bluuebunny/crossref_metadata_2025 huggingface dataset:
The use of ion exchange resins to assess the changes in mineral element availability during the production of the cultivated mushroom Agaricus bisporus
Authors: Beyer David M
Published: April 2011

Nutrient depletion and accumulation of toxic metabolites in compost are believed to be limiting factors and responsible for decreased yields as a mushroom crop ages. The objective of this study was to identify, monitor, and quantify mineral element levels in composted substrate and compost solution extracts during mushroom production. Mineral element changes were assessed by placing ion exchange resin bags in compost saturated paste extracts and directly in composted substrate. The concentration of most cations in compost solution increased as the crop aged. The addition of hypnum peat and rock phosphate to compost at spawning lowered potassium and magnesium concentration in compost solution, which suggested the accumulation of potassium, and possibly, magnesium may limit later yields. Compost solution extracted from hypnum peat moss and rock phosphate supplemented compost had less phosphorus in solution than unsupplemented compost, suggesting an increase in uptake of phosphorus by the mushroom mycelium increased later break yields. Resin-extracted potassium from the saturated paste extract solutions decreased until primordia formation, then increased as the crop aged. Hypnum peat and rock phosphate added to compost at spawning lowered resin-extracted potassium and increased resin-extracted calcium after casing. Most resin-extracted cations from around the mycelium in situ increased as the crop aged. IR-120-Na resins extracted more calcium and less potassium from around the mycelium in hypnum peat supplemented compost. The results suggested that calcium or potassium interfered with the nutrient uptake of phosphorus as the crop aged, thus reducing yield.Key words: Agaricus bisporus, hypnum peat, ion exchange resins, chelation, calcium, potassium, phosphorus.
Seed dormancy and germination in Rhexia mariana var. interior (Melastomataceae) and eco-evolutionary implications
Authors: Baskin Carol C , Baskin Jerry M , Chester Edward W
Published: April 2011

Ninety-seven percent of the Rhexia mariana L. seeds collected in Tennessee were physiologically dormant at maturity in autumn, and they became nondormant during stratification. Light was required for germination, and seeds germinated to higher percentages on filter paper than on sand. Seeds buried in soil in October 1992 and 1994 and exposed to natural seasonal temperatures were exhumed and tested for germination at monthly or bimonthly intervals for 30 and 32 months, respectively. Seeds gained the ability to germinate to 80% or more at 30:15 and 35:20°C during the first winter of burial and also at 25:15°C during the second winter, but they did not re-enter dormancy. In contrast, seeds incubated at 20:10°C exhibited an annual cycle of moderate to high germination percentages in winter-spring and low germination percentages in summer-autumn. Thus, germination can occur at habitat temperatures in Tennessee from April to September. This is the first report of physiological dormancy in seeds of the Melastomataceae in the temperate region. Like members of many plant families in temperate eastern North America, seeds of R. mariana (i) show a decrease in the minimum temperature for germination as they come out of dormancy and (ii) exhibit some seasonal variation in the temperature range for germination. Thus, these dormancy or germination characteristics appear to be adaptations of species to the climatic conditions in temperate eastern North America.Key words: seed dormancy, seed germination, dormancy cycles, buried seeds, Melastomataceae, Rhexia.
A comparison of preharvest and postharvest ethylene production and respiration rates of saskatoon (Amelanchier alnifolia Nutt.) fruit during development
Authors: Rogiers Suzy Y , Knowles N Richard
Published: April 2011

Changes in respiration and ethylene production rates of nine maturity classes of saskatoon (Amelanchier alnifolia, Nutt.) fruit after harvest were compared with those of fruit maturing and ripening on the plant. During ripening on the plant, ethylene production increased on a whole-fruit and fresh-weight basis, while respiration increased substantially on a whole-fruit basis but remained constant on a fresh-weight basis. Fruit harvested at the greenish yellow to pink stages (maturity classes four and five, respectively) increased their ethylene production until 15-20 h after harvest, and this was coincident with ripening to maturity class seven and thus a color change to red. Ethylene production then declined over the next 15 h. Respiration rates of harvested immature, mature, and ripe fruits declined over 5 days, except for a relatively brief 8-12% rise starting 15-20 h after harvest. This brief increase in respiration was characteristic of fruit of all maturity classes, likely reflecting a wound response associated with harvest rather than a ripening-induced change in metabolism. Continuous treatment of attached or detached fruit with propylene or ethylene in an open airflow system did not induce an increase in respiration earlier, relative to control fruit. The respiratory response of saskatoon fruit during postharvest ripening was thus very different from that of fruit that ripened on the plant. Thus, the increase in respiration associated with ripening could only be demonstrated on a whole-fruit basis if fruit remained on the plant. Preharvest and postharvest changes in ethylene production during ripening also differed but were both consistent with climacteric ripening.Key words: Amelanchier alnifolia, ethylene, ripening, saskatoon fruit.
Diarimella laurentidae anam.: sp.nov. from Quebec
Authors: Vujanovic Vladimir , St-Arnaud Marc , Neumann Peterjürgen , Fortin J André
Published: April 2011

