bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular biogeography and evolution of theMicrothlaspi perfoliatums.l. polyploid complex (Brassicaceae): chloroplast DNA and nuclear ribosomal DNA restriction site variation
Authors: Koch Marcus , Mummenhoff Klaus , Hurka Herbert
Published: April 2011

The genusThlaspi L. s.l. comprises numerous segregate lineages, which have been recognized as single genera. One of these, Microthlaspi, represents one such segregate. It consists of morphologically similar annual species. The species have different ploidy levels (2x, 4x, 6x) and are usually summarized under the designation Thlaspi perfoliatum agg. The assumed ancestral diploid members of the species complex, Microthlaspi granatense (Boiss. & Reut.) F.K. Meyer, Microthlaspi umbellatum (Steven ex DC.) F.K. Meyer, and Microthlaspi natolicum (Boiss.) F.K. Meyer, are restricted to northwestern Africa, southeastern Spain and Turkey, northern Iran, and Lebanon. Microthlaspi perfoliatum (L.) F.K. Meyer is widely distributed all over Europe and shows three ploidy levels. Diploid M. perfoliatum is restricted to Middle Europe, whereas tetraploid and hexaploid M. perfoliatum are distributed all over Europe. Individual plants from 125 natural populations throughout the geographic range were analysed using chloroplast DNA (cpDNA) and nuclear ribosomal DNA (nrDNA) restriction site analysis. Within Microthlaspi, 31 cpDNA restriction site mutations, six nrDNA restriction site variations, and two length mutations in the IGS region of the nrDNA were found, and a molecular phylogeny of the species complex has been derived. Polymorphisms in molecular data partitioned cytotypes of M. perfoliatum. The geographical distribution patterns apparently reflect ancient speciation processes and postglacial vegetation history.Key words: chloroplast DNA, nuclear ribosomal DNA, Microthlaspi perfoliatum polyploid complex, molecular phylogeny, biogeography.
Low-temperature scanning electron microscopic observations on endosperm in imbibed and germinated lettuce seeds
Authors: Nijsse J , Erbe E , Brantjes NBM , Schel JHN , Wergin W P
Published: April 2011

Lettuce (Lactuca sativa L.) seeds were observed using low-temperature scanning electron microscopy (LTSEM). The structure of imbibing and germinating seeds was characterized and compared with that of seeds in which these processes were inhibited by high temperature, far-red irradiation, or polyethylene glycol. Germination is not associated with general breakdown or digestion of the entire endosperm at the micropylar region. Embryos of seeds imbibed in polyethylene glycol, which inhibited germination, appeared to lack turgor and were not able to emerge from the endosperm. Thermal or far-red inhibitory treatments were associated with the appearance of complex membraneous structures in cells of the endosperm and the embryo.Key words: endosperm, germination, Lactuca sativa, lettuce, low temperature scanning electron microscopy, seed.
Seasonal activity of uridine 5'-diphosphoglucose:coniferyl alcohol glucosyltransferase in relation to cambial growth and dormancy in conifers
Authors: Savidge R A , Förster H
Published: April 2011

Uridine 5'-diphosphoglucose:coniferyl alcohol glucosyltransferase (CAGT), the enzyme catalyzing synthesis of coniferin from coniferyl alcohol and uridine 5'-diphosphoglucose, was investigated throughout an annual cycle of cambial growth and dormancy in Pinus banksiana Lamb. During dormancy, CAGT activity was not detected in the cambium. CAGT became weakly active in springtime when fusiform cells of the lateral meristem changed from densely protoplasmic to highly vacuolated states, just prior to resumption of cell-division activity. During cambial growth and xylogenesis, CAGT activity in cambial derivatives was greater than that found in the cambial zone. In both cambial zone and developing xylem, seasonally changing CAGT activity paralleled seasonal variation in endogenous coniferin content. CAGT activity disappeared when the cambium entered dormancy in August, prior to completion of lignification in the last differentiating latewood tracheids. In vitro, exogenous coniferin at 0.1 mmol ·L-1promoted CAGT activity (optimum pH 7.8, temperature 40°C); however, coniferin at >10 mmol ·L-1inhibited CAGT activity, in agreement with endogenous coniferin content of developing xylem not exceeding that level. The results indicate that the promoter controlling CAGT gene expression may be cambial specific and linked to the overall control of seasonal cambial growth and dormancy.Key words: cambium, coniferin, lignin, phenology, Pinus banksiana, xylogenesis.
Is Silene acaulis (Caryophyllaceae) a trioecious species? Reproductive biology of two subspecies
Authors: Maurice Sandrine , Desfeux Christine , Mignot Agnes , Henry Jean-Pierre
Published: April 2011

