bluuebunny/crossref_metadata_2025_split huggingface dataset:
Iǹtraspecific variation in two species of Suillus from Scots pine (Pinus sylvestris L.) forests based on somatic incompatibility and isozyme analyses
Authors: SEN R. 
Published: April 2006

SUMMARYIsolates of Suillus variegatus (Swartz ex Fr.) O. Kuntze and Suillus bovinus (Fr.) O. Kuntze cultured from basidiocarps collected in different geographically located Scots pine (Pinus sylvestris L.) forests were subjected to an analysis of axenic growth rates, somatic incompatibility and electrophoretic isozyme expression. Intraspecific variation in the radial growth rates and at certain putative enzyme loci was detected in these fungal populations which, after tests for somatic incompatibility, were identified as being composed mainly of different clones. Following a numerical analysis of the isozyme data of seven enzyme systems, considerable interspecific dissimilarity (11% similarity) and intraspecific similarity (> 65% similarity) were detected in these fungi. Isozymes of esterase, peptidase and acid phosphatase were conserved within species but differed between these species enabling their unambiguous identification. Isolates of S. variegatus were found in two main clusters that represented the two forest locations from which they were collected. A single putative locus of glutamate oxaloacetate transaminase was found to display isozyroe polymorphism directly related to the forest location of the isolates. No habitat‐related isozyme activities could be detected in the isolates of 5. bovinus which, unlike those of S. variegatus, exhibited isozyme expression that was strongly dependent upon the medium. Isolates of S. variegatus and S. botinus identified as originating from the same vegetative clone by somatic incompatibility testing were found to exhibit 100 and 93‐97% similarity in their respective isozyme activities. These studies indicate that isozyme analyses in conjunction with somatic incompatibility testing will provide powerful tools for the genetic analysis of ectomycorrhizal communities.
Iσozymic identification of individual ectornycorrhizas synthesized between Scots pine (Pinus sylvestris L.) and isolates of two species of Suillus
Authors: SEN R. 
Published: April 2006

SUMMARYMorphologically similar ectornycorrhizas between Scots pine (Pinus sylvestris L.) seedlings and different geographic isolates of Suillus variegatus (Fr.) O. Kuntze and Suillus bovinus (Fr.) O. Kuntze were synthesized under semi‐aseptic conditions in a sand and peat growth mixture containing ureaformaldehyde as the organic nitrogen source. Fourteen weeks after inoculation significant increases in shoot height were recorded in most of the infected seedlings and in two inoculated treatments where no mycorrhizal infection was detected. Based on the assumption that 50% of the dry mass of these ectomycorrhizas was of fungal origin, the soluble protein content of the synthesized ectomycorrhizas was found to be between 10‐ and 15‐fold greater than in equivalent amounts of the non‐symbiotic tissues (short roofs and axenically grown mycelium of S. variegatus and S. bovinus). Extracts from individual ectornycorrhizas exhibited considerable esterase (EST) and peptidase (PEP) isozyme activities following PAGE and it was confirmed that diagnostic species‐specific fungal isozymes, reproducibly detected in these extracts, were present in extracts of excised sheath tissue. Acid phosphatase (ACP) isozyme activities were also detected in the ectomycorrhizas but were restricted to a single isozyme known to be common to both fungal species. In addition to the identification of taxonomically useful diagnostic fungal isozymes, the lack of detectable host PEP or ACP isozymes in these individual ectomycorrhizas, which also exhibited induced isolate‐specific EST isozymes, provides further information on the biochemical relationships in the ectomycorrhizas.
The biology of mycorrhiza in the Ericaceae
Authors: LEAKE J. R. , SHAW G. , READ D. J. 
Published: April 2006