Diarimella laurentidae, a new species occurring on dead bark and decorticated twigs of American beech (Fagus grandifolia Ehrh.), is reported from the Muir's Wood ecological reserve, located in the centre of the Haut-Saint-Laurent region in the province of Quebec. Diarimella laurentidae is characterized by stromatic, pulvinate, black, setose fructifications composed of a basal stroma of textura angularis, a brown peripheral wall of textura porrecta, conidiomatal setae of two types, and unicellular multisetulate conidia. Its relationships with described Diarimella species is discussed. This is the first report of a species of Diarimella from North America.Key words: Diarimella laurentidae, new fungus species, coelomycete, Fagus grandifolia.
Phylogeny of the Erysiphales (powdery mildews) inferred from internal transcribed spacer ribosomal DNA sequences
Authors: Saenz Gregory S , Taylor John W
Published: April 2011

Phylogenetic relationships were inferred for 45 powdery mildews plus two outgroup species from internal transcribed spacer sequence data. Phylogenetic analyses revealed that the powdery mildews formed six evolutionary lineages, which corresponded well to recently revised mitosporic taxa. Clade 1 consisted of Erysiphe, Microsphaera, and Uncinula, all of which have an Oidium subgenus Pseudoidium mitosporic state. Clade 2 consisted of Erysiphe galeopsidis and Erysiphe cumminsiana, which have an Oidium subgenus Striatoidium mitosporic state. Clade 3 consisted of Erysiphe species with an Oidium subgenus Reticuloidium mitosporic state. Clade 4 consisted of Leveillula and Phyllactinia, which have Oidiopsis and Ovulariopsis mitosporic states, respectively. Clade 5 consisted of Sphaerotheca, Podosphaera, and Cystotheca, which have Oidium subgenera Fibroidium and Setoidium mitosporic states. Clade 6 consisted of Blumeria graminis, which has an Oidium subgenus Oidium mitosporic state. Seventeen morphological characters were analysed and found not to conflict with the molecular data, so the morphological and molecular data were combined. The combined data increased the overall support for the six clades.Key words: Ascomycete, Blumeria, Erysiphe, fungi, molecular evolution, plant pathogen.
Wind to insect pollination ratios and floral traits in five alpine Salix species
Authors: Peeters Liza , Totland Ørjan
Published: April 2011

This study examines the ratio of wind to insect pollination of five alpine-arctic Salix species and possible correlations between plant traits and this ratio. The field work was done in an alpine area in southwest Norway, at an elevation of 1250 m. Female catkins were enclosed within mesh cloth to prevent insect visitation, and their fruit set was determined and compared with that of open-pollinated control catkins. Simultaneously, pollen production per anther, pollen dispersal, standing crop of nectar, flower length, number of flowers per catkin, and catkin length were measured. The amount of wind pollination of the species varied from 2 to 52%. All species spread pollen in the air. Nectar content, catkin length, flower number, and flower length showed a negative relationship with the percentage of wind pollination. Significant negative linear correlations between female catkin length and flower length and amount of wind pollination were detected. Pollen production per anther did not show any relationship to the pollination system. We suggest that the evolution to insect pollination in alpine Salix species may have resulted in a lengthening of anthers and pistils, and an increase in nectar production.Key words: alpine, anemophily, entomophily, floral traits, pollination, Salix.
Scales of heterogeneity in prairie and forest
Authors: Kleb Heather R , Wilson Scott D
Published: April 2011

Few studies have compared scales of heterogeneity among plant communities. We predicted that differences in the sizes of dominant species should allow us to detect small-scale (<256 cm) heterogeneity in mixed-grass prairie but not in adjacent aspen forest. We examined light penetration, soil moisture, available N, elevation, species composition, and plant mass at 10 locations in prairie and forest in both spring and summer. Variables were measured in 1-cm2 plots arranged in pairs separated by 0-256 cm. Several variables in prairie (elevation, litter mass, light penetration, and species composition) showed significant evidence for scale within the range examined. In contrast, only one variable in forest (light penetration in summer) showed evidence for scale in the same range. The scale of heterogeneity in prairie was consistent with the scale of two possible causes, species composition and elevation variability due to northern pocket gopher (Thomomys talpoides Richardson) activity, both of which varied significantly in prairie but not in forest. Whereas some aboveground factors (light and litter mass) varied within the range examined, belowground factors (water and N) did not, suggesting that the scale of heterogeneity differs between above- and below-ground factors. In total, the results suggest that differences in the scale of heterogeneity between prairie and forest reflect the relative sizes of the dominant plants.Key words: aspen, forest, heterogeneity, light, nitrogen, prairie, scale, soil, water.
Phloem injury and repair following potato leafhopper feeding on alfalfa stems
Authors: Zhou Carol L. Ecale , Backus Elaine A
Published: April 2011

