bluuebunny/crossref_metadata_2025 huggingface dataset:
Expression of a celery mannose 6‐phosphate reductase in Arabidopsis thaliana enhances salt tolerance and induces biosynthesis of both mannitol and a glucosyl‐mannitol dimer
Authors: ZHIFANG G. , LOESCHER W. H.
Published: March 2003

Mannitol, a sugar alcohol that may serve as a compatible solute to cope with salt stress, is synthesized via the action of a mannose‐6‐phosphate reductase (M6PR) in celery (Apium graveolens L). In contrast to previous approaches that have used a bacterial gene to engineer mannitol biosynthesis in plants and other organisms, Arabidopsis thaliana, a non‐mannitol producer, was transformed with the celery leaf M6PR gene under control of the CaMV 35S promotor. In all independent Arabidopsis M6PR transformants, mannitol accumulated throughout the plants in amounts ranging from 0·5 to 6 µmol g−1 fresh weight. A novel compound, not found in either celery or Arabidopsis, 1‐O‐β‐d‐glucopyranosyl‐d‐mannitol, also accumulated in vegetative tissues of mature plants in amounts up to 4 µmol g−1 fresh weight, but not in flowers and seeds. In the absence of NaCl, all transformants were phenotypically the same as the wild type; however, in the presence of NaCl, mature transgenic plants showed a high level of salt tolerance, i.e. growing, completing normal development, flowering, and producing seeds in soil irrigated with 300 mm NaCl in the nutrient solution. These results demonstrate a major role in developing salt‐tolerant plants by means of introducing mannitol biosynthesis using M6PR.
Stomatal responses of C3, C3‐C4 and C4Flaveria species to light and intercellular CO2 concentration: implications for the evolution of stomatal behaviour
Authors: HUXMAN T. E. , MONSON R. K.
Published: March 2003

Stomatal function mediates physiological trade‐offs associated with maintaining a favourable H2O balance in leaf tissues while acquiring CO2 as a photosynthetic substrate. The C3 and C4 species appear to have different patterns of stomatal response to changing light conditions, and variation in this behaviour may have played a role in the functional diversification of the different photosynthetic pathways. In the current study, we used gain analysis theory to characterize the stomatal conductance response to light intensity in nine different C3, C4 and C3‐C4 intermediate species Flaveria species. The response of stomatal conductance (gs) to a change in light intensity represents both a direct (related to a change in incident light intensity, I) and indirect (related to a change in intercellular CO2 concentration, Ci) response. The slope of the line relating the change in gs to Ci was steeper in C4 species, compared with C3 species, with C3‐C4 species having an intermediate response. This response reflects the greater relative contribution of the indirect versus direct component of the gs versus I response in the C4 species. The C3‐C4 species, Flaveria floridana, exhibited a C4‐like response whereas the C3‐C4 species, Flaveria sonorensis and Flaveria chloraefolia, exhibited C3‐like responses, similar to their hypothesized position along the evolutionary trajectory of the development of C4 photosynthesis. There was a positive correlation between the relative contribution of the indirect component of the gs versus I response and water use efficiency when evaluated across all species. Assuming that the C3‐C4 intermediate species reflect an evolutionary progression from fully expressed C3 ancestors, the results of the current study demonstrate an increase in the contribution of the indirect component of the gs versus I response as taxa evolve toward the C4 extreme. The greater relative contribution of the indirect component of the stomatal response occurs through both increases in the indirect stomatal components and through decreases in the direct. Increases in the magnitude of the indirect component may be related to the maintenance of higher water use efficiencies in the intermediate evolutionary stages, before the appearance of fully integrated C4 photosynthesis.
Comparison of phytoplasmas infecting winter oilseed rape in the Czech Republic with Italian Brassica phytoplasmas and their relationship to the aster yellows group
Authors: Bertaccini A. , Vorácková Z. , Vibio M. , Fránová J. , Navrátil M. , Špak J. , Nebesárová J.
Published: March 2003

Winter oilseed rape grown in several areas in South Bohemia showed symptoms of stunting, leaf reddening and extensive malformation of floral parts. Phytoplasmas were consistently observed by using electron microscopy only in phloem tissue of symptomatic plants. DNA isolated from infected and healthy control plants was used in PCR experiments. Primer pairs R16F2/R2, P1/P7 and rpF2/R2, amplifying, respectively, 16S rDNA, 16S rDNA plus spacer region and the beginning of the 23S and ribosomal protein gene L22 specific for phytoplasmas, were used. According to RFLP and sequence analyses of PCR products, the phytoplasma from rape was classified in the aster yellows phytoplasma group, subgroup 16SrI‐B. The PCR products from the Czech phytoplasma‐infected rape also had RFLP profiles identical to those of phytoplasma strains from Italian Brassica. This first molecular characterization of phytoplasmas infecting rape compared with strains from Brassica does not, however, clearly indicate differences among isolates of the same 16SrI‐B subgroup. Further studies on other chromosomal DNA portions could help the research on host specificity or on geographical distribution of these phytoplasmas.
Vegetative compatibility groups within Verticillium dahliae isolates from different hosts in Greece
Authors: Elena  , Paplomatas
Published: March 2003

