bluuebunny/crossref_metadata_2025 huggingface dataset:
Reverse flow in roots of Sesbania rostrata measured using the constant power heat balance method
Authors: Sakuratani T. , Aoe T. , Higuchi H.
Published: March 2003

This investigation was performed to examine qualitatively and quantitatively the reverse flow in partially dried roots of Sesbania rostrata using the constant power heat balance method. First, a semi‐empirical technique for estimating sheath conductance of sap‐flow sensors without assuming that sap flow is zero at night was proposed. Sap flow measured with the heat balance method was compared with water uptake as measured by a potometric method. Sap flow was overestimated by 56·1% for a 3·3‐mm‐diameter root, and by 40·0% for 6·1 mm and 33·3% for 8·8 mm roots. However, high correlation coefficients between the rates of water uptake and sap flow demonstrated that calibration would provide reliable values for root sap flow. To detect reverse flow, a split root experiment was conducted using a S. rostrata plant with its root system divided between dry and wet compartments. Daily sap flow of the drying compartment declined whereas that in ‘wet’ root increased, suggesting that the decrease in water uptake by ‘dry’ roots was offset by the ‘wet’ roots. Reverse flow was observed at night in the root on the dry side of the container when the soil water potential was less than –0·30 MPa. The total amount of water released into the soil during the night period was estimated to be 22·5 g.
Expression of C‐assimilating enzymes in pea (Pisum sativum L.) root nodules. In situ localization in effective nodules
Authors: Fedorova M. , Tikhonovich I. A. , Vance C. P.
Published: March 2003

Full length cDNAs encoding alcohol dehydrogenase (ADH), fructose‐1,6‐biphosphate aldolase (ALD), nodule‐enhanced malate dehydrogenase (neMDH), phosphoenolpyruvate carboxylase (PEPC), and nodule‐enhanced sucrose synthase (neSS) were isolated from a pea (Pisum sativum L.) root nodule cDNA library and characterized. Transcript abundance and cellular expression patterns for each gene were examined at different stages of nodule development. All the genes were expressed prior to the induction of nitrogenase suggesting a developmental signal as the initial trigger for expression. RNA tissue blots demonstrated that all the genes except ALD exhibit enhanced expression in effective nodules. In situ hybridization studies showed contrasting patterns of gene expression within various nodule zones. The highest expression of ADH was observed in interzone. ALD was expressed predominantly in nodule meristem, invasion zone and interzone. The neSS transcripts were found rather uniformly throughout the nodule. Expression of neMDH and PEPC was also detected throughout the nodule, but the highest levels were associated with interzone and N2‐fixing zone.
Leaf rosette closure in the alpine rock species Saxifraga paniculata Mill.: significance for survival of drought and heat under high irradiation
Authors: Neuner G. , Braun V. , Buchner O. , Taschler D.
Published: March 2003

The significance of leaf rosette closure for survival of drought and heat under high irradiation on alpine rock sites was investigated in the cushion forming rosette plant, Saxifraga paniculata Mill. With decreasing water content the leaves fold over the rosette centre reducing reversibly the evaporative leaf surface area by 80%. Internal water redistribution driven by an osmotic gradient from older to younger leaves occurs. The oldest leaves dry out to promote the survival of the individual. Leaf temperatures above 45 °C (which match heat tolerance limits 45–57 °C; LT50) co‐occurred with low substrate water potentials (less than – 0·5 MPa) on 11·3% of summer days. Shading by leaves can be crucial to surviving high temperatures as it keeps the rosette centre up to 10 °C colder. Mutual shading prevented sustained drought‐induced photoinhibition in upper leaf surfaces at relative water contents below 60%. In exposed lower leaf surfaces restoration of photosystem II took several days. Leaf temperatures above 40 °C (21·3% of summer days) induced photoinhibition in situ. Periods with sufficient water supply can be fully utilized as rehydration is fast (< 12 h) and exposes the upper leaf surfaces that showed only minor photoinhibition. By reversible leaf rosette closure environmental extremes that otherwise could exceed tolerance are efficiently avoided.
Compatibility of glycinebetaine in rice plants: evaluation using transgenic rice plants with a gene for peroxisomal betaine aldehyde dehydrogenase from barley
Authors: Kishitani S. , Takanami T. , Suzuki M. , Oikawa M. , Yokoi S. , Ishitani M. , Alvarez‐Nakase A. M. , Takabe T. , Takabe T.
Published: March 2003

Glycinebetaine is synthesized in plants by the two‐step oxidation of choline, with betaine aldehyde as the intermediate. The reactions are catalyzed by choline mono‐oxygenase and betaine aldehyde dehydrogenase. Rice plants, which do not accumulate glycinebetaine, possess a gene encoding betaine aldehyde dehydrogenase, whose activity is detectable at low levels. To evaluate the compatibility in rice of glycinebetaine on growth and tolerance to salt, cold and heat, we produced transgenic rice plants by introduction of a cDNA for betaine aldehyde dehydrogenase of barley, which is localized in peroxisomes unlike the chloroplast‐specific localization of betaine aldehyde dehydrogenase in spinach and sugar beet. The transgenic rice plants converted high levels of exogenously applied betaine aldehyde (up to 10 mol m–3) to glycinebetaine more efficiently than did wild‐type plants. The elevated level of glycinebetaine in transgenic plants conferred significant tolerance to salt, cold and heat stress. However, very high levels of glycinebetaine, resulting from conversion of applied betaine aldehyde to glycinebetaine or from exogenous application, inhibited increases in length of rice plants but not increases in dry weight. Our results suggested that the benefits of accumulation of glycinebetaine by rice plants might be considerable under high light conditions.
The protein content of tissues in cynipid galls (Hymenoptera: Cynipidae): Similarities between cynipid galls and seeds
Authors: Schönrogge K. , Harper L. J. , Lichtenstein C. P.
Published: March 2003

