摘要:

Leaves and stems of flowering plants have been widely accepted as clearly distinguishable structural categories. Evolution, however, can blur the stem–leaf (axis–appendage) distinction. Compound leaves with apical growth and three-dimensional branching may be seen as developmental mosaics sharing some growth processes with leafy stems (shoots). To cope with fuzzy boundaries between structural categories, fuzzy morphology is proposed as a complementary way of looking at higher plant architecture. Fuzzy morphology treats structural categories (e.g., leaves and stems) as concepts with fuzzy (not sharp) boundaries. The developmental morphology of compound leaves is described comparingApium repens(Apiaceae) with less typical angiosperms ("misfits") of the rheophyte family Podostemaceae, especiallyMarathrum rubrum,Mourera fluviatilis, andTristicha trifaria. In some taxa within the Podostemaceae, typical leaf characteristics may be replaced by new properties, e.g., 90° switch of symmetry plane of the leaf primordium with production of pinnae or lobes along the adaxial and abaxial margin inMarathrum rubrumandMourera fluviatilis. InTristicha trifaria, compound photosynthetic appendages (called ramuli) combine developmental characters of typical leaves and typical stems. Thus, they may be called leaf-stem intermediates. Fuzziness of structural categories such as leaf and stem is especially obvious in Podostemaceae, which can be seen as the result of saltational evolution. The structural categories of typical flowering plants are transcended in the Podostemaceae because of developmental changes, resulting in organs with unique combinations of features.Key words: leaf development, developmental mosaic,Apium,Marathrum,Mourera,Tristicha.

ISSN:0008-4026    

DOI:10.1139/b95-142

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The distribution and seasonal patterns of arbuscular mycorrhizal fungi activity were studied in an inland boreal salt pan site in north-central Manitoba. Semipermanent study regions were set up in each of five vegetation zones along a continuous salinity gradient. Roots ofHordeum jubatum,Distichlis stricta,Agropyron trachycaulum,Sonchus arvensis,Spartina gracilis, and other species were collected from the study regions over six time periods: April, June, July, August, and October of 1991, and May of 1992. These roots were used to quantify mycorrhizal colonization, as well as arbuscule and vesicle formation. Arbuscular mycorrhizal fungi were prevalent in the three vegetation zones with lowest soil salinity, with > 40% of the observed root pieces colonized. Colonization was < 2% in the other two zones, where soil salinity was consistently greater throughout the growing season. The only common pattern in the phenology of mycorrhizal activity was a low level of activity in the early spring. Mycorrhizal activity in most plant species occurred at high levels throughout the summer and fall. Differences in patterns of activity appeared to be linked to differences in phenology of root growth, and not to edaphic differences among vegetation zones.Key words: Manitoba, arbuscules, fungi, gradient, mycorrhiza, phenology, salinity, vesicles.

ISSN:0008-4026    

DOI:10.1139/b95-143

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

A study of the first infection stages of banana byCercospora fijiensiswas carried out using an experimental host–parasite system including three cultivars, Yangambi km5 (Musa, AAA, Ibota subgroup), Fougamou (Musa, ABB,Pisang awaksubgroup), and Grande naine (Musa, AAA, Cavendish subgroup). These cultivars are representative of three host responses to infection: highly resistant (cessation of the infection process after the first streak stage), partially resistant, and susceptible. Observations on the early stages of infection and the chronology of events linked to the host plant (cellular necrosis) and to the parasite (cessation of growth) showed two different interactions in cvs. Fougamou and Yangambi. These observations were confirmed by an ultrastructural study. Partial resistance in cv. Fougamou appeared to be partly linked to a préexistent anti-fungal, plant phenolic component. In the highly resistant cv. Yangambi, an active defense mechanism took place just after penetration of stomata by the fungus.Key words:Cercospora fijiensis, banana, host–parasite interactions, mechanisms of resistance, polyphenols.

