摘要:

Healthy Norway spruce trees infested by the bark beetleIps typographuswere investigated weekly for 10 weeks to examine the early stages in fungal invasion. The study was performed in southeastern Norway during an epidemic period. The fungal association consisted ofOphiostomaspecies and an undescribedGraphiumspecies, which invaded the sapwood in an obvious succession. The pathogenic speciesOphiostoma polonicumwas the first invader of both phloem and sapwood and was always in the leading edge of fungal penetration into sapwood.Ophiostoma bicolorfollowedO.polonicumin the sapwood invasion. These species were successively replaced byGraphiumsp. 1,Ophiostoma penicillatumandOphiostoma ainoae.Ophiostoma penicillatumseems to be more adapted to colonizing the phloem than the sapwood. The earliest invaders were the species most frequently carried by the beetles. Key words: Norway spruce, Ips typographus, Ophiostoma, fungal succession.

ISSN:0008-4026    

DOI:10.1139/b92-001

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Two new pollen sequences from the Bruce Peninsula, southern Ontario, demonstrate the Holocene history of forests in the area. During the mid- and late Holocene, the southern portion of the peninsula supported a rich deciduous forest, dominated byAcer saccharumandFagus grandifolia, while the northern portion was dominated by a forest with a much higher proportion of conifers. These two sites are compared numerically with a third site, on Manitoulin Island, by means of principal components analysis. Despite similar bedrock, soils, climate, and topography, the three pollen sequences show a remarkable divergence of Holocene forest history. The role of historical factors in determining forest composition may be much greater than previously appreciated. This study emphasises the need to understand the magnitude of variation between pollen sequences within uniform terrain before ascribing the differences in pollen sequences from contrasting environments (because of climate, soils or topography) to the factors causing the obvious contrast.Key words: Holocene forest history, pollen analysis, principal components analysis, Bruce Peninsula, southern Ontario.

ISSN:0008-4026    

DOI:10.1139/b92-002

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Cytological changes induced by wheat streak mosaic virus in cereal leaf tissues were studied at the light microscope level. Starting 4–5 days after inoculating the first leaves, a number of cylindrical inclusions were present in the dense cytoplasm of the second wheat leaf epidermal cells. Amorphous inclusions could also be identified in the epidermal cells at late infection stages (from 10 days post inoculation), often associated with deformed nuclei. In mesophyll cells of wheat, barley, and triticale, virus infection induced dense cytoplasm around enlarged nuclei and cytopathie structures within these nuclei. Pyknotic nuclei could be observed at late infection stages. Nuclei and chloroplasts became degraded as the infection progressed. In addition, the cell wall composition was changed and included deposits that were most likely phenolic compounds and lignin. At late infection stages the infected mesophyll cells had collapsed. This was not observed in either senesced virus-free mesophyll cells, or virus-infected epidermal cells.Key words: wheat streak mosaic virus, virus infection, host – virus interaction, cereals, cytological changes, cell wall deposit.

ISSN:0008-4026    

DOI:10.1139/b92-003

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Mycorrhizal synthesis studies revealed that allopatric populations ofSuillus granulatusdiffer in host specificity. Isolates ofSuillus granulatusoriginated from Nepal (associated withPinus wallichiana), Korea (Pinus densiflora), and the U.S.A. (Pinus strobus). Functional compatibility of the mycorrhizal association was used to measure host specificity. Useful characters for measuring mycorrhizal compatibility were defined as those which revealed statistical differences between the uninoculated controls and mycorrhizal treatments and which were stable within one population. Useful characters, as defined by these two tests, were shoot wet weight, total wet weight, percentage mycorrhizal short roots, shoot dry weight, total dry weight, and Hartig net penetration. Data for these characters were subsequently used in anova tests to determine whether allopatric populations ofSuillus granulatusdiffer in functional compatibility. Isolates associated withPinus strobuswere most compatible withPinus strobusand least compatible with the other trees, whereas isolates fromPinus wallichianaandPinus densiflorashowed variable compatibility with all three trees. Phenetic analyses used to determine how similarly the isolates responded with the hosts confirmed these results. We conclude that isolates associated withPinus strobusare most specific for this host, whereas isolates from the other two trees are not host specific. The implications of these results are discussed in light of future investigations regarding the relatedness of these tree-associated isolates.Key words: Boletaceae,Suillus,Pinus, ectomycorrhizae.

