摘要:

After a temporary decrease in transpiration on the day of treatment, the addition of urea or of potassium nitrate to the soil of potted plants of tomato (Lycopersicon esculentumMill) increased the rate of transpiration from 10 to 40%. This increase was proportional to the amount of nitrogen applied and lasted for several days. The temporary decrease on the day of addition was a salt effect similar to the depression caused by sodium chloride or mannitol. Unlike potassium nitrate, neither potassium phosphate nor sodium chloride increased transpiration, indicating that the stimulation was a nitrogen effect. The increase in transpiration is thought to be linked to an increased nitrogen metabolism in the plants.

ISSN:0008-4026    

DOI:10.1139/b75-151

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The germination of aeciospores ofGymnosporangium fuscumDC. onJuniperusspp. takes place in the fall soon after spore deposition. The first telial horns may appear the next spring, 6 months after infection instead of 18 months as previously believed.

ISSN:0008-4026    

DOI:10.1139/b75-152

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The formation of sporangia byPhytophthora drechsleriwas examined in soil at constant matric potentials (ψm) between 0 and −0.3 bar, corresponding to soil water contents between saturation and field capacity. At ψm = −0.3 bar,P. drechslerirequired 1.5 days to form a significant number of sporangia in soil. After 3–11 days in soil, when maximum numbers of sporangia were found, all ψmvalues from −0.025 to −0.3 bar were optimum for the formation of sporangia in both sterilized and unsterilized soil. In contrast, few sporangia were formed in soil at ψmvalues of 0 and −0.01 bar. Mycelia on the soil surface at ψm = 0 formed many sporangia, indicating that aeration at a depth of 5 mm in saturated soil was inadequate for sporangia to form. Viable sporangia were recovered from soil as long as 35 days after mycelial disks were placed in soil. Evidence is presented for the release of zoospores by sporangia in soil at all ψmvalues tested.

ISSN:0008-4026    

DOI:10.1139/b75-153

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

In southwestern Ontario, Powell's pigweed (Amaranthus powelliiS. Wats.) is represented by two morphologically distinct variants. The species is nearly as frequent as redroot pigweed (A. retroflexusL.) in cultivated fields and the two species have often been confused with each other.A germination test was performed with seeds of five local collections ofA. retroflexus, two of one variant ofA. powelliiand four of the second variant ofA. powellii. Very little variation in germination behavior was revealed between the collections ofA. retroflexus, but great variability occurred between the collections of the latter species. Further germination tests under contrasting light regimes with seeds of two collections of each species affirmed these findings.Seeds ofA. retroflexusstored from 5 to 20 weeks before testing yielded more than 75% germination in all tests except in continuous darkness at alternating temperatures (30–18 °C), when 56 to 63% germinated. The total percentage germination of seeds ofA. powelliivaried between 19% and 95% over the range of test regimes and collections examined. In one collection ofA. powelliisignificantly more seeds germinated in alternating light and darkness than in continuous darkness while the reverse was true in another collection. Seeds from this latter collection developed secondary dormancy when put to germinate in alternating light and darkness.

ISSN:0008-4026    

DOI:10.1139/b75-154

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The small spherical haustorium of the white blister fungus is connected to the much larger haustorial mother cell by a slender cylindrical neck. The haustorium contains mitochondria with tubular cristae as well as ribosomes and occasional cisternae of rough endoplasmic reticulum. Nuclei and perinuclear dictyosomes are found in the mother cells but are absent from haustoria. No discontinuity is found in the fungal cell wall in the haustorial neck. Immediately adjacent to the fungal wall and extending through the penetration site to a point about midway along the neck is a dark-staining layer continuous with the host cell wall. A collar consisting of fibrillar material, also continuous with the host cell wall, is commonly found around the proximal portion of the neck external to this dark-staining layer. An electron-dense sheath surrounds the thin wall of the haustorial body but is absent from the neck region. A series of tubules is continuous with the invaginated host plasmalemma which surrounds the haustorial body. These tubules contain an electron-dense core similar in appearance to, and continuous with, the sheath matrix. No evidence was obtained for the involvement of host dictyosomes and their secretory vesicles in the formation of the haustorial sheath. A constant feature of the haustorial apparatus is the association of flattened cisternae of host endoplasmic reticulum with the distal portion of the haustorial neck. The significance of this finding is discussed in relation to the endomembrane concept.

