bluuebunny/crossref_metadata_2025 huggingface dataset:
Root hydrocarbons as potential markers for determining species composition
Authors: Dawson L. A. , Mayes R. W. , Elston D. A. , Smart T. S.
Published: March 2003

Grasslands can be a complex mixture of plant species. A method is described to allow the identification of both roots and shoots of five different grass species, thus permitting greater knowledge about whole plant allocation and competition in mixed pastures. The five species were Lolium perenne, Festuca ovina, Festuca rubra, Poa trivialis and Agrostis capillaris. N‐alkanes with odd‐numbers of carbon atoms in the chains predominate in plants and in the five grass species studied, concentrations of alkanes of chain length of C29, C31 and C33 were highest. Average concentrations of C27‐C33 alkanes in shoots and roots were 187 and 11 mg kg−1, respectively. This wide range of values required considerable modifications to the method of analysis, including expressing concentrations on an organic matter basis and scaling‐down the procedure. The n‐alkane concentrations in roots are different from those in shoots and therefore values from shoots cannot be used to predict the composition in roots. Using a canonical variate analysis, all five grass species could be separated using concentrations of C26, C31 and C33 values in the roots. The greatest difference occurred between A. capillaris and the others, whereas discrimination was least between the two Festuca species. Defoliation had contrasting effects on the concentration of a few n‐alkanes, but not in the n‐alkanes used to discriminate between grass species. Alkane analysis shows great potential as a method to quantify the species composition of the root biomass beneath mixed pasture species.
Stomatal acclimation to increased CO2 concentration in a Florida scrub oak species Quercus myrtifolia Willd
Authors: Lodge R. J. , Dijkstra P. , Drake B. G. , Morison J. I. L.
Published: March 2003

Native scrub‐oak communities in Florida were exposed for three seasons in open top chambers to present atmospheric [CO2] (approx. 350 μmol mol−1) and to high [CO2] (increased by 350 μmol mol−1). Stomatal and photosynthetic acclimation to high [CO2] of the dominant species Quercus myrtifolia was examined by leaf gas exchange of excised shoots. Stomatal conductance (gs) was approximately 40% lower in the high‐ compared to low‐[CO2]‐grown plants when measured at their respective growth concentrations. Reciprocal measurements of gs in both high‐ and low‐[CO2]‐grown plants showed that there was negative acclimation in the high‐[CO2]‐grown plants (9–16% reduction in gs when measured at 700 μmol mol−1), but these were small compared to those for net CO2 assimilation rate (A, 21–36%). Stomatal acclimation was more clearly evident in the curve of stomatal response to intercellular [CO2] (ci) which showed a reduction in stomatal sensitivity at low ci in the high‐[CO2]‐grown plants. Stomatal density showed no change in response to growth in high growth [CO2]. Long‐term stomatal and photosynthetic acclimation to growth in high [CO2] did not markedly change the 2·5‐ to 3‐fold increase in gas‐exchange‐derived water use efficiency caused by high [CO2].
CO2 transfer conductance, leaf structure and carbon isotope composition of Polygonum cuspidatum leaves from low and high altitudes
Authors: Kogami H. , Hanba Y. T. , Kibe T. , Terashima I. , Masuzawa T.
Published: March 2003

Anatomy and some physiological characteristics of the leaves in Polygonum cuspidatum Sieb. et Zucc., a dioecious clonal herb, were compared between two populations, one from a lowland in Shizuoka City (10 m above sea level), and another from a highland on Mt. Fuji (2500 m above sea level). Leaf mass per area (LMA) of the highland plants was about twice that of the lowland plants. The greater leaf thickness, thicker mesophyll cell walls and higher mesophyll cell density in the highland leaves contributed to the larger LMA. Although mesophyll area exposed to intercellular airspaces was greater in the highland leaves than in the lowland leaves by 30%, the surface area of chloroplasts facing intercellular airspaces was similar between these leaves. CO2 transfer conductance inside the leaf (gi) of the highland leaves (0·75 μmol m−2 s−1 Pa−1) is the lowest recorded for herbaceous plants and was only 40% of that in the lowland leaves. On the other hand, the difference in stomatal conductance was small. δ13C values in the leaf dry matter were greater in the highland leaves by 4‰. These data and the estimation of CO2 partial pressures in the intercellular air spaces and in the chloroplast suggested that the greater dry matter δ13C in the highland leaves, indicative of lower long‐term ratio of the chloroplast stroma to the ambient CO2 partial pressures, would be mainly attributed to their lower gi.
Does engineering abscisic acid biosynthesis in Nicotiana plumbaginifolia modify stomatal response to drought?
Authors: Borel C. , Frey A. , Marion‐Poll A. , Tardieu F. , Simonneau T.
Published: March 2003

