摘要:

Pollen grains of 12 species of western Canadian rosaceous genera,Luetkea,Oemleria,Physocarpus, andPrunus, were studied in the light microscope and scanning electron microscope. All pollen grains are produced as isopolar, radially symmetrical, usually tricolporate monads. Grains are predominantly spheroidal with a circular to triangular amb. Most of the species exhibit a well-developed chambered aperture complex at the equator, formed by a pair of sexinal flaps whereas inPrunus spinosa,Prunus americana, andPrunus virginianathe chamber is absent or weakly developed.Oemleria cerasiformishas no pore flaps. Apertures ofPrunus emarginataandPrunus virginianaoften have an equatorial bridge over the aperture complex. The exine ofPrunus,Physocarpus, andLuetkeapollen is tectate perforate, like that of many Rosaceae. Sculpturing consists of ridges and valleys that form a striate to rugulate pattern. Ridges and valleys tend to be mainly parallel to the colpus but often loop near the poles. Pollen grains ofPrunus spinosaare always rugulate or vermiculate with ridges arranged randomly.Oemleria cerasiformispollen appears tectate imperforate. Ridges and valleys intersect at triple points in the subpolar region and curve in a semicircle around the pore area. On this basisOemleriapollen is distinct from all other western Canadian Rosaceae. Pollen grain size ranges from small forLuetkea pectinata(17 μm in diameter) to medium forPrunus spinosa(36 × 33 μm).Key words: pollen morphology, Rosaceae, Western Canada, systematics.

ISSN:0008-4026    

DOI:10.1139/b91-322

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The impact of benomyl fungicide and spring burning on mycorrhizal activity and plant growth was assessed in tallgrass prairie in Kansas. We report for the first time that the productivity of mycotrophic plants can be reduced by inhibition of indigenous vesicular–arbuscular mycorrhizal fungi under field conditions. A vital stain, nitro blue tetrazolium, used to assess active mycorrhizal colonization, proved to be a more sensitive measure of treatment effects than the cell wall stain, trypan blue. Burning stimulated both plant growth and active mycorrhizal colonization. However, by 32 days after burning no differences in colonization were detected. Our observations support the hypothesis that mycorrhizal fungi play an important role in the growth of warm-season tallgrass prairie grasses and may contribute to enhanced plant growth of warm-season tallgrass prairie grasses and may contribute to enchanced plant growth following spring burning.Key words: burning, benomyl fungicide, phosphorus, tallgrass prairie, VA mycorrhizae, warm-season grasses.

ISSN:0008-4026    

DOI:10.1139/b91-323

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The association betweenAlternaria macrosporaandAlternaria alternata, responsible for the development of alternaria blight disease in cotton, was evaluated in artificially inoculated greenhouse plants and in naturally infested field plants. When greenhouse plants were inoculated with suboptimal doses of both pathogens (< 1.2 × 104 spores/mL) infection was greater than when separately inoculated by each pathogen at optimal dosage. In field-grown, naturally infected plants (Gossypium barbadense), both pathogens were found together in more than 40% of the plants. A second field-grown cotton species (Gossypium hirsutum) exhibited infection mainly by eitherA.alternataor both pathogens together. When both cotton species were naturally infected by both pathogens together, the number ofA.alternataspores (either airborne or on the leaf surface) was greater than that ofA.macrospora. We propose thatA.macrosporatogether withA.alternatacreate a disease composite responsible for alternaria blight symptoms in cotton.Key words:Alternaria, cotton diseases,Gossypium barbadense,Gossypium hirsutum.

ISSN:0008-4026    

DOI:10.1139/b91-324

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Alternaria alternata, isolated from the leaves of wild beets, infected cotton as well as wild and cultivated beets. Scanning electron microscopy of wild beet and cotton leaves infected by an aggressive isolate ofA.alternatarevealed that conidiophores of the pathogen emerged only from necrotic areas of leaf tissues. Sporulation occurred on leaves only during periods of high relative humidity (> 95%) and temperatures ranging from 20 to 28 °C. Under low relative humidity (60% at 22–25 °C), mycelium penetrated into internal tissues of the leaf or emerged through the stomata. A less virulent isolate did not develop surface mycelium on inoculated leaves, but sporulation was detected on the leaf veins. Plants in several cotton fields adjacent to the diseased wild beet plants were infected by the pathogen early in the growing season. This study proposes that isolates ofA.alternatathat are virulent on cotton may overwinter on wild beet plants, making them an important source of the pathogen inoculum in epidemics of alternaria blight of cotton.Key words:Alternaria, beet, cotton diseases, fungi overseason transfer, fungi overwintering, survival.

ISSN:0008-4026    

DOI:10.1139/b91-325

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Selection for a dark-germinating mutant was made with X-irradiated spores ofCeratopteris richardii. A single mutant line (HαDG1) was recovered and analyzed for its germination responses under different light–dark treatments and for transmission of the trait through a complete sexual cycle. HαDG1 was characterized by two phenotypes, dark germination and light inhibition of germination. These responses were exactly opposite from wild-type responses. The level of dark germination for a particular spore batch was stable through time, whereas light inhibition was unstable with time. Genetic analysis indicated that both phenotypes are associated with a single nuclear gene mutation that has been designateddkg1.Key words: fern, photomorphogenesis, mutant selection, germination, spore.

