Ecology of Armillaria species on conifers in Japan

Distribution, host preference and pathogenicity of Japanese Armillaria species on conifers were investigated on the basis of field collections of 65 isolates. We identified seven Armillaria species from 19 conifer species including six major Japanese plantation conifers using mating tests and sequences of the translation elongation‐1 α gene. Armillaria mellea, Armillaria ostoyae, Armillaria cepistipes and Armillaria sinapina were frequently collected, whereas Armillaria nabsnona, Armillaria tabescens and a biological species Nagasawa’s E were rare. On the basis of host condition when the isolates were collected, A. mellea, A. ostoyae, A. cepistipes and A. tabescens are considered as moderate to aggressive pathogens of conifers in Japan.     

伐根研究进展

伐根体现了经济和生态双重价值,它既影响立木的利用,又是森林生态系统的重要组成部分,对森林更新、林中野生动物、养分循环均产生影响。综述了目前对伐根研究的进展,同时也提出了需要解决的问题。     

Penetration of Picea sitchensis root bark by Armillaria mellea,Armillaria ostoyae and Heterobasidion annosum

Penetration of root bark tissues of Picea sitchensis by Armillaria ostoyae, Armillaria mellea and Heterobasidion annosum was examined in the absence of wounds, in superficial wounds (rhytidome tissues removed to expose the secondary phloem) and in wounds to the depth of the vascular cambium (deep wounding). Both species of Armillaria penetrated bark without prior wounding, but neither species formed rhizomorphs in this treatment. Armillaria ostoyae penetrated to 39 cell layers in depth by 48 days after inoculation of unwounded bark, whereas A. mellea penetrated 25 cell layers in the same time. Armillaria mellea penetrated superficial wounds significantly more rapidly than did A. ostoyae. Both species produced rhizomorphs within wounded host tissues. Inoculation of deep wounds with Armillaria resulted in a greater depth of bark necrosis with A. mellea than with A. ostoyae. In the absence of wounding, H. annosum failed to penetrate root bark tissues, but in both superficial and deep wounds hyphae penetrated beyond the ligno–suberized boundary zone (LSZ) by 12 days after inoculation. Where no inoculations were made, superficial or deep wounding led within 25 days to the restoration of a structurally continuous LSZ, and by day 48 the wound periderm (WP) was fully differentiated. In inoculated wounds, however, formation of the LSZ and WP was delayed or inhibited in most trees, particularly following inoculation with A. ostoyae or A. mellea. Suberization in the LSZ and WP remained diffuse and discontinuous 48 days after inoculation. Moreover, the presence of WP did not prevent further penetration of the tissues by the pathogens. Variations between trees in the depth of pathogen penetration were noted, possibly indicating differing susceptibilities of individual host genotypes. The possible host factors involved in resistance to penetration of root bark tissues by Armillaria and Heterobasidion are discussed.     

The Armillaria species in Europe

A literature survey is given of the five European honey mushrooms Armillaria mellea, A. borealis, A. bulbosa, A. cepistipes, and A. obscura (syn. A. ostoyae) (corresponding respectively to Korhonen's intersterile groups D, A, E, B, and C); two forms of A. cepistipes are discussed: the tiny A. cepistipes f. cepistipes from Czechoslovakia and West Germany and the more common A. cepistipes f. pseudo-bulbosa Romagnesi et Marxmüller. Nomenclature, geographical distribution, hosts, some characteristics, and practical importance (including pathogenicity) are treated.     

Structural responses in bark to mechanical wounding and Armillaria ostoyae infection in seedlings of Pinus sylvestris

The sequence of events leading to the restoration of an intact periderm surface in the stem bark of Pinus sylvestris following wounding and challenge with Armillaria ostoyae was determined. A sub-erized impervious tissue (SIT) was produced outside the necrophylactic periderm (NP). Al-though A. ostoyae initially infected wounded bark with intracelfularly growing hyphae, these died before penetrating deeply into the bark. Later, intercellularly growing rhizomorphs, which had also developed from the inoculum, penetrated the NP and infected the functional phloem/ cambial zone. Compared to the reactions in uninfected wounded bark, the A. ostoyae infection delayed the formation of NP and reduced the frequency of cells involved in lignification and in SIT, but increased the number of lignified cell layers. The rhizomorph infection reached deeper and lignification was more pronounced in defoliated seedlings than in non-defoliated ones. The importance of structural responses in defence against A. ostoyae is discussed.     

