Hypoxylon Mammatum Research Articles

Commodity risk assessment of Sorbus aucuparia plants from the UK.

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'high risk plants, plant products and other objects'. Taking into account the available scientific information, including the technical information provided by the applicant country, this Scientific Opinion covers the plant health risks posed by the following commodities: Sorbus aucuparia bare-root plants and rooted plants in pots up to 7 years old and specimen trees in pots up to 15 years old imported into the EU from the UK. A list of pests potentially associated with the commodities was compiled. The relevance of any pest was assessed based on evidence following defined criteria. Three EU quarantine pests (Entoleuca mammata and Phytophthora ramorum (non-EU isolates), Erwinia amylovora), were selected for further evaluation. For two of the selected pests (E. mammata and P. ramorum), the risk mitigation measures implemented in the UK and specified in the technical dossier were evaluated taking into account the possible limiting factors. For these pests, an expert judgement is given on the likelihood of pest freedom taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The degree of pest freedom varies between the pests evaluated, with P. ramorum being the pest most frequently expected on the imported S. aucuparia plants. The Expert Knowledge Elicitation indicated, with 95% certainty, that between 9812 and 10,000 bare-root S. aucuparia plants per 10,000 will be free from P. ramorum.

БОЛЕЗНИ POPULUS ALBA L. В БОТАНИЧЕСКОМ САДУ ТУВИНСКОГО ГОСУНИВЕРСИТЕТА

Poplars are used for landscaping residential areas, urban conglomerates and highways. Pathogenic microflora was revealed and studied in the zone of greening of the introduced plant - silver poplar in the conditions of dry steppes of the Republic of Tuva. A detailed examination revealed various types of lesions: leaves, branches, bark and trunk. The species composition of diseases of the infecting plant was up to ten. At the facade of student hostel No. 4, lesions of the tree trunk by the pathogen Cytospora foetida Vl. et For. In mixed crops of silver poplar among plantings of other plants near the facade of the archive, lesions of Septoria populi Desc., Virus VTM., Septoria candida, Desc. In the shelterbelt of the training and experimental field, there were leaf spots of Marssonina populi and Septoria populi Desc. In the façade of the Faculty of Philology, symptoms of Nicola salisus Wint. f. populorum Radh, Melampsora tremulae, Taphrina aurea For., Allocasuarina fraseriana (Miq.) L. A. S. Johnson. Psedomonas guercus Schem., Hypoxylon pruinatum Pon., heavily polluted with soot emissions during the heating season, mechanical damage, frost cracks were found on the facade of the Faculty of Agriculture. The reason is the northeast wind. The microflora of pathogens causing harm to silver poplar showed that the development and spread of diseases are not significant, reaching two points on the damage scale. The value of the index of development of pathogenic microflora indicates the beginning of the process of infection of poplars in the landscaped area of the student quarter of the city of Kyzyl. The annual preventive health measures contributed to the reduction in the development of lesions. Thus, in the green zone of the student quarter of Tuva State University, phytosanitary measures are regularly carried out to improve plantings of silver poplar and other plants.

Preliminary study of canker disease for development of urban tree health standard in Malaysia

Canker disease (CD) mainly infected trees planted in urban areas in Malaysia. This disease is caused by several plant pathogens and may cause tree death and tree failure. The aims of this study are to identify tree species which are susceptible to canker diseases and to identify the causal agents especially plant pathogens of the disease. To perform the study, a survey on planted trees in several urban parks and sites in Malaysia were conducted. In this study, the Canker Disease (CD) assessment procedure was developed and modified from Thousand Cankers Disease Survey Guidelines by the United State Department of Agriculture (USDA). Later, the assessment procedure was improved based on surveys in the ground to fit and get the best quality of data from the observations. As a result, several canker diseases were identified on twenty-three (23) trees, the species were, Acacia sp, Bucida molineti, Cinnamomum iners, Citrus sp, Eucalyptus urograndis, Eucalyptus camaldulensis, Eucalyptus sp, Khaya grandifoliola, Mangifera indica, Manilkara zapota, Mimusops elengi, Peltophorum indicus, Samanea saman, Swietenia macrophylla, Swietenia spicifera, Tabebuia argentea, Terminalia catappa, Terminalia mantaly, Araucaria heterophylla, Casuarina equisetifolia, Gymnostoma sumatrana and Polyalthia longifolia. Based on symptom development the canker diseases known as Sphaeropsis canker, Cryphonectria canker, Chrysoporthe canker, Biscogniauxia canker, Hypoxylon canker, Cypress canker, Nectria canker, Ceratocystis Wilt, Pink disease, and Slime flux disease. This study can be the starting point in developing the Canker Disease (CD) Assessment Standard in Malaysia. It is important for Malaysia to have a Canker Disease (CD) Assessment Standard in order to become a guideline for future study or research that specifies canker disease towards common trees planted in Malaysia especially the urban areas.

