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The mycorrhization helper bacterium Streptomyces sp. AcH 505 inhibits Norway spruce root infection and colonisation by the root and butt rot fungus Heterobasidion annosum 005 but not by the congeneric strain Heterobasidion abietinum 331 because of higher sensitivity of H. annosum 005 towards the AcH 505-derived naphthoquinone antibiotic WS-5995 B. Differences in antibiotic sensitivity between two isolates belonging to two species, H. annosum 005 and H. abietinum 331, were investigated by comparative gene expression analysis using macroarrays and quantitative RT-PCR after WS-5995 B, structurally related mollisin and unrelated cycloheximide application. Treatment with 25 µM WS-5995 B for 2 h resulted in a significant up-regulation of expression of inosine-5′-monophosphate dehydrogenase, phosphoglucomutase and GTPase genes, while the expression of genes encoding for thioredoxin and glutathione dependent formaldehyde dehydrogenase was down-regulated in the sensitive fungal strain. No differential expression in the tolerant strain was detected. Application of WS-5995 B at higher concentrations over a time course experiment revealed that H. annosum 005 and H. abietinum 331 responded differently to WS-5995 B. The fungal gene expression levels depended on both the concentration of WS-5995 B and the duration of its application. The WS-5995 B-unrelated cycloheximide caused highly specific changes in patterns of gene expression. Our findings indicate considerable variations in response to bacterial metabolites by the isolates of the conifer pathogen. [ABSTRACT FROM AUTHOR]

Heterobasidion australe sp. nov. is derived from the Heterobasidion insulare complex, and its illustrated description is given. It is similar to H. ecrustosum by morphology but closely related to H. orientale genetically. Heterobasidion australe is characterized by the effused-reflexed to sessile basidiocarps with a reddish-brown crust in the pileus, shining pore surface, regular and small pores, and by slightly smaller basidiospores than those in other taxa of the complex. Heterobasidion australe has so far been recorded only from southern China, where it seems to be relatively common in coniferous forests, growing mostly on dead wood of several genera of gymnosperm trees. Occasionally it has been recorded also on living trees, but its pathogenicity is uncertain. [ABSTRACT FROM AUTHOR]

Sixty-four wild heterokaryotic isolates of Phlebiopsis gigantea were analysed for asexual spore production, growth rate and competitive ability against Heterobasidion in vitro, as well as growth rate in Norway spruce wood. These P. gigantea traits were considered important for controlling infection of Norway spruce stumps by spores of Heterobasidion spp. Ten most promising P. gigantea isolates were crossed with each other and 172 F1 progeny heterokaryons were analysed for the above-mentioned traits. Thirteen most promising progeny heterokaryons were selected and their biocontrol ability against infection by Heterobasidion was compared with the parental isolates in stem pieces of Norway spruce. The results indicated that the progeny strains had generally better traits and control efficacy than the parental strains. The genetic effects accounted for a part of the variations between progeny and parental strains. This further suggests that there is a potential to improve the biocontrol properties of P. gigantea through breeding. [ABSTRACT FROM AUTHOR]

In Norway spruce, a fungistatic reaction zone with a high pH and enrichment of phenolics is formed in the sapwood facing heartwood colonized by the white-rot fungus Heterobasidion parviporum. Fungal penetration of the reaction zone eventually results in expansion of this xylem defense. To obtain information about mechanisms operating upon heartwood and reaction zone colonization by the pathogen, hyphal growth and wood degradation were investigated using real-time PCR, microscopy, and comparative wood density analysis of naturally colonized trees with extensive stem decay. The hyphae associated with delignified wood at stump level were devoid of any extracellular matrix, whereas incipient decay at the top of decay columns was characterized by a carbohydrate-rich hyphal sheath attaching hyphae to tracheid walls. The amount of pathogen DNA peaked in aniline wood, a narrow darkened tissue at the colony border apparently representing a compromised region of the reaction zone. Vigorous production of pathogen conidiophores occurred in this region. Colonization of aniline wood was characterized by hyphal growth within polyphenolic lumen deposits in tracheids and rays, and the hyphae were fully encased in a carbohydrate-rich extracellular matrix. Together, these data indicate that the interaction of the fungus with the reaction zone involves a local concentration of fungal biomass that forms an efficient translocation channel for nutrients. Finally, the enhanced production of the hyphal sheath may be instrumental in lateral expansion of the decay column beyond the reaction zone boundary. [ABSTRACT FROM AUTHOR]

Four-year-old seedlings of Abies nordmanniana ssp. bornmülleriana and 5-year-old seedlings of Abies nordmanniana ssp . nordmanniana were inoculated on the lower stem with 28 Heterobasidion abietinum isolates originating from four different regions of Turkey. Replicate seedlings were incubated in greenhouse and growth chamber. After 7 weeks, infection incidence, mortality, lesion length in the inner bark and fungal growth in the sapwood were examined. Infection incidence in different host–incubation combinations ranged between 70.5 and 79.5% and the average mortality rate was 4.2%. Average lesion lengths varied between 8.4 and 33.9 mm, and average fungal growth between 18.7 and 34.8 mm. There was a significant positive correlation between lesion length in the inner bark and fungal growth in sapwood on both hosts and conditions. Clear differences in virulence between H. abietinum isolates originating from different regions were not found. The results indicate that H. abietinum is pathogenic on both investigated subspecies of A. nordmanniana. Both lesion length and fungal growth were greater on ssp . bornmülleriana, indicating that it would be more susceptible than ssp. nordmanniana. [ABSTRACT FROM AUTHOR]