Forty‐four isolates of Verticillium dahliae obtained from different diseased hosts were tested by vegetative compatibility group (VCG) analysis to investigate their genetic relatedness and correlate the results with four VCGs (1, 2, 3, 4) previously described. Based on complementarity of nit mutants, only three VCGs were identified from the Greek isolates. Seventeen isolates were assigned to VCG 2 (A or B), two to VCG 3 and eight to VCG 4 (A or B). The 17 remaining isolates could not be grouped to any of the three VCGs. All isolates belonging to a distinct VCG complemented strongly with at least one of the two tester strains of that group, or with several strains of the Greek collection belonging to that VCG.
Effects of fosthiazate and aldicarb on populations of plant‐growth‐promoting bacteria, root‐lesion nematodes and bacteria‐feeding nematodes in the root zone of potatoes
Authors: Sturz  , Kimpinski
Published: March 2003

A 2‐year study investigated the relationship between the nematicides aldicarb and fosthiazate and populations of plant growth‐promoting (PGP) and plant‐growth‐inhibiting (PGI) bacteria, and root‐lesion nematodes and bacteria‐feeding nematodes in the root‐zone soils of potatoes. Fewer (P < 0.05) bacterial genera and species were recovered from aldicarb‐treated soils than from the fosthiazate and untreated soils but bacterial population densities were greatest in the aldicarb‐treated soils. In potato plantlet bioassays using root‐zone bacteria from the three soil sources, bacteria from the aldicarb‐treated soils reduced (P < 0.01) the mean wet and dry weight of shoots and roots compared with those from the fosthiazate and untreated soils. In the field, fosthiazate (but not aldicarb) significantly increased tuber yields and reduced nematode population densities of Pratylenchus penetrans in roots and soil. Population densities of bacteria‐feeding nematodes (primarily Diplogaster lheritieri) were not affected by either nematicide. Aldicarb appeared to suppress the populations of plant‐growth‐promoting bacteria that contribute to enhanced growth in potatoes. This is attributed to the long‐term use of aldicarb at the trial site, which may have encouraged the selection, or adaptation, of soil microorganisms that degrade carbamate pesticides but do not enhance potato growth.
Serotypic variation in turnip mosaic virus
Authors: Jenner  , Keane  , Jones  , Walsh
Published: March 2003

A panel of 30 monoclonal antibodies (MAbs) was produced against four isolates of turnip mosaic virus (TuMV). The panel was tested in plate‐trapped antigen ELISA tests against 41 TuMV isolates (with different host and geographical origins and of differing pathotypes). The antibodies were also tested against four other potyviruses (bean common mosaic virus, bean common mosaic necrosis virus, lettuce mosaic virus and zucchini yellow mosaic virus). The reactions were assessed quantitatively (using multivariate analysis) and qualitatively (using the standard deviation obtained against healthy leaf material). The MAbs recognized 16–17 TuMV epitopes that were not present in the other potyviruses and a further two potyvirus epitopes. The isolates were grouped into three serotypes. Only one isolate did not fit this grouping. The classification of seven isolates in coat protein amino acid sequence homology groups correlated with serotypes. There was no correlation between serotype and pathotype, or between reactions to individual MAbs and single lines. There was therefore no evidence that the epitopes recognized by the MAbs are elicitors for the resistance genes present in the Brassicanapus lines. However, the sensitivity and specificity of the MAbs will be useful for both routine detection of TuMV and fundamental studies on plant–virus interactions.
Plum pox virus detection in dormant plum trees by PCR and ELISA
Authors: Adams  , Guise  , Crossley
Published: March 2003

An immunocapture polymerase chain reaction (IC‐PCR) protocol and ELISA were compared for their effectiveness in detecting plum pox virus (PPV) in dormant plum material. Although the IC‐PCR was about one thousand times more sensitive than ELISA, PPV was detected by ELISA in 71–80% of bark samples collected in December, January and March 1996/97 from pot‐grown rootstock trees inoculated with PPV the previous March, compared with 85–86% detection in the same samples by IC‐PCR. In similar samples from one‐year‐old shoots taken from infected branches of orchard trees, 66–81% were positive by ELISA compared with 81–87% by IC‐PCR. With bulked samples taken from the fibrous roots of the pot‐grown trees, PPV was detected in 92–100% of samples by IC‐PCR in winter compared with only 38–65% by ELISA. These results were confirmed in samples from the roots and shoots of the same trees in 1997/98. Three samples per shoot would have been sufficient to detect PPV by ELISA in 87 of the 88 infected shoots tested during the two winters. However, infected shoots are irregularly distributed in diseased trees and PCR assays of root samples offer the potential for improving the reliability of identifying trees infected with PPV.
Vegetative compatibility grouping in Fusarium oxysporum f.sp. radicis‐lycopersici from the UK, the Netherlands, Belgium and France
Authors: Katan  , Katan
Published: March 2003

The population structure of Fusarium oxysporum f.sp. radicis‐lycopersici (F.o.r.l.), the causal agent of crown and root rot disease in tomato, was studied using the vegetative compatibility grouping approach. Four vegetative compatibility groups (VCGs) were identified among 37 isolates from the UK, the Netherlands, Belgium and France. Three of these VCGs (0090, 0091, 0094) had already been described, whereas VCG 0097 was new. VCG 0094 was dominant in the UK, the Netherlands and Belgium, but not in France. The opposite was true for the cosmopolitan VCG 0091, while the cosmopolitan VCG 0090 was only found in France. Based on hyphal interactions, VCG 0094 was divided into three subgroups, each comprising isolates from at least two countries. One isolate of VCG 0094 did not belong to any of these subgroups, suggesting further variability in this VCG. Isolate FORL‐19R from France, previously assigned to VCG 0090 I, was reassigned to VCG 0090 III, a new subgroup of VCG 0090 found in Israel. FORL‐19R and additional members of its subgroup manifest cross‐VCG compatibility between VCG 0090 and VCG 0092. Along with previous studies, the multiple VCGs and subgroups found among F.o.r.l. in western Europe demonstrate a high level of genetic diversity in this pathogen.
Molecular comparisons amongst wheat bymovirus isolates from Asia, North America and Europe
Authors: Chen Jiong , Sohn  , Chen  , Lei  , Cheng  , Schulze  , Steinbiss  , Antoniw  , Adams
Published: March 2003

