摘要:

Comparisons between current vegetation patterns and deposition of modern pollen and plant macroremains in a saline lake basin on the northern Great Plains are used to assess the value of plant remains as indicators of past local vegetation dynamics and lake-level changes. Results indicate that both modern pollen spectra and assemblages of plant macroremains reflect clearly the composition of the local vegetation, whereas plant macroremains best reflect lake size. Cactaceae pollen and seeds are confined to upland prairie deposits. Liguliflorae (Compositae) and Leguminosae pollen,Selaginella densamicrospores, andEuphorbiaand Cruciferae seeds are more abundant in prairie upland deposits than in shoreline or lacustrine environments. An abundance (> 50%) ofRuppiapollen distinguishes near-shore lake sediments, indicating that this taxon is a useful marker of shallow shoreline environments in saline lakes. Seeds of Chenopodiaceae,Erigeron, Cruciferae, and Cyperaceae, as well asCharaoogonia, are more abundant in near-shore lacustrine sediments than in the central lake area, suggesting that they too are indicators of shoreline proximity. These data are useful for paleobotanical reconstructions of past lake-level dynamics.Key words: saline lakes, Great Plains, pollen, paleobotany, paleohydrology, environmental reconstruction.

ISSN:0008-4026    

DOI:10.1139/b94-072

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Tryblidiopsis pinastri(Pers.:Fr) P. Karsten, an ascomycete common on twigs and branches ofPiceaspp. is redescribed and illustrated.Tryblidiopsis piceaeVelenovský is synonymized withT.pinastriand other species ofTryblidiopsisare briefly reviewed. The taxonomic position of the genusTryblidiopsisis reviewed, concluding that it is correctly placed in the order Rhytismatales for which a new and detailed circumscription is provided. Families of that order are briefly discussed, andTryblidiopsisis disposed in the Rhytismataceae.Tryblidiopsis pinastriis reported from trunk bark of dying mature trees. Aspects of its biology and ecology are discussed.Key words: forest pathology, endophyte,Picea,Tryblidiopsis, Rhytismatales.

ISSN:0008-4026    

DOI:10.1139/b94-073

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The effects of prehelminthosporol, a toxin produced byBipolaris sorokiniana, were investigated on barley roots. A concentration of 30 μg∙mL−1prehelminthosporol or higher in nutrient solution significantly increased the rate of nuclear disintegration in the root cortex cells. The toxin also increased leakage of ATP from intact roots of barley seedlings grown in nutrient solution, but the growth rate of the seedlings was not significantly affected. However, diluted filtrate from liquid shake cultures of the fungus inhibited the growth of the seedlings by 21 – 73% over a 5-day period. The results indicate that the toxin may play an important role in pathogenesis by killing or weakening plant cells in advance of the growing hyphae and facilitating nutrient uptake and further growth of the fungus in plant tissue. Different cultivars of barley differed in sensitivity to prehelminthosporol, but sensitivities were not correlated with known levels of resistance toB.sorokiniana.Key words:Cochliobolus sativus,Hordeum vulgare, root cortex, toxin, prehelminthosporol, AT

ISSN:0008-4026    

DOI:10.1139/b94-074

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Some species ofOrobancheare parasitic weeds attacking the roots of various crops and causing extensive damage. The development of the young parasite was investigated using light and electron microscopy. GerminatingO.aegyptiacaandO.cumanaform a short root, with no root cap, which is covered by a thin cuticle. As soon as the root reaches a host, elongation stops, the apex expands, and peripheral cells become papillate. The extended apex becomes the young attachment organ. The outer papillar surface of the extended apex bears wall protuberances that are encircled with a thick cuticular belt and covered with a thin cuticle. These protuberances secrete a carbohydrate that accumulates in a subcuticular space and is released to the surface, forming a thin adhesive layer that binds the parasite to its host. Bacteria are commonly found in the secretion pool, on the papillae, and in the outer cell walls. The event of attachment of the young parasite to host surface signals a shift from the independent to parasitic phase. This change also includes a shift from the accumulation of lipids to the accumulation of starch.Key words:Orobanche, broomrape, parasitic plants, haustorium, attachment organ, root.

ISSN:0008-4026    

DOI:10.1139/b94-075

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Increasing leaf age was accompanied by increases in resistance in three incompatible cowpea cultivars inoculated with race 1 ofUromyces vignaeand in three of four cultivars that had previously been considered susceptible to race N2. Selected crosses between cultivars suggested that resistance to race 1 was controlled by the same genes in young and old leaves, and they indicated that age-related resistance to race N2 was primarily controlled by a single, and different, gene in each cultivar. All examples of resistance were expressed cytologically as a range of infection site types in a single leaf, the frequency distribution of which was affected by the type of resistance gene, gene heterozygosity, and leaf age. These frequency distributions shifted with increasing leaf age towards infection sites with less fungal growth and more rapid plant cell necrosis, often abolishing the cytological differences between cultivars and genotypes seen in younger plants. The data suggest that each rust resistance gene in cowpea can generate a range of infection site types, and that fungal growth and plant responses at each infection site are governed by a combination of the number and type of resistance genes in the plant, the race of the fungus, and age-affected features of individual plant cells.Key words: cowpea, rust fungi, age-related resistance.