SUMMARYThe effect of mycorrhizal infection on the uptake and distribution of iron in Calluna vulgaris was examined when plants were grown in sand supplied with different concentrations of calcium as CaC12 or CaCO3. Infection consistently caused highly significant increases in Fe concentration of Calluna shoots in CaCl2 treatments. A similar effect was obtained with CaCO3 but only in the lowest Ca treatments. Iron concentrations in roots followed the same pattern, being particularly high in all CaCl2 and in the three lowest CaCOa treatments.Total iron contents of shoots were increased by 225% with infection in CaCl2 treatments. In the presence of CaCO3 the average increase in Fe content in shoots of infected plants was 77%, enhancement being restricted to the lowest Ca treatments (0‐50μg ml−1). In roots, the patterns were similar except that since the total Fe contents were higher than in shoots, the proportional differences between infected and uninfected plants were greater.Mycorrhizal infection caused a significant overall increase in specific absorption rate of iron in CaCl2 treatments. In CaCO3 the specific absorption rates of mycorrhizal plants were approximately double those of uninfected plants at the four lowest Ca concentrations but at higher concentrations of the salt the reverse situation was obtained.The nutritional implications of the results are explored, special emphasis being placed upon the possible role of mycorrhizal infection in soils of high calcium content and in situations where iron is present in sparingly soluble mineral combination with phosphates.
Uptake and translocation of α‐difluoromethylornithine, a polyamine biosynthesis inhibitor, by barley seedlings: effects on mildew infection
Authors: WALTERS D. R. , KINGHAM G. 
Published: April 2006

SUMMARYUptake of the polyamine biosynthesis inhibitor, α‐difluoromethylornithine (DFMO), by barley seedlings was examined. DFMO was taken up by intact roots and approached saturation at a rate of 780 mol m−12g−1d.wt. The uptake as a function of DFMO concentration in the external medium was biphasic, with Eadie‐Hofstee transformations giving Km values for system 1 uptake of 1.61 mol m−3and for system 2 uptake of 53.31 mol m−3. DFMO uptake was reduced in darkness and was greatly influenced by transpiration rate. The inhibitor was taken up from host cells by the powdery mildew fungus, Erysiphe graminis f.sp. hordei Marchal, and DFMO fed to roots, or to excised leaves at different times after inoculation, gave substantial control of mildew infection.
The control of weeds through fungi; principles and prospects
Authors: HASAN S. , AYRES P. G. 
Published: April 2006

summaryThe biocontrol of weeds by the introduction of exotic fungi (the classical method) has proved successful, most notably in the control of skeleton weed (Chondrilla juncea) in the wheat belt of Australia by the introduced rust, Puccinia chondrillina. There is now increasing interest in an alternative, inundative, method of weed control in which the target is controlled by a massive inoculation with a host‐specific indigenous fungal pathogen. It is proposed that through an increased understanding of host ‐ parasite interactions, in particular the enzymes and toxins that fungi use to disrupt the structure and function of weeds, screening of naturally occurring pathogens can be made more efficient. It should be possible in the immediate future to improve the efficacy of many host‐specific pathogens that currently cause little injury. In the longer term, changes in host specificity may be achieved through the techniques of genetic engineering. Meanwhile, improved formulation and methods of application can improve the range and reliability of mycoherbicides. The use of integrated control methods in which fungi are used in pairs, or in combination with either reduced rates of chemical herbicides or with arthropods, also offers hope for development. Studies of competition between plants of different species show that stunting of the weed, rather than complete kill, may be sufficient to protect crop growth. Two mycoherbicides have been successfully used in the field for almost ten years; in the next ten years we may expect to see a rapid increase in their number.

CONTENTS

Summary
201

I.
Introduction
202

II.
Principles
202

III.
Successful programmes
206

IV.
Prospects
211

V.
Conclusions
217

References
218
Comparison of disease progress curves
Authors: GILLIGAN C. A. 
Published: April 2006

summaryA method of analysis, involving the comparison of parameters of nonlinear models for disease progress, is described. The method tests the effects of measures for disease control on the dynamics of botanical epidemics. It was applied to published disease progress curves for a range of host‐pathogen systems and was used to test whether treatments to control disease did so by slowing or delaying the epidemic or by reducing the asymptotic‐carrying capacity of the host population. The treatments included genetical, chemical and cultural methods including soil solarization, varietal differences and fungicide application. The logistic model was used to summarize polycyclic epidemics of Phytophthora infestans (Mont.) de Bary on potato, P. cryptogea Pethyb. & LafT. on raspberry, Fusarium oxysporum f. sp. lycopersicae (Sacc.) Snyd. & Hans, on tomato, and Puccinia recondita Rob. on wheat and triticale. The monomolecular model was used for epidemics of Sclerotium rolfsii Sacc. on carrots and S. cepivorum Berk, on garlic, that were experimentally limited to one cycle of infection. The selected model was first fitted separately to the empirical progress curve for each treatment. Subsequently, one or more common parameters were constrained to fit all treatments while the remaining parameters were separately fitted. Comparison of the changes in residual mean squares permitted approximate tests for the effects of fitting common parameters. The biological meaning of the parameters is discussed in relation to disease control. The method was sensitive in demonstrating differences amongst the treatments. Marked differences in epidemics were shown to occur when control of disease was effected by reduction in the carrying capacity or by delaying the onset of an epidemic. Few treatments, however, affected the rate parameters, especially of the logistic model.
Proteinase activity in mycorrhizal fungi
Authors: LEAKE J. R. , READ D. J. 
Published: April 2006

