bluuebunny/crossref_metadata_2025 huggingface dataset:
Dark chilling imposes metabolic restrictions on photosynthesis in soybean
Authors: VAN HEERDEN P. D. R. , KRÜGER G. H. J. , LOVELAND J. E. , PARRY M. A. J. , FOYER C. H.
Published: March 2003

Dark chilling inhibited photosynthesis in two soybean [Glycine max (L.) Merr.] cultivars (Fiskeby V and Maple Arrow). The inhibition of CO2 assimilation was characterized by a simultaneous decrease in stomatal conductance (Gs) and intercellular CO2 concentration (Ci) in Maple Arrow, whereas a similar decrease in Gs in Fiskeby V occurred without any change in Ci. Dark chilling had little effect on total ribulose‐1, 5‐bisphosphate carboxylase/oxygenase (Rubisco) activity, Rubisco protein content or Rubisco activation state in the subsequent light period. Chilling reduced the abundance of the nocturnal Rubisco inhibitor, 2‐carboxyarabinitol 1‐phosphate, only in Fiskeby V. The abundance of Rubisco small subunit transcripts was enhanced in both cultivars as a result of dark chilling. Dark chilling decreased the maximal extractable activities and activation states of stromal fructose‐1,6‐bisphosphatase (FBPase) and NADP‐malate dehydrogenase but had no effect on sucrose phosphate synthase or leaf sucrose and starch contents. It is concluded that dark chilling‐induced limitations on CO2 assimilation are predominantly due to metabolic restrictions rather than to direct effects on electron transport reactions and that stromal FBPase is particularly susceptible to dark chilling.
The ecological significance of long‐distance water transport: short‐term regulation, long‐term acclimation and the hydraulic costs of stature across plant life forms
Authors: MENCUCCINI M.
Published: March 2003

Plant hydraulic conductance, namely the rate of water flow inside plants per unit time and unit pressure difference, varies largely from plant to plant and under different environmental conditions. Herein the main factors affecting: (a) the scaling between whole‐plant hydraulic conductance and leaf area; (b) the relationship between gas exchange at the leaf level and leaf‐specific xylem hydraulic conductance; (c) the short‐term physiological regulation of plant hydraulic conductance under conditions of ample soil water, and (d) the long‐term structural acclimation of xylem hydraulic conductance to changes in environmental conditions are reviewed. It is shown that plant hydraulic conductance is a highly plastic character that varies as a result of multiple processes acting at several time scales. Across species ranging from coniferous and broad‐leaved trees to shrubs, crop and herbaceous species, and desert subshrubs, hydraulic conductance scaled linearly with leaf area, as expected from first principles. Despite considerable convergence in the scaling of hydraulic properties, significant differences were apparent across life forms that underlie their different abilities to conduct gas exchange at the leaf level. A simple model of carbon allocation between leaves and support tissues explained the observed patterns and correctly predicted the inverse relationships with plant height. Therefore, stature appears as a fundamental factor affecting gas exchange across plant life forms. Both short‐term physiological regulation and long‐term structural acclimation can change the levels of hydraulic conductance significantly. Based on a meta‐analysis of the existing literature, any change in environmental parameters that increases the availability of resources (either above‐ or below‐ground) results in the long‐term acclimation of a less efficient (per unit leaf area) hydraulic system.
Physiological specialization and pathotype distribution of Puccinia recondita in western Europe, 1995
Authors: Park R. F. , Felsenstein F. G.
Published: March 2003

A pathogenicity survey of Puccinia recondita f.sp. tritici (Prt) was conducted in western Europe in 1995. Random urediospore isolates (850) of Prt were collected from the air by means of a jet spore sampler in wheat‐growing regions of Austria, Belgium, France, Germany, northern Italy, Switzerland and the UK. Pathogenicity of the isolates was determined in tests of detached primary leaf segments maintained on water agar supplemented with benzimidazole (35 p.p.m.). The differential genotypes used were Thatcher, 20 near‐isogenic Thatcher lines each with a single leaf rust resistance gene, and five cultivars/lines with additional resistance genes. All isolates were avirulent for the genes Lr9, Lr19, Lr21, Lr24, Lr25 and Lr29, and both virulence and avirulence were detected for the remaining 19 genes. Fifty‐three pathotypes were identified, four of which predominated (64% of isolates) and were widespread throughout western Europe. Three of the four predominant pathotypes were also identified in collections of wheat leaf rust collected in Poland, Hungary, Estonia and Finland. One pathotype, which comprised 35% of isolates in the south of France, was not detected in any other region. This pathotype was indistinguishable from several isolates obtained from Morocco, which suggested that it may have originated from northern Africa. Comparisons with previously published data suggested that the four predominant pathotypes were very similar and possibly the same as pathotypes present in the former Czechoslovakia for up to 20 years. The results obtained provide evidence of migration of Prt over considerable distances in western Europe, stressing the need for a co‐ordinated approach for genetical control of the disease in this region.
Effect of temperature on symptom expression and accumulation of tomato spotted wilt virus in different host species
Authors: Llamas‐Llamas M. E. , Zavaleta‐Mejia E. , Gonzalez‐Hernandez V. A. , Cervantes‐Diaz L. , Santizo‐Rincon J. A. , Ochoa‐Martinez D. L.
Published: March 2003

