bluuebunny/crossref_metadata_2025 huggingface dataset:
Lack of discontinuous gas exchange in a tracheate arthropod, Leiobunum townsendi (Arachnida, Opiliones)
Authors: Lighton John R. B.
Published: March 2003

Abstract The discontinuous gas exchange cycle, characterized by stringent spiracular control and periods of near‐zero external CO2 emission separated by ‘bursts’ of CO2 emission, has evolved independently in several taxa of tracheate arthropods. These include the hexapoda, diplopoda, and several arachnid taxa; ticks, pseudoscorpions and solphugids. This paper presents the first data on gas exchange kinetics in a harvestman (Arachnida; Opiliones). The experimental animal, Leiobunum townsendi Weed, from an arid area of the south‐western United States, displayed a metabolic rate similar to those of other arthropods at 25 °C (129 ± 22 µW). Their CO2 emission kinetics showed, when the animals were motionless, only minor variations about a mean value of 0.0217 ± 0.0037 mL/h (n = 6, mean body mass 86 mg). Expressed on an intra‐recording basis, the coefficient of variation of CO2 emission (= SD/MEAN), which is an index of short‐term gas emission fluctuations and thus of spiracular control, had a mean value of only 0.082. In contrast, the coefficient of variation of animals employing a discontinuous gas exchange cycle is > 1.5. Gas exchange in opilionids, unlike the case with most other tracheate arthropods, may therefore be dominated by simple diffusion without a prominent role for wide modulations of spiracular conductance. Contributory to this conservative spiracular control strategy may be the weak degree of tracheation in opilionids, combined with circulating haemocyanin, which acts as both a transport medium and a buffering reservoir for respiratory gas exchange.
An interval timer controls the production of sexual morphs in Myzus persicae (Homoptera: Aphididae)
Authors: Margaritopoulos John T. , Tsitsipis John A. , Prophetou‐Athanasiadou Demetra A.
Published: March 2003

Abstract The interval timer mechanism was examined in two clones of Myzus persicae (Sulzer) originating from peach in Naousa, North Greece. Overwintering eggs were collected in April 1997 and after egg hatch the morphs of progeny were recorded at LD 10 : 14 h and 17 °C until the appearance of sexuals. In one clone, observations were continued until the 21st generation after egg hatch. In addition, the production of sexual morphs was examined in two other clones originating from Lehonia, Central Greece, when apterae (wingless females) were transferred from long to short days and 17 °C in the second and eighth generation of parthenogenetic rearing after their collection from peach trees. In clones from Naousa, the first gynoparae appear and comprise 10% of alate (winged) females in the second half of the third generation after egg hatch. The percentage of gynoparae increased in each consecutive generation, reaching 100% in fifth and seventh generations in clones Nb and Na, respectively. First males appeared later than gynoparae, in fifth and sixth generation in clones Nb and Na, respectively. In clone Nb, the number of males, after their appearance in fifth generation, was relatively constant from the sixth to the ninth generation (10.8–12.3). Then a significant increase was observed in the 10th generation, thereafter remaining relatively constant until the 21st generation (18.1–19.8). A similar trend in the number of males produced was observed in clones deriving from Lehonia.
Was Hopkins right? Influence of larval and early adult experience on the olfactory response in the granary weevil Sitophilus granarius (Coleoptera, Curculionidae)
Authors: Rietdorf Katja , Steidle Johannes L. M.
Published: March 2003

Abstract The induction of olfactory preferences by larval and early adult experience for odour from wheat or maize grain was examined for the granary weevil Sitophilus granarius L. in a static four‐chamber olfactometer. Weevils were reared on either wheat or maize grain and received different early adult experience. It turned out that weevils that were reared in wheat and isolated as pupae from the kernels preferred wheat odour in the olfactometer when they emerged without any odour or in the presence of maize odour. Weevils that emerged in the presence of wheat odour preferred both wheat and maize odour. When weevils emerged normally as adults from the wheat kernel in which they developed, maize odour was avoided. In contrast, for weevils that were reared in maize no preferences were found in most experiments. Only weevils that emerged in the presence of wheat odour preferred the maize odour over the controls. These results demonstrate that host‐selection behaviour in S. granarius weevil is shaped by experience according to the Hopkins host‐selection principle or the chemical legacy hypothesis and the neo‐Hopkins principle.
Seasonal changes in xanthophyll cycle‐dependent energy dissipation in Yucca glauca Nuttall
Authors: Adams W. W. , Barker D. H.
Published: March 2003

The evergreen species Yucca glauca was characterized at the end of September and following exposure to low temperatures at the end of November. In November the diurnal pattern of xanthophyll cycle‐dependent energy dissipation was altered such that this thermal dissipation process was engaged at a high level throughout the day, whereas in September it only became engaged when leaves received direct sunlight. An analysis of the diurnal partitioning of the absorbed excitation energy into photochemistry versus thermal dissipation suggested that a smaller fraction of that energy was utilized in photochemistry and a greater fraction was dissipated thermally at the end of November compared to September. Lower ratios of Chl a/b and β‐carotene/xanthophylls both suggested a decrease in the ratio of reaction centre plus core antenna proteins compared to light‐harvesting proteins, and a lower leaf chlorophyll content suggested a decrease in light‐harvesting capacity in November versus September. Thus adjustments to the photosynthetic apparatus occurred on several levels in response to the increase in excess excitation energy that Y. glauca experienced during the onset of winter.
Rapid‐cycling CAM; an hypothetical variant of photosynthetic metabolism
Authors: Cockburn W.
Published: March 2003

