bluuebunny/crossref_metadata_2025 huggingface dataset:
The polytenic endosperm haustorium of Rhinanthus minor (Scrophulariaceae): functional ultrastructure
Authors: Nagl Walter
Published: February 2008

The seed of Rhinanthus undergoes an uncommon differentiation in developing both a chalazal and a micropylar endosperm haustorium. The chalazal haustorium is described at the ultrastructural level. It shows two giant nuclei with polytene chromosomes and numerous complex nucleoli. The nuclear surface is highly interdigitated with the cytoplasm and displays many pores. The cell wall of the apical region of the haustorium displays a prominent wall labyrinth. A large number of mitochondria are located in this region, while leucoplasts are mainly found in vicinity of the nuclei. The structural features of the haustorium are discussed in relation to its expected functions, i.e., synthetic activity and transfer of nutritive material from surrounding tissues to the endosperm proper. Key words: endosperm, haustorium, polyteny, Rhinanthus, transfer cell.
Effects of crop sequence and rainfall on population dynamics of Fusarium solani f.sp. phaseoli in soil
Authors: Hall Robert , Phillips Lana Gay
Published: February 2008

Evidence is presented that population dynamics of Fusarium solani f.sp. phaseoli in soil depend on the effects of crop sequence and rainfall on parasitic activities of the pathogen. In a rotation trial started in 1978 and conducted over 14 years, population densities (colony-forming units/g) of the fungus in soil remained below 50 in treatments (fallow, repeated corn, repeated soybean) where the preferred host plant (common bean, Phaseolus vulgaris) was not grown. Where bean was grown every 3rd year or every year, population densities reached 475 and 660, respectively, by 1984. Thereafter, population densities of the fungus fluctuated widely from year to year in both rotation and repeated bean treatments. In the rotation treatment, peaks in population density of the pathogen coincided with the years of bean production. In repeated bean plots between 1985 and 1991, population density of the fungus in June was significantly correlated (r = 0.77, p = 0.04) with total rainfall received during the previous summer (June–August). It is postulated that higher rainfall during the growing season of the bean crop stimulated root growth and root infection, leading to the accumulation of higher levels of potential inoculum in infected tissue and the release of higher levels of inoculum into the soil by the following June. Key words: Fusarium solani f.sp. phaseoli, bean, Phaseolus vulgaris, rainfall, crop rotation.
Characterization of sterile endophytic fungi from the mycorrhizae of subalpine plants
Authors: Stoyke Godo , Egger K. N. , Currah R. S.
Published: February 2008

Isolates of 117 dematiaceous and 10 hyaline, septate, sterile fungi were obtained from the roots of 26 plants belonging to Poaceae, Caryophyllaceae, Rosaceae, Ericaceae, Primulaceae, and Asteraceae from a subalpine dwarf shrub heath in the Alberta Rocky Mountains. The isolates were sorted into 33 culture groups based on colonial morphology. Strains representative of the different culture groups were compared with fungi of known identity (Cenococcum geophilum, Hymenoscyphus ericae, Phialocephala dimorphospora, Phialocephala fortinii, Phialophora finlandia) using restriction fragment analysis of an amplified portion of ribosomal DNA. Cluster analysis and ordination based on restriction fragment polymorphisms indicated that two-thirds of the isolates were closely related to or conspecific with Phialocephala fortinii, which therefore appears to represent the dominant root endophyte of the subalpine site. In culture, many of the Phialocephala fortinii isolates had sclerotia composed of compact masses of darkly pigmented and irregularly lobed, thick-walled hyphae. Five of the isolates clustered independently of the known isolates and are probably each representative of species other than the known strains. Key words: subalpine mycorrhizae, Phialocephala fortinii, restriction fragment length polymorphism, ribosomal DNA.
Ultrastructural analysis of basidiosporogenesis in Panellus stypticus
Authors: Lingle Wilma L. , Clay Ronald P. , Porter David
Published: February 2008

The ultrastructure of events in basidiosporogenesis in Panellus stypticus was examined using conventional, aqueous-based fixation procedures and freeze substitution fixation following plunge freezing in liquid propane. Freeze substitution was superior in preserving cytological features and in retaining cell wall and extracellular materials. Synapsis, all stages of meiosis I (including prophase, metaphase, anaphase, and telophase), and prophase of meiosis II were observed. The nuclear envelope breaks down during meiosis I, temporarily reforms during interphase, and is at least partially broken down during meiosis II. Many stages of spore development, including sterigma initiation, sterigma elongation, organelle translocation, and nuclear migration, were observed. Spindle pole bodies with microtubule arrays were associated with nuclear migration into developing spores. Analysis of hymenial cells with gold-tagged lectins and enzymes revealed an α-amylase positive outer cell wall layer specific to basidiospores. Only after basidiospore release were surfaces of sterigmata and basidia similarly labeled. All cell walls observed were positive for wheat germ agglutinin, indicating the presence of chitin. Septa-delimiting basidiospores from sterigmata were heavily labeled with wheat germ agglutinin. This is the first investigation of basidiosporogenesis in a homobasidiomycete preserved for transmission electron microscopy by rapid freezing and freeze substitution. Key words: fungal cell walls, lectins, gold labeling, meiosis, rapid freezing, transmission electron microscopy.
Lipoxygenase activity in fresh, stored, and germinating pearl millet seeds resistant and susceptible to downy mildew disease
Authors: Nagarathna K. C. , Shetty Sudheer A. , Prakash H. S. , Bhat S. G. , Shetty H. Shekara
Published: February 2008

