bluuebunny/crossref_metadata_2025 huggingface dataset:
Memories of winter: vernalization and the competence to flower
Authors: Michaels S. D. , Amasino R. M.
Published: March 2003

The promotion of flowering in response to a prolonged exposure to cold temperatures (i.e. winter) is a useful adaptation for plant species that flower in the spring. This promotion is known as vernalization and results in a permanent memory of cold exposure. While the physiology of vernalization has been extensively studied in many species, the molecular mechanism of vernalization remains largely unknown. Recent studies, however, have revealed some of the molecular events that create the requirement for vernalization. In Arabidopsis, naturally occurring late‐flowering ecotypes and plants containing late‐flowering mutations in the autonomous floral‐promotion pathway are relatively late flowering unless cold treated. The vernalization requirement of these late‐flowering ecotypes and autonomous‐pathway mutants is largely created by an upregulation of the floral inhibitor FLOWERING LOCUS C (FLC). After cold treatment, as imbibed seeds or young seedlings, FLC transcript levels are downregulated and remain low for the remainder of the plant's life, but return to high levels in the next generation. Plants containing a constitutively expressed 35S:FLC construct remain late flowering after cold treatment, indicating that FLC levels must be downregulated for vernalization to be effective. Thus the epigenetic downregulation of FLC appears to be a major target of the vernalization pathway and provides a molecular marker of the vernalized state.
Data analysis in plant physiology: are we missing the reality?
Authors: Amzallag G. N.
Published: March 2003

In plant physiology, data analysis is based on the comparison of mean values. In this perspective, variability around the mean value has no significance per se, but only for estimating statistical significance of the difference between two mean values. Another approach to variability is proposed here, derived from the difference between redundant and deterministic patterns of regulation in their capacity to buffer noise. From this point of view, analysis of variability enables the investigation of the level of redundancy of a regulation pattern, and even allows us to study its modifications. As an example, this method is used to investigate the effect of brassinosteroids (BSs) during vegetative growth in Sorghum bicolor. It is shown that, at physiological concentrations, BSs modulate the network of regulation without affecting the mean value. Thus, it is concluded that the physiological effect of BSs cannot be revealed by comparison of mean values. This example illustrates how a part of the reality (in this case, the most relevant one) is hidden by the classical methods of comparison between mean values. The proposed tools of analysis open new perspectives in understanding plant development and the non‐linear processes involved in its regulation. They also ask for a redefinition of fundamental concepts in physiology, such as growth regulator, optimality, stress and adaptation.
Nutrient transfer from soil nematodes to plants: a direct pathway provided by the mycorrhizal mycelial network
Authors: Perez‐Moreno J. , Read D. J.
Published: March 2003

A pathway for the transfer of nutrients from dead nematodes to mycorrhizal plants is described for the first time. Plants of Betula pendula were grown in transparent microcosms in the mycorrhizal (M) or non‐mycorrhizal (NM) condition, either with or without nematode necromass of known nitrogen (N) and phosphorus (P) contents as the major potential source of these elements. Plants colonized by the mycorrhizal fungus Paxillus involutus produced greater yields and had larger N and P contents in the presence of nematodes than did their NM counterparts. The symbiotic systems were shown to exploit the N and P originally contained in necromass more effectively, and to transfer the nutrients to the plants in quantities approximately double those seen in NM systems. Even so, NM plants obtained sufficient N and P from dead nematodes to enable some enhancement of growth. Our observations confirm that mycorrhizal fungi provide the potential for the recycling of nutrients contained in this quantitatively important component of the soil mesofauna and demonstrate that the symbiotic pathway is considerably more effective than that provided by saprotrophs alone. The consequences of this nutrient transfer pathway for nutrient recycling in temperate forest ecosystems are considered.
Spectral dependence of flavonol and betacyanin accumulation in Mesembryanthemum crystallinum under enhanced ultraviolet radiation
Authors: Ibdah M. , Krins A. , Seidlitz H. K. , Heller W. , Strack D. , Vogt T.
Published: March 2003

Mesembryanthemum crystallinum L. (Aizoaceae) is a drought‐ and salt‐tolerant halophyte that is able to endure harsh environmental conditions. Upon irradiation with high light irradiance (1200–1500 µmol m−2 s−1) it displays a rapid cell‐specific accumulation of plant secondary metabolites in the upper leaf epidermis; a phenomenon that is not detectable with salt or drought treatment. The accumulation of these compounds, the betacyanins and acylated flavonol glycosides, increases if the plants are exposed to polychromatic radiation with a progressively decreasing short‐wave cut‐off in the ultraviolet range. The response is localized in the epidermal bladder cells on the tips of young leaves and epidermal layers of fully expanded leaves. It is demonstrated that the accumulation of flavonols and betacyanins can be described by a weakly sigmoid dose function in combination with an exponential decrease of the response function of the plant with increasing wavelength.
Modelling the limits on the response of net carbon exchange to fertilization in a south‐eastern pine forest
Authors: Lai C.‐T. , Katul G. , Butnor J. , Siqueira M. , Ellsworth D. , Maier C. , Johnsen K. , Mckeand S. , Oren R.
Published: March 2003

