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Peach is a popular and important tree fruit widely produced in the world, and the production of high-quality peach fruit does require management of pests and diseases. In this review, major peach diseases from China, Spain, and USA are described in detail for the benefit of producers, consultants, researchers, and other interested parties. Minor diseases of concern in these countries are also described. Current progress on pathogen resistance to major chemical classes of fungicides as well as current resistance management practices are discussed. Specific cultural practices applied in China, Spain, and USA are also described to provide an overview of peach disease management. A ‘Future Outlook’ section is included at the end of this review to highlight the challenges and opportunities for disease management in the future. [ABSTRACT FROM AUTHOR]

Peach is a popular and important tree fruit widely produced in the world, and the production of high-quality peach fruit does require management of pests and diseases. In this review, major peach diseases from China, Spain, and USA are described in detail for the benefit of producers, consultants, researchers, and other interested parties. Minor diseases of concern in these countries are also described. Current progress on pathogen resistance to major chemical classes of fungicides as well as current resistance management practices are discussed. Specific cultural practices applied in China, Spain, and USA are also described to provide an overview of peach disease management. A 'Future Outlook' section is included at the end of this review to highlight the challenges and opportunities for disease management in the future. [ABSTRACT FROM AUTHOR]

• Trichoderma spp. is a BCA widely studied and used in agriculture. • Armillaria spp. is a globally important pathogen of agricultural/forestry species. • So far, there are 30 studies on the effective control of ARR by Trichoderma. • Trichoderma effectively control Armillaria in different experimental conditions. • So far, there are four mechanisms of action identified in this biological control. • More research is needed on the use of Trichoderma against Armillaria. Trichoderma is a genus of filamentous fungi with several species widely studied and used as biological control agents (BCAs) in agriculture. With respect to fungal disease control, Trichoderma spp. can use different mechanisms of action, including mycoparasitism, antibiosis, competition and/or activation of plant defences. Armillaria spp. are the causal pathogens of Armillaria root rot (ARR) disease, which is widely distributed and of great economic and environmental importance in agriculture and forestry. ARR can be devastating to plant health, through colonisation and rotting of the root system and collar of the infected plant/tree, which can cause a reduction in yield and eventually death. Armillaria can live as a saprophyte that survives on dead plant material, making eradication of ARR extremely difficult. In an exhaustive analysis of work published to date on the control of Armillaria spp. by Trichoderma spp., using the WoS and Scopus databases, we identified 31 papers. We discuss these reports in light of their key findings, including number of publications per year, the countries where they were published, the journals and the citations obtained so far. Although the vast majority do not identify the mechanism of action involved in control, some describe mycoparasitism, antibiosis, competition or modification of the rhizospheric microbiota as being responsible for effective biological control of the pathogen. Further research into these mechanisms and additional in-depth analysis of less studied or currently unidentified mechanisms, such as the activation of plant defences, would be highly beneficial to our understanding of Trichoderma as a BCA of Armillaria. [ABSTRACT FROM AUTHOR]

Species of Armillaria are distributed globally and include some of the most important pathogens of forest and ornamental trees. Some of them form large long-living clones that are considered as one of the largest organisms on earth and are capable of long-range spore-mediated transfer as well as vegetative spread by drought-resistant hyphal cords called rhizomorphs. However, the virus community infecting these species has remained unknown. In this study we used dsRNA screening and high-throughput sequencing to search for possible virus infections in a collection of Armillaria isolates representing three different species: Armillaria mellea from South Africa, A. borealis from Finland and Russia (Siberia) and A. cepistipes from Finland. Our analysis revealed the presence of both negative-sense RNA viruses and positive-sense RNA viruses, while no dsRNA viruses were detected. The viruses included putative new members of virus families Mymonaviridae, Botourmiaviridae and Virgaviridae and members of a recently discovered virus group tentatively named "ambiviruses" with ambisense bicistronic genomic organization. We demonstrated that Armillaria isolates can be cured of viruses by thermal treatment, which enables the examination of virus effects on host growth and phenotype using isogenic virus-infected and virus-free strains. [ABSTRACT FROM AUTHOR]

Armillaria root rot is a fungal infection caused by the fungus “Armillaria”, which can survive for long period in plant remains. Proximity to infected roots can also be a cause for new infection. This bibliometric analysis had been conducted to understand the active authors, organizations, journals, and countries involved in the research domain of “Armillaria root rot”. All published articles related to “Armillaria root rot” from “Scopus”, were analyzed using the VOS viewer to develop analysis tables and visualization maps. This article had set the objective to consolidate the literature regarding the “Armillaria root rot” and also to find out the trends related to the same. Armillaria root rot is an interesting research domain and the most active journals related to this is the Canadian Journal of Forest Research, Forest Ecology and Management, Mycological Research, and Genetics. The USA is the most active country. The top organization focusing on Armillaria root rot is the University Of Pretoria of South Africa. The most active author who had made valuable contributions related to Armillaria root rot is Wingfield M.J., Mccarthy B.C., Rubino D.L., and Small C.J. [ABSTRACT FROM AUTHOR]

Avocado has great socioeconomic importance in Mexico because of the benefits it generates for the production chain participants and the significant foreign exchange earnings engendered by the export of its fruit. However, this crop has phytosanitary problems, caused mainly by fungi, among which the genus Fusarium stands out. The objective of this study was to characterize Fusarium species that caused root rot in avocado trees in Michoacan, Mexico. In 19 isolates of Fusarium spp., polymerase chain reactions (PCR) with primers coding for elongation factor and calmodulin genes were performed. These sequences were compared in homology using BLAST analysis and aligned in MEGA 6.0. Cladograms were created based on maximum verisimilitude. The pathogenicity of the isolates was evaluated based on their virulence and severity in the avocado plants. Morphological and molecular analyses showed that 15 isolates belonged to F. oxysporum Schl and four to F. solani Mart. All isolates were pathogenic, with virulence ranging from 16 to 56 days. All isolates produced root rot and yellowing of leaves, with 63% producing wilting and 16% producing apical necrosis, the latter being the most severe. [ABSTRACT FROM AUTHOR]

The primary focus of the stone fruit rootstock program at Byron, GA, has been the development of disease-resistant rootstocks for peach (Prunus persica L. Batsch). Historically peach tree short life (PTSL), aka bacterial canker complex, and Armillaria root rot (ARR) have been the two most important causes of premature mortality of commercial peach trees in the southeastern United States. Guardian®, a seedling peach rootstock, was cooperatively released in 1993 by the U.S. Department of Agriculture (USDA)-Agricultural Research Service (ARS) and Clemson University. It has since been widely adopted by the southeastern peach industry. As a result, trees losses to PTSL have declined sharply. However, Guardian, like most other peach seedling rootstocks, is susceptible to ARR. ARR has now moved to the forefront as the primary cause of premature peach tree death in the Southeast. In response to this threat, the USDA-ARS in cooperation with the University of Florida, released 'Sharpe', a plum hybrid rootstock in 2007. Despite its broad disease resistance, 'Sharpe' proved unsuited for widespread commercial utilization due to its relatively poor cropping performance. In 2011, 'MP-29', a semidwarf, clonal, plum × peach hybrid, was released for commercial trial. 'MP-29's broad disease and nematode resistance, in combination with its dwarfing ability and excellent productivity, offered great promise for use in this production area and in others suffering from similar issues. Since its release, testing of 'MP-29' has continued both in researcher and grower trials. To date, performance has exceeded all expectations. [ABSTRACT FROM AUTHOR]