Cynipid galls are examples of induced plant development, where the gall inducer is in control of cell differentiation and morphogenesis of a new plant organ. This study concentrates on the tissues of the larval chamber common to all cynipid galls. The protein content of the inner gall tissue was compared to that of non‐gall plant tissues. We investigated three oak and two rose galls and their respective host plants. Total protein signatures of inner gall tissues were different from those of non‐gall plant tissues, and among the five galls. N‐terminal sequences were obtained for two abundant proteins from the inner gall tissues of D. spinosa and A. quercuscalicis, which were common to all galls, at 62 and 43 kDa. Database queries suggest the 62 kDa protein to be homologous to a protein disulphide isomerase (PDI), and the 43 kDa protein to be homologous to NAD‐dependent formate dehydrogenase (FDH). A naturally biotinylated protein was detected at 33 kDa during Western analyses with streptavidin. Western analyses revealed the presence of the biotinylated protein and PDI in the inner gall tissues of all five galls, while FDH was only detected in A. quercuscalicis and A. fecundator. PDI was also common to all non‐gall tissues, while FDH was not detected in non‐gall tissues, and the biotinylated protein was only detected in seeds. The proteins identified in the inner gall tissue suggest that (a) inner gall tissues in some galls are under respiratory stress, and (b) cynipid gall formation might involve the ectopic expression of seed‐specific proteins.
Differential effects of mineral and organic N sources, and of ectomycorrhizal infection by Hebeloma cylindrosporum, on growth and N utilization in Pinus pinaster
Authors: Plassard C. , Bonafos B. , Touraine B.
Published: March 2003

The effect of ectomycorrhizal association of Pinus pinaster with Hebeloma cylindrosporum was investigated in relation to the nitrogen source supplied as mineral (NH4+ or NO3−) or organic N (L‐glutamate) and at 5 mol m−3. Plants were grown for 14 and 16 weeks with mineral and organic N, respectively, and samples were collected during the last 6 weeks of culture. Total fungal biomass was estimated using glucosamine amount and its viability was assessed using the glucosamine to ergosterol ratio. Non‐mycorrhizal plants grew better with NH4+ than with NO3− and grew very slowly when supplied with L‐glutamate. The presence of the fungus decreased the growth of the host plant with mineral N whereas it increased it with L‐glutamate. Whatever the N source, most of the living fungal biomass was associated with the roots, whereas the main part of the total biomass was assayed outside the root. The form of mineral N did not significantly affect N accumulation rates over the 42 d in control plants. In mycorrhizal plants grown on either N source, the fungal tissues developing outside of the root were always the main N sink. The ectomycorrhizal association did not change 15NH4+ uptake rate by roots, suggesting that the growth decrease of the host‐plant was related to the carbon cost for fungal growth and N assimilation rather than to a direct effect on NH4+ acquisition. In contrast, in NO3−‐grown plants, in addition to draining carbon for NO3− reduction the fungus competed with the root for NO3− uptake. With NH4+ or NO3− feeding, although mycorrhizal association improved N accumulation in shoots, we concluded that it was unlikely that the fungus had supplied the plant with N. In L‐glutamate‐grown plants, the presence of the fungus increased the proportion of glutamine in the xylem sap and improved both N nutrition and the growth rate of the host plant.
Thermographic visualization of cell death in tobacco and Arabidopsis
Authors: Chaerle L. , De Boever F. , Montagu M. Van , Straeten D. Van Der
Published: March 2003

Pending cell death was visualized by thermographic imaging in bacterio‐opsin transgenic tobacco plants. Cell death in these plants was characterized by a complex lesion phenotype. Isolated cell death lesions were preceded by a colocalized thermal effect, as previously observed at sites infected by tobacco mosaic virus (TMV) (Chaerle et al. 1999Nature Biotechnology 17, 813–816). However, in most cases, a coherent front of higher temperature, trailed by cell death, initiated at the leaf base and expanded over the leaf lamina. In contrast to the homogenous thermal front, cell death was first visible close to the veins, and subsequently appeared as discrete spots on the interveinal tissue, as cell death spread along the veins. Regions with visible cell death had a lower temperature because of water evaporation from damaged cells. In analogy with previous observations on the localized tobacco–TMV interaction (Chaerle et al. 1999), the kinetics of thermographic and continuous gas exchange measurements indicated that stomatal closure preceded tissue collapse. Localized spontaneous cell death could also be presymptomatically visualized in the Arabidopsis lsd2 mutant.
The guard‐cell apoplast as a site of abscisic acid accumulation in Vicia faba L.
Authors: Zhang S. Q. , Outlaw W. H.
Published: March 2003

