摘要:

Using light and electron microscopy, mycoparasitism byPiptocephalis unisporawas investigated. Parasitism byP. unisporais restricted to certain members of the Mucorales.Piptocephalis unisporais also shown to infect germinating spores and hyphae of the potential thamnidiaceous host,Phascolomyces articulosus. Appressoria, penetration pegs, and haustoria are formed during the infection process but further development of the mycoparasite ceases. Reaction papillae and material present at infection sites and around degenerate haustoria are associated with the mechanism of resistance. The process of infection is compared with previous studies of the infection ofCokeromyces recurvatus(Thamnidiaceae) byPiptocephalis unispora.

ISSN:0008-4026    

DOI:10.1139/b78-297

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Weather variables, leaf blight, and airborne spores ofBotrytis squamosawere monitored in onion field plots at the Holland–Bradford Marsh, Ontario, in 1976. Incidence of spores showed marked daily periodicities with peaks normally between 0900 and 1200 hours Eastern Standard Time (EST). Daily spore counts were low (< 85 spores) during 7 to 28 July, often high (> 1000 spores) during29 July to 16 August, and moderate (100 to 1000 spores) between 17 and 28 August. Spore production was observed only on necrotic portions of onion leaves. Circumstantial and correlative evidence indicated that spore production was promoted by persistent leaf wetness (> 13 h), high temperatures during wetness periods (14 to 20 °C), and by leaf dieback but was restricted by brief wetness periodsand by cool temperatures. Linear correlation analyses of 2- to 4-day running means of data indicated that important limiting factors in spore production were wetness duration during 7 to 28 July, temperature during 29 July to 28 August, and severity of dieback during 7 July to 16 August. Lodging appeared to suppress incidence of spores after 16 August. Spore release was promoted largely by declining relative humidity (RH) and by rain but occasionally by increasing RH. Striking peaks of airborne spores occurred during rain showers. Spore counts when leaves were dry failed to correlate with wind speed, and many spores were dispersed when wind speeds were low(1 to 4 km/h).

ISSN:0008-4026    

DOI:10.1139/b78-298

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Within the northwestern islands of the High Arctic, the vegetation and flora of King Christian Island are very representative. Five plant communities were recognized in a moisture gradient from a moss–rush moist meadow with 22 species of vascular plants and 13% cover (total plant cover 93%) to lichen barrens on low ridges with 8 species of vascular plants and 3% cover (total plant cover 24%). Root systems of 30 of the 34 known vascular plant species were examined. Root:shoot ratios (alive) are generally 0.2 to 0.7. Roots are estimated to live 1.5 years inPhippsia algida, 3.4–3.7 years inAlopecurus alpinusandPuccinellia vaginata, and 7–13 years inLuzula nivalis, L. confuse), andCerastium arcticum. Optimal root growth occurs at 12 to 20 °C but cold field soils (1 to 3 °C) reduce these rates by 90%. Root growth was also reduced by low soil water potentials (< − 14 bars (1 bar = 100 kPa)), conditions seldom encountered in these sites. Limited root growth due to cold soils is combined with the adaptive advantages of small roots to produce small plants and sparse cover in these polar semidesert lands.

ISSN:0008-4026    

DOI:10.1139/b78-299

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

White clover (Trifolium repensL.) contains two cyanogenic β-glucosides (G), linamarin and lotaustralin. Upon injury to the tissues a β-glucosidase (E) effects the release of cyanide from the β-glucosides. Four selections of white clover differing in cyanogenic properties (G+E+, G+E−, G−E+, G−E−) were examined for differences in susceptibility toStemphylium sarciniforme. Symptom development was determined at 24, 48, 72, 96, and 120 h after the leaves were inoculated. Symptoms for all four selections consisted initially of small brown flecks (1 mm in diameter), then dark spots (1–2 mm in diameter) with definite borders, and finally senescence and wilt of the interlesion tissue. Plants containing both β-glucosidase (EC 3.2.1.21)and cyanogenic glucosides (G+E+) and those with only glucosides (G+E−) developed symptoms 24 h earlier than did the G−E+and G−E−selections. The earliest symptoms were observed at 48 h; by 96 h all four selections showed comparable degrees of senescence and wilt. Pathogen development in infected leaves prepared as whole mounts was examined microscopically. Through 72 h after inoculation, development ofS. sarciniformein the G+E+and G+E−selections was slower than in the G−E+selections. By 96 h, however, fungal development in all four selections was comparable; commencement of leaf senescence coincided with extensive fungal colonization of necrotic tissue. Accelerated rates of symptom expression and retarded pathogen development apparently were positively correlated with cyanogenic potential of each white clover selection. Necrosis of suscept tissue was not correlated with cyanogenic potential of each selection.

ISSN:0008-4026    

DOI:10.1139/b78-300

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Callithamnion corymbosum(Sm.) Lyngb, reaches its known northern limits in the western Atlantic on the south and southwest coast of insular Newfoundland where it occurs only as tetraspore-bearing plants which reproduce by vegetative fragmentation. It is abundant in the immediate subtidal in late summer and fall but is not an obvious component of the algal flora in the winter and spring when it occurs principally as detrital fragments. Tetrasporangia occur in the fall and their production in culture is temperature dependent. Discharged tetraspores have only limited viability in culture and their behaviour in nature is unknown.