Western redcedar (WRC) trees of 48-49 years in age grown in monoculture and in admixtures with birch, Douglas-fir and pine in the interior of British Columbia were sampled for wood density and the presence and level of damage from butt decay initiated by Armillaria ostoyae in stumped and unstumped plots. Stump removal reduced butt decay incidence in WRC from 18% to 2% and damage from 3.5% of the diameter at base to 0.3% compared to when stumps remained. External lesions on tree bases caused by Armillaria root disease increased the probability of WRC stems having butt decay by 1.25 times for an average-sized lesion. The incidence of butt decay and the level of internal damage to WRC in sampled plots was not related to admixture, tree size or site index. Stump removal controlled the inoculum of Armillaria root disease, thereby reducing incidence and size of WRC basal lesions that probably act as infection courts for other fungi causing butt decay. WRC trees grown in monoculture or with birch had the highest wood densities of all planting mixes tested. Wood density in WRC was lowest at the outer edges of individual WRC trees, in larger trees, and in plots where stumps had not been removed. The lower density WRC wood is thought to occur by overtopping from fast-growing species in admixture and depletion of soil moisture affecting latewood formation. This is a first report of stump removal affecting butt decay and admixture affecting wood density in WRC. [ABSTRACT FROM AUTHOR]

Prunus dulcis (almond) is one of the most susceptible horticultural crops to Armillaria root disease. Resistance to Armillaria mellea and Armillaria tabescens, the geographically isolated causal fungi that attack almond and closely related Prunus persica (peach), has been evaluated in studies of almond, peach, and other Prunus rootstocks, but not in one comprehensive study. We evaluated the relative resistance to A. mellea and A. tabescens of six clonally propagated almond and peach rootstocks (Bright's 5, Empyrean 1, Hansen 536, Krymsk 1, Krymsk 86, and Lovell) in comparison with that of clonally propagated Marianna 2624 rootstock (resistant control) and clonally propagated Nemaguard rootstock (susceptible control). Replicate clones used in the growth chamber assay were micropropagated and rooted in vitro before inoculating the culture medium with Armillaria spp. At 2 months, the most resistant and susceptible rootstocks were Krymsk 86 and Hansen 536, respectively, with 27% vs. 89% mortality. This finding was consistent among two isolates of A. mellea and one isolate of A. tabescens in three replicate experiments. Our finding of low mortality among Krymsk 86, Krymsk 1, and Marianna 2624, which all share Prunus cerasifera (Myrobalan plum) parentage, is consistent with past reports of resistance in the field to A. mellea, but conflicts with reports of susceptibility to A. tabescens. Resistance to A. tabescens of genotypes with Myrobalan plum parentage in our assay may reflect the simplified rooting environment of tissue culture medium, which does not perfectly mimic a field trial, in which biotic and abiotic factors may affect host resistance. Nonetheless, our growth chamber assay may provide a more rapid alternative to identify sources of resistance for breeding and to screen progeny of such crosses. [ABSTRACT FROM AUTHOR]

Background: Armillaria is a globally distributed mushroom-forming genus composed primarily of plant pathogens. Species in this genus are prolific producers of rhizomorphs, or vegetative structures, which, when found, are often associated with infection. Because of their importance as plant pathogens, understanding the evolutionary origins of this genus and how it gained a worldwide distribution is of interest. The first gasteroid fungus with close affinities to Armillaria--Guyanagaster necrorhizus--was described from the Neotropical rainforests of Guyana. In this study, we conducted phylogenetic analyses to fully resolve the relationship of G. necrorhizus with Armillaria. Data sets containing Guyanagaster from two collecting localities, along with a global sampling of 21 Armillaria species--including newly collected specimens from Guyana and Africa--at six loci (28S, EF1α, RPB2, TUB, actin-1 and gpd) were used. Three loci--28S, EF1α and RPB2--were analyzed in a partitioned nucleotide data set to infer divergence dates and ancestral range estimations for well-supported, monophyletic lineages. Results: The six-locus phylogenetic analysis resolves Guyanagaster as the earliest diverging lineage in the armillarioid clade. The next lineage to diverge is that composed of species in Armillaria subgenus Desarmillaria. This subgenus is elevated to genus level to accommodate the exannulate mushroom-forming armillarioid species. The final lineage to diverge is that composed of annulate mushroom-forming armillarioid species, in what is now Armillaria sensu stricto. The molecular clock analysis and ancestral range estimation suggest the most recent common ancestor to the armillarioid lineage arose 51 million years ago in Eurasia. A new species, Guyanagaster lucianii sp. nov. from Guyana, is described. Conclusions: The armillarioid lineage evolved in Eurasia during the height of tropical rainforest expansion about 51 million years ago, a time marked by a warm and wet global climate. Species of Guyanagaster and Desarmillaria represent extant taxa of these early diverging lineages. Desarmillaria represents an armillarioid lineage that was likely much more widespread in the past. Guyanagaster likely evolved from a gilled mushroom ancestor and could represent a highly specialized endemic in the Guiana Shield. Armillaria species represent those that evolved after the shift in climate from warm and tropical to cool and arid during the late Eocene. No species in either Desarmillaria or Guyanagaster are known to produce melanized rhizomorphs in nature, whereas almost all Armillaria species are known to produce them. The production of rhizomorphs is an adaptation to harsh environments, and could be a driver of diversification in Armillaria by conferring a competitive advantage to the species that produce them. [ABSTRACT FROM AUTHOR]

Brassicaceous plants rich in glucosinolates have been used as biofumigants for the management of soilborne pathogens. Efficacy of Brassica plant tissue has mainly been attributed to toxic isothiocyanates released upon the hydrolysis of glucosinolates. Management of Phytophthora cinnamomi, the causal agent of oak root rot in rangeland ecosystems using biofumigation, is promising, but requires further validation. The biofumigation activity of 14 brassicaceous plants was evaluated under experimental conditions. All evaluated plants rich in sinigrin suppressed (100%) the mycelial growth of P. cinnamomi, while plants rich in aromatic or other aliphatic glucosinolates had little or no suppressive effect. Simulating soil amendment in field conditions, the effects on natural soil artificially infested with P. cinnamomi chlamydospores were examined with Brassica juncea, Eruca vesicaria and Lepidium sativum, three species with different glucosinolate profiles. Only B. juncea decreased the viability of chlamydospores significantly in comparison with untreated soil only 1 day after biofumigation, whereas E. vesicaria needed 8 days to reach significance and L. sativum had no effect at all. Despite the decreases in soil inoculum, biofumigation with B. juncea did not prevent the root infections in a highly susceptible host ( Lupinus luteus). However, biofumigation with plants rich in sinigrin, such as B. juncea, decreased P. cinnamomi soil inoculum under the experimental minimum threshold for oak disease expression. Although biofumigation should be considered as an effective measure to be incorporated in integrated control of the oak disease, biofumigation by itself would not be effective enough for the substantial suppression of P. cinnamomi inoculum. [ABSTRACT FROM AUTHOR]