Abscisic acid (ABA) integrates the water status of a plant and causes stomatal closure. Physiological mechanisms remain poorly understood, however, because guard cells flanking stomata are small and contain only attomol quantities of ABA. Here, pooled extracts of dissected guard cells of Vicia faba L. were immunoassayed for ABA at sub‐fmol sensitivity. A pulse of water stress was imposed by submerging the roots in a solution of PEG. The water potentials of root and leaf declined during 20 min of water stress but recovered after stress relief. During stress, the ABA concentration in the root apoplast increased, but that in the leaf apoplast remained low. The ABA concentration in the guard‐cell apoplast increased during stress, providing evidence for intra‐leaf ABA redistribution and leaf apoplastic heterogeneity. Subsequently, the ABA concentration of the leaf apoplast increased, consistent with ABA import via the xylem. Throughout, the ABA contents of the guard‐cell apoplast, but not the guard‐cell symplast, were convincingly correlated with stomatal aperture size, identifying an external locus for ABA perception under these conditions. Apparently, ABA accumulates in the guard‐cell apoplast by evaporation from the guard‐cell wall, so the ABA signal in the xylem is amplified maximally at high transpiration rates. Thus, stomata will display apparently higher sensitivity to leaf apoplastic ABA if stomata are widely open in a relatively dry atmosphere.
Computer‐based analysis of steady‐state and transient heat transfer of small‐sized leaves by free and mixed convection
Authors: Roth‐Nebelsick A.
Published: March 2003

In order to study convective heat transfer of small leaves, the steady‐state and transient heat flux of small leaf‐shaped model structures (area of one side = 1730 mm2) were studied under zero and low (= 100 mm s−1) wind velocities by using a computer simulation method. The results show that: (1) distinct temperature gradients of several degrees develop over the surface of the model objects during free and mixed convection; and (2) the shape of the objects and onset of low wind velocities has a considerable effect on the resulting temperature pattern and on the time constant τ. Small leaves can thus show a temperature distribution which is far from uniform under zero and low wind conditions. The approach leads, however, to higher leaf temperatures than would be attained by ‘real’ leaves under identical conditions, because heat transfer by transpiration is neglected. The results demonstrate the fundamental importance of a completely controlled environment when measuring heat dissipation by free convection. As slight air breezes alter the temperature of leaves significantly, the existence of purely free convection appears to be questionable in the case of outdoor conditions. Contrary to the prognoses yielded by standard approximations, no quantitative effect of buoyancy on heat transfer under the considered conditions could be detected for small‐sized leaf shapes.
Rate of acclimation of the capacity for isoprene emission in response to light and temperature
Authors: Hanson D. T. , Sharkey T. D.
Published: March 2003

Isoprene emission from plants accounts for nearly half of all non‐methane hydrocarbons entering the atmosphere. Light and temperature regulate the instantaneous rate of isoprene emission but there is increasing evidence that they also affect the capacity for isoprene emission (i.e. the rate measured under standard conditions). We tested the rate of acclimation of the capacity for isoprene emission following step changes in growth conditions. Acclimation to new growth temperatures was very rapid, with most of the change occurring within a few hours and complete adjustment occurring within a day. Acclimation to new light levels was more complicated. Following a switch from low‐light growth conditions to standard assay conditions (30 °C and 1000 µmol photons m−2 s−1), there was a rapid (5–10 min) and a slightly slower (10–50 min) acclimation of the capacity for isoprene emission. After accounting for these short‐term changes, there was also a small, long‐term (4–6 d) acclimation of the isoprene emission capacity to the light level of growth conditions. We found no effect of growth conditions on the coefficients used to describe the instantaneous light and temperature response of isoprene emission. Therefore, current models of isoprene emission will only need to be altered to account for changes in the capacity for isoprene emission.
Fluorescence and photochemical properties of phytochromes in wild‐type wheat and a transgenic line overexpressing an oat phytochrome A (PHYA) gene: functional implications
Authors: Sineshchekov V. , Koppel L. , Shlumukov L. , Barro F. , Barcelo P. , Lazzeri P. , Smith H.
Published: March 2003

Etiolated seedlings of wild‐type wheat and a transgenic line overexpressing an oat PHYA gene were investigated by the use of in situ low‐temperature fluorescence spectroscopy. The red‐absorbing phytochrome form, Pr, was characterized by (1) fluorescence emission spectrum; (2) total phytochrome content, and (3) by the extent of the Pr → lumi‐R photoconversion at low temperature (γ1), and of the Pr → Pfr photoconversion at ambient temperature (γ2) as derived from emission data. All the characteristics were shown to be variable and to depend on (1) organ and tissue used; (2) seedling age; (3) transgenic wheat modification, and (4) continuous far‐red irradiation of seedlings during their growth. These variations were interpreted in terms of the existence in wheat seedlings of the two phenomenological Pr types: (a), Pr′– major longer wavelength (687/673 nm, emission/absorption maxima) variable and light‐labile with γ1 ≈ 0·5; and (b), Pr′′– minor, shorter wavelength (682/668 nm), relatively constant with its concentration not changing significantly with the increase of total phytochrome content in tissues and light‐stable with γ1 ≤ 0·05–0·1. Overexpression of oat phyA increases primarily the content of Pr′ suggesting that it is comprised of phyA (phyA′) whereas Pr′′ is believed to consist of the minor phyA fraction (phyA′′) and phyB. The transgenic wheat line has been demonstrated to have a modified phenotype – the appearance of the far‐red high irradiance reaction (FR‐HIR) (Shlumukov et al. Plant, Cell and Environment 24, 703–712). The increased content of phyA′ in the transgenic line, whereas the total [phyA′′ + phyB] remains the same as in the wild type, indicates that the phyA′ pool is primarily responsible for the observed modification of the phenotype and suggests that even in wild‐type plants the phyA′ component of the phyA pool may mediate the FR‐HIR.
The effect of three rootstocks on water use, canopy conductance and hydraulic parameters of apple trees and predicting canopy from hydraulic conductance
Authors: Cohen S. , Naor A.
Published: March 2003

