and pot experiments to investigate the effects of brassinolide on 1-year-old Robinia pseudoacacia L. seedlings. In the field experiment, seedling roots were soaked in brassinolide solutions containing 0–0.4 mg/l pure brassinolide before planting. Survival and growth of the seedlings were determined 8 months later. The results showed that soaking roots in brassinolide prior to planting significantly increased the survival and growth of seedlings. The best results were in the 0.2 mg/l brassinolide treatment. In the pot experiment, roots were soaked in 0–0.4 mg/l brassinolide before planting followed by a foliar application of brassinolide when the seedlings leafed out. After the seedlings were established, the soil water content in the pots was regulated to simulate drought conditions and various physiological parameters were measured. The results showed that treatment with 0.2 mg/l brassinolide decreased the transpiration rate, stomatal conductance and malondialdehyde (MDA) content of seedlings growing under moderate or severe water stress compared to untreated seedlings. Leaf water content, predawn water potential, soluble sugar content, free proline content, and superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities were all greater in water-stressed seedlings in the 0.2 mg/l brassinolide treatment compared to the control. The results indicate that the application of brassinolide can ameliorate the effects of water stress and enhance drought resistance of Robinia seedlings. Treatment of seedlings with brassinolide may be a useful management tool for afforestation projects in arid and semiarid areas.     

Genetic and morphological variation in natural teak （Tectona grandis） populations of the Western Ghats in Southern India

Teak(Tectona grandis L.f.) is a popular hardwood species native to South and South-East Asia. The possible association of amplified fragment length polymorphism(AFLP) marker with morphological variables of eleven important characters viz. girth at breast height(GBH), height of tree, bole height, branch knots, presence of fluting, spiral stem, leaf hair, leaf length/breadth ratio, branching pattern, bark colour and petiole shape for nine natural populations comprising 180 genotypes of teak(9 populations × 20 trees). The phenogram constructed using Euclidean distances for the eleven morphological characters showed that the populations were not grouped according to their geographical origin. The Mantel's test for pairwise correlation between Euclidean distances of different morphological variables and genetic distances from AFLP data revealed that only petiole character(r =0.269; p =0.046) and height of tree(r =0.200; p =0.001) were significantly correlated with that of AFLP data matrix. The nine populations in this study covered a geographic area of about 1000 km stretch along the Western Ghat of South India. A test of correlation between genetic and geographic distance matrices revealed a significant positive correlation(r =0.475; p =0.009). The lack of perfect congruence between morphological and molecular data except for geographic distance, tree height and petiole character suggested that the morphological system might be useful for the morphotypes management but not appropriate to study the genetic structure of the teak populations.     

Chemical content and seasonal variation of throughfall and litterflow under individual trees in the Hyrcanian forests of Iran

We assessed the effect of seasons and the tree species velvet maple (Acer velutinum Boiss), Hainbuche hornbeam (Carpinus betulus L.) and chestnut-leaved oak (Quercus castanefolia C. A. Mey.; Fagaceae) on nutrient fluxes (Na⁺, K⁺ and Ca²⁺) in throughfall (TF) and litter flow (LF) from January 2012 to February 2013. Potassium (K⁺) and calcium (Ca²⁺) in total TF and LF over the measurement period significantly differed between 3 the species (p < 0.05). Maple and oak trees had significantly higher fluxes of K⁺ and Ca²⁺ in their TF, respectively. The average quantity of nutrients in LF was significantly higher in the leafy season than in the leafless season for all cations except for Na⁺. Under velvet maple trees, the average flux of nutrients (Na⁺, K⁺, and Ca²⁺) in TF was significantly higher than LF. Lastly, leaching of potassium (K⁺) and calcium (Ca²⁺) in LF during the measurement period was significantly lower than TF under the hornbeam trees. Our results suggest that different tree species may impact the nutrient availability and possibly the sustainability of Hyrcanian forests. Further research is needed to determine how managing different species will affect the long-term nutrient status of these forests.     

Local and regional environmental variation influences the growth of tropical trees in selection trials in the Republic of Panama

Native Neotropical trees are being increasingly planted for restoration purposes and timber production, but we lack species-specific data on growth responses to different regional climates and local environmental variation. We used regression trees and variance components to quantify the effects of within- and among-site environmental variation on the basal area (BA) of 21 Neotropical and two exotic tree species at three selection trials in the Republic of Panama. Sites represented distinct regional climates in which annual rainfall varied from 1100 to 2226 mm, with dry seasons of 4.1–6.7 months. Local environmental variables included measures of slope steepness and position, soil texture, soil color, and indicators of soil condition, such as subsoil rockiness.     

落羽杉属种源研究：扦插生根能力变异

研究了不同种源、家系落羽杉扦插繁殖生根能力的遗传变异。结果表明,落羽杉嫩枝扦插一般7d开始产生愈伤组织,15d开始发根。活条率、生根率、发根数、不定根总长、生根力指数和抽梢长度等6个性状在种源、家系间均有显著或极显著差异。1600号、401号、502号和鸡公山种源是生长和生根能力兼优的种源家系。500×10-6NAA快浸可以显著提高落羽杉种源扦插生根率。同时还分析了扦插生根性状间及生根力与母树生长间的相关关系。     

Fusarium root infection of container-grown Douglas-fir: effect on survival and growth of outplanted seedlings and persistence of the pathogen

Greenhouse-grown Douglas-fir (Pseudotsuga menziesii var.glauca [Beissn.] Franco) seedlings with roots infected with eitherFusarium oxysporum Schlect. orFusarium proliferatum (Matsushima) Nirenberg were outplanted on a forest site in northern Idaho, U.S.A. No residentFusarium populations were detected in the forest soil.Fusarium persisted the first four years on roots initiated during the greenhouse phase, but occurred sparingly or was absent on roots that grew after outplanting. Height growth was unaffected, and mortality was not often associated withFusarium. A seasonal pattern ofFusarium activity was observed. Low levels (10–40%) of initial root infection apparently have little adverse effect on outplanting performance of Douglas-fir seedlings.University of Idaho, Idaho Forest, Wildlife and Range Experiment Station Contribution No. 640.