Based on morphological characters, Silene acaulis subsp. exscapa and Silene acaulis subsp. cenisia have been previously described as dioecious and trioecious, respectively. Here we examine whether these subspecies are truly dioecious (subsp. exscapa) and trioecious (subsp. cenisia) based on individual seed and pollen production. Nine populations of subsp. cenisia and five populations of subsp. exscapa were studied in the French Alps. The ratio of staminate to female plants within populations did not in general differ from 1:1, the sex ratio expected in dioecious populations. Staminate plants of both subspecies were found to set fruits. In subsp.exscapa, the ratio of fruit production in female versus staminate plants is around 900; in subsp. cenisia, this ratio is around 10. The advantage of female plants in fruit production is not always sufficient to explain their frequencies in natural populations. Staminate plants cannot be divided in two distinct categories: males and hermaphrodites. The two subspecies can be best described as subdioecious, although S. a. exscapa is effectively closer to exhibiting true dioecy than S. a. cenisia.Key words: breeding systems, trioecy, subdioecy, Silene acaulis.
Population ecology of Cirsium pitcheri on Lake Huron sand dunes. III. Mechanisms of seed dormancy
Authors: Chen Hua , Maun M A
Published: April 2011

Growth chamber studies were conducted to examine seed dormancy and germination requirements of Pitcher's thistle (Cirsium pitcheri (Torr. ex Eaton) Torr. & Gray), a threatened species endemic to the shoreline sand dunes of the Great Lakes. We determined the effects of different environmental regimes on breaking seed dormancy of this monocarpic perennial. The data showed that seeds of C. pitcheri possessed innate dormancy that was caused by a hard seed coat as well as inhibitory compounds within the seed. Seed germination requirements were very specific. Exposure of seeds to different temperatures and photoperiods in a growth chamber had little effect on breaking seed dormancy unless the seeds had been pretreated. Pretreatment of seeds by cold stratification and its duration, scarification by sand paper or sulphuric acid, and application of gibberellic acid were also not very effective for breaking dormancy of C. pitcheri. High germination was obtained only when seeds were pretreated either by surgically removing the seed coat or by nicking the seed on the radicle or cotyledonary end. After this pretreatment seeds germinated over a temperature range of 15-30°C, but the highest proportion of seeds germinated when temperatures were above 20°C. Under natural conditions, germination of C. pitcheri seeds occurs in spring after they have overwintered and experienced the pretreatment of stratification and scarification through freezing and thawing of the substrate. Aqueous extract of C. pitcheri seeds had a strong inhibitory effect on germination of Oenothera biennis L. seeds indicating an allelopathic chemical in the seed. There was no relationship between the seed size of C. pitcheri and the germinability of seeds.Key words: Cirsium pitcheri, threatened species, seed dormancy, seed germination, scarification, stratification, nicking of seeds.
Habitats of native and exotic plants in Colorado shortgrass steppe: a comparative approach
Authors: Kotanen Peter M , Bergelson Joy , Hazlett Donald L
Published: April 2011

Invading species often are close relatives, and therefore share many characteristics as a consequence of their common ancestry. This tends to confound studies of invasions, since many irrelevant characteristics are likely to be correlated with a species' geographic origin (alien or native). We address this problem by using phylogenetically independent comparisons to investigate the habitat characteristics of plants of the Central Plains Experimental Range (Colorado, U.S.A.). We initially show that exotic species are more likely than natives to occur in riparian zones, roadsides, and disturbed sites, and less likely to occur in grassland. The relationship between exotic origins and disturbed sites disappears when phylogenetic dependence is removed from the analyses; in contrast, the other associations persist following phylogenetic detrending, indicating that aliens and their native relatives consistently differ in their ability to exploit riparian, roadside, and grassland habitats. Our results indicate that disturbed sites currently are dominated by only a few groups of related exotic ruderals, while the ability to exploit roadsides and riparian zones has been and may continue to be important for the success of many taxa of invaders.Key words: biological invasions, comparative methods, disturbance, grasslands, phylogeny.
Release, germination, and pathogenicity of ascospores of Uncinula necator under controlled conditions
Authors: Jailloux F , Thind T , Clerjeau M
Published: April 2011

A laboratory technique was standardized for studying the release, maturation, germination, and pathogenicity of ascospores of Uncinula necator (Schw.) Burr. Surface disinfestation and wetting of grape (Vitis vinifera L.) leaf disks bearing cleistothecia collected in the vineyard before incubation in a humid chamber for 48 h at 20°C were found essential for obtaining the release of ascospores (8 ascospores/cm2). Storage conditions involving periodic wetting treatments of cleistothecia at 5°C during 110 days were necessary to induce both ascospore release (80 ascospores/cm2) and germination ability (62%). The matured ascospores were pathogenic on healthy leaf disks at 20°C indicating their probable role as a primary inoculum source. This technique can be helpful in studying the inheritance of characteristics such as pathogenicity and fungicidal resistance.Key words: cleistothecia, ascospores, maturation, germination, pathogenicity, Uncinula necator, grapevine, powdery mildew.
Na+-dependent HCO3-transport in the cyanobacteriumSynechocystisPCC6803
Authors: So Anthony KC , Kassam Aleem , Espie George S
Published: April 2011

