摘要:

Chaparral on the central coast of California can occur as relatively stable patches of ectomycorrhizalArctostaphylosdirectly adjacent to arbuscular mycorrhizalAdenostoma. Vegetation surveys and seedling survival assays show thatPseudotsugaestablishes only inArctostaphylos. We found no significant differences betweenArctostaphylosandAdenostomain allelopathy; light; temperature; or soil NH4+, NO3-, or K.Arctostaphylossoils tended to be higher in phosphate and were lower in pH, Ca, Mg, Ni, and Cr than those fromAdenostoma. After 1 year of growth ofPseudotsugaseedlings in anArctostaphylospatch, 17 species of fungi colonized bothPseudotsugaandArctostaphylos. Fifty-six of 66 seedlings were colonized by fungi that also colonizedArctostaphyloswithin the same soil core. Forty-nine percent of thePseudotsugaectomycorrhizal biomass was colonized by fungi that were also associated withArctostaphyloswithin the same core. Another 12% was colonized by fungi known to associate withArctostaphylosfrom different cores. After 4 months of growth,Pseudotsugaseedlings in four of fiveArctostaphylosplots were ectomycorrhizal and colonized by fungi in Russulaceae, Thelephoraceae, and Amanitaceae.Pseudotsugaseedlings in two of fiveAdenostomaplots were ectomycorrhizal but colonized by only two species of fungi in Thelephoraceae. These results provide compelling evidence that ectomycorrhizal fungi associated withArctostaphyloscontribute toPseudotsugaseedling establishment.Key words: arbutoid, Douglas-fir, ectomycorrhizae, manzanita, RFLP, PCR.

ISSN:0008-4026    

DOI:10.1139/b98-208

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Forty-eight plant species in 40 genera representing 20 families were screened for susceptibility toAlternaria alternata(Fr.) Keissler f.sp.sphenocleae, a candidate biological control agent forSphenoclea zeylanicaGaertner (gooseweed). Gooseweed was the only species susceptible toA. alternataf.sp.sphenocleaewhen plants were treated with 3.5 × 105conidia/mL (approximately 107conidia/m2) in the presence or absence of supplemental dew. All inoculated gooseweed plants were killed when subjected to a 14- to 15-h dew.Lactuca sativaL. (lettuce),Glycine max(L.) Merrill (soybean),Phaesolus vulgarisL. (common bean),Psophocarpus tetragonolobus(L.) DC. (winged bean),Vigna radiata(L.) R. Wilcz. (mung bean),Vigna unguiculata(L.) Walp. (string bean),Musa sapientumL. (banana), and someOryza sativaL. (rice) cultivars showed highly resistant reactions.Brassica oleraceaL. (cabbage),Raphanus sativusL. (radish), andAbelmoschus esculentus(L.) Moench (okra) showed highly resistant to moderately resistant reactions whileGossypium hirsutumL. (cotton) showed moderately resistant to moderately susceptible reactions. Symptoms on cotton were restricted to the cotyledons. Sporulation, however, was observed only on detached excised gooseweed leaves, and no sporulation occurred on any of the other plant species evaluated. Gooseweed was the only compatible host plant ofA. alternataf.sp.sphenocleaefound in these studies.Key words:Alternaria alternataf.sp.sphenocleae, biological weed control, host specificity, gooseweed,Sphenoclea zeylanica

ISSN:0008-4026    

DOI:10.1139/b98-225

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Tissues in adventitious roots ofHydrocharis morsus-ranaeL. developed from a four-tiered apical meristem. A set of periclinal divisions in the outermost layer of the ground meristem produced a hypodermis, which was normally uniformly biseriate. Aerenchyma formed from the adjacent inner layer of the cortex by a series of cell divisions and cell lyses; three- to five-celled, radial aerenchyma strands formed by periclinal divisions in radial cell files 0.3-5 mm behind the apex. Intervening cells underwent anticlinal and periclinal divisions followed by cell lyses within 1 mm of the apex to produce air spaces. Aerenchyma formation in this species is unusual and presents a unique system suitable for a study of developmentally programmed cell death in parenchyma cells. The endodermis formed a complete Casparian band about 10 mm behind the root apex and did not develop further; it had neither suberin lamellae nor secondary walls. The hypodermis was parenchymatous and was without Casparian bands, suberin lamellae, and secondary walls. Following acid digestion, the wavy walls of the endodermis and the walls of the epidermis remained.Key words: aerenchyma, cell death, endodermis,Hydrocharis, hypodermis, root development.