The consequences of manipulating abscisic acid (ABA) biosynthesis rates on stomatal response to drought were analysed in wild‐type, a full‐deficient mutant and four under‐producing transgenic lines of N. plumbaginifolia. The roles of ABA, xylem sap pH and leaf water potential were investigated under four experimental conditions: feeding detached leaves with varying ABA concentration; injecting exogenous ABA into well‐watered plants; and withholding irrigation on pot‐grown plants, either intact or grafted onto tobacco. Changes in ABA synthesis abilities among lines did not affect stomatal sensitivity to ABA concentration in the leaf xylem sap ([ABA]xyl), as evidenced with exogenous ABA supplies and natural increases of [ABA]xyl in grafted plants subjected to drought. The ABA‐deficient mutant, which is uncultivable under normal evaporative demand, was grafted onto tobacco stock and then presented the same stomatal response to [ABA]xyl as wild‐type and other lines. This reinforces the dominant role of ABA in controlling stomatal response to drought in N. plumbaginifolia whereas roles of leaf water potential and xylem sap pH were excluded under all studied conditions. However, when plants were submitted to soil drying onto their own roots, stomatal response to [ABA]xyl slightly differed among lines. It is suggested, consistently with all the results, that an additional root signal of soil drying modulates stomatal response to [ABA]xyl.
A novel approach to the in situ measurement of oxygen concentrations in the sapwood of woody plants
Authors: Gansert D. , Burgdorf M. , Lösch R.
Published: March 2003

A novel technique for the physico‐chemical analysis of xylem sap by underwater access to the sapwood of trees is described. In situ measurements of dissolved oxygen in the sapwood are performed by combining this technique with a novel optical method for oxygen detection. In early spring, the oxygen concentration of the sapwood of Betula pendula was in the range of 80–230 µmol O2 L−1, corresponding to an oxygen deficit of 40–75% of air saturation. Oxygen concentration maxima and minima occurred early in the morning and in the afternoon, respectively, whereas xylem sap temperatures showed the reverse pattern. In the sapwood, hypoxia increased from the beginning of bud break until frondescence, when a deficit of 86% of air saturation marked the upper limit of oxygen depletion. There seemed to be no relationship between daily variations of oxygen concentration and xylem sap pressure. In summer, sap flow was a major determinant for the diurnal variation of dissolved oxygen concentration. Oxygen supply to the sapwood was determined by both radial influx into the trunk through intercellular gas spaces and transport of dissolved oxygen via xylem sap flow. Radial influx seemed to be favoured during night‐time, when the trunk was warmer than ambient air. During daytime, the hypoxia of the sapwood rose and increased sharply in the evening, when sap flow velocity approximated zero. High temperature in the sapwood enhanced the respiratory oxygen consumption of the wood parenchyma while the supply of dissolved oxygen via the transpiration stream became ineffective.
Rapid changes in cell wall pectic polysaccharides are closely associated with early stages of aerenchyma formation, a spatially localized form of programmed cell death in roots of maize (Zea maysL.) promoted by ethylene
Authors: Gunawardena A. H. L. A. N. , Pearce D. M. E. , Jackson M. B. , Hawes C. R. , Evans D. E.
Published: March 2003

Aerenchyma formation in roots of maize (Zea maysL.) involves programmed death of cortical cells that is promoted by exogenous ethylene (1 µL L−1) or by endogenous ethylene produced in response to external oxygen shortage (3%, v/v). In this study, evidence that degeneration of the cell wall accompanies apoptotic‐like changes previously observed in the cytoplasm and nucleus (Gunawardenaet al. Planta 212, 205–214, 2001), has been sought by examining de‐esterified pectins (revealed by monoclonal antibody JIM 5), and esterified pectins (revealed by monoclonal antibody JIM 7). In controls, de‐esterified wall pectins were found at the vertices of triangular junctions between cortical cells (untreated roots). Esterified pectins in control roots were present in the three walls bounding triangular cell‐to‐cell junctions. After treatment with 3% oxygen or 1 µL L−1ethylene, this pattern was lost but walls surrounding aerenchyma gas spaces became strongly stained. The results showed that cell wall changes commenced within 0·5 d and evidently were initiated by ethylene in parallel with cytoplasmic and nucleoplasmic events associated with classic intracellular processes of programmed cell death.
Water‐conducting properties of lipids during pollen hydration
Authors: Wolters‐Arts M. , Van Der Weerd L. , Van Aelst A. C. , Van Der Weerd J. , Van As H. , Mariani C.
Published: March 2003

Based on the authors’ previous work an attempt has been made to study water flow in the lipid matrix during pollen hydration. The present study has demonstrated that in the presence of small amounts of water, the type of lipids used defined the time of hydration of pollen in vivo on the stigma and in vitro. Several approaches were used including cryo‐scanning electron microscopy, magnetic resonance imaging and Fourier transform infrared microspectroscopic imaging, with the purpose of detecting very small amounts of water. The results show that no water is detectable in the lipid matrix. It was observed and concluded that the water for pollen hydration accumulates as a thin layer at the contact side between pollen and stigma, during the normal process of pollination in plant species with a wet stigma. However, using the same species deprived of the stigma by cell ablation, it was shown that the layer of water observed in wild‐type plants is not necessary for pollen hydration.
Stomatal acclimation over a subambient to elevated CO2 gradient in a C3/C4 grassland
Authors: Maherali H. , Reid C. D. , Polley H. W. , Johnson H. B. , Jackson R. B.
Published: March 2003