The genomes of Armillaria fuscipes, Ceratocystiopsis minuta, Ceratocystis adiposa, Endoconidiophora laricicola, E. polonica, and Pénicillium freii DAOMC 242723 are presented in this genome announcement. These six genomes are from plant pathogens and otherwise economically important fungal species. The genome sizes range from 21 Mb in the case of Ceratocystiopsis minuta to 58 Mb for the basidiomycete Armillaria fuscipes. These genomes include the first reports of genomes for the genus Endoconidiophora. The availability of these genome data will provide opportunities to resolve longstanding questions regarding the taxonomy of species in these genera. In addition these genome sequences through comparative studies with closely related organisms will increase our understanding of how these pathogens cause disease. [ABSTRACT FROM AUTHOR]

The genomes of Armillaria fuscipes, Ceratocystiopsis minuta, Ceratocystis adiposa, Endoconidiophora laricicola, E. polonica, and Penicillium freii DAOMC 242723 are presented in this genome announcement. These six genomes are from plant pathogens and otherwise economically important fungal species. The genome sizes range from 21 Mb in the case of Ceratocystiopsis minuta to 58 Mb for the basidiomycete Armillaria fuscipes. These genomes include the irst reports of genomes for the genus Endoconidiophora. The availability of these genome data will provide opportunities to resolve longstanding questions regarding the taxonomy of species in these genera. In addition these genome sequences through comparative studies with closely related organisms will increase our understanding of how these pathogens cause disease. [ABSTRACT FROM AUTHOR]

Two studies were undertaken in a young New Zealand Pinus radiata stand to find a biological control agent for armillaria root disease caused by Armillaria novae-zelandiae. Fresh thinning stumps were inoculated with saprophytic basidiomycete species as wooden dowel cultures or as homogenized aqueous mycelial suspensions, while all stumps were also inoculated with dowel cultures of A. novae-zelandiae. After a period of between one and two years, no differences were found among test fungi in the percentage of Armillaria species isolated from stumps. However, inoculation of Stereum sanguinolentum as homogenate, and of Phlebiopsis gigantea, Sistotrema brinkmannii, Hypholoma acutum and Rigidoporus concrescens as dowel cultures, significantly increased their isolation incidence in comparison with stumps not treated by these species. Phlebiopsis gigantea, Resinicium bicolor and R. concrescens were also isolated with greater frequency nearer to their dowel inoculation points. Results suggest that P. gigantea and S. sanguinolentum should be included in further testing. However, a future trial is likely to be more effective if evaluation is directed towards the portion of the stump below the soil surface, particularly the root system. [ABSTRACT FROM AUTHOR]

Ectomycorrhizal symbiosis is essential for the life and health of trees in temperate and boreal forests where it plays a major role in nutrient cycling and in functioning of the forest ecosystem. Trees with ectomycorrhizal root tips are more tolerant to environmental stresses, such as drought, and biotic stresses such as root pathogens. Detailed information on these molecular processes is essential for the understanding of symbiotic tissue development in order to optimize the benefits of this natural phenomenon. Next generation sequencing tools allow the analysis of non model ectomycorrhizal plant-fungal interactions that can contribute to find the “symbiosis toolkits” and better define the role of each partner in the mutualistic interaction. By using 454 pyrosequencing we compared ectomycorrhizal cork oak roots with non-symbiotic roots. From the two cDNA libraries sequenced, over 2 million reads were obtained that generated 19552 cork oak root unique transcripts. A total of 2238 transcripts were found to be differentially expressed when ECM roots were compared with non-symbiotic roots. Identification of up- and down-regulated gens in ectomycorrhizal roots lead to a number of insights into the molecular mechanisms governing this important symbiosis. In cork oak roots, ectomycorrhizal colonization resulted in extensive cell wall remodelling, activation of the secretory pathway, alterations in flavonoid biosynthesis, and expression of genes involved in the recognition of fungal effectors. In addition, we identified genes with putative roles in symbiotic processes such as nutrient exchange with the fungal partner, lateral root formation or root hair decay. These findings provide a global overview of the transcriptome of an ectomycorrhizal host root, and constitute a foundation for future studies on the molecular events controlling this important symbiosis. [ABSTRACT FROM AUTHOR]

Armillaria species display diverse ecological roles ranging from beneficial saprobe to virulent pathogen. Armillaria solidipes (formerly A. ostoyae), a causal agent of Armillaria root disease, is a virulent primary pathogen with a broad host range of woody plants across the Northern Hemisphere. This white-rot pathogen grows between trees as rhizomorphs and attacks sapwood as mycelial fans under the bark. Armillaria root disease is responsible for reduced forest productivity due to direct tree mortality and non-lethal infections that impact growth. Here, we characterize a transcriptome of a widespread, virulent genet (vegetative clone) of A. solidipes isolated from a mycelial fan on a natural grand fir ( Abies grandis) sapling in northern Idaho, USA. cDNA from polyA+-purified total RNA was sequenced using a single-end read approach on the Illumina GAIIx platform which generated 24 170 384 reads. A BLASTx search against the NCBI nr database using 39 943 de novo assembled contigs resulted in 24 442 sequences with significant hits (e-value < 1e−3), predominantly to fungi (85%). A filtered data set of 20 882 assembled transcripts that encoded putative homologous fungal proteins was created and used for all subsequent analyses. Signal P identified 10 668 putative signal peptides from these fungal transcripts, and 14 360 were annotated with gene ontology terms. Several sequences showed strong homology to annotated genes with functions in pathogenesis, specifically those involved in plant cell wall degradation and response to the post-infection host environment. This transcriptome contributes to the growing body of resources for studies on fungal pathogens of woody plants, and our results provide useful insights towards identifying specific genes with potential roles associated with pathogenesis and other metabolic functions. [ABSTRACT FROM AUTHOR]

Incidence of peach [ Prunus persica (L.) Batsch] tree mortality attributed to Armillaria root disease was assessed from 2009 to 2011 in 15 orchards in the State of Mexico, Mexico. Incidence increased gradually every year of assessment, reaching average values of 9.7, 15.3 and 20.3% tree mortality and 23.2, 24.7 and 28.3% disease-impacted area of the orchards during 2009, 2010 and 2011, respectively. The cultivars 'Nemaguard' and 'Criollo of La Goleta', a local rootstock used in the region, were both susceptible to the disease. To identify species of Armillaria isolated from infected peach trees, two nuclear rDNA regions (partial 5.8S-ITS2- LSU D-domains and partial 3′ LSU-IGS1) and the translation elongation factor-1α ( tef-1α) gene were sequenced and compared with sequences of known Armillaria species. DNA sequence analysis from 49 Armillaria isolates revealed that five isolates (10.2%) were Armillaria mellea and eight isolates (16.3%) were Armillaria gallica. DNA sequences from the remaining 36 isolates (73.5%) showed no close similarity to Armillaria sequences in GenBank, and apparently represent an undescribed Armillaria species. This undescribed species was the most widely distributed in the region of study. Separate phylogenetic analyses of the LSU region ( D1- D3 domains concatenated with the partial 3′ end) and the tef-1α region show that the undescribed species is quite distinct from other Armillaria spp. reported in North America. [ABSTRACT FROM AUTHOR]