We examined phloem injury and repair over an 8-day period following probing (feeding with piercing-sucking mouthparts inserted in plant) by the potato leafhopper, Empoasca fabae (Harris) (Homoptera: Cicadellidae), in stems of alfalfa, Medicago sativa L. A videomicrography technique was used to apply standard-duration probing by potato leafhoppers on alfalfa stems. Leafhopper-induced plant responses, observed using transmission electron microscopy and fluorescence microscopy, included phloem cell wall loosening and collapse, increased cytoplasmic density and dissolution of necrotic phloem cells, enlargement of nuclei and nucleoli in surviving cells, increased mitotic activity, thickening of phloem cell walls, formation of short and irregularly shaped wound sieve elements (often with side-wall sieve plates), accelerated chloroplast maturation and formation of abnormally large starch grains, and generation of phloem transfer cells from companion cells. Aniline blue staining of callose in sieve elements revealed that wound sieve tubes circumvented damaged phloem by 8 days after leafhopper-induced injury. These new sieve tubes often developed in the interfascicular area adjacent to the wounded bundles.Key words: plant wound response, wound phloem, sieve element, transfer cell, leafhopper feeding, Empoasca fabae, Medicago sativa.
Infection process and resistance in the weed pathosystem Senecio vulgaris - Puccinia lagenophorae and implications for biological control
Authors: Wyss Gabriela S , Müller-Schärer Heinz
Published: April 2011

The infection process and the level and type of resistance in the pathosystem of a native weed and a naturalized rust fungus, Senecio vulgaris L. - Puccinia lagenophorae Cooke, were examined. Four inbred plant lines from Switzerland (2), The Netherlands, and the United Kingdom, each at two stages of devolpment, were exposed to corresponding rust lines under controlled conditions. Fluorescence and light microscopy were used to assess the infection process and to quantify genotype effects. Component analysis was used to partition disease development and define the infection process. Germinating aeciospores of P. lagenophorae showed all the characteristics of the monokaryotic parasitic stage of rust infection with direct penetration and monokaryotic haustoria formation. Haustoria formed between 3 and 6 days after inoculation at low frequency. The highest level of resistance, for which differences between plant lines were detected, occurred at penetration peg formation. All the studied host-pathogen interactions were compatible. The Dutch plant line was most susceptible to all rust lines, and the Dutch rust line was the most aggressive. Susceptibility of leaves increased with the leaf developmental stage. There was a continuous range of variation in susceptibility without differential genetic interactions, thus indicating race-nonspecific quantitative resistance. The use of the more aggressive Dutch rust line may increase the level of disease, thus stimulating epidemics for biological control. Over the long term, less susceptible genotypes of the weed may be selected, although differences in susceptibility among plant lines were relatively small.Key words: rust fungus, infection structures, direct penetration, component analysis, race-nonspecific quantitative resistance.
Taxonomy, ultrastructure, and distribution of some gomphonemoid diatoms (Bacillariophyceae: Gomphonemataceae) from rivers in the United States
Authors: Kociolek J P , Kingston J C
Published: April 2011

Using the continental-scale collections of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program, we examined selected members of the family Gomphonemataceae to expand the current state of knowledge of diatom taxonomy, morphology, and distribution. Ten taxa in the genera Gomphonema, Gomphoneis, and Gomphosphenia are examined. The taxonomic status of two taxa is revised, and one new species is described. Two new features are described for the genus Gomphonema: slit-like areolae and ridge-like flaps or flanges on pseudosepta. Many North American gomphonemoid species appear to be restricted to certain geographic regions; the differences between western and eastern North America are striking. Trained analysts have had difficulty identifying and discriminating many of these taxa. We believe that this difficulty, in large part, results from our poor knowledge of the North American flora. Large-scale monitoring programs such as NAWQA, when teamed up with research organizations with common interests, hold great promise to expand our knowledge of the biodiversity of North American ecosystems.Key words: biogeography, Gomphoneis, Gomphonema, Gomphosphenia, National Water-Quality Assessment (NAWQA) Program, taxonomy; ultrastructure.
Defective control of growth rate and cell diameter in tip-growing root hairs of therhd4mutant ofArabidopsis thaliana
Authors: Galway M E , Lane D C , Schiefelbein J W
Published: April 2011

A recessive mutation in the RHD4 gene of Arabidopsis thaliana L. affects the control of tip growth in seedling root hairs. Fully grown rhd4 root hairs are half the length of wild-type (WT) hairs. The hairs are wider, and they vary in diameter during tip growth. Light microscopy and motion analysis revealed that rhd4 hairs grow more slowly and that hair growth rate varies more than in WT hairs. Hair diameter increases at the rhd4 hair tips when tip growth slows. Ultrastructural analysis revealed cell wall thickenings in some mutant hairs. WT hairs were grown in a hyperosmotic medium in an attempt to mimic the rhd4 hairs and investigate the control of root hair morphology. Osmotic stress increased WT hair diameter and induced hair bulging and also increased the diameters of rhd4 hairs. Osmotic stress could disrupt tip growth through reduced turgor pressure and (or) reduced concentrations of cytosolic calcium. Together these results indicate that RHD4 is required to maintain a uniform rate of tip growth in root hairs.Key words: Arabidopsis thaliana, cell wall, cryofixation, mutant, root hairs, tip growth.
The effects of achene dimorphism on the dispersal in time and space in Crepis sancta (Asteraceae)
Authors: Imbert Eric
Published: April 2011