The effect of two temperature regimes (daytime, 29 ± 2°C, night‐time, 24 ± 3°C; and daytime, 23 ± 1°C, night‐time, 18 ± 2°C) on the symptoms caused by tomato spotted wilt virus (TSWV), and the accumulation of TSWV virions, was compared in Datura stramonium, Nicotiana tabacum cv. White Burley and Physalis ixocarpa. Tobacco plants were more severely affected by TSWV at the high temperature regime, but the incidence (percent of plants with symptoms) was 100% for both regimes. In P. ixocarpa and D. stramonium the higher temperature caused an increase in both incidence and rate of development of symptoms. At high temperature, all three species showed both local and systemic symptoms; however, at low temperature only P. ixocarpa consistently developed systemic symptoms. In general, virus accumulation in the inoculated leaves (presumably the combined effect of virus replication and local movement) of all plants was higher at the lower temperature. Long distance movement in tobacco, leading to virion accumulation in other plant organs, was favoured by high temperature; but there was relatively little effect in P. ixocarpa and D. stramonium.
Colonization of roots, stolons, tubers and stems of various potato (Solanum tuberosum) cultivars by the black‐dot fungus Colletotrichum coccodes
Authors: Andrivon D. , Lucas J.‐M. , Guérin C. , Jouan B.
Published: March 2003

In an attempt to better understand the importance of tuber‐borne inoculum in black dot development, several potato cultivars were inoculated with various Colletotrichum coccodes isolates. Symptoms developed first on underground organs (starting 2 weeks after inoculation on roots, and later on stolons and tubers) of inoculated plants; stem infections developed only after 7–10 weeks, depending on the cultivar. Infection with C. coccodes resulted in a reduction in numbers of stolons and tubers in cv. Bintje, but not in the later maturing cv. Roseval. Significant isolate by cultivar interactions were detected from the analysis of root symptoms after inoculation of three potato cultivars (Bintje, Spunta and Desiree) with five C. coccodes isolates. Such an interaction was also detected for stolon/tuber symptoms at the latest scoring date (98 days after inoculation), but not at earlier dates (58, 70 and 84 days after inoculation). These results suggest that protocols based on root colonization might be used for investigating cultivar response to black dot and pathogenicity of C. coccodes isolates, and that some specificity exists in the reaction of potato genotypes to this pathogenic fungus.
Genetic diversity in the coconut lethal yellowing disease phytoplasmas of East Africa
Authors: Mpunami  , Tymon  , Jones  , Dickinson
Published: March 2003

DNA primers, based on the ribosomal sequences of lethal yellowing‐type disease (LYD) phytoplasmas, were used to analyse genetic variation within the lethal yellowing‐type diseases of coconut in East Africa. Samples were collected from palms in Kenya, Mozambique and high, medium and low disease incidence areas of Tanzania. The mollicute‐specific primer pair P1 and P6 amplified a 1.5 kbp product from all diseased palms and no product from symptomless palms, indicating that phytoplasmas were associated with all of these diseases. However, the Rohde forward and Rohde reverse primers (a second rRNA primer pair designed to detect East African LYD‐associated phytoplasmas) only amplified products from Tanzanian and Kenyan diseased palms and not from those of Mozambique. Conversely, primers Ghana 813 and AK‐SR, designed for specific detection of coconut‐associated phytoplasmas in West Africa, amplified products only from the Mozambique palms, indicating that the phytoplasma associated with LYD in Mozambique is more closely related to those from West Africa. This was supported by restriction enzyme digestion of PCR products. DNA sequencing of PCR products from phytoplasmas within Tanzania revealed no detectable differences in the rDNA sequences of isolates from high, medium and low incidence areas.
Fusarium ear blight of wheat: the use of quantitative PCR and visual disease assessment in studies of disease control
Authors: Doohan  , Parry  , Nicholson
Published: March 2003

Quantitative PCR analysis and visual disease assessment (VDA) were used to study Fusarium culmorum and F. poae ear blight of wheat and its fungicidal control in three glasshouse trials (1994–5 and 1996–7). VDA indicated high levels of both diseases in the trials, while PCR analysis showed that the amounts of F. poae detected in infected plants were low relative to the amounts detected for F. culmorum. PCR and VDA analysis both indicated that the demethylase‐inhibiting (DMI) fungicides prochloraz and tebuconazole significantly decreased F. culmorum and F. poae ear blight. The PCR results, however, revealed levels of disease control by fungicide treatments that were consistently higher than those suggested by VDA. Overall, both fungicides appeared equally effective in controlling the two pathogens. PCR and VDA analysis indicated that the anilino‐pyrimidine fungicide pyrimethanil had no significant effect on F. culmorum ear blight. Correlations between VDA at cereal growth stage 80 and PCR analysis were similar for F. culmorum and F. poae. Yield analysis, as measured by 1000 grain weight, indicated that DNA content more accurately predicted yield loss than did VDA scores. Inoculation with F. culmorum significantly reduced yield and significant relationships were observed between F. culmorum disease (as assessed visually or by PCR) and yield, with yield decreasing as disease increased. In contrast, inoculation with F. poae had no significant effect on yield and no significant relationships were observed between F. poae disease and yield. These results have important implications for field studies of Fusarium ear blight of wheat because they highlight the importance of identification of the causal organisms to the species level.
Evaluation of bacterial wilt resistance in tomato lines nearly isogenic for the Mi gene for resistance to root‐knot
Authors: Deberdt  , Olivier  , Thoquet  , Quénéhervé  , Prior
Published: March 2003