Using a combination of model simulations and detailed measurements at a hierarchy of scales conducted at a sandhills forest site, the effect of fertilization on net ecosystem exchange (NEE) and its components in 6‐year‐oldPinus taedastands was quantified. The detailed measurements, collected over a 20‐d period in September and October, included gas exchange and eddy covariance fluxes, sampled for a 10‐d period each at the fertilized stand and at the control stand. Respiration from the forest floor and above‐ground biomass was measured using chambers during the experiment. Fertilization doubled leaf area index (LAI) and increased leaf carboxylation capacity by 20%. However, this increase in total LAI translated into an increase of only 25% in modelled sunlit LAI and in canopy photosynthesis. It is shown that the same climatic and environmental conditions that enhance photosynthesis in the September and October periods also cause an increase in respiration The increases in respiration counterbalanced photosynthesis and resulted in negligibleNEEdifferences between fertilized and control stands. The fact that total biomass of the fertilized stand exceeded 2·5 times that of the control, suggests that the counteracting effects cannot persist throughout the year. In fact, modelled annual carbon balance showed that gross primary productivity (GPP) increased by about 50% and that the largest enhancement inNEEoccurred in the spring and autumn, during which cooler temperatures reduced respiration more than photosynthesis. The modelled difference in annualNEEbetween fertilized  and  control  stands  (approximately  200 1;g 2;C 3;m−2y−1)  suggest that the effect of fertilization was sufficiently large to transform the stand from a net terrestrial carbon source to a net sink.
The role of CAM in high rainfall cloud forests: an in situ comparison of photosynthetic pathways in Bromeliaceae
Authors: Pierce S. , Winter K. , Griffiths H.
Published: March 2003

Crassulacean acid metabolism (CAM), an advanced photosynthetic pathway conferring water conservation to plants in arid habitats, has enigmatically been reported in some species restricted to extremely wet tropical forests. Of these, epiphytic Bromeliaceae may possess absorbent foliar trichomes that hinder gas‐exchange when wetted, imposing further limitations on carbon dioxide (CO2) uptake. The hypothesis that the metabolic plasticity inherent to CAM confers an ecological advantage over conventional C3 plants, when constant rainfall and mist might inhibit gas‐exchange was investigated. Gas‐exchange, fluorometry and organic acid and mineral nutrient contents were compared for the bromeliads Aechmea dactylina (CAM) and Werauhia capitata (C3) in situ at the Cerro Jefe cloud forest, Panama (annual rainfall >  4 m). Daily carbon gain and photosynthetic nutrient use efficiencies were consistently higher for A. dactylina, due to a greater CO2 uptake period, recycling of CO2 from respiration and a dynamic response of CO2 uptake to wetting of leaf surfaces. During the dry season CAM also had water conserving and photoprotective roles. A paucity of CAM species at Cerro Jefe suggests a recent radiation of this photosynthetic pathway into the wet cloud forest, with CAM extending diversity in form and function for epiphytes.
Seasonal and diurnal variations in gene expression in the desert legume Retama raetam
Authors: MERQUIOL E. , PNUELI L. , COHEN M. , SIMOVITCH M. , RACHMILEVITCH S. , GOLOUBINOFF P. , KAPLAN A. , MITTLER R.
Published: March 2003

Studying plants growing naturally within their habitat can contribute greatly to our understanding of molecular and biochemical processes involved in the response of plants to changes in environmental conditions. Seasonal and diurnal variations in the expression of several transcripts involved in the defence of plants against abiotic stresses, i.e. transcripts encoding dehydrins, heat shock proteins, and antioxidative enzymes, were followed in Retama raetam plants that grow naturally within an arid dune ecosystem. These were associated with changes in environmental parameters simultaneously recorded at the research sites. It was found that the expression pattern of some transcripts correlated with changes in environmental conditions in the different plants during the year. In contrast, the expression pattern of other transcripts appeared to be plant specific and may be associated with phenotypic variability (plasticity). Transcripts encoding different heat shock proteins were induced in a co‐ordinated manner, suggesting that their corresponding products function as a chaperone network. Measurements of photosynthetic activity revealed a diurnal cycle in R. raetam. Photosynthesis was highest during early morning, declined toward the stressful midday hours and recovered at late afternoon. The present analysis suggests that R. raetam uses a combination of different avoidance strategies in co‐ordination with active defence mechanisms to withstand the stressful conditions that prevail within the desert ecosystem.
Response of in vitro pollen germination and pollen tube growth of groundnut (Arachis hypogaea L.) genotypes to temperature
Authors: KAKANI V. G. , PRASAD P. V. V. , CRAUFURD P. Q. , WHEELER T. R.
Published: March 2003

Air temperatures of greater than 35 °C are frequently encountered in groundnut‐growing regions, especially in the semi‐arid tropics. Such extreme temperatures are likely to increase in frequency under future predicted climates. High air temperatures result in failure of peg and pod set due to lower pollen viability. The response of pollen germination and pollen tube growth to temperature was quantified in order to identify differences in pollen tolerance to temperature among 21 groundnut genotypes. Plants were grown from sowing to harvest in a poly‐tunnel under an optimum temperature of 28/22 °C (day/night). Pollen was collected at anther dehiscence and was exposed to temperatures from 10° to 47·5 °C at 2·5 °C intervals. The results showed that a modified bilinear model most accurately described the response to temperature of percentage pollen germination and maximum pollen tube length. Genotypes were found to range from most tolerant to most susceptible based on both pollen characters and membrane thermostability. Mean cardinal temperatures (Tmin, Topt and Tmax) averaged over 21 genotypes were 14·1, 30·1 and 43·0 °C for percentage pollen germination and 14·6, 34·4 and 43·4 °C for maximum pollen tube length. The genotypes 55‐437, ICG 1236, TMV 2 and ICGS 11 can be grouped as tolerant to high temperature and genotypes Kadiri 3, ICGV 92116 and ICGV 92118 as susceptible genotypes, based on the cardinal temperatures. The principal component analysis identified maximum percentage pollen germination and pollen tube length of the genotypes, and Tmax for the two processes as the most important pollen parameters in describing a genotypic tolerance to high temperature. The Tmin and Topt for pollen germination and tube growth, rate of pollen tube growth were less predictive in discriminating genotypes for high temperature tolerance. Genotypic differences in heat tolerance‐based on pollen response were poorly related (R2 = 0·334, P = 0·006) to relative injury as determined by membrane thermostability.
Relative enhancement of photosynthesis and growth at elevated CO2 is greater under sunflecks than uniform irradiance in a tropical rain forest tree seedling
Authors: LEAKEY A. D. B. , PRESS M. C. , SCHOLES J. D. , WATLING J. R.
Published: March 2003