This study investigated the effect of the dwarfing M9, semi‐dwarfing MM106 and local Hashabi rootstocks on the water use, canopy conductance (Gc) and hydraulic conductance (k) of apple orchards with the same scion, Golden Delicious. The average summer leaf area index (LAI) was 2·4, 2·7 and 1·7 for M9, MM106 and Hashabi, respectively. Irrigation in 1997 was less than water use until June, and excessive afterwards. In 1998, irrigation was doubled, and was excessive throughout the season. Sap flow (J) in June–August 1998 totalled 476, 682 and 606 mm (or 0·60, 0·86 and 0·76 of class A pan evaporation) for M9, MM106 and Hashabi, respectively. Maximum sap velocity in the three rootstocks (approximately 70 cm h−1) occurred in the outer 30–60% of the stem, and its decrease with depth was greater in M9 than in the other rootstocks. Midday Gc during both summers was least for M9, intermediate for Hashabi and greatest for MM106. The k value of M9 and MM106 for the soil to stem, stem to leaves and soil to leaves pathways were determined from daily courses of water potential of leaves, Ψl, stem, Ψstem and J. Specific k (ks, i.e. relative to stem sapwood area) did not significantly differ between the two rootstocks for soil to stem and soil to leaf pathways, but leaf specific k (kl) was greater for MM106 soil to stem (71% greater) and soil to leaf (63%) pathways, respectively. The inverse slopes of the relationships between midday canopy resistance (Rc) and vapour pressure deficit (D) for MM106 was 1·75 of that for M9, and the ratio of their Huber values, i.e. the ratio of sapwood to leaf area, was 1·6. These findings indicate that differences in water use are attributable to differences in kl, and not to differences in wood properties (ks). Application of a model relating Rc to orchard area specific k (kg) showed that the slope of the relationships between midday Rc and D for the 1998 data could be predicted using common values of ks (0·134 kg m−2 s−1 MPa−1) and midday Ψl (−1·34 MPa) for the three rootstocks. The implications of these findings, and the similarities in the differences between rootstocks of Gc, kl, kg and Huber values, are discussed with respect to rootstock water use and irrigation.
Scaling relationships for woody tissue respiration in two tropical rain forests
Authors: Meir P. , Grace J.
Published: March 2003

The relationship between gross primary productivity (GPP) and net primary productivity (NPP) is not fully understood. One of the uncertainties relevant to this issue is the magnitude of woody tissue respiration. Although some data exist for temperate and boreal zones, measurements of woody tissue respiration in tropical forests are sparse. We made in situ chamber measurements of woody tissue respiration in two tropical rain forests, one in the Brazilian Amazon (Reserva Jarú) and one in Central Cameroon (Mbalmayo Reserve). We made measurements on a wide range of species at each site and over a range of stem diameters from 0·02 to 1·4 m. The rate of efflux of carbon dioxide (CO2) from bark at 25 °C, Rt, varied from 0·1 to 5·2 µmol m−2 s−1 across the two sites, and the efflux was related to both volume and surface area components of the measured stem sections. The temperature response in Rt was slightly higher at Jarú than at Mbalmayo, with Q10 values of 1·8 (± 0·1 SE) and 1·6 (± 0·1 SE), respectively. A log–log regression showed that Rt was significantly related to stem diameter, D (P < 0·001; r2 = 0·58–0·62) and was significantly higher at Mbalmayo than at Jarú (P < 0·001), but that the rate of increase in Rt with stem diameter, D, was similar between sites. At the Mbalmayo site, tree growth measurements made over a 4 month period were used to make two estimates of the maintenance (Rm) and construction (Rc) components of respiration embedded in Rt. The two methods agreed closely, suggesting that Rm was approximately 80% of Rc at this site. Rm could be strongly related to D using a sigmoidal relationship that described both surface area and volume components as sources of respiratory CO2 (r2 = 0·71). This functional model was combined with inventory, growth and climate data for the Mbalmayo site to make a first estimate of annual above‐ground woody tissue respiration, RA, which was 257 (± 18 SE) g C m−2 year−1. This value corresponds to approximately 10% of GPP, slightly lower than that found for another tropical rain forest, but higher than for temperate forests. When combined with data from six other sites in tropical, temperate and boreal settings, a very strong relationship was found between RA and leaf area index (LAI), and between RA/GPP and LAI (P < 0·001, r2 = 0·98). This indicates that RA exerts an appreciable constraint on NPP and that this constraint varies closely with LAI across widely differing types of woody vegetation.
Sugar beet yellow net complex contains a luteovirus component
Authors: Sugars J. M. , Lennon E. A. , Plumb R. T. , White R. F.
Published: March 2003

Yellow net virus of sugar beet has, until now, been listed as a tentative member of the luteovirus genus, but this is the first study to show that the yellow net symptom (YN) is always associated with a luteovirus. This virus is related to beet mild yellowing virus (BMYV) and when transmitted alone causes a mild yellowing symptom similar to that caused by BMYV in beet. Plants with YN have been found to contain, in addition to the luteovirus, two prominent, low molecular weight double‐stranded (ds)RNA species. This dsRNA is indicative of an extra component in a complex with the luteovirus, which gives rise to the conspicuous symptom. The range of experimental hosts for this virus has been extended to include Capsella bursa‐pastoris and Physalis floridana.
Differentiation between cucurbit yellow stunting disorder virus and beet pseudo‐yellows virus by a reverse transcription‐polymerase chain reaction assay
Authors: Livieratos I. C. , Katis N. , Coutts R. H. A.
Published: March 2003

