Distribution of Frankia, ectomycorrhizal fungi, and bacteria in soil after the eruption of Miyake-Jima (Izu Islands, Japan) in 2000

Miyake-Jima, a round island of about 8 km in diameter, is located about 200 km south of Tokyo, Japan (34°08′ N, 139°53′ E). In July 2000, the central cone of this island collapsed and a new eruption started with the falling of volcanic ash and SO₂ emission. In October 2001, we measured the distribution of bacteria, and Frankia, a symbiotic nitrogen-fixing actinomycete that forms root nodules, and ectomycorrhizal fungi associated with alder in newly deposited ash and its underlying soil by cultivation of Alnus sieboldiana seedlings in these soils. There were fewer bacteria growing on the nutrient broth agar and fewer bacteria growing on 100-fold diluted nutrient broth agar in newly deposited volcanic ash than there were growing in the buried old soil. In four out of five sites, little or no nodulation was observed in newly deposited ash; abundant root nodules were formed in the underlying soil. Ectomycorrhizae formed in the seedlings cultivated in the underlying soil. In May 2003, the distribution of Frankia and ectomycorrhizal fungi in soil at different depths (up to 160 cm) was also investigated. Frankia and ectomycorrhizal fungi were relatively abundant in surface soil layers.     

Control of Hymenoscyphus fraxineus,the causal agent of ash dieback,using composting

Viability of Hymenoscyphus fraxineus inocula following temperature treatments for different exposure times was examined in vitro and in aerated flask‐ and large‐scale composting tests using green waste. After an exposure for up to 10 days at 20°C, 97.3% of H. fraxineus mycelium and pseudosclerotia plate cultures remained viable. No viability was detected following a 3‐day exposure to 40°C or a 1‐day exposure to 45°C although pseudosclerotia were more tolerant than mycelium to an exposure to 35°C. Primordial apothecia of H. fraxineus emerged from 62%–100% of infected ash rachises collected from two infected sites and stored at 4°C for 0–5 months; exposure to compost for up to 10 days at 20°C did not affect this emergence. No emergence of H. fraxineus apothecia was observed from ash rachises that were exposed to compost at 45°C for 1 day or at 35°C or 40°C for 3 days in flasks or at 40°C for 1 day or at 30°C for 5 days in a large‐scale composting system. Based on a fitted model, estimates of the survival of H. fraxineus inoculum in infected ash rachises exposed to compost at 50°C for 1 day were 0.081% of that in the untreated H. fraxineus ash rachis inoculum. Increasing loss in viability of H. fraxineus inoculum in infected ash rachises during longer and warmer exposures to compost at 35°C–45°C corresponded with a reduced concentration of pathogen DNA detected in the rachises using real‐time PCR. However, exposure of rachises to compost at >53°C resulted in a smaller reduction in pathogen DNA detected than exposure to compost at lower temperatures, possibly due to the inhibition of enzymatic degradation of DNA at elevated temperatures.     

Seed Biology,Stand Characteristics,and Regeneration of Fraxinus rhynchophylla Hance

Fruit size and seed moisture content were measured and seed production and dispersal were monitored to understand the seed biology of the Korean ash (Fraxinus rhynchophylla Hance) in two Korean ash forests. A combination of four ground treatments and four crown closure levels were created in a natural forest to understand the site conditions needed for seedling emergence in natural stands and to determine practical regeneration methods for direct seeding. The seed size of Korean ash increased until late May and its moisture content decreased rapidly in early November. Prolific seed bearing occurred every 3 yr. The distance of seed dispersal by wind was about 30 m, but more than 90% of the seeds dispersed within 10 m from the seed trees. Twenty-five seed trees per hectare provided for successful natural regeneration. The seedling emergence in the natural stands was best with scarification treatment and 25～50% of crown closure.     