Resistance to bacterial wilt, caused by Ralstonia solanacearum, in tomato lines CRA 66 and Caraïbo is reported to be decreased by root‐knot nematode galling and by introduction of the Mi gene for nematode resistance. The Mi gene is located on tomato chromosome 6, which also carries a major quantitative trait locus (QTL) for resistance to bacterial wilt. Bacterial wilt resistance was evaluated in F3‐progenies derived from two crosses between near‐isogenic lines, Caraïbo × Carmido and CRA 66 × Cranita, differing for small and large introgressions from Lycopersicon peruvianum that carry the Mi gene, respectively. These introgressed regions were mapped using RFLP markers. Plants homozygous Mi+/Mi+ (susceptible to the nematode) and homozygous Mi/Mi (resistant) for the Mi gene were selected in F2 and used to produce F3 progenies. Parents and F3‐lines with Mi/Mi had resistance to bacterial wilt reduced by 30% in Caraïbo × Carmido and by 15% in CRA 66 × Cranita. Caraïbo and Carmido were demonstrated to be isolines and the small introgression from L. peruvianum resulted in loss of the QTL for bacterial wilt resistance, which is probably allelic or linked in repulsion to the Mi gene. In contrast, resistance to bacterial wilt segregated in the F3 lines from the cross CRA 66 × Cranita, giving families varying in resistance between the levels shown by the parents. Consequently, two hypotheses were considered: (i) after only four backcrosses, the parents were not isolines and the genes for resistance to bacterial wilt from CRA 66 were still segregating, and (ii) the parents were isolines and variation in resistance to bacterial wilt in F3 was due to recombination events among the large L. peruvianum introgressed chromosome region from Cranita.
Generation of volatile ammonia from urea fungicidal to Phellinus noxius in infested wood in soil under controlled conditions
Authors: Chang  , Chang
Published: March 2003

Phellinus noxius was not recovered from pieces of artificially infested wood placed in or on soil amended with urea (NH4)2CO3 or aqueous ammonia. High concentrations of volatile NH3 were detected in these treatments, indicating that NH3 generated from these chemicals was fungicidal to P. noxius. A high concentration of volatile NH3 was detected from nonautoclaved soil amended with urea, but not from amended autoclaved soil, indicating that soil microorganisms were involved in NH3 generation. To kill P. noxius completely required 3000 p.p.m. urea in soil. Volatile NH3 was generated from urea in alkaline soil, but not in acidic soil. In acidic soil 1 month after urea amendment, populations of both fungi and bacteria, and the concentration of NH4+ (but not of NH3 in the air), were significantly greater than in the no urea treatment and in the urea treatment 3 d after amendment, indicating that NH4+, generated from urea in the soil enhanced the activity of soil microorganisms. In contrast, 1 month after amendment of alkaline soil, the concentration of NH4+ in the soil and NH3 in the air increased significantly and the populations of both fungi and bacteria decreased, indicating that NH3 in the air inhibited activity of soil microorganisms. Similar quantities of volatile NH3 were generated at temperatures ranging from 12 to 32°C. A large quantity of NH3 was generated at low soil matric potentials (− 0.75 to − 0.15 MPa) while high potentials (> − 0.025 MPa) and flooded soil hindered production of volatile NH3. Ammonia was more effective at killing P. noxius growing in smaller pieces of wood than in larger pieces. The fungus was not recovered from wood pieces less than 3 cm in diameter. Volatile NH3 was also lethal to six other root rotting fungi (Ganoderma australe, G. lucidum, G. tropicum, Rigidoporus vinctus, Heterobasidion annosum, and Rosellinia necatrix) in addition to P. noxius.
Comparison of Puccinia graminis f.sp. tritici from South America and Europe
Authors: McCallum  , Roelfs  , Szabo  , Groth
Published: March 2003

Twenty isolates of Puccinia graminis f.sp. tritici from South America were compared with 19 from Europe using virulence, isozymes and random amplified polymorphic DNA (RAPD) markers. The isozyme and virulence patterns for these isolates were also compared with those of 11 isolates representative of the common race clusters in North America. All three types of marker showed a level of similarity between the South American and European isolates comparable with that between isolates from the same continent. The average similarity coefficients between the South American and European isolates were 0.65 for virulence, 0.67 for isozymes, and 0.70 for RAPD markers. Among South American isolates the values were 0.63 for virulence, 0.64 for isozymes and 0.72 for RAPDs. For the South American and European isolates, correlation between the similarity matrices based on RAPDs and on isozyme markers, respectively (r = 0.52), was higher than that between the RAPD and virulence matrices (r = 0.32) or between isozyme and virulence matrices (r = 0.16). The North American isolates had a comparable level of similarity for virulence and isozymes to both the South American and European populations. There was no clear distinction between the South American, North American and European isolates, which is consistent with the hypothesis that these populations may have had a common origin.
Stomatal penetration of cowpea (Vigna unguiculata) leaves by a Colletotrichum species causing latent anthracnose
Authors: Latunde‐Dada  , O'connell  , Nash  , Lucas
Published: March 2003

The infection process of a Colletotrichum species causing latent infection and anthracnose in cowpea (Vigna unguiculata) was studied in seedlings by light and confocal microscopy. Leaf surfaces were extensively colonized by an anastomosing network of germ‐tubes and conidia. This epiphytic mycelium produced abundant secondary conidia on short conidiophores. Although melanized appressoria were developed, the host surface was not penetrated directly. The fungus only gained ingress into leaves through stomatal openings, by means of undifferentiated germ‐tubes, and slowly colonized the mesophyll by intercellular hyphae, without initially producing visible symptoms. Anthracnose lesions with multisetate acervuli appeared on senescent leaves after a prolonged symptomless period of host colonization lasting > 2 weeks. Analysis of the nucleotide sequences of the amplified D2 and ITS‐2 regions of rDNA revealed close similarities (95–96%) between this cowpea pathogen and isolates of C. gloeosporioides from Aeschynomene virginica,Stylosanthes scabra and Mangifera indica. These results, in addition to other morphological and growth attributes, identify this endophytic anthracnose pathogen of cowpea as a Colletotrichum species distinct from C. capsici and C. destructivum.
Genetic diversity among isolates of Fusariumoxysporum f.sp. canariensis
Authors: Plyler  , Simone  , Fernandez  , Kistler
Published: March 2003

