摘要:

Resistant and susceptible alfalfa clones derived from the cultivar Arc were spray inoculated with conidia from race 1 or race 2 isolates ofColletotrichum trifoliiBain in compatible and incompatible combinations. No significant differences were found in the frequencies of formation of immature or mature appressoria or in germ-pore formation by either race ofC.trifoliion resistant or susceptible plants. These results indicate that incompatibility is not associated with the failure of conidia to germinate or to form appressoria with germ pores. In a small number of observations, penetration pegs were observed in tissue of both resistant and susceptible plants.Colletotrichum trifoliiinitiated infections in alfalfa by direct penetration of the epidermis via a penetration peg from the appressorium. Although the fungus spread rapidly throughout susceptible hosts, we observed fungus penetration only of epidermal cells of resistant hosts. Therefore, it appears that expression of alfalfa resistance toC.trifoliioccurs near the time of epidermal cell wall penetration.

ISSN:0008-4026    

DOI:10.1139/b88-011

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Permanent plots dominated by the feather moss,Pleurozium schreberi(Brid.) Mitt., were established at a Canadian boreal forest site to study the effects of simulated acid precipitation on percent cover, growth, and photosynthesis of vegetation. For a 5-year period, beginning in 1981, plots ofP.schreberireceived twice-monthly sprayings of simulated rain, adjusted to pH 5.6, 4.0, 3.5, 3.0, or 2.5 with a 2:1 molar mixture of sulfuric and nitric acids. Unsprayed plots were also monitored. Almost complete elimination of the moss had occurred in the plots sprayed with pH 2.5 by the end of the 2nd year of treatment, and substantial decreases in cover were also recorded at pH 3.0 and 3.5 over the 5 years. Significant reductions of up to 75% in total and living frond height and dry weight were recorded at pH 3.5 and lower. Lateral branches produced in acid-treated plots also were stunted and few in number. This decline in growth and percent cover ofP.schreberimay have resulted from the decreased net photosynthetic rates measured in the field and would be accelerated by increased rates of evapotranspiration in the altered moss microhabitat.

ISSN:0008-4026    

DOI:10.1139/b88-012

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Two types of crude extracts were obtained from 10 cultivars of date palm (Phoenix dactyliferaL.); the Tris buffer extracts from acetone powder were assayed for peroxidase activity and the phosphate buffer extracts were subjected to polyacrylamide gel electrophoresis. The gels were stained for esterase activity using α-naphthylacetate and α-naphthylbutyrate as substrates. The cultivars were divided into four sets on the basis of their esterase isoenzyme phenotypes. These sets were further separated into their individual cultivars on the basis of peroxidase activities. The results are discussed with respect to the possible relationship of the peroxidase activity in the vascular fusariosis of date palm (Bayoud disease). This study has potential for practical application; however, some additional refinements in procedures appear necessary to reduce extraction time.

ISSN:0008-4026    

DOI:10.1139/b88-013

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The tissue previously described as paraveinal mesophyll in soybean leaves is shown to have the characters of bundle sheath rather than mesophyll cells and is renamed "extended bundle sheath" (EBS) tissue. Its presence was surveyed by leaf clearing in 66 species of legumes of all three subfamilies. A complete extended bundle sheath system similar to that previously described in soybean was identified in 21 of the species. This system is a paradermally oriented tissue, one cell deep, between the spongy and palisade mesophylls, consisting of extended bundle sheath cells, which join each other across the interveinal space either directly or via bridging cells of somewhat similar shape and size. A newly recognized, attenuated extended bundle sheath system, in which bundle sheath cells extend but do not form a continuum except in very narrow interveinal spaces, is described; it was found in 32 species. Extended bundle sheath tissue was absent from 13 of the species. The presence or form of extended bundle sheath tissue does not follow traditional taxonomic divisions. Extended bundle sheath systems were also found in 3 of 5 nonlegume species.

