bluuebunny/crossref_metadata_2025 huggingface dataset:
Biology and Control of Entyloma eryngii (Cda.) de By., the Cause of a Leaf Spot Disease on the Blue Thistle (Eryngium alpinum L.)
Authors: Rüegg J.
Published: May 2008

The blue thistle (Eryngium alpinum L.), an indigenous perennial flower of the alps, is grown in mountainous regions of south‐eastern Switzerland. The commercial value of the fresh cut flowers can be seriously reduced due to a leaf spot disease caused by the smut fungus Entyloma eryngii (Cda.) de By. The fungus produces thick walled chlamydospores and two types of conidia. The disease appears to be favoured by cool‐rainy weather and a dense foilage resulting in long periods of leaf wetness. Control of the disease can be achieved with the protective fungicide mancozeb or even more efficiently with the systemic ergosterol‐biosynthesis‐inhibiting fungicides cyproconazole and difenoconazole.
Maintenance of MLOs (Mycoplasma‐like Organisms) on Populus alba Micropropagation
Authors: Cousin Marie‐Thérèse , Roux Jacqueline , Millet Nadège , Michel Marie‐France
Published: May 2008

Populus alba plantlet micropropagation has been used for maintaining MLOs more than three years in samples collected from infected trees in Paris. Symptoms were observed on plantlets obtained from subcultures of the apical, middle and basal parts of the stems, and from the roots. Fluorescent microscopy failed to detect MLOs in the apical part of the plantlets and showed that they increased near the roots. Electron microscopy confirmed their presence. Some root sieve tubes were completely packed with MLOs. The sensitivity of the two methods used, subculturing and microscopy, for detection of MLOs is discussed. The symptoms remained for one year in plants regenerated from diseased plantlets and grown in the greenhouse. Then they started to disappear.
Temperature‐induced Alterations in the Expression of Susceptibility of Cassava to Colletotrichum gloeosporioides f. sp. manihotis
Authors: Bruggen P. van der , Gregoire D. , Maraite H.
Published: May 2008

Cassava plants (Manihot esculenta Crantz) were incubated at 15, 25 or 35 °C after inoculation of green stems with Colletotrichum gloeosporioides (Penz.) f. sp. manihotis Chev. At 25 °C, the cultivar TMS 30211 was less susceptible than the cultivar TMS 30337. At 35 °C, compared to 25 °C, the lesion diameter was reduced in both cultivars, the cassava stem extracts showed an enhanced fungitoxicity, the grem tubes were more sensitive to the stem extracts and a layer of lignified, cells developed earlier around the infected tissues. At 15 °C, the lesions in both cultivars extended more rapidly than at the other temperatures, even though 15 °C, compared to 25 °C, caused a 50% reduction of mycelial growth rate on oat meal agar.
Effects of Different Cropping Systems on the Occurrence of Fluorescent Pseudomonads
Authors: Mohamed Elsherif Dr. , Grossmann F.
Published: May 2008

In field experiments, winter wheat was grown under different crop rotation regimes (monoculture; rotation with field beans) and differentiated intensity (cv.‘Jubilar’ with 120 kg N/ha and 1l CCC/ha; cv.‘Okapi’ with 180 kg N/ha and l CCC/ha). Plant, protection measures were carried out at three levels (no treatment; specific treatments under consideration of damage thresholds; routine spraying program). The occurrence of aerobic bacteria, fluorescent pseudomonads and strong siderophore‐producers as well as the effect of the different cropping systems on the two groups of bacteria mentioned last were determined during the vegetation period at the beginning of shooting, at full bloom and after harvesting on the surface of the roots of wheat plants. In comparison to the total population of aerobic bacteria, the populations of fluorescent pseudomonads and of the strong siderophore‐producing bacteria changed in a characteristic way: whereas at the beginning of shooting the highest and at full bloom the, lowest numbers were determined, a slight increase could be observed after harvest.

On roots of wheat plants in monoculture, higher numbers of fluorescent pseudomonads and strong siderophore‐producers were detected at the begining of shooting and at full bloom, than on those grown in rotation with field beans. The roots of cv. ‘Okapi’ (higher cropping intensity) were colonized to a higher degree by both groups of bacteria as compared to those of cv. ‘Jubilar’. After application of herbicides, a stimulation of these micro‐organisms was observed at the beginning of shooting.