Lipoxygenase activity was studied in fresh, stored, and germinating pearl millet seeds of downy mildew resistant and susceptible genotypes. In both fresh and stored seeds, the enzyme activity was greater in resistant genotypes compared with that of the susceptible ones. In seeds stored for a period of 6 months, a significant reduction in the lipoxygenase activity was recorded, the reduction being greater in resistant seeds. Lipoxygenase activity decreased significantly in germinating seedlings of resistant genotypes, whereas it increased significantly in the susceptible seedlings. The high vigour in the resistant seeds of downy mildew resistant genotypes is attributed to their high enzyme activity. Key words: lipoxygenase, pearl millet, downy mildew, resistant, susceptible.
Mycorrhizal dependence of modern wheat varieties, landraces, and ancestors
Authors: Hetrick B. A. D. , Wilson G. W. T. , Cox T. S.
Published: February 2008

Using mycorrhizal fungi known to colonize wheat, the mycorrhizal dependence of various small grains including modem wheat varieties, primitive wheat lines, and wheat ancestors was studied. With the exception of the United States cultivar Newton and the German cultivars Apollo, Kanzler, and Sperber, dry weight of eight other modern wheats from the United States and Great Britain were increased by 29–100% following inoculation with mycorrhizal fungi. All landraces from Asian collections or early introduced American cultivars were also dependent on the symbiosis, with dry weight increases averaging 169 and 55%, respectively. All wheat ancestors of the AA and BB genomes (except Aegilops speltoides) benefitted significantly from the symbiosis, whereas no benefit was observed for ancestors of the DD genome, tetraploid wheats of the AABB or AAGG genomes, or in the hexaploid ancestor Triticum zhukovskyi (AAAAGG genome). These differences in mycorrhizal response of the ancestors, lines, and cultivars were highly correlated with root fibrousness ratings. When the fungi used as a combined inoculum in the previous experiment were inoculated individually onto selected plant species or cultivars, 6 of the 10 isolates stimulated growth of Andropogon gerardii, a highly dependent grass species, and 8 of the 10 stimulated the growth of 'Turkey' wheat. In contrast, none of the isolates positively affected growth of 'Newton' or 'Kanzler' wheat cultivars, and in fact several fungi decreased the biomass produced by these two cultivars. These studies have demonstrated a strong genetic basis for differences in mycorrhizal dependence among cultivars. A trend for greater reliance on the symbiosis in older cultivated wheats than iin wheat ancestors or modern wheats was also observed. The depression in growth associated with certain mycorrhizal fungi and wheat cultivars demonstrates that colonization of roots does not guarantee benefit from the symbiosis. Key words: root fibrousness, growth response, vesicular–arbuscular mycorrhizae.
Le développement du bourgeon axillaire du Manihot esculenta
Authors: Médard R. , Sell Y. , Barnola P.
Published: February 2008

The vegetative aerial apparatus of cassava consists of two kinds of axes: sylleptic and proleptic. After its determination, an axillary meristem may have either an advanced development, which characterizes a sylleptic axis, or a later development, which characterizes a proleptic axis. The morphological differences between the two categories of axes are easily explained as the result of differences in development. Proleptic development undergoes four stages: (i) determination, (ii) first latent period in the apical meristem, (iii) organogenesis, and (iv) second latency. The second and fourth stages do not occur in the advanced form of development. The first latent stage is due to a double precedency of both the upper part of the apical meristem and the axillary leaf primordium. The hypothesis of a control of the determination and the first latency of the axils from the whole apical meristem is discussed. The regulation of the two types of interruptions of development do not take place on the same scale and are probably not of the same type. Key words: axillary bud, stem, development, cassava, proleptic, sylleptic.
A revision of the species of Porphyra (Rhodophyta: Bangiales) occurring in British Columbia and adjacent waters
Authors: Lindstrom Sandra C. , Cole Kathleen M.
Published: February 2008

Starch gel electrophoresis of proteins of Porphyra species occurring in British Columbia and nearby areas has provided new data on species identities. One new species is described, Porphyra kurogii (formerly identified as North Pacific P. purpurea), and its eastern Pacific distribution limit is extended from northern to southern British Columbia. Porphyra maculosa is recognized to be a taxonomic synonym of P. fucicola; new distribution records are provided. Porphyra cuneiformis is the correct name for specimens formerly identified as P. miniata in the area, and P. occidentalis is the correct name for most local specimens of P. "variegata." A key to the 21 species and 2 subspecies of Porphyra currently recognized in Oregon, Washington, British Columbia, and southeast Alaska is provided. The key includes the recently described P. mumfordii, P. fallax ssp. fallax, and P. fallax ssp. conwayae. Key words: isozymes, key, Porphyra, taxonomy.
The host – pathogen interaction in the wasting disease of eelgrass, Zostera marina
Authors: Muehlstein Lisa K.
Published: February 2008

