摘要:

The mountain pine beetle (Dendroctonus ponderosae) is commonly associated with the blue-stain fungiOphiostoma clavigerumandOphiostoma montium.Ophiostoma clavigerumis the primary invader of sapwood after beetle infestation and is thought to be the most virulent of the two fungi. Growth of these fungi was studied under oxygen-deficient conditions on malt agar in test tubes and Petri dishes. In addition, growth was studied in phloem and sapwood of young living shore pines (Pinus contortavar.contorta) and western white pines (Pinus monticola) inoculated with fungus in low densities (eight inoculations per tree). In test tubes with limited oxygenO. clavigerumgrew for a longer time thanO. montium. Both fungi are fast growing on malt agar (maximum growth 4.4-9.0 mm/day), butO. clavigerumgrew better at temperatures below 25°C. The rapid growth and the ability to tolerate low oxygen levels may be important adaptations forO. clavigerumas the primary invader of fresh sapwood. However, althoughO. clavigerumgrew better in the phloem of both tree species, there were no differences between the two fungi in their ability to colonize the sapwood of the inoculated trees.Key words: blue-stain fungi,Dendroctonus ponderosae, growth rate, oxygen deficiency, virulence.

ISSN:0008-4026    

DOI:10.1139/b98-020

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Respiration and stem water potential ( psi ) were examined in parental and hybrid big sagebrush (Artemisia tridentataNutt. ssp.tridentataandArtemisia tridentataNutt. ssp.vaseyana(Rydb.) Beetle) grown in common gardens within each parental zone and in the hybrid zone. Plants were sampled in July, August, and September, i.e., immediately before, during, and after flowering. The habitats differed from one another, and there were significant garden by date interactions. The source populations also differed significantly from one another. There were no significant garden by source interactions. Hybrid plants had intermediate respiration rates and did not suffer greater water stress than parental plants. Hybrid plants showed no apparent decrease in adaptation in the important physiological traits respiration and water stress in the hybrid zone.Key words:Artemisia, hybrid zones, respiration, water potential.

ISSN:0008-4026    

DOI:10.1139/b98-018

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Growth chamber studies were conducted to examine seed dormancy and germination requirements of Pitcher's thistle (Cirsium pitcheri(Torr. ex Eaton) Torr. & Gray), a threatened species endemic to the shoreline sand dunes of the Great Lakes. We determined the effects of different environmental regimes on breaking seed dormancy of this monocarpic perennial. The data showed that seeds ofC. pitcheripossessed innate dormancy that was caused by a hard seed coat as well as inhibitory compounds within the seed. Seed germination requirements were very specific. Exposure of seeds to different temperatures and photoperiods in a growth chamber had little effect on breaking seed dormancy unless the seeds had been pretreated. Pretreatment of seeds by cold stratification and its duration, scarification by sand paper or sulphuric acid, and application of gibberellic acid were also not very effective for breaking dormancy ofC. pitcheri. High germination was obtained only when seeds were pretreated either by surgically removing the seed coat or by nicking the seed on the radicle or cotyledonary end. After this pretreatment seeds germinated over a temperature range of 15-30°C, but the highest proportion of seeds germinated when temperatures were above 20°C. Under natural conditions, germination ofC. pitcheriseeds occurs in spring after they have overwintered and experienced the pretreatment of stratification and scarification through freezing and thawing of the substrate. Aqueous extract ofC. pitcheriseeds had a strong inhibitory effect on germination ofOenothera biennisL. seeds indicating an allelopathic chemical in the seed. There was no relationship between the seed size ofC. pitcheriand the germinability of seeds.Key words:Cirsium pitcheri, threatened species, seed dormancy, seed germination, scarification, stratification, nicking of seeds.