An investigation to determine whether stomatal acclimation to [CO2] occurred in C3/C4 grassland plants grown across a range of [CO2] (200–550 µmol mol−1) in the field was carried out. Acclimation was assessed by measuring the response of stomatal conductance (gs) to a range of intercellular CO2 (a gs–Ci curve) at each growth [CO2] in the third and fourth growing seasons of the treatment. The gs–Ci response curves for Solanum dimidiatum (C3 perennial forb) differed significantly across [CO2] treatments, suggesting that stomatal acclimation had occurred. Evidence of non–linear stomatal acclimation to [CO2] in this species was also found as maximum gs (gsmax; gs measured at the lowest Ci) increased with decreasing growth [CO2] only below 400 µmol mol−1. The substantial increase in gs at subambient [CO2] for S. dimidiatum was weakly correlated with the maximum velocity of carboxylation (Vcmax; r2 = 0·27) and was not associated with CO2 saturated photosynthesis (Amax). The response of gs to Ci did not vary with growth [CO2] in Bromus japonicus (C3 annual grass) or Bothriochloa ischaemum (C4 perennial grass), suggesting that stomatal acclimation had not occurred in these species. Stomatal density, which increased with rising [CO2] in both C3 species, was not correlated with gs. Larger stomatal size at subambient [CO2], however, may be associated with stomatal acclimation in S. dimidiatum. Incorporating stomatal acclimation into modelling studies could improve the ability to predict changes in ecosystem water fluxes and water availability with rising CO2 and to understand their magnitudes relative to the past.
Transient releases of acetaldehyde from tree leaves − products of a pyruvate overflow mechanism?
Authors: Karl T. , Curtis A. J. , Rosenstiel T. N. , Monson R. K. , Fall R.
Published: March 2003

Emissions of acetaldehyde from tree leaves were investigated by proton‐transfer‐reaction mass spectrometry (PTR‐MS), a technique that allows simultaneous monitoring of different leaf volatiles, and confirmed by derivatization and high‐performance liquid chromatography analysis. Bursts of acetaldehyde were released by sycamore, aspen, cottonwood and maple leaves following light–dark transitions; isoprene emission served as a measure of chloroplastic processes. Acetaldehyde bursts were not accompanied by ethanol, but exposure of leaves to inhibitors of pyruvate transport or respiration, or anoxia, led to much larger releases of acetaldehyde, accompanied by ethanol under anoxic conditions. These same leaves have an oxidative pathway for ethanol present in the transpiration stream, resulting in acetaldehyde emissions that are inhibited in vivo by 4‐methylpyrazole, an alcohol dehydrogenase (Adh) inhibitor. Labelling of leaf volatiles with 13CO2 suggested that the pools of cytosolic pyruvate, the proposed precursor of acetaldehyde bursts, were derived from both recent photosynthesis and cytosolic carbon sources. We hypothesize that releases of acetaldehyde during light–dark transitions result from a pyruvate overflow mechanism controlled by cytosolic pyruvate levels and pyruvate decarboxylase activity. These results suggest that leaves of woody plants contribute reactive acetaldehyde to the atmosphere under different conditions: (1) metabolic states that promote the accumulation of cytosolic pyruvate, triggering the pyruvate decarboxylase reaction; and (2) leaf ethanol oxidation resulting from ethanol transported from anoxic tissues.
Temperature dependence of two parameters in a photosynthesis model
Authors: Leuning R.
Published: March 2003

The temperature dependence of the photosynthetic parameters Vcmax, the maximum catalytic rate of the enzyme Rubisco, and Jmax, the maximum electron transport rate, were examined using published datasets. An Arrehenius equation, modified to account for decreases in each parameter at high temperatures, satisfactorily described the temperature response for both parameters. There was remarkable conformity in Vcmax and Jmax between all plants at Tleaf < 25 °C, when each parameter was normalized by their respective values at 25 °C (Vcmax0 and Jmax0), but showed a high degree of variability between and within species at Tleaf > 30 °C. For both normalized Vcmax and Jmax, the maximum fractional error introduced by assuming a common temperature response function is < ± 0·1 for most plants and < ± 0·22 for all plants when Tleaf < 25 °C. Fractional errors are typically < ± 0·45 in the temperature range 25–30 °C, but very large errors occur when a common function is used to estimate the photosynthetic parameters at temperatures > 30 °C. The ratio Jmax/Vcmax varies with temperature, but analysis of the ratio at Tleaf = 25 °C using the fitted mean temperature response functions results in Jmax0/Vcmax0 = 2·00 ± 0·60 (SD, n = 43).
Causes of variation in cold hardiness among fast‐growing willows (Salix spp.) with particular reference to their inherent rates of cold hardening
Authors: Lennartsson M. , Ögren E.
Published: March 2003

Causes of variation in cold hardiness in the autumn were assessed among closely related, fast‐growing clones of willow of northern/continental and southern/maritime origins, under controlled regimes and natural conditions. Cold hardiness was assessed by controlled freezing followed by injury analysis, based on measurements of chlorophyll fluorescence (stems) and electrolyte leakage (leaves). During growth at a given temperature, the cold hardiness of the clones' stems was negatively correlated with their rate of growth. This apparently phenotypic variation was independent of temperature and, hence, the absolute growth rate. At later stages, cold hardiness of stems varied mainly with respect to genetic differences in the timing and rate of cold hardening. Cold hardening began up to 7 weeks earlier in northern/continental clones, and their rates of hardening in cool temperature regimes were up to three times higher than in southern/maritime clones. Ranking of clones with respect to rates was essentially the same whether natural or abrupt reductions of day length were used to trigger cold hardening. Results closely agreed with those of a previous field trial. Comparisons of rates at cool and warm temperatures suggest that cold hardening became increasingly dependent on cool temperatures with time. Increasing sucrose‐to‐glucose ratios, and especially dry‐to‐fresh weight ratios, paralleled early cold hardening. Before leaves were shed in the autumn they underwent cold hardening in parallel with stems, eventually allowing them to tolerate temperatures down to −10 °C.
Effect of chilling on antioxidant enzymes and DPPH‐radical scavenging activity of high‐ and low‐vigour cucumber seedling radicles
Authors: Kang H.‐M. , Saltveit M. E.
Published: March 2003