First record of Entoleuca mammata in hybrid aspen plantations in hemiboreal Estonia and stand–environmental factors affecting its prevalence

Entoleuca mammata [causing Hypoxylon canker (HC)] is one of the most serious pathogens that are colonising Populus species. The area of fast-growing hybrid aspen plantations has remarkably increased in northern Europe because of the high demand for woody biomass, but the prevalence of HC and the stand-related and environmental factors that favour its presence have rarely been monitored in such monocultural plantations. The presence of E. mammata in Estonia was proven by ITS sequence on hybrid aspen. Repeated monitoring after 4 years in 24 hybrid aspen plantations found that the share of visually damaged trees by HC increased from 0.6% (15-year-old trees) to 1.6% (19-year-old trees). The mortality rate of the infected trees during the 4 years was 100%. The probability of HC incidence was favoured by tree vigour and higher soil acidity. The higher susceptibility of more vigorous trees might be related to their trade-off between productivity and defence compounds. The share of trees with clear visual symptoms of HC can be considered marginal, but the aggressive nature of the pathogen suggests the need to extend the monitoring period, especially in recently thinned sites, and to expand the observations to native Populus tremula stands.

Biscogniauxia (Hypoxylon) Canker or Dieback in Trees

Biscogniauxia canker or dieback (formerly called Hypoxylon canker or dieback) is a common contributor to poor health and decay in a wide range of tree species (Balbalian & Henn 2014). This disease is caused by several species of fungi in the genus Biscogniauxia (formerly Hypoxylon). B. atropunctata or B. mediterranea are usually the species found on Quercus spp. and other hosts in Florida, affecting trees growing in many different habitats, such as forests, parks, green spaces and urban areas (McBride & Appel, 2009).
 Typically, species of Biscogniauxia are opportunistic pathogens that do not affect healthy and vigorous trees; some species are more virulent than others. However, once they infect trees under stress (water stress, root disease, soil compaction, construction damage etc.) they can quickly colonize the host. Once a tree is infected and fruiting structures of the fungus are evident, the tree is not likely to survive especially if the infection is in the tree's trunk (Anderson et al., 1995).

Pest categorisation of Entoleucamammata.

Following a request from the European Commission, the EFSA Plant Health (PLH) Panel performed a pest categorisation of Entoleuca mammata, a well‐defined and distinguishable fungus of the family Xylariaceae native to North America. The species was moved from the genus Hypoxylon to the genus Entoleuca following a revision of the genus. The former species name H. mammatum is used in the Council Directive 2000/29/EC. E. mammata is the causal agent of Hypoxylon canker of quaking aspen (Populus tremuloides) and other poplars (Populus spp.). The pathogen has been reported in 16 EU Member States (MS), without apparent limiting ecoclimatic factors, but mostly (with the exception of Sweden) with a restricted distribution. E. mammata is a protected zone (PZ) quarantine pest (Annex IIB) for Ireland and the UK (Northern Ireland). The main hosts present in the EU (P. tremula, P. nigra and hybrid poplars) are widespread throughout most of the risk assessment area, including the PZ. The main means of spread are wind‐blown ascospores, plants for planting and wood with bark. E. mammata is not currently reported to be of significant economic importance in the EU MS where the pathogen is reported, but has been shown to cause significant damage in the USA. Risk reduction options include appropriate site selection for poplar plantations, avoiding wounds, and debarking wood. The main uncertainties concern the distribution of the pathogen in the EU, the susceptibility of cultivated hybrid poplars to the pathogen and thus the potential damage to poplar plantations in the RA area. The criteria assessed by the Panel for consideration as potential PZ quarantine pest are met. The criterion of plants for planting being the main pathway for spread for regulated non‐quarantine pests is not met: plants for planting are only one of the means of spread of the pathogen.