ISSN:0008-4026    

DOI:10.1139/b92-004

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Susceptibility to barley yellow dwarf RPV (BYD – RPV) relative to BYD – PAV has been studied for 21 species of the genusBromus. The following species belonging to sectionsBromus(B.arvensisL.,B.commutatusShrad,B.danthoniaeTrin.,B.grossusDesf. ex DC.B.hordeaceusL.,B.lanceolatusRoth.,B.scopariusL.),Stenobromus(B.diandrusRoth.,B.madritensisL.,B.sterilisL.,B.rubensL.,B.tectorumL.), andNeobromus(B.triniiDesvaux) are all susceptible to BYD–RPV. Of the three species of thePnigmasection,B.erectusHudson is susceptible to BYD–RPV, although the percentage of infected plants is low;B.setifoliusPresl. is resistant to BYD–RPV; and the two biotypes ofB.inermisLeyss. that were tested are both resistant to BYD–RPV. Most biotypes of the species in sectionCeratochloaare resistant to BYD–RPV and susceptible to BYD–PAV. InB.catharticusVahl. a few biotypes are also susceptible to both viruses. The resistance to BYD–RPV in different biotypes ofCeratochloaand in one biotype ofB.setifoliuscannot be explained by the resistance to the vectorRhopalosiphum padiL., as BYD – PAV is efficiently transmitted to these biotypes by the same aphid species. These results show that most biotypes of the species in sectionCeratochloaare probably immune to BYD–RPV and that the virus has a restricted host range in the genusBromuscompared with BYD –PAV.Key words: BYDV, RPV, PAV,Bromusgenus.

ISSN:0008-4026    

DOI:10.1139/b92-005

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Asplundiasp.,Evodianthus funifer, andThoracocarpus bissectusare root-climbing lianas that each have absorbing roots and anchoring roots. On stems appressed to the trunks of host trees, both types of roots arise mainly from internodes, generally emerging from those halves of stem surfaces facing the trunks (Asplundiasp.,E.funifer), and may form nonreplacement roots and replacement roots. Aerial portions of absorbing roots differ from anchoring roots according to direction of growth, abundance of nonreplacement roots, diameter 1 cm distal to base, length, abundance, and color (T.bissectus). In all species the anchoring roots (with or without replacement roots) are interpretable as determinate because on long specimens their distal portions appear anatomically narrowed and reduced. In contrast, aerial parts of absorbing roots are indeterminate. The determinate aspects of anchoring roots and the general restriction (on stems appressed to tree trunks) of roots to trunk-facing stem surfaces are advantageous as means for conserving biomass.Key words: roots, root morphology, root dimorphism, Cyclanthaceae.

ISSN:0008-4026    

DOI:10.1139/b92-006

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Inoculation of lower leaves of tobacco cultivar Ky 14, which carries theNgene for resistance to tobacco mosaic virus, with tobacco mosaic virus induced systemic resistance toPeronospora tabacinaand a systemic accumulation of cell wall hydroxyproline. Hydroxyproline increased significantly 12 days after induction with tobacco mosaic virus, and more so after challenge withP.tabacina. During this period, hydroxyproline levels in the control plants remained unchanged. Four salt-soluble cell wall proteins were systemically induced. These proteins were not β-1,3-glucanases, chitinases, or hydroxyproline-rich glycoproteins. Light microscopy showed that blue mold development in the induced plants was severely restricted 2 days after challenge; some fungal hyphae were disorganized near the center of infection sites, and adjacent host cells were plasmolyzed and a few collapsed 3 days after challenge. All infection sites in the induced plants were associated with necrotic cells 5–6 days after challenge. Electron microscopy revealed that damage to fungal hyphae, plasmolysis and shrinking of infected cells, and more electron-opaque host cell walls and wall appositions were characteristics of induced resistance.Key words: induced systemic resistance, Nicotiana tabacum, blue mold (Peronospora tabacina).