The currently recognized forms of CAM photosynthesis do not represent all possible variants on the theme. It is predicted here that there may exist an undiscovered variant in which the CO2‐acquiring and CO2‐reducing phases of CAM alternate over time periods shorter (possibly much shorter) than the diel cycle. The process would occur entirely in the photoperiod and may be likened to a form of C4 photosynthesis in which the same photosynthetic cell alternates between performing the functions of a C4 mesophyll and C4 bundle sheath cell. Rapid‐cycling CAM, which would be unlikely to be detected by methods commonly used to measure photosynthesis, could provide a CO2‐concentrating mechanism in both unicellular and multicellular plants.
Sulphur accumulation and redistribution in wheat (Triticum aestivum): a study using stable sulphur isotope ratios as a tracer system
Authors: Monaghan J. M. , Scrimgeour C. M. , Stein W. M. , Zhao F. J. , Evans E. J.
Published: March 2003

Wheat plants were grown hydroponically and fed with two sulphate sources differing in stable isotope composition, one having a δ34S of 13·7‰ and the other 4·1‰. Plant sulphur (S) isotope ratios were determined using an on‐line continuous flow‐isotope ratio mass spectrometer. This method greatly simplified the procedure for the measurement of S isotope ratios, and was found to be precise for samples containing > 1 mg S g–1 dry weight. The δ34S values of plant shoots, which had been grown on a single sulphate source, were very close to the source values, suggesting little isotope fractionation during sulphate uptake and transport from roots to shoots. By changing the sulphate sources at different growth stages, it was possible to estimate S accumulation and redistribution within different plant parts. At maturity, wheat grain derived 14, 30, 6 and 50% of its S from the accumulation during the following successive growth stages: between emergence and early stem extension, between stem extension and flag leaf emergence, between flag leaf emergence and anthesis, and after anthesis, respectively. It was estimated that 39, 32 and 52% of the S present in the flag leaves, older leaves and stems, respectively, at anthesis, was exported during the postanthesis period. These results demonstrate considerable cycling of S within wheat plants, and highlight the importance of S uptake after anthesis to the accumulation of S in grain under the experimental conditions employed.
Measuring and modelling the radiation balance of a heterogeneous shrubland
Authors: Domingo F. , Villagarcía L. , Brenner A. J. , Puigdefábregas J.
Published: March 2003

The accurate quantification of the energy available for sensible and latent heat transfer from plant canopies is essential for the prediction of impacts of climate on vegetation water use and growth. Unlike agricultural fields and extensive forests of more humid zones, vegetation growing in semi‐arid climates is usually sparse creating a heterogeneous surface of shrubs, annuals and bare soil. Under these conditions many of the assumptions of the basic equations used in microclimatology, which assume a uniform vegetated surface, may be violated. It is proposed here that heterogeneous canopies may require a formulation of their energy balance that includes a measure of the canopy complexity in order to both interpret field measurements and be used in predictive models. This paper explores the need for a more complex formulation of the vegetation energy balance through a series of experiments on a sparse clumped shrubland of Retama sphaerocarpa in the Tabernas Desert, Almería, south‐east Spain. These experiments investigated the importance of the radiative properties of each surface on energy balance of soil, annuals and shrubs individually, and the surface as a whole. The study evaluated the use of the fractional vegetative cover (f) and the radiative characteristics of each surface (reflection coefficients and emissivities) for calculating net radiation partitioning between shrubs and bare soil. Results indicated that partitioning of net radiation between components could be accurately calculated from values of fractional vegetative cover, reflection coefficients and emissivities for both bare soil and plant surfaces. A sensitivity analysis showed the importance of specific radiation properties of each surface. Measurements of horizontal long‐wave fluxes between components showed that the location of a plant with respect to other plants made little difference to its long‐wave energy balance. The results also emphasized the importance of soil water content on the energy balance, through its influence on albedo and soil heat storage. This was particularly true when measurements of soil heat flux were used to measure the available energy for soil under shrubs and bare soil because of strong hysteresis cycles. These cycles were larger in the bare soil than in the substrate under shrubs.
Acid phosphomonoesterase and phytase activities of wheat (Triticum aestivum L.) roots and utilization of organic phosphorus substrates by seedlings grown in sterile culture
Authors: Richardson A. E. , Hadobas P. A. , Hayes J. E.
Published: March 2003

Wheat seedlings exhibited a differential ability to utilize P from a range of organic P substrates when grown in agar culture under sterile conditions. Plants showed limited ability to obtain P from inositol hexaphosphate (IHP), whereas other monoester substrates such as glucose 1‐phosphate (G1P), were equivalent sources of P for plant growth as compared with inorganic phosphate (Pi). Poor utilization of IHP was exemplified by significantly lower rates of dry matter accumulation and reduced P content of tissues, which were generally not significantly different to control plants that were grown in the absence of added P. The inability of wheat seedlings to obtain P from IHP was not associated with poor substrate availability but was due to either insufficient root phytase activity or inappropriate localization of phytase within root tissues. Phytase activities of 4 and 24 mU g−1 root fresh weight (FW) were determined for crude root extracts prepared from plants that were grown with either adequate P or under deficient conditions, respectively. Similar levels of phytase activity (approximately 12 mU g−1 FW) were observed in assays using intact roots, although no secreted activity was detected. By comparison, a secreted acid phosphomonoesterase activity was observed, and activities of between 466 and 1029 mU phosphomonoesterase g−1 root FW were measured for intact roots. On the basis of the differences in enzyme activity, and the observed differences in the ability of wheat seedlings to utilize G1P and IHP, it is evident that low intrinsic levels of phytase activity in wheat roots is a critical factor that limits the ability of wheat to obtain P from phytate when supplied in agar under non‐limiting conditions. This hypothesis was further supported by the observation that the ability of wheat to obtain P from IHP was significantly improved when the seedlings were inoculated with a soil bacterium (Pseudomonas sp. strain CCAR59) that possesses phytase activity.
Carbon and nitrogen deposition in expanding tissue elements of perennial ryegrass (Lolium perenne L.) leaves during non‐steady growth after defoliation
Authors: Schäufele R. , Schnyder H.
Published: March 2003