A marine epidemic of wasting disease decimated populations of eelgrass, Zostera marina L., in the early 1930s. Labyrinthula, a marine slime mold was the suspected pathogen, although the cause was never clearly determined. Presently, a recurrence of wasting disease of Z. marina was documented in populations along the coasts of North America and Europe. A pathogenic species of Labyrinthula, described as Labyrinthula zosterae Porter et Muehlstein, was identified as the primary microorganism causing the present wasting disease. Of all the microorganisms tested in laboratory disease tests, only L. zosterae caused disease symptoms. Direct microscopic observations revealed that Labyrinthula cells were found most frequently associated with marginal areas of disease symptoms and appeared to move rapidly through the tissue, directly penetrating cell walls. The ectoplasmic network that surrounds Labyrinthula cells appeared to have an important role in the enzymatic degradation of plant cell walls and presumably a role in the destruction of cytoplasmic contents of the plant cells. Direct contact of diseased leaves with healthy leaves was the mechanism of disease spread from plant to plant. Key words: Labyrinthula, Zostera marina, eelgrass wasting disease.
Observations on the seasonal occurrence of marine endophytic and parasitic fungi
Authors: Stanley Susan J.
Published: February 2008

Information is presented on three fungal–algal associations on intertidal marine algae. They comprise two members of the Ascomycotina, Lautitia danica parasitic on Chondrus crispus, and Mycosphaerella ascophylli, an obligate endophyte of Ascophyllum nodosum, and a member of the Basidiomycotina, Mycaureola dilseae, that is parasitic on Dilsea carnosa. Details are given of life cycles and seasonal periodicity. The reproductive cycles of Mycosphaerella ascophylli and Ascophyllum nodosum are synchronised, with the fungal sporocarps being confined to the algal receptacles. Lautitia danica occurs on cystocarpic Chondrus crispus throughout the year, with older fronds being more likely to have fungal sporocarps on them. Mycaureola dilseae infecting Dilsea carnosa was only found during September and October. The systemic nature of the association between Mycosphaerella ascophylli and Ascophyllum nodosum is compared with the apparently localized occurrence of Lautitia danica and Mycaureola dilseae. Key words: marine algicolous fungi, seasonality, Ascomycetes, Basidiomycetes.
Dendryphiella salina and Debaryomyces hansenii: models for ecophysical adaptation to salinity by fungi that grow in the sea
Authors: Clipson N. J. W. , Jennings D. H.
Published: February 2008

The physiology of adaptation to life in the marine environment is reviewed in two species of marine fungus, Dendryphiella salina, a filamentous Hyphomycete and Debaryomyces hansenii, an Ascomycete yeast. The constraints of living in an environment of highly negative water potential are assessed in terms of the overall water relations of these fungi and how osmotic potential is generated within the mycelium. The relative contribution of ionic and organic solutes to the osmotic potential, and how these compounds are compartmentalized within the hyphal cell, are discussed, together with what is known about how the processes leading to the generation of internal osmotic potential are regulated by the fungus. Key words: Dendryphiella salina, Debaryomyces hansenii, marine fungi, adaptation, osmotic potential, polyols.
Use of natural and artificial seawater for investigation of growth, fruit body production, and enzyme activities in marine fungi
Authors: Rohrmann S. , Lorenz R. , Molitoris H. P.
Published: February 2008

Investigation of marine fungi suffers from an often inadequate comparability of methods and results, e.g., the use of natural as opposed to artificial seawater. Consequently, several marine fungi of different systematic positions were tested for growth, enzyme activity, and fructification on solid media with natural and artificial seawater. Growth as colony diameter and production of enzymes by the basidiomycete Halocyphina villosa and the ascomycete Lulworthia sp. were compared on both media. In all cases the results showed either no difference or only minor quantitative differences. Investigation of further species (two ascomycetes, one basidiomycetous yeast, two deuteromycetes) and other enzymes also showed no differences between the two media with the exception of three cases. Fructification in Halocyphina villosa occurred on both types of seawater. Addition of boric acid in natural concentrations to the artificial seawater medium had no effect on the growth of nine marine fungi. Artificial seawater medium gives comparable results to natural seawater in experiments with marine fungi, results in better comparability and reproducibility of experiments, and is often cheaper and easier to obtain. Key words: natural seawater, artificial seawater, marine fungi, growth, enzymes, fruit bodies.
Combined influence of salinity and temperature (Phoma-pattern) on growth of marine fungi
Authors: Lorenz R. , Molitoris H. P.
Published: February 2008

Investigating the combined influence of temperature and salinity on growth of some marine fungi, Ritchie (1957. Am. J. Bot. 44: 870 – 874) showed for some species (e.g., Pestalotia sp., Phoma sp.) an increased salinity optimum with increasing incubation temperature (Phoma-pattern). This was confirmed later for several marine fungi but using different methods and parameters. In this paper the investigations were repeated and enlarged using one method over a broader range of salinities (0–300% seawater) and temperatures (12–42 °C) for seven marine fungi from different taxonomic and ecological groups and biogeographical zones where the Phoma-pattem was reported. The Phoma-pattern was confirmed for all seven fungi for temperatures of 22 °C and higher. For Curvularia and Pestalotia, the Phoma-pattern was evident only at the highest temperatures tested. In addition, three strains of one species, Dendryphiella salina, from different geographical regions of the oceans were examined. All three isolates of Dendryphiella salina showed the Phoma-pattern. The Phoma-pattem does not seem to be correlated with certain taxonomic and ecological groups of marine fungi or biogeographical zones. Key words: Phoma-pattern, marine fungi, growth, salinity, temperature.
Screening for wood-degrading enzymes in marine fungi
Authors: Rohrmann S. , Molitoris H. P.
Published: February 2008