The most common rootstock for Juglans regia (Persian or "English" walnut) in California is Paradox, typically a hybrid of J. hindsii (Northern California black walnut) x J. regia. Unfortunately, Paradox is very susceptible to Armillaria root disease. The relative resistance to Armillaria mellea of six clonally propagated Paradox rootstocks (AX1, Pxl, RR4 11A, RX1, Vlach, VX211) was evaluated and compared with that of clonally propagated J. hindsii rootstock selection W17, J. regia scion cultivar Chandler, and Pterocarya stenoptera (Chinese wingnut). In a growth-chamber assay, plants were micropropagated and rooted in vitro before inoculating the culture medium with A. mellea. At two months post-inoculation, the most resistant and susceptible Paradox rootstocks were AX1 and VX211, respectively, with 9% vs. 70% mortality, and this finding was consistent across three isolates of A. mellea and three replicate experiments. This broad range of resistance within Paradox is consistent with past field trials that tested other genotypes. Our finding of similarly high susceptibility of 'Chandler' and W17 (61% vs. 69% mortality) is in contrast to two field trials, in which other /. regia genotypes were more susceptible than those of J. hindsii. A third trial, however, identified some J. regia genotypes as more resistant than those of J. hindsii. Therefore, it is possible that W17, which was not previously tested, is an Armillaria-susceptible genotype of J. hindsii. Based on our findings of repeatable mortality levels across three isolates of A. mellea and three replicate experiments, the growth-chamber assay has promise, albeit with confirmed resistant and susceptible controls, for identifying putative resistant rootstocks (e.g., AX1) in preparation for a field trial with controlled inoculations. [ABSTRACT FROM AUTHOR]

Trunk infusion of peach with propiconazole has been suggested as a potential strategy to protect roots from colonization by Armillaria species. In the present study, we investigated the persistence of propiconazole in peach roots following fall infusions and its potential for Armillaria root rot control in a commercial peach orchard. Four 12-year-old trees were infused with either 2 liters of a propiconazole solution at 0.4 mg ml-1 or water in September 2007. Bark tissue collected from primary roots of propiconazole-infused trees 48 hr and 6 and 12 months after infusion and analyzed using gas chromatography-mass spectroscopy contained 6.4, 1.4, and 0.9 μg propiconazole per gram fresh bark, respectively. Asymptomatic trees adjacent to trees that had died from Armillaria root rot (protective treatment) and symptomatic but alive trees (curative treatment) were infused with 1 liter of a propiconazole solution (0.4 mg ml-1) in spring and fall of 2008 and 2009 at a commercial peach orchard planted in 2005. Trees were rated for Armillaria root rot severity 6, 12, 24, and 36 months post-infusion. In the protective treatment, the survival rate in both non-infused and infused trees was 80% 36 months post-infusion. However, more (60%) of the propiconazole-infused trees remained asymptomatic compared to the control trees (30%). A significant difference was observed between the non-infused and propiconazole-infused trees following curative treatment. None of the control trees were alive after 36 months compared to 40% of propiconazole-infused trees. We conclude that fall infusion of peripheral trees of infection centers with propiconazole can slow the expansion of Armillaria root rot infection centers in commercial peach orchards. [ABSTRACT FROM AUTHOR]

We used allometric relationships to quantify Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) stem and crown adaptation to Armillaria root disease (caused by Armillaria ostoyae (Romagn.) Herink). At four sites, we measured height, diameter, height to live crown, crown width and length, sapwood area at base of live crown, and infection duration for healthy and infected Douglas-fir trees. Diseased trees were on average smaller than healthy trees for all measured variables, but there were also proportional changes between tree parts suggesting allocation shifts to disease. Infected trees were shorter in relation to stem diameter compared with healthy trees by 4% on average. Crown diameter was positively related to stem diameter (0.24 m·cm-1) but not to disease or competition. Diseased tree crown lengths were on average 0.5 m shorter for a given crown diameter than healthy trees-akin to response to light competition except this also occurred in the upper canopy. Prolonged infection reduced crown length probably through shedding of lower branches and by reducing stem apical growth, possibly related to changed hydraulic architecture or light requirements. Crown surface area was related to stem sapwood area (0.81 m2·cm-2) but unaffected by disease or competition. We discuss how shifting allocation could reveal important implications for life strategies involving whole tree adaptations to disease and tree to tree interactions, and for wood quality and forest inventory. [ABSTRACT FROM AUTHOR]

Root collar excavation (RCE) has been applied to established citrus trees and grapevines for Armillaria root rot (ARR) control but, despite its demonstrated effectiveness, this cultural management system is not routinely used for ARR protection in disease-infested replant sites. One major drawback is the difficulty of excavating the belowground root collar, the potential of excavated roots to be covered again with sur- rounding soil, and the associated labor cost. In this study, a new cul- tural method was investigated that resulted in trees with aboveground excavated root collars, potentially eliminating many of the drawbacks. Experimental peach trees were planted in two commercial orchards (designated Landrum and Monetta) in South Carolina; each tree re- placed one that had declined from ARR disease the year before. Trees were planted approximately 40cm higher than normal in open-bottom Smart Pots and root collars were excavated above ground level 8 months later. Five years after planting, 30 and 70% of all control trees (planted according to grower standard) had declined from ARR disease in Landrum and Monetta, respectively, whereas only 0 and 1O%, respectively, of trees in the aboveground root collar excavation (AG- RCE) treatment had declined. The difference in disease pressure be- tween the two locations could not be attributed to differences in nema- tode pressure. Nonexcavated trees in Smart Pots revealed significantly less tree decline (P ≤ 0.05) compared with the control but tree decline in both locations was greater compared with the AG-RCE treatment (P ≤ 0.05). Trees in the AG-RCE treatment were as vigorous as the con- trols but produced more root suckers. In this 'rototype' tudy, we demonstrate the potential of aboveground root collar excavation for ARk management. Its potential for commercial use is discussed. [ABSTRACT FROM AUTHOR]

Ponderosa pine ( Pinus ponderosa) in the Black Hills National Forest, SD, USA, was surveyed for Armillaria root disease (ARD). The root pathogen Armillaria ostoyae occurred on ponderosa pine seedlings, saplings, pole-size trees and large-diameter trees. The mean incidence of aboveground disease symptoms by stem count was low (0.2%), but in certain areas, the incidence was higher, affecting the regeneration success and tree longevity. Symptomatic ponderosa pine were in areas characterized by having higher elevation, greater annual precipitation, more seedlings, bigger large-diameter trees and greater odds of past harvesting activity than in areas without root disease. Stump density was positively spatially correlated with root disease incidence. No particular soil type was related to disease occurrence; though, in areas with symptomatic trees, soil available water holding capacity (AWC) was greater and soil permeability was less where root disease was present. Spatial analysis confirmed the relationships found in linear correlations, with soil AWC and stump density positively and soil permeability negatively correlated with per cent infected stems ha−1 and basal area infected. [ABSTRACT FROM AUTHOR]

The translation elongation factor-1 alpha (EF-1α) gene was used to examine the phylogenetic relationships among 30 previously characterized isolates representing ten North American Armillaria species: A. solidipes (= A. ostoyae), A. gemina, A. calvescens, A. sinapina, A. mellea, A. gallica, A. nabsnona, North American biological species X, A. cepistipes, and A. tabescens. The phylogenetic relationships revealed clear separation of all ten North American Armillaria species, with the exception of one A. gallica isolate that perhaps represents an unnamed cryptic species. These results indicate that the EF-1α gene could potentially serve as a diagnostic tool for distinguishing among currently recognized North American biological species of Armillaria. [ABSTRACT FROM AUTHOR]