Fusarium oxysporum f.sp. canariensis causes vascular wilt disease of Phoenix canariensis, the Canary Island date palm. Seventy‐two isolates of this fungus were obtained from diverse geographic locations including France, Japan, Italy, the Canary Islands, and California, Florida and Nevada, USA. The isolates were tested for vegetative compatibility and for similarities based on mitochondrial DNA (mtDNA), single‐copy sequences and repetitive DNA (pEY10) polymorphisms. Seventy‐one percent of the isolates belonged to a single vegetative compatibility group (VCG 0240), and four closely related mitochondrial RFLP patterns were found. A subset of the isolates was further tested for single‐copy RFLPs and repetitive DNA fingerprints. Only four single‐copy RFLP haplotypes were found among 25 representative isolates of F. oxysporum f.sp. canariensis tested, using nine polymorphic single‐locus probe/enzyme combinations. Finally, 32 different pEY10 DNA fingerprints were found out of 57 isolates examined. Overall the results indicate that F. oxysporum f.sp. canariensis is a single lineage with a low to moderate level of genetic diversity.
Mechanical transmission of maize rayado fino marafivirus (MRFV) to maize and barley by means of the vascular puncture technique
Authors: Madriz‐Ordeñana K. , Rojas‐Montero R. , Lundsgaard T. , Ramírez P. , Thordal‐Christensen H. , Collinge D.B.
Published: March 2003

Maize rayado fino marafivirus (MRFV) was mechanically transmitted to kernels of three Costa Rican maize cultivars by the vascular puncture technique. A transmission rate of up to 43.2% was obtained for cultivar HC‐57. The rate of MRFV transmission to maize was possibly affected by the morphology of the kernel, which may influence physical access to the vascular tissue after water imbibition. Transmission to maize was confirmed by western blot and immunosorbent electron microscopy. By slight modifications of the procedure, MRFV was also transmitted to barley. This is the first report of MRFV infecting a species outside the supertribe Andropogonodae. Virus infection and replication in barley were confirmed by RT‐PCR detection of MRFV RNA and by detection of the virus by ELISA.
Production, survival and infectivity of oospores ofPhytophthora infestans
Authors: Turkensteen L. J. , Flier W. G. , Wanningen R. , Mulder A.
Published: March 2003

The formation of oospores ofPhytophthora infestanswas studied in tomato and potato crops and volunteer plants under field conditions, and in laboratory tests with leaf discs of potato cultivars differing in their level of race‐nonspecific resistance. Oospores were readily detected in blight‐affected tomato leaflets and fruits, and in leaflets of field crops and volunteer potato plants. Oospores extracted from blighted potato leaflets yielded 13 oospore‐derived progeny. Oospores were also produced following inoculation of leaf discs of eight potato cultivars expressing different levels of race‐nonspecific resistance with a mixture of sporangia of A1 and A2 isolates. The highest numbers of oospores were produced in cvs Bintje (susceptible) and Pimpernel (resistant), and the lowest in Nicola (intermediate resistance). The relationship between lesions per leaflet and oospore incidence, affected by varying A1 : A2 ratios, was explored using a simple mathematical model, and validated by comparing actual oospore production in leaflets with multiple lesions of the race‐nonspecific‐resistant potato clone Lan 22‐21 with the predictions generated by the model. Survival of oospores was investigated after their incorporation in either a sandy or a light clay soil in buried clay pots exposed to the local weather conditions. Over 6 years these soils were regularly assessed for their infection potential using floating leaflets in a spore‐baiting bioassay. Sandy and clay soils contaminated with oospores remained infectious for 48 and 34 months, respectively, when flooded. Infections of floating potato leaflets occurred within 84–92 h and ceased after 11 days. Soil samples remained infective if dried and re‐flooded on two, but not more, occasions.
Importance of different sources of inoculum and dispersal methods of conidia of Colletotrichum musae, the causal agent of banana anthracnose, for fruit contamination
Authors: De Lapeyre de Bellaire L. , Chillet M. , Dubois C. , Mourichon X.
Published: March 2003

Different populations of Colletotrichum were characterized and quantified on floral parts of banana plants from flowering until harvest. Isolates of Colletotrichum found to be pathogenic and attributed to the species C. musae (77% of isolates) were differentiated from other species by abundant sporulation, a short mycelium, and rapid growth. Colletotrichum musae was isolated from floral parts mainly during the month following bunch emergence. The respective involvement of different sources of inoculum (leaves, bunch bracts, floral parts) in the levels of fruit contamination was evaluated. When the floral parts and bunch bracts were removed at flowering, the severity of anthracnose disease was considerably reduced. The severity of the disease is strongly correlated with cumulative rainfall during the first 35 days after bunch emergence, and was considerably reduced when rainwater runoff over the bunches was limited by placing plastic sleeves over them. The disease was not observed on banana fruit grown under shelters, protected from rain. The results obtained from this study show clearly that contamination of fruit by conidia takes place largely due to the trickling of rainfall over the floral parts, which are the main source of inoculum. The application of these results for integrated control is discussed.
Resistance to infection and translocation of Tomato spotted wilt virus in potatoes
Authors: Wilson C. R.
Published: March 2003