To study the variation between wheat bymovirus isolates and to resolve uncertainties about the identity of the virus in some countries, leaves of infected plants were obtained from nine sites in China and from one each in Italy, Germany, USA and Canada. The German isolate was obtained from rye and the Canadian isolate was the type strain of wheat spindle streak mosaic virus (WSSMV). In RT‐PCR, using primers designed from a partial sequence of a French isolate (tentatively described as WSSMV), genome fragments were obtained from the Italian and the French isolates but not from the Chinese ones. Conversely, products were consistently obtained from the Chinese isolates, but not from the Italian or French ones, when primers were designed from the sequence of a Japanese isolate of wheat yellow mosaic virus (WYMV). Nucleotide sequences were obtained from regions at or near the 3′‐terminus of RNA1 of six Chinese isolates and the four from Europe and North America, usually including the coat protein. Nucleotide and amino acid sequence comparisons demonstrated that the European and North American isolates were extremely similar and were therefore WSSMV, while the Chinese isolates were close to the Japanese isolate and were thus WYMV.
Pathogen resistance in aerial tubers of potato cultivars
Authors: Percival  , Karim  , Dixon
Published: March 2003

Increases in resistance of aerial tubers (cultivars Désirée, Epicure and King Edward) against nine pathogenic potato fungi were determined in vitro using freeze‐dried powder derived from subterranean and aerial tubers as a culture medium, and in vivo by inoculating both tuber types with the storage pathogens Fusarium sulphureum,F. solani var. coeruleum,Phoma exigua var. foveata and Polyscytalum pustulans. Significantly reduced growth rates and spore and conidiophore numbers were recorded when pathogens were cultured on freeze‐dried powder derived from aerial tubers. No effects on spore size of F. solani var. coeruleum were recorded but spore and conidiophore lengths of remaining pathogens were reduced and width increased, except for Colletotrichum coccodes, where the diameter of acervuli increased, and P. exigua var. foveata, where spore length and width were reduced. Reduced disease incidence, severity and spore numbers were recorded on aerial compared with subterranean tubers inoculated in vivo with the four storage pathogens. Spore length of P. pustulans was reduced and spore width increased, while spore length and width of P. exigua var. foveata were reduced on aerial compared with subterranean tubers inoculated with these pathogens. No effects on spore size of Fusarium spp. were recorded. Concentrations of glycoalkaloids, chlorogenic acid, calcium and magnesium were higher in aerial than in subterranean tuber tissue, which may have contributed to increased resistance and effects on size and morphology of fungal spores. The implications of using aerial tubers as an alternative technique for the production of seed potatoes and their importance to the potato industry are discussed.
Comparison of the reaction of tomato lines to infection by tomato yellow leaf curl begomovirus in Lebanon
Authors: Abou‐Jawdah  , Maalouf  , Shebaro  , Soubra
Published: March 2003

Tomato yellow leaf curl begomovirus (TYLCV), transmitted by the whitefly Bemisia tabaci, is epidemic in Africa, the Middle East and South‐East Asia. It is also reported in some European countries and the American continent. In Lebanon, it is the major limiting factor for summer and autumn production of tomato. Comparison of the nucleotide sequence in the intergenic region with other reported leaf curl viruses showed the Lebanese TYLCV isolate to be closely related to Egyptian, Israeli and Jamaican isolates (94–96% identity). However, it is not closely related to isolates from Sardinia, Spain and Thailand, or to tomato leaf curl isolates from India, Taiwan and Australia. In field and greenhouse screening tests conducted for 5 years on 67 tomato lines, several were identified as promising. TY‐Carla, PSR and RS lines were among the most promising with determinate growth, while S&G 143 and the DR lines were the most promising with semi‐determinate and indeterminate growth, respectively. Virus concentrations in most, but not all, tolerant tomato lines were significantly lower than in the susceptible lines. None of the lines tested was immune to the virus. A survey of TYLCV alternative hosts on at least 58 plant species, using nucleic acid hybridization, showed that Amaranthus sp., Malva sp., Sonchus oleraceus, Plantago sp., Solanum melongena, Phaseolus vulgaris and Mercurialis annua may play an important role in the epidemiology of TYLCV in Lebanon. Mercurialis annua is a newly reported host for TYLCV.
Sclerotinia rot losses in processing tomatoes grown under centre pivot irrigation in central Brazil
Authors: Lobo Jnr  , Lopes  , Silva
Published: March 2003