A stand of ponderosa pine (Pinus ponderosa) severely affected by Armillaria root disease was treated with five different levels of sanitation by root removal to reduce root disease losses in the regenerating stand. Treatments included the following: (1) all trees pushed over by machine, maximum removal of roots by machine ripping, and visible remaining roots removed by hand; (2) all trees pushed over by machine and maximum removal of roots by machine ripping; (3) all trees pushed over by machine with no further removal of roots; (4) smaller trees pushed over by machine but large stumps left, otherwise maximum removal of roots by machine ripping; and (5) all trees felled and removed by skidding, area cleared of slash, sod scalped, and no removal of roots. After 35 years, we found that the more intense and thorough root-removal treatments were generally more effective in reducing the occurrence of Armillaria root disease. However, even the most intensive treatment (treatment 1), which experienced significantly less disease than most other treatments, had 23% of the area expressing mortality. The only operationally feasible treatment (treatment 3) also reduced levels of mortality, but not significantly (40% mortality versus 52% in the control, treatment 5). Although these results support the concept that inoculum removal can reduce root disease levels, the treatment necessary to provide a meaningful reduction in disease loss does not seem to warrant its cost. [ABSTRACT FROM AUTHOR]

This trial, conducted near Nakusp, British Columbia, compares pushover logging (combination tree felling and root removal technique using large machines to push trees out of the ground) with handfalling logging (no root removal) for effects on the incidence of armillaria root disease in postharvest regeneration. Pushover logging did not reduce levels of root disease, expressed as percentage tree mortality, over handfalling harvesting on this site. High variability of measured disease levels within some treatments and few replicates lowered the power of the trial. However, in addition to being statistically insignificant, the mean differences between the two main treatments were small and biologically uninteresting, and the response was inconsistent in direction. The trial also included three mature timber retention levels as treatments, and there seemed to be a trend of declining root disease with increased retention of stems. This phenomenon should be further investigated as current literature is not clear on the response of armillaria to partial harvesting. There was a strong suggestion of a difference between susceptibility of natural and planted seedlings to armillaria root disease, with natural regeneration being less susceptible. Thuja plicata Donn ex D. Don was less affected by armillaria root disease than other species in this trial, whether it was planted or naturally regenerated. [ABSTRACT FROM AUTHOR]

Results are presented from several studies on the epidemiology of Armillaria ostoyae in Douglas-fir plantations in the interior cedar-hemlock (ICH) biogeoclimatic zone of British Columbia. Two plantations were monitored for mortality by A. ostoyae and other agents for 35 years after establishment. In these and other plantations ranging in age from 7 to 32 years, one or more of the following factors were determined: source of inoculum, mode of spread and characteristics of lesions on roots of excavated trees; symptom expression in relation to tree age and damage to the root system and years from initial infection to death on trees killed by the fungus. Mortality from A. ostoyae began in both plantations about 5 years after planting, reaching 30% in one and 11% in the other after 35 years. The spatial pattern of mortality was similar to that reported from New Zealand, France and South Africa; however, the temporal pattern differed, beginning later and, instead of declining, continuing at a nearly constant rate to the present. To age 10, nearly all infections were initiated by rhizomorphs; as plantations aged, the proportion of infections occurring at root-root contacts increased. In seven plantations, in moist and wet subzones of the ICH, from 23 to 52% of Douglas-firs had root lesions, with the higher incidences occurring on moist sites. The occurrence of aboveground symptoms, reduced leader growth and basal resinosis, was related to the percentage of root length colonized by A. ostoyae on trees with more than 30% of root length killed. Average time from infection to death increased from 1 to 2 years at age 6 to 22 years at age 33. The outlook for timber yield from Douglas-fir plantations in the cedar-hemlock zone is discussed. Management alternatives for reducing damage from A. ostoyae when regenerating sites are reviewed. [ABSTRACT FROM AUTHOR]

The article presents abstracts on plant disease topics which include the bacterial stem and root rot of sweet potato caused by Ervinia chrysanthemi in China, shoot blight in kiwifruit caused by botryosphaeria dothidea and Armillaria root disease pathogen.

Species of Armillaria were identified from 645 isolates obtained in a nation-wide survey in Albania. The material was collected from ca. 250 permanent plots, established for monitoring forest health, and from forests and orchards attacked by Armillaria. Armillaria mellea s.s. occurred on several coniferous and broadleaved trees in most areas examined, although it was absent above 1100-1200 m in northern Albania. This species damaged Abies and Quercus spp. and, to a lesser extent, other forest trees. Armillaria mellea was also commonly recorded causing damage in orchards and vineyards. Armillaria gallica was a common saprophyte or weak pathogen in coniferous and deciduous forests at altitudes from 600 to 1600 m, and less commonly on oaks at lower altitudes. Armillaria ostoyae was rare in central and southern Albania, but common in northern Albania, causing significant damage to pine and other conifers, mostly at altitudes from 600 to 1800 m. Armillaria cepistipes was recorded at altitudes from 800 to 1800 m as a saprophyte or weak pathogen on conifers and deciduous trees, mostly in beech and silver fir forests. Armillaria tabescens was found in oak forests at altitudes from sea level to 900 m. In orchards, A. tabescens occasionally attacked almond and pear trees. Armillaria borealis was found in a few locations in northern Albania, at altitudes from 800 to 1800 m. [ABSTRACT FROM AUTHOR]

Symptoms of Armillaria root rot were observed on the herbaceous ornamental, Hemerocallis sp. (daylily), in a residential area in Walhalla, South Carolina, which was surrounded by dense, hardwood forest that also contained diseased hosts. Our objectives were to describe a natural occurrence of Armillaria root rot on daylily, a newly discovered host for the pathogen, and to characterize the Armillaria species involved. To characterize the Armillaria species collected from daylily, we used all available methods, including both traditional (sexual compatibility tests, basidiome morphology) and molecular (phylogenetic analyses of rDNA internal transcribed spacer, ITS, and intergenic spacer I, IGS-I) approaches. The presence of rhizomorphs in the topsoil of daylily beds and on the roots of symptomatic daylilies, coupled with our finding of identical ITS1 sequences among isolates originating from each of a rhizomorph, a daylily, and a neighbouring dogwood, suggests that Armillaria rhizomorphs had spread from native hosts to infect the daylilies. Basidiocarp morphology and basidiospore size best matched that documented for A. gallica. However, rDNA sequence analysis and sexual compatibility were not 100% conclusive. Phylogenetic analysis of ITS sequences revealed that the unknown Armillaria isolates were most closely related to A. calvescens and A. gallica. Analysis of IGS-I sequences was even less informative, grouping our isolates with A. cepistipes, A. gallica and A. sinapina. Sexual compatibility (mating) tests revealed that haploid isolates from daylily were compatible with three of the A. gallica tester isolates, but also one of the A. calvescens tester isolates. Our findings suggest a possible southerly distribution and expanded host range for A. gallica, and raise further questions about the Armillaria species concept as it pertains to the two closely related species, A. calvescens and A. gallica. [ABSTRACT FROM AUTHOR]