Individual resistance of Fraxinus angustifolia clones to ash dieback

The presumed resistance of individual ash trees to ash dieback caused by invasive pathogen Hymenoscyphus fraxineus is an important issue for the maintenance of ash in European forests. All known studies regarding the resistance of ash trees to ash dieback were conducted in plantations and stands of F. excelsior; however, no such data exist for F. angustifolia. Crown damage assessments were performed over four consecutive years between 2009 and 2012 at a F. angustifolia clonal plantation in Hra??ica, Slovenia. Inoculation of H. fraxineus into the branches of the most and least damaged clones of F. angustifolia and leaf phenology assessments was performed to verify the presence of defence mechanisms that limit fungal growth or promote disease escape. Additionally, root collars of selected clones were inspected for fungal infections. The crown damage assessments showed considerable differences among F. angustifolia clones, indicating genetic variability in susceptibility to ash dieback. Crown dieback progressed significantly over the 4‐year time period; the mean crown damage of individual clones in 2012 varied between 16.7% and 83.8%. Significant differences among F. angustifolia clones were found in the inoculation trials and leaf phenology assessments. However, defence mechanisms such as early leaf flushing, early leaf shedding and the ability to inhibit pathogen growth in host tissues were not confirmed. High frequency of Armillaria spp. and H. fraxineus root collar infection demonstrated the need for whole tree inspection to determine causal agent of damages on individual ash trees. Armillaria spp. may be highly associated with ash decline epidemiology.     

First definite report of natural infection of Fraxinus ornus by Hymenoscyphus fraxineus

Hymenoscyphus fraxineus was isolated from four leaf rachises with necrotic lesions of flowering ash (Fraxinus ornus) seedlings, which had been planted on a forest site in Austria where they were exposed to a massive natural infection pressure. This represents the first definite report of natural infection of this ash species by the ash dieback pathogen.     

Analyses of the ash dieback pathogen,Hymenoscyphus fraxineus,suggest role of tree species diversity on colonization and population structure differentiation

Microsatellite markers were used to investigate the population structure of the Ash Dieback pathogen, Hymenoscyphus fraxineus, across a tree species diversity gradient containing common ash, Fraxinus excelsior, in the Hainich National Park in central Germany. Population differentiation was determined at a local spatial scale that may be driven by tree species mixtures.     

Stress resistance levels change little during dormancy in ash,sessile oak and sycamore seedlings

The physiological status of ash (Fraxinus excelsior L.), sessile oak (Quercus petraea (Matt.)) and sycamore (Acer pseudoplatanus L.) seedlings sampled from nurseries in Ireland between October and May, 1995/1996 and 1996/1997 was investigated. The results of heat treatments applied to taproots in vitro and evaluated using root electrolyte leakage (REL) indicated that sycamore was more easily damaged than the other species but lift date effects were small in all species. Dormancy release began later each year in ash (mid-November) than in oak or sycamore (late October to early November). The results of the REL and other data indicated that there was little change in stress resistance from November to about March (and April for some parameters). Sycamore was most active (highest shoot xylem pressure potential, REL, and root growth potential) during the winter, suggesting that adverse handling during this period is likely to reduce plant quality than in ash or oak. Field performance was good regardless of lifting/planting date.     

Growth Characteristics of Introduced Green Ash (Fraxinus pennsylvanica Marshall) and Narrow-leaved Ash (F. angustifolia L.) in Lowland Forest Region in Croatia

American ash and green ash were used about 100 years ago in the lowland regions of Croatia to afforest and fill the depressions where narrow-leaved ash (Fraxinus angustifolia Vahl) could not survive. The growth of mean stand trees of green ash and narrow-leaved ash were studied in 14 sites (a systematic sample of 0.03 ha circular plots). A total of 212 trees were cored and 11 cross-section samples were taken for stem analysis. The Mann-Whitney U-test showed statistically significant differences in radial growth between narrow-leaved and green ash at all sites. In green ash, the test revealed a statistically significant difference in the radial growth between the last 20-year-period and the preceding 20-year-period. Green ash are characterised by the fact that annual radial growth in the first 20–30 years is very high (above average), while after that it is consistently suppressed below average growth and amounts to only about 1.5 mm. The obtained results of faster growth and a low final growth value suggest that green ash should be managed with short rotations, since this important pioneer species is intended to improve the conditions in those sites where forest vegetation has regressed.     