ISSN:0008-4026    

DOI:10.1139/b98-029

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

DNA fingerprinting was used to examine genetic variation in populations ofPuccinia striiformisWestend. f.sp.tritici, an obligate fungus that causes wheat stripe rust, using as a probe a moderately repetitive DNA sequence PSR331 that shows species specificity in the genome of this pathogen. One hundred and sixty isolates sampled from six provinces throughout China were examined for genetic variation over 26 putative genetic loci defined by PSR331 and the restriction enzymeBglII. Because of the dikaryotic nature of this fungus, DNA fingerprints can not differentiate heterozygotes from homozygotes. We refer to the PSR DNA fingerprints as phenotypes rather than genotypes. Phenotypic diversity analysis revealed a high level of genetic variation. A total of 97 phenotypes was detected among 160 isolates. Phenotypic diversity varied among regions, ranging from 0.3742 in Shaanxi to 0.9380 in Gansu, as calculated with the normalized Shannon's index. Genetic subdivision analysis revealed a low level of genetic differentiation (GST= 0.0084) among regions (Gansu, Henan, Shaanxi, Sichuan, and Yunnan provinces) as well as within regions (Gansu and Sichuan provinces). This, together with the detection of the same phenotypes among regions, provided the molecular evidence for gene flow inP. striiformisf.sp. tritici. The results support conclusions from virulence surveys that Tianshui of southern Gansu is probably the most important "hotspot" area with respect to the potential to generate and maintain virulence variation. DNA polymorphism analysis also detected potential hotspot areas in addition to southern Gansu. This may result in more difficulties in management of genetic variation and thus the potential virulence variation inP. striiformisf.sp.triticias well as providing opportunities for searching disease resistance factors.Key words: genetic diversity,Puccinia striiformis, DNA fingerprinting, virulence variation.

ISSN:0008-4026    

DOI:10.1139/b98-035

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The macromycota of an evergreen cloud forest was described using a simple method, intended to minimize taxonomic work but still provide an accurate account of diversity. The method showed that the fungal community in the area is spatially structured and that area sampled limited the recording of fungal richness in this study. Parameters derived from the Clench equation suggest that an area of 1 ha will maximize the proportion of recorded taxa and minimize sampling effort.Key words: fungal diversity, macrofungal communities, tropical mycoecology, El Triunfo.

ISSN:0008-4026    

DOI:10.1139/b98-012

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Boerlagiomyces velutinus(Penz. & Sacc.) Butzin andBoerlagiomyces laxus(Penz. & Sacc.) Butzin are lectotypified and the latter species, considered by some mycologists to be a synonym ofB. velutinus, is reinstated as a distinct species.Boerlagella effusa(Syd., P. Syd., & E.J. Butler) J.L. Crane, Shearer, & M.E. Barr, comb.nov. is transferred toBoerlagiomyces. These three species are redescribed and illustrated. A key is provided to the six recognized species ofBoerlagiomyces.Boerlagiomyces macrosporusV.G. Rao & Varghese is redescribed and illustrated and is placed inThaxteriella. Diagnostic characters separating genera allied toBoerlagiomycesare presented in a revised key to the saprobic genera of Tubeufiaceae.Thaxteriellopsis bambusicolaSivanesan & Sharma andThaxteriellopsis lignicolaK.S. Panwar & S.J. Kaur are transferred toChaetosphaerulinaand illustrated. New combinations are made inAcanthostigmellaandThaxteriella.Key words: fungal systematics, Tubeufiaceae, Loculoascomycetes.

ISSN:0008-4026    

DOI:10.1139/b98-024

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Seedlings and adults ofHypericum perforatumL., common St. John's wort, were grown together in an experiment of factorial design, where the presence of root competition and arbuscular mycorrhizal inoculation were used as treatments. There was moderate shoot competition, the intensity of which was not manipulated. To check the response of plants to arbuscular mycorrhiza in noncompetitive conditions, adults and seedlings were also grown singly in pots. Single individuals of seedlings and adults responded positively to mycorrhizal inoculation, with the response of seedlings significantly greater. In the competition experiment the positive effect of mycorrhizal colonization on seedling growth vanished, since with root competition, both mycorrhizal and nonmycorrhizal seedlings were of the same size. Without root competition, the shoots of mycorrhizal adults were much larger than of nonmycorrhizal adults, but under root competition the shoot weight did not differ. Arbuscular mycorrhiza increased the biomass differences between competing seedlings and adults. We did not confirm our hypothesis that mycorrhiza makes competition between seedlings and adults more balanced because of the stronger positive response of seedlings to inoculation. The positive effect of arbuscular mycorrhizae on growth vanishes in more crowded conditions. It was concluded that if mycorrhizal inoculation has age-specific positive effect of seedlings in field conditions, it is more probably due to higher tolerance to abiotic stress than due to higher competitive ability of seedlings.Key words: arbuscular mycorrhiza, intraspecific root competition, seedlings,Hypericum perforatum.