Abstract: Pairings between heterokaryons and homokaryons of Agaricomycete fungi (he-ho pairings) can lead to either heterokaryotization of the homokaryon or displacement of the homokaryotic nucleus through migration of nuclei from the heterokaryon into the homokaryon. In species of Agaricomycetes with multinucleate cells (>2 nuclei per cell), he-ho pairings could result in the stable or transient formation of a hypha with three genetically different nuclei (trikaryons). In this study, he-ho pairings were conducted using the multinucleate Agaricomycete Heterobasidion parviporum to determine whether trikaryons can be formed in the laboratory and whether nuclear genotype affects migration and heterokaryon formation. Nuclei were tracked by genotyping the heterokaryotic mycelium using nucleus-specific microsatellite markers. The data indicated that certain nuclear combinations were favored, and that nuclei from some strains had a higher rate of migration. A high percentage of trikaryons (19%) displaying three microsatellite alleles per locus were identified among subcultures of the he-ho pairings. Using hyphal tip and conidial isolation, we verified that nuclei of three different mating types can inhabit the same mycelium, and one of the trikaryotic strains was judged to be semi-stable over multiple sub-culturing steps, with some hyphal tips that retained three alleles and others that reduced to two alleles per locus. These results demonstrate that nuclear competition and selection are possible outcomes of heterokaryon-homokaryon interactions in H. parviporum and confirm that ratios of component nuclei in heterokaryons are not strictly 1:1. The high rate of trikaryon formation in this study suggests that fungi with multinucleate cells may have the potential for greater genetic diversity and recombination relative to dikaryotic fungi. [Copyright &y& Elsevier]

We describe and illustrate three Heterobasidion species distributed in East Asia, based on both dried specimens and cultures. Heterobasidion parviporum, formerly known as H. annosum from Asia, is characterized by effused-reflexed basidiocarps with cuticulate pilei, small round pores, thin context and short tubes in each layer. Examination of the type specimen of Trametes insularis revealed that this is distinct from the East Asian species widely known as “ H. insulare”. No prior correct name for this taxon exists, and thus we propose the name H. orientale sp. nov. Heterobasidion orientale is characterized by sessile to effused-reflexed basidiocarps covered by a thin crust, reddish brown pileus with a marginal white zone and regular to labyrinthiform pores. Heterobasidion ecrustosum sp. nov. is characterized by convex basidiocarps frequently covered by a crust only at the base, large regular pores and long tubes. Morphological characters of these three species are compared with other Heterobasidion species. Cultural characters of these three species are also described. All isolates show oedocephaloid conidiophores bearing subglobose to ovoid conidia. Conidia of H. parviporum are smaller than those of the other two species. Descriptions and a key to the known species of Heterobasidion are provided. [ABSTRACT FROM AUTHOR]

The properties of 64 heterokaryotic strains of Phlebiopsis gigantea, isolated mostly from Norway spruce stumps, were tested for asexual spore production, growth rate and competitive ability against Heterobasidion spp. on agar medium, and for growth rate in spruce wood. Eighteen isolates were also tested for the efficacy of control against Heterobasidion spp. in stem pieces of spruce. The results revealed high variation in traits between different P. gigantea isolates. The efficacy of control against Heterobasidion spp. and the growth rate in spruce wood were closely related to each other ( r = 0.727, p < 0.001). These preliminary tests indicate that the growth rate of a P. gigantea strain in spruce wood is the most important characteristic determining its efficiency in controlling the infection and spread of Heterobasidion spp. in spruce stumps. [ABSTRACT FROM AUTHOR]

The management of a Norway spruce [Picea abies (L.) Karst.] stand established on a Heterobasidion coll.-infected site is problematic because the disease spreads vegetatively from the previous to the next generation. This study determined optimal management schedules for such Norway spruce stands growing in southern Finland that had Heterobasidion coll.-colonized stumps from the previous generation. A stochastic simulation model describing the infection and spread of Heterobasidion coll. was used in combination with a non-linear optimization algorithm to find the most profitable management schedules. The thinnings were always conducted in winter. The optimal number of thinnings was either one or two. Increasing discounting rate increased the optimal number and intensity of thinnings, and shortened rotations. The soil expectation value (SEV) of a healthy stand was 7-54% higher than the SEV of stands with Heterobasidion coll.-colonized stumps from the previous generation. Increasing number of colonized clear-felling stumps tended to decrease the number of thinnings, delay thinnings, increase thinning intensity and shorten rotations. The first thinning was in most cases a low thinning, whereas the second thinning, as well as the only thinning of one-thinning schedules, was always a high thinning. The optimal management schedule of a heavily Heterobasidion coll.-infected stand includes one very late and intensive high thinning. If the discounting rate is 2% or more and there are many colonized stumps, optimal rotations are up to 7 years shorter than in a healthy stand. [ABSTRACT FROM AUTHOR]