ISSN:0008-4026    

DOI:10.1139/b95-144

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

This study aims to identify the role of the beetleEpuraea obliquusHatch in disseminatingScytalidium uredinicolaKuhlman et al., a mycoparasite of western gall rust,Endocronartium harknessii(J.P. Moore) Y. Hiratsuka. The study was conducted in a lodgepole pine,Pinus contortaDougl. var.latifoliaEngelm., stand near Hinton, Alberta. Mycoparasite spores were observed on the integument of adult beetles collected from western gall rust. In field and greenhouse experiments, adult beetles inoculated with spores of the mycoparasite caused significant numbers ofS.uredinicolainfections on western gall rust. SinceE.obliquusadults migrate between galls, the beetle can transfer the mycoparasite from parasitized to unparasitized galls. Scanning electron microscopy showed that spores of the mycoparasite were common on the body of overwintering beetles. It is believed that these overwintering spores are viable because a culture was successfully established from them. This suggests that beetles emerging in the spring can disseminateS.uredinicolato previously uninfected galls.Epuraea obliquusis an important insect vector ofS.uredinicolain western Canada.Key words: mycoparasite, vector, spore dispersal, western gall rust, pine stem rusts.

ISSN:0008-4026    

DOI:10.1139/b95-145

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

A new interspecific hybrid inIsoetes,I.maritimaUnderw. ×I.howelliiEngelm., is delineated and described from the Shuswap Highlands region of British Columbia by means of cytology and scanning electron microscopy of spores.Isoetes×marensisD.M. Britton and D.F. Brunton, hyb.nov. is the name proposed for this taxon. It is triploid (3x; 2n = 33) and is believed to produce only sterile and (or) aborted spores. Hybrid plants have polymorphic spores that demonstrate size and surface ornamentation features intermediate between those of the putative parents. Three populations were examined, each growing with both of the putative parents in silt and sand among granite cobble over clay along an emergent lakeshore.Isoetes×marensisis the first described North American hybrid involving an amphibiousIsoetes. It is expected to be a rare taxon owing to the restricted sympatric area of the putative parents and their tendency to occupy different habitats.Key words:Isoetes,Isoetes howellii,Isoetes maritima, hybrid, British Columbia.

ISSN:0008-4026    

DOI:10.1139/b95-146

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

In a random block field experiment, life-history traits associated with colonizing ability of diploid and tetraploid cytotypes ofCapsella(Brassicaceae) were compared. These were germination, flowering, growth-form parameters, and leaf shape. Data are not in favour of differences in germination behaviour between the diploid and tetraploidCapsellaspecies, as germination rate and capacity are highly influenced by inception and release of seed dormancy. Although our data at first glance seem to suggest that diploidC.rubellastart flowering later than tetraploidC.bursa-pastoris, considerable ecotypic variation for flowering in both species makes it difficult to assign an effect specifically to ploidy level. We also conclude that plant height, rosette diameter, and branching number are not directly determined by ploidy level. In contrast however, leaf shape is clearly determined by ploidy level. In the light of all available data including data of previous experiments, we suggest that gene duplication by polyploidization may have been a key element that providedC.bursa-pastoriswith additional genetic flexibility. It is not primarily the gain of colonization ability, as both species are weeds and colonizers. Rather, the greater genetic flexibility enabledC.bursa-pastoristo extend its range beyond that ofC.rubella.Key words: ploidy level, germination, flowering, growth form, leaf morphology,Capsella.

ISSN:0008-4026    

DOI:10.1139/b95-147

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Canonical discriminant analysis was used to assess the taxonomic status ofAntennaria neodioicaGreene var.gaspensisFernald. Results based on these analyses indicate thatAntennaria howelliiGreene,Antennaria microphyllaRydberg,A.neodioicavar.gaspensis,Antennaria pulvinataGreene, andAntennaria roseaGreene are morphologically distinct. High cross-validation assignment rates as well as high Geisser assignment probabilities for each of the taxa support this statement. Elevating var.gaspensisto the rank of species is in part supported by the data analysis, but doing so would be contrary to the species standard method and inconsistent with recent practice in revisions of the genus. The presence of scarious appendages at the tips of the upper cauline leaves, the open pedicellate inflorescence, the whitish-green capitula, general growth form, agamospermous reproduction, chromosome number, provenance, and quantitative morphology, in addition to the results of the canonical discriminant analysis, support recognition of var.gaspensisat an infraspecific rank. In keeping with the criteria utilized in recent revisions of the genus, var.gaspensisshould more appropriately be treated as a subspecies. Recent nomenclatural rearrangements inA.neodioicaandA.howelliifounded on the priority of the latter lead to the following new combination:Antennaria howelliisubsp.gaspensis(Fernald) Chmielewski.Key words:Antennaria howelliivar.gaspensis, Asteraceae, Newfoundland flora, Gaspé Bay Peninsula flora.