Sclerotinia rot caused by Sclerotinia sclerotiorum is one of the most important diseases of processing tomatoes in Central Brazil. Yield losses in tomato cultivars (cv.) IPA‐5 were assessed in mature plants from 1995 to 1997, and related to different disease intensities, in a naturally infested area irrigated by centre pivot. Over the 3 years, there were no differences (Tukey at 5%) in fruit numbers between plants without symptoms (NS) and with intermediate symptoms (IS), which yielded higher numbers than plants with severe symptoms (SS). The greatest reduction in fruit number was 56.8% in 1997. Significant differences were observed in fruit weight and size among NS, IS and SS plants in 1995 and 1997. In 1996, NS and IS plants were similar, but different from SS, which yielded significantly less. Weight and size reductions in SS plants reached 84.3% and 62.0%, respectively, in 1997. In 1996 and 1997, yield losses related to time of symptom appearance and physiological age were also assessed. Significant correlations were found (P < 0.01), with nearly total losses observed when plants were infected from early to mid bloom, as opposed to plants infected near harvest, which had lower disease incidence and produced economically acceptable yields. Quadratic and exponential models best fitted the relationship between yield and time of symptom appearance, and yield vs physiological age could be explained by logistic and Gompertz functions.
Differences in host range, pathogenicity to potato cultivars and response to soil temperature among Streptomyces species causing common and netted scab in France
Authors: Bouchek‐Mechiche  , Pasco  , Andrivon  , Jouan
Published: March 2003

The pathogenicity and ecology of some isolates representative of the four main Streptomyces species (S. scabies, S. europaeiscabiei, S. stelliscabiei and S. reticuliscabiei) identified as pathogenic to potato tubers were investigated. Three pathogenicity groups could be distinguished. Group 1 included all isolates of S. scabies, S. europaeiscabiei and S. stelliscabiei from common scab lesions of potato and other susceptible root crops. All these produced similar symptoms and were pathogenic to potato, carrot and radish. Group 2 included all isolates from S. reticuliscabiei netted scab lesions; they were pathogenic to both tubers and roots of only a few potato cultivars, and did not infect carrot or radish. Group 3 included three isolates of S. europaeiscabiei from netted scab lesions on cv. Bintje, which produced either common or netted scab symptoms depending on the potato cultivar or plant species. In an experiment on a few isolates from each of the three groups, held at various soil temperature regimes, the three from group 1 were most pathogenic at higher temperatures (20°C or 20/30°C), the two from group 2 were most pathogenic at a lower temperature (17°C). The group 3 isolate caused netted scab symptoms on susceptible cultivars at low temperatures (≤ 20°C) and deep‐pitted lesions at higher temperatures. Since the groups identified differ in ecological requirements, it is important to adapt the control methods to the pathogenic species present in the soil.
Phenotypic variability of Leptosphaeria lindquistii (anamorph: Phoma macdonaldii), a fungal pathogen of sunflower
Authors: Roustaee A. , Costes S. , Dechamp‐Guillaume G. , Barrault G.
Published: March 2003

Growth of 17 isolates of Phoma macdonaldii, the causal agent of sunflower black stem, was investigated for response to pH and temperature, and for morphology and asexual morphogenesis (pycnidiogenesis and pycnidium size). For all isolates, the optimum pH for growth was between 4 and 5, and the optimum temperature varied between 20 and 30°C and radial growth was slowest at 5 and 35°C. Significant differences in the number and size of pycnidia were observed between isolates. Pycniospore germination was investigated under various conditions in five isolates chosen for their geographical origins, pigmentation, optimum growth temperature and pycnidiogenesis. Increasing the concentration from 106 to 107 pycniospores per mL decreased the germination rate. The optimum temperature for pycniospore germination varied between 15 and 30°C, depending on the isolate, and the optimum and maximum pH values were 5 and 7, respectively. The optimum and minimum relative humidities allowing pycniospore germination were 100 and 95%, respectively. Pycniospore germination was photo‐independent. An artificial inoculation method was developed and the aggressiveness of the pathogen was assessed on a susceptible sunflower cultivar, using a 1–9 scale that integrated the percentage of necrotic area on the cotyledon petiole at the stage when the first pair of leaves was fully developed. Significant differences in aggressiveness were observed among the 17 isolates. The parameters investigated clearly suggest the occurrence of a wide phenotypic variability in Phoma macdonaldii.
Specific adaptation by Mycosphaerella graminicola to a resistant wheat cultivar
Authors: Cowger C. , Hoffer M. E. , Mundt C. C.
Published: March 2003

Three cultivars of winter bread wheat (Gene, Madsen and Stephens) were each inoculated as seedlings in the greenhouse with seven or eight individual isolates of Mycosphaerella graminicola collected in 1997 from each of the same cultivars in the field. Isolates collected from Gene were virulent to all three cultivars, while isolates obtained from Madsen and Stephens were virulent to those two cultivars and, in all but one case, avirulent to Gene. At its release in 1992, Gene was resistant to M. graminicola, as indicated by both field observations and greenhouse tests, but by 1995 its resistance had substantially deteriorated. This indicated that its resistance was vertical (sensu Vanderplank) or race‐specific, and that commercial cultivation of Gene rapidly selected for strains in the local M. graminicola population that were specifically adapted to overcome its resistance.
Effects of temperature on the incubation and latent periods of hawthorn powdery mildew (Podosphaera clandestina)
Authors: Xu X‐M. , Robinson J. D.
Published: March 2003