The effect of defoliation on the deposition of carbon (C) and nitrogen (N) and the contribution of reserves and current assimilates to the use of C and N in expanding leaf tissue of severely defoliated perennial ryegrass (Lolium perenne L.) was assessed with a new material element approach. This included 13C/12C‐and 15N/14N‐steady‐state labelling of all post‐defoliation assimilated C and N, analysis of tissue expansion and displacement in the growth zone, and investigation of the spatial and temporal changes in substrate and label incorporation in the expanding elements prior to and after defoliation. The relationship between elemental expansion and C deposition was not altered by defoliation, but total C deposition in the growth zone was decreased due to decreased expansion of tissue at advanced developmental stages and a shortening of the growth zone. The N deposition per unit expansion was increased following defoliation, suggesting that N supply did not limit expansion. Transition from reserve‐ to current assimilation‐derived growth was rapid (<1 d for carbohydrates and approximately 2 d for N), more rapid than suggested by label incorporation in growth zone biomass. The N deposition was highest near the leaf base, where cell division rates are greatest, whereas carbohydrate deposition was highest near the location of most active cell expansion. The contribution of reserve‐derived relative to current assimilation‐derived carbohydrates (or N) to deposition was very similar for elements at different stages of expansion
Co‐permeability of 3H‐labelled water and 14C‐labelled organic acids across isolated Prunus laurocerasus cuticles: effect of temperature on cuticular paths of diffusion
Authors: Schreiber L.
Published: March 2003

Co‐permeability of 3H‐labelled water and 14C‐labelled benzoic acid or 2,4‐dichlorophenoxyacetic acid across isolated cuticular membranes of Prunus laurocerasus L. was measured at temperatures ranging from 15 to 50 °C. The water and benzoic acid permeances were highly correlated over the whole temperature range investigated, whereas water and 2,4‐dichlorophenoxyacetic acid permeances were only correlated between 15 and 30 °C. The activation energies of cuticular permeability calculated from Arrhenius plots were 40 kJ mol−1 for water and benzoic acid and 115 kJ mol−1 for 2,4‐dichlorophenoxyacetic acid. The slopes of the Arrhenius plots of 2,4‐dichlorophenoxyacetic acid were linear between 15 and 50 °C, whereas pronounced phase transitions around 30 °C were observed for water and benzoic acid permeability. However, with isolated polymer matrix membranes, where cuticular waxes forming the transport‐limiting barrier of cuticles have been extracted, phase transitions were not observed for water and benzoic acid. It is concluded that temperatures above 30 °C caused structural changes in the transport‐limiting barrier of the cuticles leading to additional paths of diffusion for water and benzoic acid but not for 2,4‐dichlorophenoxyacetic acid.
Expression and promoter activity of the desiccation‐specific Solanum tuberosum gene, StDS2
Authors: Dóczi R. , Csanaki C. , Bánfalvi Z.
Published: March 2003

Environmental stresses induce the expression of several plant genes via multiple and cross‐talking signalling pathways. Previously it was shown that ScDS2, a gene of the wild potato species, Solanum chacoense, is highly inducible by dehydration but not by abscisic acid (ABA), the mediator of many plant stress responses. Herein it is shown that ScDS2‐related genes are present in the cultivated potato, Solanum tuberosum (StDS2) and also in the non‐tuberizing Solanum species, Solanum brevidens (SbDS2). We show that expression of StDS2 is dehydration‐specific, is not inducible by cold, heat, salt, hypoxia or oxidative stresses, and is independent of ABA. Signalling of StDS2 induction, however, is dependent on the synthesis of novel proteins because cycloheximide can block StDS2 expression. To analyse the promoter region of StDS2 a genomic library of Solanum tuberosum was established and 1140 and 498 bp regions of the StDS2 promoter were isolated. The promoter fragments were fused to the β‐glucuronidase (GUS) reporter gene and tested in transgenic potato plants. Both promoter fragments were able to induce GUS activity in response to dehydration. This result suggests that drought‐specific cis‐elements are located within 498 bp upstream to the StDS2 coding sequence.
Aetiology of Rhizoctonia in sheath blight of maize in Sichuan
Authors: Li H. R. , Wu B. C. , Yan S. Q.
Published: March 2003