ISSN:0008-4026    

DOI:10.1139/b98-037

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Selection of sites for wetland restoration requires analysis of probable success at recreating diverse natural vegetation. We studied the seed banks and the remnant vegetation at restoration sites to determine their degree of similarity to the vegetation that developed following restoration of wetland hydrology. The study sites had been used for forage crops and pasture following long-term drainage. The seed bank was a very poor predictor of plant species abundances following restoration. Similarity between remnant vegetation and restored vegetation was consistently higher than similarity values using seed banks at both restored and natural wetlands. Our results suggest that seed-bank analysis is an inefficient technique for predicting restored vegetation in sites with prolonged disturbance, and that analysis of remnant vegetation on the sites is probably more useful. However, results would probably differ at sites with tile drainage that have limited remnant vegetation or created wetlands with bare soil where seed germination would play a greater role in revegetation. In addition, seed-bank studies are important to determine if aggressive invasive species are present at potential restoration sites.Key words: seed banks, wetlands, restoration, marshes, vegetation.

ISSN:0008-4026    

DOI:10.1139/b98-038

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Decomposer fungi and microbial processes were examined in harvested and adjacent unharvested areas of two mixedwood forests in northwestern Ontario. Seven to 9 years following harvesting, organic and mineral soil from treated and control areas was sampled with the objective of examining the impact of clear-cutting and site preparation on soil basal respiration, microbial biomass carbon (C), metabolic quotients (qCO2), microbial C to organic C ratios (Cmic:Corg), nitrogen mineralization, and fungal community structure. Relative sensitivity of fungal community indices at species and genus levels was also examined. Soil microbial processes and fungal community structure were similar in harvested and unharvested stands. Although reductions were not significant, basal respiration, microbial biomass C,qCO2, Cmic:Corg, and nitrogen mineralization tended to be lower in organic soil from the harvested sites than the unharvested sites, with the exception ofqCO2. Fungal community structure indicated by rank abundance curves and indices of fungal richness, diversity, evenness, and dominance was similar in harvested and unharvested soil. When comparing organic and mineral soil layers, fungal richness, diversity, and community composition corresponded more closely in the harvested sites than unharvested sites. The isolation frequencies of all frequently found fungal species were equivalent in harvested and unharvested soil. In this study, identifying fungi to the genus level instead of the species level did not alter any major conclusions.Key words: harvesting, fungal community, microbial processes.

ISSN:0008-4026    

DOI:10.1139/b98-048

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

We examined the effects of woody substrate and stand age on diversity and relative abundance of bryophytes, lichens, and fungi in trembling aspen (Populus tremuloidesMichx.) mixedwood boreal forests in Alberta. Point sampling was carried out on surfaces of downed woody material in young (23-26 years), mature (51-63 years), and old (122-146 years) aspen mixedwood stands. Downed woody material was categorized into one of seven decay stages. Diversity and relative abundance of bryophytes, lichens, and fungi were related to decay stage of the log and to stand age. Old aspen mixedwood stands had the highest nonvascular species richness and the greatest diversity of woody substrates in each of the decay stages. The seven decay stages shared many species. Species of bryophytes, lichens, and fungi on particular decay stages were different across the age-classes, indicating that time, as well as structural attributes, were important in determining species assemblages. These results suggest that both the presence of old aspen mixedwood stands and downed wood in different stages of decay are important to maintaining assemblages of bryophytes, lichens, and fungi.Key words: bryophytes, lichens, decay, aspen mixedwood, downed woody material.

ISSN:0008-4026    

DOI:10.1139/b98-030

出版商:NRC Research Press    

年代:1998

数据来源: NRC