The effect of Na+on HCO3-transport, inorganic carbon (Ci) accumulation, and photosynthesis was investigated in the unicellular cyanobacterium Synechocystis sp. PCC6803 using the silicone fluid filtering centrifugation technique. Unlike other cyanobacteria, Synechocystis cells grown at low Ciin standing culture had little capacity for Na+-independent HCO3-transport, when assayed at pH 9.6. However, 25 mM NaCl, but not KCl, strongly promoted HCO3-transport and accumulation. Kinetic analysis indicated that the HCO3-concentration required for one half the maximum rate of transport, K0.5(HCO3-), decreased in the presence of Na+while the maximum rate of transport, VMAX, increased by up to 15-fold. Na+-dependent HCO3-transport occurred against an electrochemical potential of up to 24 kJ ·mol-1, indicating the involvement of carrier-mediated active transport. Li+(1-3 mM) partially substituted for Na+in that K0.5( HCO3-) values were similar (38 vs. 50 µM), but VMAXwas reduced by twofold. At higher concentrations, Li+counteracted the effects of Na+. Monensin reversibly inhibited Na+-dependent HCO3-transport and acted by reducing VMAXwithout affecting K0.5(HCO3-). Monensin inhibition suggested that the electrochemical potential for Na+may play a role in Na+-dependent HCO3-transport, possibly through an involvement in intracellular pH regulation during transport. Na+also stimulated photosynthetic C fixation and O2evolution and these effects were correlated with the Na+-dependent increase in intracellular Ciaccumulation. The Na+-requirement for photosynthesis could be relieved by the provision of CA to the cell suspension, in agreement with the proposal that Na+is required for transport and not directly involved in the photosynthetic process.Key words: active transport, CO2-concentrating mechanism, cyanobacteria, Na+-dependent HCO3-transport, photosynthesis, Synechocystis PCC6803.
Regulation of dissolved inorganic carbon transport in green algae
Authors: Matsuda Yusuke , Bozzo Gale G , Colman Brian
Published: April 2011

The regulation of the expression of the inorganic carbon concentrating mechanism (CCM) in aquatic photoautotrophs, particularly green algae, has been thought to require light and active photosynthesis. Recent studies, however, have indicated that there may be a light-independent pathway of signal transduction in green algae that may regulate the expression of CCMs in response to changes in ambient dissolved inorganic carbon (DIC) concentration. In the green alga, Chlorella ellipsoidea, changes in the rate of transport of both CO2 and HCO3- were shown to occur in response to the CO2 concentration in the bulk medium, independent of pH, whereas other inorganic carbon species, which might induce or repress DIC transport expression, were shown to change markedly with the pH of the medium. Furthermore, neither changes in the CO2 concentration around ribulose bisphosphate carboxylase-oxygenase (Rubisco) nor light were shown to be critical factors in regulating CCM expression in this alga. CO2-insensitive mutants of Chlorella ellipsoidea were recently isolated in which DIC transport operates constitutively at maximum activity. These results strongly suggest that a direct CO2 sensing mechanism may operate at the cell surface in Chlorella ellipsoidea and that this mechanism may trigger the repression of the expression of DIC transport in response to high CO2. Some supportive evidence for this hypothesis has also been obtained in other green algae, Chlamydomonas reinhardtii and Chlorella kessleri. The possibility of the occurrence of a direct sensing mechanism for CO2, its implications, and possible coexistence of other regulatory systems for CCM expression are discussed.Key words: green algae, Chlorella, signal transduction, CO2-insensitive mutants, CO2-sensing mechanism.
The diversity and coevolution of Rubisco, plastids, pyrenoids, and chloroplast-based CO2-concentrating mechanisms in algae
Authors: Badger Murray R , Andrews T John , Whitney S M , Ludwig Martha , Yellowlees David C , Leggat W , Price G Dean
Published: April 2011

Algae have adopted two primary strategies to maximize the performance of Rubisco in photosynthetic CO2fixation. This has included either the development of a CO2-concentrating mechanism (CCM), based at the level of the chloroplast, or the evolution of the kinetic properties of Rubisco. This review examines the potential diversity of both Rubisco and chloroplast-based CCMs across algal divisions, including both green and nongreen algae, and seeks to highlight recent advances in our understanding of the area and future areas for research. Overall, the available data show that Rubisco enzymes from algae have evolved a higher affinity for CO2when the algae have adopted a strategy for CO2fixation that does not utilise a CCM. This appears to be true of both Green and Red Form I Rubisco enzymes found in green and nongreen algae, respectively. However, the Red Form I Rubisco enzymes present in nongreen algae appear to have reduced oxygenase potential at air level of O2. This has resulted in a photosynthetic physiology with a reduced potential to be inhibited by O2and a reduced need to deal with photorespiration. In the limited number of microalgae that have been examined, there is a strong correlation between the existence of a high-affinity CCM physiology and the presence of pyrenoids in all algae, highlighting the potential importance of these chloroplast Rubisco-containing bodies. However, in macroalgae, there is greater diversity in the apparent relationships between pyrenoids and chloroplast features and the CCM physiology that the species shows. There are many examples of microalgae and macroalgae with variations in the presence and absence of pyrenoids as well as single and multiple chloroplasts per cell. This occurs in both green and nongreen algae and should provide ample material for extending studies in this area. Future research into the function of the pyrenoid and other chloroplast features, such as thylakoids, in the operation of a chloroplast-based CCM needs to be addressed in a diverse range of algal species. This should be approached together with assessment of the coevolution of Rubisco, particularly the evolution of Red Form I Rubisco enzymes, which appear to achieve superior kinetic characteristics when compared with the Rubisco of C3higher plants, which are derived from green algal ancestors.Key words: Rubisco, CO2-concentrating mechanism, carbonic anhydrase, aquatic photosynthesis, algae, pyrenoids, inorganic carbon.
Environmental regulation of CO2-concentrating mechanisms in microalgae
Authors: Beardall John , Johnston Andrew , Raven John
Published: April 2011