Two whitefly‐transmitted viruses elicit identical symptoms of interveinal chlorosis (yellowing) in greenhouse‐ and field‐grown cucurbits in Mediterranean countries. The agents of these diseases are partially characterized closteroviruses and are known as beet pseudo‐yellows virus (BPYV), which is transmitted by Trialeurodes vaporariorum, and cucurbit yellow stunting disorder virus (CYSDV), transmitted by Bemisia tabaci. Using previously determined sequence information for fragments of the HSP70 homolog genes of both BPYV and CYSDV, oligonucleotide primers were designed for reverse transcription‐polymerase chain reaction (RT‐PCR) protocols to differentiate between the two viruses. RT‐PCR amplified products for each virus were subsequently cloned and specifically hybridized with the homologous dsRNA (approximately 9 kbp in size for both viruses) following Northern hybridization analysis. Minor dsRNAs of approximately 5 kbp for both viruses and one dsRNA of 3 kbp for CYSDV were also identified by Northern hybridization and might represent defective RNA species. In order to compare the predicted amino acid sequence of fragments of the HSP70 homolog genes of BPYV and CYSDV, oligonucleotide primers were designed for RT‐PCR amplification of a previously unknown segment of the BPYV gene from a Greek isolate and the American isolate of the virus. The RT‐PCR products of both isolates were cloned and found to be identical in sequence. Computer assisted analysis of the deduced amino acid sequence of the assembled HSP70 homolog gene fragments showed that BPYV and CYSDV are closely related to each other and individually as closely related to the corresponding gene of lettuce infectious yellows virus, which is the prototype member of the recently proposed Crinivirus genus of whitefly‐transmitted, bipartite closteroviruses.
Modelling and forecasting epidemics of apple powdery mildew (Podosphaera leucotricha)
Authors: Xu
Published: March 2003

A model developed to simulate epidemics of powdery mildew on vegetative shoots of apple generates two types of output. Firstly, it forecasts disease severity (percentage of host tissue infected) by incorporating effects on disease development of the amount of healthy susceptible tissue and current infectious (sporulating) disease, the level of initial inoculum (overwintered ‘primary’ mildew) and weather conditions. The effects of weather variables are considered on only two aspects of the fungal life cycle: initial spore germination and the subsequent development during the incubation period. Secondly, the model generates indices of the relative favourability of weather conditions on disease development by incorporating effects of weather on conidial production/dispersal and germination. On each day, forecasts of the (relative) severity of new infection and total current infectious disease are given for both types of output. The model was evaluated by comparing its predictions with the mildew epidemics observed in two unsprayed orchards over four years. In all the years, the temporal patterns of the predicted and the observed disease were generally similar. The pattern of the disease severity forecasts was marginally closer to the observed than that derived from two weather indices. Potential roles of the model in practical management of apple powdery mildew are discussed.
A two‐step multiplex RT‐PCR method for simultaneous detection of soil‐borne wheat mosaic virus and wheat spindle streak mosaic virus from France
Authors: Gitton  , Diao  , Ducrot  , Antoniw  , Adams  , Maraite
Published: March 2003

A sequence of 942 nucleotides, located in the helicase gene of RNA1 of a French isolate of soil‐borne wheat mosaic virus (SBWMV), is presented. This sequence was compared with the corresponding sequences published for Nebraskan and Chinese isolates and showed a 74.8% and 73.4% identity, respectively, with these isolates, whereas the Nebraskan and Chinese isolates shared a 78.2% identity. A set of primers specific to the French SBWMV isolate was designed on the basis of this sequenced 942 nucleotide fragment. A primer set for wheat spindle streak mosaic virus (WSSMV) was designed from the published partial sequence of a French isolate. Both sets of primers were combined into a two‐step multiplex reverse‐transcription polymerase chain reaction, allowing simultaneous detection of both viruses in leaves of infected wheat samples. The amplification specificity of the two sets of primers was checked against isolates of SBWMV from Oklahoma and China, Indian peanut clump virus strains H, L and D from India, barley mild mosaic virus and barley yellow mosaic virus from France. SBWMV primers were specific for French isolates of this virus, whereas the primers designed from the sequence of a French isolate of WSSMV could also faintly detect barley yellow mosaic virus in barley plants. The RT‐PCR technique was also compared with ELISA (enzyme‐linked immunosorbent assay) on 100 wheat leaf samples collected from the field on the basis of symptoms, and was shown to be reliable and reproducible.
Analysing disease incidence data from designed experiments by generalized linear mixed models
Authors: Piepho
Published: March 2003

As a result of aggregation or clustering of sampling units, disease incidence data from designed experiments frequently show overdispersion relative to the binomial distribution. This paper discusses generalized linear mixed models (GLMM) suitable for analysing overdispersed disease incidence data. The methods are exemplified using data from a randomized complete block experiment on the incidence of downy mildew (Plasmopara viticola) of grape (Vitis lambrusca). Hints are given regarding implementation of the methods using the %GLIMMIX macro for the SAS system.
Host frequency and density effects on powdery mildew and yield in mixtures of barley cultivars
Authors: Finckh  , Gacek  , Czembor  , Wolfe
Published: March 2003

