bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of neighbors on node production, stolon growth, and branching of Trifolium repens transplants in a pasture
Authors: Turkington Roy , Klein Elena
Published: April 2011

Ten individual plants of Trifolium repens L. were transplanted into a 49-year-old cattle pasture in British Columbia. They were protected from grazing and their subsequent growth was monitored at 2- to 3-week intervals throughout the summer from May to October. The rate of stolon elongation was greatest (2.01 cm ∙ week−1) in late July and a maximum rate of node production (1.48 new nodes per stolon ∙ week−1) occurred in early August. As stolons extended through the pasture they encountered a number of different grass species: Dactylis glomerata, Holcus lanatus, Lolium perenne, Phleum pratense, and Poa spp. The stolons grew through a total of 2 m of H. lanatus neighborhood and produced only 3 branches, whereas they produced 11 branches in only 57.2 cm of P. pratense neighborhood. Neighboring grasses impose different local environments on the nodes and stolons of T. repens and consequently influence the dynamics of node production, the rate of stolon elongation, and the amount of stolon branching. Key words: stolon branching, neighbors, light quality, Trifolium repens.
Genetic variation in Bromus tectorum (Poaceae): introduction dynamics in North America
Authors: Novak Stephen J. , Mack Richard N. , Soltis Pamela S.
Published: April 2011

The Eurasian grass Bromus tectorum was collected first in its 19th century invasion of western America in six widely separated locales. We used allozyme variability to evaluate whether populations at these locales and elsewhere in North America stem from different founders. By identifying the same geographically restricted alleles in both introduced populations and potential source populations and tracing the distribution of these alleles in western North America, we identified a minimum of five or six independent founder events. These alleles were often at their highest frequencies in populations at or near the earliest collection sites. Founder events likely occurred near Cache Creek, B.C., Ritzville, Wash., Juniper Flat, Nev., Emigrant Pass, Nev., and either Dubois, Idaho, or Provo, Utah, or both. Multiple introductions and the spread of allelic variants produced a mosaic of genotypes throughout western North America and partially offset the reduction in genetic variation this alien grass would have probably incurred during intercontinental migration. Key words: Bromus tectorum, biological invasions, multiple introductions, shared alleles, enzyme electrophoresis.
Flat top decay syndrome of the giant cardon cactus (Pachycereus pringlei): description and distribution in Baja California Sur, Mexico
Authors: Bashan Yoav , Toledo Gerardo , Holguin Gina
Published: April 2011

The giant columnar cardon cactus (Pachycereus pringlei) appears to have an ailment(s) that is destroying a large number of plants. The causal agent(s), whether biotic or abiotic, has yet to be determined. Two forms of symptom development have been recorded. The first is a circular tissue decay on a branch leading to death of the growing tip. In this case, the dead portion detaches and forms a "flat top" on the living part (hence the proposed name for this phenomenon). Progressive degeneration and death of the plant ensue. The second form is an initial circular crack on the branch without decay. Later, the green branch above the crack detaches, creating the characteristic flat top. A third type of degeneration was also observed: fatal bleaching. The time period between symptoms is unknown. It primarily affects mature, more than 100-year-old plants, but relatively young plants are also affected. Thirty-one field surveys covering the entire state of Baja California Sur found four major and three smaller centers of flat top decay. We believe that flat top decay syndrome of the cardon cacti in Baja California is common and widespread. Key words: cactus decay, cactus deformation, cactus diseases, columnar cacti, Pachycereus, phytopathology.
Paclobutrazol enhances tolerance to increased levels of UV-B radiation in soybean (Glycine max) seedlings
Authors: Kraus Trevor E. , Fletcher R. Austin , Evans Rodger C. , Pauls K. Peter
Published: April 2011

Paclobutrazol increased the tolerance of soybean (Glycine max L. cv. AC Bravor) seedlings to elevated levels of ultraviolet-B radiation (UV-B: 280 – 320 nm). Within 3 days of exposure to elevated UV-B, nontreated seedlings were photosynthetically less efficient, and by the end of the 11th day of treatment their leaf areas and fresh masses were, respectively, 55 and 44% smaller than their counterparts not irradiated with UV-B. In contrast, paclobutrazol-treated seedlings maintained full photosynthetic efficiency throughout the duration of UV-B irradiation, and their leaf areas and fresh masses were only reduced by 30 and 22%, respectively. No changes in flavonoid composition occurred as a result of the paclobutrazol or UV-B radiation treatments, but UV-B tended to increase the quantities of photosynthetic pigments. The leaves from paclobutrazol-treated seedlings were significantly thicker than those of nontreated seedlings, and SEM analyses showed that the treated seedlings had much denser epicuticular wax layers than the controls. No significant changes in protein expression occurred during exposure to elevated UV-B and (or) paclobutrazol. Further studies with paclobutrazol-treated plants may lead to a better understanding of one or more of the mechanisms employed by plants to tolerate elevated levels of UV-B. Key words: leaf fluorescence, paclobutrazol, pigments, protein synthesis, SEM, UV-B radiation.
Growth responses of Urtica dioica to nutrient supply
Authors: Šrůtek Miroslav
Published: April 2011