Forty marine and 15 terrestrial fungi in the Ascomycetes, Basidiomycetes, and Deuteromycetes were screened for presence and relative amount of enzymes involved in wood degradation (cellulases and redox enzymes) using seawater and deionized water media. Distribution of cellulases, laccase, tyrosinase, and peroxidase among marine and terrestrial groups of fungi was investigated. β-Glucosidase (C4) and endoglucanase (C3) were the most frequent enzymes (80 – 100% of the strains) of cellulose metabolism. Acid-swollen cellulose (C1) was generally more easily degraded than microcrystalline-dyed Avicel® (C2).All groups of strains showed relatively high percentages of cellulases C1, C3, C4, whereas production of cellulase C2 was lower. In comparison with Sporotrichum pulverulentum, a strongly cellulolytic terrestrial Deuteromycete, about 25% of the marine fungi tested showed the same high cellulase activity. Peroxidase was formed by nearly all strains tested at least on seawater medium; tyrosinase was the least frequent enzyme (20 – 35%). The presence of laccase was different among the various fungal systematic groups, reaching its highest percentages in the marine and terrestrial Basidiomycetes and the marine Ascomycetes, which mostly belong to the ecological groups of white-rot and soft-rot fungi, respectively. Enzymes involved in wood degradation were demonstrated in large number and sometimes considerable amounts in wood-inhabiting marine fungi. Key words: marine fungi, wood degradation, cellulase, phenoloxidases, screening, ecology.
Low-temperature stress and photoperiod affect an increased tolerance to photoinhibition in Pinus banksiana seedlings
Authors: Krol M. , Gray G. R. , Huner N. P. A. , Hurry V. M. , Öquist G. , Malek L.
Published: February 2008

The capacity to develop tolerance to photoinhibition of photosynthesis was assessed in jack pine seedlings (Pinus banksiana Lamb.). Photoinhibition induced at 5 °C in control jack pine seedlings grown at 20 °C was saturated above an irradiance of 1000 μmol ∙ m−2 ∙ s−1 but was detectable at an irradiance as low as 25 μmol ∙ m−2 ∙ s−1. However, 20 °C seedlings shifted to 5 °C were 2-fold more tolerant to photoinhibition than 20 °C unshifted control seedlings, as detected by either the light-dependent decrease in photochemical efficiency or the apparent quantum yield of O2 evolution. The extent of this tolerance of photoinhibition was dependent upon time, photoperiod, and irradiance during exposure to the low-temperature shift. Furthermore, the tolerance of photoinhibition was correlated with anthocyanin accumulation in 20 °C grown seedlings shifted to 5 °C. In addition, seedlings shifted to 5 °C and an 8-h photoperiod exhibited a 2-fold higher yield of photosystem II electron transport, which was associated with an increased capacity to keep QA, the first stable quinone electron acceptor of photosystem II, oxidized at high irradiance. This was consistent with a 2-fold higher rate of photosynthesis on a chlorophyll basis. We propose that the combination of light attenuation by anthocyanin in the epidermis and enhanced rates of photosynthesis may, in part, account for the reduced sensitivity of jack pine to photoinhibition at low temperature. Key words: anthocyanin, light attenuation, low temperature, Pinus banksiana Lamb, (jack pine), photosynthesis, photoinhibition, photoperiod.
Colonization of Orchis morio protocorms by a mycorrhizal fungus: effects of nitrogen nutrition and glyphosate in modifying the responses
Authors: Beyrle H. F. , Smith S. E. , Franco C. M. M. , Peterson R. L.
Published: February 2008

Effects of nitrogen nutrition and application of glyphosate (as Roundup™) on the interactions between protocorms of Orchis morio and a mycorrhizal Rhizoctonia species were investigated. Protocorms for all experiments were raised clonally in liquid culture. Split plates were used to separate the direct effects of composition of the media from effects mediated via the fungus. Mycorrhizal interactions, including coil formation and prolonged protocorm growth, were established when a relatively low nitrogen supply to the fungus (as NH4)2SO4) was combined with a high carbohydrate supply. Rejection of the fungus, associated with phenolic production, wall thickening, and lack of protocorm growth, was observed with high-carbon, high-nitrogen medium. Low carbohydrate supply, with either high or low nitrogen supply, was associated with breakaway parasitism, symptoms of soft rot, and lack of subsequent protocorm growth. Application of glyphosate at 0.5 or 1.0 mM had no effect on fungal growth and at 1.0 mM did not cause death of asymbiotic protocorms, but resulted in failure of mycorrhizal initiation. Coils were never formed and the fungus ramified through the tissues of the protocorms. The parasitism induced by glyphosate differed from breakaway parasitism, and there were no symptoms of soft rot. Assays for activity of phenylalanine ammonia lyase (PAL) and for orchinol were carried out to assess the effects of the treatments on the shikimic acid pathway. Low activity of PAL and low quantities of orchinol (together with another unidentified phenolic compound) were detected in asymbiotic protocorms. Concentrations of both were increased in the presence of the fungus, but no significant differences were observed in the various symbiotic responses in the absence of glyphosate. This is the first report of the presence of orchinol in orchid protocorms. Previous work has always been carried out on tubers, which are not usually colonized by the mycorrhizal fungi. Application of glyphosate resulted in increases in both PAL activity and orchinol production. The results are discussed in the context of orchid–fungus interactions and the mechanism of glyphosate action. Key words: orchid, mycorrhiza, parasitism, cell walls, glyphosate, phenylalanine ammonia lyase (PAL), orchinol.
Effects of sand deposition on the interaction between Ammophila arenaria, plant-parasitic nematodes, and pathogenic fungi
Authors: de Rooij – van der Goes P. C. E. M. , van der Putten W. H. , Peters B. A. M.
Published: February 2008

