摘要:

Fifty-six plant species in 43 genera and 19 families, selected by using the centrifugal phylogenetic method, were screened againstExserohilum monoceras, a fungus collected in the Philippines onEchinochloa colona. Trials were performed under both optimum greenhouse conditions with supplemental 24-h dew and natural field conditions with no dew supplement. The compatibility of host–pathogen interactions was characterized by the time and level of sporulation observed on detached inoculated leaves. AllEchinochloaspecies proved to be highly susceptible to this fungus under optimum greenhouse conditions as well as in the absence of a dew supplement.Rottboellia cochinchinensiswas also highly susceptible to this pathogen regardless of the presence of a supplemental dew period. Among the crops tested, only corn seedlings were slightly infected under supplemental 24-h dew conditions, but no disease symptoms were observed on corn in the absence of a dew supplement. Sorghum and sugarcane were hypersensitive to the pathogen under supplemental 24-h dew conditions, but no infection was detected in the absence of a dew supplement. All other species tested were immune toE.monoceras. Data on sporulation on detached leaves from inoculated plants indicated thatE.monoceraswas weakly compatible with corn. No disease symptoms and no conidia were detected on leaves of trap plants. In the field,E.monocerasproduced no symptoms on corn plants.Key words: host range, bioherbicide,Exserohilum monoceras,Echinochloa crus-galli,Echinochloa colona,Echinochloa glabrescens.

ISSN:0008-4026    

DOI:10.1139/b97-077

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Sequences in the 5.8S rDNA and internal transcribed spacer region were obtained for taxa belonging toGremmeniellaspp., and a phylogenetic analysis was carried out using parsimony and distance methods. A set of hypotheses concerning evolutionary relationships between members of that genus was tested. The hypothesis that all members ofGremmeniella abietinavar.abietinaare closely related was rejected. It appears that the Asian race is quite divergent from the European and North American races, but could be more closely related toG.abietinavar.balsamea. The phylogeny was consistent with host specificity: members ofG.abietinavar.abietinagenerally do not infectAbiesorPiceaspp. but the Asian race occurs onAbies sachalinensisin Japan. The hypothesis that host specialization has created divergence withinG.abietinavar.balsameawas supported by our analysis because the levels of divergence between isolates originating fromPiceaspp. andAbiesspp. were similar to those found between the North American and European races ofG.abietinavar.abietina. The hypothesis that greater divergence occurred betweenGremmeniella abietinaandGremmeniella laricinathan betweenG.abietinavar.abietinaandG.abietinavar.balsameawas not supported. The level of divergence was as large between the two varieties withinG.abietinaas between the two speciesG.abietinaandG.laricina. These results indicate that similar taxonomic levels should be applied to these three taxa.Key words: scleroderris canker, internal transcribed spacer (ITS).

ISSN:0008-4026    

DOI:10.1139/b97-078

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Dematious hyphomycetes such asVerticicladium trifidumandThysanophora penicillioidesare examples of equivalent species occupying the same ecological niche in different fungal successions. These two species fructify through the stomata of coniferous needles a few months after litter fall. Litter samples of 23 coniferous species from different European sites were examined to explain the fungal distribution.Thysanophora penicillioidescolonizedAbies,Picea,Pseudotsuga, andTsuganeedles, whereasV.trifidumwas restricted toPinusandCedrus. Sometimes other fungal species occupied the stomata: onPinus pineaneedles, the niche was occupied byCladosporiumspp. andAlternaria alternata;Chaetopsina fulvahave been found only onPseudotsuganeedles andThysanophora canadensisonPicea.Verticicladium trifidumwas apparently absent onPinuslitters from cold climates (high altitude or latitude) and probably from warm mediterranean regions, suggesting a climatic determinism. However, coexistence ofVerticicladiumandThysanophorain some samples or colonization of somePinuslitter byThysanophorasuggests that these distributions result from competition rather than strict host specificity.Key words: ecological niche, equivalent species, conifers, needles,Verticicladium trifidum,Thysanophora penicillioides.