This study examines the effects of nutrient supply (three N–P–K treatments: 75, 225, and 375 kg∙ha−1; 12.5% N, 8.5% P, 16% K) on growth, allometry, and architecture of Urtica dioica L., an expansive clonal plant found throughout Central Europe. Biomass allocation was significantly affected by nutrient supply: higher nutrient doses resulted in less biomass allocation to belowground organs, whereas the period of intensive production of aboveground biomass was prolonged. Shoot height increases with nutrient supply. The height ratios were constant over time. Within each treatment and each harvest, inflorescence biomass was positively correlated with shoot height. Branching of the main shoots (number of lateral branches) was positively correlated with plant height and changed with time. The number of new rhizomes was affected by both treatment and harvest, especially in older plants. The results suggest that high nutrient supply increased the allocation of biomass both to reproductive organs and to vegetative organs. Key words: allometry, biomass allocation, clonal plant, nutrients, plant architecture, Urtica dioica.
Variation in mating competence and random amplified polymorphic DNA inLaccaria bicolor(Agaricales) associated with three tree host species
Authors: Raffle V. L. , Anderson N. A. , Furnier G. R. , Doudrick R. L.
Published: April 2011

We examined the population genetic structure of the ectomycorrhizal fungus Laccaria bicolor (Maire) Orton using single spore homokaryotic cultures from 33 basidiomes collected in northern Minnesota in association with red pine (Pinus resinosa Ait.), jack pine (Pinus banksiana Lamb.), and trembling aspen (Populus tremuloides Michx.) of three age-classes (0–20 years, 21–40 years, and > 41 years). Mating competence between cultures of isolates, as determined by the presence of clamp connections, revealed the presence of two subpopulations that were not freely interbreeding, one composed of 29 dikaryons, the other of 3 dikaryons. Phenetic cluster analysis using random amplified polymorphic DNA markers did not reveal differentiation between these subpopulations. Clustering failed to reveal genetically distinct groups based on incompatibility group, tree host species, or geographic origin of isolates. Key words: heterogenic incompatibility, RAPD, population genetics.
Response of arctic tundra plant communities to winter vehicle disturbance
Authors: Emers Michael , Jorgenson Janet C. , Raynolds Martha K.
Published: April 2011

Effects of 1984 and 1985 winter seismic exploration on arctic tundra were evaluated at 104 sites on the coastal plain of northeastern Alaska in 1991. Plant cover increased between initial years and 1991 at sites with low to moderate initial disturbance. All disturbed sites had species whose cover values remained lower than controls, especially nonvascular plants and evergreen shrubs. Graminoids were less affected by disturbance. At high initial levels of disturbance, impacts included (i) surface compression at moist sites, with replacement of shrubs and mosses by hydrophytic sedges and (ii) persistence of bare patches in drier sites and replacement of prostrate shrubs with grasses. Although recolonizing species were generally common in controls, forbs and graminoids not present in adjacent areas were recolonizing some highly disturbed sites. Active layers were deeper at 55% of sites but shallower at 6 highly disturbed sites, where dead sedge leaves insulated permafrost. Plant biomass and nutrient concentrations were initially higher on disturbed plots, but by 1991 differences only persisted at the most disturbed mesic plot. Previous studies of winter disturbance had predicted short-term and mainly aesthetic impacts. We found impacts to the active layer and plant communities persisting eight growing seasons after disturbance. Key words: arctic coastal plain, nutrient, permafrost, plant community, tundra, winter trail disturbance.
Phylogenetic relationships and patterns of character change in the tribe Lactuceae (Asteraceae) based on chloroplast DNA restriction site variation
Authors: Whitton Jeannette , Wallace Robert S. , Jansen Robert K.
Published: April 2011

The Lactuceae is perhaps the most easily recognizable tribe in the Asteraceae, distinguished by the presence of milky latex and of ligulate florets in the inflorescence. Three existing taxonomic treatments of the tribe establish subtribal classifications but fail to resolve relationships among major lineages. Our study of chloroplast DNA restriction site variation sampled 60 Lactuceae taxa. We detected 1268 mutations, 612 of which are phylogenetically informative. Despite the large amount of variation detected, little resolution of relationships among major lineages was obtained from parsimony analyses, although the monophyly of many groups is strongly supported. These results, when considered along with data from morphological analyses of other workers, suggest that rapid diversification played an important role in early stages of the tribe's evolution. Our examination of character change further reveals that as noted by other workers, restriction site variation is not evenly distributed across the chloroplast genome and that regions with higher levels of variation do not necessarily have higher amounts of homoplasy. This is somewhat surprising, since we found that amounts of homoplasy along terminal branches of our phylogenetic tree are related to levels of divergence. Key words: Asteraceae, chloroplast DNA, homoplasy, Lactuceae, phylogeny, restriction site variation.
Reduced seed set in Elytrigia repens caused by allelopathic pollen from Phleum pratense
Authors: Murphy Stephen D. , Aarssen Lonnie W.
Published: April 2011