Most microalgae possess a mechanism for actively transporting inorganic carbon that concentrates CO2at the active site of the carbon fixing enzyme ribulose bisphosphate carboxylase-oxygenase (Rubisco). This review considers the effects of environmental factors on the capacity and activity of microalgal CO2-concentrating mechanisms. Limitation of energy supply by light availability decreases the rate of inorganic carbon transport and cells grown under light-limited conditions have a reduced capacity for CO2accumulation. Phosphorus limitation also reduces the capacity of algal cells to accumulate CO2, whereas both the rate of supply of nitrogen and the form in which it is made available interact in various complex ways with carbon utilization. The potential role of other nutrients in modulating inorganic carbon transport is also discussed. The capacity of algae for carbon accumulation is also affected by CO2supply, which, in turn, is a function of the interactions between ionic strength of the growth medium, pH, cell density in culture, aeration rate, and inorganic carbon concentration in the medium. The effects of these interacting parameters are discussed, together with an assessment of the possible roles and significance of CO2-concentrating mechanisms to microalgae in marine and freshwater ecosystems.Key words: carbon acquisition, microalgae, CO2-concentrating mechanism, light, nutrient limitation, CO2supply.
Protein phosphorylation and its possible involvement in the induction of the high-affinity CO2 concentrating mechanism in cyanobacteria
Authors: Sültemeyer Dieter , Klughammer Barbara , Badger Murray R , Price G Dean
Published: April 2011

Cyanobacteria as well as eukaryotic algae possess a CO2 concentrating mechanism that enables the cells to use low CO2 concentrations very efficiently for photosynthesis. The efficiency of the CO2 concentrating mechanism changes in response to environmental changes, especially the availability of inorganic carbon, but the underlying mechanisms that are involved in the regulation of the induction are unknown. This review deals with the occurrence of protein phosphorylation in cyanobacteria and highlights the possible involvement of post-translational modifications of existing proteins in the induction process, which leads to a high-affinity state of the CO2 concentrating mechanism.Key words: cyanobacteria, CO2 concentrating mechanism, protein kinase, protein phosphorylation, post-translational regulation.
Photosynthesizing marine microorganisms can constitute a source of CO2 rather than a sink
Authors: Tchernov Dan , Hassidim Miriam , Vardi Assaf , Luz Boaz , Sukenik Assaf , Reinhold Leonora , Kaplan Aaron
Published: April 2011

The unexpected finding that certain major marine photosynthetic microorganisms can serve as a source of CO2 rather than a sink emerged during measurements of inorganic carbon fluxes associated with the CO2-concentrating mechanism. During steady-state photosynthesis, CO2 was evolved at sustained rates up to 5-fold that of photosynthesis; the steady-state external CO2 concentration reached was significantly higher than that at CO2-HCO3- equilibrium. The evolved CO2 originated from HCO3- taken up and intracellularly converted to CO2 in a light-dependent process. Our results bear implications for carbon cycling in the marine environment; the use of naturally-observed stable carbon isotope fractionations as paleobarometer and productivity probe; and for intracellular energy balance and pH regulation.Key words: carbonic anhydrase, CO2 evolution, cyanobacteria, photosynthesis, Synechococcus.
Sequence homologs of the carboxysomal polypeptide CsoS1 of the thiobacilli are present in cyanobacteria and enteric bacteria that form carboxysomes - polyhedral bodies
Authors: Shively J M , Bradburne C E , Aldrich H C , Bobik T A , Mehlman J L , Jin S , Baker S H
Published: April 2011

Carboxysomes containing the Calvin cycle enzyme ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) have been demonstrated in a variety of chemoautotrophic prokaryotes and cyanobacteria. The genes in the ccm and cso operon in Synechococcus sp. PCC7942 and Thiobacillus neapolitanus, respectively, code for several carboxysome polypeptides. The polypeptides CcmK and CsoS1 exhibit a high degree of conservation, and in turn show significant homology to the CchA and PduA polypeptides of the ethanolamine and propanediol operons of enteric bacteria. Probing Southern blots of Escherichia coli genomic DNA with csoS1A showed positive hybridization indicating the presence of a csoS1-like gene. Growing Salmonella enterica and Klebsiella oxytoca with propanediol, and E.coli with ethanolamine as the energy source under anaerobic conditions resulted in the formation of polyhedral bodies in these bacteria. The DNA - deduced amino acid sequence of three additional csoS1 genes in both Thiobacillus intermedius and Thiobacillus denitrificans was determined. The nine CsoS1 polypeptides, which includes the three previously determined for T.neapolitanus, exhibited greater than 67% sequence identity. Identity and similarity comparisons and phylogenetic analysis of known polyhedral body CsoS1-like polypeptides indicate a close structural relationship between polyhedral bodies of potentially very different function.Key words: polyhedral bodies, carboxysomes, ribulose-1,5-bisphosphate carboxylase-oxygenase, cyanobacteria, thiobacilli, enteric bacteria.
Multiplex conidium morphology in species of the Ulocladium atrum group
Authors: Simmons Emory G
Published: April 2011