The chilling tolerance of cucumber seedling radicles was influenced by their relative levels of vigour. Radicles of high‐vigour seedlings grew to 20 mm in length in 36 h at 25 °C, whereas it took 60 h for low‐vigour seedling radicles to reach that length. Chilling at 2·5 °C for 48 h inhibited the subsequent growth of high‐ and low‐vigour seedlings by 39 and 68%, respectively. The 2,3,5‐triphenyltetrazolium chloride (TTC) viability index, and α,α‐diphenyl‐β‐picrylhydrazyl (DPPH)‐radical scavenging activity were higher in high than low‐vigour radicles. Higher ascorbate peroxidase (APX) and catalase (CAT) enzyme activity, DPPH‐radical scavenging activity, and recovery of CAT activity after chilling in high‐vigour radicles corresponded with their higher level of chilling tolerance in comparison with low‐vigour radicles. In contrast, elevated levels of superoxide dismutase, glutathione reductase and guaiacol peroxidase appear to be correlated with chilling injury since they only showed substantial increases in activity in the more chilling‐­sensitive low‐vigour radicles after chilling. Manipulation of APX, CAT, and/or DPPH activity could produce plants with superior and persistent chilling tolerance.
Regulation of root respiration in two species of Plantago that differ in relative growth rate: the effect of short‐ and long‐term changes in temperature
Authors: Covey‐Crump E. M. , Attwood R. G. , Atkin O. K.
Published: March 2003

This study investigates the effect of short‐ and long‐term changesin temperature on the regulation of root respiratory O2 uptakeby substrate supply, adenylate restriction and/or the capacityof the respiratory system. The species investigated were the lowland Plantagolanceolata L. and alpine Plantago euryphylla Briggs, Carolin& Pulley, which are inherently fast‐ and slow‐growing, respectively. Theplants were grown hydroponically in a controlled environment (constant23 °C). The effect of long‐term exposure to lowtemperature on regulation of respiration was also assessed in P.lanceolata using plants transferred to 15/10 °C(day/night) for 7 d. Exogenous glucose and uncoupler (CCCP)were used to assess the extent to which respiration rates were limitedby substrate supply and adenylates. The results suggest that adenylatesand/or substrate supply exert the greatest control overrespiration at moderate temperatures (e.g. 15–30 °C)in both species. At low temperatures (5–15 °C),CCCP and glucose had little effect on respiration, suggesting thatrespiration was limited by enzyme capacity alone. The Q10 (proportionalincrease of respiration per 10 °C) of respirationwas increased following the addition of CCCP and/or exogenousglucose. The degree of stimulation by CCCP was considerably lowerin P. euryphylla than P. lanceolata. This suggeststhat respiration rates operate much closer to the maximum capacity in P.euryphylla than P. lanceolata. When P. lanceolata wastransferred to 15 °C for 7 d, respirationacclimated to the lower growth temperature (as demonstrated by an increasein respiration rates measured at 25 °C). In addition,the Q10 was higher, and the stimulatory effectof exogenous glucose and CCCP lower, in the cold‐acclimated rootsin comparison with their warm‐grown counterparts. Acclimation of P.lanceolata to different day/night‐time temperatureregimes was also investigated. The low night‐time temperature wasfound to be the most important factor influencing acclimation. The Q10 valueswere also higher in plants exposed to the lowest night‐time temperature.The results demonstrate that short‐ and long‐term changes in temperaturealter the importance of substrate supply, adenylates and capacityof respiratory enzymes in regulating respiratory flux.
Metabolic regulation of genes encoding cytochromecand cytochromecoxidase subunit Vb inArabidopsis
Authors: WELCHEN E. , CHAN R. L. , GONZALEZ D. H.
Published: March 2003

In this study an analysis of the expression of fourArabidopsisnuclear genes encoding components of the mitochondrial cyanide‐sensitive respiratory pathway: two genes encoding cytochromecoxidase subunit Vb (COX5b) and two genes encoding cytochromec(Cytc), was carried out. Northern blot analysis indicated that these genes are expressed in several organs. Incubation of plants in solutions containing metabolizable sugars produced an increase in transcript levels. The effect of carbohydrates showed the same time and concentration dependence for the four genes, suggesting the operation of a common regulatory mechanism. Light produced an increase in transcript levels, although smaller than that produced by sugars. Incubation of plants in solutions with different nitrogen sources also produced changes in expression. In the presence of ammonium, higher transcript levels were observed with respect to plants treated with either nitrogen‐free or nitrate solutions. Nitrate, on the other hand, produced a slight decrease in transcript levels and abolished the inducing effect of ammonium. Reporter enzyme activity in transgenic plants carrying a fusion of aCytcgene promoter with the beta‐glucuronidase coding region was increased by the inclusion of sucrose and ammonium in the culture medium. The present results suggest that carbon and nitrogen metabolites act in concert to regulate the expression of different components of the cyanide‐sensitive respiratory pathway.
Long‐distance transport in non‐vascular plants
Authors: RAVEN J. A.
Published: March 2003