ISSN:0008-4026    

DOI:10.1139/b94-076

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The influence of inoculation with rhizosphere bacteria on Douglas-fir (Pseudotsuga menziesii(Mirb.) Franco) seedling emergence in a controlled environment and on survival and growth in the field was investigated. Seed or seedlings of interior and coastal Douglas-fir ecotypes originating from the vicinity of Williams Lake and Chilliwack, British Columbia, Canada, respectively, were inoculated with two strains of rhizosphere bacteria,Arthrobacter oxydansstrain N74 andPseudomonas aureofaciensstrain K23. These strains were previously isolated from naturally regenerating Douglas-fir seedlings collected from the Williams Lake and Chilliwack sites, respectively. Seed inoculation with either strain of bacteria, K23 or N74, stimulated the rate of seedling emergence, but these effects were not ecotype specific. While inoculation did not affect germination percentage, ecotype-specific seedling growth responses were detected 13 months after field planting.Arthrobacter oxydansstrain N74 significantly stimulated seedling branching and enhanced root and shoot dry weight of the Williams Lake ecotype but had no significant stimulatory effect on growth of the Chilliwack ecotype.Pseudomonas aureofaciensstrain K23 significantly stimulated shoot branching and root dry weight of Chilliwack Douglas-fir but had no significant stimulatory effect on growth of that from Williams Lake. When treatments of Douglas-fir seedlings and rhizosphere bacteria that originated from the same geographic site were pooled and compared with uninoculated controls, significant increases in shoot branch number and root dry weight were also detected. No significant difference in seedling growth was detected when treatments of seedlings and bacteria that originated from different sites were pooled and compared with uninoculated controls. Based on these results, we hypothesize that plant–microbe specificity may be an important component of Douglas-fir – beneficial rhizosphere bacteria interactions in the field.Key words: Douglas-fir seedlings, emergence, growth, rhizosphere bacteria, inoculation.

ISSN:0008-4026    

DOI:10.1139/b94-077

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Meiotic studies on 26 taxa, including two hybrids, of the genusCarexare presented. Results obtained with the hybrid betweenCarex remotaandCarex paniculatassp.lusitanicawere remarkable, since they showed a great number of configurations and even different chromosome numbers in metaphase I. The karyology of theCarex muricatagroup in the SW of Europe was studied for the first time. I also performed the first studies on the karyology of two species belonging to sectionCarexin the SW of Europe, namelyCarex hirta, which gave the highest chromosome number reported so far for the genusCarex(2n = 114), andCarex lasiocarpaErhr., for which I found a putative triploid whose chromosome number (2n = 78–85) was not constant in metaphase I. Agmatoploidy seems to be the most important process involved in the cytogenetic evolution of the species studied here. The idea of the existence of "fragile points" in the chromosomes is suggested to explain the formation of bivalents upon chromosome breakage. In addition, the chromosome number forCarex canariensisis reported here for the first time.Key words:Carex, Cyperaceae, cytogenetics, western Mediterranean.

ISSN:0008-4026    

DOI:10.1139/b94-078

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A new heteropolar nostocalean cyanoprokaryoteMicrochaete robinsoniisp.nov. is described from the benthic periphytic assemblage found on stones in the eutrophic Souris River near Dunclody in southwestern Manitoba, Canada. This species belongs to the group of species with narrow trichomes attenuated to the apex but never forming hairs. The morphology of this species is described and its taxonomic position within the genusMicrochaeteis presented. It differs from otherMicrochaetespecies by morphology of filaments, trichomes and sheaths, dimensions, mode of disintegration of trichomes into hormogonia, and its ecology. The morphological features of heteropolar nostocalean genera useful in generic delimitation are reviewed and discussed.Key words: cyanoprokaryotes,Microchaete, new species, rivers, periphyton, Canada.

ISSN:0008-4026    

DOI:10.1139/b94-079

出版商:NRC Research Press    

年代:1994

数据来源: NRC

ISSN:0008-4026    

DOI:10.1139/b94-080

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

This paper defines different states of mind that have been developed towards plant forms by professional botanists and others. A discussion leads to proposals for an open morphology, keeping a scientific status for this discipline.Key words: plant morphology, history of botany, philosophy of botany. [Journal translation]

ISSN:0008-4026    

DOI:10.1139/b94-081

出版商:NRC Research Press    

年代:1994

数据来源: NRC