In forest breeding, growth has been used as the main selection trait in Norway spruce (Picea abies L. Karst.), whereas wood properties or resistance to pathogens have been taken as secondary traits. We aimed to investigate, in laboratory conditions, the rate of wood decay caused by Heterobasidion parviporum (Fr.) Niemelä & Korhonen (strains 5 and 7) in 20 Norway spruce clones. We also studied if, on average, growth, wood density, and fibre properties differed in the most and least decayed clones as well as from pith to bark. After 6 months of incubation, strain 7 effected significantly higher wood decay than strain 5 (mean 16.9% and 1.7%, respectively). The difference between the five most decayed and five least decayed clones by strain 7 was also statistically significant (P < 0.05). Moreover, regardless of clone or strain, the wood decay was highest near the pith and lowest near the bark, which is the opposite for wood density and fibre length and width. However, neither wood density nor fibre properties explained, statistically, the differences in average wood decay and decay from pith to bark. On the other hand, we could identify clones that simultaneously provided high wood quantity and relatively high wood density and low decay rate. [ABSTRACT FROM AUTHOR]

A molecular study using M13 minisatellite amplification was carried out to ascertain the origin of the fungal isolates of Heterobasidion abietinum collected from Abies pinsapo in Andalucia (Spain). Isolates were compared with those from A. alba in neighboring countries. Analysis of molecular variance (AMOVA) detected significant differences between H. abietinum isolates from A. pinsapo and isolates from A. alba in France and Italy. Variance within the population from A. pinsapo was lower. The genetic differentiation of the fungus reflects differences in the distribution of the host species such as A. pinsapo and A. alba. [ABSTRACT FROM AUTHOR]

Genets of Heterobasidion were identified in eight 43- to 56-year-old Norway spruce (Picea abies (L.) Karst.) stands in southern Finland. Four of the stands had been thinned in winter ca. 10 years prior to the study, and four had been left unthinned. It was hypothesized that the felling of decayed trees promotes the vegetative spread of the fungus from thinning stumps into the adjacent trees, and hence the Heterobasidion genets should be larger in thinned stands. Although the number of infected stumps per areal unit was lower and the genets were slightly smaller in the previous tree generation of thinned plots, the genets, particularly the old ones, in the present tree generation were larger on thinned plots. The genets originating from the previous rotation included, on average, 12.2 trees on thinned plots and 6.7 trees on unthinned plots. The mean number of trees infected by new genets (not found in previous generation) was also slightly higher (p < 0.05) on thinned than on unthinned plots, 1.8 and 1.2 trees, respectively. The results indicate that the rapid expansion of old Heterobasidion infections after a thinning operation may significantly contribute to the occurrence of root rot in the residual stand. [ABSTRACT FROM AUTHOR]

Abstract: The necrotrophic pathogen Heterobasidion annosum sensu lato (Fr.) Bref. causes severe root rot on coniferous trees in the boreal and temperate forests. The annual economic losses caused by this fungus in Europe are estimated to at least 790 million €. In managed forests, the major route of infection is via stump surfaces from which the H. annosum s.l. grows through the roots and attacks adjacent healthy trees. A biocontrol method to reduce H. annosum s.l. infection is to apply the wood degrading fungus Phlebiopsis gigantea in a spore solution (Rotstop) directly on the freshly cut stumps immediately after cutting. We investigated the potential risk for a build-up in the capacity of H. annosum s.l. to resist overgrowth by P. gigantea. Wood blocks of Picea abies, precolonized with the two fungal species, were juxtaposed on top of agar and the overgrowth of the P. gigantea strain (Rotstop) on the H. annosum s.l. was measured periodically. We found a natural variation in Heterobasidion parviporum to resist overgrowth by P. gigantea. There was no difference between homo- and heterokaryotic strains. In a mapping population of 91 progenies from a H. annosum hybrid strain we were able to identify one quantitative trait locus (QTL) which controls the examined resistance capacity. We estimated the broad sense heritability to 0.336 for the capacity to resist the P. gigantea overgrowth. We conclude that there exists a theoretical risk for resistance build-up in the H. annosum s.l. population towards its biological control agent P. gigantea. [Copyright &y& Elsevier]

Abstract: The making of high-stumps to benefit wood living organisms is a common practice in Scandinavian forestry. To minimise the cost of this action trees of low quality, e.g. rotten trees, are chosen if possible. In this study we investigated if the wood decay fungi Heterobasidion spp. affects saproxylic beetles assemblages in Norway spruce (Picea abies) high-stumps. In total we caught 43 species of saproxylic beetles (Coleoptera) of which one was red-listed. Associations with the fungi were tested on 13 beetle species and three of them showed negative associations with the occurrence of Heterobasidion, while none of the tested species showed a positive association with Heterobasidion. Species richness did not differ between infected (30) and non-infected (33) stumps, but the beetle assemblages differed to some extent. Two additional bracket fungi species were found on some of the high-stumps, Fomitopsis pinicola and Trichaptum spp. Both these fungi had beetle species significantly associated with them. Interestingly, we found that F. pinicola and Trichaptum spp. never occurred together in the same stumps. None of them, however, seemed to be affected by presence of Heterobasidion spp. In conclusion, Heterobasidion spp. infections influence the beetle fauna by disfavouring some beetle species but we did not find any species positively associated with Heterobasidion spp. This suggests that increasing the proportion of pre-rotten high-stumps could have a negative effect on beetle diversity on clear-cuts. [Copyright &y& Elsevier]