ISSN:0008-4026    

DOI:10.1139/b88-014

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The analysis of the total buried seed population along an altitudinal gradient in the Mont Jacques-Cartier area, southern Quebec, reveals a close relationship between buried seed flora and aboveground vegetation. Eighty-one percent of the species present in the total buried seed population were present in the aboveground vegetation of the study sites. The total number of seeds in the buried seed population, the number of species in the total buried seed population, and the number of seeds and species in the seed bank did not show any significant linear correlation with altitude. A shift from a boreal to an arctic–alpine buried seed population with increasing altitude was observed, instead of a decrease in seed bank size.

ISSN:0008-4026    

DOI:10.1139/b88-015

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

In angiosperm plants subjected to plasmolysis, pollen tubes may undergo substantial ultrastructural changes accompanied by a gradual deterioration of those processes involved in cell syntheses. However, some tubes quickly regenerate a polysaccharide wall and thus ensure their extension. Others undergo fragmentation of their cytoplasm and a serious breakdown in processes involved in cell wall synthesis. In these extreme cases, the endoplasmic reticulum is the only compartment that is readily discernible.

ISSN:0008-4026    

DOI:10.1139/b88-016

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Seasonal growth and occurrence of an exotic submersed aquatic macrophyte,Nitellopsis obtusa, was monitored at the head of the Detroit River of the Great Lakes from June 1984 to April 1985.Nitellopsis obtusafirst appeared in early July, increased in biomass from July to September, remained at relatively high biomass from September to late January, and decreased substantially as ice breakup began in mid-February. By March it had become senescent, lacking chlorophyll and disintegrating easily.Nitellopsis obtusawas therefore available as a source of food and shelter for benthic and juvenile fish populations in late fall and winter, when other macrophytes were absent.

ISSN:0008-4026    

DOI:10.1139/b88-017

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Isolates of several ectomycorrhizal fungi, some from a Cu- and Ni-contaminated smelter site near Sudbury, Ont., and some from an uncontaminated site, were grown on solid media containing 25 or 100 mg nickel/L, or 25 or 100 mg copper/L. The influence of the metals on lag time prior to the commencement of growth, on the maximum increase in colony diameter, and on the final colony dry weight was determined. Isolates from the metal-contaminated site did not outperform those from the uncontaminated site on any of the metal-amended media. In a second experiment, isolates ofLaccaria proximo,Lactarius hibbardae,Lactarius rufus, andScleroderma flavidumwere grown in liquid media containing 2 or 5 mg Ni/L or 4 mg Cu/L. These fungi have previously been shown to vary in their effect on the metal tolerance ofBetula papyrifera, at these concentrations. The axenic growth of the fungi in the presence of Ni showed no relationship to their effect on the birch seedlings. In general, the fungi that were least tolerant to Cu in liquid culture,Lactarius rufusandLaccaria proximo, were the same ones that proved most detrimental to the birch grown in the presence of Cu. These results indicate that axenic screening tests will not necessarily select fungi that will increase host metal tolerance.

ISSN:0008-4026    

DOI:10.1139/b88-018

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

The difference in vigour betweenPicea abies(L.) Karst. andAbies albaMill, in an area exposed to fine dust containing MgO is reflected in scanning electron microscope studies of the needle surfaces. The greater vitality of the silver fir is correlated with intact wax structures and a somewhat lower dust load. In contrast, the spruce reveals a marked effect on the epicuticular wax by a heavy fine-dust load. Possible causes and physiological consequences are discussed.

ISSN:0008-4026    

DOI:10.1139/b88-019

出版商:NRC Research Press    

年代:1988

数据来源: NRC

摘要:

Mudflow deposits, when dated, offer an excellent opportunity to examine vegetation and soil development overtime. Vegetation on a 33-year-old mudflow deposit at Mount Rainier National Park, WA, is compared with data collected 4 and 7 years after deposition. Four plant communities are recognized on the mudflow deposit and one is recognized in the adjacent, undisturbed forest. Soil characteristics in each community are compared with soil data collected 8 and 15 years after deposition. Key factors influencing plant succession and soil development on the mudflow deposit are (i) presence of residual standing dead trees and associated organic debris and (ii) proximity of sample stands to adjacent, undisturbed forest. Successional trends and changes in soil characteristics over a 33-year period are discussed.

ISSN:0008-4026    

DOI:10.1139/b88-020

出版商:NRC Research Press    

年代:1988

数据来源: NRC