Earlier studies have shown that extracts from pollen of Phleum pratense reduce pollen germination and seed set in Elytrigia repens (L.) Nevski (Poaceae), but the effect of in situ pollen from P. pratense on seed set in E. repens in the field has not been previously demonstrated. By clipping the inflorescences of P. pratense just prior to flowering, we reduced pollen dispersal in fields at three old-field sites. In adjacent fields at all three sites, P. pratense was allowed to flower unimpeded. In the clipped fields, the mean number of pollen grains of P. pratense per stigma of E. repens was reduced to less than 1 versus 9–10 grains in the unmanipulated fields. Mean percent seed set of E. repens in the clipped fields was approximately 65–70%, whereas in the unmanipulated fields it was approximately 15–20%. In the following year, when no treatments were applied (i.e., P. pratense was allowed to disperse naturally in all fields), mean percent seed set in the same plants of E. repens was uniformly reduced to less than 15% in all fields. Several lines of evidence suggest that this reduction in seed set in E. repens was caused by allelopathic pollen of P. pratense, rather than by physical occlusion: (i) previous studies using extracts of P. pratense pollen elicited similar decreases in seed set in E. repens, and the seed set decreases were nonlinear (i.e., not indicative of displacement); (ii) the number of P. pratense pollen grains on E. repens stigmas needed to cause pollen allelopathy (based on previous pollen extract studies) existed in the unmanipulated fields but not in the clipped fields; and (iii) E. repens pollen outnumbered P. pratense pollen on E. repens stigmas by at least 5:1 (even when P. pratense inflorescences were not clipped). Key words: competition, Elytrigia repens, heterospecific pollen transfer, Phleum pratense, pollen allelopathy, reproductive success.
Mycorrhizal fungi associated with three species of turfgrass
Authors: Koske R. E. , Gemma J. N. , Jackson N.
Published: April 2011

Small plots of highly maintained turfs of creeping bentgrass (Agrostis palustris cv. Penncross) and velvet bentgrass (Agrostis canina cv. Kingstown) and a marginally maintained stand of annual bluegrass (Poa annua) were sampled intensively over a 15-month period to measure the populations of spores of arbuscular mycorrhizal fungi (AMF) associated with their root systems. Direct isolation of spores and trap cultures were used to assess the AMF communities. Spores of more than 18 species of AMF were isolated. The six dominant species (as measured by the abundance and frequency of occurrence of spores) were Acaulospora mellea, an undescribed species of Acaulospora, Scutellospora calospora, Glomus occultum, Glomus etunicatum, and Entrophospora infrequens. Spores of 17 species of AMF were recovered from the root zones of velvet bentgrass, 15 species from creeping bentgrass, and 14 from annual bluegrass. Soil fertility differed among the three sites, and it was not possible to ascribe differences in the AMF communities in each plot to any particular variable (e.g., host, pH, soil P). Average spore abundance was greatest in the creeping bentgrass plot (191.0 spores/100 mL), next in the velvet bentgrass plot (82.4 spores/100 mL), and least in the bluegrass plot (28.4 spores/100 mL). Spores were recovered from a significantly greater percentage of the samples from the bentgrass plots (88.5 – 96.8%) than from the bluegrass plot (76.6%). Spores of an average of 4.5 species of AMF were isolated monthly from creeping bentgrass, 3.3 from velvet bentgrass and 2.0 from bluegrass. Average species richness and spore abundance were positively correlated in the creeping bentgrass and bluegrass plots (r = 0.77, p = 0.001, and r = 0.68, p = 0.006), but not in the velvet bentgrass plot. Spore abundance showed strong seasonal trends in all three plots (p = 0.03 – 0.001), with numbers increasing from spring until November. Richness and abundance declined from December until the following spring. In the bluegrass area, which experienced summer drought, spore populations and richness also showed a precipitous decline in July and August in the 1st year of the study (1990), but not in the 2nd year (1991). No such summer decline occurred in the bentgrass plots that received irrigation. The AMF community that was circumscribed by direct spore counts from the field usually was highly dissimilar to the community that was estimated by trap cultures initiated using soil from the turf areas. Key words: annual bluegrass, arbuscular mycorrhizal fungi, creeping bentgrass, putting greens, turfgrass, velvet bentgrass.
Host specificity and vegetative compatibility of Dutch isolates ofFusarium oxysporumf.sp.asparagi
Authors: Blok Wim J. , Bollen Gerrit J.
Published: April 2011

The host range of Fusarium oxysporum f.sp. asparagi (Foa) was studied in inoculation experiments with 21 plant species. Typical root rot symptoms were incited only in asparagus, in all experiments; lupin and pea were susceptible under in vitro conditions but showed only mild symptoms occasionally when tested in soil; none of the other species showed external disease symptoms. Root colonization by Foa was studied for 14 plant species. The pathogen was detected in externally disinfested roots of all species except leek and onion, with asparagus the most extensively colonized species. Asparagus was not susceptible to isolates of F. oxysporum f.sp. pisi, lupini, cepae, lilii, and gladioli and Fusarium sacchari var. elongatum. Naturally infested field soil was planted twice for 11 – 13 weeks with 11 plant species, including asparagus and several symptomless hosts, and subsequently with asparagus as a biotest plant. Of these crops, only asparagus greatly increased the severity of Foa root rot. It was concluded that Foa has a narrow host range as a pathogen but a broad host range as a parasite. The consequences of the latter for the epidemiology of Foa are discussed. Twenty-four Foa isolates were assigned to 18 different vegetative compatibility groups (VCGs); three additional F. oxysporum isolates, which were not pathogenic on asparagus, each belonged to a unique VCG. These findings indicate that the Dutch Foa population is very diverse genetically, as was found previously for the Foa population in the United States. Key words: asparagus, Fusarium oxysporum f.sp. asparagi, host range, lupin, pea, symptomless hosts, vegetative compatibility.
High rates of O2 photoreduction by the unicellular cyanobacterium Synechocystis PCC 6803 as determined by the quenching of chlorophyll fluorescence
Authors: Goosney Danika L. , Miller Anthony G.
Published: April 2011