ISSN:0008-4026    

DOI:10.1139/b78-301

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

After the inception of usually five sepals and five petals, five primary androecial primordia are initiated as broad bulges in alternation with the narrow petal primordia. On each of these primary androecial primordia, usually seven stamen primordia (i.e., secondary androecial primordia) are formed centripetally in a definite pattern. The fasciculate pattern of the androecium is noticeable only in very early stages of floral development since the stamen primordia of adjacent primary androecial primordia approach each other as closely as the stamen primordia of the same primary androecial primordium. Furthermore, the number and arrangement of the stamen primordia on the primary androecial primordia may vary even within the same floral bud. The total number of stamens per floral bud varied from 26 to 43, while the number of petals varied from 4 to 6. Some of the stamen primordia, especially among the inner ones, sometimes develop into filament-like staminodia. The findings support the view that the Dilleniidae cannot be generally characterized by a centrifugal androecium. The sequence of stamen inception is not necessarily of such fundamental importance that it is a reliable criterion for the reconstitution of major phylogenetic lineages at or above the rank of families. Shifts from a centrifugal to a centripetal androecium orvice versamay have occurred during the evolution of taxa at the ordinal (or even family) level. [Translated by the journal]

ISSN:0008-4026    

DOI:10.1139/b78-302

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

To investigate the possibility that white spruce (Picea glauca(Moench) Voss) and black spruce (P. mariana(Mill.) B.S.P.) produce natural hybrids, a morphological analysis of cone and twig characters was performed on 41 white and black spruce trees from three sites in northwestern Ontario and on the Rosendahl spruce from Cromwell, Minnesota. For each tree 13 quantitative and 10 qualitative characters were determined, and the diagnostic ability of all characters was tested by frequency histograms. Scatter diagrams and two hybrid indices were constructed; one index was based only on quantitative data left in continuous form, while the second index was based on all diagnostic characters. Scatter diagrams consistently separated the two taxa, and both hybrid indices clearly showed a bimodal distribution of trees coinciding with species boundaries and not correlating with site or environmental factors. Some spruce trees were intermediate in certain respects, but no tree exhibited a pattern of consistent intermediacy. These results strongly suggest that(1) no hybrids or introgressed spruces were sampled from northwestern Ontario and (2) the Rosendahl spruce is not an F1hybrid between white and black spruce, contrary to several reports, but rather is a white spruce. Earlier conclusions that white and black spruce successfully hybridize in nature apparently have resulted from the use of nondiagnostic characters, underestimation of the variation present in both species, and a priori weighting inherent in the methods used to calculate conventional hybrid indices.

ISSN:0008-4026    

DOI:10.1139/b78-303

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Several techniques employing mechanical, chemical, or enzymatic methods have been suggested for the production of essentially single-cell plant suspension cultures. If single-cell cultures can be obtained, the effects of the media composition on growth can be unambiguously determined. Additionally, such cultures would be amenable to optical and electronic methods for rapidly determining cell mass, number, and volume and could easily be used in experiments on continuous cultivation. Most methods to produce single-cell cultures have been applied to only one or two species. In this paper, these techniques are compared when extended to cultures of Paul's Scarlet Rose (Rosasp.) cells and soybean cells (Glycine maxL.). It is concluded that no technique will generally give sustained disaggregation without affecting the apparent biochemical state of the culture.

ISSN:0008-4026    

DOI:10.1139/b78-304

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Monilia roreriCif., the causal agent of an important pod rot of cocoa in South America, is redescribed and illustrated. The presence of dolipore septa in the vegetative mycelium indicating basidiomycetous affinities and the development of the conidia in basipetal chains necessitate the transfer of the fungus to another genus. The new genusMoniliophthorais proposed. Conidium ontogeny shows similarities with the generaBasipetosporaand the anamorph ofBlumeria(=Erysiphe).

ISSN:0008-4026    

DOI:10.1139/b78-305

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Growth patterns and biomass allocation to component plant parts inPlantago majorandP. rugeliiwere compared under greenhouse conditions. Within 3 months of germination individuals ofP. majorwere larger and had devoted more dry weight to seed and production of ramets than those ofP. rugeliiregardless of the number and kind of neighbours. No significant differences in percent resource allocation to roots, caudex, leaves, and spikes were observed between plants ofP. majorsubjected to increased interference, although the actual biomass and number of leaves and spikes were reduced. Mean reproductive (spike) allocation inP. majorwas about 21%. Although the root biomass within a treatment was similar for the two species, the percent allocation to roots inP. rugeliiwas two and one-half times greater. Growth ofP. majorwas depressed more by intraspecific neighbours and ofP. rugeliiby interspecific neighbours. These perennial herbs exhibit disparate allocation patterns as young plants that suggest adaptations to different temporary environments.Plantago major, with its early and sustained diversion of biomass to seed production, is distinctly adapted to exploitation of frequently disturbed sites, whileP. rugelii, because of its more extensive root allocation and delayed seed production, seems better adapted to less frequent disturbance.

ISSN:0008-4026    

DOI:10.1139/b78-306

出版商:NRC Research Press    

年代:1978

数据来源: NRC