The influences of different crop rotation schemes, intensities of cropping and plant protection measures on the occurrence of fluorescent pseudomonads were altogether less pronounced than the natural fluctuations of the population during the growth of the wheat.

On the basis of morphological, physiological and biochemical properties, it could be shown that different biovars of the species Pseudomonas fluorescens dominated in the experimental field.
Effect of Nitrogen and Powdery Mildew on the Yield Formation of Two Winter Barley Cultivars1
Authors: Oerke E.‐C. , Schönbeck F.
Published: May 2008

In field experiments the effect of powdery mildew on the yield formation of two barley cultivars ‘Catinka’ (partially resistant) and ‘Tapir’ (susceptible) was investigated in relation to three levels of nitrogen fertilization (40, 90, 150 kg N/ha). Nitrogen increased especially the single ear yield of cv.‘Catinka’, whereas cv.‘Tapir’ showed symptoms of N oversupply. Infection density of Erysiphe graminis hordei also increased with increased nitrogen supply, although it decreased transiently, at the highest N level for cv.‘Tapir’. In general, cv.‘Catinka’ was less tolerant to infections with E. graminis than cv.‘Tapir’, but yield response of both cultivars to powdery mildew (17, 11 and 8 % and 12, 16, and 12 % yield losses for cv.,‘Catinka’ and ‘Tapir’. respectively) showed cultivar × nitrogen interrelationships. Starch and protein contents of grains indicated differences in the intensity of detrimental effects caused by powdery mildew limiting the formation of carbohydrates and/or the translocation processes. Regression analysis demonstrated a closer correlation of yield losses with the photosynthetically active leaf area (r =+0.96 and +0.93 for ‘Catinka’ and ‘Tapir’) than with disease intensity (r =−0.32 and −0.85). Theinte,rpretation of disease/yield loss relations and the detrimental effect of powdery mildew are discussed with reference to plant resistance, remaining green leaf area, the availability of nutrients, to ‘sink and source’ conditions and to the occurrence of,additional environmental stresses.
Pathogenicity of Some European Collections of Crown Rust (Puccinia coronata Corda) on Cultivars of Perennial Ryegrass
Authors: Potter L. R. , Cagaś B. , Paul V. H. , Birckenstaedt E.
Published: May 2008

Three collections of crown rust (Puccinia coronata), from Czechoslovakia, West Germany and the U.K., were tested for their pathogenicity on sixteen cultivars of perennial ryegrass. The Czechoslovakian collection had the highest level of infection on twelve of the cultivars, although with most cultivars there were no significant differences in infection levels. Three cultivars, although with most cultivars there were no significant differences in infection levels. Three cultivars, Kerem, Loret, ta and Tando, contained qualitative resistance to crown rust which was overcome by the Czechoslovakian collection, although they retained a moderately high level of background resistance to this collection.
Differentiation of Closely Related Globodera pallida (Stone) Populations by Means of DNA Restriction Fragment Length Polymorphisms (RFLPs)
Authors: Schnick D. , Rumpenhorst H. J. , Burgermeister W.
Published: May 2008

A small genomic library from DNA of G. pallida population Delmsen (pathotype 3) was constructed. A number of clones were tested as hybridization probes with 21 G. pallida and 6 G. rostochiensis populations. The two species were easily distinguished by their hybridization patterns. A total of 32 RFLP markers were identified which permitted the differentiation of all G. pallida populations. By means of cluster analysis of the RFLP data the genetic distances between the 21,G. pallida populations were calculated and a dendrogram was constructed. The arrangement of the 21 G. pallida populations in the dendrogram suggests a partial correlation between genetic distance and virulence according to biological pathotyping.
Biological Control of Macrophomina phaseolina Charcoal Rot of Sunflower and Mung Bean
Authors: Hussain S. , Ghaffar A. , Aslam M.
Published: May 2008