Rhizoctonia isolates obtained from maize grown in commercial fields in 33 representative counties (or cities) in Sichuan province in China were characterized according to colony morphology, hyphal anastomosis and pathogenicity. Of 141 isolates, 116 were identified as R. solani, 23 as R. zeae and two as binucleate Rhizoctonia. The isolates of R. solani were assigned to four anastomosis groups (AG): AG‐1‐IA (101 isolates, accounting for 71.6% of the total), AG‐1‐IB (2, 1.4%), AG‐4 (9, 6.4%) and AG‐5 (4, 2.8%). The two isolates of binucleate Rhizoctonia belonged to AG‐K. On maize, isolates of AG‐1‐IA caused typical sheath blight symptoms. Lesions produced by isolates of AG‐4, AG‐5, AG‐1‐IB and AG‐K were darker than those of AG‐1‐IA. Rhizoctonia zeae usually caused discontinuous lesions with a dark brown margin and a brown centre on the leaf sheaths, as well as ear rot. Isolates of AG‐1‐IA were the most virulent to maize, with an average lesion length of approximately 15 cm. Isolates of R. zeae produced lesions approximately 12 cm long, while those of AG‐4, AG‐5, AG‐1‐IB and AG‐K were progressively shorter. On potato dextrose agar (PDA; pH 6.4), the minimum temperature for mycelial growth of R. zeae isolates was 14–18°C, the maximum 38–40°C and optimum 30°C. Isolates of R. zeae did not grow on PDA (28°C) at pH 2.0, the optimum for growth being pH 6.4.
Evaluation of Banksia species for response to Phytophthora infection
Authors: Tynan K. M. , Scott E. S. , Sedgley M.
Published: March 2003

Phytophthora cinnamomi was the species isolated most frequently from soil associated with dead or dying proteaceous plants in the Adelaide region of South Australia. The association of P. citricola with diseased Banksia species in South Australia is reported for the first time. The response of a range of Banksia species to inoculation with P. cinnamomi and P. citricola was assessed. P. cinnamomi was generally more pathogenic than P. citricola. Inoculation of 10‐month‐old seedlings with colonized millet seed or zoospores showed that B. hookeriana and B. ashbyi were the most susceptible of the species tested, whereas B. coccinea, B. menziesii and B. prionotes were moderately susceptible. B. ericifolia, B. serrata, B. spinulosa var. collina and B. lemanniana showed tolerance. Similarly, 2–3‐week‐old seedlings of B. ericifolia, B. serrata and B. spinulosa var. collina inoculated in vitro showed little disease 6 and 12 days after inoculation, whereas B. baueri, B. baxteri, B. coccinea and B. solandri, as well as B. hookeriana and B. ashbyi, showed severe symptoms of disease after 6 days. Results suggested that the in vitro assay may have potential in the evaluation of breeding material. Development of infection was studied microscopically in 2–3‐week‐old seedlings of B. coccinea, B. menziesii, B. serrata and B. spinulosa var. collina inoculated in vitro with zoospores of P. cinnamomi. Roots of B. coccinea and B. menziesii were colonized rapidly and root tips became necrotic within 24 h and hypocotyls by day 5. Penetration was delayed in B. spinulosa var. collina, and callose deposition was delayed in B. coccinea. Necrosis of roots of B. serrata and B. spinulosa var. collina began 3 days after inoculation but rarely extended more than half way up the root by 9 days.
Genetic and pathogenic variation of Xanthomonas axonopodis pv. manihotis in Venezuela
Authors: Verdier  , Restrepo  , Mosquera  , Duque  , Gerstl  , Laberry
Published: March 2003

DNA polymorphism and variation in virulence of Xanthomonas axonopodis pv. manihotis (Xam), the causal agent of cassava bacterial blight, were studied within a pathogen population from Venezuela. Collections were made in several fields at different sites within an edaphoclimatic zone where cassava is a major crop. DNA polymorphism was assessed by RFLP analysis, using an Xam plasmidic DNA sequence (pthB) as a probe to determine the relatedness of 91 Venezuelan isolates. A high degree of polymorphism existed among the isolates, whether collected from the same or different fields. Based on a multiple correspondence analysis, the Xam population was distributed into eight clusters and no correlation was observed between genetic diversity and geographic origin. One set of haplotype strains representing the range of variability detected in Venezuela was further characterized by another RFLP analysis using two repetitive genomic probes (pBS6 and pBS8) to establish the usefulness of these probes and their complementarity with the pthB probe. Variation for virulence was observed in the Xam Venezuelan collection by inoculating a set of cassava cultivars with 28 isolates of the pathogen, each representing a haplotype. Understanding the genetic and pathogenic variation in the pathogen population is useful for designing cassava bacterial blight management strategies.
The effect of cropping history and the role of cowpea debris in the epidemiology of cowpea scab
Authors: Mungo  , Emechebe  , Florini
Published: March 2003

The role of cowpea (Vigna unguiculata) debris as a primary source of inoculum for Sphaceloma sp., the pathogen of cowpea scab, was studied in field experiments. Three fields were selected in 1993 and three in 1994, in which cowpea had been grown 1, 2 or 3 years previously as part of a crop rotation. Polyethylene mulch was spread over the soil to prevent soil/debris splash in half of the plots. No scab symptoms were observed on the primary leaves. It took an average of 25 days for primary symptoms to be observed in each field, irrespective of mulching. Mulching had a significant effect on disease severity only in the two sites where cowpeas were last grown a year before the trial (sites 1a and 1b). In both years, interaction between time (days after sowing) and site (fields in which cowpea had been grown 1–3 years earlier) had a significant effect on disease incidence while in 1994, interaction between time, site and mulching was also significant (P < 0.05). Higher disease incidence was observed in 1994 than in 1993. In all fields, there were increases in disease incidence over time. Rain splashing may have contributed to higher disease incidence in plots without mulch. The presence of scab in the mulched plots in fields last sown to cowpea 3 years before the trial suggests that the pathogen may survive on infected cowpea debris, which acts as one of the sources of primary inoculum. Hence longer periods of crop rotation with nonhosts may be required to control the disease.
Detection of a pigeon pea witches'‐broom‐related phytoplasma in trees of Gliricidia sepium affected by little‐leaf disease in Central America
Authors: Kenyon  , Harrison  , Ashburner  , Boa  , Richardson
Published: March 2003

