摘要:

A collection of 471 isolates ofFusarium oxysporumwas obtained from symptomless tomato roots of plants grown at eight locations in Louisiana. Isolates that produced nitrate metabolism mutants (317 isolates) were included in an analysis of vegetative compatibility groups. One hundred and eighty-six isolates were assigned to 48 vegetative compatibility groups (2015–2062) containing 2–15 members from one to three different collection sites. Even though each site contained sub-populations ofF.oxysporumcommon to other sites, only about half of the vegetative compatibility groups (21 groups) contained isolates from more than one site. In addition, there were 131 isolates ofF.oxysporumthat formed single-member vegetative compatibility groups. This diverse population composition is probably the result of several factors, including breeding strategies for resistance to fusarium wilt and tomato production practices in Louisiana. Resistance genes and horticultural traits from several sources (Lycopersiconspp.) have been incorporated into commercial tomato cultivars currently being grown. In addition, the long growing season in Louisiana allows several tomato cultivars containing different genes for resistance to be grown consecutively in the same field in a single year. Furthermore, other vegetable crops may be alternated with the tomato crops. Thus, the selection pressures that influence the composition of the nonpathogenic populations ofF.oxysporumare in a constant state of flux.Key words:Fusarium oxysporum, genetic diversity, nonpathogens, vegetative compatibility groups.

ISSN:0008-4026    

DOI:10.1139/b91-263

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A quantitative description of primary growth from the apical meristem activity is proposed for four tropical plants:Alstonia vieillardiivar.vieillardii(Apocynaceae),Miconia ciliata(Melastomaceae),Ricinus communis(Euphorbiaceae), andSolanum rugosum(Solanaceae). The development of these four plants corresponds to Leeuwenberg's model. Three parameters were measured at different stages of plant growth: leaf surface, length of the underlying internode, and the surface of the internode section. Two other parameters were derived from these three: parameterT, which summarizes the first three parameters and corresponds to the overall dimension of the leaf–internode system, and parameterD, showing the differential evolution of the leaf surface and the corresponding axial volume. The higher theDvalue, the higher the predominance shown by the twig over the leaf component. This phenomenon is named axialization. The reciprocal situation is called foliarization. For parameterT, the observed variations are present in all four species and showed an increase followed by a decrease in dimensions during the growth process. From the evolution of parameterD, two processses can be recognized. InA.vieillardiivar.vieillardiiandSolanum rugosum, the amplitude of variation is wide and can be compared with that of parameterT. InM.ciliataandR.communis, the amplitude of variation is significantly reduced. A link can be established between this morphometric evolution and flowering. The results obtained for these four species are compared with those obtained by other researchers and bring new elements to the study of the relationship between the vegetative evolution of the plant and its flowering.Key words: architecture, morphometry, Leeuwenberg's model, ontogeny. [Journal translation]

ISSN:0008-4026    

DOI:10.1139/b91-264

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The effects of salinity on growth along with water and ion relations were studied on two cultivars of triticale (Clercal and Beagle) after 21 days of growth under controlled conditions in nutrient solutions with or without 150 mM NaCl, and on nutrient solutions with 150 mM NaCl + 20 mM KCl or 150 mM NaCl + 20 mM CaCl2. Growth was strongly affected by an increased NaCl concentration in the culture medium, causing a water deficit linked to a drop in water (ψ) and osmotic (π) potentials, followed by an accumulation of Na+and a reduction of K+in the aboveground part of the triticales. Addition of KCl or CaCl2to NaCl-containing media improved NaCl tolerance of the plant: growth increased more than 30%, hydration of tissues improved, and K+uptake was normal, as seen by an increased K+/Na+selectivity ratio in the aboveground parts. The two cultivars did not show the same degree of tolerance on these media. The protection afforded by KCl or CaCl2in the NaCl-containing media was more significant for 'Clercal' than for 'Beagle'. Moreover, it seems that in presence of KCl or CaCl2, the improved K+uptake was greater in 'Clercal' than in 'Beagle'. It is therefore possible that 'Beagle' requires less K+than 'Clercal' for normal cell functioning. It is suggested that the K+/Na+selectivity ratio is critical for salinity tolerance in the triticales.Key words: NaCl, KCl, and CaCl2tolerance, growth, water, relationships, osmotic adjustment, K+–Na+selectivity, 'Clercal', 'Beagle', triticale.