Thirty-five Norway spruce, Picea abies, clones from Sweden were tested for resistance to Heterobasidion parviporum. Rooted cuttings of the clones were planted in Italy and Greece and cultivated for two growing seasons before inoculation with H. parviporum. Extent of infection was determined 6 weeks later. The results were compared to those of earlier inoculations in Sweden. Plant growth traits were under strong genetic control in all locations with broad sense heritability estimates between 0.14 and 0.54. Lesion and fungal extension heritabilities were moderate, H2 ranged from 0.09 to 0.20, and exhibited rather large genetic variation. There was significant genotypic correlation between Italy and Greece with respect to both lesions and fungal extension. No such correlations were found between Sweden and the two other countries. The lack of repeatability in testing susceptibility is unsatisfactory. It could be explained by C-effects associated with propagation of the host plants. Height growth correlated significantly and positively among all countries. [ABSTRACT FROM AUTHOR]

Fruiting of Heterobasidion on cull pieces and stumps of Norway spruce was investigated in cutting areas and mature spruce stands located in southern Finland. Cull pieces of variable size and showing butt rot were left on three clear-cut areas and in one thinned stand. Additionally, a part of the cull pieces was transported to mature forest sites with closed canopy. During the succeeding 3–4 years the cull pieces were investigated annually for sporocarps of Heterobasidion, and the area of actively sporulating pore layer of each sporocarp was measured. Root bases of spruce stumps in the logging areas were excavated and sporocarps found on the stumps also measured. At the onset of the experiment, Heterobasidion spp. were isolated from 76% of the cull pieces showing butt rot; 85% of the isolates were identified as H. parviporum and 15% as H. annosum s.s. During the following 3–4 years sporocarps were found on 20% of the 1938 cull pieces where Heterobasidion butt rot was initially detected visually. Sporocarp formation was promoted by advancement of butt rot, increasing cull piece diameter and end-to-end ground contact, but restricted by the colonization of the cull piece by Stereum sanguinolentum. Between-site differences were significant but could not be explained by differences in tree cover. At the end of the investigation period the average sporulating area of Heterobasidion sporocarp per metre of cull piece was higher than the average sporulating area per stump at three of four logging sites. Hence, leaving cull pieces containing Heterobasidion butt rot at logging areas in southern Finland can considerably increase local production of Heterobasidion spores. [ABSTRACT FROM AUTHOR]

Abies pinsapo, a fir endemic to a small area in southernmost Spain, is frequently attacked in natural stands by Heterobasidion root rot. To identify the Heterobasidion species causing the disease, pure cultures of the fungus were isolated from symptomatic trees in five localities in Sierra de las Nieves Natural Park and identified by pairing tests. In addition, genets of the fungus were identified in two pure stands of A. pinsapo. All the Heterobasidion specimens collected belonged to the species Heterobasidion abietinum. The largest genet found was 57 m long, and had colonized 10 trees. The large size of the main genets implied that H. abietinum had spread via root contacts from old infections generated before the establishment of the Sierra de las Nieves National Park in 1989. Exceptionally dry summers in the last 20 years may have weakened A. pinsapo and favoured spread of the disease. [ABSTRACT FROM AUTHOR]

Amplification profiles of the M13 minisatellite core sequence from 47 isolates of Heterobasidion annosum s.l., collected mostly from Abies alba in different European countries, were analysed in comparison with profiles of four isolates of H. annosum s.s. and three isolates of H. parviporum. Genetic variation within and among groups of populations was studied by analysis of molecular variance. A dendrogram constructed with the Neighbor-Joining method differentiated the three species from each other. Isolates of H. abietinum from Balkan peninsula, Italian peninsula and French Pyrenees each separated into clusters according to geographical origin. Such clear geographic clustering was not detected among isolates from central Europe. The variations between H. abietinum isolates in relation to the migration history of Abies are discussed. [ABSTRACT FROM AUTHOR]

The mechanisms underlying defence reactions to a pathogen attack, though well studied in crop plants, are poorly understood in conifers. To analyze changes in gene transcript abundance in Pinus sylvestris L. root tissues infected by Heterobasidion annosum (Fr.) Bref. s.l., a cDNA microarray containing 2109 ESTs from P. taeda L. was used. Mixed-model statistical analysis identified 179 expressed sequence tags differentially expressed at 1, 5 or 15 days post inoculation. In general, the total number of genes differentially expressed during the infection increased over time. The most abundant group of genes up-regulated upon infection coded for enzymes involved in metabolism (phenylpropanoid pathway) and defence-related proteins with antimicrobial properties. A class III peroxidase responsible for lignin biosynthesis and cell wall thickening had increased transcript abundance at all measurement times. Real-time RT-PCR verified the microarray results with high reproducibility. The similarity of the expression profiling pattern observed in this pathosystem to those documented in crop pathology suggests that angiosperms and gymnosperms use similar genetic programs in responding to invasive growth by microbial pathogens. [ABSTRACT FROM AUTHOR]

The monoterpene composition of Picea abies and Abies alba resin was analysed in relation to growth by Heterobasidion spp. Fifteen-year-old P. abies and A. alba trees were inoculated on branches with three species of Heterobasidion annosum s.l. After 4 months of incubation, each host was colonized to a significantly greater degree by the pathogen specific to that host ( H. parviporum on P. abies, H. abietinum on A. alba) than by the other fungi. Analysis of the enantiomeric monoterpene profiles in the spruce and fir showed that the response in terms of the relative proportions of the monoterpene compounds in the resin differed between tree species. Following challenge with Heterobasidion spp., A. alba trees did not show changes in monoterpene composition in addition to those in the wounding response (increase in (−)- α-pinene and (−)-camphene, and decrease in β-phellandrene). In P.abies, (−)- α-pinene, (+)- α-pinene and δ-3-carene increased following Heterobasidion attack but not after wounding alone. [ABSTRACT FROM AUTHOR]