The polymerase chain reaction (PCR) incorporating phytoplasma‐specific ribosomal RNA primer pair P1 and P7 consistently amplified a product of expected size (1.8 kb) when template DNA for PCR was extracted from leaf and shoot samples of Gliricidia sepium from Honduras exhibiting symptoms of little‐leaf disease (LLD). Restriction fragment length polymorphism analysis (RFLP) of amplified rDNA products indicated that phytoplasmas detected in LLD‐affected G. sepium were very similar although not identical to phytoplasmas associated with pigeon pea witches'‐broom (PPWB) disease in the western Caribbean region. Phytoplasma detection in trees was enhanced by reamplification of the P1/P7‐primed PCR products with nested primers PPf1 and Tint. Nested reactions enabled additional positive detections in foliage of several G. sepium trees showing only mild or no apparent LLD symptoms. Neither rDNA RFLP nor sequence analyses of 16–23 S rRNA spacer regions revealed differences among Honduran LLD phytoplasma or between these strains and phytoplasmas detected in G. sepium with LLD‐like symptoms in El Salvador, Guatemala, and Nicaragua, indicating that closely related, possibly identical, pathogens presently affect this tree species in all four countries.
Characterization of cucumber mosaic cucumovirus isolates in Greece
Authors: Varveri  , Boutsika
Published: March 2003

Since 1990, massive cucumber mosaic cucumovirus (CMV) outbreaks of various symptomatology, especially on tomato, have been observed all over Greece. To characterize local virus populations, 40 CMV isolates of different origin and symptomatology in the field and glasshouse were examined for subgroup identification and presence of satellite RNA (satRNA). The IC‐PCR method was used to amplify part of the coat protein gene of the isolates; the products were submitted to RFLP analysis using EcoRI and MspI restriction enzymes. Most isolates gave the characteristic pattern attributed to CMV subgroup I, confirming the results obtained by serotyping with monoclonal antibodies. Some Greek isolates, however, possessed additional EcoRI and MspI sites unusual for subgroup I isolates, and the patterns obtained, especially for MspI, could be confused with those of subgroup II. These data suggest that restriction enzyme analysis of amplified PCR products used for strain characterization needs to be treated with caution, especially for viruses such as CMV showing genomic heterogeneity. IC‐PCR was also developed for satRNA amplification and the results agreed with those of molecular hybridization with a dig‐DNA probe. A satRNA was carried by 77% of the isolates.
Effect of temperature on epidemiological parameters of Puccinia lagenophorae
Authors: Kolnaar R. W. , Van Den Bosch F.
Published: March 2003

The effect of temperature on latent period and aeciospore production of Puccinia lagenophorae on Senecio vulgaris was determined in small‐scale experiments under controlled conditions. A clear effect of temperature on latent period was demonstrated. Latent period decreased exponentially with increasing temperature. Both total aeciospore production and net reproductive number increased linearly with increasing temperature in a range from 10 to 22°C. The three parameters were incorporated in models to determine the effect of temperature on epidemic development. The present study suggests an increase in the exponential growth rate, r, and the velocity of focus expansion, V, with temperature. This increase in epidemic development was caused mainly by the effect of temperature on latent period and on net reproductive number. The effect of temperature on the sporulation curve appeared to be less important.
Mapping the spread of apricot chlorotic leaf roll (ACLR) in southern France and implication of Cacopsylla pruni as a vector of European stone fruit yellows (ESFY) phytoplasmas
Authors: Jarausch W. , Danet J. L. , Labonne G. , Dosba F. , Broquaire J. M. , Saillard C. , Garnier M.
Published: March 2003

An epidemiological study on European stone fruit yellows (ESFY) phytoplasmas infecting Prunus fruit trees was carried out from 1994 to 2000 in Languedoc‐Roussillon (southern France). The spread of the disease was monitored for 7 years by visual observation of symptoms and by PCR detection of the phytoplasma in an experimental orchard planted with apricot hybrid seedlings. This indicated that aerial vectors were responsible for disease spread, and that transmission rates were low at the beginning of the spread. Seventy thousand homopteran insects were captured within and in the surroundings of highly ESFY‐infected apricot orchards, of which about 10 000 were used in PCR and nested‐PCR assays with universal ribosomal and ESFY‐specific nonribosomal primers to detect ESFY phytoplasmas. The other insects were confined in cages for trials of transmission to test plants. ESFY phytoplasmas could not be detected by PCR in any of the leafhopper species captured but could be detected in the psyllid Cacopsylla pruni caught on Prunus domestica and Prunus cerasifera rootstock suckers of apricot trees and on Prunus spinosa. Nested PCR revealed ESFY phytoplasmas in one individual of the deltocephalid Synophropsis lauri captured on an apricot tree. Transmission trials confirmed the role of Cacopsylla pruni as the ESFY phytoplasma vector in France. When apricot seedlings were used as bait plants from April to November during two consecutive years, no natural transmission could be demonstrated. However, one out of 50 apricot seedlings left for the whole year in the orchard became infected. An early spring ESFY infection is in agreement with both the natural transmission results and the life cycle of Cacopsylla pruni.
Epidemiology of a Neotropical rust (Puccinia psidii): periodical analysis of the temporal progress in a perennial host (Syzygium jambos)
Authors: Tessmann D. J. , Dianese J. C. , Miranda A. C. , Castro L. H. R.
Published: March 2003