Cultures of many isolates of Ulocladium Preuss mature with conidium populations dominated by dark, obovoid to spherical, densely ornamented spores similar to those of typical Ulocladium atrum Preuss. Early-growth conidia of such isolates frequently are quite different morphologically from those of U. atrum and are considered to be useful in defining species within a U. atrum species group. Four species are compared from this viewpoint in both early-growth and late-growth stages: U. atrum, Ulocladium cucurbitae (Letendre & Roumeguère) Simmons, Ulocladium multiforme Simmons sp.nov. (from soil), and Ulocladium dauci Simmons sp.nov. (from seed of Daucus carota L.).Key words: Ulocladium, classification, conidium variability.
Growth relationships of individual flowers during late stages of floral development of Rhododendron L. 'Prize' and 'Gloria'
Authors: Pemberton H Brent , Wilkins Harold F , Hodges James S
Published: April 2011

Single terminal inflorescences from two-stemmed plants of Rhododendron L. cv. 'Prize' and 'Gloria' were recurrently sampled during a 9°C cold treatment and subsequent forcing period in an 18°C growth chamber until plants reached anthesis. At each sample period, bud length and width were measured on each inflorescence, while subtending bud scale, petal, stamen ('Gloria' only), style, peduncle and ovary length, ovary width, and flower weight were determined on the two most basally attached flowers within an inflorescence for each cultivar. Polynomial regression models were calculated for each floral growth measurement over time, except for bud length and width, for each of the four flowers within a cultivar. Comparison of regression models revealed differences in floral part growth patterns among the various flowers within each cultivar. During the first week of placement in 18°C forcing temperatures after the cold treatment, bud length was the only floral part to grow on 'Prize' plants, while only female flower parts grew on 'Gloria' plants. These results indicate differences in growth resumption patterns between cultivars after cold storage. However, petal and style length were strongly correlated to flower weight for both cultivars indicating that these measurements could be used in laboratory or field situations to determine the floral stage of growth. The growth equations described would be useful for controlling the variability among shoots and flowers for analytical determinations, such as hormonal content analysis, and for studying relationships of floral growth patterns to environmental stimuli that could be used to control flowering. The statistical techniques used in this research make it possible to reduce the number of plants for such studies, as measurements taken on different flowers on the same plant can be used for floral part growth comparisons despite the inherent correlation present between such measurements.Key words: morphology, dormancy, growth modeling, multivariate multiple regression, controlled environment.
Leptographium engelmannii, a synonym of Leptographium abietinum, and description of Leptographium hughesii sp.nov.
Authors: Jacobs K , Wingfield M J , Crous P W , Harrington T C
Published: April 2011

Leptographium abietinum occurs in North America on various members of the Pinaceae, especially spruce (Picea spp.), usually in association with bark beetles (Coleoptera: Scolytidae). It is characterized by noticeably curved, clavate conidia. All the isolates were from species of Pinaceae in North America except two isolates examined by Kendrick, originating from Parashorea plicata imported to England from Borneo and from Melia sp. imported into New Orleans, U.S.A. After examination of the isolate from Borneo and a similar isolate from Vietnam, we have concluded that these do not represent L. abietinum. They are described as a new species, Leptographium hughesii. Leptographium engelmannii, described from Engelmann spruce in Colorado, U.S.A., is indistinguishable from L. abietinum and is considered a synonym of the latter species.Key words: Hyphomycetes, Ophiostoma, bark beetles.
Marielliottia, a new genus of cereal and grass parasites segregated from Drechslera
Authors: Shoemaker R A
Published: April 2011

Marielliottia, a new genus of hyphomycetes, is described. Three species formerly treated in Drechslera are included: D. biseptata, the type, D. dematioidea, and D. triseptata. The species differ from Drechslera in having mostly three-septate, obovoid to ovoid conidia that germinate primarily from the basal cell, occasionally from the apical cell, and not from the central cells. These fungi are occasional parasites of cereals and grasses, are sometimes seed borne, and may infect nongrass plants. The type species is implicated in mycotoxicosis of sheep and produces zaragozoic acid A.Key words: mycotoxins, Helminthosporium, M. biseptata, M. dematioidea, M. triseptata.
Efficacy of Typhula phacorrhiza as a biocontrol agent of grey snow mould of creeping bentgrass
Authors: Wu C , Hsiang T , Yang L , Liu L X
Published: April 2011

Isolates of the fungus Typhula phacorrhiza Fries (TP) were evaluated in field tests over a 3-year period for suppression of grey snow mould caused by Typhula ishikariensis Imai (Tish) and Typhula incarnata Lasch ex Fr. (Tinc). Isolates of TP were collected across southern Ontario in the spring of 1994. In December 1994, 46 of these isolates, which had been cultured on mixed grains, were applied to creeping bent grass (Agrostis stolonifera L.) at a rate of 200 g/m2 (4 × 105 colony forming units (cfu)/m2) with inoculum of Tish or Tinc at 10 g/m2 (2 × 104 cfu/m2). In December 1995, 30 selected TP isolates were inoculated onto a new set of plots along with grey snow mould fungi. In November 1996, 22 of these isolates were re-inoculated onto the 1995 plots. All plots were rated for injury after snowmelt, 1995-1997. Isolates of TP varied significantly in their ability to suppress disease. No strong correlations were found between in vitro growth characteristics and field performance; however, significant positive correlations were found between the disease suppression trials for the 3 years, with several isolates showing statistically significant control of grey snow mould equal to a fungicide treatment.Key words: biocontrol, turfgrass disease, fungi.
Histological observations of latent infection and tissue colonization by Diaporthe toxica in resistant and susceptible narrow-leafed lupins
Authors: Shankar M , Cowling W A , Sweetingham M W
Published: April 2011