ISSN:0008-4026    

DOI:10.1139/b91-326

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Survival patterns ofCakile maritimaScop. ssp.maritimaseedlings in adjacent open-beach and foredune habitats differed, with significant cohort and seasonal effects only for open-beach plants. Open-beach plants were usually killed by fall storms. Some foredune plants (5.3%) survived into a second reproductive season, producing 85% of mature fruits in the foredune.Peromyscus maniculatus(Wagner) removed 95% of fruits matured by foredune plants. Sand burial of fruits increased their chances of escaping predation. Burial was 52-fold more likely for fruits on open-beach plants compared with foredune plants, resulting in lower seed predation on the open beach. Germination fromP.maniculatuscaches produced 63% of foredune plants, but they represented only 0.002% of all removed seeds. Cache plants had lowered survival relative to noncache plants, so that seed dispersal byP.maniculatusdid not benefitC.maritima. Both foredune and open-beach populations were likely to decline if transition patterns among age-classes and fruit production rates observed in 1983 and 1984 remained constant. Because of high fruit production by overwintering plants, foredune plants produced more fruits than needed to maintain plant numbers, but predation byP.maniculatusreduced seed survival to less than 20% of the replacement rate for that habitat.Key words:Cakile maritima,Peromyscus maniculatus, plant–animal interactions, seed dispersal, seed bank, plant demography.

ISSN:0008-4026    

DOI:10.1139/b91-327

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Using wooden cubes as experimental seed mimics we tested whether differences in seed deposition among riverbank sites predictably affect the structure of riparian vegetation. Although cube deposition was not interpretable in terms of environmental variables like current velocity, riverbank width, and substrate, it was related to species composition of the riparian vegetation. We found an excess of species with short-floating seeds among those that were most frequent in sites capturing few cubes and an excess of species with long-floating seeds among those that were most frequent in sites capturing many cubes. This result provides the first evidence that water dispersal interacting with floating time may play a role in small-scale structuring of riparian plant communities.Key words: floating time, hydrochory, riparian vegetation, river, seed mimics, seed deposition.

ISSN:0008-4026    

DOI:10.1139/b91-328

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

An immunofluorescent cytochemical technique to detect microtubules was developed to examine the involvement of microtubules in incipient responses of barley coleoptile cells to fungal attacks. Infiltration of antibodies into target cells was promoted by scratching cell walls of chemically-fixed coleoptile cells with a micromanipulator. In uninoculated control cells, cortical microtubules were arranged obliquely or transversely to the longitudinal axis of the cells. On the other hand, in coleoptile cells which had been fixed 8–10 h after inoculation with a nonpathogen,Erysiphe pisi, microtubules gathered in coleoptile cells beneath mature appressoria of the fungus. When coleoptiles had been fixed 12 h after inoculation, many of the microtubules gathered around an incipient, small papilla, giving a network appearance. The present technique would be helpful for studying the role of microtubules in host cell responses to fungal attack.Key words: microtubules, immunofluorescent cytochemistry, barley coleoptile,Erysiphe pisi.

ISSN:0008-4026    

DOI:10.1139/b91-329

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Experiments were conducted to determine the histological effects of simulated acidic rain on the cuticle ofZea maysL. cv. B73 × Mo 17 and to ascertain whether subsequent drought stress might elicit interacting effects. Greenhouse-grown plants were treated twice weekly with simulated acidic rain of pH 5.0 or 3.0 for 3–4 weeks. Half of the plants in each pH treatment were then subjected to a 10-day drought stress by withholding water, while the remaining plants continued to receive rain treatments. At the end of the treatment period, leaf tissue was sampled and fixed for light or scanning electron microscopy. Small elongated white lesions approximately 1 mm in diameter appeared in a random pattern on leaves 5–7 that were treated with rain of pH 3.0 for 3 weeks. Plants treated with rain of pH 5.0 did not exhibit these lesions. Lesions were clearly defined areas of collapsed necrotic tissue extending through the leaf. Within lesions, the basal region of 50% of the trichomes had collapsed bases in confluence with adjacent cells. Epicuticular morphology was unaffected by simulated acidic rain or drought stress and appeared as a crystalline platelet-like formation. From our observations, it appeared that factors that maximized droplet retention or droplet deposition, e.g., leaf wettability and leaf orientation, maximized lesion formation. Drought stress had no observable influence on the cuticle of plants treated with either simulated acidic rain treatment.Key words: corn, acid rain, drought stress, histology, cuticle, transpiration.

ISSN:0008-4026    

DOI:10.1139/b91-330

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Growth of twoSphagnumspecies,S.magellanicumBrid. andS.papillosumLindb., was studied in the laboratory, field, and greenhouse in relation to photoperiod. Short days (less than 10 h light) induce both species into dormancy. Both species exhibit a high correlation of growth in length and biomass with photoperiod, having maximum length and biomass increase under continuous illumination. Likewise, the ability to lower pH increases with photoperiod. The greater increase in biomass ofS.papillosumunder 18-h photoperiods could provide short-term niche partitioning.Key words:Sphagnum, photoperiod, growth, pH-lowering ability.

ISSN:0008-4026    

DOI:10.1139/b91-331

出版商:NRC Research Press    

年代:1991

数据来源: NRC