summaryThe effect of pH on the production and specific activity of the extracellular proteinase enzymes of two ecologically distinct ericoid mycorrhizal fungi is described. The proteinase of Hymenoscyphus ericae (Read), Korf & Kernan, isolated from roots of Calluna vulgaris (L.) Hull growing in soil of pH 35, was compared with a similar enzyme from an endophyte of the calcicolous alpine shrub Rhodothamnus chamaecistus (L.) Reichenb. growing in soil of pH 6.5. The fungi were grown in liquid culture at pH values ranging from 3.0 to 8.0 with pure protein, bovine serum albumin, as sole source of N.Both fungi yielded an extracellular acid proteinase with pH optimum for activity between 20 and 30. The production and activity of these enzymes was strongly affected by pH of the culture medium. Maximum enzyme production during exponential growth occurred in both fungi at a culture pH of 4.0–5.0, whereas higher pH treatments severely inhibited enzyme production.The acid proteinase of H. ericae was tolerant of extreme acidity and retained near‐optimal activity in solutions of pH 2.0. In contrast, the activity of the enzyme from the Rhodothamnus endophyte was almost completely inhibited at this pH. However, proteinase from the Rhodothamnus endophyte retained activity at much higher pH values than did the proteinase from H. ericae. Unlike H. ericae, the isolated endophyte of Rhodothamnus was able to grow and use protein as sole source of N at pH 7.0 and 8.0.The effects of pH on enzyme production and upon growth of the fungi are discussed in relation to the characteristics of the environments of their host plants.
Root hydraulic conductivity and xylem sap levels of zeatin riboside and abscisic acid in ectomycorrhizal Douglas fir seedlings
Authors: COLEMAN MARK D. , BLEDSOE CAROLINE S. , SMIT BARBARA A. 
Published: April 2006

summaryMechanistic hypotheses to explain mycorrhizal enhancement of root hydraulic conductivity (Lp) suggest that phosphorus (P) nutrition, plant growth substances and/or altered morphology may be responsible. Such ideas are based on work with VA (vesicular‐arbuscular) mycorrhizas. Since VA mycorrhizas and ectomycorrhizas differ in many respects, they may alter host plant water uptake via different mechanisms. This paper examines LT in various ectomycorrhizal associations while considering factors which are important to the VA mycorrhizal effect on Lp. Douglas fir Pseudotsuga menziesii (Mirb.) Franco] seedlings inoculated with the ectomycorrhizal fungi Laccaria bicolor (Maire) Orton and Hebeloma crustuliniforme (Bull, ex St. Amans) Quel. and non‐inoculated seedlings infected naturally with Thelephora were grown under three low levels of P fertilization (1, 10 and 100 fim P). Seedling morphology, tissue P levels, Lp and plant growth substance levels in xylem sap were measured after nine months growth. Increased tissue P and decreased root/shoot ratio correlated with increased Lp in each of the mycorrhizal treatments. When adjusted for the effect of these two factors, Lp of Laccaria and Hebeloma seedlings was still lower than the Thelephora seedlings. In a subsequent experiment, the Lp of seedlings with Hebeloma and Rhizopogon vinicolor Smith mycorrhizas was compared to the Lp of non‐mycorrhizal seedlings (grown at 100 mM P) and no differences were found among treatments. The lack of an ectomycorrhizal effect on Lp is quite different from the enhancement of host Lp by VA mycorrhizas. Zeatin riboside concentrations of Thelephora‐ and Hebeloma‐iniected seedlings were similar, yet higher than with Laccaria. There was no relationship between plant growth substances and Lp in ectomycorrhizal Douglas fir, despite lower zeatin riboside concentrations for Laccaria‐inoculated plants.
An apparent increase in symplastic water contributes to greater turgor in mycorrhizal roots of droughted Rosa plants*
Authors: AUGÉ ROBERT M. , STODOLA ANN J. W. 
Published: April 2006