The survivorship of dipterocarp seedlings in the deeply shaded understorey of South‐east Asian rain forests is limited by their ability to maintain a positive carbon balance. Photosynthesis during sunflecks is an important component of carbon gain. To investigate the effect of elevated CO2 upon photosynthesis and growth under sunflecks, seedlings of Shorealeprosula were grown in controlled environment conditions at ambient or elevated CO2. Equal total daily photon flux density (PFD) (∼7·7 mol m−2 d−1) was supplied as either uniform irradiance (∼170 µmol m−2 s−1) or shade/fleck sequences (∼30 µmol m−2 s−1/∼525 µmol m−2 s−1). Photosynthesis and growth were enhanced by elevated CO2 treatments but lower under flecked irradiance treatments. Acclimation of photosynthetic capacity occurred in response to elevated CO2 but not flecked irradiance. Importantly, the relative enhancement effects of elevated CO2 were greater under sunflecks (growth 60%, carbon gain 89%) compared with uniform irradiance (growth 25%, carbon gain 59%). This was driven by two factors: (1) greater efficiency of dynamic photosynthesis (photosynthetic induction gain and loss, post‐irradiance gas exchange); and (2) photosynthetic enhancement being greatest at very low PFD. This allowed improved carbon gain during both clusters of lightflecks (73%) and intervening periods of deep shade (99%). The relatively greater enhancement of growth and photosynthesis at elevated CO2 under sunflecks has important potential consequences for seedling regeneration processes and hence forest structure and composition.
Characterization of Pseudomonas syringae ssp. savastanoi strains isolated from ash
Authors: Iacobellis N. S. , Caponero A. , Evidente A.
Published: March 2003

Isolates of Pseudomonas syringae ssp. savastanoi from ash were examined for their ability to produce phytohormones in culture and for pathogenicity, in comparison with isolates from olive and oleander. Nineteen out of 20 ash isolates produced low levels of indole‐3‐acetic acid and its methyl ester but no cytokinins. In contrast, the remaining isolate, NCPPB3474, accumulated high levels of auxins and cytokinins in culture, comparable to those of olive and oleander strains. Hybridization of DNA preparations with tryptophan mono‐oxygenase (iaaM) and isopentenyl transferase (ipt) gene‐containing probes showed sequences of DNA homologous to both probes only in isolate NCPPB3474, and in which the iaaM and ipt genes were located on the chromosome and on a plasmid of about 80 kb, respectively. When assayed for pathogenicity on ash, olive and oleander, 19 of the 20 ash isolates caused disease only on ash but NCPPB3474 caused knots on both ash and olive. Oleander isolates infected all three hosts whereas those from olive caused symptoms only on olive and ash. All the cultures were able to multiply in host plant tissues, but the growth rates and final population densities were correlated to the plant species inoculated and the host origin of the isolates. In particular, the highest population densities were reached by isolates capable of causing symptoms on the inoculated host. The phytohormone production shown by ash, olive and oleander isolates of P. syringae ssp. savastanoi was in accordance with the type of symptoms: cankers accompanied by wart‐like excrescences on ash and knots on olive and oleander. Furthermore, the pathogenic features of these isolates and, in particular, their growth patterns in the different host tissues, support previous evidence on the existence of three distinct pathovars in P. syringae ssp. savastanoi.
Allelism of rice blast resistance genes in two Chinese rice cultivars, and identification of two new resistance genes
Authors: Pan Q. , Wang L. , Tanisaka T. , Ikehashi H.
Published: March 2003

Blast, caused by Pyricularia grisea, is a major constraint on rice production. To broaden genetic diversity for resistance to this disease, two rice cultivars, GA20 and GA25 from Yunnan Province, China, were analysed for the genetic basis of their high resistance to blast. GA20 was crossed with 10 Japanese differential cultivars, and GA25 was crossed with nine of them and with the susceptible Chinese cultivar Lijiangxintuanheigu (LTH). The resistance of GA20 was governed by two dominant genes allelic to genes at the Pi‐k and Pi‐ta loci. The allele at the Pi‐k locus was new, based on a reaction pattern different from known alleles at this locus. It could not be shown whether or not the allele at the Pi‐ta locus is new, because races with virulence for Pi‐ta were not tested. GA25 has one resistance gene, which is not allelic to genes at the loci Pi‐a, Pi‐k, Pi‐z, Pi‐ta, Pi‐b, and Pi‐t, but is linked to the Pi‐i gene on chromosome 9 with a recombination frequency of 15.1 ± 2.8%.