ISSN:0008-4026    

DOI:10.1139/b92-007

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The ventral epidermal cells of the photosynthetic, surface-living gametophytes ofLycopodium cernuum, collected from moist shaded banks in Peninsular Malaysia, contain an aseptate fungus. In some cells the hyphae are thick walled and form coils encapsulated by a thin layer of host wall material. In others the fungus is thin walled and shows limited differentiation into larger trunk hyphae and arbuscules. The adjacent host cytoplasm, separated from the fungus by a granular interfacial matrix, contains numerous chloroplasts, mitochondria, and microtubules. The hyphae contact the substratum via the ventral walls of the epidermal cells and the rhizoids are free from infection. In the protocorm and root nodules, aseptate hyphae initially colonize mucilage-filled schizogenous intercellular spaces. Subsequent invasion of the host cells is associated with the development of massive overgrowths of host wall material. The fungal associations inL.cernuumshare a mixture of attributes otherwise found in different angiosperm mycorrhizae and in mycotrophic relationships in liverworts. Wall ingrowths are present in both the gametophyte and sporophyte cells in the placenta ofL.cernuum. The very limited development of the placenta, compared withL.appressum, certain bryophytes and ferns, the diminutive size, and early senescence of the gametophytes ofL.cernuumare all linked to the presence of the protocorm. This massive absorptive organ, homologous to a foot, in terms of its position in sporophyte ontogeny, but external to the parent gametophyte, derives its nutrition partly from photosynthesis and partly from its fungal endophyte.Key words: chloroplasts,Lycopodium, mycorrhiza, pteridophytes, root nodules, symbiosis, transfer cells.

ISSN:0008-4026    

DOI:10.1139/b92-008

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Savannas growing on stony, old and nutrient-poor soils of southern Venezuela were severely disturbed by removal of the soil organic layers with bulldozers for road building. Introduced speciesBrachiaria decumbens,Brachiaria humidicola,Pueraria phaseoloides, andCalopogoniumsp. were sown. The substrate was fertilized and limed. Plant cover, vesicular – arbuscular mycorrhizae colonization, spore number, and most probable number of propagulels in undisturbed savanna, disturbed nonrevegetated savanna, and six revegetated savannas were assessed. The perturbation reduced the mycorrhizal propagule number in comparison with the undisturbed savanna. In the nonrevegetated areas the mean percent ground cover 2 years after disturbance was low (0.04%). In revegetated areas an increase in mycorrhizal propagule number occurred and the mycorrhizal colonization of the sown species was high. In restored areas there was an increase in species of nonmycotrophic Amaranthaceae. The results support other predictions on the mycorrhizae in successional biomes, because in the extremely nutrient-poor soils studied the colonizing species were mainly mycotrophic. The reclamation program applied in disturbed areas was useful because it has allowed the recovery of vesicular – arbuscular mycorrhizal inoculum and there was an increase in the recolonization of native plants.Key words: disturbance, endomycorrhizae, revegetation, savanna, vesicular – arbuscular mycorrhizae.

ISSN:0008-4026    

DOI:10.1139/b92-009

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Chromosome counts were obtained on 117 plants of the circumpolar grassArctagrostis latifolia(R. Br.) Griseb. collected across mainland Alaska. Three chromosome races were found in the state. A widespread distribution was indicated for the tetraploids (2n = 28) and octoploids (2n = 56) and a limited distribution for the hexaploids (2n = 42), heretofore unreported for North America. Both tetraploids and octoploids appeared to be well represented through the boreal interior and arctic, unglaciated refugia of Alaska. Only tetraploids were found on the heavily glaciated terrain of southcentral Alaska. Six hexaploid counts were obtained on plants collected from two locales at the ecotone of glaciated and unglaciated areas. Cytotype distribution was interpreted as indicating a greater mobility for the tetraploid race, better enabling it to occupy deglaciated terrain and other disturbances, and the possibility of survival of the tetraploid in local refugia within the extensively glaciated southcentral region. The data provided support for the inclusion of different chromosome races within a single taxon.Key words: refugia, cytotype, polyploidy, recolonization.

ISSN:0008-4026    

DOI:10.1139/b92-010

出版商:NRC Research Press    

年代:1992

数据来源: NRC