ISSN:0008-4026    

DOI:10.1139/b98-210

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The development of the endodermis and hypodermis in adventitious roots ofTypha angustifoliaL. andTypha glaucaGodr. was followed from the apical meristem to full maturity. The endodermis was typical, developing a thin Casparian band near the root tip, followed by suberin lamellae and asymmetric, secondary, lignified walls (C-type at maturity). Passage cells were present at an intermediate stage but eventually disappeared when all cells developed lamellae and secondary walls. The hypodermis was multiple (four to six layers at maturity) and began differentiating near the root tip. Here, the radial and transverse walls of the outermost layer did not dissolve in strong acid and the former were wavy in the longitudinal direction, both features characteristic of a Casparian band, but these walls were permeable to berberine. No other indication of a wall modification was seen for 3 weeks, at which time the root had become determinate and aerenchyma was beginning to form in the midcortex. Casparian bands, which were impermeable to berberine, matured in the hypodermis; thus, it proved to be an exodermis. Different forms of Casparian band were detected: one was typical and occupied the radial and transverse walls of the outermost layer, but others were novel and included tangential walls, often forming an H-shaped structure (as seen in cross section of the root). We propose calling the latter type an H-type Casparian band. It functioned as an apoplastic barrier to berberine applied either externally or internally by injection into the cortical aerenchyma. Following maturation of the Casparian band, the outer two layers of the exodermis soon produced suberin lamellae. These continued to be deposited in a centripetal pattern until they were found in all layers of the multiple exodermis. Development of the suberin wall modifications correlates with the development of the aerenchyma and may play a role in preventing gas exchange between the root and the rhizosphere. Later, all exodermal cells produced lignified, secondary walls. These were asymmetric in the outermost and innermost layers of the hypodermis (like the C-type endodermis); eventually, all layers had Casparian wall materials. Thus, the mature hypodermis consisted of two to six layers of exodermis, except at the tips of determinate roots where the exodermis was uniseriate with typical Casparian bands.Key words: cattail, endodermis, exodermis, hypodermis, roots,Typha.

ISSN:0008-4026    

DOI:10.1139/b98-173

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Three species of arbuscular mycorrhizal (AM) fungi,Glomus aggregatumSchenck and Smith emend. Koske,Glomus intraradicesSchenck and Smith, andGlomus mosseae(Nicol. and Gerd.) Gerdemann and Trappe, were evaluated for their effectiveness to suppress the plant parasitic nematodeMeloidogyne incognita(Kofoid and White) Chitwood in white clover (Trifolium repensL.) in a greenhouse study. Forty 1-day-old seedlings not colonized or colonized to the same extent by the fungi were transplanted into a growth medium uninoculated or inoculated with 10 000M. incognitaeggs. After 40 days of further growth, root mass, shoot mass, extent of galling, number of nematodes and nematode eggs in roots, and extent of mycorrhizal colonization of roots were determined. Growth of white clover was significantly stimulated by mycorrhizal colonization, and nematodes caused the greatest damage when plants were not colonized by the fungi. The degree to which mycorrhizal fungi reduced nematode damage varied with the species of mycorrhizal fungus; the extent of damage reduction ranged from 19 to 49.8%, based on loss of shoot mass. The effectiveness of the mycorrhizal fungal species in suppressing nematodes was not related to the degree to which they colonized roots or their effectiveness in enhancing host growth.Key words: AM colonization, galls,Glomus aggregatum,Glomus intraradices,Glomus mosseae, inoculum potential,Meloidogyne incognita, nematode eggs, phosphorus.

ISSN:0008-4026    

DOI:10.1139/b98-188

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The fecundity of rare plants is a commonly used indicator of performance at the population or species level. However, accurately interpreting reproductive output requires an understanding of a particular species's breeding system. The purpose of this study was to determine if reproductive biology contributes to the restricted distribution ofAster curtusCronq. We hypothesized that (i)A. curtus, like many Asteraceae species, is self-incompatible, and (ii) that pollinations between patches produce significantly more filled seeds than pollinations within patches. Fluorescent microscopy of pistils harvested after greenhouse pollination showedA. curtusto be partially self-compatible. Cross-pollination resulted in significantly more pollen grains per stigma and significantly greater pollen germination than self-pollination. Similarly, field pollination trials showed that between-patch crosses produced significantly more filled seeds than within-patch crosses. Nevertheless, within-patch pollinations produced substantial levels of filled seed. Results from the greenhouse and field trials suggest that the reproductive biology ofA. curtuscontributes little to its rarity. Understanding whyA. curtusis rare has important implications to the conservation of the glacial outwash prairie. Moreover, the data from this research can be used in further developing predictive models for plant species rarity based on reproductive biology.Key words:Aster, endemic, Pacific Northwest, rarity, reproductive biology, self-incompatibility.