The effects of frequency and density of susceptible plants on barley powdery mildew epidemics were studied in a combined set of addition and replacement series of field trials. In the addition series, plant densities in pure stands of three cultivars, Rambo, Rodos and Grosso (susceptible, moderately resistant and immune, respectively) were varied six‐fold. In the replacement series, the three possible two‐way mixtures were analysed at different frequencies but at a density corresponding to the maximum pure stand density. Disease and yield were assessed on a per‐plant basis. In the pure stands, tillering reduced the range of densities from six‐fold to between three‐ and four‐fold, while in the mixtures, frequencies changed only slightly over time, indicating that competitive interactions among the cultivars were roughly equal. Yield per plant decreased logarithmically with increasing density as expected. However, yield per seed head was not correlated with the final number of heads per plot, indicating low competition among heads even at the highest density. Disease in susceptible pure stands increased strongly with decreasing density in 1994 and to a lesser degree in 1995. These differences could have been caused by differences in plant nutritional status and consequent epidemiological effects. Disease reduction on the susceptible cultivars in mixtures varied between 33% and 71% among years. Depending on the length and strength of the epidemic, the effects of host density and frequency on disease severity varied substantially among years.
Rhizogenic Agrobacterium biovar 1 and cucumber root mat in the UK
Authors: Weller  , Stead  , O'neill  , Hargreaves  , McPherson
Published: March 2003

An unusual root disease of cucumbers has affected an increasing number of hydroponic crops in the UK since 1993. Symptoms include upward growth of roots, root proliferation sufficient to distort the shape of rockwool cubes and slabs, thickened roots and occasionally reduced root production and an increase in bent fruit. Rhizogenic Agrobacterium biovar 1 has previously been associated with the problem. In a survey of 37 nurseries in 1997, rhizogenic Agrobacterium bv. 1 isolates were obtained from 17 of 22 nurseries with symptoms and only occasionally from nurseries without symptoms. Young cucumber plants inoculated with rhizogenic Agrobacterium bv. 1 isolates, previously obtained from cucumber roots with symptoms, developed typical symptoms. The survey data and pathogenicity test support rhizogenic Agrobacterium bv. 1 as the primary causal agent of root mat in the UK. Although Agrobacterium bv. 1 isolates that do not harbour an Ri‐plasmid are considered avirulent, their abundance in rockwool slabs as potential vectors of the Ri‐plasmid may be a major factor in the epidemiology of the disease.
Effect of 2,6‐dichloroisonicotinic acid, its formulation materials and benzothiadiazole on systemic resistance to alternaria leaf spot in cotton
Authors: Colson‐Hanks E.S. , Deverall B.J.
Published: March 2003

A wettable powder (WP) formulation providing 5–25 μg mL−1 of 2,6‐dichloroisonicotinic acid (INA) and 15–75 μg mL−1 of WP applied to cotton cotyledons significantly increased the resistance of the next two leaves to challenge inoculation by Alternaria macrospora. The wettable powder alone at 15–75 μg mL−1 had a lesser effect. A wettable granule (WG) formulation supplying 35 μg mL−1 of benzo‐(1,2,3)‐thiadiazole‐7‐carbothioic acid S‐methyl ester (BTH) and 35 μg mL−1 of WG, applied as a cotyledonary treatment, significantly reduced the formation of lesions on the subsequent two leaves when challenged with A. macrospora. The WG control had no effect. Each treatment except for the WG control also raised the activities of β‐1,3‐glucanase in unchallenged leaf and stem tissue. Each of the components of the wettable powder without INA applied to cotyledons raised enzyme activities in the next leaves. Individual components, as suspensions of silicic acid and kaolin and solutions of the detergent Attisol II, the wetting agent Ultravon W300 and pure INA, applied to cotyledons increased the resistance of the next leaves to A. macrospora. The responsiveness of cotton to BTH and to each of the components of formulated INA is discussed in relation to knowledge of the effects of BTH and INA on other plants and to possible ways in which the other components of the wettable powder may affect the process of signalling for systemic resistance to disease.
Effects of temperature and wetness duration on conidial infection, latent period and asexual sporulation ofPyrenopeziza brassicaeon leaves of oilseed rape
Authors: Gilles T. , Fitt B. D. L. , Kennedy R. , Welham S. J. , Jeger M. J.
Published: March 2003