Tomato spotted wilt virus (TSWV) was detected by ELISA within freshly harvested infected tubers of all cultivars tested, but had an erratic distribution which could affect detection reliability. The lack of detectable virus within many tuber eye samples was reflected in production of healthy shoots from infected tubers, some of which did eventually succumb to TSWV infection after 1–4 weeks' growth, and observations suggested this may be enhanced by virus multiplication in diseased shoots produced from the mother tuber. Breeding populations of Thrips tabaci were found within a field exposure trial, and trapping confirmed this as the only known TSWV vector present. In this trial, relying on natural thrips transmission, there was no significant variability in susceptibility of the cultivars tested to initial foliar infection. However, in a glasshouse trial using mechanical inoculation, significant cultivar differences in the rate of foliar systemic infection were observed. Substantial cultivar differences were also found in the efficiency of TSWV translocation from infected plant to tuber, and from infected tuber to progeny plants. Tuber infection rate was further affected by the age of plants at infection, and by the proportion of stems of each plant showing symptoms of TSWV infection. Two apparent resistance mechanisms operated to restrict TSWV translocation to tubers. The first showed strong but incomplete resistance at all ages of challenge; the second showed initial susceptibility to tuber infection but, in challenges after tuber initiation, showed a strong resistance phenotype. Expression of tuber necrosis also varied with cultivar and was affected by plant age at infection. Malformed tubers and secondary growth were also found following foliar TSWV infection, but were not necessarily associated with tuber infection. Current certification tolerance levels for TSWV infection in seed potatoes in Tasmania overestimate the risk of TSWV infection. Given that disease risk varies markedly with cultivar, perhaps certification tolerance levels should reflect this on a cultivar‐specific basis.
Aggressiveness of Verticillium dahliae isolates from different vegetative compatibility groups to potato and tomato
Authors: Tsror (Lahkim) L. , Hazanovsky M. , Mordechi‐Lebiush S. , Sivan S.
Published: March 2003

Aggressiveness of Verticillium dahliae isolates from three vegetative compatibility groups (VCGs) was tested on potato and tomato. VCG4B was the most aggressive to potato and VCG2A was the most aggressive to tomato; VCG2B was the least aggressive to both potato and tomato. In potato, disease incidence, symptom severity and colonization index of stem segments were significantly higher in plants inoculated with VCG4B isolates than in those inoculated with VCG2B and VCG2A isolates. Inoculation with VCG4B and VCG2A decreased plant height and fresh weight more than inoculation with VCG2B. In tomato, VCG2A caused significantly more severe symptoms than either VCG4B or VCG2B. The colonization index in tomato plants inoculated with VCG2A was also significantly higher than in those inoculated with VCG4B and VCG2B. Similar patterns of relative aggressiveness were observed in potato and tomato when the pathogenicity of isolates of various VCGs, each originating from a specific host (cotton, potato or eggplant), was compared.
Distinguishing characteristics and vegetative compatibility of Colletotrichum kahawe in comparison with other related species from coffee
Authors: Varzea V. M. P. , Rodrigues C. J. , Lewis B. G.
Published: March 2003

On the basis of pathogenicity tests on green berries or hypocotyls of coffee and by morphological and biochemical characteristics in culture, 31 isolates of Colletotrichum were classified into C. kahawe (24 isolates), C. gloeosporioides (six isolates) or C. acutatum (one isolate). Within these groups of isolates, vegetative compatibility groups (VCGs) were determined by complementation tests with mutants in the nitrate assimilation pathway. There were distinct incompatibility barriers between the three species. Among the C. gloeosporioides group, the three isolates tested were self‐compatible but incompatible with each other. Within C. kahawe, 18 isolates were self‐compatible and only one main VCG was detected. However, partial compatibility in C. kahawe was also indicated by variation in the intensity of heterokaryon formation between different pairs of isolates and between different types of mutant. The existence of only one VCG in C. kahawe is consistent with the low level of variation found in previous work on DNA polymorphism.
Quantification of seedborne infection by Rhynchosporium secalis in barley using competitive PCR
Authors: Lee H. K. , Tewari J. P. , Turkington T. K.
Published: March 2003

The potential of the competitive polymerase chain reaction (PCR) assay for quantification of seedborne infection by Rhynchosporium secalis in barley was examined using a primer set (RS1 and RS3) derived from the internal transcribed spacer (ITS) regions of ribosomal RNA genes of this pathogen. Introduction of a heterologous internal control, which competes for the same primer set in the conventional PCR assay, allowed for detection and quantification of R. secalis fungal biomass. In order to generate a standard calibration curve, DNA prepared from infected seeds with different levels of R. secalis infection was subjected to competitive PCR assay. The resulting PCR product ratio for each PCR reaction (R. secalis‐amplified DNA/internal control template‐amplified DNA) increased proportionally with increasing levels of infected seed DNA in the reaction mixture. Naturally infected seed lots collected from 1995 to 1999 were used to demonstrate the potential of the competitive PCR assay as an alternative seed health testing method. The results from this competitive PCR assay were compared with those from conventional visual disease assessment and an agar plate assay. Although relatively good correlation between visual disease assessment and the competitive PCR was found in the case of artificially mixed seed samples, there was poor correlation in the experiments using naturally infected seed samples.
Formation of overwintering structures of Uncinula necator and colonization of grapevine under field conditions
Authors: Rügner A. , Rumbolz J. , Huber B. , Bleyer G. , Gisi U. , Kassemeyer H.‐H. , Guggenheim R.
Published: March 2003