The new allele at the Pi‐k locus in GA20 is designated as Pi‐kg(t), and the new resistance gene in GA25 as Pi15(t).
Sclerotial formation and strand growth of Phymatotrichopsis omnivora in minirhizotrons planted with cotton at different soil water potentials
Authors: Kenerley C. M. , White T. L. , Jeger M. J. , Gerik T. J.
Published: March 2003

In situ strand growth and sclerotium formation of Phymatotrichopsis omnivora were observed in minirhizotrons using a microvideo camera. Strand growth was greater in soils subject to decreasing levels of soil matric potential (high water stress) compared with a continuously wet treatment. Intermediate levels of water stress (−0.5 to −0.9 MPa) resulted in less strand growth than either the dry or wet treatments. In all treatments strand growth increased to a maximum within 10 days of inoculum placement in soil but then declined to approach an apparent steady‐state value. The effects of soil matric potential on sclerotium formation were apparent when barley seeds were sown in the experimental units 3 weeks after the experiment had begun, permitting differential water cycling patterns to be obtained. Sclerotia were recovered in larger numbers from experimental units in which high water potentials (> −0.2 MPa) occurred 2 weeks prior to and following the death of host plants.
Distribution and incidence of faba bean necrotic yellows virus in Jordan
Authors: Al‐Nsour A. , Mansour A. , Al‐Musa A. , Salem N.
Published: March 2003

Faba bean necrotic yellows virus (FBNYV) was isolated from naturally infected faba bean plants in Jordan. The identification was based on host range, mode of transmission, symptomatology and serological properties. FBNYV occurred naturally in several leguminous crops including cultivated legumes and wild forage legumes, such as species of Medicago, Trifolium and Lathyrus. and infected other plant species belonging to the Malvaceae, such as Malva parviflora and Hibiscus esculentus. Such hosts may act as important natural reservoirs for both the virus and its aphid vectors. This is the first report of infection of M. parviflora and H. esculentus with FBNYV. The virus was not recovered from samples taken from some cultivated crops, including squash, cucumber, tomato, eggplant and pepper, growing near to faba bean fields. Also, it was not detected in commercial faba bean seeds collected from local companies or in seeds collected from infected faba bean plants. It was transmitted efficiently by Aphis craccivora. Serological testing of 1392 samples from faba beans showing virus‐like symptoms and collected randomly from 16 locations (fields) in the Jordan Valley and Jarash areas showed that FBNYV occurred in 54.5% of the samples. These results indicate that FBNYV was an important pathogen of beans during the growing season of 1996 in Jordan.
Vegetative compatibility, biosynthesis of GA3 and virulence of Fusarium moniliforme isolates from bakanae disease of rice
Authors: Sunder  , Satyavir
Published: March 2003

Twenty‐eight isolates of Fusarium moniliforme were established from bakanae‐infected rice plants of a range of cultivars collected from various localities in Haryana, India. They were characterized by vegetative compatibility, virulence pattern on five paddy cultivars, and biosynthesis of gibberellins and were assigned to 10 vegetative compatibility groups (VCGs). Isolates from different VCGs and also within the same VCG varied considerably in virulence and GA3 production. The 28 isolates were categorized into five gibberellic acid production groups (GPG‐I–GPG‐V) and five virulence groups (VG‐I–VG‐V). Vegetative compatibility was independent of pathogenicity and of ability to produce GA3. However, GA3 production was positively correlated (r = 0.731) with pathogenic behaviour.
Protection of cucumber against Pythium root rot by fluorescent pseudomonads: predominant role of induced resistance over siderophores and antibiosis
Authors: Ongena  , Daayf  , Jacques  , Thonart  , Benhamou  , Paulitz  , Cornélis  , Koedam  , Bélanger
Published: March 2003

Four Pseudomonas strains were evaluated for their intrinsic properties conferring their ability to protect long English cucumber against Pythium aphanidermatum in hydroponic culture. Two of the strains, BTP1 and its siderophore‐negative mutant M3, increased plant yield as compared with the non‐inoculated control plants. Strain BTP7 was intermediate in its biocontrol activity while strain ATCC 17400 failed to reduce disease development. The role of pyoverdines could not be confirmed since treatment with either BTP1 or its siderophore‐negative mutant M3 provided similar suppression of Pythium disease. In addition, no siderophores were detected in the nutrient solution. BTP1 did not inhibit pathogen growth in vitro on several media, suggesting that antibiosis was not a mechanism of suppression. Quantification of root bacterial populations did not indicate differences among the strains. On the other hand, roots treated with either BTP1 or its sid− mutant M3 contained more antifungal phenolics than roots from any other treatments including controls. These results suggest that antifungal compounds induced by inoculation of cucumber roots with the fluorescent Pseudomonas strains BTP1 and M3 participate actively in the protection of cucumber plants against P. aphanidermatum
RAPD and rep PCR‐based fingerprinting of vascular bacterial pathogens of Musa spp.
Authors: Thwaites  , Mansfield  , Eden‐Green  , Seal
Published: March 2003