The effects of temperature on the length of the incubation and latent periods of hawthorn powdery mildew, caused byPodosphaera clandestina, were studied. At constant temperatures over the range 10–28°C, the incubation period ranged from 5 to 14 days and the latent period from 5 to 16 days; no visible colonies had developed at 30°C after 15 days. The relationships between temperature and the rates of fungus development within the incubation and latent periods were well described by a nonlinear model. The resulting curves were asymmetrically bell‐shaped with an optimum temperature of approximately 23°C. The lengths of the incubation and latent periods under fluctuating temperatures were also determined, and were used to evaluate the models developed from constant temperature experiments for their accuracy of prediction. The incubation and latent periods under fluctuating temperature regimes were predicted using a rate‐summation scheme with a time step of 24 min, by integrating the respective incubation and latent rate functions obtained under constant temperatures. The predicted incubation or latent periods agreed well with the observed values. Under constant temperature the interval between the times when symptoms and sporulation on the same leaflet were first observed was very short, on average <1 day, and was not significantly correlated with temperature. However, this interval was negatively correlated with mean temperature under fluctuating regimes.
The process of antagonism of Sclerotium cepivorum in white rot affected onion roots by Trichoderma koningii
Authors: Metcalf D. A. , Wilson C. R.
Published: March 2003

Trichoderma koningii (strain Tr5) grew in the epidermal mucilage of onion roots without entering healthy epidermal tissue. When placed on the epidermis of Sclerotium cepivorum‐infected roots, T. koningii colonized epidermal passage cells, with little colonization of other epidermal tissues, then branched and spread throughout the root cortical tissues damaged by enzymes and toxins which diffused ahead of S. cepivorum hyphae, and impeded the path of the infection. When T. koningii colonized infected tissue, many S. cepivorum hyphae became detached at septa, cell walls dissolved and many hyphal apices burst. Contact between hyphae was not necessary for lysis to occur. T. koningii produced two endochitinases (Rf 0·15 and 0·24) and two exo‐acting chitinolytic enzymes (Rf 0·46 and 0·62) during degradation of crabshell chitin and S. cepivorum cell walls. The Rf 0·24 and 0·46 proteins were detected when T. koningii colonized S. cepivorum‐infected roots and are likely to be a component of the antagonism process.
Induction of disease resistance in Norway spruce (Picea abies) by necrotizing fungi
Authors: Krokene P. , Solheim H. , Christiansen E.
Published: March 2003

Norway spruce trees (Picea abies) preinoculated with the root rot fungus Heterobasidion annosum, Nectria fuckeliana or a pathogenic strain of the blue‐stain fungus Ceratocystis polonica were more efficiently protected against a subsequent massive inoculation with pathogenic C. polonica than trees pretreated with nonpathogenic C. polonica or sterile malt agar. Control trees that received no pretreatment were extensively colonized by the mass inoculation. There was a strong negative correlation between the length of the phloem necroses induced by the pretreatment inoculations and the extent of host symptoms caused by mass inoculation with pathogenic C. polonica. The degree of induced resistance in Norway spruce thus depended on the amount of host tissue destroyed by the pretreatment.
Phenols as a biochemical basis of resistance in wheat against Karnal bunt
Authors: Gogoi Robin , Singh D. V. , Srivastava K. D.
Published: March 2003

The effects of the highly aggressive isolate KB‐2 of the Karnal bunt pathogen (Neovossia indica) on phenol metabolism, peroxidase (POX) and its isoenzymes were studied in wheat. Two resistant genotypes, HD 29 of bread wheat (Triticum aestivum) and DWL 5023 of durum wheat (T. durum), and one susceptible bread wheat, WL 711, were used. In the bread wheats, total phenols reached a maximum 2 days after inoculation (d.a.i.). In the resistant durum line, total phenols did not change significantly for 6 d.a.i., but declined significantly at 10 d.a.i. Three phenolic compounds, caffeic acid, l‐tyrosine and hydroquinone, were detected using thin‐layer chromatography. The first two were detected at all times at and after inoculation, but hydroquinone was detected only in the resistant wheats at 6 d.a.i. The activity of POX was highest at 2 d.a.i. in the two resistant wheats, but increased more slowly to a peak at 6 d.a.i. in the susceptible wheat. The number of isoenzymes of POX detected by polyacrylamide gel electrophoresis (PAGE) changed after inoculation with KB‐2. The maximum number of isoenzymes occurred at 2 d.a.i. in the two resistant wheats and at 6 d.a.i. in the susceptible wheat. Although the isoenzymes detected in seedlings were not identical to those detected in seeds, the PAGE banding patterns of seeds and seedlings were the same for the two resistant wheats. The potential use of the additional band at a relative mobility of 0·42 in seeds and 0·28 in seedlings as markers for Karnal bunt resistance is discussed.
Accounting for photosynthetic efficiency of bean leaves with rust, angular leaf spot and anthracnose to assess crop damage
Authors: Bassanezi R. B. , Amorim L. , Filho A. Bergamin , Hau B. , Berger R. D.
Published: March 2003

The relationships between the net photosynthetic rate of bean leaves and severity of rust, angular leaf spot and anthracnose were quantified at different temperatures of plant incubation, stages of disease development, and phenological stages of the crop, in two bean cultivars. Several experiments were performed in controlled environment chambers and in the field. The virtual lesion concept was used to quantify the reduction in photosynthetic efficiency of the green leaf tissue surrounding the lesions. The β parameter that expressed the ratio between areas of the virtual and visual lesions was estimated according to the model Px /P0 = (1 − x)β, where Px was the net photosynthetic rate of a leaf with severity x and P0 was the average net photosynthetic rate of healthy leaves. The β‐value was 2·17 ± 0·02 (R2 = 0·88) for rust, 3·81 ± 0·04 (R2 = 0·91) for angular leaf spot, and 7·97 ± 0·13 (R2 = 0·94) for anthracnose. For each disease, the parameter β was consistent regardless of incubation temperature, stage of disease development, bean phenological stage and bean cultivar. In addition, the relationships between bean yield and the variables of area under the disease progress curve (AUDPC), healthy leaf area index duration (HAD) and healthy leaf area index absorption (HAA), published in the literature for rust, angular leaf spot and anthracnose, were recalculated with the virtual disease severity. Bean yield was more closely related to the new variables ‘photosynthesizing leaf area index duration’ (PAD) and ‘photosynthesizing leaf area index absorption’ (PAA) than to those variables previously published, but only for diseases with a large β‐value and at high levels of disease severity.
Production of pathogenesis‐related proteins in the cauliflower (Brassica oleracea var. botrytis)–downy mildew (Peronospora parasitica) pathosystem treated with acibenzolar‐S‐methyl
Authors: Ziadi S. , Barbedette S. , Godard J. F. , Monot C. , Le Corre D. , Silué D.
Published: March 2003