Lesion formation and host response to infection by Armillaria ostoyae in the roots of western larch and Douglas‐fir

The process of lesion formation and host response to natural infection by Armillaria ostoyae were studied in the roots of western larch (Larix occidentalis) and Douglas‐fir (Pseudotsuga menziesii ssp. glauca) trees in the three age classes, 6–8, 18–19 and 85–95 years. The characteristics of lesions on infected roots were recorded and bark samples were dissected from infection points and lesion margins in the field and stored in liquid nitrogen for macroscopic study in the laboratory. Infection in the roots of 6‐ to 8‐year‐old trees advanced freely, overcoming any host resistance, quickly girdling the root collar and killing the trees. In 18‐ and 19‐year‐old trees, however, 43% of infections on western larch and 27% of the infections on Douglas‐fir roots were confined to lesions bounded by necrophylactic periderms with multiple bands of phellem. Host response was similar in 85‐ to 95‐year‐old trees, but the percentage of confined lesions was higher than in younger trees. The results suggest that larch shows resistance to A. ostoyae at a younger age and with greater frequency than Douglas‐fir.     

Penetration and colonization of oak roots by Armillaria mellea in Wisconsin

The level of Armillaria mellea activity on root systems of living and herbicide-killed oâks was assessed. Epiphytic rhizomorphs were almost always present on living and dead oak roots. After an oak was killed or completely defoliated, A. mellea usually penetrated directly through the root-collar bark and spread rapidly in the cambium. Sapwood in the root collar and main lateral roots was colonized within 2 years. The production of thizomorphs from this region was assessed on trees that had been killed by herbicide sprays 2 to 14 years before sampling.     

Rhizomorph production and stump colonization by co‐occurring Armillaria cepistipes and Armillaria ostoyae: an experimental study

In managed spruce forests, Armillaria cepistipes and A. ostoyae are efficient stump colonizers and may compete for these resources when they co‐occur at the same site. The aim of this experiment was to quantify the mutual competitive ability of the two Armillaria species in producing rhizomorphs and in colonizing Norway spruce (Picea abies) stumps. Five isolates of A. cepistipes and two isolates of A. ostoyae were simultaneously inoculated pair‐wise into pots containing a 4‐year‐old spruce seedling. For comparison, each isolate was also inoculated alone. One year after inoculation, stumps were created by cutting down the seedlings. Six months after creation of the stumps, rhizomorph production and stump colonization were assessed. Armillaria spp. were identified from 347 rhizomorphs and 48 colonized stumps. Armillaria cepistipes dominated both as rhizomorphs in the soil and on the stumps. Nevertheless, A. ostoyae was relatively more frequent on the stumps than in the soil and A. cepistipes was relatively more frequent in the soil than on the stumps. In both species, the ability to colonize the stumps in simultaneous inoculations was significantly reduced compared with single inoculations. In respect to rhizomorph production, simultaneous co‐inoculations had a slightly stimulatory effect on A. cepistipes and no significant effect on A. ostoyae. Our study suggests a rather neutralistic co‐existence of A. cepistipes and A. ostoyae as rhizomorphs in the soil. Concerning the ability to colonize stumps, the two species experience a mutual negative effect from the interaction, probably because of interspecific competition.     

Armillaria in an ancient broadleaved woodland

In an ancient broadleaved woodland in eastern England that had been coppiced regularly for over 700 years Armillaria mellea and A. gallica were common, A. tabescens was moderately frequent, whilst A ostoyae and A cepistipes were local. Fruit bodies were often abundant in areas coppiced the previous winter. The largest focus of A gallica occupied 9 ha and was probably over 500 years old. Large trees were rarely killed but A mellea caused some root decay in birches. The number of coppice shoots killed by Armillaria was small but became greater as the period since coppicing increased; A gallica was most often involved. Alder coppice was the most, and hazel coppice the least, affected. The productivity of coppiced woodland in general seemed little reduced by Armilaria.     

Identification and partial characterization of an extracellular manganese-dependent peroxidase in Armillaria ostoyae and Armillaria mellea

Laccase and manganese-dependent peroxidase (Mn peroxidase) activities were detected in the culture media of Armillaria ostoyae and A. mellea. Mn peroxidase was produced in significantly higher quantity by the A. ostoyae isolates and was purified by chromatography from one isolate of this species. Some properties of the purified enzyme were examined (absorption spectrum, H₂O₂ and MnSO₄ optimal concentrations, pH optimum and lactate stimulation). Enzymes of potential importance in the lignin degradation (especially Mn peroxidase) by Armillaria sp. are compared to those of other root-rotting fungi. The possible role of Mn peroxidase in modulating the pathogenicity of Armillaria sp. is discussed.     