In a search for alternative methods for managing armillaria root disease in Pinus radiata plantations in New Zealand, a thinning trial was established in a 1985 planted stand infested by Armillaria novae-zelandiae. The incidence of chronic (non-lethal) infection rose significantly following a first thinning at age 7 years that provided additional inoculum in the form of colonized stumps. However, this effect diminished before age 19 years when the small stumps had decomposed and, contrary to expectations, a further increase in infection did not follow a second thinning at age 13.5 years, despite a high incidence of larger colonized second thinning stumps. Apparently the increased vigour and associated resistance in the released older trees was sufficient to counter any increase in inoculum potential following treatment. It therefore now appears that thinning may not be detrimental to the final crop volume in contemporary diseased second-rotation plantations. However, this treatment furnishes no disease control benefit, and should still be deployed judiciously in heavily infested stands. There was a small, but significant reduction in volume growth on the more severely infected trees during the first 13 years in this trial, but on the larger trees later in the rotation at age 19 years there was no difference in stem volume between infection severity categories. A previous assessment based only on the earlier data therefore overestimates the impact of Armillaria in present and future pine plantations in New Zealand. Nevertheless, its widespread distribution and its demonstrated pathogenicity indicate that forest owners should be conscious of the presence of Armillaria during plantation management. [ABSTRACT FROM AUTHOR]

Options are currently limited for the management of armillaria root disease in plantations of Pinus radiata in New Zealand. One possibility may be to plant genetically resistant clones on infested sites. Studies were undertaken over four consecutive years to examine variation in inherent resistance in P. radiata. Rooted cuttings in pots were treated with wood segment cultures of Armillaria novae-zelandiae and disease symptoms were monitored during the following summer. Disease was severe among inoculated cuttings in all studies, with an overall mean of 54% plants infected. There were significant differences in both infection and mortality between studies and between four pathogen isolates, but not among 25 radiata pine clones. The rate at which symptoms first appeared also did not vary significantly between clones. Results suggest that while genetic resistance cannot be ruled out as an option in P. radiata, potential gains may be limited in extent and costly to achieve. [ABSTRACT FROM AUTHOR]

Nonaerated compost teas produced from composted green waste of various ages were used to challenge the growth of Armillaria mellea, the causal agent of the Honey fungus white root-rot disease. Three trials were carried out: in vitro agar based assays over a period of 16 days employing repeated application of the teas; timber billet trials over a period of 30 days using a single pretreatment; and a pot trial using deliberately infected young beech trees watered with compost teas at 4 day intervals. The compost samples used were from a commercial source and sampled after storage for one, two, three and six months. Control treatments used distilled water applications in place of compost teas. In all cases compost tea applications inhibited the growth of rhizomorphs significantly and resulted in changes in their morphology. In the pot trials none of the treatments prevented infection, but rather slowed the development of wilt symptoms. Age of compost had an effect in all trials. The results indicate that such treatments may have potential in the treatment of this damaging infection and also highlight the significance of the maturity of green waste composts and teas proposed for the suppression of plant diseases. [ABSTRACT FROM AUTHOR]

Ringbarking is a girdling technique that is used prior to timber harvesting to reduce losses to Armillaria root disease in some parts of the world. The technique had not previously been evaluated in British Columbia, Canada. Small plots of primarily Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) trees that were ringbarked prior to timber harvesting had approximately 50% lower levels of Armillaria root disease caused tree mortality in young trees after 15 years than plots of trees that were not ringbarked. Ringbarking did not reduce Armillaria root disease in this trial as much as has been reported in other research. This could be attributable to the centre of the small plots being within 5-10 m of live and dead Armillaria-infected trees in the surrounding forest. The treatment did reduce the severity of the disease by both statistically and biologically significant amounts and, therefore, warrants further investigation as a possible treatment where timber harvesting is conducted in Armillaria root disease affected stands. [ABSTRACT FROM AUTHOR]

The Landes de Gascogne forest (southwestern France) is the largest maritime pine ( Pinus pinaster) plantation in Europe. Armillaria root disease ( Armillaria ostoyae) has been reported since the early 1920s in the coastal area (western sector), but its incidence over the last 20 years has increased in the eastern sector. We investigated the genetic structure of the A. ostoyae population in this forest, focusing particularly on geographical differentiation potentially indicative of disease expansion in this area. In total, 531 isolates obtained from mycelial fans on symptomatic trees or undecayed stumps in 31 different disease foci were genotyped at five microsatellite loci. In 20 of these disease foci, a single genotype dominated, reflecting a predominantly clonal local spread of A. ostoyae. By contrast, at the regional scale, A. ostoyae probably spreads mostly via basidiospores (sexual spores), as no genotype common to several disease foci was identified. The absence of a clear pattern of isolation by distance may indicate either substantial gene flow or stochastic colonisation independent of spatial distance. The gradient of genetic diversity from the coast inwards and the greater genetic divergence of the eastern disease foci are consistent with the expansion of the A. ostoyae population from the coast eastwards. [ABSTRACT FROM AUTHOR]

In response to an infection, traumatic resin canals (TRCs) are formed in the roots of many conifers, which may be used to determine the timing and sequence of infection events essential for epidemiological studies of root diseases. Juvenile Douglas-fir ( Pseudotsuga menziesii) tree roots at coastal and interior sites in British Columbia were wounded at various times of the year or were inoculated with an isolate of Armillaria ostoyae, and root sections were taken to determine the timing and extent of TRC formation. Naturally infected Douglas-fir were also examined to determine the extent of the TRCs in infected and uninfected roots on infected trees and in the lower stem. Wounds made in March and October had poor or no TRC formation while the summer wounds responded strongly and were associated with resin soaking. Roots wounded in October did not respond until the following year in all trees except one. Trees produced TRCs and resin soaked tracheids at all times in response to the fungal inoculations. The most striking difference between wounding or fungal inoculation was the multiple bands of TRCs produced in response to the fungus. TRCs at natural A. ostoyae infections were found 92% of time in roots at the stem junction and 74% of the time in the stem at soil line. TRCs were produced in uninfected roots on infected trees but disappeared with increasing distance from the initiating lesion. TRCs can be used to time yearly and seasonal root infections when they can be traced from an identified lesion. [ABSTRACT FROM AUTHOR]

Planting material with superior resistance to Armillaria root disease was identified in a field trial established to investigate variation in Armillaria infection among different Pinus radiata nursery stock types. At stand age 6.4 years, total infection incidence, mortality, and degree of root collar girdling by Armillaria spp. were all significantly lower among trees derived from both rooted stool bed cuttings (physiological age 1 to 3 years) and rooted field cuttings (physiological age 3 to 6 years) than among those grown from seedlings. Cutting types did not differ significantly from one another. No significant differences were found between stock types in stem diameter, but trees from stool bed cuttings were significantly taller than seedling trees. Whether these differences remain detectable later in the rotation, initial results suggest that it may be advantageous to plant robust stock, of either cuttings or seedlings, on Armillaria-infested sites. The incidence of infection in living, green-crowned trees was unevenly distributed across the trial site, and was greater nearer to trees killed by Armillaria spp. than further away (significant within a radius of 10 m). By mapping visible Armillaria-caused mortality prior to thinning, it may be possible to delineate areas with a higher incidence of concealed chronic infection, thus defining infested sites for postharvest treatment. [ABSTRACT FROM AUTHOR]