It is well established that various strains of Synechococcus, a genus of unicellular cyanobacteria, can photoreduce O2, at high rates even during concomitant photosynthetic CO2 fixation. This photoreduction probably involves photosystem I (PS1) and the so-called Mehler reaction. Although all photosynthetic organisms carry out this reaction to some extent, the mechanistic details remain unclear. Good candidates for the study of this reaction should be the various cyanobacteria that exhibit high rates of O2 photoreduction. Unfortunately, the strains of Synechococcus that have been examined so far in this context are obligate photoautotrophs, which precludes the dissection of the photoreduction process by mutational analysis of PS1. In the present study, we show that Synechocystis PCC 6803, a species capable of growth on glucose can photoreduce O2 at high rates. When grown photoautotrophically, the cells exhibited an O2-dependent quenching of chlorophyll a fluorescence that was 50–70% that of CO2-dependent quenching. The magnitude of this O2-dependent photochemical quenching could be related to the rate of linear photosynthetic electron flow. For cells grown at a photosynthetic photon flux density of 50 μmolm−2 ∙ s−1, the rate of O2, photoreduction was saturated at about 200 μmolm−2 ∙ s−1. Unlike Synechococcus UTEX 625 and PCC 7942, the rate of photoreduction of O2 was high even at the CO2 compensation point, when there would be very little active accumulation of inorganic carbon (Ci). The O2 concentration, or Km(O2), that supported the half-maximal rate of O2 photoreduction was in the order of 6 μM. This low value for the Km(O2) and also the ability of the cells to photoreduce O2 in the presence of glycolaldehyde, which inhibits ribulose bisphosphate (RuBP) regeneration, ruled out the involvement of RuBP oxygenase. Cells grown photomixotrophically, on Ci and glucose, were also capable of high rates of O2 photoreduction as manifest by high rates of O2-dependent quenching of chlorophyll fluorescence. The response to O2 of these cells was very similar to that observed with Synechococcus UTEX 625 and PCC 7942, in that O2 photoreduction was greatly stimulated by the accumulation of Ci by the active CO2 and HCO3− transport systems. The demonstration that the facultatively heterotrophic Synechocystis PCC 6803 photoreduces O2 at high rates opens up the possibility of using targeted genetic inactivation of PS1 to study the Mehler reaction. Key words: O2 photoreduction, cyanobacteria, chlorophyll a fluorescence.
Molecular phylogenetics ofThlaspis.l. (Brassicaceae) based on chloroplast DNA restriction site variation and sequences of the internal transcribed spacers of nuclear ribosomal DNA
Authors: Mummenhoff Klaus , Franzke Andreas , Koch Marcus
Published: April 2011

Systematics of the genus Thlaspi s.l. is difficult and controversial. Previous hypotheses have been based on morphological and anatomical data. We have analyzed sequence variation of the internal transcribed spacer (ITS) regions of nuclear ribosomal DNA (nrDNA) among 13 Thlaspi s.l. taxa, representing all sections of the genus. Phylogenetic relationships among ITS sequences of the Thlaspi s.l. taxa studied are in general concordance with a previously published chloroplast DNA based phylogeny of this group. Most-parsimonious trees from ITS and chloroplast DNA data support three groups that are congruent with lineages (Thlaspi s.str., Noccaea–Raparia, Microthlaspi) previously described by Meyer on the basis of seed anatomy. The ITS data grouped Microthlaspi granatense outside the Microthlaspi clade and, therefore, Microthlaspi appeared paraphyletic on the ITS tree, in contrast with the chloroplast DNA phylogeny. We speculate that concerted evolutionary forces have acted among different nrDNA arrays (brought together in M. granatense by hybridization with a related taxon), resulting in the fixation of the alien species nrDNA type in M. granatense, which, however, maintains a Microthlaspi chloroplast genome type. Both molecular data sets detected intraspecific variation among Microthlaspi perfoliatum accessions of different geographic origin and different ploidy levels. Our molecular evidence would suggest the hybrid origin of polyploid M. perfoliatum from diploid M. perfoliatum and M. natolicum. Key words: chloroplast DNA, restriction site variation, sequence analysis of nuclear ribosomal DNA ITS regions, Thlaspi s.l. (Brassicaceae), molecular phylogeny, congruence.
No evidence for interspecific interactions between plants in the first stage of succession on coastal dunes in subarctic Quebec, Canada
Authors: Houle Gilles
Published: April 2011