Experiments in controlled environments were carried out to determine the effects of temperature and leaf wetness duration on infection of oilseed rape leaves by conidia of the light leaf spot pathogen,Pyrenopeziza brassicae. Visible spore pustules developed on leaves of cv. Bristol inoculated withP. brassicaeconidia at temperatures from 4 to 20°C, but not at 24°C; spore pustules developed when the leaf wetness duration after inoculation was longer than or equal to approximately 6 h at 12–20°C, 10 h at 8°C, 16 h at 6°C or 24 h at 4°C. On leaves of cvs. Capricorn or Cobra, light leaf spot symptoms developed at 8 and 16°C when the leaf wetness duration after inoculation was greater than 3 or 24 h, respectively. The latent period (the time period from inoculation to first spore pustules) ofP. brassicaeon cv. Bristol was, on average, approximately 10 days at 16°C when leaf wetness duration was 24 h, and increased to approximately 12 days as temperature increased to 20°C and to 26 days as temperature decreased to 4°C. At 8°C, an increase in leaf wetness duration from 10 to 72 h decreased the latent period from approximately 25 to 16 days; at 6°C, an increase in leaf wetness duration from 16 to 72 h decreased the latent period from approximately 23 to 17 days. The numbers of conidia produced were greatest at 12–16°C, and decreased as temperature decreased to 8°C or increased to 20°C. At temperatures from 8 to 20°C, an increase in leaf wetness duration from 6 to 24 h increased the production of conidia. There were linear relationships between the number of conidia produced on a leaf and the proportion of the leaf area covered by ‘lesions’ (both log10‐transformed) at different temperatures.
Reductive detoxification of the acetophenone skeleton of the carnation phytoanticipin by Fusarium oxysporum f.sp. dianthi
Authors: Curir P. , Danieli B. , Dolci M. , Pasini C. , Guglieri L. , Sacco M.
Published: March 2003

The skeleton of the carnation phytoanticipin, acetophenone, was detoxified by Fusarium oxysporum f.sp. dianthi, the main fungal parasite of carnation. This process consisted of the reduction to ethanol of the acetyl group, leading to the formation of phenylethanol, which has lower fungitoxic activity than the parent molecule. The conversion took place through the activity of an adaptive fungal oxidoreductase, which was NADH‐dependent and was released by the fungus as two enzymatic forms within the culture substrate in the presence of acetophenone. Reduction was stereospecific and gave rise to only one of the two possible enantiomeric forms.
Disease severity and pathotype dynamics of Puccinia striiformis f.sp. tritici in Denmark
Authors: Hovmøller M. S.
Published: March 2003

Disease severity of wheat yellow rust, Puccinia striiformis f.sp. tritici, was analysed in Denmark from 1985 to 1999 in relation to the effects of weather on winter survival, distribution of host cultivars and pathotype dynamics. Below‐average temperatures in January and February (midwinter) reduced yellow rust on the susceptible cv. Anja, and in three of four growth seasons following cold winters no yellow rust was observed on any cultivar under natural conditions. The agronomic consequences of dispersal of yellow rust urediniospores from external sources to Denmark, in a period during which large areas were planted with relatively few wheat cultivars, were demonstrated in several cases, most evidently when the Yr9 and Yr17 resistance genes became ineffective. Yr9 was overcome by the pathogen in a period with severe yellow rust epidemics on commercial cultivars, while virulence for Yr17 was first observed in a year with almost no yellow rust. In contrast, the resistance in cv. Kraka (Yr1, CV) was increasingly effective in controlling yellow rust, because pathotypes with the matching combination of virulence declined in the pathogen population. Pathotype frequency dynamics were thus influenced by selection forces within the country, and by selection forces in areas where spores were spread to Denmark from outside. The importance of a sufficient level of partial resistance in the wheat germplasm to prevent too much damage by yellow rust epidemics, in the event that the resistance genes are overcome by the pathogen population, is emphasized.
Variation in the response of cashew genotypes to the targeted application of fungicide to flower panicles for control of powdery mildew disease
Authors: Sijaona M. E. R. , Mansfield J. W.
Published: March 2003

Application of the fungicide triadimenol (Bayfidan) directly to inflorescences of cashew was investigated as a means of controlling powdery mildew disease caused by Oidium anacardii. Disease development and nut production were studied in 12 cashew genotypes that differed in their susceptibility to mildew. Panicle colonization by O. anacardii reached 100% coverage in all genotypes without fungicide treatment, but rates of infection differed significantly. Triadimenol sprays reduced mildew to less than 9%, even in panicles of highly susceptible genotypes. In the absence of disease, particularly good yield responses with more than nine times more nuts set than untreated controls were achieved by AM6 and AC1, which were categorized as highly susceptible and intermediate, respectively, in reaction to powdery mildew. By contrast, the partially resistant genotypes AZA2 and AC6 both produced yield response ratios of less than 3·0. The targeted treatment of flower panicles to control mildew is recommended, rather than the current practice of wastefully treating whole trees on which all mature leaves are naturally immune to infection.
Brown spot caused by Sphingomonas sp. on yellow Spanish melon fruits in Spain*
Authors: Buonaurio R. , Stravato V. M. , Cappelli C.
Published: March 2003

Brown fruit spot symptoms were observed on yellow Spanish melons (Cucumis melo var. inodorus) grown in greenhouses at Almeria in Spain. Nonsporing, motile, rod‐shaped bacteria were isolated from diseased fruits, which on nutrient agar produced small yellow colonies. Two bacterial isolates, used for further investigations, were pathogenic on fruits but not on cotyledons of Spanish melon plants. They provoked disease symptoms similar to those observed in the greenhouse. Both isolates were Gram‐negative, catalase‐positive, weakly oxidase‐positive and phenylalanine deaminase‐negative. They hydrolysed esculin but not gelatin and they utilized glucose oxidatively. Fatty acid analysis revealed that both isolates belong to the genus Sphingomonas. In addition, 16S rDNA sequence analysis, performed on one isolate, demonstrated that it had a significant sequence similarity (more than 98%) with Sphingomonas pruni and Sphingomonas mali, nonphytopathogenic bacteria isolated from plants. Although enterobacterial repetitive intergenic consensus PCR and repetitive extragenic palindromic PCR seem to indicate that the Sphingomonas isolates from Spanish melon fruits may belong to a new species, DNA–DNA hydridization analysis is necessary to verify this hypothesis.
Molecular characterization of the Cassava brown streak virus coat protein
Authors: Monger W. A. , Seal S. , Isaac A. M. , Foster G. D.
Published: March 2003