Developing shoots of grapevine (Vitis vinifera cv. Kerner) were inoculated with conidia of the powdery mildew, Uncinula necator, at well‐defined phenological stages of the host to provoke the development of flag shoots in the field and to investigate these shoots as early as possible in the following growing season for the presence of the pathogen. The disease progress was monitored and fungal growth and development on samples from a field trial were analysed by means of low‐temperature scanning electron microscopy (LT–SEM). Mycelium was detected on the surface and in the interior parts of buds. The suitability of the field plot to analyse flag shoots was proven by the occurrence of such shoots in the following spring. Furthermore, early stages of cleistothecia development on berries were described for the first time. Establishment of U. necator in dormant buds of grapevine, giving rise to flag shoots in the following spring, is considered to play a significant role in overwintering of the pathogen in the vineyards of southern Germany.
Induction of resistance in cocoa against Crinipellis perniciosa and Verticillium dahliae by acibenzolar‐ S‐methyl (ASM)
Authors: Resende M. L. V. , Nojosa G. B. A. , Cavalcanti L. S. , Aguilar M. A. G. , Silva L. H. C. P. , Perez J. O. , Andrade G. C. G. , Carvalho G. A. , Castro R. M.
Published: March 2003

The benzothiadiazole compound acibenzolar‐S‐methyl (ASM) was assessed as an inducer of resistance against Crinipellis perniciosa, agent of witches’ broom, and Verticillium dahliae, agent of vascular wilt, both on cocoa. ASM induced a reduction in incidence of witches’ broom of up to 84·5% when sprayed 30 days before inoculation on cocoa seedlings of cv. Catongo. ASM also induced a reduction in severity of Verticillium wilt to 55·4% on cv. Theobahia. For both pathosystems, effects of dose on disease were not clearly observed. The efficacy of the inducer increased with the interval between sprayings and the respective inoculations with the pathogens. In another experiment, the effect of ASM on the control of witches’ broom on cocoa seedlings was compared with that of cuprous oxide and tebuconazole, all sprayed 15 days before inoculation. ASM reduced disease incidence by 60·1% compared with the inoculated control. ASM was superior to tebuconazole, and there was also a tendency for ASM to be better than cuprous oxide. To understand the mechanism of action of ASM as an inducer of resistance, alterations in the levels of total phenolics, polyphenol oxidases and peroxidases were evaluated 3, 15 and 30 days after spraying of seedlings of cv. Catongo. Enzyme activities from seedlings of cv. Theobahia were evaluated 30 days after spraying. On cv. Catongo, no significant differences in total phenolic content and polyphenol oxidase activity were detected after spraying. However, an increase in peroxidase activity was detected at all times of evaluation. On cv. Theobahia, significant increases in activities of peroxidase and polyphenol oxidase were detected, indicating that defence responses due to ASM were dependent on host genotype.
Resistance toTurnip mosaic virusinBrassica rapaandB. napusand the analysis of genetic inheritance in selected lines
Authors: Hughes S. L. , Green S. K. , Lydiate D. J. , Walsh J. A.
Published: March 2003

Forty‐twoBrassica rapaandBrassica napuslines were tested for resistance toTurnip mosaic virus(TuMV) isolates representing the three major pathotypes in Europe. Of these lines, 11 were susceptible to all pathotypes; nine were resistant to one pathotype; eight were resistant to two pathotypes; and 14 were resistant to all three pathotypes. Of the lines tested, 23 were either able to, or had the potential to, discriminate between two different pathotype‐3 isolates. Genetic models for inheritance of resistance were proposed for fourB. rapalines: Jong Bai No. 2 had dominant resistance to pathotype 1 conferred by a single allele; PI418957C and Jin G 55 had recessive resistance to pathotype 4 where a single allele was required; PI418957C also had recessive resistance to pathotype 3 where a model with one of two epistatic, unlinked loci was proposed. Jong Bai No. 1 also had recessive resistance to pathotype 3, apparently conferred by alleles at three loci, where any two of the three loci were epistatic and required for resistance.
Disease complexes involving plant parasitic nematodes and soilborne pathogens
Authors: Back M. A. , Haydock P. P. J. , Jenkinson P.
Published: March 2003

This review discusses the mechanisms underlying synergistic interactions between phytophagous nematodes and soilborne pathogens, and identifies biotic and abiotic factors affecting these interactions. Approaches towards the resolution and management of nematode–pathogen complexes are considered and discussed.
Effects of benzothiadiazole and acetylsalicylic acid on β‐1,3‐glucanase activity and disease resistance in potato
Authors: Bokshi A. I. , Morris S. C. , Deverall B. J.
Published: March 2003

Benzothiadiazole (BTH), as Bion WG50, and acetylsalicylic acid (ASA) treatments of potato foliage of field‐ and glasshouse‐grown potato plants were compared for control of two foliar diseases, early blight (Alternaria solani) and powdery mildew (Erysiphe cichoracearum). The effect of these treatments on harvested tubers wound‐inoculated with the dry rot fungus (Fusarium semitectum) was also evaluated. BTH (50 mg a.i. L−1) gave almost complete control of both foliar pathogens on inoculated glasshouse‐grown plants and reduced the severity of leaf spotting diseases (mainly early blight) in the field. BTH (100 mg a.i. L−1) and ASA (400 mg a.i. L−1) reduced the severity of dry rot in field‐grown tubers in some post‐harvest wound‐inoculated treatments but not others and a similar reduction occurred with tubers inoculated post‐harvest from BTH‐treated plants grown under glasshouse conditions. BTH treatment increased β‐1,3‐glucanase activity in leaves > stem > tubers > stolons but not in roots. Increased enzyme activity was recorded for up to 45 days post‐treatment.
Aberrant Expression of Tissue‐Specific Proteins in the Thymus: A Hypothesis for the Development of Central Tolerance
Authors: Werdelin  , Cordes  , Jensen
Published: March 2003