summaryUsing psychrometric pressure‐volume analysis, root water relations following drought were characterized in Rosa hybrida L. plants colonized by the vesicular‐arbuscular mycorrhizal fungus Glomus intraradices Schenck & Smith. Measurements were also made on uncolonized plants of similar size and adequate phosphorus nutrition. Under well‐watered conditions mycorrhizal colonization resulted in lower solute concentrations in root symplasm, and hence lower root turgors. Following drought, however, mycorrhizal roots maintained greater turgor across a range of tissue hydration. This effect was apparently not due to increased osmotic adjustment (osmotic potentials at full turgor were similar in mycorrhizal and non‐mycorrhizal roots after drought) or to altered elasticity but to an increased partitioning of water into the symplast. Symplast osmolality at full turgor was similar in mycorrhizal and non‐mycorrhizal roots but, because of their higher symplastic water percentages, mycorrhizal roots contained a greater amount of osmotic (symplastic) solutes. Drought‐induced changes in osmotic potential were observed only in mycorrhizal roots, where a 0.4 MPa decrease (relative to well‐watered controls) brought the full turgor osmotic potential of mycorrhizal roots to the same level as that of non‐mycorrhizal roots under either watering treatment.
Measurement of development of endomycorrhizal mycelium using three different vital stains
Authors: HAMEL C. , FYLES H. , SMITH D. L. 
Published: April 2006

summaryThe extraradical hyphae of Glomus intraradices Schenck & Smith associated with a mixture of alfalfa (Medicago sativa L. cv. Saranac) and bromegrass (Bromus inermis Leyss. cv. Tempo) were tested for metabolic activity by three enzyme staining procedures. Mycorrhizal plants were grown for 6, 9 or 12 weeks and the vital staining methods were evaluated and compared at each date. Succinate dehydrogenase activity was assessed by the reduction of nitro blue tetrazolium (nitro‐BT), and NADH diaphorase activity by the reduction of indonitrotetrazolium (INT). Fluorescein diacetate (FDA) hydrolysis was used to assess the activity of esterases in the extraradical hyphae. Percentages of intraradical hyphae that were active in alfalfa and bromegrass were also determined after staining root samples with nitro‐BT and chlorazol black E. The percentage of live intraradical infection declined with the maturing symbiosis. In contrast, no reduction with time in the percentage of extraradical hyphae that were metabolically active was shown by nitro‐BT, suggesting a different turnover for extra‐ and intraradical hyphae.The FDA method gave the most precise estimates of enzyme activity (low SE) followed by the INT method, while the nitro‐BT method was the least precise. Different percentages of extraradical hyphae that were metabolically active were obtained with the different methods. The nitro‐BT assay deviated from the others as it did not show declining percentage of active extraradical hyphae as the symbiosis aged.
Nitrogen affects the phosphorus response of VA mycorrhiza
Authors: SYLVIA D. M. , NEAL L. H. 
Published: April 2006

summaryRoot colonization by vesicular‐arbuscular (VA) mycorrhizal fungi is often suppressed by phosphorus (P) additions; however, nitrogen (N) additions have been reported to both stimulate and suppress root colonization. The objective of this research was to examine colonization of Allium cepa L. roots at a range of P and N concentrations in order to clarify the effects of these nutrients on root colonization. In the first experiment, conducted under N‐limiting conditions, P addition had no effect on root colonization by Glontus etunicatum Becker & Gerdemann and increased root colonization by Gigaspora margarita Gerdemann and Trappe. In the second experiment, conducted under N‐sufficient conditions, P addition suppressed colonization by G. etunicatum. In the third experiment, P and N additions were such that tissue P:N ratios ranged from 0–03 (P limiting) to 017 (N limiting). No relationship was found between P:N ratio and root colonization for two isolates of G. etunicatum. Root colonization was not affected by P addition when plants were deficient in N but, when N was sufficient, P addition suppressed root colonization. These results demonstrate that plant N stress affects the resistance of the host root to colonization by VA mycorrhizal fungi.
Occurrence of cluster roots onMyrica ceriferaL. (Myricaceae) in water culture in relation to phosphorus nutrition
Authors: LOUIS ISABELLE , RACETTE SUZANNE , TORREY JOHN G. 
Published: April 2006