The production of rhizomorphs by Armillaria mellea from stumps

The production of rhizomorphs by Armillaria mellea from stumps samples collected in East Anglia was studied: those of broad-leaved trees produced greater yields than those of pines and, in the absence of poisoning, over a much longer period after felling. The ability of A. mellea to form rhizomorphs is often reduced after prolonged growth in pine tissues. The interaction of A. mellea and other fungi is briefly considered. Some implications of these observations for forestry practice are discussed.     

Factors affecting somatic embryogenesis in conifers

This review seeks to examine the extreme response of isolated somatic plant cells of apical meristematic tissues of mature conifer trees towards specific stress conditions in vitro resulting in somatic embryogenesis.Signal molecules regulating embryo development have been described in angiosperms,but very little is known about somatic rejuvenation in conifers.Recent studies on cloning of mature conifers provide new perspectives on signal molecules on cellular dedifferentiation into the embryogenic pathway.Our recent studies show that signal molecules such as butenolide,calcium ions,salicylic acid,antioxidants,amino acids,triacontanol and 24-epibrassinolide all play an important role in the conversion of somatic cells into an embryogenic pathway in many recalcitrant pines.This constitutes a major breakthrough in forest biotechnology with many practical applications in clonal forestry.     

Ungulate browsing on conifers during summer as revealed by DNA

Young trees are particularly vulnerable to browsing by ungulates, since most, or all, of their canopies are within browsing height. In tree species with strong apical dominance, browsing may also affect the structural development of the tree, causing impaired timber quality. Across Sweden, ungulate communities comprise multiple coexisting species, making it a challenge to determine which herbivore species have caused the browsing damages. However, correct identification of the culprits is pivotal for the appropriate management actions to be undertaken. In central Sweden, forest plantation owners recently reported a perceived increase in browsing damages on conifers, primarily Scots pine (Pinus sylvestris). Concurrent with this increase in browsing damages, they noticed an increase in the population of red deer in the area, leading them to suspect that the red deer (Cervus elaphus) were the primary browsers responsible for the damages. Browsed twig samples were sent to us so that we could identify the responsible browsing species using DNA. We discovered that 73.7% of the damages were actually attributable to moose (Alces alces) with 24.7% caused by red deer and 1.5% by fallow deer (Cervus dama). DNA diagnostics can thus yield important information regarding multispecies assemblages enabling managers to correctly identify the relative contributions of different species to browsing damages.     

Freezing behaviors in leaf buds of cold-hardy conifers visualized by NMR microscopy

1H-Nuclear magnetic resonance (NMR) microscopy was used to study freezing behavior in wintering leaf buds of Momi fir (Abies firma Sieb. et Zucc.) and Japanese red pine (Pinus densiflora Sieb. et Zucc.). The images acquired predominantly reflected the density of mobile (i.e., non-ice) protons mainly from unfrozen water. By comparing images taken at various subfreezing temperatures, we determined which tissues produced the high and low temperature exotherms detected by differential thermal analyses. Typical extra-organ freezing was successfully imaged in leaf buds of A. firma. The bud scales readily froze at -7 degrees C, but shoot primordia remained supercooled to -14 degrees C in December buds and to -21 degrees C in March buds. The size of supercooled shoot primordia was reduced with decreasing temperature, indicating a gradual decrease in water content of the shoot primordia. In contrast, the signal from shoot primordia of P. densiflora disappeared between -7 and -14 degrees C, corresponding to the high temperature exotherm at -8 degrees C, indicating extracellular freezing of the shoot primordia. The xylem and bark tissues readily froze at -7 degrees C in A. firma and between -7 and -14 degrees C in P. densiflora. We conclude that NMR microscopy can noninvasively provide more spatially specific information about freezing behavior in leaf buds than traditional methods such as differential thermal analysis. In particular, it allows the organized and harmonized freezing behaviors in complex organs to be visualized directly thereby revealing the diversity of mechanisms involved in freezing behaviors.     

Harvest index in northern temperate cultivated conifers

Harvest index is defined and its relationship with primary production, biomass partitioning and yield components in forest trees examined. As stand density has been found to have a major effect on harvest index, it is concluded that further development of the harvest index concept in forest trees will need to take account of density-yield relationships.     