Polymerase chain reaction (PCR) amplification with random decamer primers, and primers targeted to conserved repetitive sequences were used to investigate the genetic relationship between strains of Ralstonia solanacearum that cause the ‘moko’ and ‘bugtok’ vascular wilt diseases of banana and plantain (Musa spp.). The closely related bacteria R. pickettii, Pseudomonas syzygii and the banana blood disease bacterium were also included in this study. Data from several PCR fingerprints were collated by cluster analysis and principal coordinate analysis. Random Amplified Polymorphic DNA (RAPD) analysis divided the isolates into three groups. Group 1 contained a subset of Central American R. solanacearum moko strains. Group 2 consisted of the blood disease bacterium, P. syzygii and some R. solanacearum isolates from clove trees whilst group 3 comprised South‐east Asian moko and bugtok isolates as well as another subset of Central American moko strains. Fingerprinting by PCR amplification with repetitive primers (rep‐PCR) produced groupings broadly concurrent with those obtained from RAPDs. Both sets of groupings supported previous subdivisions made within R. solanacearum on the basis of tRNA fingerprints and 16 S rRNA sequences, and the data lend support to the renewed description of the blood disease bacterium either as a separate species or as a subspecies within R. solanacearum.
Cultural, molecular and pathogenic variability of Mycosphaerella pinodes and Phoma medicaginis var. pinodella isolates from dried pea (Pisum sativum) in France
Authors: Onfroy  , Tivoli  , Corbière  , Bouznad
Published: March 2003

The characteristics of 50 isolates of Mycosphaerella pinodes and 17 isolates of Phoma medicaginis var. pinodella, originating from several regions of France where ascochyta blight is prevalent, were investigated using cultural, physiological, molecular and pathogenicity analyses. M. pinodes was distinguished from P. medicaginis var. pinodella on the basis of presence of pseudothecia, a higher proportion of larger, bicellular conidia, compared with the smaller, predominantly unicellular conidia of P. medicaginis var. pinodella, and a slower linear growth rate on agar under a 12‐h light regime. RAPD analysis clearly distinguished the two species, which had low intraspecific variability. Although both species gave identical symptoms, they could be distinguished by their incubation period and aggressiveness, respectively, shorter and higher for M. pinodes. Virulence tests gave no definitive evidence for the existence of pathotypes among the M. pinodes isolates. Two unidentified isolates had similar characters to both M. pinodes and P. medicaginis var. pinodella in some features but were distinguished from them by their RAPD patterns.
Description of a new disease on Erythrina sp. in Martinique (French West Indies) and preliminary characterization of the causal agent as a novel Erwinia species
Authors: Sutra  , Prior  , Perlemoine  , Risede  , Cao‐Van  , Gardan
Published: March 2003

In spring 1995, symptoms of partial defoliation were observed on Erythrina indica var. fastigiata trees, commonly used as windbreaks in banana plantations in Martinique (French West Indies). Browning of the bark surface was consistently observed at the base of defoliated branches. Bacteria were isolated as nearly pure cultures from typical necrotic lesions on the bark. Results of Gram stain, staining of flagella and biochemical tests indicated that all isolates belonged to the Enterobacteriaceae, and to the genus Erwinia. Numerical analysis of the results of 48 biochemical properties showed that Erwinia isolates from diseased erythrina trees constituted a homogenous phenotypic cluster, and that, although weakly pectolytic, these isolates were closely related to pectolytic Erwinia species: E. carotovora ssp. betavasculorum and ssp. wasabiae, and E. cacticida. However, they could be clearly distinguished by different biochemical characteristics from type strains of known plant pathogenic species of Erwinia, Pantoea and Enterobacter. Under greenhouse conditions, the isolates were pathogenic to Erythrina indica var. fastigiata cuttings, but not to banana and pineapple, which are major crops in Martinique.
Differentiating A and B groups of Leptosphaeria maculans, causal agent of stem canker (blackleg) of oilseed rape
Authors: Williams  , Fitt
Published: March 2003

Stem canker or blackleg of brassicas, caused by Leptosphaeria maculans, is one of the most damaging diseases of winter oilseed rape in the UK. Airborne ascospores, released in autumn and winter, initiate leaf infections which may lead to colonization of the petiole and, later in the season, formation of stem lesions and cankers. Although isolates of the pathogen differ in ability to cause damaging stem cankers, this is not readily apparent from leaf spotting or stem lesion symptoms. However, several cultural, biochemical and genetic characteristics appear to be associated with the ability to form damaging stem cankers and isolates can be assigned to one of two groups, termed A and B, on the basis of differences in these characteristics. To investigate the relationship between leaf spotting symptoms and subsequent stem canker formation, and to improve understanding of the epidemiology of this pathogen, it is desirable to differentiate between the stem canker forming A group and the less damaging B group of L. maculans. Characterization of isolate type is also important in seed testing and crop breeding programs, particularly in countries such as Canada and Poland where the A type is not ubiquitous. This article reviews methods, including plant assays, assessments of growth characteristics in vitro, isozyme analyses, secondary metabolite profiling, serology, and nucleic acid analyses, that can be used to differentiate the A and B groups.
Survival of Oidium anacardii on cashew (Anacardium occidentale) in southern Tanzania
Authors: Shomari  , Kennedy
Published: March 2003

