摘要:

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.

ISSN:0008-4026    

DOI:10.1139/b98-228

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Populations ofPuccinia triticina(causal agent of wheat leaf rust) in Ontario, Quebec, Manitoba, and Saskatchewan were analysed for frequency of isolates with virulence to leaf rust resistance genesLr1,Lr2a,Lr2c,Lr3,Lr9,Lr16,Lr24,Lr26,Lr3ka,Lr11,Lr17, andLr30for the years 1987-1997. Winter wheats in the southern plains of the United States with resistance genesLr24,Lr26,Lr11,Lr3ka,Lr17, andLr16selected virulentP. triticinaphenotypes in the Manitoba and Saskatchewan population. TheP. triticinapopulation in Quebec and Ontario was comparatively stable, showing no directional trends in selection of virulence phenotypes. In the Manitoba and Saskatchewan population, diversity of virulence phenotypes changed relatively little despite the selection that occurred in this population. The average number of virulences per isolate in the Manitoba and Saskatchewan population increased from 1987 to 1994 during the period of selection for virulence toLr24,Lr26,Lr3ka, andLr11, and declined from 1995 to 1997 when selection for virulence toLr16andLr17occurred. The most complex virulence phenotypes were not necessarily selected in the Manitoba and Saskatchewan population because of how the resistance genes were deployed in the host population and the nonrandom distribution of virulences in theP. triticinapopulation.Key words:Puccinia reconditaf.sp.tritici, specific resistance, wheat leaf rust,Triticum aestivum, specific virulence.

ISSN:0008-4026    

DOI:10.1139/b98-221

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

An integrated approach, based on the analysis of both molecular and morphological characters, has led to the unambiguous detection and identification of the rust hyperparasiteCladosporium tenuissimumfrom aeciospores of the two-needle pine rust fungiCronartium flaccidumandPeridermium pini.Cladosporium tenuissimumwas first detected from contaminated field-collected rust spores using the polymerase chain reaction (PCR) method. The similar-sized amplified DNA of the parasite was then separated from rust DNA using electrophoretic migration, reamplified separately with the nested PCR, and sequenced. Sequence comparison in the data banks enabled the hyperparasite to be recognised as a species ofCladosporium. Molecular detection was followed by conventional identification, obtained by plating rust spores on potato dextrose agar, a selective medium for rusts, since they are unable to grow on such a common substrate, and isolating the hyperparasite in pure culture. It was subsequently identified asC. tenuissimum. Traditional identification would not have been possible without guidance from the molecular data, which focused attention on the mycoparasite. Macro- and micro-scopic features of colonies are also given to help with future identification on spore sources from other geographical areas and, if this should occur, future identification on other rusts.Key words: mycoparasitism, PCR detection, traditional detection,Cladosporium tenuissimum,Cronartium flaccidum,Peridermium pini.

ISSN:0008-4026    

DOI:10.1139/b98-203

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

To the best of our knowledge, this is the first soft X-ray radiographic study of the development of an entire young root system of western red cedar (Thuja plicataD. Don). The experimental device was adapted to radiographic constraints and allowed the plant to grow for several months. Successive radiographs revealed primary growth and differentiation, secondary growth, and primordium development. The younger (8-day-old) part of the root system appeared fully opaque. Afterwards, the stele and the cortex could be distinguished from each other progressively in a second zone where most of the primary differentiation had already occurred. Measuring early cambial growth was made possible by spacing the radiographs at 10-day intervals. Time-course developments of primordia and their histolysis cavities were traced for 8-15 days, depending on the sample. The acropetal sequences of primordia along the same adventitious root were shown. Primordia had different growth curves, most of which were nearly logistic. These meristems were produced by unequal primordia, which generated axes of unequal diameters. Our techniques provide new opportunities for understanding the differentiation of axes and defining potential root growth during primordium development.Key words: soft X-ray radiography, root development, primordia, root differentiation, radial growth, morphogenesis.

ISSN:0008-4026    

DOI:10.1139/b98-232

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The infection process and the level and type of resistance in the pathosystem of a native weed and a naturalized rust fungus,Senecio vulgarisL. -Puccinia lagenophoraeCooke, 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 ofP. lagenophoraeshowed 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.