Fuelwood characteristics of tree species in homegardens of Kerala, India

Indiscriminate use of natural resources in the past has lead to fuelwood shortages in many parts of the tropical world. To surmount this domestic energy crisis, not only degraded sites must be planted with trees having high fuel value potential, but also agroforestry promoted on arable lands. To enable choice of species for such energy plantations/agroforests in the humid tropics of peninsular India, we assessed the heat of combustion and physical properties that determine combustion of phytofuels, such as ash content, specific gravity and moisture content. Bark and wood samples of 45 multipurpose tree species in the homegardens of Kerala, India and three fuel materials of local importance (coconut [Cocos nucifera] endocarp, dried coconut spathe and dehiscent rubber [Hevea braziliensis] pericarp) were evaluated. Variations abound in the calorific values and physical properties of species and tissue-types. In general, heat of combustion and specific gravity followed the sequence: heartwood > sapwood > bark, while mean ash percentage followed a reverse order (bark > sapwood > heartwood). Ash content had a negative correlation with heat of combustion, but specific gravity exerted a positive influence. Furthermore, ash content and wood specific gravity were inversely related. Although green moisture content increased in the order: bark < heartwood < sapwood, it failed to show any predictable relationship with heat of combustion.This revised version was published online in November 2005 with corrections to the Cover Date.     

Effects of full and partial clearing, with and without herbicide, on weed cover, light availability, and establishment success of white ash in shrub communities of abandoned pastureland in southwestern Quebec, Canada

Shrub communities established on former pasture land are currently under-used and their forestry potential is of interest to land owners wishing to increase valuable hardwood regeneration on their properties. The comparative effects of strip clearing and total clearing, both treatments applied with or without herbicide, on competing vegetation cover, light availability, and survival and growth of planted white ash (Fraxinus americana L.) were examined in two different shrub dominated sites for 3 years in southwestern Québec, Canada. Survival was high in all treatments. At the site with the richest soil and in comparison to total clearing, strip clearing produced the lowest light level in the third year, which induced lower total herbaceous weed cover. These combined effects produced the same growth results for white ash seedlings in all treatments. At the second site, with the highest woody vegetation regrowth, strip clearing has promoted seedling height growth and produced the highest height: diameter ratio for white ash. This ratio was also superior at this site in the absence of herbicide. Treatment effects were soil/site dependant. Because partial clearing in strips has never reduced tree growth in comparison to total clearing, it represents a promising method for the establishment of valuable hardwoods in shrubby vegetation, with lower management intensity and lower landscape impact than total clearing.     

Phytophthora root and collar rot of mature Fraxinus excelsior in forest stands in Poland and Denmark

In recent years, Common ash (Fraxinus excelsior) throughout Europe has been severely impacted by a leaf and twig dieback caused by the hyphomycete Chalara fraxinea. The reasons for its current devastating outbreak, however, still remain unclear. Here, we report the presence of four Phytophthora taxa in declining ash stands in Poland and Denmark. Phytophthora cactorum, Phytophthora plurivora, Phytophthora taxon salixsoil and Phytophthora gonapodyides were isolated from rhizosphere soil samples and necrotic bark lesions on stems and roots of mature declining ash trees in four stands. The first three species proved to be aggressive to abscised roots, twigs and leaves of F. excelsior in inoculation experiments. Soil infestation tests also confirmed their pathogenicity towards fine and feeder roots of ash seedlings. Our results provide first evidence for an involvement of Phytophthora species as a contributing factor in current decline phenomena of F. excelsior across Europe. Specifically, they may act as a predisposing factor for trees subsequently infected by C. fraxinea. Phytophthora species from ash stands also proved to be aggressive towards a wide range of tree and shrub species commonly associated with F. excelsior in mixed stands. Although damage varied considerably depending on the Phytophthora species/isolate–host plant combination, these results show that many woody species may be a potential source for survival and inoculum build‐up of soilborne Phytophthora spp. in ash stands and forest ecosystems in general.     