ISSN:0008-4026    

DOI:10.1139/b97-079

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Roots of 75 tree species, belonging to 28 families, were sampled on different types of soil in the forest of French Guiana. Both seedlings and mature trees of each species were studied. The roots were first observed for ectomycorrhizas, then thinned and stained to observe and quantify endomycorrhizal associations. Ectomycorrhizas were found only on two genera:Coccoloba(Polygonaceae) andNeea(Nyctaginaceae). All the species studied had zygomycetous endomycorrhizas with hyphal coils and vesicles. It is remarkable that some families (Caesalpiniaceae, Myrtaceae, Tiliaceae, Euphorbiaceae, Lauraceae), considered as frequently ectomycorrhizal in other regions of the world, were not so in our sample. In addition, the results contradict the theory that ectomycorrhizal species are dominant in the poorest soils in tropical rainforests (tropical podzols).Key words: tropical rainforest, symbioses, mycorrhizas, French Guiana.

ISSN:0008-4026    

DOI:10.1139/b97-080

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Leaf scars from 13 peach cultivars and clones with varying susceptibility to peach canker disease were collected during the period November 1986 through May 1987 and were examined histologically. Leaf scar sections were examined with light and fluorescence microscopy for tissue changes related to wound healing, including depth and width of the polysaccharide-impregnated zone, the timing and tissue depth at which the ligno-suberized layer occurred, the thickness and numbers of cells in the ligno-suberized layer, the longitudinal length of the ligno-suberized layer and whether or not the tissue was complete in longitudinal section through the leaf scar, and the presence and numbers of phellem cells in the wound periderm and whether or not the periderm was complete across the longitudinal section of the leaf scar. The percentage of leaf scars with a complete polysaccharide-impregnated zone varied by date with 94–96% of the leaf scars exhibiting the zone in January and April. The thickness of the polysaccharide-impregnated zone also varied by date, reaching its thickest in January and April. Percentages of lignified leaf scars were mostly similar among cultivars on four of the five dates; however on 1 May, there was considerable variation among cultivars with percent lignification ranging from 0 to 100%. The proportion of leaf scars with lignification was not significantly correlated with the field susceptibility rankings for peach canker disease at any of the five dates. The proportion of leaf scars with complete ligno-suberized layers varied by date only, with the highest values observed on 12 January and 14 May. The lowest values was observed on 1 May, and this was significantly less than that observed on 7 November and 10 April. The highest percentage of leaf scars possessing periderm occurred on 12 January (74%), with all the other dates not significantly different from each other (ranging from 29 to 40%). Analysis of cultivar across all dates combined indicated that Candor generally showed the highest percentages of leaf scars with periderm (64%), and this was significantly higher than Sunhaven (24%), Earlired (14%), and V68101 (13%), which were not different from each other. The proportion of leaf scars with periderm was not significantly correlated with the field susceptibility rankings for peach canker disease at any of the five dates.Key words:Prunus, wounding,Leucostoma.

ISSN:0008-4026    

DOI:10.1139/b97-081

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The influence of an arbuscular mycorrhizal fungus,Glomus mosseae, on the adverse effects of soil compaction on growth and phosphorus (P) uptake of red clover was studied in a model experiment. The pots used in the experiment had three compartments, a central one with a soil bulk density of 1.3 g ∙ cm−3and two outer compartments with three different levels of soil bulk density (1.3, 1.6, or 1.8 g ∙ cm−3). The soil in the outer compartments was fertilized with P and was either freely accessible to roots and hyphae, or separated by nets and accessible to hyphae only. At a soil bulk density of 1.3 g ∙ cm−3, mycorrhizal plants did not absorb more P than nonmycorrhizal plants except when access of roots to the outer compartments was restricted by nets. At high soil bulk density, root growth was drastically decreased. However, hyphae ofG.mosseaeabsorbed P even from highly compacted soil, and induced a P-depletion zone of about 30 mm from the root surface. In consequence, at higher soil bulk density shoot P concentration and the total amount of P in the shoot were higher in mycorrhizal than in nonmycorrhizal plants. This experiment showed that hyphae ofG.mosseaeare more efficient in obtaining P from compacted soil than mycorrhizal or nonmycorrhizal roots of red clover.Key words: arbuscular mycorrhiza, phosphorus, red clover (Trifolium pratenseL.), soil bulk density, soil compa