Ammophila arenaria is a dominant sand-fixing plant species of the European coastal foredunes. It remains vigorous under regular burial conditions on seaward slopes, but starts to degenerate when sand accumulation diminishes. Several hypotheses have been put forward to explain this degeneration. In this study, we test the hypothesis that upward growth of plants following sand burial enables them to escape harmful soil organisms. Plants in a degenerating field stand of A. arenaria and potted plants grown in sterilized sand (outdoor pot experiment) were buried with sterilized or nonsterilized sand. Burial in both sterilized and nonsterilized sand resulted in stem elongation, increased numbers of living shoots, and increased shoot and root biomass. However, when plants were grown in and buried with sterilized sand, the numbers of shoots were significanlty higher than those buried with nonsterilized sand. The new root zone of buried plants was colonized by pathogenic soil organisms (nematodes and fungi) during the same growing season. It is concluded that by upward growth through pathogen-free sand, the plants benefit, at least temporarily, from escaping its pathogens and parasites. Key words: clonal growth, upward growth, migration, soil-borne disease, growth reduction.
Congruence of chloroplast DNA restriction site characters with morphological and isozyme data in Solanum sect. Lasiocarpa
Authors: Bruneau Anne , Dickson Elizabeth E. , Knapp Sandra
Published: February 2008

Chloroplast DNA restriction site characters were analyzed cladistically in species of Solanum sect. Lasiocarpa (subg. Leptostemonum), and results were compared with previously published analyses of morphological and isozyme characters. Cladistic analysis of the chloroplast DNA restriction site characters resulted in a single tree in which two main clades were detected: one comprised three morphologically distinct lowland Amazonian species, and the other included the Andean and the two Asian species. Character congruence among the three data sets was assessed with a previously described index and with a permutation test derived from this index. Taxonomic congruence was evaluated with a measure modified from that of another researcher. The three assessments of congruence indicate that the chloroplast DNA and isozyme analyses are the most incongruent, but they differ as to their evaluation of relative (in)congruence for the other comparisons. Combining the three data sets resulted in two most parsimonious trees whose topologies incorporate elements from each of the separate analyses. The combined chloroplast DNA and morphological analyses support a previously proposed hypothesis that the two Asian species are sister taxa and of a single origin, rather than having originated separately from two distinct South American groups. Key words: Solanum, chloroplast DNA, congruence, combined data, cladistics.
Endomycorrhizal status of sugar maple in relation to tree decline and foliar, fine-roots, and soil chemistry in the Beauce region, Quebec
Authors: Ouimet Rock , Camiré Claude , Furlan Valentin
Published: February 2008

The Beauce region of Quebec has been relentlessly affected by sugar maple (Acer saccharum Marsh.) tree decline since the late 1970s. Nutrient disturbances are generally associated with maple decline, but the severity of decline symptoms can vary quite dramatically between individuals within a stand. Possible causes of this variability were investigated, including soil chemistry and endomycorrhization. Within 18 mature sugar maple stands, a comparative study of fine root colonization rate by endomycorrhizal fungi, and foliar, fine-roots, and soil-nutrient status between healthy and declining sugar maple trees was carried out. Three individuals showing a very low degree of decline symptoms (healthy) and three individuals in the vicinity exhibiting severe decline symptoms (declining) were selected in each stand. Although trees of both health classes were K and Ca deficient, the diagnosis revealed that those in the declining group were experiencing a more severe nutrient stress and lower stem radial growth than those in the healthy group. The percent colonization by endomycorrhizal fungi in fine roots of sugar maple varied from 8 to 40% among stands, with an average of 23%. However, the endomycorrhization rate was not related to tree health status. The frequency of endomycorrhization was positively correlated to soil pH and soil exchangeable Mg saturation, but negatively to the proportion of H + Al held on the soil exchange complex. Also, the rate of endomycorrhization was correlated positively to foliar and root Ca content, but negatively to foliar and root N content. Foliar N, P, K, Ca, Mg, and Mn contents were positively correlated to corresponding nutrient content in fine roots. Fine-root chemistry was only partly related to soil chemistry. Declining trees had a lower foliar K content and a lower P and Ca content in fine roots than healthy ones. The results do not support the hypothesis that sugar maple decline and its disturbed nutrient status is associated with lower colonization by endomycorrhizal fungi in fine roots. They suggest, however, that soil chemical properties, particularly the soil composition in cations, regulates fine-root colonization by endomycorrhizal fungi and sugar maple nutrition and health. These results can neither confirm nor invalidate the hypothesis according to which a deleterious microbial population may have colonized the soil under declining trees. Key words: Acer saccharum, soil cation saturation, forest decline, nutrient status, fine root, endomycorrhizae.
Further studies on efficiency of artificial foam in trapping conidia of Ingoldian fungi
Authors: Iqbal S. H.
Published: February 2008