Herein we present the case for the existence of a thymic cortical epithelial cell that possesses an unusual gene transcription. It produces tissue‐specific proteins that have their usual physiological functions outside the thymus and presents them, as well as household proteins, to the differentiating thymocytes. We suggest that this specialized cell enforces tolerance to most self‐proteins by causing release of a signal for programmed cell death to thymocytes that express receptors for these self‐antigens.
T‐Cell Recognition of Mycobacterial Proteins MPB70 and MPB64 in Cattle Immunized with Antigen and Infected with Mycobacterium bovis
Authors: Lightbody  , Girvin  , Mackie  , Neill  , Pollock
Published: March 2003

Defined antigenic reagents and knowledge of T‐cell responses are required for the design of improved diagnostic tests for bovine tuberculosis. The limited species distribution of Mycobacterium bovis antigens MPB70 and MPB64 has indicated their potential for inclusion in future tests. The strategy adopted in this study was to define bovine T‐cell responses to these antigens at the epitope level, using cattle immunized with recombinant forms of the antigens, and to compare these responses with cattle which had been experimentally infected with M. bovis. Panels of synthetic peptides (20‐mers with 10‐residue overlaps) were used and five epitopes were identified and found to be powerful stimulators of T‐cell responses in both types of animal (residues 81–100 and 174–190 for MPB70; and residues 1–20, 41–60 and 181–200 for MPB64). Further investigation in larger numbers of cattle (n = 14) of mixed breeds from tuberculosis‐infected herds confirmed that each peptide produced response in several of the cattle, but no single peptide was recognized by all animals. However, the limited numbers of animals in this study suggest that peptide reagents may identify as many positive animals as the intact antigenic protein and could form components of a future diagnostic test. The use of cattle immunized with the proteins of interest has proved to be an interesting model for studying the nature of bovine T‐cell responses to defined mycobacterial proteins.
Immunological Response of Major Histocompatibility Complex Class II‐Deficient (Aβ°) Mice Infected by the Parasite Schistosoma mansoni
Authors: Angyalosi  , Pancré  , Herno  , Auriault
Published: March 2003

We have characterized the immunological behaviour of major histocompitibility complex (MHC) Class II molecule‐deficient (Aβ°) mice after infection by Schistosoma mansoni. In Aβ° mice, morbidity developed dramatically 7 weeks after infection leading to death, despite the absence of an increase in parasite burden or of eggs trapped in the liver. Histological examination of the liver revealed the absence of a classical granulomatous reaction. Antibodies were produced only against schistosomulum antigens. Specific antibodies against adult worm (SWAP) or egg antigen (SEA) were not detected. Cytokine production (IFN‐γ and IL‐4) was absent after in vitro restimulation of splenic cells from infected Aβ° mice with parasite antigens. Adoptive transfer of primed splenic cells (total, purified CD4+ or CD8+ T cells) failed to improve survival or to induce a granulomatous reaction in infected Aβ° mice. Survival, cellular and humoral responses in CD8+ T‐cell‐depleted Aβ° mice or MHC° mice (lacking MHC class I and II molecules) were similar to nondepleted Aβ° mice, suggesting that anti‐schistosomula antibody production was thymo‐independent. Our results demonstrate a high degree of susceptibility of Aβ° mice to infection and corroborate the importance of CD4+ T cells in the initiation of the granulomatous response. However, our results do not show evidence for the involvement of CD8+ T cells in response to S. mansoni infection.
Interleukin‐4 and Interferon‐γ: The Quintessence of a Mutual Antagonistic Relationship
Authors: PALUDAN
Published: March 2003

The two cytokines interleukin (IL)‐4 and interferon (IFN)‐γ play major roles in the generation and regulation of immune responses. Central in this respect is their mutually antagonistic functions. First, IL‐4 promotes T helper cell type 2 (Th2) differentiation and stability and inhibits Th1‐cell differentiation. A direct role of IFN‐γ in Th1‐cell differentiation is debatable, whereas inhibition of Th2‐cell differentiation and roles in Th1‐cell stabilization are well established functions of IFN‐γ. Secondly, IL‐4 and IFN‐γ also affect antibody class switch and expression of Fc receptors differentially, which strongly affect the effector mechanisms following antibody production. Thirdly, macrophage activities induced or enhanced by IFN‐γ, such as expression of certain cytokines, surface molecules and enzymes, are antagonized by IL‐4. Together, these functions of IL‐4 and IFN‐γ place the two cytokines at cardinal positions in the regulation of immune reactions. In this review the known molecular mechanisms underlying the observed functions of IL‐4 and IFN‐γ are presented and discussed.
Secreted Proteins of Mycobacterium leprae
Authors: Harboe  , Wiker
Published: March 2003