ISSN:0008-4026    

DOI:10.1139/b98-214

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Phylogenetic relationships were inferred for 45 powdery mildews plus two outgroup species from internal transcribed spacer sequence data. Phylogenetic analyses revealed that the powdery mildews formed six evolutionary lineages, which corresponded well to recently revised mitosporic taxa. Clade 1 consisted ofErysiphe,Microsphaera, andUncinula, all of which have anOidiumsubgenusPseudoidiummitosporic state. Clade 2 consisted ofErysiphe galeopsidisandErysiphe cumminsiana, which have anOidiumsubgenusStriatoidiummitosporic state. Clade 3 consisted ofErysiphespecies with anOidiumsubgenusReticuloidiummitosporic state. Clade 4 consisted ofLeveillulaandPhyllactinia, which haveOidiopsisandOvulariopsismitosporic states, respectively. Clade 5 consisted ofSphaerotheca,Podosphaera, andCystotheca, which haveOidiumsubgeneraFibroidiumandSetoidiummitosporic states. Clade 6 consisted ofBlumeria graminis, which has anOidiumsubgenusOidiummitosporic state. Seventeen morphological characters were analysed and found not to conflict with the molecular data, so the morphological and molecular data were combined. The combined data increased the overall support for the six clades.Key words: Ascomycete,Blumeria,Erysiphe, fungi, molecular evolution, plant pathogen.

ISSN:0008-4026    

DOI:10.1139/b98-235

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Cylindrocladium floridanumSobers and Seymour, principal causal agent of root rot of conifers in forest nurseries, was grown in vitro with four species of ectomycorrhizal fungi,Paxillus involutus,Hebeloma cylindrosporum,Laccaria bicolor, andTricholomasp. The effect of inoculating black spruce seedlings (Picea mariana(Mill.) B.S.P.) withP. involutuswas also investigated.Tricholomasp. and especiallyP. involutusandH. cylindrosporuminhibited growth ofC. floridanumin Petri dishes, whileL. bicolorwas inhibited and completely covered byC. floridanum. Hyphae of the pathogen in the contact zone were deteriorated in the presence ofP. involutusandH. cylindrosporum. The inoculation ofP. involutusreduced the number of infected black spruce seedlings by approximately 50%. However, the simultaneous inoculation of two different strains ofP. involutusdid not significantly reduce disease development. Linear regression demonstrated that the percentage of infected plants was negatively correlated with mycorrhiza formation. The relation between these two variables also showed that even if colonization byP. involutusis poor or null, it has some inhibitory effect against Cylindrocladium root rot.Key words:Paxillus involutus,Cylindrocladium floridanum, root rot, ectomycorrhizal fungi, biological control,Picea mariana.

ISSN:0008-4026    

DOI:10.1139/b99-025

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Stem lesions in sunflower caused byAlbugo tragopogonis(Pers.) S.F. Gray developed individually from primary infections and did not result from a systemic infection. Cell division and callose formation were not observed, but weak lignin deposition occurred in infected tissues. Hyphae occurred intercellularly in stems in the cortex, cambium, vascular rays, and pith. In petioles parenchymatous tissue was heavily colonized in contrast to lightly colonized collenchymatous hypodermis. The middle lamellae of cells in infected tissue were dissolved, and cells degenerated and eventually collapsed. Stem infections lead to deterioration of tissue integrity, weakening of stems, and finally to lodging of stems (breaking over).Key words:Albugo tragopogonis,Helianthus annuus, histopathology, stem lodging.

ISSN:0008-4026    

DOI:10.1139/b99-016

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The white-rot wood decay fungusResinicium bicolor(Abertini & Schwein.: Fr.) Parmasto was studied for its ability to solubilize and translocate ions from the naturally occurring mineral strontianite.Resinicium bicolorcolonized a soil mixture culture medium containing strontianite sand, solubilized strontium ions from this mineral phase, translocated the ions vertically, and reprecipitated the strontium into strontium-containing calcium oxalate crystals. Storage of the Sr in crystals was highest in mycelial cords and was dynamic in character. These results suggest that non-mycorrhizal saprotrophic fungi should be evaluated for their potential participation in forest nutrient cycling via biologically weathering parent material and translocating the mobilized mineral nutrients vertically within soils.Key words: fungi, strontium, calcium oxalate, translocation, soil, minerals nutrient cycling.

ISSN:0008-4026    

DOI:10.1139/b99-018

出版商:NRC Research Press    

年代:1999

数据来源: NRC