Infection by Macrophonina phaseolina was substantially reduced following treatment of sunflower and mungbean seeds with Trichoderma harzianum, Gliocladium virens, Paecilomyces lilacinus or Streptomyces sp. which gave promising control of charcoal rot disease. Treatment of mungbean seeds with Rhizobium meliloti also gave good disease control.
Alternaria cassiae Alters Phenylpropanoid Metabolism in Sicklepod (Cassia obtusifolia)
Authors: Hoagland R. E.
Published: May 2008

Phenylpropaniod metabolism has been implicated in plant defence mechanism(s) against pathogen attack. In this study, phenylpropanoid metabolism was examined over a 72 h time course in the weed sicklepod (Cassia obtusifolia) in relation to pathogenic effects of the fungus Alternaria cassiae. When 3‐ to 4‐week old seedlings were challenged by the pathogen, extrable phenylalanine ammonia‐lyase (PAL, E.C. 4.3.1.5) activity was dramatically increased above that in uninfected plants severalhours after inoculation and exposure to dew. Greatest increases of enzyme activity (3‐fold, specific activity basis) occurred at ca 15–23 after treatment with fungal spores. After this peak of activity, PAL activity declined with time in infectedtissue, but remained greater than in uninfected plants through 65 h after treatment. Total methanol‐soluble hydroxyphenolic compound levels (PAL products) were higher in shoots (stems and leaves) of infected plants at 48–72 h. Leaves contained a higherconcentration (per gram fresh weight) of hydroxyphenolic compounds than did stems, and infected leaves exhibited a phenolic content greater than that of uninfected leaves at ca 27–72 h. Increased soluble phenolic compound production correlated with the appearance of lesions and necrotic spots on leaves and stems. UV irradiation examination and spectrofluorometric analysis of thin layer chromatographic separations of methanolic exatracts revealed a substantial increase of several components ininfected tissue 48 h after inoculation. Results support the view that PAL activity increases correlate with increased phenolic compound production in this host/pathogen interaction.
Induction of β‐1,3‐Glucanase and Chitinase Activity in Compatible and Incompatible Interactions Between Colletotrichum lindemuthianum and Bean Cultivars
Authors: Daugrois J. H. , Lafitte C. , Barthe J. P. , Touze A.
Published: May 2008

Inoculation of different bean cultivars with Colletotrichum lindemuthianum race β results in a marked increase of β‐1,3‐glucanase and chitinase activities. The increase is much faster in incompatible than in compatible interactions. Induced β‐1,3‐glucanase (pI 9,5) differs from the constitutive β‐1,3‐glucanase (pI 4,5) of healthy plants. The induced enzyme can partly degrade, in vitro, the cell walls of C. lindemutianum. The possible role of these hydrolytic enzymes inplants defence is discussed.
The Effects of Temperature on the Respiratory Responses of Groundsel (Senecio vulgaris) to Infection by Rust (Puccinia lagenophorae)
Authors: Jennings Diane , Ayres PeterG.
Published: May 2008

Groundsel (Senecio vulgaris) was grown in either a warm (20°C) or a cool (8°C) controlled environment and infected with Puccinia lagenophorae. Dark respiration, measured over the range 6 to 18°C, was higher in leaves of healthy plants grown under low temperatures than in those of plants grown under high temperatures. Infection increased the rates of dark respiration in the region of sporulating lesions in both sets of plants, but the greater increase in plants grown under warm conditions resulted in both sets having similar respiration rates across the range 6 to 18°C. The conclusion that the magnitude of the respiratory increase following rust infection depends upon the conditions under which plants were grown is supported by literature on other rust diseases and has implications for the utilization of carbohydrate reserves and the survival of both rust and host populations over winter.
Physiologische Eigenschaften des PilzesTrichoderma longibrachiatumRifai und seine Pathogenität für Maiskeimlinge bzw. junge Maispflanzen1
Authors: Maček J. , Celar F.
Published: May 2008

Physiological properties of the fungusTrichoderma longibrachiatumRifai and its pathogenicity for maize seedling and young maize plants