In mycobacteria, secreted proteins represent a distinct group, probably of particular importance for development of immune responses following infection. Quantification of individual proteins in culture fluid and corresponding disrupted bacilli permits determination of a localization index for identification of secreted proteins. This procedure cannot be applied to Mycobacterium leprae because secreted proteins are lost during isolation of bacilli from tissues. The DNA sequences of secreted proteins of Mycobacterium tuberculosis were compared with sequences of M. leprae. Genes for homologues of the 85a, 85b, 85c, mpt32 (apa), mpt51, erp, mtc28, Rv2376c, Rv3354 and Rv0526 genes were identified. All of these contain signal sequences typical for secretion in M. leprae. In several instances the local distance between marker genes and occurrence on the same or the complementary DNA strand was similar in these two species. The genomic organisation of genes for secreted proteins is thus very similar in M. leprae and M. tuberculosis, the homology being higher for the mature polypeptide chains than for the corresponding signal peptides.
Kinetics of Cytokine Release and Expression of Lymphocyte Cell‐Surface Activation Markers After In Vitro Stimulation of Human Peripheral Blood Mononuclear Cells with Streptococcus pneumoniae
Authors: ARVÅ  , ANDERSSON
Published: March 2003

The aim of this study was to describe the kinetics of the cytokine release and the expression of activation markers on lymphocytes after stimulation of peripheral blood mononuclear cells (PBMC) with whole killed Streptococcus pneumoniae. The cytokine release and the expression of CD25 and HLA‐DR on T cells, and CD69 on T cells, B cells and NK cells, were measured at different times. Our results show that tumour necrosis factor (TNF)‐α, interleukin (IL)‐1β, IL‐10 and IL‐12 reached maximal levels at 24 h, while IL‐6, IL‐8, TNF‐β and interferon (IFN)‐γ increased throughout the 1‐week test period. The strains tested gave an increased expression of CD69 on all cell types, as well as an increase of CD25 and HLA‐DR expression on T cells. The maximal CD69 expression was seen after 24 h on T cells and NK cells, while the B‐cell expression of CD69 reached a plateau at the same time. All the cells still expressed CD69 on their surfaces after 1 week. In conclusion the results indicate that there was probably an early activation of monocytes leading to a polyclonal activation of lymphocytes.
Characterization of Two Infectious Mouse Mammary Tumour Viruses: Superantigenicity and Tumorigenicity
Authors: BUGGIANO  , GOLDMAN  , NEPOMNASCHY  , BEKINSCHTEIN  , BERGUER  , LOMBARDI  , DEROCHE  , FRANCISCO  , PIAZZON
Published: March 2003

Mouse mammary tumour virus (MMTV) is a type B retrovirus that causes mammary tumours in susceptible mice. MMTV encodes a superantigen (SAg) that has the property of stimulating T‐cell populations expressing a particular variable region of the T‐cell receptor (TCR) β chain (Vβ) and needs to be presented in the context of major histocompatibility complex (MHC) class II molecules. Previously, we described two exogenous MMTV, MMTV BALB14, which encodes a superantigen that induces the deletion of Vβ14+ T cells, and MMTV BALB2, which encodes a SAg that induces the deletion of Vβ2+ T cells. We now describe their biological activity: the deletions involve both CD4+ and CD8+ populations, are progressive and can be detected in blood, lymph nodes and spleen. Such deletions reflect, at least in part, those occurring during intrathymic development. Both BALB2 and BALB14 viral variants are capable of inducing a strong increase of Vβ‐specific T cells in BALB/c mice (I–A+, I–E+). However, when injected into the footpad, their initial stimulatory capacity differs in that the presence of MHC I–E molecules is essential only for the stimulation of Vβ2+ T cells. Both viral variants are able to induce deletion even in the absence of the I–E molecule in which case, however, deletion appears later and is less pronounced. Both exogenous MMTVs induce, at the end of a year, 30–35% of pregnancy‐dependent mammary adenocarcinomas.
Specific Immune Response to Human Immunodeficiency Virus (HIV)‐1 in Patients Assessed Through the Production of Interferon‐γ and Interleukin‐4 in HIV‐1 p24‐Activated Whole Blood Cultures: Relationship with the Viral Load in Plasma
Authors: Hober  , Benyoucef  , Chieux  , De Groote  , De La Tribonnière  , Bocket  , Lion  , Mouton  , Wattré
Published: March 2003

We studied the in vitro HIV‐1 antigen‐stimulated production of IFN‐γ and IL‐4 in HIV‐1‐infected patients and its relationship with viral replication as assessed through the plasma level of HIV‐1 RNA. The levels of IFN‐γ and IL‐4 were higher in supernatants of stimulated whole blood cultures than in stimulated peripheral blood mononuclear cell cultures, therefore whole blood cultures were used in the rest of the study. Specific IFN‐γ and IL‐4 responses to HIV‐1 p24 antigen were observed in HIV‐1‐infected patients but not in healthy controls (n = 23). A lower proportion of individuals with a positive IFN‐γ response to HIV‐1 p24 was observed in patients at a declining clinical stage: 62% in asymptomatic patients (CDC group A, n = 16) versus 19% in symptomatic patients (CDC groups B and C, n = 21; P = 0.007, χ2 testing), whereas the proportion of individuals with a positive IL‐4 response to HIV‐1 p24 was almost similar in both groups of patients (25% versus 23.8%). Increased IL‐4 production by HIV‐1 p24‐activated immunocompetent cells of patients and a predominant IL‐4 response to HIV‐1 p24 (with IL‐4/IFN‐γ > 1) were positively correlated with an increased viral load. In contrast, there was no correlation between the mitogen‐stimulated production of IL‐4 and IFN‐γ and the viral load in plasma. The CD8 T cells from whole blood of patients, but not from controls played a significant role in the HIV‐1 p24‐activated production of IFN‐γ and IL‐4. In conclusion, HIV‐1‐antigen‐stimulated whole blood appears to be a valuable tool to study the production of IL‐4 in HIV‐1‐infected patients. The cytokine profile pattern in response to epitopes of HIV‐1 gag p24 may play an important role in the host immune response to HIV‐1.