ISSN:0008-4026    

DOI:10.1139/b91-265

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Drought exposure in the upper canopy of tropical montane rain forest (Guadeloupe) leads to the pulsed release of solutes from epiphytic bryophytes within the cloud forest canopy. This efflux, leached from newly rewetted mosses and hepatics, was greatest for ions normally held within intracellular pools. Estimates of solute efflux from stem segments of canopy bryophytes reached 80.1 kg ha−1 year−1for K, 1.4 kg ha−1 year−1for P, and 11.8 kg hal−1 year−1for N during experimental rewetting episodes. Estimates of solute efflux from intact bryophyte mats during field rewetting episodes were smaller, only 28.7 kg ha−1 year−1for K and 0.2 kg ha−1 year−1for P. The difference between these measurements is thought to reflect internal recycling of released ions within the canopy bryophyte mats during rewetting episodes. Nonetheless, nutrient loss to throughflow solution represents a significant portion of the standing nutrient capital held within canopy bryophyte mats. By releasing previously sequestered nutrients, bryophyte communities not only provide access to resource pools that would otherwise be inaccessible, but may stimulate the further transformation of nutrients as leaf epiphyll and decomposer communities respond to enriched throughflow solution pulses. These data suggest that recycling of nutrients between members of the standing biomass in tropical montane rain forest is not a steady state process, as often envisaged, but rather may be highly episodic in nature.Key words: tropical montane rain forest, bryophytes, epiphytes, nutrient cycling, throughflow.

ISSN:0008-4026    

DOI:10.1139/b91-266

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Sib selection for mating competence among isolates ofMagnaporthe griseathat are pathogenic on rice has led to the selection of isolates where the mating type alleles are the only restriction on mating competence. Isolates are able to mate with all sibling isolates of opposite mating type and produce asci with ascospores. Isolates can function as male, female, or hermaphrodite in mating depending on the isolates with which they are mated. Mating competence is controlled by the genes in both mated isolates.Key words: mating competence, sib selection, rice blast, genetics.

ISSN:0008-4026    

DOI:10.1139/b91-267

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Seedlings ofPinus banksianawere grown in growth pouches and inoculated withWilcoxina mikolaevar.mikolae,Wilcoxina mikolaevar.tetraspora, andWilcoxina rehmii. Ectendomycorrhizae formed betweenP.banksianaandW.mikolaevar.mikolaedeveloped rapidly following inoculation. The mantle was of variable width, and a large amount of mucigel was evident on the root surface. Intracellular penetration of the cortical cells by hyphae occurred one to two cells distal to Hartig net formation. Both light and transmission electron microscopy revealed labyrinthic growth of Hartig net hyphae that were densely cytoplasmic during early penetration stages but became vacuolate as the association aged. Intracellular colonization of the cortex was extensive, with the hyphae highly branched and surrounded by an interfacial matrix and cortical cell plasma membrane. The external morphology and anatomy of ectendomycorrhizae formed betweenW.mikolaevar.tetrasporaandW.rehmiiandP.banksianawere similar to those described forW.mikolaevar.mikolae.Key words: ectendomycorrhizae,Wilcoxina,Pinus banksiana, intracellular, Hartig net, E-strain.

ISSN:0008-4026    

DOI:10.1139/b91-268

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The structure of ectomycorrhizae synthesized between the E-strain fungus,Wilcoxina mikolaevar.mikolaeand two tree species,Picea marianaandBetula alleghaniensis, was characterized by light microscopy and scanning electron microscopy. For both mycorrhizal types, mantle formation was visible on lateral roots within 10 days of inoculation.Picea marianaectomycorrhizae had a very thin mantle whereasB.alleghaniensisectomycorrhizae had a mantle consisting of several layers. For both mycorrhizal types, the innermost mantle hyphae were embedded in a considerable amount of mucigel on the root surface. A well-developed Hartig net with labyrinthic growth occurred in both types of mycorrhizae.Betula alleghaniensisectomycorrhizae had a paraepidermal Hartig net, and the root epidermal cells were radially elongate at an oblique angle. The Hartig net ofP.marianaectomycorrhizae penetrated the epidermis and all layers of the cortex. The cytoplasmic density of the intercellular hyphae was greatest towards the root apex. Ectomycorrhizal associations formed by E-strain fungi were similar to ectomycorrhizae formed by other fungi.Key words: E-strain, ectomycorrhizae,Wilcoxina,Picea,Betula, Hartig net.