Effects of intercropping systems of trees with soybean on soil physicochemical properties in juvenile plantations

The intercropping system of tree with soybean in juvenile plantations, as a short-term practice, was applied at Lao Shan Experimental Station in Mao’er Shan Forest of Northeast Forestry University, Harbin, China. The larch (Larix gmelinii)/soybean (Glycine max.) and ash (Fraxinus mandshurica) intercropping systems were studied in the field to assess the effects of the intercropping on soil physicochemical properties. The results showed that soil physical properties were improved after soybean intercropping with larch and ash in one growing season. The soil bulk density in larch/soybean and ash/soybean systems was 1.112 g·cm⁻³ and 1.058 g·cm⁻³, respectively, which was lower than that in the pure larch or ash plantation without intercropping. The total soil porosity also increased after intercropping. The organic matter amount in larch/soybean system was 1.77 times higher than that in the pure larch plantation, and it was 1.09 times higher in ash/soybean system than that in the pure ash plantation. Contents of total nitrogen and hydrolyzable nitrogen in larch/soybean system were 4.2% and 53.0% higher than those in the pure larch stand. Total nitrogen and hydrolyzable nitrogen contents in ash/soybean system were 75.5% and 3.3% higher than those in the pure ash plantation. Total phosphorus content decreased after intercropping, while change of available phosphorus showed an increasing trend. Total potassium and available potassium contents in the larch/soybean system were 0.6% and 17.5% higher than those in the pure larch stand. Total potassium and available potassium contents in the ash/soybean system were 56.4% and 21.8% higher than those in the pure ash plantation. Biography: FAN A-nan (1972–), female, Ph. Doctor in Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P. R. China.     

Aqueous leaf extract of Ligustrum vulgare inhibits ascospore germination and mycelial growth of Hymenoscyphus fraxineus

Hymenoscyphus fraxineus, the causal agent of common ash dieback, possesses a low level of genetic diversity in Europe. The introduction of novel strains of this fungus must be prevented, due to the possible emergence of new virulence alleles, which could result in the infestation of the small proportion of hitherto resistant or tolerant ash trees. More comprehensive knowledge of the host spectrum of H. fraxineus is necessary for preventing further introductions. It is possible that H. fraxineus manifests itself in hosts beyond the genus Fraxinus, though this proposition has received little attention thus far. Two in vitro experiments were set up to investigate whether privet (Ligustrum vulgare) could serve as a host: germination rate of fresh H. fraxineus ascospores and colony growth of H. fraxineus were tested on agar media containing leaf extracts of privet, common ash (Fraxinus excelsior) and manna ash (Fraxinus ornus). Two different media with leaf extracts were tested, one with high (60%) and one with low (12%) extract content. Barely any significant differences were recorded in the case of the media with low extract content. Significant effects occurred only at the higher extract content level: germination was completely inhibited on the privet medium. Mycelial growth on the privet medium was slower than on both the common ash and manna ash media and, in addition, one of the three H. fraxineus strains was completely inhibited. These observations indicate the presence of inhibitors in privet. It is therefore unlikely to be a suitable host for H. fraxineus.     

First record of Chalara fraxinea in Finland and genetic variation among isolates sampled from Åland,mainland Finland,Estonia and Latvia

We have isolated and confirmed the identification of ash dieback fungus (Chalara fraxinea, teleomorph Hymenoscyphus albidus) for the first time in Finland. In a preliminary analysis, considerable amount of genetic variation was detected among 20 Finnish (Åland and mainland Finland), one Latvian and 11 Estonian isolates, analysed by random amplified microsatellite (RAMS) markers.     

On the longevity of Hymenoscyphus pseudoalbidus in petioles of Fraxinus excelsior

Air‐dried pseudosclerotia produced by the ash dieback pathogen Hymenoscyphus pseudoalbidus (anamorph: Chalara fraxinea) can survive up to 3 months. Under field conditions, they are capable of postponing fructification for 1 year. The implications of this observation for epidemiology and control of ash dieback are discussed.     

Temperature effect on Chalara fraxinea: heat treatment of saplings as a possible disease control method

Ash dieback is an emerging disease caused by the fungus Chalara fraxinea that severely affects Fraxinus excelsior and F. angustifolia stands in Europe. Previous studies have shown that this pathogen prefers temperatures around 20°C, while its growth in pure cultures at 30°C proved to be very limited. The purpose of this study was to determine the effects of temperature on the development and growth of C. fraxinea in pure cultures and in plant tissues, as well as to test the heat tolerance of F. excelsior saplings. The sensitivity of fungus to heat in ash tissues was higher than in pure cultures. Low isolation success rate from diseased ash tissue after a five‐hour hot water treatment at 36°C and the relatively high survival rate of ash saplings after hot water treatments at 36°C and 40°C indicate possibilities for the development of a C. fraxinea eradication method in ash saplings. Field monitoring showed that in hot weather periods, thermal conditions inside the ash tissues can be extreme enough to markedly decrease the viability of C. fraxinea in infected plant tissues.     