• The aim of the present study was to determine whether the mycorrhiza helper bacterium Streptomyces sp. AcH 505 could serve as a biocontrol agent against Heterobasidion root and butt rot. • Bacterial influence on mycelial growth of Heterobasidion sp. isolates, on the colonization of wood discs and Norway spruce ( Picea abies) roots was determined. The effect of AcH 505 on plant photosynthesis, peroxidase activity and gene expression, and needle infections were investigated. • AcH 505 was antagonistic to 11 of 12 tested fungal Heterobasidion isolates. The antagonism resulted in a suppression of fungal colonization of Norway spruce roots and wood discs. Mycelial growth rate of the 12th strain, Heterobasidion abietinum 331 was not affected by AcH 505, and colonization of roots by this fungal strain was promoted by AcH 505. Bacterial inoculation led to decreased peroxidase activities and gene expression levels in roots. • AcH 505 promotes plant root colonization by Heterobasidion strains that are tolerant to antifungal metabolites produced by the bacterium. This may result from unknown bacterial factors that suppress the plant defence response. [ABSTRACT FROM AUTHOR]

The article explores the mechanisms and specificity of mycorrhization helper bacteria (MHB). It provides discussions on the mycorrhizosphere, mycorrhizal fungi, the capacity of bacterial strains to enhance fungus growth, inoculation of MHB with low specificity into a nonsterile environment and root colonization. The author notes that the capacity of bacterial strains to enhance fungus growth in vitro is not a useful indicator of MHB activity. Some MHB appear to have specificity for certain strains of mycorrhizal fungus.

It was recently reported that North American (NA) individuals of the forest pathogen Heterobasidion annosum were found in a single pine stand near Rome, in association with the movement of US troops during World War II. Here, we report on some aspects of the invasion biology of this pathogen in Italian coastal pinewoods, and on its interaction with native (EU) Heterobasidion populations. Spores of Heterobasidion were sampled using woody traps in pine stands along 280 km of coast around Rome. DNA of single-spore colonies was characterized by two sets of nuclear and one set of mitochondrial taxon-specific polymerase chain reaction primers. NA spores were found not only in a single site, but in many locations over a wide geographic area. Invasion occurred at an estimated rate of 1.3 km/year through invasion corridors provided by single trees, and not necessarily by sizable patches of forests. Within the 100-km long range of expansion, the NA taxon was dominant in all pure pine stands. Because abundance of the EU taxon is low and identical among stands within and outside the area invaded by NA individuals, we infer that the exotic population has invaded habitats mostly unoccupied by the native species. Discrepancy between a mitochondrial and a nuclear marker occurred in 3.8% of spores from one site, a mixed oak-pine forest where both taxa were equally represented. Combined phylogenetic analyses on nuclear and mitochondrial loci confirmed these isolates were recombinant. The finding of hybrids indicates that genetic interaction between NA and EU Heterobasidion taxa is occurring as a result of their current sympatry. [ABSTRACT FROM AUTHOR]

Spatial distribution of Heterobasidion genets over a period of ca 50 years in two successive generations of Norway spruce ( Picea abies) was unravelled. The genets were first identified in 1993 in a naturally regenerated 43-year-old spruce stand that had been thinned the previous winter. Heterobasidion parviporum was found in 17.5% of the old stumps of the previous spruce generation. Nine genets were identified on the study plot; seven of them were present in old stumps of the previous tree generation and two only in the new spruce generation. Eighteen spruce trees of the new generation were infected, 15 of them by vegetative growth of genets originating from the old stumps. The study plot was investigated again in 2005. No new genets had been established after thinning, and three old genets had died out. The remaining genets had infected five new trees, most likely from the thinning stumps of diseased trees. At the age of 56 years, 16.1% of the residual spruces were infected by Heterobasidion. The results of this study suggest that if spore infection to stumps of spruce can be prevented, the decay frequency caused by H. parviporum will not necessarily increase in successive generations. [ABSTRACT FROM AUTHOR]

Two Rotstop® preparations, one containing a Phlebiopsis gigantea strain from Finland (Rotstop F) and the other one from Sweden (Rotstop S), were used in different concentrations to treat thinning stumps of Picea abies against spore infections by Heterobasidion spp. in southern Sweden. Trees were cut on three sites during the summer of 2004, and 285 stumps were treated manually ensuring 100% coverage. Spore concentrations in the treatment suspensions were ca 5 × 106 and 10 × 106 spores/l, and approximately 10 ml of suspension was applied per 100 cm2 of stump surface. An additional 31 stumps on one of the sites were treated mechanically with Rotstop S; in this treatment the spore concentration was high, about 20 × 106 spores/l, but the coverage was incomplete. Three months later there was a significant reduction in frequency and relative areas of Heterobasidion spp. infections on stumps with manual treatment compared with the untreated stumps. However, there was no significant difference between the preparations or the concentration of active ingredient in terms of their reduction of Heterobasidion infection. Mechanical treatment with incomplete coverage failed to control infection. Therefore, in conditions of moderate Heterobasidion spore load in the environment there seems to be no reason to use higher concentrations of P. gigantea in the treatment of spruce stumps. [ABSTRACT FROM AUTHOR]