summaryWhenMyrica ceriferawas grown in a number of 1/1‐strength Hoagland's solutions, each lacking one mineral nutrient, cluster roots formed only in solutions lacking phosphorus (P). In seedlings initially fertilized with various P concentrations, cluster root formation decreased with increasing P supply and was totally suppressed in solutions containing ≥ 1 mg P l−1. As total root weight did not vary significantly between P treatments, the proportion of the root system expressed as cluster roots or non‐cluster roots varied with phosphorus supply. A similar response to increasing levels of foliar‐applied P suggests that it may be internal P concentration in the plant that determines the initiation of cluster roots and not external P levels in the soil. Nitrogen, supplied as fixed dinitrogen or nitrate, did not have any effect on development of cluster roots and it appears that the capacity of actinorhizal plants to fix nitrogen by symbiotic association with a soil micro‐organism is of no significance to cluster root formation. While abundant root hair development and extensive mycorrhizal mycelium distribution in the rhizosphere may represent more efficient morphological forms of improving plant P uptake, the significance of cluster roots in relation to P nutrition and the mechanisms involved in their development warrant further investigation.
Fructan and cryoprotection in ryegrass (Lolium perenne L.)
Authors: GONZALEZ B. , BOUCAUD J. , SALETTE J. , LANGLOIS J. 
Published: April 2006

summaryChanges in carbohydrate content and composition of ryegrass (Lolium perenne L.) cv. Reveille field‐grown in Normandy were investigated from May 1987 to May 1988. During the winter period, the concentrations of high DP (degree of polymerization) fructan were the lowest whilst those of ethanol‐soluble carbohydrates were the highest. Ethanol‐soluble carbohydrates also accounted for most of the non‐structural carbohydrates of four cultivars of Lolium perenne field‐grown in central France in January 1989. The accumulation of osmotically active carbohydrates during winter leads only to a small depression of freezing point and consequently, these sugars cannot be considered as efficient cryoprotectants in ryegrass.
Long‐term exposure of Norway spruce,Picea abies(L.) Karst., to ozone in open‐top chambers
Authors: WALLIN G. , SKÄRBY L. , SELLDÉN G. 
Published: April 2006

summaryRates of net photosynthesis were measured on Norway spruce,Picea abies(L.) Karst. exposed to three different concentrations of ozone for three seasons (1985–7) in open‐top chambers. The treatments were non‐filtered air + ozone (NF +), non‐filtered air (NF) and charcoal‐filtered air (CF). Ozone was added daily between 11.00–18.00 local time. The study was performed during September and October, 1987. The rate of net photosynthesis was determined using an infrared gas analyser (IRGA) connected to a small cuvette, which was equipped with an artificial light source for unilateral illumination. The measurements were made on shoots of three different age classes: current year, 1 year old and 2 years old. Measurements took place at saturating light intensity (1150 μmol m1s1), at a temperature of 16.6 ±0.7°C, and at a relative humidity of 67.5 ± 5.3%. In current‐year shoots the rate of net photosynthesis expressed on a needle‐area basis was lowest in the CF treatment and highest in the NF treatment. In 1‐ and 2‐year‐old shoots, a decreased rate of the net photosynthetic assimilation rate, expressed on a needle area basis, was observed in trees from the NF and NF+ treatment compared with that of trees from the CF treatment. The effect increased with increasing ozone concentration and shoot age. A significant increase in the rate of respiration, expressed on a dry‐weight basis, was observed in current year shoots from trees exposed to NF+. A significant decrease of the leaf conductance to carbon dioxide was obtained in 2‐year‐old shoots exposed to NF and NF+. A decrease in the content of chlorophyll was observed in 1‐ and 2‐year‐old needles from trees exposed to NF+.