ISSN:0008-4026    

DOI:10.1139/b95-148

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

InDatura feroxL. seeds induced to germinate by the far-red light absorbing form of phytochrome (Pfr) and alternating temperatures, protein degradation started before radicle protrusion. Proteolysis was, however, restricted to the micropylar region of the endosperm in which the protein content decreased 51% by 48 h after red light treatment. There was no change during that time in the protein content of the rest of the endosperm or in the embryo. Light and electron microscopy preparations show the vacuolation of protein bodies along with other changes in cellular structure in the micropylar portion of the endosperm in seeds treated with red light (R). No changes were detected in the rest of the endosperm or in the micropylar portions of far-red light (FR) treated seeds. In the embryonic axes there were some alterations but only in a small sector of the calyptra. In contrast, shortly after radicle protrusion (5 h), there was extensive degradation of protein bodies in the embryonic axes. A Pfris required for the induction of protein degradation in the micropylar portion of the endosperm in the intact seed before radicle protrusion. Incubation of isolated micropylar portions induced protein degradation in tissues from seeds treated with either R or FR. The results do not support a source–sink type of control of protein degradation in the endosperm driven by the beginning of embryo growth but suggest the participation of regulatory signals in the determination of a temporal and spatial pattern of protein degradation in both the endosperm and the embryo.Key words: germination, dormancy, phytochrome, protein degradation, micropylar endosperm.

ISSN:0008-4026    

DOI:10.1139/b95-149

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Three types of colonies (WH, WA, and RA) have been characterized among 2245 isolates ofPseudocercosporella herpotrichoideson the basis of colony growth rate and appearance (W, rapid growth and regular margin; R, slow growth and irregular margin) and of the shape of the majority of conidia (H, coiled; A, straight). Apothecia ofTapesia yallundae(anamorph :P.herpotrichoides) were produced on naturally infected stems of winter wheat and barley. Apothecia of an undetermined discomycete were occasionally observed. The progeny of more than 1700 ascospores from 72 apothecia ofT.yallundaewas distributed among the three types of colonies. These types remained stable through successive conidial and mycelial subcultures. All three colony types were sometimes obtained from a single apothecium. WH and WA were the most common, while RH was never observed. WA isolates were more often resistant than WH isolates to carbendazim. Inoculations of wheat and barley stems with ascospores ofT.yallundaewere unsuccessful, while inoculations with conidia or mycelium resulted in eyespot lesions. During equivalent periods, RA isolates were less virulent than WH and WA.Key words: cereals, eyespot, Deuteromycetes, sexual stage,Hordeum vulgare,Triticum aestivum.

ISSN:0008-4026    

DOI:10.1139/b95-150

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Powellomyces(order Spizellomycetales) is erected for soil-inhabiting chytrids previously classified inEntophlyctis. Fischer's narrative and figures indicate thatEntophlyctiswas originally described to accommodate aquatic, chytridialean species, and consequently this is not an appropriate genus for spizellomycetalean species.Powellomyces hirtussp.nov. andPowellomyces variabilisnom.nov. both develop exogenously but differ in distribution of rhizoids on germlings and in colour of colonies in culture.Key words: Chytridiales,Entophlyctis,Powellomyces, Spizellomycetales.

ISSN:0008-4026    

DOI:10.1139/b95-151

出版商:NRC Research Press    

年代:1995

数据来源: NRC