In the annual species, Crepis sancta (L.) Bornm., peripheral and central florets of the capitulum yield achenes that differ in mass, colour, morphology, and in the presence-absence of pappus. To examine the consequences of seed dimorphism on dispersal in time in this species, I compared the viability of central and peripheral achenes stored for up to 5 years. Both the germination percentage and the early seedling survival of both morphs decreased progressively with duration of storage. However, the loss in viability was lower for peripheral achenes than for central ones. Furthermore, two independent experiments showed that peripheral achenes have reduced dispersal ability, whereas the pappus unit of central achenes confers greater dispersal ability. These differences between achene types may explain the persistence of this colonizing species in communities dominated by perennial species, which is a major ecological feature of C. sancta.Key words: dispersal, dormancy, mixed strategy, secondary succession.
Protection of black spruce seedlings against Cylindrocladium root rot with ectomycorrhizal fungi
Authors: Morin Chantal , Samson Julie , Dessureault Michel
Published: April 2011

Cylindrocladium floridanum Sobers and Seymour, principal causal agent of root rot of conifers in forest nurseries, was grown in vitro with four species of ectomycorrhizal fungi, Paxillus involutus, Hebeloma cylindrosporum, Laccaria bicolor, and Tricholoma sp. The effect of inoculating black spruce seedlings (Picea mariana (Mill.) B.S.P.) with P. involutus was also investigated. Tricholoma sp. and especially P. involutus and H. cylindrosporum inhibited growth of C. floridanum in Petri dishes, while L. bicolor was inhibited and completely covered by C. floridanum. Hyphae of the pathogen in the contact zone were deteriorated in the presence of P. involutus and H. cylindrosporum. The inoculation of P. involutus reduced the number of infected black spruce seedlings by approximately 50%. However, the simultaneous inoculation of two different strains of P. involutus did not significantly reduce disease development. Linear regression demonstrated that the percentage of infected plants was negatively correlated with mycorrhiza formation. The relation between these two variables also showed that even if colonization by P. involutus is poor or null, it has some inhibitory effect against Cylindrocladium root rot.Key words: Paxillus involutus, Cylindrocladium floridanum, root rot, ectomycorrhizal fungi, biological control, Picea mariana.
Isolation, identification, and antifungal activity of a macrolide antibiotic, oligomycin A, produced by Streptomyces libani
Authors: Kim Beom Seok , Moon Surk Sik , Hwang Byung Kook
Published: April 2011

The antibiotic As1A, strongly inhibitory to Phytophthora capsici Leonian in vitro and in vivo, was isolated from the broth culture of Streptomyces libani Baldacci & Grein using various chromatographic procedures. The molecular formula of the antibiotic As1A was deduced to be C45H74O11 (M+H, m/z 791.5307) by high resolution fast atom bombardment - mass spectroscopy. The analysis of 1H-NMR (nuclear magnetic resonance) and 13C-NMR spectroscopy, DEPT experiment, and two-dimensional NMR spectral data revealed that the antibiotic is a macrolide antibiotic having a 26-membered alpha, beta-unsaturated macrolactone ring with a conjugated diene fused to a bicyclic spiroketal. Based on the comparison of NMR data and other chemical properties, the antibiotic As1A turned out to have the same structure as oligomycin A. The antibiotic As1A showed a high level of inhibitory activity against Botrytis cinerea Pers.: Pers., Cladosporium cucumerinum Ellis & Arthur, Colletotrichum lagenarium (C.P. Robin) Berkhout, Magnaporthe grisea (Herb.) Barr, and P. capsici, ranging from 3 to 5 µg·mL-1 of MICs. However, no antimicrobial activity was found against yeasts and bacteria. In further evaluation under greenhouse conditions, developments of the Phytophthora disease, anthracnose, and leaf blast were markedly inhibited on pepper (Capsicum annuum L. cv. Hanbyul), cucumber (Cucumis sativus L. cv. Baekrokdadaki), and rice (Oryza sativa L. cv. Nakdong) plants by treatments with the antibiotic As1A, respectively. Control efficacies of the antibiotic As1A against these plant diseases were in general similar to those of metalaxyl, chlorothalonil, and tricyclazole. The antibiotic As1A did not show any phytotoxicity on pepper, cucumber, and rice plants even at 500 µg·mL-1.Key words: Streptomyces libani, oligomycin A, antifungal activity, plant disease control.
Macrofungal diversity of a temperate oak forest: a test of species richness estimators
Authors: Schmit John Paul , Murphy John F , Mueller Gregory M
Published: April 2011

Two 0.1-ha plots, each divided into 10 contiguous subplots, were established in a Quercus-dominated deciduous forest in the Indiana Dunes National Lakeshore. Macrofungi were surveyed on these plots at weekly intervals during the fruiting season over 3 years. During this survey 177 species were recorded, including 30 species inhabiting leaf litter, 36 ectomycorrhizal species, 29 non-mycorrhizal soil-inhabiting species, and 79 wood-inhabiting species. This species richness is comparable to, but slightly higher than, that reported by other plot-based studies undertaken in hardwood forests. We compared the ability of seven species-richness estimation techniques to determine the true species richness on these plots. While some estimators performed better than others, in general the estimations were too low based on the following year's data and were not consistent from year to year. We found some evidence of spatial autocorrelation of communities of fungi found in adjacent subplots. This indicates that the benefit of using contiguous subplots to increase the homogeneity of the area sampled needs to be balanced against the possibility of underestimating the species richness of an area because of spatial autocorrelation.Key words: macrofungi, species diversity, diversity estimates, Indiana Dunes.
Response of respiration and nitrogenase activity in Datisca glomerata (Presl.) Baill. to changes in pO2
Authors: Tjepkema John D , Du Gangyi , Schwintzer Christa R
Published: April 2011

