摘要:

The method of transcellular osmosis was used to compare the hydraulic permeability (LP) ofNitellamembranes at different pH's.LPdid not change when the pH ranged from 5.0 to 7.0 but dropped slightly when the pH was 4.4 or below. Tris(hydroxymethyl)aminomethane buffer and abscissic acid (ABA) both increasedLPsignificantly.

ISSN:0008-4026    

DOI:10.1139/b77-001

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The appressorium, seen after penetration of the apple leaf cuticle, has a two-layered wall, an electron-dense outer layer, and an electron-transparent inner layer. The pore of the appressoriumis bordered by the electron-dense outer layer, which tapers at the margin of the pore. The penetration hypha is derived from the infection sac, a structure or organelle within the appressorium.

ISSN:0008-4026    

DOI:10.1139/b77-002

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Sclerotia ofSclerotinia sclerotiorum(Lib.) de Bary buried in a heavy clay soil at 15 °C germinated over a range of moisture levels from 15% to 50%. A method of germinating sclerotia held at constant matric water potentials was tested. Sclerotia were placed in soil in bags of a semipermeable membrane; the bags were immersed in solutions of polyethylene glycol 20 000.Germination occurred between 0 and −7.5 bars but not at lower potentials.

ISSN:0008-4026    

DOI:10.1139/b77-003

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

In the root cortex,Fusariumusually grows in the walls and intercellular spaces, but in the stele it grows within the cells. It does not appear in the large central tracheal tubes. Hyphal strands have a tendency to grow longitudinally in and on the root. Mechanical force is involved in splitting the walls as the fungus grows within the walls. Chemical action is involved in wall penetration. Papillae form opposite penetrating pegs but disappear soon after theFusariumhyphae have penetrated the wall or passed through the papillae.

ISSN:0008-4026    

DOI:10.1139/b77-004

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Nineteen isolates ofPhytophthoraspecies and two isolates ofPythiumspecies, most of them selected because they were originally isolated from the host families Solanaceae. Malvaceae, and Leguminosae, were evaluated for their ability to cause disease when inoculated into stems of plants of these families or when incorporated into soil into which plants were transplanted. When inoculated into stems, some isolates were extremely host-specific, parasitizing and killing only one plant species, while other isolates were parasitic to several. The isolates parasitic to three hosts all attacked the same hosts: snap bean, okra, and tomato. Plant species also varied insusceptibility to parasitism. Tomato, okra, and snap bean were attacked by a number of isolates, while tobacco, pepper, cotton, soybean, and lima bean were attacked by one isolate or none. In nearly every case, stem inoculation with an isolate produced a brown, necrotic reaction readily distinguishable from the reaction of control plants, which were wounded but not inoculated. Growth of plants transplanted into infested soil was often inhibited by isolates which were unable to parasitize the plants when inoculated by either stem inoculation or soil infestation. Ability to parasitize plants, ability to produce a necrotic reaction in stems without killing plants, and ability to stunt growth of plants transplanted into infested soil were not related. The Pythiaceae apparently possess mechanisms of pathogenesis not dependent on parasitism.

ISSN:0008-4026    

DOI:10.1139/b77-005

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The relationship between populations of soil-borne propagules and inhibition of growth of tobacco plants by isolates ofPhytophthora cryptogeaandP. parasiticaincapable of killing tobacco plants was investigated. Although plants usually were severely stunted, they had no effect on populations of the two fungi. This relationship supports the concept that growth inhibition of tobacco plants by these fungi is due to nonparasitic pathogenesis.

ISSN:0008-4026    

DOI:10.1139/b77-006

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Burley tobacco plants were severely reduced in growth when transplanted into soils infested with nonviablePhytophthora cryptogea. Soils that were infested with the fungus and then sterilized by autoclaving or methyl bromide fumigation stunted tobacco transplanted into them. Mycelium produced on a defined medium and lyophilized, powdered, and mixed with soil was toxic to plants at between 0.5 and 1.0 g per 400 grams of soil. These results provide direct evidence that severe reduction in growth of Burley tobacco caused byP. cryptogeais not due to parasitism.

ISSN:0008-4026    

DOI:10.1139/b77-007

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

In the greenhouse, subcrown internodes of wheat plants were inoculated withCochliobolus sativus(Ito & Kurib.) Drechsler ex Dastur,Fusarium culmorum(W. G. Smith) Sacc.,F. acuminatumEll. & Ev., orF. sulplureumSchlecht. and at various times subsequently withC. sativus; or the internodes were inoculated withC. sativusand subsequently with it or aFusariumsp. Using isolation of the fungi as the criterion for infection, it was found that prepossession of the internode byC. sativusdid not prevent later invasion by it or by the fusaria; however,C. sativuswas a relatively unsuccessful challenger toF. culmorumandF. acuminatum. The results suggest that whenC. sativusand one of these twoFusariumspp. appear together in isolations from common root rot diseased plants that the initial invader wasC. sativus.

ISSN:0008-4026    

DOI:10.1139/b77-008

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The structural organization of mature root nodules ofMedicago salivaL. is studied by thin-sectioning, scanning, and freeze-fracturing techniques. The nodules are club-shaped, with their meristematic tissue near the tip of each nodule. The bacteroidal cells situated closer to the tip area are young, whereas those located closer to the neck where the nodule and root join are older. The shape of the bacteroids changes as they grow older. The bacteroids evolve gradually from uniform long-rod or long-club shapes into short-club, short-rod. pear-shaped, ellipsoid, spherical, and Y-shapes, which in turn evolve into pear and spherical shapes. During the early part of the bacteroid's life, the bacteroid is enclosed in a membrane envelope. In older bacteroidal cells, it was observed that a few membrane envelopes contained more than one bacteroid. In senescent bacteroidal cells, the membrane envelopes have disintegrated and dissolved. The plasma membranes of mature bacteroidal cells have high endo- and exo-cytotic activities relative to nonrhizobial-infected root nodule cells or newly infected bacteroidal cells. Endo- and exo-cytotic activities are also evident on the membrane envelopes of bacteroids. The plasma membrane of the bacteroids appears to have no endo- and exo-cytotic activity, for the vesicle-like structures observed on the plasma membrane in thin-sectioning and freeze-fracturing preparations are in fact constricted invaginations of the plasma membrane of the bacteroids, somewhat resembling the cristae of mitochondria.

ISSN:0008-4026    

DOI:10.1139/b77-009

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Pythium graminicolaSubrm. entered barley roots within 2 h after inoculation, and sporangial development began immediately. By 10-14 h after infection most root cells were filled with sporangia. For the first 2-3 days the fungal thallus was mostly sporangial and in the cortex; later it consisted of sexual bodies mainly in the stele. Host cell walls were penetrated rapidly, and chemical breakdown at the place of penetration was obvious. A rim of distorted wall material, caused by lateral expansion of infection hyphae, occurred around the penetration hole on the side of the wall approached by the fungus.

ISSN:0008-4026    

DOI:10.1139/b77-010

出版商:NRC Research Press    

年代:1977

数据来源: NRC