ChemInform Abstract: Isolation and Structure Elucidation of Hymatoxins B - E and Other Phytotoxins from Hypoxylon mammatum Fungal Pathogen of Leuce Poplars.

Abstract Two groups of phytotoxic substances were isolated from a culture filtrate of the plant pathogenic fungus Hypoxylon mammatum (Wahl.) Miller, responsible of the canker formation in aspen. The main group consists of a mixture of original diterpenes, hymatoxins, from which have been isolated hymatoxins A, B, C, D and E that belong to the pimarane class. The minor group of toxins is composed of isomeric 3,4,5- and 3,4,8-trihydroxynapthalenones. The structures of the isolated compounds were determined by spectroscopic methods.

North American populations of Entoleuca mammata are genetically more variable than populations in Europe

Entoleuca mammata (syn. Hypoxylon mammatum) is a damaging pathogen of Populus tremuloides and P. grandidentata in North America and P. tremula in Europe, where the fungus occurs only sporadically in alpine regions and Scandinavia. It has been hypothesized that E. mammata was introduced to Europe from North America. In this study, E. mammata isolates collected from Europe and North America were compared by a sequence analysis of two DNA markers derived from DNA fingerprints. The objective of the study was to elucidate the relationship between North American and European E. mammata populations by testing two hypotheses: (1) North American and European isolates are conspecific; and (2) the fungus was introduced between continents causing both a founder effect and a genetic bottleneck. North American populations were found to be more polymorphic, but no major phylogenetic differences between fungal isolates collected from different continents were found. This result combined with the historical observations of the disease in Europe implies that E. mammata was introduced to Europe several centuries ago.

Bacterial disease resistance of transgenic hybrid poplar expressing the synthetic antimicrobial peptide D4E1.

Important losses in poplar productivity occur because of susceptibility to microbial pathogens. To enhance disease resistance in susceptible genotypes, the gene coding for D4E1, a synthetic antimicrobial peptide consisting of 17 amino acid residues, was introduced into poplar (Populus tremula L. x Populus alba L.) via Agrobacterium-mediated transformation. Four kanamycin-resistant transformants were selected based on significant accumulation of the D4E1 transcript and confirmed by reverse transcription-polymerase chain reaction and RNA dot-blot analysis. These transgenic poplar lines were tested for resistance to Agrobacterium tumefaciens, Xanthomonas populi pv. populi and Hypoxylon mammatum (Wahl.) Miller. One transgenic poplar line, Tr23, bearing the highest transcript accumulation for the D4E1 gene, showed a significant reduction in symptoms caused by A. tumefaciens and X. populi. However, none of the transgenic poplar lines showed a significant difference in disease response to the fungal pathogen H. mammatum.

Precommercial thinning of trembling aspen in northern Ontario: Part 2 – Interactions with Hypoxylon canker

Hypoxylon canker [Entoleuca mammata (Wahlenberg:Fr) J.D. Rogers and Y.-M. Ju] incidence and mortality were monitored in six northern Ontario trembling aspen (Populus tremuloides Michx.) stands following precommercial thinning. At each of the six sites, a randomized complete block design experiment was established with four replicates of five thinning levels (none, 2-, 3-, 4-, and 5-m spacing). At the time of thinning, three stands were five years old; the remaining were ages 10, 15, and 22. Over the 15- to 17-year observation period, Hypoxylon-related mortality increased to 6–9% by the end of the period, regardless of thinning age or density. Hypoxylon infection incidence (excluding mortality) also increased, to 2–6% in unthinned stands and 8–11% in thinned stands by year 15. No differences among the thinning levels were observed. Prevalence, infection expressed as a percentage of surviving trees, did not differ among thinned and unthinned stands. Mortality attributed to factors other than Hypoxylon was 31–44% in unthinned stands and 7–23% in thinned stands, with no significant differences among thinning levels. Trees dying of other causes were typically small in diameter and of more subordinate crown classes than survivors. In contrast, Hypoxylon-caused mortality was independent of tree size and canopy position. Results suggest that log size and stand yield may be manipulated through density regulation, without concern for interacting impacts associated with Hypoxylon canker. Models are provided for estimating disease losses; predictions can then be factored into the crop-planning process. Key words: trembling aspen, precommercial thinning, Hypoxylon canker, growth and yield, crop planning

Wood-inhabiting microfungi isolated from Populus tremuloides from Alberta and northeastern British Columbia