ISSN:0008-4026    

DOI:10.1139/b75-155

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

A study was conducted at two peatland sites in southern Ontario to test the hypothesis that flowering-time diversification among ericaceous plants has resulted from interspecific competition for pollinators. Exclusion of pollinators from plants indicated that insect visitation was important to the seed set of all species tested. The species composition of insects visiting five ericaceous species overlapped considerably, which suggested that interspecific competition could be responsible for observed differences in peak flowering times. While previous experimentation has demonstrated that seed set is influenced by intraspecific competition for pollinators, evidence of interspecific competition is lacking. The inconstancy of pollinators rather than their low numbers is proposed as an additional explanation of why the peak flowering times of ericaceous shrubs do not overlap.

ISSN:0008-4026    

DOI:10.1139/b75-156

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Myzocytium humicolais described as a new nematophagous fungus endoparasitic onRhabditis. This species possesses unequally biflagellate zoospores. These do not attack the nematodes directly but encyst and produce adhesive buds that attach to the cuticle of passing nematodes. The oogonium is fertilized by the passage of the antheridial protoplasm through a pore in the contiguous wall. The resultant oospore has a thick, smooth or finely roughened wall.

ISSN:0008-4026    

DOI:10.1139/b75-157

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

Studies have been made of the ultrastructure and cytochemistry of zoospores, cysts, and germinating cysts ofPhytophthora palmivora. The bulk of the zoospore cytoplasm is occupied by lipid bodies, crystalline vesicles containing lipid plus other unknown material(s), and granular vesicles containing protein. During a 6-h motile period after zoospore release no noticeable changes occur in crystalline and granular vesicles or in lipid bodies. Granular vesicles are retained if encystment is caused by centrifugation or agitation, but few remain when zoospores encyst under undisturbed conditions. Cysts begin to germinate 15 min after encystment is complete. Granular vesicles begin to disappear 30 min after germination starts and the process is complete 60 min later. Crystalline vesicles and lipid bodies also begin to disintegrate 30 min after germination begins, resulting in osmiophilic network-like breakdown products. The breakdown of these products increases with time but is not complete 90 min after germination.

ISSN:0008-4026    

DOI:10.1139/b75-158

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The soaking of wheat seed (Triticum vulgareL.) in water or CaCl2solutions followed by air-drying before planting accelerated the germination but did not affect the final percentage germination and subsequent growth of the seedlings under normal conditions. However, under conditions of 0.5% NaCl salinity the soaking and drying of the seeds before planting stimulated the germination and growth of the seedlings. In no case were the presowing treatments more effective in improving the germination and root and shoot growth under 0.5% NaCl salinity than under normal condition. Under 0.5% NaCl salinity the seedlings grown from treated seeds had more extensive and deeper root systems than the seedlings grown from untreated seeds. Presowing soaking of the seed failed to improve the germination under increasing salinity of 1.0 and 1.5% NaCl.

ISSN:0008-4026    

DOI:10.1139/b75-159

出版商:NRC Research Press    

年代:1975

数据来源: NRC

摘要:

The invertase (EC 3.2.1.26) of leaves from two cultivars of wheat (Triticum aestivumL. emend Thell. ssp.vulgare), Rescue (cold-sensitive) and Kharkov 22 MC (cold-hardy), grown at 20 °C (non-hardening conditions) and at 4–6 °C (cold-hardening conditions), has been separated into three different forms by gel filtration. In Rescue wheat, the complement of different forms of invertase from the leaves did not change greatly when the plants were grown at different temperatures. In Kharkov 22 MC grown at 20 °C, the quantity of the medium-molecular-weight form of invertase was much greater than that of the high-molecular-weight form of invertase; however, when this variety was grown at 4–6 °C, the relative quantities of these two forms of invertase were reversed. This change in the ratio of the different forms of invertase in the leaves appears to be associated with the process of cold-hardening.

ISSN:0008-4026    

DOI:10.1139/b75-160

出版商:NRC Research Press    

年代:1975

数据来源: NRC