Acibenzolar‐S‐methyl (ASM), a member of the benzothiadiazoles (BTH), was tested on cauliflower (Brassica oleracea var. botrytis) seedlings for its ability to induce resistance against downy mildew (Peronospora parasitica). Seven‐day‐old seedlings of the susceptible cultivar Billabong, sprayed with solutions containing 0·015 or 0·075 mg a.i. mL−1 ASM and inoculated 1–8 days later with P. parasitica, were assessed for disease 7 days after inoculation. Sporulation was reduced by 50% at the highest dose of ASM in plants inoculated 1 day later, with complete protection exhibited by plants inoculated 2 days after ASM treatment. Seedlings treated with 0·05 mg a.i. mL−1 ASM solution, inoculated 4 days later and harvested 0–7 days later, were analysed for pathogenesis‐related (PR) proteins, chitinase and β‐1,3 glucanase. ASM significantly induced β‐1,3 glucanase activity which increased with time in inoculated seedlings, as confirmed by the presence of PR‐2. Chitinase activity was not significantly induced by ASM, and the treated seedlings also did not accumulate the basic PR‐3C and the acidic PR‐3Q which both exhibit chitinase activity. Analysis of three other acidic (PR‐1C, PR‐5S, PR‐8) and one basic (PR‐6) PR proteins in the ASM‐treated seedlings showed that only PR‐1 and PR‐5 were slightly and slowly induced (4–5 days after treatment), but this induction was more pronounced after inoculation with P. parasitica.
Induction of resistance to downy mildew (Peronospora parasitica) in cauliflower by DL‐β‐amino‐n‐butanoic acid (BABA)
Authors: Silué D. , Pajot E. , Cohen Y.
Published: March 2003

Of the three isomers of aminobutyric acid, only the β isomer (BABA) was effective in inducing resistance against Peronospora parasitica, the causal agent of downy mildew, in cauliflower (Brassica oleracea var. botrytis). A single foliar spray applied to 7‐day‐old seedlings protected the plants against Peronospora parasitica for at least 15 days. Of the enantiomers (R and S), only the R was effective. Resistance was accompanied by a hypersensitive‐like reaction (necrotic spots) which was evident before inoculation. BABA was systemically effective when applied to the roots, but failed to protect cotyledons adjacent to treated ones. Unlike other chemical inducers, BABA was effective when applied several hours postinoculation. It had no effect on P. parasitica spore germination. In cauliflower seedlings, BABA did not induce the accumulation of the pathogenesis‐related protein PR‐1, PR‐2, PR‐3, PR‐5 and PR‐9. Only treated and challenged seedlings accumulated PR‐2.
Systemic spread of Plum pox virus (PPV) in Mariana plum GF 8‐1 in relation to shoot growth
Authors: Ferri M. Bodin , Costes E. , Quiot J.‐B. , Dosba F.
Published: March 2003

Infection of Prunus spp. by Plum pox virus (PPV) is characterized by an uneven distribution of the virus within the tree and branches. In order to gain a better understanding of this distribution, a method for modelling tree growth was used. PPV spread was followed within susceptible Mariana plum clone GF 8‐1 shoots for 4 months after inoculation. Shoot growth was unaffected by the presence of the virus. Symptoms appeared on leaves produced in the most actively growing parts of the shoots, i.e. at the beginning of the season. PPV was detected in leaves other than those showing symptoms. The proportion of leaves with detectable virus decreased from the zone showing symptoms, with 100% ELISA‐positive responses, to the shoot tip with no detectable virus in leaves produced between 111 and 127 days after inoculation. Furthermore, a higher proportion of positive ELISA results was obtained below the zone showing symptoms (77%) compared with 50% above. PPV was detected in 95% of the most vigorous shoots 71 days after inoculation compared with 37% of slower‐growing, later‐produced shoots.
Genetic, phenotypic and pathogenic diversity of Xanthomonas arboricola pv. corylina strains question the representative nature of the type strain
Authors: Scortichini M. , Rossi M. P. , Marchesi U.
Published: March 2003

A collection of 31 Xanthomonas arboricola pv. corylina strains isolated from Corylus maxima and C. avellana of different countries were assessed by means of repetitive PCR using ERIC, BOX and REP primer sets and analysis of whole‐cell protein extracts; pathogenicity tests to three hazelnut (C. avellana) cultivars; and some key biochemical tests. From these studies, the X. arboricola pv. corylina strains were clustered into five and three groups by repetitive PCR and protein analysis, respectively, and by using UPGMA cluster analysis, with two strains forming an outlier group to these. The groups showed a high degree of similarity. Strain membership between the groups designed by the two methods exhibited a high degree of congruence, and diversity between the groups was low. Surprisingly, the two strains originating from C. maxima, that include the type strain NCPPB 935, formed the most distinctive group. No relationship to geographic origin of the strains was evident. All strains proved pathogenic towards three different hazelnut cultivars, although the strains obtained from C. maxima did not incite any significant symptoms on buds and twigs. No other relationships between rep‐PCR and whole‐cell protein groups and pathogenicity were evident. The distinctiveness of the C. maxima strains was supported further by atypical negative gelatin liquefaction test and reduced quinate metabolism results.
In vitro inhibition of soil microorganisms by 2‐phenylethyl isothiocyanate
Authors: Smith B. J. , Kirkegaard J. A.
Published: March 2003