Effects of benomyl and captan on growth and mycorrhizal colonization of Sitka‐spruce (Picea sitchensis) and ash (Fraxinus excelsior) in Irish nursery soil

The effects of two fungicides (benomyl and captan ‐ at recommended doses and up to three soil drenches) on root development and mycorrhizal colonization of Sitka‐spruce (Picea sitchensis) and ash (Fraxinus excelsior) were examined after 20 weeks growth, under environmentally controlled conditions, in soil from an Irish tree nursery. Although four mycorrhizal types have been found on Sitka‐spruce at the nursery, only one ectomycorrhizal type (Piceirhiza horti‐inflata) was identified on the short roots in this study. An inoculant (Vaminoc: MicroBio Ltd, Hemel Hempstead, UK) was used to inoculate ash and 20‐week‐old seedlings had a higher arbuscular mycorrhizal (AM) colonization in comparison with uninoculated controls. Multiple applications (2–3) of benomyl reduced the length of root and shoot and shoot dry mass of Sitka‐spruce, whereas in ash, it only depressed root length. Benomyl decreased the numbers of ectomycorrhizas of Sitka‐spruce and arbuscular mycorrhizal colonization of Vaminoc‐inoculated ash. A single application of captan stimulated root length and ectomycorrhizal colonization of Sitka‐spruce and root dry mass in ash compared with uninoculated controls. Applications of captan reduced arbuscular mycorrhizal colonization of Vaminoc‐inoculated ash to levels near to those of uninoculated controls. Of the two fungicides used, benomyl had the most deleterious effect on root length and mycorrhizal colonization of Sitka‐spruce and ash.     

Ascocarp formation of Hymenoscyphus fraxineus on several‐year‐old pseudosclerotial leaf rachises of Fraxinus excelsior

The ash dieback pathogen Hymenosycphus fraxineus can form ascocarps on pseudosclerotial leaf rachises of Fraxinus excelsior not only in the year after leaf fall but also on older rachises, at least up to five growing seasons after the leaves have been shed. The significance of this finding for the epidemiology of ash dieback is discussed.     

Determination of potassium and sodium in an ash sample by gamma-ray spectroscopy

Neutron activation analysis and gamma-ray spectroscopy were used to determine the quantity of potassium and sodium in an ash sample of Tabebuia sp bombarded with thermal neutrons. These techniques, widely applied in nuclear physics, can be used in the context of wood science as an alternative for the usual physical chemistry methods applied in this area. The quantity of K and Na in an 8.60±0.10 mg of ash was determined as being 1.3±0.3 mg and 11.0±1.8 μg, respectively. The ratio of Tabebuia sp converted into ash was also determined as 0.758±0.004%.     

Fungal colonization patterns in necrotic rootstocks and stem bases of dieback‐affected Fraxinus excelsior L.

European ash (Fraxinus excelsior) trees currently face the major threat of ash dieback caused by an invasive fungus, Hymenoscyphus fraxineus. Collar rots in F. excelsior have been increasingly associated with infections by this pathogen. However, the aetiology of the collar rots is still unclear and remains heavily debated. In contrast to most studies of this kind, entire rootstocks of four diseased ash trees were dug out to examine necrotic tissues in these rootstocks and stem bases in detail and to sample necrotic wood for fungal isolation. With the aid of morphological and molecular identification techniques, five to twelve fungal taxa were detected per tree. Members of the Nectriaceae family and Botryosphaeria stevensii, the causal agent of stem and branch cankers on many tree species, were frequently isolated from outer xylem. In contrast, H. fraxineus was the dominating species in interior wood layers. Microsatellite genotyping of 77 H. fraxineus isolates helped to identify up to six different genotypes per tree. The role of H. fraxineus and other isolated fungi in the aetiology of ash collar rots are discussed.