The phylogenetic relationships of two Japanese Heterobasidion species, H. annosum sensu lato and an undetermined species, were revealed based on three gene loci, glyceraldehyde 3-phosphate dehydrogenase (gpd), heat shock protein (hsp) and elongation factor 1-α (ef). The tree, based on combined data of gpd, hsp and ef, showed that Japanese H. annosum s.l. was close to the European S-group, forming a subclade. The results of this study also provided strong support for the recognition of the undetermined Heterobasidion sp. as a distinct phylogenetic species closely related to H. araucariae. [ABSTRACT FROM AUTHOR]

Twenty-one basidiocarp specimens of Heterobasidion annosum s.l. were collected in six forest areas in western and central China, from host trees Picea schrenkiana, Abies fabri, Abies fargesii and Larix griffithii. Single-spore cultures were isolated from the basidiocarps and identified by mating tests. All the specimens proved to belong to the species Heterobasidion parviporum. The results show that this fungus has a wide distribution in China. It seems to be a less aggressive pathogen in China than in Europe, although reliable data on the occurrence of Heterobasidion root rot in coniferous forests of China are so far lacking. [ABSTRACT FROM AUTHOR]

Forty-five basidiocarp specimens of Heterobasidion were collected from native Abies species in three locations in western Turkey: A. nordmanniana ssp. bornmülleriana in Bolu province, A. nordmanniana ssp. equi-trojani in Balikesir province and A. cilicica in Antalya province. Pure cultures were isolated from the basidiocarps and identified to the species level with the aid of mating tests. All the specimens proved to belong to the species Heterobasidion abietinum. This root rot fungus is common in the forests investigated and appears to be relatively virulent on Abies in Turkey. This is the first report of H. abietinum outside Europe. [ABSTRACT FROM AUTHOR]

Abstract: Quantitative trait loci (QTL) for mycelial growth rate were identified and positioned on a genetic linkage map of Heterobasidion annosum sensu lato (s.l.), an important root rot pathogen on conifers. The mycelial growth rate among 84 progeny isolates were analysed in two different temperature regimes, 12 and 24°C on malt extract agar and found to segregate as a continuous character. The assay identified three QTL for growth rate at low temperature positioned on the linkage groups 1, 17 and 19 with peak LOD values of 3.2, 2.9 and 4.8, respectively. At the QTL for high temperature growth, peak LOD values of 1.3, 2.8 and 2.2, were identified. The three QTL for the low temperature regime explained 20.9, 18.1 and 24.0 % of the variation in the mycelial growth rate, respectively. The broad-sense heritability was estimated to be 0.97 and 0.95 for growth rate at low and high temperatures, respectively. Two of the QTL for the mycelial growth rate were shown to be tightly linked to the intersterility genes S and P, which control mating within and between closely related species and intersterility groups of H. annosum s.lat. Isolates with a plus allele at the intersterility loci had a higher growth rate than isolates that harboured minus alleles. [Copyright &y& Elsevier]

Twigs of 22 clones of 15-year-old Picea abies grafts were inoculated with Heterobasidion parviporum in July and in September 2003. Fungal growth varied between clones and exclusion of the pathogen varied significantly among clones inoculated in July. The results indicate that twigs exhibit the same infection pattern as cuttings when inoculated with H. parviporum and that exclusion of the pathogen in twigs is a clone-dependent character that occurs during the vegetation period. [ABSTRACT FROM AUTHOR]

Natural root and butt rot infection with Heterobasidion spp. was recorded on three occasions in trees from a 20-year-old Norway spruce [ Picea abies (L.) Karst.] clone trial. In the first assessment, carried out when the trial had been running for 15 years, 29.5% of the trees felled were infected with Heterobasidion spp., but no statistically significant differences were found between the different clones. In the second assessment, also at 15 years, bore cores were taken from 595 trees. Of these cores, 16.5% were infected, but again no statistically significant differences were found between the different clones. Combining the two first assessments also revealed no significant differences. The discrepancy in rot incidence between the two assessments was explained by the inaccuracy of the bore core method. The third assessment was carried out after the trial had been running for 20 years. At that time, 424 trees of 50 clones were felled and sampled. Visible infection was recorded in 46.5% of the trees. The differences between clones were statistically significant and the broad-sense heritability estimate was 0.18. There were no significant genotypic correlations between tree size and rot infection; this is important for the Norway spruce breeding strategy. Calculations show that economic viability would increase by 0.28 SEK per plant for every 10% decrease in root rot frequency at final felling. [ABSTRACT FROM AUTHOR]

Annosum root rot, caused by Heterobasidion annosum s.l., is the economically most devastating disease of coniferous forests in the northern hemisphere. We have analysed virulence of the progeny isolates of a H. annosum interspecific cross between one S and one P homokaryotic isolate from North America. Virulence was measured as mortality rate among 29 pine ( Pinus sylvestris) or 58 spruce ( Picea abies) seedlings per homokaryotic progeny isolate. The assay showed a wide range of virulence among the 97 progeny isolates on pine and segregated as a continuous character. The heritability of virulence on pine was estimated to be 0.088 in this study. A strong correlation between virulence on pine and spruce was also found, although the range of virulence between isolates on spruce was smaller than that on pine. No correlation between high virulence and either fast radial growth rate on malt extract agar or high wood decay capacity was found. [ABSTRACT FROM AUTHOR]