Isothiocyanates (ITCs) are produced by the enzymatic hydrolysis of glucosinolates in cruciferous plants and can kill fungi, oomycetes and bacteria. The effect of 2‐phenylethyl ITC (2‐PE ITC), the main ITC liberated from the roots of canola, was tested in vitro on a range of fungi, oomycetes and bacteria. Bacteria were generally more tolerant than the eukaryotic pathogens to 2‐PE ITC, although both groups showed considerable variability in response (ED90 ranging from 0·005 to 1·5 mm for eukaryotes, and from 0·33 to greater than 3·34 mm for complete inhibition of bacterial growth). While intraspecies variability was low, interspecies variability was high within some genera. Amongst the eukaryotes, Trichoderma spp. were the most tolerant to 2‐PE ITC, while other genera, including Aphanomyces, Gaeumannomyces, Phytophthora and Thielaviopsis, were very sensitive. A range of responses was exhibited by Pythium spp. and the different anastomosis groups of Rhizoctonia solani. A simple laboratory screening may be an effective way to identify candidate soilborne pathogens for control in rotation cropping systems which include a Brassica crop phase.
Identification, occurrence and pathogenicity of Rhizopycnis vagum on muskmelon in Spain
Authors: Armengol J. , Vicent A. , Martínez‐Culebras P. , Bruton B. D. , García‐Jiménez J.
Published: March 2003

Rhizopycnis vagum is a recently described coelomycetous fungus that contributes to vine decline of muskmelons in Honduras, Guatemala, Texas and California. This fungus has been associated with roots of muskmelon plants affected by vine decline in most Spanish muskmelon production areas. Isolates were collected from 1996 to 2000 and identified from their cultural and morphological characteristics and by sequencing the ITS region of the ribosomal coding nuclear DNA (rDNA) and phylogenetic analysis. A few isolates from muskmelon with growth characteristics similar to R. vagum were identified as Phoma terrestris. Watermelon, Cucurbita hybrids used as rootstocks for watermelon production, Amaranthus sp. and grapevine were also hosts for R. vagum. Based on disease reaction in muskmelon roots, the pathogenicity of 10 isolates of R. vagum from different hosts and geographical origins was verified. The fungus caused root discoloration, corky lesions, and eventually the presence of pink coloration on the roots. Rhizopycnis vagum appears to be a minor pathogen that contributes to muskmelon vine decline complex in Spain through infection of roots.
Molecular detection of Fusarium solani f. sp. glycines in soybean roots and soil
Authors: Li S. , Hartman G. L.
Published: March 2003

A polymerase chain reaction (PCR)‐based method was developed to detect DNA of Fusarium solani f. sp. glycines, the cause of soybean sudden death syndrome. Two pairs of primers, Fsg1/Fsg2 designed from the mitochondrial small subunit ribosomal RNA gene, and FsgEF1/FsgEF2 designed from the translation elongation factor 1‐α gene, produced PCR products of 438 and 237 bp, respectively. Primer specificity was tested with DNA from 82 F. solani f. sp. glycines, 55 F. solani non‐SDS isolates, 43 isolates of 17 soybean fungal pathogens and the oomycete Phytophthora sojae, and soybean. The sensitivity of primer Fsg1/Fsg2 was 10 pg while that of FsgEF1/FsgEF2 was 1 ng when using F. solani f. sp. glycines total genomic DNA or down to 103 macroconidia g−1 soil. Nested PCR increased the sensitivity of the PCR assay 1000‐fold to 10 fg using primers Fsg1/Fsg2, and 1 pg using primers FsgEF1/FsgEF2. F. solani f. sp. glycines DNA was detected in field‐grown soybean roots and soil by PCR using either single pairs of primers or the combination of two pairs of primers. The occurrence of F. solani f. sp. glycines was determined using nested PCR for 47 soil samples collected from soybean fields in 20 counties of Illinois in 1999. F. solani f. sp. glycines was detected in soil samples from all five Illinois Agricultural Statistic Districts including 100, 89, 50, 92 and 50% of the samples from East, Central, North‐east and West Districts, respectively.
Chemical Denaturation of Ovalbumin Abrogates the Induction of Oral Tolerance of Mouse Reaginic Antibody Responses
Authors: Peng  , Chang  , Lin  , Han  , Chang
Published: March 2003