Many macroalgae have significant spatial differentiation involving higher rate resource use at a site than of acquisition of that resource from the environment at that site. Long‐distance symplasmic transport of solutes occurs in some large green algae where the solutes are moved in streaming cytoplasm. In some large brown algae there is evidence of long‐distance symplasmic transport of organic C and other solutes. Structural and physiological data suggest that while the transport in ‘sieve tubes’ of Macrocystis might be by a Munch pressure flow mechanism the transport in many other brown algae is less likely to be by this mechanism. Less is known of long‐distance symplasmic transport in red algae. In terrestrial bryophytes transpiration occurs and in some liverworts and many mosses (but not in hornworts) there are files of dead cells in their tissues which may, and in some cases certainly, function in long‐distance apoplasmic water transport. The hydraulic conductivity of these conduits is poorly characterized. Long‐distance symplasmic transport in some mosses have been characterized both structurally and physiologically, but in other mosses and in liverworts the evidence is only structural. Most of these symplasmic transport pathways seem to have a high resistance to flow.
Cope's Rule and the evolution of long‐distance transport in vascular plants: allometric scaling, biomass partitioning and optimization
Authors: ENQUIST B. J.
Published: March 2003

Recent advances in allometric theory have proposed a novel quantitative framework by which to view the evolution of plant form and function. This general theory has placed strong emphasis on the importance of long‐distance transport in shaping the evolution of many attributes of plant form and function. Specifically, it is hypothesized that with the evolutionary increase in plant size natural selection has also resulted in vascular networks that minimize scaling of total hydrodynamic resistance associated with increasing transport distances. Herein the central features of this theory are reviewed and a broad sampling of supporting but yet preliminary empirical data are analysed. In particular, subtle attributes of the scaling of tracheid and vessel anatomy are hypothesized to be crucial for the evolution of increased plant size. Furthermore, the importance of minimizing hydrodynamic resistance associated with increased transport distances is also hypothesized to be reflected in an isometric scaling relationship between stem mass,MSand root mass,MR(i.e.MS ∝ MR). Preliminary data from multiple extant and fossil plant taxa provide tantalizing evidence supporting the predicted relationships. Together, these results suggest that selection for the minimization of the scaling of hydrodynamic resistance within plant vascular networks has in turn allowed for the enormous diversification in vascular plant size.
Ascochyta blight of chickpea in Australia: identification, pathogenicity and mating type
Authors: Khan  , Ramsey  , Corbière  , Infantino  , Porta‐Puglia  , Bouznad  , Scott
Published: March 2003

The aetiology of blight of chickpea in South Australia was studied following sporadic disease outbreaks over several years that had been tentatively identified as Phoma blight. Nine fungal isolates from diseased chickpeas were tested for pathogenicity in the glasshouse, of which two caused symptoms resembling those of Ascochyta blight. The two aggressive isolates were identified asAscochyta rabieibased on morphological characteristics of cultures and RAPD analysis. This was further confirmed by successful mating to international standard isolates, which showed that the two Australian isolates were MAT1‐1. These isolates are accessioned as DAR 71767 and DAR 71768, New South Wales Agriculture, Australia. This is the first time thatA. rabieihas been positively identified in commercial chickpeas in the southern hemisphere. The pathogen was found (in 1992) in only one of 59 seed samples harvested throughout Australia between 1992 and 1996 and tested using International Seed Testing Association methods. The teleomorph has not been found in Australia and results to date suggest that only one mating type is present. This suggests that quarantine restrictions on imported chickpea seed should be retained to prevent the introduction of the opposite mating type.
Stability of the aphid transmission phenotype in cucumber mosaic virus
Authors: Ng  , Perry
Published: March 2003

The stability of the aphid transmission phenotype in seven field isolates of cucumber mosaic virus (CMV) was studied, using aphids Aphis gossypii and Myzus persicae. Field isolates, obtained from four vegetable crops, were propagated in squash and Nicotiana glutinosa, and passaged by either aphid transmission or mechanical transfer. All seven isolates were transmissible by both aphids and this aphid transmission phenotype was stable after 20–24 mechanical passages. Upon further mechanical passaging, one of the seven isolates, CMV‐2 A1‐MT 60x, lost its transmissibility by Myzus persicae but was still transmissible by Aphis gossypii, although at a reduced rate. Isolates maintained by both aphid transmission and mechanical transfer were transmitted more efficiently by Aphis gossypii than by Myzus persicae. A comparison of the RNA profiles showed no major differences among the CMV isolates before and after mechanical passage.
Modelling the spatio‐temporal deployment of resistant varieties to reduce the incidence of rice tungro disease in a dynamic cropping system
Authors: Holt  , Chancellor
Published: March 2003

A dynamic cropping system was represented by a square lattice of fields in which crops were successively harvested and replanted. A spectrum of crop ages existed at any one time and the virus disease persisted by spread of inoculum between crops. Such a situation is typical of many areas of tropical irrigated rice cultivation in which rice tungro virus disease (RTVD) occurs. Using a mathematical model of the epidemiology of RTVD in the cropping system, the deployment of fields of a genotype expressing some resistance to the disease was investigated. Previous studies on the effect of genotype mixtures on disease progress within a single crop have shown that both the rate of disease increase and the rate of focus expansion were proportional to the logarithm of the fraction of susceptible plants in the mixture. Here, looking at long‐term disease incidence in a dynamic cropping system, it was found that this same ‘logarithmic rule’ applied, provided that resistant crop deployment was spatially random. A relatively large proportion of fields had to be planted with resistant varieties in order to have sufficient area‐wide impact on inoculum to reduce disease incidence in fields of susceptible varieties. In many rice cropping systems there are two growing seasons per year and the modelling indicated that the best strategy was to concentrate deployment of resistant varieties in the season of greatest disease spread. Attempts to minimize inoculum carry‐over to the ‘high spread’ season by concentrating resistant varieties in the previous season had little effect over a range of simulated conditions. In considering recommendations for the management of RTVD, a conflict existed between the reduction of disease incidence strategically and in the individual fields of a newly deployed variety. To maximize area‐wide strategic impact, small genotype units and random patterns were best, but to protect individual fields, large units and concentrated deployment were best.
Seedling and adult plant resistance to downy mildew (Peronospora parasitica) in cauliflower (Brassica oleracea convar. botrytis var. botrytis)
Authors: Jensen  , Hockenhull  , Munk
Published: March 2003