Artificial foam traps conidia of rare species in rich communities of freshwater hyphomycetes as efficiently as it traps conidia in a community showing poor species composition with low conidial numbers. A large number of conidia, particularly the tetraradiate ones, are lost from the stream water as it passes through rapids and waterfalls. Addition of a detergent results in greater loss of conidia in the effluent water. The trapping of conidia in the foam concentrate and their loss while passing through the rapids and waterfalls is not related to conidial concentration. It may be influenced by water chemistry. Key words: artificial foam, conidia, Ingoldian fungi.
Classification of airborne plant pathogens based on sporulation and infection characteristics
Authors: Sache Ivan , Vallavieille-Pope Claude de
Published: February 2008

The infection cycles of 26 airborne fungal plant pathogens were compared using six monocyclic variables: latent period, infectious period, sporulation capacity, relative date of sporulation peak, lesion size, and infection efficiency. All variables were measured at the seedling stage in conditions highly conducive to disease development. Multivariate analyses of literature and experimental data were used to describe epidemic strategies based on compensation, addition, and multiplication effects between the monocyclic variables. A typology of fungi according to these effects is proposed, the main divisions of which follow the pattern of lesion growth (semisystemic, local, or negligible). Further subdivisions were obtained based on the other sporulation and infection variables. With a few exceptions, pathogens belonging to the same taxonomic (powdery mildews, downy mildews, rusts) and ecological (biotrophs, necrotrophs) group were grouped together in the proposed typology. Among rusts and necrotrophs, the fungi adapted to temperate and warm climates were also distinguished. The wheat stripe rust was not grouped with the other rusts because of unique epidemiological characteristics, especially semisystemic growth of lesions. Key words: biotrophic fungus, comparative epidemiology, monocyclic process, necrotrophic fungus.
Ramalina eckloniias a bioindicator of atmospheric pollution in Argentina
Authors: Levin Adolfo G. , Pignata Maria L.
Published: February 2008

The lichen Ramalina ecklonii (Spreng.) Mey. and Flot. was transplanted to 24 biomonitoring sites along three transects in the western area of Córdoba, Argentina, and tested for chlorophyll, phaeophytin conjugated dienes concentration, soluble protein content, and sulfur accumulation. The transects represented three levels of vehicular traffic. Significant differerences were observed in sulfur content, phaeophytin b, total phaeophytin, and dry mass to fresh mass ratio (DM/FM). A pollution index (PI) was calculated based on the ratio of phaeophytin a to chlorophyll a and the ratio of sulfur and conjugated dienes in transplanted specimens to sulfur and conjugated dienes in the control specimens. Significant differences in PI among the transects were observed; the lowest PI was at the control site, and the highest along the sampling line having the greatest amount of traffic. Key words: lichen, Ramalina ecklonii, biomonitoring, air pollution.
Effects of mycorrhizal fungi on in vitro nitrogen response of some Dutch indigenous orchid species
Authors: Dijk Eeuwe , Eck Nelly D.
Published: February 2008

The effect of mycorrhizal infection on the response to mineral nitrogen was studied in Orchis morio L., Dactylorhiza praetermissa (Druce) Soó var. junialis (Vermln.) Sengh., Dactylorhiza majalis (Reichb.) Hunt & Summerh., and Dactylorhiza incarnata (L.) Soó, using two strains of Ceratorhiza sp. and two of Epulorhiza repens (Bernard) Moore as mycorrhizal symbionts. Both types of endophyte appeared to be able to stimulate orchid growth at relatively low nitrogen availability in the culture medium. The Ceratorhiza strains decreased nitrogen tolerance of associated orchid protocorms and had pronounced negative effects on the growth and survival of D. majalis and D. incarnata at high concentrations of ammonium nitrate. Such effects did not occur in symbioses involving the Epulorhiza strains. Within orchid species, differences were observed in the extent to which fungal strains stimulated growth. The Ceratorhiza isolates were incompatible with O. morio while the Epulorhiza strains were generally less efficient for Dactylorhiza spp. Key words: orchid mycorrhiza, nitrogen, Dactylorhiza spp., Orchis morio, Ceratorhiza spp., Epulorhiza repens.
Multiple paternity inAsclepias syriacausing a paired-fruit analysis
Authors: Gold Julie J. , Shore Joel S.
Published: February 2008

We investigated the extent of multiple paternity within and between fruits of the common milkweed, Asclepias syriaca, at one site. Using isozyme polymorphisms at four loci and the maximum likelihood methods of Williams and Evarts (1989), we found no statistical evidence for multiple paternity within fruits. When pairs of fruits obtained from individual ramets were analyzed in a similar manner, extensive multiple paternity was observed, indicating that fruits on the same ramet are sired by different paternal parents. This extensive multiple paternity between fruits provides considerable opportunity for maternal choice via selective fruit abortion. Key words: Asclepias, isozyme polymorphisms, multiple paternity, pollinia.
The impact of species introduced to control tree invasion on the vegetation of an electrical utility right-of-way
Authors: Brown Doug
Published: February 2008