A partial sequence of 1114 nucleotides of a virus from cassava brown streak diseased (CBSD) material was obtained. Alignment of the predicted amino acid sequence with those of other members of the Potyviridae showed closest identity with the coat protein of Sweet potato mild mottle virus (genus Ipomovirus). The predicted amino acid sequence has one open reading frame with a 3′ untranslated region of 144 nucleotides and a poly(A) tail. The expressed protein was shown to cross‐react with an antiserum raised previously to a virus isolated from CBSD material. Evidence presented suggests that CBSD is caused by Cassava brown streak virus, a tentative member of the genus Ipomovirus, as this virus is consistently found associated with CBSD.
Pathogenic characteristics of isolates of Aphanomyces euteiches from pea in France
Authors: Wicker E. , Hullé M. , Rouxel F.
Published: March 2003

Aphanomyces root rot (Aphanomyces euteiches) has become a very destructive disease in French pea crops since 1993. The host specificity of the French pea‐infecting populations of this pathogen was investigated by inoculating pea, common vetch, alfalfa, broad bean and green bean with 91 pea‐infecting A. euteiches isolates, originating from the main areas of infestation in France. These isolates were compared to 13 isolates from various countries and hosts (pea, green bean, alfalfa). Virulence phenotypes were defined according to the pathogenicity data on the different hosts: all isolates from France infected two to five legume species, with most infecting pea, vetch, alfalfa and broad bean. Four pathotypes were characterized within the French isolates: one type corresponded to broad host range isolates, the second was composed of isolates preferentially agressive on pea/vetch/alfalfa and weakly aggressive on broad bean, and two others corresponding to more specialized isolates that preferentially infected pea/vetch or pea/vetch/alfalfa. Most isolates from France were preferentially pathogenic on pea, like the pea‐infecting isolates from other countries, but were less specialized than the alfalfa‐ and green bean‐infecting isolates from other countries. These results suggest that A. euteiches isolates may be maintained on wild or cultivated legumes other than pea in France.
Breeding for resistance to Meloidogyne exigua in Coffea arabica by introgression of resistance genes of Coffea canephora
Authors: Bertrand B. , Anthony F. , Lashermes P.
Published: March 2003

Breeding for resistance to root‐knot nematode Meloidogyne exigua in coffee may help in controlling this nematode, which causes substantial harvest losses throughout Latin America. Accessions of Coffea arabica, C. canephora and lines derived from the Timor Hybrid (wild C. arabica × C. canephora interspecific hybrid) were tested in a greenhouse for resistance to gall formation by counting individual galls on the roots of plants inoculated with second‐stage juveniles of a M. exigua population from Costa Rica. The level of introgression from C. canephora was also assessed on 28 resistant and susceptible genotypes in a molecular study with amplified fragment length polymorphism (AFLP) markers. The frequency of resistant plants was very low or even nonexistent in C. arabica and very high in C. canephora with > 78% immune plants and 100% resistant plants. Several lines derived from the interspecific hybrid revealed a high level of resistance similar to that observed in the parent C. canephora species. A molecular study of Timor Hybrid‐derived lines revealed high variability for the number of markers present in the study genotypes. A larger number of introgression markers was found in the group of resistant genotypes than in the susceptible genotypes. However, there were also lines with little introgression that had retained resistance. Based on genetic distances calculated from these markers, two groups of lines were revealed: those derived from Timor Hybrid CIFC1343, and those derived from Timor Hybrids CIFC832/1 and CIFC832/2, which may indicate the existence of different resistance genes in the two groups. The segregations observed in F1 and F2 progeny may be explained by at least a dominant gene. The lines derived from the Timor Hybrid are a worthwhile source of resistance to M. exigua that can be exploited to improve C. arabica with the help of molecular‐assisted selection.
Polygenic powdery mildew disease resistance in Arabidopsis thaliana: quantitative trait analysis of the accession Warschau‐1
Authors: Schiff C. L. , Wilson I. W. , Somerville S. C.
Published: March 2003

To further the understanding of the natural genetic diversity for disease resistance to powdery mildew (Erysiphe cichoracearum) in Arabidopsis thaliana, quantitative trait loci analysis was undertaken on recombinant inbred lines derived from a cross between the resistant accession Warschau‐1 and the susceptible Columbia‐0. Powdery mildew grew less well on Warschau‐1, but the resistance was not associated with a specific block in the infection sequence. Two potential powdery mildew disease‐resistance loci were identified and mapped, one with a major effect and one with a minor effect on disease resistance. The two loci acted in an additive manner to confer resistance, and together they explained 65% of the variation in resistance. In addition, the major powdery mildew disease‐resistance locus was genetically mapped to the bottom of chromosome III, a region containing the powdery mildew resistance loci RPW7, RPW8 and RPW10. Unlike resistance mediated by the RPW8 locus in the accession Moscow‐1, resistance in Warschau‐1 was not correlated with the hypersensitive response, highlighting the influence of genetic background or environmental factors on the expression of disease resistance. Together with the powdery mildew resistance loci described in other studies, these results suggest that A. thaliana is a useful source of natural powdery mildew disease resistance, which potentially can be utilized in fundamental studies and as a tool for applied studies.