Seedlings of six cauliflower cultivars (Brassica oleracea convar. botrytis var. botrytis) were assessed for resistance to a Danish isolate of Peronospora parasitica, under controlled conditions. Resistance, characterized by restricted sporulation and necrotic dark flecks at the inoculation site on the cotyledons, was expressed in the hybrids 9306 F1, 9311 F1, and the open pollinated cultivar Perfection. Testing of the parent lines and F2 generations of the two resistant hybrids suggested that resistance was a dominantly inherited trait controlled by a single gene. Inoculation of the cultivars with seven isolates, from different geographical origins, showed that the resistance was isolate specific. The two hybrid cultivars expressing cotyledon resistance and two hybrids expressing susceptibility were assessed for adult plant resistance under field conditions. The AUDPC (Area Under the Disease Progress Curve), based on disease incidence and severity, revealed significant differences between the cultivars. At harvest, the cultivars exhibited significantly different levels of defoliation and curd attack. The cultivars 9306 F1 and 9311 F1 showed high levels of resistance in all assessments, whereas the two cultivars exhibiting susceptibility at the seedling stage, 9304 F1 and 9305 F1, also exhibited susceptibility through the adult plant stage. Thus, the resistance exhibited under field conditions resembled that identified at the seedling stage under controlled conditions. The results suggest that cotyledon resistance similar to that described could provide resistance throughout the adult plant stage, including curds.
European stone fruit yellows phytoplasmas associated with a decline disease of apricot in southern England
Authors: Davies D. L. , Adams A. N.
Published: March 2003

Phytoplasmas detected by fluorescence microscopy and polymerase chain reaction (PCR) have been discovered infecting Prunus trees at a site in south‐east England. The pathogens were detected in tissue samples taken in autumn and also in spring. The symptoms in infected trees varied from severe decline to absence. PCR experiments using group‐specific primers to amplify regions of the 16S RNA gene indicated that the phytoplasmas are similar to European stone fruit yellows isolates occurring in southern and eastern Europe. This is the first record of phytoplasmas in Prunus species in the UK. The origin of the infection is unknown. The implications of this new disease for the fruit industry are discussed.
Different forms of interference between two tobamoviruses in two different hosts
Authors: Aguilar I , Sánchez F , Ponz F
Published: March 2003

Oilseed rape mosaic (ORMV) and tobacco mild green mosaic (TMGMV) tobamoviruses interfered with each other when infecting the same host, and interference was host‐dependent. In tobacco cross‐protection was obtained in two ways: the protecting virus prevented the accumulation of the challenging virus, even in the inoculated leaf; in Arabidopsis, protection was obtained only when the protecting virus was TMGMV. The protecting mechanism in Arabidopsis appeared to differ from that operating in tobacco. Although ORMV could be detected in the inoculated leaf, TMGMV prevented systemic infection by ORMV. Thus the host appears to play an important role in this type of cross‐protection.
Estimating the global severity of potato late blight with GIS‐linked disease forecast models
Authors: Hijmans R. J. , Forbes G. A. , Walker T. S.
Published: March 2003

Global severity of potato late blight was estimated by linking two disease forecast models, Blitecast and Simcast, to a climate data base in a geographic information system (GIS). The disease forecast models indirectly estimate late blight severity by determining how many sprays are needed during a growing season as a function of the weather. Global zonation of estimated late blight severity was similar for both forecast models, but Blitecast generally predicted a lower number of sprays. With both forecast models, there were strong differences between potato production zones. Zones of high late blight severity include the tropical highlands, western Europe, the east coast of Canada and northern USA, south‐eastern Brazil and central‐southern China. Major production zones with a low late blight severity include the western plains in India, where irrigated potato is produced in the cool dry season, north‐central China, and the north‐western USA. Using a global GIS data base of potato production, the average number of sprays was calculated by country. These averages were compared with estimates of current fungicide use. The results using Blitecast and Simcast were correlated but only Blitecast estimates correlated with observed data for developed countries. The estimated number of sprays, whether from Blitecast or Simcast, did not correlate with the observed number of sprays in developing countries, and in a number of developing countries the predicted optimal number of sprays was much higher than the actual number observed. In these countries, increased access to host resistance and fungicides could have a strong economic impact.
Reverse transcription–detection of immobilized, amplified product in a one‐phase system (RT–DIAPOPS) for the detection of potato virus Y
Authors: Nicolaisen M. , Rasmussen H. N. , Husted K. , Nielsen S. L.
Published: March 2003