The epidemiology of the Neotropical rust caused by Puccinia psidii in the Indian Myrtaceae Syzygium jambos (rose apple) was investigated in central Brazil. Disease severities recorded during a 12‐month period were fitted by a Fourier curve with three cyclic components or harmonics. The first, second and third harmonics accounted for 49·6, 25·9, and 1·5% of total disease measured, respectively. A highly significant linear correlation was observed between the first harmonic and the accumulated number of days having at least 6 h wetness, or a minimum of 90% relative humidity, combined with temperatures that ranged from 18 to 20°C. No significant correlation was observed between the second and third harmonics and the weather variables evaluated. Rose apple trees showed a flush of growth with new susceptible host tissue during the evaluation period, with two major outbreaks of rust of variable intensity. Host growth was fitted by a Fourier curve with two significant harmonics. The first and second harmonics accounted for 37·5 and 22·1% of total host growth measured, respectively. A highly significant negative linear correlation was observed between the first harmonic and daily maximum and minimum temperatures, rainfall, and duration of the light period. Inoculum availability was not a limiting factor for disease progress since urediniospores were present during most of the period studied. A major peak in numbers of rust spores followed the main peak of disease severity. Thus, rust epidemics on rose apple in central Brazil were shown to depend on the duration of leaf wetness in the dark, and also on night‐time temperatures during that same wetness period. This study is the first example of a periodical analysis of an epidemic in a perennial crop.
Variation for aggressiveness within and between lineages of Xanthomonas oryzae pv. oryzae
Authors: Mundt C. C. , Nieva L. P. , Vera Cruz C. M.
Published: March 2003

Isolates of Xanthomonas oryzae pv. oryzae (causal agent of bacterial blight of rice) from the Philippines representing two phylogenetic lineages, and five haplotypes within those two lineages, were evaluated for aggressiveness in two glasshouse trials. Aggressiveness was determined by clip‐inoculating leaves of a rice cultivar lacking known, effective major genes for resistance and measuring the lengths of resulting lesions. Variance components analysis indicated that 55 and 46% of the lesion length variation were genetic in origin for the first and second trials, respectively. Variation of lesion length among isolates within haplotypes was highly significant in both trials (P = 0·002 and 0·027), but the effects of lineage and haplotype within lineage were not (P = 0·08 and 0·30 for lineage and P= 0·23 and 0·07 for haplotype). These results suggest that substantial heritable variation for aggressiveness exists within Philippine populations of X. oryzae pv. oryzae. This variation appears to be more prevalent within than among known phylogenetic groups, although mean differences among phylogenetic groups may still be of significant biological importance.
Seasonal changes in susceptibility of Quercus suber to Botryosphaeria stevensii and Phytophthora cinnamomi
Authors: Luque J. , Parladé J. , Pera J.
Published: March 2003

Monthly inoculations of both intact plants and excised shoots of Quercus suber with the pathogenic species Botryosphaeria stevensii and Phytophthora cinnamomi were performed to investigate seasonal changes in susceptibility of this forest tree species in relation to environmental parameters and plant water status. Infection symptoms were mainly detected on seedlings inoculated from spring to autumn (April through October) with either pathogen. Mean canker sizes also showed a seasonal pattern, the higher values being recorded in the same period as above. Lesion lengths were significantly (P < 0·001) related to environmental minimum temperature. Mean daily minimum temperatures within the range of 5–12°C clearly inhibited lesion development of P. cinnamomi, whereas B. stevensii showed a less pronounced decrease in canker expansion at the same temperature range. In excised shoots of Q. suber inoculated monthly with B. stevensii, a negative linear relationship was found between the studied range of plant relative water content (81–91%) and canker length. In contrast, the lesions caused by P. cinnamomi were not significantly (P = 0·32) related to any seasonal change in water content. Some control measures for the diseases caused by both pathogens are discussed on the basis of the seasonal changes in host susceptibility observed in this study.
Field testing of honeybee‐dispersed Trichoderma spp. to manage sunflower head rot (Sclerotinia sclerotiorum)
Authors: Escande A. R. , Laich F. S. , Pedraza M. V.
Published: March 2003

Efficacy of Trichoderma spp. to reduce sunflower head rot caused by Sclerotinia sclerotiorum was evaluated in the field. A mixture of six isolates, including Trichoderma koningii, T. aureoviride and T. longibrachiatum, was tested in five field trials at Balcarce, Argentina. Trichoderma formulation (TF) included Trichoderma conidia and viable hyphal fragments, industrial talc and milled corn kernels. Honeybees (Apis mellifera) were used to disperse TF for six weeks from the onset of flowering. Two days after the first TF delivery, sunflower heads were inoculated with S. sclerotiorum ascospores. When 100 g TF was taken by honeybees in a 10‐h per day period, head rot incidence was significantly reduced. This approach was successful in reducing disease incidence until physiological maturity of the crop, in environments highly conducive to head‐rot development.
Effect of take‐all root infections on nitrate uptake in winter wheat
Authors: Schoeny A. , Devienne‐Barret F. , Jeuffroy M.‐H. , Lucas P.
Published: March 2003