During March and April of 1993 and 1994, surveys on the incidence and severity of cashew powdery mildew (Oidium anacardii) were conducted in the Newala, Mtwara, Nachingwea and Tunduru areas of southern Tanzania to determine the variation in perennation between localities. Only immature cashew shoots, panicles and fruit can be infected by O. anacardii conidia. Cashew trees at sites in each district were assessed for shoot and panicle production and cashew powdery mildew. Survival of O. anacardii between seasons, in any area, was determined by the degree of production of shoots that were within the canopy and by the incidence of infection. Immature shoots produced from the main branches within the tree canopy were the main source of active powdery mildew in all districts; trees in the Newala district had the highest numbers of infected immature shoots in comparison with survey sites in the other areas. During the 1994 cashew‐growing season (June–August), powdery mildew developed more rapidly and affected more shoots on the inside of the tree canopy than on the outside. Germination of conidia was reduced after aqueous suspension for 3 h. Germination on cashew leaves submerged under 2 mm of water was not affected. Appressorial and hyphal formation by germinating conidia on leaves decreased with increasing duration under water. Germination of conidia on glass slides at 100% r.h. was higher at 25 and 30°C than at 15°C and there was no germination at 35°C.
Genotypic diversity in barley powdery mildew populations in northern France
Authors: Caffier  , Brändle  , Wolfe
Published: March 2003

Diversity in populations of Erysiphe graminis (Blumeria graminis) f.sp. hordei was studied with virulence and molecular markers. Isolates were sampled in two locations in northern France from a winter barley cultivar (Plaisant) and a spring cultivar (Caruso). Only a few pathotypes (determined by virulence markers) were common. The rest of the population was diverse. Diversity within common pathotypes, estimated by five RAPD and two SCAR markers, was generally high, except for one pathotype, which was frequent on Plaisant. This pathotype carried only one virulence, Va22, out of the 11 virulences tested. It appeared as a clonal lineage, which had occurred previously, at least in 1992, in northern France, demonstrating survival of asexual lineages in populations that often reproduce sexually.
Occurrence of two serotypes of sweet potato chlorotic stunt virus in East Africa and their associated differences in coat protein and HSP70 homologue gene sequences
Authors: Alicai  , Fenby  , Gibson  , Adipala  , Vetten  , Foster  , Seal
Published: March 2003

Amongst samples of the sweet potato chlorotic stunt crinivirus (SPCSV) obtained from crops of sweet potato in Uganda, two serotypes (SEA1 and SEA2) were distinguished using a panel of monoclonal antibodies (Mabs) to a Kenyan isolate of SPCSV. SEA1 serologically resembled the Kenyan isolate of SPCSV whereas SEA2 has not previously been reported. SEA1 was predominant in eastern Uganda whereas SEA2 was predominant in southern and western Uganda. SEA2 tended to occur in more severely diseased sweet potato plants than SEA1. RNA was extracted from eight plants and replicate clones representing the heat shock protein 70 (HSP70) homologue and coat protein (CP) genes were generated by reverse transcription and PCR. Sequence analyses revealed substitutions at two nucleotide positions in the HSP70 homologue gene, although neither affected deduced amino‐acid sequences. Nucleotide substitutions in the CP gene region, which led to 11 amino‐acid substitutions, revealed two major groupings plus other minor variants.

The EMBL accession numbers of the sequences reported in this paper are AJ010754 through to AJ01769 (coat protein sequences) and AJ010914 through to AJ010929 (partial HSP70 homologue gene sequences).
Sensitivity among species of Solanaceae to AAL toxins produced by Alternaria alternata f.sp. lycopersici
Authors: Mesbah L. A. , Van Der Weerden G. M. , Nijkamp H. J. J. , Hille J.
Published: March 2003

The necrotrophic fungus Alternaria alternata f.sp. lycopersici produces AAL toxins that cause necrosis in tomato tissues with high specificity. Resistance or susceptibility of tomato to the fungus and insensitivity or sensitivity to AAL toxins are determined by a single locus, Asc. In order to investigate further the specificity of the host–fungus interaction, 200 species of Solanaceae were tested for their sensitivity to AAL toxins TA and TB. Twenty‐five species were found to be sensitive to AAL toxins at a concentration of (0·2 µm) used for distinguishing sensitive and insensitive tomato plants. Three species were as sensitive as the sensitive tomato line, indicating that AAL toxins effectively act on a broader range of plant species within the Solanaceae.
Characterization of pathotypes among isolates of Xanthomonas axonopodis pv. manihotis in Colombia
Authors: Restrepo S. , Duque M. C. , Verdier V.
Published: March 2003

Cassava bacterial blight, caused by Xanthomonas axonopodis pv. manihotis (Xam) is a destructive disease occurring in most cassava growing‐areas. Although Colombian isolates of Xam differ in DNA polymorphism and pathogenicity, no suitable host differentials have been identified to demonstrate physiological specialization. A set of 26 Xam isolates from three edaphoclimatic zones (ECZs) in Colombia was selected for inoculation on a set of 17 potential cassava differentials. Leaf inoculation and stem puncture were used in order to detect possible specific interactions between cultivars and isolates. Cultivar × isolate interaction was highly significant (P < 0·001) after stem inoculation, but not after leaf inoculation. The stem inoculation technique was selected as a method for resistance screening of cassava cultivars for bacterial blight resistance. A highly significant interaction was also detected when cultivar behaviour was rated as area under the disease progress curve (AUDPC) after stem inoculation. Different pathotypes were defined among the 26 isolates and differential cultivars were proposed to define the pathotypic composition of Xam populations in three ECZs in Colombia. The results should help to improve selection of sources of resistance to cassava bacterial blight.
Effect of resistance variation in a natural plant host–pathogen metapopulation on disease dynamics
Authors: Thrall P. H. , Burdon J. J.
Published: March 2003