Abstract: Armillaria root rot, caused by Armillaria tabescens and Armillaria mellea, is a major cause of premature tree death in peach orchards in the southeastern United States. The root systems of infected trees can become entirely colonized by Armillaria, serving as an inoculum source for adjacent trees and providing massive inoculum levels in replant situations. If dead or dying trees could be colonized by an effective competitor of Armillaria before their removal, the extent of root colonization by the pathogen could be reduced, thus decreasing the threat to adjacent trees and/or subsequent plantings. Interactions between five species of saprobic lignicolous fungi (Ganoderma lucidum, Hypholoma fasciculare, Phanerochaete velutina, Schizophyllum commune, and Xylaria hypoxylon) and the two Armillaria species were examined in controlled conditions to provide proof of concept for competitive exclusion of Armillaria from peach roots. On agar-coated glass slides, all five potential antagonists induced detrimental reactions in >58% of the Armillaria hyphae observed, with the majority resulting in hyphal swelling or granulation. On poplar wood blocks, all antagonists consistently either overgrew Armillaria colonies or—in the case of S. commune—engaged in deadlock reactions; in all cases, the viability of Armillaria colonies was reduced to <30% of that of unchallenged controls. When inoculated simultaneously onto opposite ends of peach root segments, all antagonists consistently reduced growth and viability of Armillaria on and under the bark, whereby reduction of pathogen growth underneath the bark, Armillaria’s primary ecological niche, was most pronounced for G. lucidum, S. commune, and X. hypoxylon. When root segments were allowed to be colonized entirely by Armillaria before being inoculated with the antagonists, the latter were able to overgrow the pathogen on the root surface but unable to pre-empt it from underneath the bark. In summary,G. lucidum, S. commune, and X. hypoxylon caused strong hyphal and mycelial interference reactions and the most pronounced reductions in growth of Armillaria above and below the bark, indicating that they would be the most promising candidates for field-scale evaluations to restrict colonization of dead or dying peach trees by Armillaria in the orchard. [Copyright &y& Elsevier]

The aim of this study was to identify seven Armillaria isolates obtained from diseased tea bushes in Kenya using pectic enzyme profiles, PCR-RFLP and IGS-I DNA sequence data. The combination of these identification methods confirmed the presence of three distinct Armillaria groups. One of these groups resembled Zimbabwean group I ( A. fuscipes). The second group was phylogenetically closely related to A. mellea ssp. nipponica. The third group was different from all other African isolates examined, but had isozyme patterns, especially of pectin methylesterases (PMEs), similar to those of isolates related to A. mellea ssp. nipponica. Analyses of sequence data suggested that this group is phylogenetically closely related to A. hinnulea from Australia and New Zealand. [ABSTRACT FROM AUTHOR]

Armillaria root rot is a serious disease in fir and mixed conifer forests of Bhutan, Eastern Himalayas. The species causing this disease have, however, never been identified. The aim of this study was to identify field isolates collected at four localities in Bhutan. Identification was based on RFLP analysis of the IGS-1 region, comparisons of ITS and IGS-1 sequence data with those available on GenBank, cladistic analyses and sexual compatibility studies. Isolates were found to reside in two distinct RFLP groups. RFLP group 1 isolates fromPinus wallichianaat Yusipang had RFLP profiles and IGS-1 sequences similar to those ofArmillaria melleassp.nipponica. Although ITS sequence data are not available forA. melleassp.nipponica, sequences from this DNA region were most similar to the closely relatedA. melleafrom Asia. The RFLP profile and IGS-1 sequences for RFLP group 2 isolates fromAbies densaat Changaphug,Tsuga dumosaat Chimithanka as well asPicea spinulosaandT. dumosain the Phobjikha valley were similar to those published forArmillaria borealis,Armillaria cepistipes,Armillaria geminaandArmillaria ostoyae. Distance analysis based on IGS-1 and ITS sequence data indicated that these isolates are closely related toA. cepistipes,Armillaria gallicaandArmillaria sinapina. The isolates were, however, sexually incompatible with tester strains ofA. cepistipes,A. gallicaandA. sinapina. Although closely related to these species, they appear to represent a distinct taxon that will be referred to as Bhutanese phylogenetic species I (BPS I) until basidiocarps are found and the species can be described. [ABSTRACT FROM AUTHOR]

Root collar excavation for control of Armillaria root disease of grapevine was investigated in two California vineyards (vineyard K1 and vineyard N1) from 2002 to 2004. The hypothesis tested was that root collar excavation, when timed in early stages of root collar infection, may cause mycelial fans of the pathogen Armillaria mellea to recede from the root collar before severe disease results from vascular tissue decay. In vineyard N1, excavation significantly increased yield and cluster weight of symptomatic grapevines; symptomatic-excavated grapevines had the same high mean cluster weight as healthy grapevines, and there were no significant effects of excavation on yield or pruning weight of healthy grapevines. In vineyard K1, where excavated root collars frequently refilled with soil, excavation had no significant effects on yield or pruning weight of symptomatic grapevines, and significantly reduced pruning weight and shoot weight of healthy grapevines. Reexamination in March 2004 revealed that mycelial fans had receded from root collars of symptomatic-excavated grapevines, but remained on root collars of symptomatic- nonexcavated grapevines. Root collar excavation appears to be a promising cultural approach for control of Armillaria root disease, as long as excavated root collars are kept clear of soil. [ABSTRACT FROM AUTHOR]

Armillaria root rot is a well-known disease on a wide range of plants, world-wide. In Ethiopia, the disease has previously been reported on Pinus spp., Coffea arabica and on various native hardwoods. The causal agent of the disease has been attributed to Armillaria mellea, a species now known to represent a complex of many different taxa. The aim of this study was to determine the extent of Armillaria root rot and the identity of the Armillaria sp. in Ethiopian plantations. As part of a plantation disease survey in 2000 and 2001, samples were collected in plantations at and around Munessa Shashemene, Wondo Genet, Jima, Mizan and Bedele, in south and south-western Ethiopia. Basidiocarps were collected and their morphology studied. Morphological identification was confirmed by sequencing the intergenic spacer (IGS-1) region of the ribosomal rRNA operon and comparing data with published sequences of Armillaria spp. Armillaria isolates were collected from Acacia abyssinica, Pinus patula, Cedrela odorata and Cordia alliodora trees. Sporocarps were found on stumps of native Juniperus excelsa. Basidiocarp morphology and sequence data suggested that the fungus in Ethiopia is similar to that causing disease of Pinus spp. in South Africa and previously identified as A. fuscipes. This identification was confirmed for all isolates, based on sequence data. Armillaria fuscipes is known to be common in southern Africa. Its widespread occurrence in Ethiopia suggests that it is also the major cause of Armillaria root rot in that country. [ABSTRACT FROM AUTHOR]