Latent infection and tissue colonization by Diaporthe toxica was examined by light, scanning, and transmission electron microscopy in stems, leaves, and petioles of resistant and susceptible narrow-leafed lupins (Lupinus angustifolius). Resistance was observed during the latent phase of the disease as an incompatible reaction between the host and pathogen that appeared to occur after penetration of the cuticle. Conidia were attached firmly to the cuticle by an extracellular substance presumably exuded from the conidia. Conidia penetrated the cuticle directly via an infection peg and formed subcuticular coralloid hyphae. The frequency of subcuticular coralloid hyphae was similar on stems, leaves, and petioles of each line. At 14 days after inoculation, resistant plants had a high frequency of small coralloid hyphae (10-80 µm length). The epidermal cells beneath these small coralloid hyphae appeared necrotic and collapsed with accumulation of polyphenolics and electron-dense substances and a loss of internal organisation in the cytoplasm. Necrosis was occasionally observed in small coralloid hyphae as well. Susceptible plants had a high frequency of large coralloid hyphae (80-400 µm length) in which intrahyphal hyphae were observed, and host epidermal cells beneath large coralloid hyphae appeared normal. Colonization of tissues below the cuticle began immediately after excision of stems from susceptible plants, but was delayed in resistant plants. At 8 days after excision, hyphae had invaded all stem tissues and initiated the formation of pycnidia in susceptible plants, but few hyphae were observed in stems of resistant plants.Key words: Diaporthe toxica, coralloid hyphae, Lupinus angustifolius, resistance.
Development of the sorus in tree ferns: Dicksoniaceae
Authors: Churchill Hugh , Tryon Rolla , Barrington David S
Published: April 2011

Studies of soral development in the tree-fern family Dicksoniaceae in comparison with the Cyatheaceae led to (1) recognition of two basic patterns in the Dicksoniaceae, (2) clarification of marginal versus superficial sori and their indusia in tree ferns, and (3) phylogenetic interpretations. In Cibotium the sorus originates directly from the marginal initial file. The outer and inner indusia arise simultaneously, early in development, on the adaxial and abaxial sides of the receptacle, respectively. The receptacle in Dicksonia originates from a shifted segment of the marginal initial file. The outer indusium is initiated first, approximately at the same time as the receptacle. The initial cells of the marginal meristem give rise to the soral receptacle in both groups of dicksoniaceous genera. Preliminary studies of soral morphogenesis in some cyatheaceous genera indicate that abaxial derivatives originate the sorus. The Cyatheaceae have a single, abaxial indusium proximal to the sorus at maturity, or none. Consideration of these morphogenetic data in light of recent molecular phylogenies suggests that fundamental changes in the meristematic origin of tree-fern sori have taken place since the origin of the lineage that includes both Dicksoniaceae and Cyatheaceae.Key words: Cibotium, Dicksonia, Dicksoniaceae, sorus, tree ferns.
The effect of reduced quantities of photosynthetically active radiation on Fraxinus pennsylvanica growth and architecture
Authors: Bartlett G A , Remphrey W R
Published: April 2011

The quantity and quality of light have significant effects on tree growth and architecture that can be highly variable depending on the shade tolerance of the species. A study was conducted to determine the effect of decreased availability of photosynthetically active radiation (PAR) on the growth and architecture of green ash (Fraxinus pennsylvanica var. subintegerrima (Vahl) Fern.), a moderately shade-tolerant species. Twenty-four seedlings were planted in each of five shade treatments (4, 8, 20, 40, and 100% of full sun, respectively). Measurements made over a 2-year period revealed that with decreased PAR levels there was generally a reduction in leaf thickness, number of shoot units per shoot, shoot-unit length, shoot growth, branching frequency, lateral shoot growth, and shoot biomass. However, in moderate reductions of PAR, there were increases in shoot unit numbers, overall shoot length, and branch numbers. The overall effect of heavy shading was to produce a tree with little height growth and a poorly developed crown.Key words: Fraxinus, shading, seedling morphology, shoot unit, light quantity, architecture.
Flowering and mating system in hybridizing Carpobrotus (Aizoaceae) in coastal California
Authors: Vilà Montserrat , Weber Ewald , D'Antonio Carla M
Published: April 2011

Patterns of flowering and pollination visit of Carpobrotus spp. were examined to determine the hybridization potential between the introduced succulent perennial Carpobrotus edulis and its native congener, Carpobrotus chilensis, in coastal California. Both species flower from March to July and both are visited by the same Thysanoptera and Coleoptera taxa. Flowers from hybrid-appearing individuals were intermediate in corolla diameter. Emasculation and bagging experiments suggest that C. edulis and hybrid morphotypes have facultative agamospermia, whereas C. chilensis has facultative self-fertilization. Emasculated C. chilensis did not set seeds. Pesticide application and flower bagging suggest that 80% of seed set in self-pollinated C. chilensis flowers is mediated by thrips. Our results suggest that there is high potential for natural hybridization in Carpobrotus species in California and that Carpobrotus populations can persist without cross-pollination.Key words: Carpobrotus, exotic species, facultative agamospermia, hybrid fitness, invasion, pollination preference.
Morphological and histochemical analysis of galls of Lipara lucens (Diptera, Chloropidae) on Phragmites australis (Poaceae)
Authors: Vandevyvere Inez , De Bruyn Luc
Published: April 2011