An RT–DIAPOPS (reverse transcription–detection of immobilized, amplified product in a one‐phase system) assay was developed for the detection of potato virus Y (PVY). The sensitivity of the assay was 0·5 pg when virions were added directly to the RT reaction. The assay was capable of detecting all isolates investigated, representing several taxonomic groups of PVY. The RT–DIAPOPS offers an attractive alternative to RT–polymerase chain reaction (PCR) as it does not depend on gel electrophoresis to detect virus‐specific PCR products. Finally, as amplicons are covalently attached to a solid phase, it minimizes the risk of contamination.
Presence in Leptosphaeria maculans populations of isolates virulent on resistance introgressed into Brassica napus from the B. nigra B genome
Authors: Brun H. , Ruer D. , Levivier S. , Somda I. , Renard M. , Chèvre A. M.
Published: March 2003

The resistance carried by chromosome 4 of the Brassica B genome confers on the Brassica napus–B. nigra addition line ‘LA4+’ a high level of resistance to Leptosphaeria maculans isolates at the cotyledon stage under controlled conditions and at all growth stages under field conditions. This resistance has never been used commercially in B. napus varieties. To determine the potential durability of this new resistance, it is necessary to investigate whether it exerts selective pressure on fungus populations. A study of the pathogenicity of 57 single ascospore isolates of L. maculans on this line at the cotyledon stage was carried out to examine possible race specificity of the resistance. Two isolates were clearly virulent and three had intermediate aggressiveness on the ‘LA4+’ line. Two B‐group isolates and 53 A‐group isolates, including isolates from darkening tissue of resistant plants of the ‘LA4+’ line and cv. Junius (B. nigra), were virulent on the susceptible isogenic ‘LA–’ line. These results demonstrate that: (i) the resistance of the ‘LA4+’ oilseed rape line, conferred on B. napus by B. nigra chromosome 4, is race specific at the cotyledon stage; and (ii) the resistant material can act as a reservoir of virulent isolates for susceptible oilseed rape lines.
Presence of European stone fruit yellows (ESFY or 16SrX‐B) phytoplasmas in apricots in Austria
Authors: Laimer Da Câmara Machado M. , Paltrinieri S. , Hanzer V. , Arthofer W. , Strommer S. , Martini M. , Pondrelli M. , Bertaccini A.
Published: March 2003

A severe decline of apricot trees, present in Austria for several years, has recently reached notifiable levels. Initial symptoms on affected trees resemble deficiencies in water and nutrient supplies, expressed as leaf rolling, chlorosis and early reddening, leading to sudden dieback during the growing season. Small, wilted fruit and dried leaves may also persist during the autumn. Phytoplasmas belonging to the 16SrX‐B subgroup of European stone fruit yellows (ESFY) were identified by nested polymerase chain reaction/restriction fragment length polymorphism analysis in a high percentage of affected trees from two different regions of Austria.
Detection of Xylophilus ampelinus in grapevine cuttings using a nested polymerase chain reaction
Authors: Botha W. J. , Serfontein S. , Greyling M. M. , Berger D. K.
Published: March 2003

A sensitive and specific assay was developed to detect bacterial blight of grapevine caused by Xylophilus ampelinus (Panagopoulos, 1969) comb. nov. in grapevine cuttings. The 16S−23S rDNA intergenic spacer region of X. ampelinus was sequenced and pathogen‐specific primers were designed from a region in the spacer between the tRNA (Ala) and the 23S genes. A nested PCR (n‐PCR) reaction was applied with a first‐stage PCR using universal primers within the ends of the 16S and 23S genes, followed by a second‐stage PCR with nested primers specific to the X. ampelinus spacer region. A 277‐bp fragment was amplified from 38 Xylophilus strains tested, but not from saprophytes associated with grapevine or phylogenetically related phytobacteria. The 277‐bp product was shown to be derived from the X. ampelinus spacer region by restriction with Dra I, Sau 3AI, Taq I and Msp I, Southern hybridization and genomic DNA dot blots. When the (n‐PCR) procedure was applied in the absence of nontarget DNA, the limit of detection was less than 10 colony‐forming units (CFU) per µL. The same number of X. ampelinus CFU could be detected in the presence of 1·5 × 105 CFU µL−1 of Erwinia herbicola cells using the n‐PCR procedure.
Effects of nutrient solution pH on the survival and transmission of Clavibacter michiganensis ssp. michiganensis in hydroponically grown tomatoes
Authors: Huang R. , Tu J. C.
Published: March 2003

The effect of pH on the survival of Clavibacter michiganensis ssp. michiganensis and its transmission via roots of tomato in hydroponic culture was studied in laboratory and greenhouse experiments. In a laboratory experiment, C. m. ssp. michiganensis could not survive for 24 h in nutrient solutions with a pH of 4·0 or 4·5, while 1, 14, 51 and 62% of inoculum survived at pH 5·0, 5·5, 6·0 and 6·5, respectively. When tomato plants were inoculated with C. m. ssp. michiganensis through wounds on the stems, the bacteria moved downward from the inoculation site to the roots and infectious bacteria were released from the roots into the nutrient solution. Of two pH regimes tested in greenhouse nutrient‐film technique (NFT) culture, the C. m. ssp. michiganensis population was significantly lower in pH 5·0 than in pH 6·5 in most sampling data. In treatments in which C. m. ssp. michiganensis was introduced by transplanting two root‐inoculated plants, significantly more plants developed canker at pH 6·5 (34 out of 48 plants) than at pH 5·0 (11 out of 48 plants). When the bacterium was introduced by transplanting two stem‐inoculated plants at pH 6·5, seven out of 24 plants developed canker. The potential of pH manipulation in controlling tomato bacterial canker in hydroponic culture is discussed.
Loss of pathogenicity in the blue‐stain fungus Ceratocystis polonica
Authors: Krokene P. , Solheim H.
Published: March 2003