Coastal dunes are very dynamic systems, particularly where the coast is rising as a result of isostatic rebound. In those environments, succession proceeds from plants highly tolerant to sand accumulation, salt spray, and low nutrient availability to less disturbance-tolerant and stress-tolerant, more nutrient-demanding, and supposedly more competitive species. In the subarctic, the regional climate exacerbates the stresses imposed by local abiotic conditions on the dunes. I hypothesized that facilitation would be particularly significant on the foredune of subarctic coastal dune systems because of intense stresses (local and regional) and frequent disturbance in the form of sand deposition. Belowground and aboveground plant biomass was sampled at three different periods during the 1990 growing season along transects perpendicular to the shoreline on a coastal dune system in subarctic Quebec (Canada). The three herbaceous perennials found on the foredune (Honckenya peploides, Elymus mollis, and Lathyrus japonicus) were segregated in time during the growing season and in space along the topographical gradient. The biomass of Honckenya, the first species encountered as one progresses from the upper part of the beach towards the foredune ridge, was not correlated to substrate physicochemistry. However, the biomass of Elymus and that of Lathyrus, the next two species to appear along the flank of the foredune, were related to pH, Mg, Na, and Cl (negatively), and to P and Ca (positively). These results suggest variable linkages between substrate physicochemistry and plant species along the foredune, possibly in relation to species-specific tolerance for abiotic conditions and requirements for substrate resources or to microscale influence of the plants themselves on substrate physicochemistry. Removal experiments carried out over 2 years revealed only one significant unidirectional interaction between these three species along the topographical gradient, and little plant control over abiotic variables (e.g., soil temperature, wind velocity, and photosynthetically active radiation). Early primary succession on subarctic coastal dunes (and elsewhere) appears to be under the control of strong limiting abiotic conditions. As plants slowly gain more control over the physical environment, interspecific interactions (positive and negative) may become more significant. Key words: Elymus mollis, facilitation, Honckenya peploides, inhibition, Lathyrus japonicus, removal experiment, succession, tolerance.
Effects of intrinsic and environmental factors on seedling survival of Rumex obtusifolius in Mediterranean alfalfa crops
Authors: Pino J. , Sans F. X. , Masalles R. M.
Published: April 2011

This paper focusses on the survivorship pattern of seedlings of Rumex obtusifolius L. in the irrigated alfalfa crops (Medicago sativa L.) in central Catalonia (NE Spain). The relationship between this pattern and seasonal environmental change was evaluated by monitoring seedling cohorts that had germinated at different times of the year for 31 months. Paired comparisons of cohort survivorship curves were performed over their life-spans and for their coexistence period, using Peto and Peto's log rank test. The significance of intrinsic variables such as age and size in determining seedling survival was tested using hierarchical log-linear analysis applied on a three-way contingency table and by means of Goodman and Kruskal's association coefficients. Results showed that seedling cohorts emerging at different times in the year exhibited a similar Deevey type III survivorship pattern. Therefore, survivorship was scarcely affected by seasonal environmental variation. However, since age had little effect on seedling survival compared with size, this age-specific survivorship pattern was, in fact, a consequence of both size-dependent mortality and changes in size distribution with age. In the first weeks of life, cohort size distribution was greatly skewed to the smallest classes, with the highest mortality rates, and therefore the risk of death in the cohort was high. Afterwards, the frequency of the largest size classes increased with age, thus reducing the risk of death of the cohort. Key words: Rumex obtusifolius, seedling survivorship pattern, size versus age dependency, survival analysis.
Aquatic hyphomycetes in three rivers of southwestern France. III. Relationships between communities spatial and temporal dynamics
Authors: Fabre Eric
Published: April 2011

Spatial and temporal dynamics of individual species of aquatic hyphomycetes in three southwestern French rivers have been previously studied using water filtration techniques. In this paper, relationships between these spatial and temporal dynamics were explored using correspondence analysis. Correspondence analyses were performed for conidial concentration and presence-absence of species. The analysis of conidial concentration data indicated that species temporal dynamics is more important in determining changes in conidial communities than species spatial dynamics. However, the interconnectedness of these dynamics was revealed by a Guttman effect between the first two factorial axes. A linear gradient Tech-Adour-Nive, which corresponds to the geographical disposition of these rivers in southwestern France, was observed on the first three axes of the correspondence analysis of conidial concentrations. This gradient did not exist in the correspondence analysis of species presence-absence, but the analysis revealed a qualitative difference of the communities between the summer season and the beginning of autumn. The comparison of eigenvalues for the two correspondence analyses pointed out that conidial abundance is more significant than presence-absence of species for the structure of the data table. Key words: aquatic hyphomycete, spatial dynamic, temporal dynamic, climatic gradient.
Visualization of mycorrhizal fungal structures in resin embedded tissues with xanthene dyes using laser scanning confocal microscopy
Authors: Melville Lewis , Dickson Sandy , Farquhar Melissa L , Smith S E , Peterson R. Larry
Published: April 2011

The xanthene dyes sulforhordamine G, phloxine B, rose Bengal, and 4,5,6,7-tetrachloroflorescein were used as fluorochromes for laser scanning confocal microscopy of LR-White resin-embedded mycorrhizae. Sulforhodamine G was the most effective dye, giving an even staining of cell components throughout the material, with minimal background fluorescence of LR-White resin. Confocal microscopy of stained blocks of tissue on a slide, viewed without the use of a coverslip, revealed the three-dimensional nature of various mycorrhizal structures; these structures included arbuscules, vesicles, and coiled hyphae in arbuscular mycorrhizae; coiled hyphae in orchid mycorrhizae; mantle and Hartig net hyphae in ectomycorrhizae; and intracellular hyphae in arbutoid mycorrhizae. Sections mounted on slides viewed with confocal microscopy provided exceptional clarity of fungal form and cytoplasmic contents and showed the relationship to the plant cells, also with negligible background fluorescence. Mounting and staining blocks of resin-embedded material provided a fast and effective technique for the visualization of a variety of plant and fungal tissues. Stain penetration in whole-mounted samples was sufficient to reconstruct clear three-dimensional images using confocal microscopy.Key words: mycorrhizae, xanthene dyes, confocal microscopy, resin embedding.
An explanation for size-dependent reproductive allocation in Plantago major
Authors: Reekie Edward G
Published: April 2011