ISSN:0008-4026    

DOI:10.1139/b91-269

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Two-year-old seedlings of green ash,Fraxinus pennsylvanicaMarsh., representing five native populations from an east to west precipitation gradient, were grown under contrasting moisture regimes in the greenhouse. At midsummer and the end of the growing season, leaf areas, earlywood and latewood transverse areas, and several structural attributes of the xylem hydraulic system were compared between well-watered and drought-stressed seedlings. Xylem hydraulic capacity was essentially fixed by midsummer. Drought significantly reduced both earlywood and latewood production but had no significant effect on potentially functional xylem area (Apf) or flow velocity (v). The principal effect of drought on hydraulic architecture was a significant reduction in leaf area and therefore the ratios of potentially functional xylem area to unit leaf area (ApftoA1) and leaf specific conductivity (LSC). In contrast, populations differed significantly in all measured parameters, especially under drought conditions. Path analysis of LSC and its component variables revealed that treatment differences in LSC arose primarily through differences inA1; contributions from variation inApfand especially flow velocity were relatively minor. In contrast, population variation in LSC could be attributed in roughly equal measure to variation inApfandA1, and to a lesser degree to variation in flow velocity. The covariance betweenA1andApfwas important for both treatment and population variation in LSC, suggesting a fundamental physiological linkage between these two aspects of plant hydraulic architecture. Among populations, high flow velocity tended to be associated with lowApftoA1values, thereby minimizing population differences in the composite character LSC. Populations differed significantly in all attributes studied, in one environment or another, but those at either end of the precipitation gradient did not differ in several presumably important structural attributes. Although plant hydraulic architecture is genetically controlled and variable in green ash seedlings, its adaptive significance cannot be considered in isolation from other factors that control plant response to water stress.Key words: leaf specific conductivity, ecotypic variation, xylem structure.

ISSN:0008-4026    

DOI:10.1139/b91-270

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The total element content and the subcellular distribution of mineral nutrients were investigated in a species that has very minute seeds. The major storage substances in the seed ofBegonia semperflorenswere lipids sequestered in lipid vesicles and proteins concentrated in protein bodies. Transmission electron microscopy revealed the presence of protein crystalloids and electron-dense globoid crystals in the protein bodies. These inclusions varied both in size and number in protein bodies from different tissues. Energy dispersive X-ray analysis of the globoid crystals showed the high Mg, K, and P levels characteristically found in phytin from large-sized seeds. Small traces of Ca were found in globoid crystals within protein bodies found in the provascular tissue of the embryo. Neutron activation analysis was used to measure the elemental composition of the whole seed and these results were correlated with the findings of energy dispersive X-ray analysis studies of globoid crystals.Key words:Begoniaseed, energy dispersive X-ray analysis, protein body, globoid crystal, protein crystalloid, neutron activation analysis.

ISSN:0008-4026    

DOI:10.1139/b91-271

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Melanconium apiocarpum(anamorph ofMelanconis alni),Melanconium marginale(anamorph ofMelanconis marginalis), and otherMelanconiumspecies isolated from healthy and diseased tissues ofAlnusspecies in Canada, England, and Switzerland were compared by means of morphological, cultural, and biochemical techniques, and the results were analyzed by numerical methods. No differences were recorded between symptomless endophytes and disease syndrome associated isolates ofM.apiocarpum, although European and Canadian isolates could be consistently and clearly differentiated by protein profiles and cellulose utilization patterns. On the basis of cultural and biochemical characters as well as conidia morphology,M.apiocarpumandM.marginaleare distinct species. Two intraspecific groups ofM.marginale, particular to separateAlnusspecies, were identified.Melanconiumisolates fromFagus sylvaticaandQuercus roburare clearly distinct from those onAlnus.Key words:Melanconium,Melanconis,Alnus, numerical taxonomy.

ISSN:0008-4026    

DOI:10.1139/b91-272

出版商:NRC Research Press    

年代:1991

数据来源: NRC