Respiration and nitrogenase activity by root systems of Datisca glomerata (Presl.) Baill. decline rapidly after exposure to C2H2. We measured C2H2 reduction and CO2 evolution to determine whether this decline is due to a variable barrier to O2 diffusion and to examine the nature of O2 regulation in these nodules. Changes in pO2 between 16 and 30 kPa during the decline had only small effects on respiration and nitrogenase activity. Thus the decline is not due to an increase in resistance to O2 diffusion. In contrast, in peas (Pisum sativum L.) nitrogenase activity was strongly reduced when the pO2 was lowered from 20 to 16 kPa during the decline. In Datisca there was little difference in nitrogenase activity when measurements in He-O2 mixtures were compared with Ar-O2 mixtures, showing that there is no gas phase limitation on diffusion. Therefore the major diffusion resistance in Datisca nodules is in the infected cells. We propose that this resistance is in the vesicles of Frankia and that the vesicles represent a series of compartments that vary in the degree to which nitrogenase is protected from O2. As pO2 increases or decreases, various compartments turn on and off keeping the overall rate of nitrogenase activity and respiration nearly constant.Key words: actinorhizal plants, Datisca glomerata, Frankia, nitrogenase, oxygen protection, Pisum sativum.
Structural and functional comparison of Frankia root hair deforming factor and rhizobia Nod factor
Authors: Cérémonie Hélène , Debellé Frédéric , Fernandez Maria P
Published: April 2011

The infectious processes of the Frankia-Alnus and Rhizobium-legume symbioses present strong similarities, suggesting the existence of analogies between Frankia root hair deforming factor and rhizobia Nod factors. Biochemical and functional analogies were tested using ACoN24d Frankia strain. The putative chitin-like nature of the Frankia deforming factor was explored by (i) gas chromatography coupled to mass spectrometry and thin layer chromatography, after radioactive labeling of the culture for detection of chitin oligomers, and (ii) following the root hair deforming activity of the supernatant after discriminating treatments (temperature, chitinase, butanol extraction). In parallel, the functional analogy was questioned by testing the mitotic activity of the Frankia supernatant onAlnus glutinosa (L.) roots. The implication in the symbiotic process of the Frankia factor was indirectly explored by testing the effect of a nodulation inhibitor (combined nitrogen) on root hair deformation. The studies of the combined nitrogen effect on root hair deformation indicate that the deformation induced in vitro by the Frankia factor is linked to the symbiotic process. Moreover, the various approaches used suggest that rhizobia Nod factors and Frankia root hair deforming factor are two structurally divergent symbiotic factors. However, functionnal differences between Frankia root hair factor and the Nod factors have to be confirmed.Key words: Frankia, root hair deforming factor, Nod factor, actinorhizal plants.
Stimulatory effects of aluminum on in vitro growth ofFrankia
Authors: Igual J M , Dawson J O
Published: April 2011

To investigate the effects of aluminum (Al) on in vitro growth (total protein content) of Frankia, seven isolates were incubated for 25 days at five nominal Al concentrations (0-500 µM) at pH 4.8. The concentrations of monomeric Al ranged between 25.6 and 106.7 µM. The experimental medium was devoid of inorganic phosphate and Fe-EDTA to avoid Al precipitation. There was an Al-free control at pH 6.4 to assess the effects of low pH alone on Frankia growth. Growth estimated as total protein of all strains was notably increased at pH 6.4, but only Frankia CcI3 was able to grow in the Al-free medium at pH 4.8. Nominal Al concentrations from 125 to 500 µM enhanced the growth of all Frankia isolates. The Al response was strain dependent, but all strains were stimulated at the 500 µM (107 µM monomeric) Al concentration. The final pH of media decreased as Al concentrations increased. At the end of the experiment, the presence of citric, oxalic, malic, and lactic acids as possible Al binding agents in media at 500 µM Al was assayed by enzymatic techniques. However, none of them could be detected. These results suggest that the survival and growth of Frankia strains in acid soils that are characteristically high in Al are more likely than previously estimated from in vitro growth assays.Key words: acid soils, actinorhizal plants, aluminum, Frankia.
Frankia forms infection threads
Authors: Berg R Howard
Published: April 2011

Frankia forms symbioses with a great variety of plant hosts, and because nodule development is under plant control, this results in an interesting diversity in the structure of developing symbiotic cells. However, it is apparent that, in all these symbioses, the microsymbiont Frankia follows a similar pattern of development within symbiotic cells of the nodule: the cell is invaded by formation of an infection thread containing invasive hyphae sheathed in plant cell wall material, parasitic vegetative hyphae proliferate by branching from this infection thread, and N2-fixing symbiotic vesicles differentiate from tips of these vegetative hyphae. Infection threads are recognized by their ontogeny and morphology, being the cell-invasive structures in the case of the former and straight-growing hyphae in the case of the latter. Formation of infection threads is a feature shared in common with legumes. Unlike in legumes, the infection thread in actinorhizae is not defined by the presence of sheathing plant cell wall material; all forms of the bacterium have this. Rather than using the term "encapsulation," which suggests a bacterial origin, it is proposed the term "interfacial matrix" be used to describe this plant cell wall material separating Frankia from host cytoplasm.Key words: Frankia, infection thread, interfacial matrix, microsymbiont, nodule, symbiosis.
Russian olive invasion into cottonwood forests along a regulated river in north-central Montana
Authors: Lesica Peter , Miles Scott
Published: April 2011