This study examined whether variation in reproductive allocation with size could be explained by differences in the trade-off between reproduction and growth. Seeds from 42 half-sibling families were collected from sites differing in mowing frequency and availability of light, nutrients, and water. Six seedlings from each family were grown in controlled environments and photoperiod manipulations were used to control reproduction. Mass of vegetative and reproductive plants of the same family were compared to assess the trade-off between reproduction and growth. Families collected from habitats with a tall canopy were larger and experienced a greater decrease in growth with reproduction than families from habitats where mowing maintained a short canopy. Reproductive output showed no relationship with size, while reproductive allocation (capsule mass to vegetative mass) decreased with size. This decrease may be a direct consequence of the increase in reproductive cost with size. The increase in cost can be partially explained by increased allocation to reproductive support structures; large individuals produce capsules on more elongate scapes and have a lower capsule to scape ratio. Differences in size and morphology among habitats are presumably the result of selection to avoid damage in mown sites and to avoid shade and ensure pollination in sites with a tall canopy and reduced wind movement.Key words: allometry, life-history theory, size constraints, reproductive effort, reproductive cost.
Russulaceous ectomycorrhizae of Abies lasiocarpa and Picea engelmannii
Authors: Kernaghan G. , Currah R. S. , Bayer R. J.
Published: April 2011

During a 3-year study of the ectomycorrhizal fungi of subalpine forests in the Front Ranges of the Canadian Rockies, species of Russula and Lactarius were conspicuous mycobionts of both erect and krummholz forms of Abies lasiocarpa (Hook.) Nutt. and Picea engelmannii Parry. Morphological identifications of Russulaceous mycorrhizae were confirmed by comparing polymerase chain reaction amplified ribosomal DNA (internal transcribed spacer region) with that of sporocarp tissue. Restriction fragment length polymorphism analysis using AluI, HhaI, HinfI, and RsaI gave a distinctive profile for each of 14 Russulaceous sporocarps and facilitated the identification of five mycorrhizae. Mantles formed by Lactarii (Lactarius alnicola, Lactarins caespitosus, and Lactarius deliciosus var. areolatus) exhibit characteristic laticifers and pigments comparable to the associated sporocarp. Those formed by species of Russula (R. brevipes and R. silvicola) bear distinctive cystidia or sulphovanillin-reactive cells. Key words: ITS, Lactarius, RFLP, Russula, subalpine, tree line.
Patterns of seed polymorphism and allozyme variation in the bladder campions, Silene vulgaris and Silene uniflora (Caryophyllaceae)
Authors: Runyeon Helena , Prentice Honor C.
Published: April 2011

Seed morphology (testa ornamentation and seed shape) and allozyme variation were investigated in three closely related and partially sympatric taxa of Silene in the Nordic region. Within this region, Silene vulgaris is a widespread weed of anthropogenic habitats. The two subspecies of Silene uniflora are restricted to naturally open habitats; ssp. uniflora has a coastal distribution, whereas the Swedish endemic, ssp. petraea, is restricted to limestone habitats on the islands of Öland and Gotland. All three taxa show a seed ornamentation polymorphism, with individuals producing either tubercled or smooth ("armadillo") seeds. Both seed morphology and allozymes show a separation between the two species Silene vulgaris and Silene uniflora and support the present taxonomic treatment of the endemic "petraea" as a subspecies of Silene uniflora. Tubercled seeds predominate in Silene vulgaris and armadillo seeds predominate in Silene uniflora. However, there is considerable between-population variation in seed morph frequencies within taxa. In contrast to the other two taxa, populations of Silene uniflora ssp. petraea consistently show intermediate frequencies of both seed morphs. Silene uniflora ssp. petraea has the lowest between-population component of diversity in both seed shape (18–46%) and allozymes (0.8%) and shows no significant geographic structure in any of the character sets. Both Silene uniflora ssp. uniflora and Silene vulgaris show significant geographic differentiation in allozymes and seed morphology. The highest between-population component of diversity was found in Silene uniflora ssp. uniflora, where 17% of the total allozyme diversity and 39–82% of the seed shape diversity are accounted for by differences between populations. Key words: allozymes, geographic differentiation, diversity, seed shape, elliptic Fourier coefficients, Landmark characters.
Conservative allocation of globoid-held mineral nutrients in Banksia grandis (Proteaceae) seeds
Authors: Egerton-Warburton Louise M. , West Marcia , Lott John N.A.
Published: April 2011

Analysis of globoid-held mineral nutrients and aluminum in Banksia grandis seeds collected from two sites, one with a high aluminum content in the soil, demonstrated that there was no significant difference in the concentration or distribution of mineral nutrients between seed stocks. Even in seeds from high-aluminum soils, aluminum was not detected in the globoids and only traces of the metal were noted within calcium-rich crystals. It was concluded that a conservative regulation of nutrients occurred in B. grandis, and even in a family known for it's aluminum-accumulating potential the metal was largely excluded from the propagules. Key words: Banksia grandis, Proteaceae, aluminum, globoids, energy-dispersive X-ray microanalysis.
Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae). VI. Respiration and water potential
Authors: McArthur E Durant , Freeman D Carl , Graham John H , Wang Han , Sanderson Stewart C , Monaco Thomas A , Smith Bruce N
Published: April 2011