The effect of chemical denaturation of ovalbumin (OVA) on the induction of oral tolerance of reaginic antibody responses was studied. Both urea‐denatured OVA (UD‐OVA) and carboxymethylated UD‐OVA (CM‐OVA) were purified by centrifugation. When compared with OVA and UD‐OVA, CM‐OVA had the least sensitizing capacity and allergenicity in IgE responses to OVA. BALB/c IgE, IgG1 and IgG antibody responses were suppressed by OVA, but not by UD‐OVA or CM‐OVA, fed prior to sensitization with OVA, UD‐OVA, or CM‐OVA in alum, respectively. The priming effect of specific IgG and IgG1 antibody responses was induced by CM‐OVA fed prior to sensitization with OVA or CM‐OVA. The proliferation of BALB/c spleen cells and their secretion of T helper type 2 (Th2) cytokines interleukin‐4 (IL‐4) and IL‐5 were also orally tolerized by OVA, but not by denatured OVA. Although denatured OVA is hypoallergenic, the present result indicates that denaturation of a soluble protein prevents the induction of oral tolerance of Th2 responses.
Comparison of Antigen‐Specific T‐Cell Responses of Tuberculosis Patients using Complex or Single Antigens of Mycobacterium tuberculosis
Authors: MUSTAFA  , AMOUDY  , WIKER  , ABAL  , RAVN  , OFTUNG  , ANDERSEN
Published: March 2003

We have screened peripheral blood mononuclear cells (PBMC) from tuberculosis (TB) patients for proliferative reactivity and interferon‐γ (IFN‐γ) secretion against a panel of purified recombinant (r) and natural (n) culture filtrate (rESAT‐6, nMPT59, nMPT64 and nMPB70) and somatic‐derived (rGroES, rPstS, rGroEL and rDnaK) antigens of Mycobacterium tuberculosis. The responses of PBMC to these defined antigens were compared with the corresponding results obtained with complex antigens, such as whole‐cell M. tuberculosis, M. tuberculosis culture filtrate (MT‐CF) and cell wall antigens, as well as the vaccine strain, Mycobacterium bovis bacillus Calmette–Guérin (BCG). In addition, M. tuberculosis and MT‐CF‐induced T‐cell lines were tested in the same assays against the panel of purified and complex antigens. The compiled data from PBMC and T‐cell lines tested for antigen‐induced proliferation and IFN‐γ secretion showed that the most frequently recognized antigen was ESAT‐6, followed by MPT59, GroES, MPB70, MPT64, DnaK, GroEL and PstS. The frequency of ESAT‐6 responders, as measured both by proliferation (18/19) and secretion of IFN‐γ (16/19) was comparable to the results obtained with whole‐cell M. tuberculosis, MT‐CF and M. bovis BCG. We also observed that most of the high responders to complex antigens recognized all of the antigens tested (covariation), demonstrating that the repertoire of human T‐cell specificities induced by natural infection is directed towards several unrelated culture filtrate as well as somatic‐derived protein antigens. In conclusion, the results obtained suggest that the cellular immune response in humans is directed against several important target antigens of M. tuberculosis and that some antigens, such as ESAT‐6, are recognized by a high number of individuals. Such antigens represent candidates to be used for development of specific diagnostic reagents or in subunit vaccines.
Signalling of Bruton's Tyrosine Kinase, Btk
Authors: MOHAMED  , NORE  , CHRISTENSSON  , SMITH
Published: March 2003

Bruton's tyrosine kinase, which is encoded by the BTK gene, is a cytoplasmic protein tyrosine kinase (PTK) crucial for B‐cell development and differentiation. It belongs to the Tec family of PTKs containing several domains that are characteristic of signalling molecules. In humans, mutations that disrupt the function of this gene lead to the classical XLA syndrome (X‐linked agammaglobulinaemia), a primary immunodeficiency mainly characterized by lack of mature B cells as well as low levels of immunoglobulins. In contrast, animal models of this disease such as the xid mice display profoundly milder XLA phenotype. BTK phosphorylation and activation in response to engagement of the B‐cell receptor (BCR) by antigen is a dynamic process whereby a variety of proteins interact with each other and recruit signalling molecules resulting in a physiological response such as B‐cell proliferation and antibody production. The main players, however, that participate in the intracellular downstream cascade have not yet been identified and are therefore under intense scrutiny in several laboratories. This review discusses certain aspects of BTK activation following receptor stimulation by agonists and how this event is translated into the biochemical signals within the cell that eventually lead to nuclear responses.
Change in the Th1/Th2 Phenotype of Memory T‐Cell Clones from Rheumatoid Arthritis Synovium
Authors: Aarvak  , Chabaud  , Källberg  , Miossec  , Natvig
Published: March 2003

The stability of established memory T helper (Th)1/Th2 cells in chronic inflammatory diseases is not clear, and a shift of the cytokine balance could control chronic inflammation. In order to study the regulation of the Th phenotype of memory T cells, polyclonal T‐cell lines and clones with a Th1, Th0 or Th2 phenotype were developed from rheumatoid synovial tissue. Th1 [interleukin (IL)‐12 + anti‐IL‐4] and Th2 (IL‐4 + anti‐IL‐12) promoting environments and IL‐2 were used to manipulate the cytokine profile. Polyclonal T‐cell lines of predominantly Th1 type could be shifted to produce Th2 cytokines, and polyclonal Th2/Th0 lines could be shifted to produce Th1 cytokines. However, this shift was due to an amplification of CD8+ T cells with a memory phenotype and a loss of the CD4+ T cells, giving Tc2 or Tc1 profiles, respectively. Th2 clones cultured repeatedly with IL‐2 switched to either a Th0 or a Th1 phenotype, while both Th1 and Th0 memory clones kept a stable phenotype. Addition of Th2‐promoting conditions strongly reduced the production of both interferon‐gamma and IL‐17, while Th1‐promoting conditions increased the production of these cytokines. These results demonstrate that RA Th2 clones readily switch, while Th1 and Th0 clones are stable. However, induction of Th2 cytokines can be obtained in polyclonal polarized memory T cells due to amplification of Tc2 cells.