Identification of European Armillaria species by analysis of isozyme profiles

Studies were carried out to test the possibility of identifying European Armillaria species by using isozyme patterns. Twenty-two different enzymes were used to analyse the haploid and diploid mycelium extract of Armillaria borealis, Armillaria cepistipes, Armillaria gallica, Armillaria mellea, Armillaria ostoyae and Armillaria tahescens. Tests for fumarase (E.C. 4.2.1.1.), aconitase (E.C. 4.2.1.3.), leucine-amino peptidase (E.C. 3.4.11.1.), isocitrate dehydrogenase (E.C. 1.1.1.42.), shikimic dehydrogenase (E.C. 1.1.1.25), glucose-6-P-dehydrogenase (E.C. 1.1.1.49.), malic enzyme (E.C. 1.1.1.40.), 6-P-gluconic dehydrogenase (E.C. 1.1.4.4.), pectin esterase (E.C. 3.1.1.11.), and pectic lyase (E.C. 4.2.99.3.) did not reveal enzyme activity. Isozyme profiles of acid phosphatase (E.C. 3.1.3.2.), phospho-gluco-isomerase (E.C. 5.3.1.9.), peroxidase (E.C. 1.11.1.7.), polyphenoloxidase (E.C. 1.14.18.), malic dehydrogenase (E.C. 1.1.1.37.), glutamic dehydrogenase (E.C. 1.4.1.3.) and superoxide dismutase (E.C. 1.15.1.1.) were ineffective for species identification. In contrast, esterase (E.C. 3.1.1.1.), glutamic-oxalacetic transaminase (2.6.1.1.), phospho-gluco-mutase (E.C. 2.7.5.1.), alcohol dehydrogenase (E.C. 1.1.1.1.), and polygalacturonase (E.C. 3.2.1.15.) isoenzyme patterns showed enough polymorphism to allow the identification of the different Armillaria species. However, it is necessary to compare several enzyme profiles for a conclusive identification. Intraspecific crosses of A tabescens were confirmed by the presence of a heteromeric isozyme pattern of alcohol dehydrogenase and phospho-gluco-mutase.     

Butt rot in conifers caused by Serpula himantioides (Fr.) Karst.

Serpula himantioides was found to be a causal agent of butt rot in Douglas fir and Japanese larch in northern Germany. The decay started predominantly from tap roots and main side roots and extended few meters into the stem. In final stages of rot the basal heartwood was completely destroyed and the residual width of healthy sapwood was reduced. Laboratory tests revealed a tolerance by the fungus to extremely acid substrates.     

Nematological problems in the production of conifers

Several conifer nurseries were visited in Piedmont (Italy) and soil and root-samples were taken and examined for plant-parasitic nematodes. In these investigations damage to the mycorrhizae caused by phytohelminths, most frequently through their trophic activity on the tissue of the host plant, has been observed.     

The silviculture of conifers in Great Britain

The original paper by H.M. Steven, with this title, describedthe silvicultural characteristics of the main coniferous speciesthen available in British forestry. The use of these introducedconifers was justified by the limited site tolerances of theone native species, Scots pine, and the need to expand forestcover on to sites with infertile soils in harsh climatic conditions. This paper reviews the developments in silvicultural techniquesand understanding that have enabled the rapid expansion of productiveforestry in the last seventy years:

• The problems associated with afforestation, requiring ameliorationof soil physical and chemical conditions, have been resolvedand the climatic limits to the use of individual species aremore clearly defined.
• Increased knowledge of the physiologicalresponses of individualspecies to environmental factors hasinfluenced silviculturalpractice from nursery production tothe regeneration of maturestands.
• Analysis of genetic variationwithin introduced conifer specieshas refined their use andis leading to improvements in theirproductivity and timberquality.
• The application of ecological principles, based onthe ecosystemconcept, has led to an understanding of foreststand dynamicsthat should ensure production from exotic specieson a sustainablebasis.

Future requirements in the silviculture of conifers includethe transferof the results of computer simulation modellinginto practice, the developmentof silvicultural systems appropriateto British conditions and greater emphasis on the quality ofproduction.     

Studies on Armillaria mellea in East Africa

The effect of unsterile soil leachates on the colonisation by Armillaria mellea of cylinders of Pinus patula and Cupressus lusitanica was studied and is discussed with relevance to East Africa.