Lipara lucens Meigen (Diptera, Chloropidae) is a monophagous herbivore of the common reed, Phragmites australis Cav. (Trin.) ex Steud. (Poaceae), on which it induces typical cigar-shaped galls. In this paper, the anatomy and histochemistry of galls, cultivated in a greenhouse and collected in the field, were examined. Gall growth takes place while the larva feeds outside the actual developing gall. During gall growth, internode elongation is reduced. Internally, the pith parenchyma, destined to become the nutritive tissue, proliferates instead of degenerating as is seen in uninfested stems. The tissue cylinder around the gall chamber widens up to three times its normal size, while the pith parenchyma doubles its width. The central pith of nutritive cells becomes surrounded by an inner layer of longitudinal and an outer layer of radial parenchymatous cells. Vascular strands, likely connected to the vascular tissue of the host plant, run through this special band of parenchyma cells. The bundles are oriented perpendicular to the stem axis, surrounding the larval chamber. When the gall is completed, the larva gnaws through the growing point and enters the gall chamber, where it consumes the nutritive tissue. A sclerenchymatization process starts now resulting in an extremely hardened gall. Histochemical staining reveals the presence of proteins, DNA, RNA, and a gradient of lipid globules in the nutritive tissue. No starch was detected.Key words: plant-insect interactions, Lipara lucens, Phragmites australis, gall structure.
Systematics of North American Petasites (Asteraceae: Senecioneae). II. Isozyme analysis and population genetic structure
Authors: Cherniawsky Donna M , Bayer Randall J
Published: April 2011

Petasites Mill. (Asteraceae: Senecioneae) is a genus of diploid, perennial, clonal herbs with a widespread distribution across North America. Because of the low variability in floral morphology and high diversity in leaf morphology, considerable taxonomic confusion surrounds the genus. Petasites is generally recognized in North America by five ill-defined native taxa and two introduced species. Enzyme electrophoresis was conducted to assess the genetic variation in Petasites and obtain an understanding of the evolutionary relationships within the genus. Results show divergence at isozyme loci is not associated with morphological divergence. The mean number of alleles per locus and proportion of polymorphic loci are comparable with plants with similar life-history traits; however, levels of heterozygosity ranged substantially. Although there is a weak, negative association between geographical distance and genetic identity, this is not concordant with morphological differences. Typical of clonal species, genetic identities of Petasites are more comparable with selfing plants than with other diploid, outcrossing perennials. Petasites also maintains a level of genetic diversity that is similar to other clonal plants and exhibits high levels of differentiation among its populations. This study provides the first contribution to the population genetic structure of Petasites. The relatively high values of genetic identities between the different taxa of Petasites and the similarity in isozymes and chromosome number indicates a rapid and recent origin in North America. These data, in accordance with the close morphological associations of the four taxa in Petasites, suggest the recognition of one species only, Petasites frigidus.Key words: Petasites, Asteraceae, North America, clonal, systematics, genetic variation.
Arbuscular mycorrhizal fungi associated with Festuca species in the Canadian High Arctic
Authors: Dalpé Yolande , Aiken Susan G
Published: April 2011

Root and soil samples from 13 collecting sites located in the Canadian High Arctic were harvested between July 18 and 29, 1991, and surveyed for root colonization and spore populations of arbuscular mycorrhizal fungi. Grasses of the genus Festuca (Festuca brachyphylla Schult. & Schult., Festuca baffinensis Polunin, and Festuca hyperborea Holmen ex Frederiksen) served as target plants. Of the 197 plant-root systems and soil rhizospheres examined, 28% were associated with arbuscular mycorrhizae. Roots of both F. brachyphylla andF. baffinensis were colonized, while none were detected in F. hyperborea root specimens. Five arbuscular mycorrhizal fungal species were extracted from indigenous soils. The most frequent and abundant species was Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe, which was isolated from 8 of the 13 sites sampled. Other Glomales species in Arctic soils were Glomus macrocarpum Tul & Tul., Glomus fasciculatum (Thaxter sensu Gerd.) Gerd. & Trappe emend. Walker & Koske, and two other unidentified Glomus species. Trap cultures of the indigenous soil with leek (Allium porrum L.) plants confirmed the identity of the species previously identified from original soil and allowed the detection of an additional species, Glomus aggregatum Schenck. & Smith. The novelty of these observations and the relationship between plant mycorrhizal status, fungal species, and soil disturbance are discussed.Key words: mycorrhizae, Arctic, biodiversity, Glomus, Festuca.
Effects of UV-B radiation on growth, pigmentation, and spore production in the phytopathogenic fungus Alternaria solani
Authors: Fourtouni Antonia , Manetas Yiannis , Christias Christos
Published: April 2011