ISSN:0008-4026    

DOI:10.1139/b97-082

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The structure of the pollen wall as revealed by transmission electron microscopy is presented for 34 species representing two subtribes and 12 genera of New World Senecioneae. The genusPackera(=aureoidSenecio), with the exception ofPackera zimapanica, is characterized by the helianthoid wall structure. In light of these results, the disposition of the latter species requires review. The generaRobinsonecioandTelanthophoraof the subtribe Tussilagininae also possess helianthoid pollen. All other taxa surveyed have senecioid pollen. So far as known no taxa exist within the tribe Senecioneae with a base chromosome number ofn = 20 and helianthoid pollen. This suggests that the evolution ofPackeramay have involved hybridization between members of the two subtribes Senecionineae and Tussilagininae.Key words: Asteraceae,Packera, Senecioneae, pollen, TEM, systematics.

ISSN:0008-4026    

DOI:10.1139/b97-083

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The breeding system of the alpine shrubRhododendron ferrugineumwas studied at two sites of a population (site L and site H) in the French Alps. The aims were to estimate the degree of selling and (or) outcrossing and to determine if floral traits (including floral morphology, pollen to ovule ratio, stigma receptivity) may be related to the breeding system of the shrub. First, floral traits (corolla length and anther, and style heights) were measured, the number of pollen tetrads and ovules were counted, and the date of stigma receptivity and anther dehiscence were recorded. Second, five pollinations treatments (unmanipulated flowers, natural selfing, hand selfing, natural outcrossing, and hand outcrossing) were performed on 35 randomly chosen individuals in each site, and after each treatment the number of seeds per fruit was recorded. The results demonstrate thatRhododendron ferrugineumis self-compatible (self-compatibility index = 0.95 and 0.97; auto-fertility index = 0.92 and 0.98; selfing rate = 0.24 and 0.11 at sites L and H, respectively). Indices values are not significantly different between the two sites and facultatively xenogamous (pollen to ovule ratio = 669.5 ± 280.5 and 845.2 ± 246.9 at sites L and H, respectively).Key words: breeding system,Rhododendron ferrugineum, floral morphology, phenology, P:O ratio.

ISSN:0008-4026    

DOI:10.1139/b97-084

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Riparian forests are productive and species rich ecosystems where the vegetation is structured by sharp environmental gradients. The study describes community patterns of bryophytes in stream-side forests, relates these patterns to major environmental gradients, and compares within-site factors with site level variables. Samples were collected from 360 plots 2 × 4 m in size distributed among 42 sites in old-growthPseudotsuga–Tsugaforests. The sites ranged from 420 to 1250 m asl and stream size from 1st to 5th order streams. There were significant changes in species richness and composition along several environmental gradients. Richness within sites varied among different geomorphic surfaces with the highest number of species on areas periodically flooded. Richness was also higher in plots with high abundance of woody debris. No site level factors influenced richness at the sample plot level, while the highest species number at the site level was for large streams. The main gradients in the species composition within sites were changes with increasing distance from the stream and amount of woody debris. Both elevation and stream size significantly influenced species composition. The complex set of factors that influenced species richness and composition implies that management of riparian vegetation must be based on both coarse scale considerations such as regional distribution of different stream types and fine scale factors such as spatial availability of different substrate types.Key words: old-growth forest; CCA analysis; fluvial disturbance; bryophytes; elevation effects; coarse woody debris.

ISSN:0008-4026    

DOI:10.1139/b97-085

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Infection of nematodes byMeristacrum asterospermumandZygnemomyces echinulatuswas initiated by conidia adhering to the nematode's cuticle. Each conidium developed an infection peg to penetrate the nematode after adhesion. InM.asterospermum, an infection peg just under the penetration was found in ultrathin sections, in which the peg's cell wall was broken into several lobes that were covered entirely with an amorphous mass of electron-opaque substance. Septa formed in the apical portion of aerial conidiophore under conidiation. The septal wall was nonperforate and often contained electron-opaque inclusions. Vegetative hyphae ofZ.echinulatushad typical bifurcate septa, but septa at both ends of the pedicel of conidia were often slightly deformed.Key words: infection of nematodes,Meristacrum asterospermum, septum,Zygnemomyces echinulatus.

ISSN:0008-4026    

DOI:10.1139/b97-086

出版商:NRC Research Press    

年代:1997

数据来源: NRC