Utilities must remove trees from their rights-of-way on a frequent basis. Many use selective removal methods that leave the nontarget ground cover intact. It is thought that this ground cover will inhibit the subsequent establishment of trees, thus reducing future maintenance needs. An alternative approach is to plant highly competitive species that are able to produce stable communities. This paper describes a project set out to determine if seeding such cover crops would affect the composition of the right-of-way vegetation, and to what extent the resulting community would affect the time course of succession towards a forest. Four cover crops (Festuca rubra L., Dactylis glomerata L., Lotus corniculatus L., and Coronilla varia L.) were evaluated for a 5-year period. The cover and abundance of all vegetation was assessed annually, and the ordination program DECORANA was used to investigate the changes in the vegetation over time. To provide a measure of the effect of the crops on tree growth, 1-year-old transplants of Fraxinus pennsylvanica Marsh. and Acer saccharum Marsh and unrooted cuttings of Populus ×canadensis Moench. were planted into each plot. Dactylis has the largest effect on the vegetation. This grass reduced forb biomass by 70%, producing a community with significantly lower species richness. The time trajectories of the ordination indicate that this treatment is changing the overall development of the plant community. In addition, the survival of the Fraxinus and Populus planted into the Dactylis plots was reduced to 75 and 0% of the unseeded controls. These results indicate that some crops are capable of altering the community composition in the early stages of development, and may inhibit the establishment of trees. Key words: power corridor, vegetation control, competition, interference.
Differential responses of Pisolithus tinctorius isolates to aluminum in vitro
Authors: Egerton-Warburton Louise M. , Griffin Brendon J.
Published: February 2008

Isolates of Pisolithus tinctorius collected from old coal mining (pH 4.3, Al 327 mg/L, mine sites), rehabilitated (pH 4.9, Al 22 mg/L), and forest sites (pH 5.3, Al 6 mg/L) were grown in axenic culture with 0–2000 mg/L Al and assessed for aluminum tolerance by comparing the mass of mycelia produced and levels of Al, Ca, and Mg in mycelia as detected by energy-dispersive X-ray microanalysis. Mine-site isolates demonstrated mycelial growth to 2000 mg/L Al, a threshold of 90 mg/L Al before accumulation of Al in mycelia, and higher levels of Ca and Mg within the mycelia than either rehabilitated- or forest-site isolates at substrate concentrations greater than 4 mg/L Al. In contrast, mycelial growth ceased at 22 and 12 mg/L Al for rehabilitated- and forest-site isolates, respectively, and was strongly correlated with a high Al and low Ca and Mg content in the mycelia. These differences indicated that an increase in Al tolerance of mine-site isolates may operate through an increase in the presence of Ca and Mg in mycelia and a physiological tolerance to the metal. Key words: Pisolithus tinctorius, Al, Ca, Mg, axenic culture, energy-dispersive X-ray microanalysis.
Pollen limitation in a northern population of Hepatica acutiloba
Authors: Murphy Stephen D. , Vasseur Liette
Published: February 2008

Pollen and (or) pollinator limitation may be most likely to occur in spring wildflowers or populations of species near their distribution limits. From 1990 to 1992, we examined a 2-ha population of a perennial spring wildflower, Hepatica acutiloba (Ranunculaceae), at the northern distribution limit of the species. To distinguish between the often confounded effects of pollen and resource limitation, we applied partial and whole-plant treatments. Ramets were open-pollinated, cross-pollinated, open- and cross-pollinated (50% of flowers were open-pollinated, and 50% were hand-pollinated), or self-pollinated. Although there was year to year variation, plants with cross-pollinated flowers produced significantly more viable seeds and heavier seeds than plants with self- or open-pollinated flowers. Comparisons between seed numbers and masses from complete and partial treatments suggested that there was no reallocation of resources among flowers on a plant. From 1990 to 1992, a minimum of 95% of all visits to a subset of ramets of H. acutiloba were from Asclera ruficollis (Coleoptera: Oedemeridae), i.e., virtually the only insect active during flowering. Mark–recapture data for A. ruficollis indicated that even after 6–48 h, 22–40% of the individuals remained within 10 m of the same ramet of H. acutiloba. Observational data indicated that less than 50% of all flowering ramets of H. acutiloba may be visited by A. ruficollis. We conclude that pollen limitation, mediated by reliance on one sedentary pollinator, was the main cause of low seed production in open-pollinated flowers of H. acutiloba. Key words: Hepatica acutiloba, pollen limitation, pollinator limitation, distribution limit, Asclera ruficollis, Oedemeridae.
Instream flows and the decline of riparian cottonwoods along the St. Mary River, Alberta
Authors: Rood Stewart B. , Mahoney John M. , Reid David E. , Zilm Leslie
Published: February 2008

