摘要:

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. dracontiumis 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 thegot-2locus. 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.

ISSN:0008-4026    

DOI:10.1139/b99-089

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Carpobrotusedulis(L.) N. E. Br., an exotic perennial that invades the coastal habitats of California, hybridizes with the presumed nativeCarpobrotuschilensis(Mol.) N. E. Br. To investigate the potential role of hybrids in the invasion process byC.edulis, we compared the growth and plasticity of clones of hybrids and parental species. Ramets of three hybrid classes and both parental species were grown in a common garden with four different environments. Both the parental species and the hybrids exhibited strong plastic responses to the test environments for characters describing clonal growth and physiology.Carpobrotusedulisconsistently had the largest biomass, butC.chilensisproduced longer branches. Carbon isotope ratios (<$QFD0E00000010446D80BFFEFF88A6750DA8D9C8282ADCC6210090483DA6ECD7658F80>13C) showed only weak differences among morphotypes. Hybrids were mostly intermediate relative to parental species in both growth and physiological characters. The intermediacy of hybrids in their response to environmental variation indicates that they do not have inferior growth compared with parental species. The high amount of plasticity of the hybrids andC.edulis, as well as their overall similarity, may account for their invasion success in different habitats of coastal California.

ISSN:0008-4026    

DOI:10.1139/b99-091

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

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 ofV. encelioidesroot leachate (full strength and 1:2 and 1:4 (v/v) ratios of root leachate to water) on the growth of radish seedlings (Raphanus sativusL.). 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 ofV. encelioidesroot 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 withV. encelioidesroot 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 toV. encelioidesroot 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 ofV. encelioidesroots and the probable involvement of allelopathy in its interference success.

ISSN:0008-4026    

DOI:10.1139/b99-097

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

We assessed the effects of red:far-red (R:FR) ratio on net CO2assimilation, photosynthetic activity, and morphology of young white clover leaves developed under a simulated canopy light environment. Isolated cuttings ofTrifolium repensL. were grown in controlled conditions under two irradiances in combination with two R:FR ratios. We used far-red light emitting diodes to reduce the R:FR ratio on leaves that were successively developing on the main stolon and were subject to strong competition for light within a sward. A leaf that developed under a low R:FR ratio had a lower chlorophyll content than the controls. However, this change had no consequences on the net CO2assimilation rate and on the biomass allocated to shoots. The low R:FR ratio modified the leaf morphology by increasing the leaf area. A leaf that developed in lower irradiance had a lower net CO2assimilation rate and a greater leaf area and petiole length than leaves that developed in higher irradiance. Therefore, irradiance was the main factor limiting the leaf CO2assimilation under a canopy. Capture of light by clover leaves was improved by FR light only via modifications of leaf morphology, because there were no significant effects of FR light on photosynthesis.

ISSN:0008-4026    

DOI:10.1139/b99-099

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Previously, we have shown that theGlycine max(L.) Merr. -Bradyrhizobium japonicumsymbiosis is very sensitive to inhibition by NH4+. The current study addresses whether the supernodulating soybean mutant,nts382, which is known to be tolerant of NO3-, is also tolerant of NH4+. Thents382 mutant and its wild-type parent, Bragg, were grown in continuous-flow hydroponic culture in the presence of 0, 0.25, 0.5, or 1.0 mM15N-enriched NH4+. Plants were harvested at 14, 21, and 28 days after inoculation. Both cultivars had the highest dry weight (DW) at each harvest date when grown on 0.25 mM NH4+. At 0.25 mM NH4+, whole plant DW increased by 5.3- and 3.2-fold in Bragg andnts382, respectively, compared with the 0.0 mM NH4+control by the end of the experiment. As expected, whole-plant nodulation (nodules per plant), DW-specific nodulation (nodules per gram root dry weight), and nodule DW were severely inhibited in Bragg at all levels of NH4+. However, innts382, whole-plant nodulation was not affected by NH4+treatment, and nodule DW increased by as much as fivefold. Whereas DW-specific nodulation decreased by 94% in Bragg, this parameter decreased by only 52% in thents382 mutant. Likewise, while the nitrogen derived from the atmosphere decreased by approximately 40% in NH4+-supplied Bragg, it increased 2.8-fold at 0.25 and 0.5 mM NH4+innts382. This study demonstrates that both nodulation and N2fixation innts382 are more tolerant of NH4+than in the wild-type Bragg.