Forty-nine taxa of sporulating microfungi were isolated in pure culture from the bark and wood of living and recently cut stems of trembling aspen (Populus tremuloides) from several sites in central Alberta and northeastern British Columbia. Stems were either healthy, blue stained, or decayed, or else possessed cankers or black galls. Several ecological groupings of fungi were recognized, including wood-staining fungi (e.g., Ophiostoma piliferum), black-gall-associated fungi (e.g., Hyphozyma lignicola, Knufia cryptophialidica,Phoma etheridgei), canker-causing pathogens (e.g., Nectria cinnabarina, Tympanis spermatiospora, Valsa sordida), and fungi that could be referred to as endophytes. This latter group consisted of an assortment of fungi normally found in niches other than wood (e.g., Ciborinia whetzelii, Sporormiella similis), microfungi associated with decayed wood (e.g., Cryptosphaeria lignyota, Phialocephala fusca, Phialophora alba, Phialophora bubakii, or canker-causing fungi isolated from healthy tissue (e.g., Hypoxylon mammatum, Leucostoma nivea.Key words: microfungi, endophytes, Populus, aspen, wood, Ascomycota, hyphomycetes, coelomycetes.

Histochemical and microspectrophotometric analyses of early wound responses of resistant and susceptible Populus tremuloides inoculated with Entoleuca mammata (=Hypoxylon mammatum)

Stem tissue of resistant and susceptible genotypes of Populus tremuloides Michx. wounded or wound-inoculated with Entoleuca mammata (Wahlenberg: Fr.) J.D. Rogers & Y.-M. Ju was prepared for histochemical and microspectrophotometric analysis. Samples were collected over a 96-h period. Parenchyma cell walls associated with the response zone of infected resistant and susceptible genotypes accumulated phenolic substances having lignin-like properties. Features of the lignified zone distinguished resistant from susceptible genotypes. This zone in the resistant genotype was uniformly lignified, while in the susceptible genotype, it was discontinuous. Wound callus developed in the infected resistant but not in the susceptible genotype. In the former, callus developed internal to the lignified zone, contained phenolic substances, and was visible 48 h after inoculation. In the susceptible, callus failed to develop. Wounded tissue of both genotypes displayed no distinguishing response characteristics. Both produced equivalent amounts of callus, accumulated similar levels of lignin-like substances, and deposited it in identical locations. It is concluded that resistant P. tremuloides limits infection by E. mammata by two distinct mechanisms: (i) by the development of an intact and localized lignified barrier zone and (ii) by the development of wound callus rich in phenolic substances. The susceptible is ineffective at developing either of these barriers.Key words: aspen, Hypoxylon canker, disease resistance.

Inoculation methods for selecting Populus tremuloides resistant to Hypoxylon canker

Canker expansion and the amount of callus tissue formed were measured monthly on 60 ramets from each of five trembling aspen (Populus tremuloides Michx.) clones that had been inoculated in wounds with Entoleuca mammata (= Hypoxylon mammatum (Wahl.) Mill.) over a 12-month period. At the clone level, the prevalence of nonlethal cankers within clones prior to the study had no correlation with canker expansion with three of the five clones. Greenhouse inoculation of ramets derived from the same five clones resulted in the same resistance rankings as main-stem inoculations in the field. One isolate, Hm-27, produced longer cankers, and less callus developed on all clones compared with trees inoculated with the less aggressive strain, Hm-24. Cankers developed only on clones that were inoculated during the months of April through July with April inoculations resulting in the largest cankers. These results indicate that there is a limited time frame when wounds on aspen are susceptible to infection by artificial inoculation with the pathogen as many wound inoculations neither produced cankers nor wound callus. Comparing inoculation methods, either main-stem inoculations in the field or greenhouse inoculations coupled with the natural canker prevalence could be used to include or exclude clones for use in an aspen breeding program.