The effect of take‐all root lesions on nitrate uptake of wheat was investigated in two experiments under controlled conditions. Plants were supplied with a nutrient solution labelled with 15N during stem elongation and flowering to assess the distribution of the isotopic tracer in the different plant organs, and particularly in root segments located on both sides of take‐all lesions. The 15N atom percentage excess measured in root segments located below lesions longer than 1 cm was reduced on average by half compared with that in healthy roots and root segments above lesions, reflecting a reduction in nitrogen uptake by these root segments. This reduction probably resulted from the invasion and breakdown of phloem vessels by the fungus hyphae, interrupting energy supply and thus the uptake process. Severely infected plants showed an increase in the uptake rate per unit of efficient root, which appeared to be a compensatory response to reduction of efficient root biomass in order to satisfy shoot nitrogen demand. However, this compensatory response was insufficient to ensure nitrogen accumulation equivalent to that of healthy plants, as reductions in nitrogen accumulated in roots and aerial parts at flowering were up to 56 and 49%, respectively, for plants with more than 50% of the root system below lesions longer than 1 cm.
Phenotypical Characterization of Cells in the Thoracic Duct of Patients with and without Systemic Inflammatory Response Syndrome and Multiple Organ Failure
Authors: Lemaire  , Van Deventer  , Van Lanschot  , Meenan  , Gouma
Published: March 2003

The subset composition and recirculation properties of the migrating lymphocyte pool in humans is largely unknown. The present study was conducted in order to phenotypically characterize cells in human thoracic duct lymph of patients under non‐inflammatory and inflammatory conditions. These data were compared with data from peripheral blood, with special emphasis on those cells homing to the gut. Thoracic duct lymph and peripheral blood contained comparable proportions of B and T lymphocytes and CD8+ cells. Thoracic duct lymph contained proportionally more CD4+ cells, more CD4+CD45RO+ that express α4β7 cells and more CD8+CD45RO+ that express α4β7, as compared to peripheral blood. These data suggest an equal recirculation rate of B and T lymphocytes; a more active recirculation of CD4+ cells compared to CD8+ cells; and a more active recirculation of memory cells to the gut as compared to other extra‐lymphoid sites in patients under non‐inflammatory conditions. Data were also obtained in patients with the system inflammatory response syndrome and multiple organ failure. Although it is generally assumed that granulocytes and monocytes do not recirculate, lymph of multiple organ failure patients contained significantly more granulocytes than monocytes, indicating that in severe generalized inflammatory states these cells re‐enter the circulation through the thoracic duct. Furthermore, no increased activation of cells homing to the gut was found in these patients.
Targeted Disruption of the Murine Gene Coding for the Third Complement Component (C3)
Authors: Pekna  , Hietala  , Rosklint  , Betsholtz  , Pekny
Published: March 2003

Complement is a system of more than 30 proteins found both in plasma and on cell membranes. The complement system has several important functions in the immune response including initiation of inflammation, neutralization and elimination of pathogens, regulation of antibody responses, clearance of immune complexes and disruption of cell membranes. Under certain conditions complement may, however, act as a mediator of deleterious inflammatory reactions and complement activation has been implicated in the pathogenesis of autoimmune disorders, atherosclerosis, neurodegenerative diseases, bioincompatibility reactions and decompression sickness. Using gene targeting, we have generated mice deficient for the third complement component (C3). These mice represent an animal model in which complement activation by any pathway is prevented at an early stage. The C3‐deficient mice should be valuable for the study of the roles of the complement system in vivo in a variety of physiological and pathological situations.
Characterization of Local Memory Cells in Stage‐Classified Pulmonary Tuberculosis: Preliminary Observations
Authors: Urdaneta  , Feo‐Figarella  , Montalvo  , Tálamo  , Castillo  , Carrasco  , Rivera  , Blanca  , Machado  , Echeverría De Pérez  , De Sanctis  , Bianco
Published: March 2003

Immunophenotype analysis and proliferative responses were investigated in bronchoalveolar lavage (BAL) cells from 21 patients with stage‐classified tuberculosis: six with localized pulmonary infiltrate (LPI); seven with diffuse pulmonary infiltrate (DPI); and eight with pleural effusions (PE). Bronchoalveolar lavage cells from these patients contained a high number of cells/ml. The macrophage number was significantly lower in the DPI group (P < 0.05) compared to the LPI or PE groups. Conversely, neutrophils were markedly increased in DPI patients compared to LPI (P < 0.01) and PE (P < 0.01) patients. Lymphocyte infiltration (97.7 ± 2.3% CD3+, > 83% αβ+ and CD4+ > CD8+) was observed in the three groups. A significant increase in the number of total lymphocytes (P < 0.01) and CD4+ cells (P < 0.05) was observed in the LPI group compared to the PE group. In the LPI group CD4+ CD45RO+ cell infiltration was higher than CD4+ CD45RA+ cells (P < 0.001), contrasting to similar numbers of these subpopulations in the DPI group. Lymphocytes from three out of three LPI patients (αβ+ CD4+ CD45RO+) responded against tuberculin purified protein derivative contrasting to the unresponsiveness of five patients with either DPI or PE. This impaired response was reverted in two out of five patients by using peripheral blood monocytes instead of alveolar macrophages. It is suggested that, in humans, αβCD4+CD45RO cells are the main lymphocyte type involved in the initial local cell‐mediated immune response against Mycobacterium tuberculosis.
Immunological Characterization of α Antigen of Mycobacterium kansasii: B‐Cell Epitope Mapping
Authors: Naito  , Ohara  , Matsumoto  , Yamada
Published: March 2003