Periderm formation was studied in bark samples collected from the roots of western larch ( Larix occidentalis) and Douglas-fir ( Pseudotsuga menziesii) trees infected with Armillaria ostoyae. Necrophylactic periderms were formed in advance of infection and successfully restricted continued fungal spread in 68 and 45% of the samples collected from 10- and 27-year-old western larch, respectively. However, all periderms formed in 11- and 25-year-old Douglas-fir had been breached by the advancing fungus. In both species, necrophylactic periderms were commonly breached at the junction of the periderm with the vascular cambium. In western larch, stone phellem often comprised the external phellem layer of necrophylactic periderms with multiple bands of phellem. In 27-year-old western larch, infection was often confined to discrete lesions bounded by multiple periderms with multiple bands of phellem. In both tree species, phellem production was greater in response to infection than in response to abiotic wounding. [ABSTRACT FROM AUTHOR]

The sequence of events leading to necrophylactic periderm formation was studied throughout the year following the abiotic wounding of the non-infected roots of 10- and 27-year-old western larch ( Larix occidentalis) and 11- and 25-year-old Douglas-fir ( Pseudotsuga menziesii) trees that were infected with Armillaria ostoyae. The sequence was the same for both ages and species of trees. Wound repair was more rapid in the summer compared with the spring and autumn. Following cell hypertrophy, a zone of lignified impervious tissue was in the initial stages of formation within 10 days of wounding in the summer and 14 days in the spring or autumn. The new phellogen produced a layer of phellem three to four rows of cells thick after 20 days in the summer or 40 days in the spring. Modified cells abutting the inner boundary of the impervious zone frequently developed thick lignified abaxial walls and thin suberized adaxial walls. A typical exophylactic periderm in healthy root bark tissue of both western larch and Douglas-fir consisted of stone phellem one to four rows of cells thick and a layer of thin-walled phellem three to six rows of cells thick in western larch and two to three rows thick in Douglas-fir, a single row of phellogen cells and one to three rows of phelloderm cells. Mature thin-walled phellem cells had pigmented contents, red in western larch and light brown in Douglas-fir. In response to wounding, 27-year-old western larch and 25-year-old Douglas-fir developed necrophylactic periderms with annual bands of phellem. The bands included a layer of phellem that was six to 12 and nine to 15 rows of cells thicker than the layer of phellem observed in the respective naturally developed exophylactic periderms. Fifty days following wounding in the summer, stone phellem, one to three rows of cells thick, was observed in the necrophylactic periderm of 10-year-old trees. When fully developed, the necrophylactic periderm in 27-year-old western larch also had a layer of stone phellem three to five rows of cells thick in each band. Stone phellem development was only sporadic in 25-year-old Douglas-fir. Wounds in the winter showed no signs of activity associated with repair until dormancy broke in the spring. [ABSTRACT FROM AUTHOR]

The basidiomycetes Armillaria cepistipes and Armillaria ostoyae frequently occur in the same forest stand. In this study, we determined the virulence of 20 isolates of A. cepistipes and 16 isolates of A. ostoyae on four different provenances of 2-year-old Norway spruce ( Picea abies). Within 30 months after inoculation, 1.1 and 19.1% of the seedlings inoculated with A. cepistipes and A. ostoyae, respectively, had died or were dying. The incidence of dead and dying seedlings varied between 3 and 49% among the A. ostoyae isolates. The virulence of an isolate was positively correlated to its ability to produce rhizomorphs. One Norway spruce provenance showed significantly lower susceptibility to A. ostoyae than the other three. Rhizomorphs of both Armillaria species were attached to the root surface. The attached rhizomorphs of A. ostoyae, however, were associated with significantly more lesions. The virulence of the isolates was not correlated with their wood-degrading capability for either of the Armillaria species. [ABSTRACT FROM AUTHOR]

Armillaria root rot symptoms were observed on native Protea and Leucadendron (Proteaceae) species in Kirstenbosch Botanical Gardens in the Western Cape Province of South Africa. Intergenic spacer (IGS)-1 polymerase chain reaction (PCR) restriction fragment-length polymorphism (RFLP) profiling indicated the presence of at least two Armillaria species. The profiles of two isolates were identical to those of A. mellea s. str., originating in Europe. Phylogenetic analyses incorporating internal transcribed spacer (ITS) and IGS-1 sequence data identified the remaining isolates as closely related to A. calvescens, A. gallica, A. jezoensis and A. sinapina. These isolates displayed mating compatibility with A. gallica. From the RFLP profiles, sequencing results and sexual compatibility studies, it is concluded that the two species on Proteaceae in Kirstenbosch represent A. mellea and A. gallica. These are northern hemisphere fungi that have apparently been accidentally introduced into South Africa. This is the second report of Armillaria being introduced into South Africa. The introduction probably occurred early in the colonization of Cape Town, when potted plants from Europe were used to establish gardens. [ABSTRACT FROM AUTHOR]

Summary Armillaria root disease (ARD) occurrence on ponderosa pine (Pinus ponderosa ) is not uniform in the Black Hills of South Dakota, USA. To help manage this ecosystem, a model was developed to predict the probability of observing diseased trees. A kernel density estimator was used to estimate the probability of observing ARD using presence data from two field studies. An eight-parameter regression equation using topographical data (Universal Trans Mercator coordinates, elevation and slope) derived from a Digital Elevation Model was fitted to the estimated probabilities and the residuals kriged to produce correction factors for the regression estimates. The final model, which had a relative mean squared error of 0.128, identified two peaks of high probability in the north-west portion of the Black Hills and several peaks of moderate probability throughout the Black Hills. [ABSTRACT FROM AUTHOR]

Provides information on a study that identified a collection of isolates from dying trees, showing typical symptoms of Armillaria root rot in various parts of South America and Indo-Malaysia. Methodology of the study; Results and discussion on the study.

Focuses on a study which described several species of the Kenyan root rot pathogen Armillaria. Materials and methods; Results; Discussion.

The relationship between forest stand composition in southern interior British Columbia and fluorescent pseudomonad bacteria populations was investigated using seedling bioassays. The objectives of this study were to (i) compare the relative population sizes of fluorescent pseudomonads baited from soils in pure paper birch (Betula papyrifera Marsh.), pure Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), and mixed stands of the two species and (ii) determine if fluorescent pseudomonads from these soils have inhibitory effects against the root pathogen Armillaria ostoyae (Romagn.) Herink in vitro. Soil from birch stands supported four times more pseudomonads on seedling baits than soil from Douglas-fir stands, with the mixed stands intermediate. Soil from young stands yielded twice as many rhizosphere pseudomonads as soil from mature stands. Pseudomonad population size was positively correlated with percent cover and density of birch, and negatively correlated with basal area of Douglas-fir, percent cover of Douglas-fir, and carbon/nitrogen ratio of the soil. Greater than 50% of the fluorescent isolates reduced radial growth of A. ostoyae by more than 20% and greater than 90% reduced biomass of the fungus in dual culture tests. Cell-free bacterial culture filtrates added to the growth medium also reduced growth of A. ostoyae. This study provides evidence that paper birch provides a more favorable environment for fluorescent pseudomonads than Douglas-fir and suggests a mechanism by which paper birch can positively influence the susceptibility of managed forest stands to Armillaria root disease. [ABSTRACT FROM AUTHOR]

Presents the results of a test of stem cross-sectional areas for accuracy and precision of area measurements in healthy and Armillaria ostoyae (Romagn.) Herink infected 18-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Introduction; Materials and methods; Results; Discussion; Conclusions.