Existing theory suggests that increasing the diversity of resistance and virulence types in host–pathogen interactions will result in qualitative shifts in spatial and temporal dynamics, and greater among‐population asynchrony in disease dynamics and prevalence. Here, data are presented from a biologically realistic metapopulation model of gene‐for‐gene interactions that indicate that population level variation in resistance diversity will be negatively associated with disease prevalence (fraction of individuals infected). The model also predicts that disease incidence (presence/absence) will be positively related to total resistance diversity across the metapopulation, because high resistance diversity also selects for more virulent pathogens. These results are then contrasted with empirical data from a natural host–pathogen system. While the argument that high resistance diversity should generally lead to lower disease levels has been applied extensively in agricultural situations, the connection between genetic diversity, resistance and disease dynamics has never been demonstrated in natural systems. Here, through analysis of multiyear data on disease prevalence in the context of knowledge of resistance variation among host populations in a natural plant host–pathogen metapopulation, the first evidence is provided that observed levels of asynchrony in disease dynamics may indeed be related to resistance structure.
Infection and colonization of bean leaf byPhaeoisariopsis griseola
Authors: Monda E. O. , Sanders F. E. , Hick A.
Published: March 2003

Infection and spread ofPhaeoisariopsis griseolain the leaf of bean (Phaseolus vulgaris) were investigated by scanning and transmission electron microscopy. Conidia ofP. griseolagerminated by releasing a germ tube either at one end of the conidia or both ends. The germ‐tube growth followed the contours of epidermal cells. The fungus entered the leaf through the stomata and grew mainly intercellularly between mesophyll and palisade cells. The chloroplast envelope and plasma membrane of adjacent cells disintegrated, lost structural integrity and dried out. Hyphae did not penetrate host cells. A stroma subsequently formed on the leaf surface. Conidiophores elongated under favourable conditions forming synnemata with conidia at the tips of conidiophores. Conidiophores also emerged through stomata.
Control of Blumeria graminis f.sp. hordei by treatment with mycelial extracts from cultured fungi
Authors: Haugaard H. , Lyngs Jørgensen H. J. , Lyngkjær M. F. , Smedegaard‐Petersen V. , Collinge D. B.
Published: March 2003

High levels of protection against infection from Blumeria graminis f.sp. hordei in the susceptible barley cv. Pallas were obtained by pretreatment with mycelial extracts or culture filtrates from seven different fungi (Bipolaris oryzae, B. sorokiniana, Drechslera teres f. maculata, Fusarium culmorum, Trichoderma harzianum, Pythium ultimum and Rhizopus stolonifer). Three mycelial extracts from the taxonomically different fungi B. oryzae, P. ultimum and R. stolonifer were selected for detailed study. In general the number of colonies formed was reduced by 70–98% compared with controls. Furthermore, the few colonies that developed on treated leaves were generally smaller and showed reduced spore production. Protection was limited to the area of the leaves treated with mycelial extracts and a systemic effect could not be detected. No differences in the protection level were observed when treatment was conducted between 2 h and 3 days before inoculation. It is suggested that components in the mycelial extracts interacted directly with B. graminis and that this antifungal effect was responsible for the observed protection. However, indirect effects of the mycelial extracts mediated by locally induced resistance cannot be precluded.
Limited movement of Cucumber mosaic virus (CMV) in yellow passion flower in Brazil
Authors: Gioria R. , Espinha L. M. , Rezende J. A. M. , Gaspar J. O. , Kitajima E. W.
Published: March 2003

Symptoms of Cucumber mosaic virus (CMV) on yellow passion flower (Passiflora edulis f. flavicarpa) are characterized by bright yellow mottling on leaves, starting at random points on the vine and diminishing in intensity towards the tip, which becomes symptomless as it grows. To determine whether symptomless portions of vines are CMV‐free or represent latent infection, leaves with and without symptoms were collected from infected vines in the field. Biological, serological (plate‐trapped antigen enzyme‐linked immunosorbent assay, PTA‐ELISA), Western blot and dot‐blot hybridization assays showed that portions of the vines without symptoms were CMV‐free. Vegetatively propagated vines with symptoms showed remission of symptoms on newly developed leaves. One year later, no CMV was detected in the upper leaves of these plants. Mechanically inoculated passion flower seedlings behaved similarly; symptoms were shown by few leaves after inoculation. Afterwards, plants became symptomless and CMV was not detected in the upper leaves or root system, 40 or 85 days after inoculation. The mechanism responsible for remission of symptoms accompanied by CMV disappearance is not known.
Genetic variability within Phaeoisariopsis griseola from Central America and its implications for resistance breeding of common bean
Authors: Mahuku G. S. , Jara C. , Cuasquer J. B. , Castellanos G.
Published: March 2003

The genetic and virulence variability of 112 isolates of Phaeoisariopsis griseola, collected from various locations in Central America, were studied using seven random amplified polymorphic DNA (RAPD) primers and 12 common‐bean differential genotypes. Broad molecular diversity (H = 0·92) among isolates was found using RAPD markers. Fifty pathotypes were identified on 12 differential bean genotypes, 29 of which were represented by only one isolate. Only 18 pathotypes were found in two or more countries. Pathotype 63‐63 was the most virulent and caused leaf spots on all 12 common‐bean differential genotypes. Comparison of virulence phenotypes and RAPD profiles to known Andean P. griseola isolates confirmed that all isolates belonged to the Mesoamerican group. Pairwise comparison between individual RAPD loci showed that the majority were in gametic phase linkage disequilibrium, revealing that P. griseola maintains a genetic structure that is consistent with asexual reproduction. The molecular and virulence diversities of P. griseola isolates from Central America imply that using single resistance genes to manage angular leaf spot is inadequate and stacking resistance genes may be necessary to manage the disease effectively.
Rapid preparation of Fusarium DNA from cereals for diagnostic PCR u sing sonification and an extraction kit
Authors: Knoll S. , Mulfinger S. , Niessen L. , Vogel R. F.
Published: March 2003