Russian olive (Elaeagnus angustifolia L.) is an exotic tree that is invasive in western North America where it may replace native riparian cottonwood forests. We mapped the occurrence of Russian olive and measured the size, density, and age of it and cottonwood in sandbar, low-terrace, and high-terrace habitats along the lower Marias River below Tiber Dam in Montana. Russian olive occurs along the entire study reach but is more abundant near domesticated plantings. It establishes in moist lower terrace habitat as well as under mature cottonwood on high terraces. Seventy-seven percent of cottonwood trees in all size classes were damaged by beavers in low terrace sites, while only 22% of Russian olives showed damage. Since construction of Tiber Dam, cottonwood establishment has been restricted to lower terrace sites. Beaver prevent cottonwood from developing a mature canopy close to the river while having little effect on the continued invasion of Russian olive. Riparian cottonwood forests will eventually be replaced by Russian olive as old cottonwoods die on upper terraces and young plants on low terraces are removed by beaver or shaded by the less palatable species.Key words: Russian olive, cottonwood, riparian, beaver, exotic, dam.
Population genetic structure in green dragon (Arisaema dracontium, Araceae)
Authors: Boles Ruben L , Lovett-Doust Jon , Lovett-Doust Lesley
Published: April 2011

The clonal perennial herb, Arisaema dracontium (L.) Schott., is considered "vulnerable" in Canada but is more abundant in the adjacent northeastern United States. In Canada, sexual reproduction may be limited since the species is self-incompatible, and populations at the edge of a species' range may contain limited genetic diversity. We compared genetic variation in nine enzymes systems, sampled at 19 populations across eastern North America. Based on chromosome counts and interpretable banding patterns, A. dracontium is tetraploid over most of its range (2n = 56). However, plants in Florida were diploid, lacked 10 out of a total of 19 interpretable alleles, had distinct allelic frequencies, and clustered a large distance from the other populations. Some plants from Baton Rouge, Louisiana, were also diploid, but all allozyme samples were tetraploid. Most genetic variation occurred within populations; only 29% of variation was between populations. Individuals in two adjacent, otherwise isolated Ontario populations were fixed for most loci and were balanced heterozygotes for the got-2 locus. All samples but one were also identical for an additional six non-interpretable enzyme banding patterns, suggesting these two populations comprise multiple ramets of a single multilocus genotype, propagated clonally via corms. Ecologically marginal populations were typically more distant from the nearest neighboring population and were more genetically distinct from one another; however, with the exception of the two monoclonal populations, marginal populations were not genetically depauperate.
Susceptibility ofPinus contorta - Pinus banksianacomplex toEndocronartium harknessii: host-pathogen interactions
Authors: Yang Rong-Cai , Ye Zhihong , Hiratsuka Yasu
Published: April 2011

Lodgepole (Pinus contorta Dougl. ex Lound.) and jack (Pinus banksiana Lamb.) pines occur sympatrically and hybridize in central and northwestern Alberta, providing opportunities for studying unique ecological and evolutionary interactions. We conducted a greenhouse inoculation experiment to investigate interactions between 40 populations of lodgepole and jack pines and their putative hybrids across this hybrid zone and two sources of the western gall rust fungus, Endocronartium harknessii (J.P. Moore) Y. Hiratsuka, one from lodgepole pine and the other from jack pine. Rust susceptibility and height were assessed when the seedlings were 6 months and 1 year old. Lodgepole pine and the hybrids were significantly more susceptible to the rust infection than jack pine. Jack pine grew significantly faster than the hybrids and lodgepole pine. In addition, the seedlings infected with spores from lodgepole pine grew significantly slower than those with spores from jack pine. While the overall rust scores indicated that spores from lodgepole pine was more virulent to the hosts than those from jack pine, both spore sources were better adapted to their own host species, causing significant spore source × host group interactions. However, such host specificity in the western gall rust is far from stabilized (equilibrium) because of continued gene exchanges among the two parental species and their hybrids.Key words: Pinus contorta - Pinus banksiana complex, western gall rust, natural hybridization, coevolutionary genetics.
Allelopathic potential of Verbesina encelioides root leachate in soil
Authors: Inderjit  , Asakawa Chikako , Dakshini KMM
Published: April 2011