The effectiveness against Heterobasidion natural airborne infections on Norway spruce stumps was tested for six treatments: aqueous suspension of Phlebiopsis gigantea oidiospores, 10%, 20% and 30% aqueous urea solutions, 4% copper oxychloride aqueous solution, and borax powder. The experiment was carried out in four naturally regenerated forests in the western Alps, each characterized by a different airborne inoculum potential. Within each stand, all treatments, with the exception of urea 10%, were effective and resulted in colonized areas of stumps significantly lower than controls. The effect of ambient spore loads on the stump colonization is discussed. [ABSTRACT FROM AUTHOR]

Patterns of spore deposition by Heterobasidion species were studied between the spring of 1998 and December 2000 in four forests in the western Alps using woody traps. The maximum spore deposition rate (DR) ranged from 169 to 1,550 spores m-2 h-1. Although spores were captured from February to October at most sites, inoculum concentration consistently peaked in the late summer or early fall. In one of the four study sites, similar patterns of DR were recorded in 2 years of sampling. A significant correlation (r = 0.654, P = 0.001) was found between DR and the average minimum air temperature in the 4 weeks before sampling. Approximately 1,200 spores were isolated and identified at the species level by polymerase chain reaction-based methods. Single-spore isolates were consistently clampless, indicating the sampled airspora was almost exclusively composed of haploid basidiospores. No significant variations of basidiospore frequencies were detected for either H. abietinum or H. annosum among sampling periods. However, the frequency of H. parviporum spores was always significantly higher in the summer. These findings suggest different patterns of sporulation among Heterobasidion species. [ABSTRACT FROM AUTHOR]

The efficacy of a native isolate ofPhlebiopsis giganteain protecting the stumps ofPinus pineaagainst spore infection byHeterobasidion annosums.str. was investigated. In preliminary tests carried out in stem pieces ofP. pineain confined environment, the efficacy of the isolate was compared with Rotstop®, the commercial formulation prepared from a north EuropeanP. giganteastrain. Both showed a fully protective effect against artificial inoculation ofH. annosum. Moreover, in stump treatment experiments carried out in a coastalP. pineaforest close to Rome, the nativeP. giganteawas effective against heavy airborne inoculum ofH. annosum. Some natural infection byP. giganteaoccurred in the stumps, but it was unable to control the pathogen. Random amplified microsatellite analysis allowed to recognize the presence of differentP. giganteastrains in the forest. [ABSTRACT FROM AUTHOR]

Abstract: A new double-activation catalysis is presented for the Morita–Baylis–Hillman (MBH) reaction of an α,β-unsaturated ketone and an aldehyde by the combined use of a heterobimetallic asymmetric complex and tributylphosphine ((n-Bu)3P) to afford the α-methylene-β-hydroxy ketone with up to 99% ee. [Copyright &y& Elsevier]

Abstract: The SOD1 gene, encoding a manganese-type superoxide dismutase (Mn-SOD), was identified from a Heterobasidion annosum infection-stage cDNA library. The SOD1 gene consists of an open reading frame of 618bp, predicted to encode a protein of 205 amino acids with an estimated molecular mass of 22.7kDa. All conserved amino acids of the Mn-SOD family, including the Parker-Blake signature and four metal-binding residues, are present in the predicted sod1 protein. SOD1 expression is induced by paraquat and during early infection of Scots pine, but is not regulated by nitrogen availability. [Copyright &y& Elsevier]

The aim of this study was to test the usefulness of direct PCR-amplification in analysing fungal diversity in stumps. The analysis was conducted on stumps treated against Heterobasidion spp. using a commercial formulation of Phlebiopsis gigantea (Rotstop), and carried out using denaturing gradient gel electrophoresis (DGGE) of small subunit (SSU) ribosomal DNA (rDNA) fragments PCR-amplified directly from wood DNA samples using two separate fungus-specific primer pairs. On average, two (range 09) different amplification products were observed by DGGE in single wood samples of approximately 500 mm3. The PCR products were classified into operational taxonomical unit (OTU) groups based on their DGGE mobility. Six OTUs could be affiliated with a known species based on a reference fungal collection of 37 species: Heterobasidion annosum, H. parviporum. Hypholoma capnoides, P. gigantea, Resinicium bicolor and Stereum sanguinolentum. Sequence analyses did not give further identifications. OTU profiles from old (6 yr-old) and fresh (1-year-old) Scots pine and Norway spruce stumps from treated and untreated forest plots were compared statistically, and some significant differences were observed in the species composition between the treated and untreated plots. However, the frequency of most of the OTUs did not seem to be affected, and the treatment did not seem to have reduced the overall level of fungal diversity. Based on these results, direct PCR-amplification seems to be useful in analyses of fungal communities in decaying conifer stumps. [ABSTRACT FROM AUTHOR]