The effects of mild UV-B radiation doses on growth, pigmentation, and spore production in the leaf spot pathogen Alternaria solani Sorauer grown under a polychromatic (UV-A plus visible) radiation environment were investigated. UV-B radiation reduced significantly the radial growth of the fungus. It also had a negative effect on dry mass production and stimulated increased hyphal density. The highest values for UV-B absorbing compounds and melanin content (expressed on a dry mass basis) were observed in the treatment without UV-B. Low doses of UV-B radiation depressed UV-B absorbing capacity and melanin content with a gradual increase with increasing doses. However, the final attained values never surpassed those of the treatment without UV-B. Spore production was significantly enhanced by UV-A radiation. UV-B radiation had either a stimulatory or suppressive effect on spore production depending on the fluence rates of background UV-A radiation. The results indicate that A. solani employs mainly a morphological (i.e., increased density) rather than chemical (i.e., UV-B absorbing compounds) protective strategy against UV-B radiation damage. They also suggest that UV-B radiation reaching the surface of the earth may adversely affect the growth of this highly virulent fungus, although additional studies are required to test this hypothesis.Key words: Alternaria solani, growth, pigments, sporulation, UV-B.
Development of the endodermis and hypodermis of Typha glauca Godr. and Typha angustifolia L. roots
Authors: Seago, Jr. James L , Peterson Carol A , Enstone Daryl E , Scholey Chris A
Published: April 2011

The development of the endodermis and hypodermis in adventitious roots of Typha angustifolia L. and Typha glauca Godr. was followed from the apical meristem to full maturity. The endodermis was typical, developing a thin Casparian band near the root tip, followed by suberin lamellae and asymmetric, secondary, lignified walls (C-type at maturity). Passage cells were present at an intermediate stage but eventually disappeared when all cells developed lamellae and secondary walls. The hypodermis was multiple (four to six layers at maturity) and began differentiating near the root tip. Here, the radial and transverse walls of the outermost layer did not dissolve in strong acid and the former were wavy in the longitudinal direction, both features characteristic of a Casparian band, but these walls were permeable to berberine. No other indication of a wall modification was seen for 3 weeks, at which time the root had become determinate and aerenchyma was beginning to form in the midcortex. Casparian bands, which were impermeable to berberine, matured in the hypodermis; thus, it proved to be an exodermis. Different forms of Casparian band were detected: one was typical and occupied the radial and transverse walls of the outermost layer, but others were novel and included tangential walls, often forming an H-shaped structure (as seen in cross section of the root). We propose calling the latter type an H-type Casparian band. It functioned as an apoplastic barrier to berberine applied either externally or internally by injection into the cortical aerenchyma. Following maturation of the Casparian band, the outer two layers of the exodermis soon produced suberin lamellae. These continued to be deposited in a centripetal pattern until they were found in all layers of the multiple exodermis. Development of the suberin wall modifications correlates with the development of the aerenchyma and may play a role in preventing gas exchange between the root and the rhizosphere. Later, all exodermal cells produced lignified, secondary walls. These were asymmetric in the outermost and innermost layers of the hypodermis (like the C-type endodermis); eventually, all layers had Casparian wall materials. Thus, the mature hypodermis consisted of two to six layers of exodermis, except at the tips of determinate roots where the exodermis was uniseriate with typical Casparian bands.Key words: cattail, endodermis, exodermis, hypodermis, roots, Typha.
Spruce growth response specificity after treatment with plant growth-promoting Pseudomonads
Authors: Shishido Masahiro , Chanway Christopher P
Published: April 2011

Naturally regenerating hybrid spruce seedlings (Picea glauca (Moench) Voss beta Picea engelmannii Parry) were collected from sites near Mackenzie, Salmon Arm, and Williams Lake, British Columbia, Canada. Bacteria were isolated from roots and screened in greenhouse trials for their ability to enhance spruce growth. Three strains belonging to the genus Pseudomonas were selected for study based on their disparate geographic origins and their capacity to consistently stimulate spruce seedling growth in screening trials. Factorial experiments were performed in the greenhouse to evaluate the effectiveness of these Pseudomonas strains with different spruce ecotypes. Factors tested were spruce seed sources, Pseudomonas isolates, and forest floor soils originating from different sites. Three levels of each factor were studied: one spruce seedlot, one Pseudomonas isolate, and one forest floor type each originated from a site at Mackenzie, Salmon Arm, and Williams Lake, British Columbia. Fourteen weeks after treatments were established, spruce biomass accumulation was greatest when spruce ecotypes were inoculated with bacteria originating from the same geographical area as spruce seed. However, Pseudomonas strains originating from sites other than the seed collection area also stimulated seedling growth significantly, rendering the difference in growth promotion between bacterial treatments small and insignificant. In addition, spruce growth promotion was not enhanced when seed was treated with combinations of Pseudomonas strains and forest floor soils originating from the same forest ecosystem. We conclude that specificity between spruce ecotypes and plant growth-promoting rhizobacteria strains can be detected under carefully controlled conditions, thereby supporting the hypothesis that growth-promoting bacteria may adapt to their plant hosts. However, the growth advantage accruing to seedlings treated with bacteria originating from the same ecosystem is small and suggests that it is not necessary to match Pseudomonas strains with spruce ecotypes and soil types for effective seedling growth promotion.Key words: Pseudomonas, spruce, specificity, growth promotion.