Completed in 1951, the St. Mary Dam enables water storage and diversion for irrigation; river flows downstream are consequently dramatically reduced during summer months. To assess historical changes in the abundance of riparian cottonwoods (Populus balsamifera, Populus angustifolia, and a few Populus deltoides), airphoto analyses were conducted for 40-km river reaches upstream and downstream from the dam and along adjacent dammed and undammed rivers. Cottonwoods along the lower St. Mary River are confined by steep-walled canyons to narrow bands and consequently analyses of the lineal river distance associated with cottonwoods were conducted. These revealed a 68% decline from 1951 to 1985. The decline was progressive, with 28.9, 27.6, 15.1, and 7.6% of the reach associated with cottonwoods in 1951, 1961, 1981, and 1985, respectively. Ground surveys from 1985 to 1994 indicated further decline after 1985 and an absence of cottonwood seedlings and saplings. Cottonwood stands upstream from the St. Mary Dam and along adjacent rivers are more extensive and analyses of the areal extent of stands were consequently appropriate. These indicated minor change along the upper St. Mary (−0.5%), the upper (+1.9%) and lower Waterton (+3.5%), and the upper Belly (−9.1%) rivers, and an increase in forest abundance along the lower Belly River (+52.2%), between 1951 and 1985. Thus, the decline of cottonwoods along the lower St. Mary River was not symptomatic of a general pattern of decline in the region. Analyses of historical stream flows indicated that the cottonwood mortality was drought induced as a result of insufficient flows during the hot, dry summer periods and abrupt flow reductions following the high-flow period in the late spring. The riparian water table was determined to be closely coordinated with river stage, as changes in river elevation were followed by quantitatively similar changes in water table depth. Along the St. Mary River, reduced sedimentation downstream from the dam was not considered to be responsible for the cottonwood decline. The historically sparse cottonwood abundance along the lower St. Mary River may have reflected environmental conditions that were naturally only marginally suitable, and those groves may have been particularly vulnerable to the impacts of river flow regulation. Key words: Populus, cottonwoods, instream flows, mortality, riparian vegetation.
La détermination de la forme des lobes du limbe de manioc (Manihot esculenta Crantz)
Authors: Médard R. , Miesch R.
Published: February 2008

The shape of the leaf blade of each lobe is progressively settled in. First, the midvein separates two lateral areas with equivalent mitotic potentialities. In each of these lateral areas, these potentialities, which at first are evenly spread out, are then concentrated only in the basal part, which will be referred to as the leaf blade generative center. Great regulation potentialities are maintained in these centers throughout their duration, i.e., over three plastochrons. Cellular clusters, which will progressively differentiate and correlatively lose their abilities to regulate, arise from generative centers toward an apical direction. The evenness of the lamina edge is linked with the wholeness of the generative centers. Any subdivision of any one of these centers will generate a lobule, which, in turn, will behave as a miniature lobe. The subdivision occurs as a result of cutting but can also be achieved by application of exogenous cytokinin. The physiological and biochemical mediums of mitotic potentialities are still to be found. It is the same for the way the cytokinins act. Key words: cassava, leaf blade, morphogenesis, cytokinin.
Architecture of cauliflory in the genus Cercis (Fabaceae : Caesalpinioideae)
Authors: Owens Shirley A. , Ewers Frank W. , Flegler Stanley L. , Klomparens Karen L.
Published: February 2008

Cercis is a genus with a geographically disjunct distribution in North America, southern Europe, and eastern Asia. The architecture of cauliflory (flowering from the lower branch and trunk areas of woody plants) was examined in 10 taxa, including 9 of the 11 recognized species in the genus Cercis. In each taxon, a linear series of first-order buds (distinguished as 1) was formed in the axils of vegetative leaves before shoot elongation ceased. The first-order bud developed into either a vegetative shoot or more frequently into an inflorescence. Inflorescences matured and then abscised. Second-order and higher order buds were produced in the axils of the basal bud scales of abscised inflorescences. In addition, vegetative shoots that were from first- or higher order buds produced first order buds (distinguished as 1′) in their leaf axils. Buds from the axils of the basalmost leaves of these vegetative shoots, together with higher order buds from the parent shoot, perpetuated the cauliflorous condition in all taxa studied. Since cauliflory was present and since the architecture of cauliflory was similar in all taxa studied, regardless of geographic distribution, cauliflory probably arose only once in Cercis, before the genus radiated from its site of origin. Key words: cauliflory, Cercis, serial buds, order of buds, geographic distribution, architecture of cauliflory.
The cuticle on Psilotum gametophytes
Authors: Whittier Dean P. , Peterson R. L.
Published: February 2008

The surfaces of Psilotum gametophytes from soil and axenic culture were examined with electron microscopy and histochemistry. A lipid layer, which gave a positive reaction for all lipid stains employed, covers the surface of these gametophytes. In apical regions the lipid coating is almost as thick as the wall it coats. The wall was not stained with lipid stains but did stain for polysaccharides, cellulose, pectin, and polyphenols materials. The surface of gemmae from gametophytes grown in axenic culture was examined with electron microscopy. In young areas the lipid was amorphous, but it had a lamellate outer area in older regions of the gemmae. The surface of Psilotum gametophytes range from white in the apical region to dark brown in older areas. The browning of the surface resulted from the incorporation of tanniniferous materials into the surface wall of the older region. The cuticle along with the tanniniferous materials in the wall make the surface of these subterranean gametophytes resistant to decay and may protect them from certain biota in the soil. The cuticle may help these long-lived gametophytes to withstand any periodic drying of the soil. Key words: Psilotum, gametophyte, cuticle.
Nouvelles observations cytologiques chez Festuca rubra sensu lato (Poaceae) dans l'Est du Canada
Authors: Dubé Martin , Morisset Pierre
Published: February 2008

Sixty-one chromosome number determinations in Festuca rubra L. from eastern Canada show that hexaploids plants (n = 21) are found in both natural habitats and ruderal places, octoploids rhizomatous plants (n = 28) are mostly found in ruderal places, but also in disturbed natural habitats. Morever, one aneuploid (2n = ca. 48) is found from a natural habitat and intercytotype hybrids are found in ruderal places or disturbed natural habitats. Key words: Festuca rubra, cytotypes, hybrids.