ISSN:0008-4026    

DOI:10.1139/b99-006

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

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-cm2plots 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 talpoidesRichardson) 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.

ISSN:0008-4026    

DOI:10.1139/b99-004

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The effects of two types of anthropic disturbances (reaping and plowing) were followed over 3 years, on four calcicolous meadows of the Seine valley (Haute-Normandie) in France, using the quadrat points method. Multivariate analysis performed on the overall data show that compositions and structures of the different plant communities are mainly influenced by the site geographic position along an ecological gradient developing from the Seine river estuary toward the uppper stream of the river. Over the 3 years of observation, a significant increase of the species diversity (Shannon's index) and richness was observed in the reaped plots compared with the plots that were abandoned after disturbances. However, there was no significant difference between the two treatments in the species diversity as well as richness. Results are discussed in view of conservative management of calcicolous meadows, since these seminatural ecosystems are especially threatened in Western Europe.Key words: calcicolous meadows, disturbances, species diversity and richness, conservation, Haute-Normandie, France.[Journal translation]

ISSN:0008-4026    

DOI:10.1139/b98-231

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The chromosomal locations of the genes coding for the 18S-5.8S-26S rRNA was investigated inCucumisspecies using fluorescence in situ hybridization. Cucumber (Cucumis sativusL., 2n= 2x= 14) possesses four pairs of rDNA loci that were mapped to chromosomes 1C, 2C, 4C, and 7C. The distinctive hybridization sites of the 18S-5.8S-26S rRNA genes provide several useful cytogenetic markers for identification of chromosomes inC. sativus. The 18S-5.8S-26S rDNA genes have also been detected on two chromosome pairs, one major and one minor pair of loci, in melon (CucumismeloL., 2n= 2x= 24) and on three pairs ofCucumis hystrixChakr. chromosomes. The different number and pattern of rDNA sites is consistent with the hypothesis that considerable phylogenetic distance exists among these species.Key words: fluorescence in situ hybridization, 45S rRNA gene, cytogenetics,Cucumis sativus,Cucucmis melo,Cucumis hystrix.

ISSN:0008-4026    

DOI:10.1139/b98-226

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

This paper summarizes the processes involved in designing a mathematical model of a growing pasture plant,Stylosanthes scabraVog. cv. Fitzroy. The model is based on the mathematical formalism of Lindenmayer systems and yields realistic computer-generated images of progressive plant geometry through time. The processes involved in attaining growth data, retrieving useful growth rules, and constructing a "virtual plant" model are outlined. Progressive output morphological data proved useful for predicting total leaf area and allowed for easier quantification of plant canopy size in terms of biomass and total leaf area.Key words: Lindenmayer systems, modelling,Stylosanthes, morphogenesis, plant form.

ISSN:0008-4026    

DOI:10.1139/b98-217

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

To examine the effects of day length on the induction of crassulacean acid metabolism (CAM) by drought in the tropical species,Talinum triangulare(Jacq.) Willd. (Portulacaceae), plants were subjected to drought under different photoperiods. Nocturnal acid accumulation was 52 µmol H+··g-1fresh mass (FM) in plants grown under a 10 h light : 14 h dark photoperiod and 76 µmol H+·g-1FM in plants grown under 13 h light : 11 h dark, whereas it was only 10 µmol H+·g-1FM in plants grown under 18 h light : 6 h dark. Plants were subjected to drought under short days and under short days with a night interruption of 1.5 h white light, aiming to simulate a long day, while minimally affecting daily carbon balance. Only droughted plants under normal short days accumulated acids during the night. Absence of CAM could not be attributed to differences due to photoperiod in either biomass allocation, chlorophyll content, or leaf water content. Photoperiod did not significantly affect fecundity in watered plants, whereas drought markedly reduced fecundity in plants with night interruption relative to plants under normal short days. Reproductive effort, calculated as seeds per gram leaf, was significantly higher in droughted plants under normal short days and watered plants with and without night interruption than in droughted plants with night interruption.Key words: CAM, crassulacean acid metabolism, drought, fecundity, induction, photoperiod, reproductive effort, reproduction,Talinum triangulare

ISSN:0008-4026    

DOI:10.1139/b99-036

出版商:NRC Research Press    

年代:1999

数据来源: NRC