Histochemical and microspectrophotometric analyses of early wound responses of resistant and susceptible <i>Populus tremuloides</i> inoculated with <i>Entoleuca mammata</i> (=<i>Hypoxylon mammatum</i>)

Stem tissue of resistant and susceptible genotypes of Poyulus tremuloides Michx. wounded or wound- inoculated with Entoleuca mammata (Wahlenberg: Fr.) J.D. Rogers & Y.-M. Ju was prepared for histochemical and microspectrophotometric analysis. Samples were collected over a 96-h period. Parenchyma cell walls associated with the response zone of infected resistant and susceptible genotypes accumulated phenolic substances having lignin-like properties. Features of the lignified zone distinguished resistant from susceptible genotypes, This zone in the resistant genotype was uniformly lignified, while in the susceptible genotype, it was discontinuous. Wound ca)lus developed in the infected resistant but not in the susceptible genotype, in the former, callus developed internal to the lignified zone, contained phenolic substances, and was visible 48 h after inoculation. In the susceptible, callus failed to develop. Wounded tissue of both genotypes displayed no distinguishing response characteristics. Both produced equivalent amounts of callus, accumulated similar levels of lignin-like substances, and deposited it in identical locations. It is concluded that resistant P. tremuloldes limits infection by E. mammat, by two distinct mechanisms: (i) by the development of an intact and localized lignified harrier zone and (ii) by the development of wound callus rich in phenolic substances. The susceptible is ineffective at developing either of these barriers.

The genus Nemania s.l. (Xylariaceae) in Norden

Abstract A taxonomic study of Nemania Gray, Entoleuca Syd. and Euepixylon Füisting (= Nemania s.l.; Xylariaceae) was carried out for the Nordic countries: Norway, Sweden, Finland and Denmark. No species of Nemania have been found in the remaining Norden: Iceland and the Faeroes. Fourteen species of Nemania s. str. were found in the area: Nemania aenea, N. aureolutea comb. n., N. atropurpurea, N. carbonacea, N. chestersii, N. colliculosa comb. n., N. con.fluens, N. diffusa, N. effusa, N. prava n. sp., N. reticulata comb. n., N. serpens, and two unknown species (Nemania spp. A and B) not formally described because of scanty material. In addition the two split-outs fromNemania, Entoleuca mammata andEuepixylon udum, are treated. A dichotomous key has been prepared and the species are reviewed alphabetically with comments on taxonomy, ecology and chorology. All species have been drawn, photographed and mapped. In addition to conventional taxonomic procedures, a selection of species from Nemania s.l., Biscogniauxia and Hypoxylon were subjected to an ITS nrDNA sequencing study. This study supported the delimitation of taxa as defined in this work, and confirms Nemani a as different from Hypoxylon and Biscogniauxia. Four EuropeanNemania taxa are still unknown in Norden: Nemania gwyneddii (Whalley, R.L. Edwards & S.M. Francis) Pouzar, N. illita (Schwein.) Pouzar, Nemania serpens (Pers.: Fr.) Gray var. macrospora (J.H. Mill.) Pouzar. The fourth taxon, Hypoxylon terricola J.H. Mill. certainly also belongs to Nemania.

Inoculation methods for selecting <i>Populus tremuloides</i> resistant to Hypoxylon canker

Inoculation methods for selecting <i>Populus tremuloides</i> resistant to Hypoxylon canker

Wound response characteristics as related to phenylpropanoid enzyme activity and lignin deposition in resistant and susceptible Populus tremuloides inoculated with Entoleuca mammata (Hypoxylon mammatum)

Green internodal stem tissues of glasshouse grown Populus tremuloides were either wounded or wound-inoculated with Entoleuca mammata (Hypoxylon mammatum) and assayed for phenylalanine ammonia-lyase (PAL), caffeic acid - o-methyltransferase (CA-OMT), and cinnamyl - alcohol dehydrogenase (CAD) activity over a 96-h period. Lignin deposited in response to the treatments was analyzed by the Klason and the pyrolysis - gas chromatographic (GC) - mass spectroscopy (MS) methodologies. The wound-inoculated treatment resulted in a wound morphology congruent with a typical resistant and susceptible response to E. mammata. Wounding alone resulted in no morphological differences between the two genotypes. In wound-inoculated stem tissue PAL and CAD activities were substantially higher in the resistant relative to the susceptible genotype. Total Klason lignin was similar for both genotypes; however, pyrolysis-GC-MS analysis revealed a difference in the lignin monomeric composition between the two genotypes, with the susceptible genotype accumulating higher levels of hydroxyphenyl units relative to the resistant genotype. It is concluded that differences in PAL and CAD activity and the synthesis of distinct phenylpropanoid monomers distinguish the resistant from the susceptible aspen genotype. Alterations in boundary zone formation due to the differential synthesis of phenylpropanoid monomers and its effect on compartmentalization of the pathogen are discussed.Key words: aspen, Hypoxylon canker, phenylalanine ammonia-lyase, cinnamyl - alcohol dehydrogenase, caffeic acid - o-methyltransferase, disease resistance.