A natural first generation hybrid fungus shows interspecific heterozygosity. The nuclear condition of a rare natural hybrid between two taxa of the Heterobasidion complex is investigated. Heterobasidion species are known to be either homokaryotic (haploid) or heterokaryotic (n+n), but heterokaryons are made up of both homokaryotic and heterokaryotic sectors. The natural hybrid appears to be either a heterokaryon undergoing a primary homothallic phase or a diploid with limited ability to exchange nuclei when mated with homokaryons. The natural hybrid is stable and long lived, suggesting hybridization may play an important role in the evolutionary history of this fungal complex. [Copyright &y& Elsevier]

The natural establishment of the root and butt rot causing fungus Heterobasidion annosum s.l. on Norway spruce ( Picea abies) thinning stumps treated with Phlebiopsis gigantea was investigated on seven sites in southern Sweden. The trees were cut during summertime and the stumps were treated with different patterns simulating the effect of mechanical stump treatment with a single-grip harvester. Sampling was conducted 3 and 12 months after treatment. At both samplings, the best control was obtained when 100% of the stump surface was covered by P. gigantea: in contrast, untreated control stumps showed the highest incidences of H. annosum s.l. infection at both sampling times. However, 30 and 26% of the fully covered stumps at the first and second samplings, respectively, were diseased, and question the efficacy of treating Norway spruce stumps with this biological control agent in Sweden. [ABSTRACT FROM AUTHOR]

Crown symptoms and other aboveground variables were examined on 36 Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco.) (40–209 years old), 46 white fir (Abies concolor (Gord. & Glend.) Lindl.) (36–165 years old), and 97 ponderosa pine (Pinus ponderosa Dougl. ex Laws.) (64–220 years old) trees in northern New Mexico and southern Colorado. Root systems of all trees were excavated to determine extent of root disease. Symptoms observed on infected trees, including reductions in height growth, changes in foliage characteristics, and crown dieback, worsened as the number of infected roots increased. Trees with aboveground symptoms had a significantly higher (p < 0.05) number of infected lateral roots than trees without symptoms. In mixed conifer stands on the Archuleta Mesa, Colo., four qualitative crown symptoms were used to accurately detect Armillaria ostoyae (Romagn.) Herink and (or) Heterobasidion annosum (Fr.) Bref. infection of Douglas-fir (21/22, or 95%) and white fir (19/28, or 68%). Similarly, 61% (48/79) of the A. ostoyae infected ponderosa pine trees on the Jemez site, N.M., were detected using the qualitative Thomson vigor rating system. Discriminate analysis, using more thorough variables and analysis, resulted in correct infection classifications of 82%, 85%, and 78% for Douglas-fir, white fir, and ponderosa pine, respectively, suggesting that aboveground variables are reasonable indicators of root disease. [ABSTRACT FROM AUTHOR]

The root-rot fungus Heterobasidion annosum is a major pathogen of woody trees in temperate regions of the world. In this study, seedling root of Scots pine was used as an experimental model to investigate gene expression in conifer trees during challenge with H. annosum. Initial cellular and histochemical studies have established the systems and indicated the key sequence of events during the infection process. Also, to correlate histochemical observations with the time-dependent pattern of events in host gene expression, a transcriptome profiling of a selected set of host genes from a pine-root subtraction cDNA library was conducted. Differential screening of the subset of genes arrayed on nylon membrane with cDNA probes made from seedling roots infected for 1, 3, 7 and 15 days revealed a number of up-regulated genes [disease-resistance gene analog, antimicrobial peptide (AMP) gene homolog etc.] following inoculation. The results also showed strong expression of genes involved in cell defense and protein synthesis at the early stages of the infection (3--7 days) with a decline at late stages of infection (15 days). The decline in expression of key defense genes at late stages of infection correlated well with the period of vascular colonization and subsequent loss of root turgor. Northern analyses with two of the major induced genes (AMP homolog and disease-resistance gene analog) indicated a several-fold increase in host gene expression following infection. In addition, a particular single gene (thaumatin-like protein) was consistently expressed throughout the four sampling periods of the experiment. BlastX analyses revealed that the Scots-pine thaumatin-like gene shared 51--77% sequence homology with other thaumatin-like proteins in GenBank. The impor-tance of these results in tree defense and use of conifer seedling root in host--parasite interaction in forest trees is discussed. [ABSTRACT FROM AUTHOR]

To investigate the taxonomy of Heterobasidion in Eurasia, 49 specimens belonging to H. annosum sensu lato from Asia were identified with the aid of mating tests. Most of the specimens originated from north-eastern and south-western China and from the Altai region in southern Siberia, but a few isolates from Kirghizia, Japan and India were also tested. In addition to mating tests, the material from China was investigated with DNA fingerprinting. Heterobasidion annosum sensu stricto was identified only from the Altai region. Homokaryotic isolates from other specimens, except the Indian ones, were sexually compatible with H. parviporum, but they also showed a high degree of compatibility with H. abietinum and with the North American S group. The isolates from SW China (eastern Himalayas) mated with about equal frequency with the European strains of H. parviporum and H. abietinum. However, the DNA fingerprinting showed that these isolates were more closely related to H. parviporum, and hence they were tentatively included in this species. The North American S group was more distant from these Eurasian taxa. Four old isolates from India mated only weakly with the members of the H. annosum s.lat. According to the species concept presented, the distribution of H. parviporum extends from western Europe through southern Siberia to northern China, Japan and the eastern Himalayas. H. annosum s.str. is so far identified only from the Altai region outside Europe, and H. abietinum only from Europe. [ABSTRACT FROM AUTHOR]