ISSN:0008-4026    

DOI:10.1139/b99-101

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Growth ofArabidopsis 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 ofBrassica rapaL. and siliques ofArabidopsiswere 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. InsideBrassicasilique locules, partial pressures of oxygen averaged 12.2 kPa in darkness, and increased linearly with increasing light levels to 16.2 kPa. Measurements insideArabidopsissiliques 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.

ISSN:0008-4026    

DOI:10.1139/b99-098

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Both genetic and environmental factors can determine whether an invasive plant species will establish. To determine how these factors influence the establishment of the invasive grassPhalaris arundinaceaL. (reed canary grass), we grew three genotypes in 10 artificial environments and asked how a genotype's growth and survivorship was affected by environmental conditions. We found that genotype strongly influenced survivorship, but there was no significant effect of environment on survivorship. However, environmental conditions did significantly affect growth. Individual plants produced more aboveground and belowground biomass when grown singly than they did when grown with competitors. The identity of neighboring competitors had no effect. Although genotype had no significant efffect, there was a significant genotype × environment interaction. Clone 1 produced more root biomass than either clone 2 or clone 3 when there was no or little competition, but in competitive neighborhoods, clone 3 allocated relatively more biomass to roots than to shoots. Under ideal conditions in the greenhouse, clone 2 produced more tillers than the other two clones. Based on these results, it appears that clone 1 may have an advantage under sparse vegetative cover, but clone 3 may have a competitive advantage in highly competitive neighborhoods because it could preferentially allocate more biomass to roots. The presence of three growth patterns from such a small, localized sample suggests that different growth strategies are probably common within populations of reed canary grass and may be important for allowing reed canary grass to successfully invade new habitats

ISSN:0008-4026    

DOI:10.1139/b99-102

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

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 byE. vacciniihave immediate negative consequences to the reproductive process ofR. calendulaceum.

ISSN:0008-4026    

DOI:10.1139/b99-108

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The effect of chitosan on the growth, morphology, and ultrastructure ofCylindrocladium floridanumSobers & Seymour,Cylindrocarpon destructans(Zinss.) Scholten,Fusarium acuminatumEllis & Everh., andFusarium oxysporumSchlecht. was investigated in vitro. Chitosan was found to reduce the radial growth of all the fungi studied with some differences. Light microscope observations showed that chitosan induced morphological alterations to all fungi. Transmission electron microscope investigations revealed ultrastructural alterations such as increased vacuolation, retraction, and alteration of the plasma membrane, cell wall thickening, hyphal distortion, and cytoplasm aggregation. The possible modes of action of chitosan are discussed.

ISSN:0008-4026    

DOI:10.1139/b99-111

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

An electron- and light-microscopic study revealed that D-haustoria ofChrysomyxa rhododendri(DC.) De Bary andChrysomyxa pirolataWinter were pedicellate and had a more or less tuber-shaped haustorial body. The haustorial necks were wrapped by a fold of the extrahaustorial membrane (velopedunculate haustorial type). The aecioid uredinia ofChrysomyxa rhododendriandChrysomyxa empetri(Pers.) Schröter were covered by a one-layered peridium of the pucciniastreous type. InChrysomyxa pirolata, young uredinia were covered by one to three layers of sterile fungal cells. In all investigated species, urediniospore mother cells were formed blastically by proliferating basal cells. Subsequent cell divisions of the urediniospore mother cells led to the formation of urediniospores and intercalary cells. InChrysomyxa rhododendri, the intercalary cells had a pronounced proximal thickening of the radial wall. InChrysomyxa pirolataandChrysomyxa empetri, the wall was uniformly thickened. Telial morphology ofChrysomyxa rhododendriandChrysomyxa pirolatawas very similar. InChrysomyxa rhododendri, the probasidia formed true chains without intercalary cells, and they are probably of thallic origin. During maturation they partly separated at their septa by dissolution of the primary wall of the septa between the probasidia. No sterile elements were present in the telia. The occurrence of velopedunculate D-haustoria and a uredinial peridium of the pucciniastreous type confirm the systematic position ofChrysomyxaclose to pucciniastreous rusts,Cronartium, andColeosporiumwithin Melampsoraceae

ISSN:0008-4026    

DOI:10.1139/b99-113

出版商:NRC Research Press    

年代:2000

数据来源: NRC