Wound response characteristics as related to phenylpropanoid enzyme activity and lignin deposition in resistant and susceptible <i>Populus tremuloides</i> inoculated with <i>Entoleuca mammata</i> (<i>Hypo×ylon mammatum</i>)

Green internodal stem tissues of glasshouse grown Populus tremuloides were either wounded or wound-inoculated with Entoleuca mammata (Hypoxylon mammatum) and assayed for phenylalanine ammonia-lyase (PAL), caffeic acid - o-methyltransferase (CA-OMT), and cinnamyl - alcohol dehydrogenase (CAD) activity over a 96-h period. Lignin deposited in response to the treatments was analyzed by the Klason and the pyrolysis - gas chromatographic (GC) - mass spectroscopy (MS) methodologies. The wound-inoculated treatment resulted in a wound morphology congruent with a typical resistant and susceptible response to E. mammata. Wounding alone resulted in no morphological differences between the two genotypes. In wound-inoculated stem tissue PAL and CAD activities were substantially higher in the resistant relative to the susceptible genotype. Total Klason lignin was similar for both genotypes; however, pyrolysis-GC-MS analysis revealed a difference in the lignin monomeric composition between the two genotypes, with the sus...

Histological analyses of the host response of two aspen genotypes to wounding and inoculation with Hypoxylon mammatum

SummaryRamets derived from root sprouts of two quaking aspen (Populus tremuloides) parents were either mechanically wounded or wounded and inoculated with mycelium of Hypoxylon mammatum. Female aspen parents were considered either resistant or susceptible based on a 30‐year field trial of their open‐pollinated progenies that had 21% and 93% mortality, respectively, caused by H. mammatum. Each stem was wounded twice at the base and in the nonlignified zone. Samples were taken 5 mm above the site of wounding at 7 and 14 days. Histochemicals used were phloroglucinol‐HCl and Sudan Black B to detect lignin and suberin, respectively. Thin sections of the resistant aspen ramets showed intensive staining phloroglucinol‐HCl, which was localized along both sides of the wound margin. Collenchyma callus was well developed by day 7 and was derived from the phloem tissue internal to the cell walls staining positive for phloroglucinol‐HCl, near the vascular cambium. In contrast, the tissues of susceptible aspen ramets were less stained, the stained cells were less scattered and less collenchyma callus had formed than on the resistant ramets. The presence of the fungus increased the amount of staining observed with phloroglucinol‐HCl and delayed wound closure in both aspen genotypes. No distinguishing pattern could be identified between the two aspen genotypes with respect to suberin formation. When comparing stem response to phloroglucinol‐HCl with respect to the tissue type on the same stem (succulent versus woody), the inoculation of older woody tissue resulted in a more defined host response and thus were better in separating the two aspen genotypes.

Seedling response of two trembling aspen (Populus tremuloides) families to infection by Hypoxylon mammatum

SummaryOpen‐pollinated progenies from two trembling aspen (Populus tremuloides) families with a 30‐year field history of 91% (putatively susceptible, PS) and 45% (putatively resistant, PR) mortality, respectively, caused by Hypoxylon mammatum, were grown in a greenhouse for 3 and 9 months. Seedlings were inoculated with two isolates of H. mammatum, representing high and low aggressiveness, through a stem wound. Beginning 4 days after inoculation, host responses were examined on 312 seedlings per family for a period of 5 weeks on 3‐ and 9‐month‐old seedlings. Significant differences in host responses were observed between the two isolates, with the more aggressive isolate allowing less callus formation, causing more tissue necrosis and producing longer cankers than the less aggressive isolate on both aspen families. Between‐family difference was much greater than within‐family difference for tissue necrosis, callus formation and canker length for both seedling ages. When the 3‐month‐old seedlings were challenged with H. mammatum, the PR family showed greater tissue necrosis, longer cankers, and less callus formation than the PS family. However, when the more lignifìed 9‐month‐old seedlings of the same families were inoculated, the PR seedlings had much less tissue necrosis, shorter cankers, more callus formation and less seedling mortality than the PS family. The results indicate that artificial inoculation of seedlings in a greenhouse can differentiate two aspen families at the seedling stage, but their correlation to field performance is highly dependent upon the seedling age. Host responses of older seedlings may be a better indicator of field performance.