The pathogenicity and growth of six cultures of the bark‐beetle‐associated blue‐stain fungus Ceratocystis polonica were compared. Four were subcultures, established at different times, of the same isolate (80–53/7), and at least one of these was suspected to have lost its pathogenicity to Norway spruce (Picea abies) during subculturing. Two other cultures (93–208/115 and 94–169/13) were pathogenic. The pathogenicity of all cultures to Norway spruce was compared in three inoculation experiments, using (i) massive inoculation (≈144 inoculations per tree), (ii) low‐density inoculation (14 inoculations per tree) of larger trees and (iii) single inoculation of 2‐year‐old seedlings. Fungal growth rates were tested in vitro on malt agar, and on malt agar under oxygen‐deficient conditions. Isolates 93–208/115 and 94–169/13 and one of the subcultures of isolate 80–53/7 were pathogenic in all three inoculation experiments. Two other subcultures were nonpathogenic, while the last subculture was intermediate. The pathogenic cultures had higher growth rates on malt agar than the nonpathogenic and intermediate cultures, and they also grew better under oxygen‐deficient conditions. These results demonstrate that blue‐stain fungi may lose their pathogenicity after serial vegetative transfers on artificial substrates. The results are also consistent with the hypothesis that rapid growth and the ability to grow in oxygen‐poor environments are important pathogenicity factors in blue‐stain fungi.
Gas chromatography–mass spectrometry analyses of volatile organic compounds from potato tubers inoculated with Phytophthora infestans or Fusarium coeruleum
Authors: De Lacy Costello B. P. J. , Evans P. , Ewen R. J. , Gunson H. E. , Jones P. R. H. , Ratcliffe N. M. , Spencer‐Phillips P. T. N.
Published: March 2003

Volatile organic compounds (VOCs) collected from potato tubers inoculated with Phytophthora infestans (late blight), Fusarium coeruleum (dry rot) or sterilized distilled water (as a control) were analysed using gas chromatography–mass spectrometry (GC–MS) and gas chromatography–flame ionization detection (GC–FID). A total of 52 volatiles were identified by GC–MS in the headspaces above P. infestans‐ and F. coeruleum‐inoculated tubers after incubation for 42 days in the dark at 10°C. Of these VOCs, the six most abundant were common to both pathogens. These were benzothiazole (highest abundance), 2‐ethyl‐1‐hexanol (second highest abundance), and at approximately equal third abundance, hexanal, 2‐methylpropanoic acid‐2,2‐dimethyl‐1‐(2‐hydroxy‐1‐methylethyl)‐propyl ester, 2‐methylpropanoic acid‐3‐hydroxy‐2,4,4‐trimethyl‐pentyl ester and phenol. In addition, styrene also occurred at approximately equal third abundance in the headspace of F. coeruleum‐inoculated tubers, but at lower abundance in the headspace of P. infestans‐inoculated tubers. Some VOCs were specific to each pathogen. Butanal, 3‐methylbutanal, undecane and verbenone were found at low levels only in the headspace of tubers inoculated with P. infestans, while 2‐pentylfuran and copaene were found only in the headspace of tubers inoculated with F. coeruleum. Additionally GC–FID analysis identified ethanol and 2‐propanol in the liquid exudate from both P. infestans‐ and F. coeruleum‐inoculated tubers after incubation for 35 days, and in the headspace after incubation for 42 days. These data provide key information for developing a sensor‐based early warning system for the detection of postharvest diseases in stored potato tubers.
The effect of incorporating straw or manure into the soil on the natural microflora of winter wheat
Authors: Rodgers‐Gray B. S. , Shaw M. W.
Published: March 2003

Over 3 years, five crops of winter wheat with different fertilization or pesticide treatments were grown in replicated plots in which straw, cattle manure or nothing was incorporated into the soil. It was previously shown that severities of several foliar diseases were reduced by the treatment with straw. Treatments with straw slightly increased leaf microbial numbers at growth stage (GS) 10, and significantly but slightly decreased numbers at GS 60 and 70, when averaged over all crops. There was no evidence of differences in potential for biological control between plots, because no differences were demonstrated between treatments in the proportion of phylloplane residents able to produce chitinase, siderophores or antibiotics. There was no link between soil and leaf nitrogen and microbial populations or soil amendment. The two youngest leaves of straw‐treated plants remained green longer than leaves from untreated or manure‐treated plants. Microbial numbers differed between crops, but within crops were more stable on leaves and ears than in soil. Soil populations were larger before the crops were sown. Bacteria predominated over fungi in all habitats throughout the growing season. The ratio of Gram‐negative to Gram‐positive bacteria recovered was similar on leaves and in soil, but not on ears. Soil and leaf microbes utilized similar carbon sources. More leaf epiphytes than soil microbes produced siderophores. The majority of identified organisms belonged to only a few species. Chromogenic organisms were more abundant on aerial surfaces. A fungicide, chlorothalonil, was applied in one crop; it reduced the microbial population but did not alter its composition (without affecting the reduction in disease due to straw). It is postulated that straw acts in the field by altering plant physiology and thus altering both microbial colonization and disease.