Verbesina encelioides (Cav.) Benth. & Hook. F. ex. A. Gray (Asteraceae) is a perennial weed that interferes with the growth and establishment of crop species in semiarid regions of India. The present research was designed to understand the probable involvement of allelopathy in its interference mechanism. We studied the effect of soils amended with different dilutions of V. encelioides root leachate (full strength and 1:2 and 1:4 (v/v) ratios of root leachate to water) on the growth of radish seedlings (Raphanus sativus L.). Soils that were not amended were used as controls. We also investigated the influence of different levels of N fertilization (1, 5, and 10 mM) on the modification of the allelopathic potential of amended soils, in terms of their effect on soil total phenolics and radish seedling growth. The addition of both full strength and 1:2 dilution of V. encelioides root leachate resulted in significant (P < 0.05) suppression of root (-25.7 and -17.2%, respectively) and shoot (-21.3 and -13.8%, respectively) growth of radish seedlings. The total level of phenolics in soil amended with full-strength (8.53 ± 0.55 µg/g), 1:2 dilution (5.43 ± 0.4 µg/g), and 1:4 dilution (4.17 ± 0.36 µg/g) was significantly (P < 0.05) higher compared with that of control (2.98 ± 0.47 µg/g) soil. Although the different amounts of N fertilization in soil amended with V. encelioides root leachate could not counteract the probable allelopathic interference, we observed an increase in root growth of radish seedlings in soil amended with 10 mM N fertilization plus either a 1:2 dilution (+21.2%) or a 1:4 dilution (+36.5%) of root leachate. No significant differences in NO3- and NH4+ concentration were observed between control soil and soil amended with different amounts of root leachate and N fertlization. Since allelopathic activities include both inhibitory and stimulatory growth responses, the radish seedling growth responses to V. encelioides root leachate can be explained by allelopathy. High performance liquid chromatography data indicate qualitative and quantitative differences in phenolic peaks of both control and amended soil. Our research demonstrates the allelopathic potential of V. encelioides roots and the probable involvement of allelopathy in its interference success.
Oxygen-depleted zones inside reproductive structures of Brassicaceae: implications for oxygen control of seed development
Authors: Porterfield D Marshall , Kuang Anxiu , Smith Peter JS , Crispi Mark L , Musgrave Mary E
Published: April 2011

Growth of Arabidopsis thaliana (L.) Heynh. in decreasing oxygen partial pressures revealed a linear decrease in seed production below 15 kPa, with a complete absence of seed production at 2.5 kPa oxygen. This control of plant reproduction by oxygen had previously been attributed to an oxygen effect on the partitioning between vegetative and reproductive growth. However, plants grown in a series of decreasing oxygen concentrations produced progressively smaller embryos that had stopped developing at progressively younger stages, suggesting instead that their growth is limited by oxygen. Internal oxygen concentrations of buds, pistils, and developing siliques of Brassica rapa L. and siliques of Arabidopsis were measured using a small-diameter glass electrode that was moved into the structures using a micromanipulator. Oxygen partial pressures were found to be lowest in the developing perianth (11.1 kPa) and pistils (15.2 kPa) of the unopened buds. Pollination reduced oxygen concentration inside the pistils by 3 kPa after just 24 h. Inside Brassica silique locules, partial pressures of oxygen averaged 12.2 kPa in darkness, and increased linearly with increasing light levels to 16.2 kPa. Measurements inside Arabidopsis siliques averaged 6.1 kPa in the dark and rose to 12.2 kPa with light. Hypoxia in these microenvironments is postulated to be the point of control of plant reproduction by oxygen.
Reproductive consequences of a gall-inducing fungal pathogen (Exobasidium vaccinii) on Rhododendron calendulaceum (Ericaceae)
Authors: Wolfe Lorne M , Rissler Leslie J
Published: April 2011

We investigated the reproductive consequences of a gall-inducing fungal pathogen (Exobasidium vaccinii) on its host plant, Flame Azalea (Rhododendron calendulaceum (Michx.) Torr.) in southwestern Virginia. The percentage of infected plants ranged from 10 to 90% among the four study sites. There was a high degree of consistency in the pattern of prevalence between years at both the site and individual plant level within sites; plants and sites that showed high gall loads in 1997 were similarly infected in 1998. Infection rates and gall loads were higher in 1997 compared with 1998. All measures of reproduction were negatively affected by galls. Individuals infected in 1997 were less likely to flower the next season. Diseased inflorescences produced fewer flowers, smaller individual flowers, and had a lower probability of producing fruit. At the individual host level, the probability of fruit production was negatively correlated with the gall load on that individual. Finally, branches that were diseased in 1997 were more likely to die the following year, while healthy branches had a high probability of producing leaves and (or) flowers. Our results demonstrate that the fungal galls produced by E. vaccinii have immediate negative consequences to the reproductive process of R. calendulaceum.
Relations between biochemical characteristics and conversion ability in Hevea brasiliensis zygotic and somatic embryos
Authors: Lardet L , Piombo G , Oriol F , Dechamp E , Carron M P
Published: April 2011

The morphological, hydric, and biochemical characteristics were analysed on zygotic embryos at different stages of their development and on cotyledonary somatic embryos in Hevea brasiliensis (Müll. Arg.). The minimum level of maturity required for a good conversion ability was defined. Sixteen weeks after anthesis, the zygotic embryos had acquired a conversion ability equivalent to that of fully mature embryos (24 weeks after anthesis) and to that of somatic embryos. The conversion rates fluctuated between 50 and 60%. The water content, osmotic potential, and turgor pressure of somatic embryos were comparable with those of 16-week-old zygotic embryos. The water potential was comparable with that of immature 13-week-old embryos. Partial dehydration of somatic embryos and 16-week-old zygotic embryos was compatible with a good conversion ability. In zygotic embryos, accumulation of reserves began early in development (13th week for proteins and 15th week for starch). In the 16th week, they had virtually acquired all their reserves. The somatic embryos had equal protein and starch concentrations compared with fully mature zygotic embryos. However, they were much smaller than zygotic embryos (ratio of 1:30 for dry weight), and reserves were around 20 times lower than those of zygotic embryos. This characteristic was linked to the low vigor of plantlets formed in vitro and to the long time taken for full plantlet development.Key words: Hevea brasiliensis, embryogenesis, maturation, water status, reserve, germination.
Intraspecific variability and maternal effects in the response to nutrient addition in Chenopodium album
Authors: Wulff RD , Causin H F , Benitez O , Bacalini P A
Published: April 2011