Respiration and stem water potential ( psi ) were examined in parental and hybrid big sagebrush (Artemisia tridentata Nutt. ssp. tridentata and Artemisia tridentata Nutt. ssp. vaseyana (Rydb.) Beetle) grown in common gardens within each parental zone and in the hybrid zone. Plants were sampled in July, August, and September, i.e., immediately before, during, and after flowering. The habitats differed from one another, and there were significant garden by date interactions. The source populations also differed significantly from one another. There were no significant garden by source interactions. Hybrid plants had intermediate respiration rates and did not suffer greater water stress than parental plants. Hybrid plants showed no apparent decrease in adaptation in the important physiological traits respiration and water stress in the hybrid zone.Key words: Artemisia, hybrid zones, respiration, water potential.
The reproductive ecology of island populations of distylous Menyanthes trifoliata (Menyanthaceae)
Authors: Thompson Faye L , Hermanutz Luise A , Innes David J
Published: April 2011

Menyanthes trifoliata L. is a distylous, clonal aquatic macrophyte found in shallow bogs and river margins throughout the boreal ecosystem, including the island of Newfoundland. A combination of long-distance dispersal and colonization after deglaciation, and pollen limitation resulting from reduced pollinator diversity and abundance documented on islands, predicts the breakdown of heterostyly to favour the establishment of self-compatible homostyles on islands. To test if self-fertilizing homostyles have been selected, variation in floral characters and compatibility relationships were examined in M. trifoliata populations from the Avalon Peninsula of Newfoundland. Morph ratio and its effect on fruit and seed set were examined in nine populations. Of the seven dimorphic populations, morphs occurred in a 1:1 ratio in four populations and deviated significantly from a 1:1 ratio in three populations. The two populations monomorphic for either pin or thrum morphs set few fruits or seeds (<15%). A strictly reciprocal arrangement of stigma height and anther length was not observed between pin and thrum morphs in the majority of populations studied. Stigma-anther separation showed a bimodal distribution with few intermediate "homostylous" flowers, rather than the discreet bimodal distribution typical of distylous species. Fruit and seed set were high (>60%) in equal morph ratio populations and were not significantly correlated to stigma-anther separation, indicating that there was no selective advantage of being homostylous. All three populations tested were highly self-incompatible, confirming that there has not been a breakdown of heterostyly on the island of Newfoundland. A reduced pollinator fauna typical of island environments may have relaxed stabilizing selection for strict herkogamy between floral morphs, resulting in the observed lack of reciprocity.Key words: Menyanthes trifoliata, distyly, homostyle, reciprocal herkogamy, clonal aquatic macrophyte, island of Newfoundland.
Effect of different treatments on the seed bank of grazed and ungrazed Baltic seashore meadows
Authors: Erkkilä Heli M. Jutila b.
Published: April 2011

Seed banks of two seashore meadows were studied on the west coast of Finland (latitude 61°30'-61°33'N, longitude 21°28'-21°41'E). Samples were taken in June to a depth of 10 cm in the geolittoral zone of the grazed and ungrazed transects. The grazed samples were halved lengthwise: one half was grown immediately, the other after cold treatment. One third of the all samples was treated as controls, one third was watered with brackish water, and one third was given a pesticide treatment. Altogether, 13 926 seedlings germinated and 25 species were identified (three annuals, two biennials, and the rest perennials). Most seedlings were perennial monocots, with Juncus gerardii Loisel. the most abundant species. The seed bank was significantly larger and richer in the ungrazed site than in the grazed site. Cold treatment reduced the number of germinating species and seedlings. In the grazed and non-cold-treated samples, the numbers of species and seedlings were highest in the pesticide treatment. In ungrazed samples there were no significant differences among treatments. After the cold treatment, the least number of species and seedlings was produced by the salt-water treatment. Changing brackish water to tap water led to a burst of germination, especially of J. gerardii. The seed bank of the upper geolittoral zone was richer than that of the middle geolittoral. The multivariate classification and ordination groupings are based on the abundances of J. gerardii and Glaux maritima L.; different treatments were not distinguishable. There was a low resemblance between the seed bank and the aboveground vegetation.Key words: seed bank, salinity, pesticide, seashore meadow, cold treatment, vegetation.
Generic classification of some more hyphomycetes with solitary conidia borne on phialides
Authors: Gams W , O'Donnell K , Schroers H -J , Christensen M
Published: April 2011

Unlike most phialide-producing fungi that liberate a multiplicity of conidia from each conidiogenous cell, only single conidia are formed on phialide-like conidiogenous cells in Aphanocladium, Verticimonosporium, and some species of Sibirina. A group of isolates obtained from soil of native Artemisia tridentata (sagebrush) grassland in Wyoming and from desert soil in Iraq is compared with these genera and classified as a fourth genus, Stanjemonium, honouring Stanley J. Hughes. Phylogenetic analyses of partial nuclear small- (18S) and large-subunit (28S) rDNA sequences indicate that Stanjemonium spp. form a monophyletic group with Emericellopsis. Sequences from the nuclear 18S and 28S rDNA were too conserved to resolve morphological species of Stanjemonium; however, phylogenetic analysis of b-tubulin and translation elongation factor 1a gene exons and introns resolved all species distinguished morphologically. Numerous conidiogenous cells or denticles are scattered along the cells of aerial hyphae in Aphanocladium and Stanjemonium spp., very rapidly collapsing into denticles in the former, somewhat more persistent and leaving broad scars in the latter. In Cladobotryum-Sibirina and Verticimonosporium spp., conidiogenous cells are discrete in terminal and intercalary whorls; phialides of the latter taxon are particularly swollen. The taxonomy of Aphanocladium is not yet resolved. Two species are recognized in Verticimonosporium. Three new species of Stanjemonium are described, and one new combination from Aphanocladium is proposed, along with one new species of Cladobotryum.Key words: Aphanocladium, Cladobotryum, conidiogenesis, hyphomycetes, molecular phylogeny, phialide, Stanjemonium, systematics, Verticimonosporium.
Phylogenetic and developmental evidence supporting reclassification of cruciferous pathogens Phoma lingam and Phoma wasabiae in Plenodomus
Authors: Reddy P V , Patel R , White, Jr. J F
Published: April 2011