Mapping of B‐cell epitopes on α antigen of Mycobacterium kansasii (K‐α) was carried out by using recombinant truncated K‐α fusion peptides. We observed that two immunodominant B‐cell epitopes (amino acids 222–268 and 267–306) and one minor epitope (amino acid 249–286) were located in the C‐terminal region of K‐α. The other three minor B‐cell epitopes were mapped in N‐terminal (amino acids 80–98 and 99–166) and central (amino acid 174–204) regions of K‐α. All defined epitopes were common to Mycobacterium tuberculosis and M. kansasii. Besides these common epitopes, a region in K‐α (amino acid 290–319) revealed different reactivities between antibodies against K‐α and α antigen of M. tuberculosis. These findings may provide a basis for development of serodiagnosis that can distinguish between M. kansasii and M. tuberculosis infections.
Increased Frequencies of Allergen‐Induced Interleukin‐13‐Producing Cells in Atopic Individuals During the Pollen Season
Authors: Gabrielsson  , Söderlund  , Paulie  , Rak  , Van Der Pouw Kraan  , Troye‐Blomberg
Published: March 2003

We have reported previously that allergen‐specific serum IgE levels were correlated with allergen‐induced interleukin (IL)‐4 in type I allergic individuals. Here, we wanted to investigate whether IL‐13, another switch factor for IgE, was induced by allergen in vitro and if so, whether this was correlated with the elevated serum IgE‐levels seen in atopic individuals, and whether the cytokine profile changed during pollen season. Peripheral blood mononuclear cells from 14 atopic and 14 healthy individuals collected out of the pollen season were incubated in vitro with allergens (birch or timothy) and the number of IL‐4, IL‐13, IL‐10 and IFN‐γ producing cells was determined by ELISPOT. In response to the specific allergen, IL‐13‐producing cells were seen in allergic but not in healthy individuals. The number of IL‐13‐producing cells was significantly correlated with the allergen‐specific serum IgE levels. When the allergic individuals were tested during the pollen season, the number of allergen‐specific IL‐4‐ and IL‐13‐producing cells, as well as serum levels of specific IgE, increased. The IL‐13 increase seen in ELISPOT was confirmed by a RT–PCR assay. No seasonal changes were seen in response to purified protein derivative (PPD) or the mitogen PHA. During the pollen season, the IL‐4 and IL‐13 responses were highly correlated. Taken together, our results support the roles of both IL‐13 and IL‐4 in the regulation of allergen‐specific IgE levels in atopic individuals.
Biological Properties of Interferon‐α Produced Ex Vivo by Whole Blood of Patients Infected by Human Immunodeficiency Virus‐1
Authors: CHEHADEH  , HOBER  , CHIEUX  , ALM  , HARVEY  , LION  , MOUTON  , WATTRÉ
Published: March 2003

We investigated the biological properties of interferon (IFN)‐α produced by Sendai virus (SV)‐activated whole blood cultures in 20 patients infected with human immunodeficiency virus (HIV)‐1 and 24 healthy controls. Supernatants of cultures were assayed for IFN‐α by using an immunological method (DELFIA), biological methods and an in‐vitro MxA induction assay. The levels of intracellular MxA protein were detected by an immunochemiluminescence assay. The levels of IFN‐α in patients measured by DELFIA were significantly lower than those in healthy controls (P < 0.0001), but the antiviral activity of IFN‐α in patients infected with HIV‐1 was lower than predicted from DELFIA. The IFN‐α produced by cells of patients infected with HIV‐1 was able to induce MxA protein in human amnions WISH cells but was unable to protect these cells against Vesicular Stomatitis Virus (VSV)‐induced cytopathic effects. A relative increased capability to induce the production of MxA protein in vitro was observed with the IFN‐α contained in culture supernatant of virus‐activated whole blood of HIV‐1‐infected patients with increased levels of MxA in their peripheral blood. These data suggest that biological properties of IFN‐α produced in the course of HIV‐1 infection are different from those observed with IFN‐α of healthy subjects.
Strain‐Specific Variations in the Development of Dendritic Cells in Murine Bone‐Marrow Cultures
Authors: Petersen  , Toldbod  , Holtz  , Hokland  , Bolund  , Agger
Published: March 2003

The dendritic cell (DC) is a professional antigen‐presenting cell of central importance in immunity. In this paper, we examined DCs generated by 11‐day culture of bone‐marrow cells from the four mouse strains C57BL/6J, BALB/cA, C3H/HeN and B10.PL‐H2u (73NS)/Sn with respect to cell yield as well as surface‐marker phenotype and morphology. We also investigated the phenotypic changes and the T‐cell stimulatory activity of the DCs induced by bacterial lipopolysaccharide (LPS). Morphologically, we observed low levels (5–10%) of granulocyte contamination of the cultures after a culture period of 11 days. Considerable strain‐specific differences were found in the expression levels of the surface markers in addition to the differences in the ratio of the immature to mature DCs in the cultures that were not stimulated with LPS. Furthermore, we found that LPS strongly induces maturation of DCs in all strains investigated with the exception of the B10.PL strain.