Several PCR methods have recently been developed for Fusarium analysis in pure cultures. To use these new techniques in mycological studies and in industrial quality control, a protocol was set up for the rapid preparation of fungal DNA from cereals. An ultrasonification probe (sonotrode) and a lysis buffer were used for mechanical lysis of mycelia from infected grains. Following ultrasonification, DNA was isolated using a commercially available kit. DNA preparation was completed within 5 min per sample. The method resulted in DNA of sufficient quality and quantity for diagnostic PCR. Group‐ and species‐specific primers were used to detect DNA of Fusarium graminearum and F. culmorum in species‐specific assays as well as trichothecene‐producing Fusarium spp. in a group‐specific system. A minimum of one F. graminearum‐infected grain added to an uninfected 40 g wheat sample was detectable with a species‐specific PCR. The PCR signals produced with primers specific for the tri5 gene of trichothecene‐producing Fusarium spp. and with primers for the detection of F. graminearum (gaoA) were in accordance with corresponding concentrations of deoxynivalenol (DON) found in samples by HPLC analysis. The speed of the protocol developed may promote the use of PCR in routine applications in an agro‐industrial context.
T‐Lymphocyte Functions in Acute Leukaemia Patients with Severe Chemotherapy‐Induced Cytopenia: Characterization of Clonogenic T‐Cell Proliferation
Authors: Bruserud  , Ulvestad  , Berentsen  , Bergheim  , Nesthus
Published: March 2003

Intensive chemotherapy for acute leukaemia is followed by a period of severe chemotherapy‐induced leukopenia. We used a limiting dilution assay to investigate whether remaining CD4+ and CD8+ T lymphocytes derived from such leukopenic patients could be activated and undergo clonogenic proliferation. The activation signal in our model was accessory cells (irradiated normal peripheral blood mononuclear cells) + phytohaemagglutinin (PHA) + interleukin‐2 (IL‐2). During severe leukopenia a majority of circulating lymphocytes were CD4+ T cells. Clonogenic proliferating T lymphocytes were detected for all patients. Higher frequencies of clonogenic cells were detected in the CD8+ subset as compared to the CD4+ subset. However, for both subsets frequencies of proliferating cells were decreased compared with healthy individuals. The CD4+ and CD8+ lymphocytes were also capable of proliferation in response to alloactivation, and accessory cells mainly containing acute myelogenous leukaemia blast were efficient as accessory cells for activation. For the CD4+ cells, increased proliferation was detected in the presence of acute myelogenous leukaemia (AML) blasts compared with normal accessory cells. Based on our results we conclude that: (1) although acute leukaemia patients with therapy‐induced leukopenia have both a quantitative and a qualitative T‐cell defect, (2) the remaining T‐cell population includes a subset capable of clonogenic proliferation. However, (3) proliferation of the clonogenic CD4+ cells can be modulated by AML blasts.
Aggregated Immunoglobulin Protects Immune T Cells from Suppression: Dependence on Isotype, Fc Portion, and Macrophage FcγR
Authors: Ptak  , Paliwal  , Bryniarski  , Ptak  , Askenase
Published: March 2003

We determined the regulatory properties of heat‐aggregated immunoglobulins (HA‐Ig) that possess many activities of immune complexes (IC), such as binding and activation of cells via immunoglobulin Fc γ receptors (FcγR). HA‐Ig protected contact sensitivity (CS) effector T cells from antigen‐specific immunosuppression, while monomeric IgG were inactive. This anti‐suppressive activity of HA‐Ig was antigen non‐specific, and depended on the species from which Ig was derived, i.e. mouse and rat HA‐Ig were protective in mice, and of other species were inactive. The protecting activity of HA‐Ig was confined to IgG2a and IgG3, and to a lesser degree to IgG1 isotypes, and resided in the Fc domain. Removal of phagocytic cells from the CS‐immune target cells, or blocking with anti‐FcγR mAb, abolished HA‐Ig protection of CS‐effector T cells from suppression. We suggest that HA‐Ig multimers acted via Fc domains, in one of two ways: by binding to FcγR of macrophages to produce positive‐acting cytokines, or by blocking FcγR on macrophages, to compete with suppressive factors that can also bind to FcγR. If HA‐Ig protection of T cells is generalized, it is likely that IC in vivo may non‐specifically overcome suppression of responses to antigen that normally are under the control of T suppressive cells, and thus may contribute to the development of autoimmunity.
Peptide Dependence of Major Histocompatibility Complex Class II Specific Alloreactive Responses
Authors: Vidović  , Toral  , Bolin  , Ito  , Nagy
Published: March 2003

Splenic cells from transgenic mice, in which a single peptide is complexed to all major histocompatibility complex (MHC) class II molecules, are found to be incapable of triggering primary allogeneic mixed lymphocyte/leucocyte reactions (MLR) when co‐cultured with lymphocytes from MHC class II congenic mouse strains. In addition, a single HLA‐DR‐blocking peptide can completely abrogate the capacity of splenocytes from chimeric HLA‐DR/H2‐E transgenic mice to stimulate primary MLR of T cells from wild‐type mice. These results indicate that the primary alloreactive response is directed against a multitude of peptides presented by allogeneic MHC molecules.