Intrapopulational variability in the response to nutrient addition was studied in plants of the widespread annual weedChenopodium album L. Five seed "families" (each the progeny of a single individual) were selected at random from a natural population, and the germinated seeds were grown for two generations with either a high or a low nutrient supply. Sequential harvests were performed in which we measured plant height, total biomass, leaf area, root/shoot ratios, and reproductive characteristics for each plant. The data were analysed with two- or three-way analysis of variance. The response to nutrient treatments varied among families and depended on both the particular trait considered and the stage of development. Maternal environment affected plant growth especially when the offspring was grown at low nutrient levels. Seed germination varied significantly according to both the maternal and the grand-maternal nutrient environment. The results show a high plasticity in the response to nutrient levels and the persistence of environmental effects for more than one generation.Key words: Chenopodium album, nutrients, maternal effects, phenotypic plasticity.
An experimental study of wetland invasibility by purple loosestrife (Lythrum salicaria)
Authors: Rachich J , Reader R J
Published: April 2011

We examined the effects of vegetation and herbivores on the seedling establishment, survival, and inflorescence mass of purple loosestrife (Lythrum salicaria L.), a Eurasian plant that invades North American wetlands. The study was conducted in a stand of reed canary grass (Phalaris arundinacea L.). All grass was removed experimentally from 1.2 × 1.2 m plots to simulate a disturbance. The establishment of sown seeds was compared in disturbed and undisturbed plots. Fifty-three percent of seeds became established in disturbed plots, while no seedlings became established in undisturbed plots, suggesting that disturbance is required for wetland invasion by L. salicaria. In plots without grass, the effect of herbivores on Lythrum's survival and inflorescence mass (i.e., sexual reproduction) was assessed by excluding herbivores from some plots but not from others. After two growing seasons, Lythrum's survival did not differ significantly between plots with herbivores excluded (100% plant survival) and plots with herbivores not excluded (60-80% plant survival). However, only plants protected from herbivores produced inflorescences. Mammals such as deer and rodents ate the shoot tips of unprotected plants, which prevented terminal inflorescences from being produced. These results only partly support the claim that North American herbivores are ineffective predators of L. salicaria. One mechanism underlying wetland invasion by L. salicaria is likely a combination of disturbance permitting seedling establishment and insufficient herbivory in disturbed areas to prevent newly established plants from surviving.
Phylogenetic relationships in tribe Lepidieae (Brassicaceae) based on chloroplast DNA restriction site variation
Authors: Zunk Karsten , Mummenhoff Klaus , Hurka Herbert
Published: April 2011

Tribal and subtribal boundaries within the Brassicaceae are often artificially drawn. Most of the currently recognized tribes and subtribes are separated by only a few morphological characters. Furthermore, these characters are variable even within genera, or they conflict with one another in their distribution patterns, resulting in controversial classification systems. Therefore, tribes and subtribes as traditionally delimited may not reflect natural groups. Up to now no cladistic analysis has been performed in tribe Lepidieae. In the current study, we have analyzed restriction site variation of chloroplast DNA among 41 species representing 19 genera to get insights into phylogenetic relationships within the Lepidieae. Phylogenetic lineages derived from our chloroplast data were critically compared with the traditional concepts. Our chloroplast DNA phylogeny most easily supports the classification of genera in the system of Hayek with some modifications.
Phylogenetic relationships in Hypomyces and allied genera, with emphasis on species growing on wood-decaying homobasidiomycetes
Authors: Põldmaa Kadri , Larsson Ellen , Kõljalg Urmas
Published: April 2011

To infer phylogenetic relationships among species of Hypomyces (Fr.) Tul and allied genera, partial sequences of the 28S rDNA were obtained for 21 strains representing 19 species. On the basis of these data and 38 sequences obtained from GenBank, phylogenetic analyses were performed using the programs PAUP and Pee-Wee. Hypomyces appears to be paraphyletic, with species having wet-conidial phialidic anamorphs more closely related to other genera. Hypomyces chrysostomus Berk & Broome is a sister group to the clade that includes species of Aphysiostroma Barrasa et al., Arachnocrea Moravec, and Hypocrea Fr. Based on morphological and molecular evidence, a new genus, Sporophagomyces, is described for Hypomyces chrysostomus and two allied species. Hypomyces broomeanus Tul. forms one clade with species of Sphaerostilbella Sacc. and is transferred to this genus. The recognition of Arachnocrea is justified. The integration of Cladobotryum Nees species that are not known to undergo sexual reproduction with Hypomyces species that possess Cladobotryum anamorphs receives strong support, but the whole complex of these species appears to be paraphyletic. However, constraint trees, which require monophyly of all these ana- and pleo-morphic species, do not appear significantly less likely than the other trees obtained under maximum likelihood or parsimony criteria. For the remaining species of Hypomyces, four distinct lineages are distinguished.