To evaluate the classification of Phoma lingam (Tode:Fr.) Desm. and Phoma wasabiae Yokogi in the genus Phoma, a phylogenetic study of Phoma spp. was conducted using ribosomal DNA internal transcribed spacer 1 sequences. The majority of the Phoma species included in the study clustered in a Phoma-Didymella clade (Venturiaceae). Phoma lingam and P. wasabiae consistently clustered outside of the Phoma-Didymella clade, instead forming the Plenodomus clade (Leptosphaeriaceae). This result supports classification of P. lingam and P. wasabiae in Plenodomus as has been proposed by earlier investigators. Features of the morphology and development of pycnidia of Phoma americana Morgan-Jones & White and P. lingam suggest that Phoma and Plenodomus may also be distinguishable morphologically. Our results suggest that difficulties of identification and classification in Phoma may be resolved by using a phylogenetic approach to classification.Key words: Coelomycetes, molecular systematics, pathogens, taxonomy.
Effects of genotypes, soil moisture, and competition on the growth of an invasive grass, Phalaris arundinacea (reed canary grass)
Authors: Morrison Shannon L , Molofsky Jane
Published: April 2011

The successful establishment of an invasive plant species in a new environment depends upon the interplay between the plant's genetic diversity and morphological plasticity and the physical and biotic environment it encounters. To determine the relative importance of these factors in influencing the spread of the invasive grass, Phalaris arundinacea L. (reed canary grass), we transplanted three genotypes into a pasture that contained variable soil moisture, species composition, and vegetative cover. We found that P. arundinacea produced more above- and below-ground biomass in sparsely vegetated plots than in densely vegetated plots, but biomass production was not affected by soil moisture. There was also a significant clone beta vegetative cover interaction. Genotypes differed in how strongly their growth was inhibited by dense vegetative cover. Vegetative cover also influenced biomass allocation patterns. As vegetative cover increased, P. arundinacea allocated more biomass to roots, a strategy that gives transplants a competitive advantage during the following spring. Our results suggest that, because it grows poorly in high vegetative cover, P. arundinacea is most likely to become a pest in disturbed or low-density plant communities. Furthermore, differences among genotypes in their response to vegetative cover suggest that continual introductions of new genotypes of reed canary grass substantially increase the chance that a particular genotype will flourish and spread.Key words: biomass allocation, competition, invasive species, morphological plasticity, plant invasions, Phalaris arundinacea, reed canary grass.
Antifungal effects of hydrogen peroxide and peroxidase on spore germination and mycelial growth ofPseudocercosporaspecies
Authors: Joseph Leina Mary , Koon Tan Teck , Man Wong Sek
Published: April 2011

Spore germination in Pseudocercospora abelmoschi (Ell. & Ev.) Deighton USDB1312 and Pseudocercospora cruenta (Sacc.) Deighton USDB1313, pathogens of Hibiscus esculentus L. and Vigna sinensis ssp. sesquipedalis (L.) van Eseltine, was significantly inhibited when incubated with different levels of hydrogen peroxide (0.03 × 10-5- 4.59 × 10-5M H2O2) and 1-100 µg/mL peroxidase (equivalent to 1.06-106 enzyme units). Significant reduction in mycelial growth was also observed in both fungi at different levels of H2O2(0.03 × 10-5- 7.71 × 10-5M) and 1-1000 µg/mL peroxidase. The spores and mycelium of P. cruenta USDB1313 could tolerate higher levels of H2O2(0.03 × 10-5- 2.61 × 10-5M) compared with that of P. abelmoschi USDB1312. The effects of peroxidase on spore germination and mycelial growth were similar in both P. abelmoschi and P. cruenta isolates. Spore germination and mycelial growth were inhibited significantly at higher levels of peroxidase. The results of this study complemented earlier field observations on the resistance or susceptibility of H. esculentus and V. sinensis ssp. sesquipedalis to both fungi.Key words: hydrogen peroxide, peroxidase, Pseudocercospora spp.
Spadicoides palmicola sp.nov. on Licuala sp. from Brunei, and a note on Spadicoides heterocolorata comb.nov.
Authors: Goh T K , Hyde K D
Published: April 2011

Spadicoides palmicola sp.nov. is described from a senescent leaf of Licuala sp. collected in Brunei. It differs from other Spadicoides species in having verruculose conidiophores producing verrucose, obclavate, rostrate, multi-euseptate, versicoloured conidia. Spadicoides obclavata Kuthub. & Nawawi var. heterocolorata R.F. Castañeda, Guarro & Cano is considered distinct from Spadicoides obclavata, and Spadicoides heterocolorata comb.nov. is proposed.Key words: Hyphomycetes, Licuala, palm fungi, systematics, tropical fungi.