In the 1977–1980 periodTrichoderma longibrachiatumwas found to make 1.7 % of the maize seed mycoflora in Slovenia/Yugoslavia. Its mycelium growth was investigated on complex as well as on defined substrates with regard to spore formation, light induction (which is indispensable for spore formation), temperature requirements, relative humidity and different C‐ and N‐sources. These observations showed that the properties of the investigated fungus are those which characterize otherTrichodermaspecies as well.
Mechanisms Involved in Biological Control of Dutch Elm Disease
Authors: Scheffer R. J.
Published: May 2008

An effective suppression of Dutch elm disease symptom development was observed in elms resistant to the non‐aggressive strain of Ophiostoma ulmi, but not to the aggressive strain, after a preventive treatment by this non‐aggressive strain. Anequally effective isolate of Verticillium dabliae suppressed symptom development even in the very susceptible field elm (Ulmus carpinifolia).

Induction of resistance is proposed for the major mechanism explaining these and earlier experiments. The primary stimuli initiating a resistance reaction are unknown, but the intermediates of the univalent reduction of oxygen may play a role. In an experiment the activities of two groups of enzymes involved in the catalytical scavenging of these radicals, superoxide dismutase and peroxidase, were monitored, but no correlation with induction of resistance was observed. Resistant elms showed the highest activities, probably reflecting a more effective defence against radicals than susceptible ones.
Some Hosts and Properties of a Potyvirus Infecting Vanilla fragrans (Orchidaceae) in the Kingdom of Tonga
Authors: Pearson M. N. , Brunt A. A. , Pone S. P.
Published: May 2008

Abstract A potyvirus was isolated from Vanilla fragrans exhibiting leaf distortion, chlorotic and necrotic lesions and vine die‐back. The virus can be propagated in Nicotiana clevelandii and N. benthamiana and induces local lesions in Chenopodium amaranticolor and C. quinoa. The flexuous particles have a mean length of 765 nm, pinwheel inclusions are found in systemically infected N. benthamiana leaves and SDS‐polyacrylamide gel electrophoresis indicates a single polypeptide of M 32.7 × 103. The virus is transmissible from N. clevelandii to N. clevelandii by the aphid species Myzus persicae and Aphis gossypii. A polyclonal antiserum raised to the Tongan potyvirus failed to react, with the potyvirus associated with mosaic symptoms of V. tahitensis in French Polynesia and ISEM failed to detect any close relationship to 22 other potyviruses.
Erwinia amylovra Infection of Hawthorn Blossom: III. The Nectary
Authors: Wilson M. , Sigee D. C. , Epton H. A. S.
Published: May 2008

Abstract The nectaries of hawthorn flowers on detached branches were inoculated with Erwinia amylovora and the population development was followed by viable counts and light and electron microscopy. On nectaries bearing surface moisture at the time of inoculation (“wet nectary” material), the population increased rapidly after a short drop, or lag, lasting 6–12 h. Scanning electron microscopy showed that bacteria had multiplied within the nectarthodes during the first 6 h after inoculation, although, the total population had dropped. Death of cells on the surface of the nectary, possibly due to desiccation, may account for the overall drop. This differential response is not consistent with a bactericidal effect of the hawthorn nectary. On nectaries lacking surface moisture at the time of inoculation (“dry nectary” material), there was a 36 h lag period before the population started to increase – which coincided with the commencement of nectar production.

Although the nectary is an important site of infection during humid periods, the role of contaminated nectar in blossom‐to‐blossom spread of the disease is probably not of great importance.
Preinoculation with Tobacco Necrosis Virus Enhances Peroxidase Activity and Lignification in Cucumber, as a Resistance Response to Sphaerotheca fuliginea
Authors: Conti G. G. , Bassi M. , Carminucci D. , Gatti L. , Bocci A. M.
Published: May 2008

Abstract Cucumber plants were mechanically inoculated with TNV and challenge‐inoculated after 7 days with Sphaerotheca fuliginea. The development of the fungus was followed by light microscopy and the modifications of the host leaf cells were studied by histochemical and cytochemical reactions. Conidial germination was similar in control and TNV‐infected plants, and in the following 2 or 3 days S. fuliginea development was also similar. Thereafter in control plants S. fuliginea development progressed steadily and no modifications appeared in the leaf host cells, while in TNV‐infected plants strongly autofluorescing papillae were formed, and peroxidase activity was detected in the walls of many epidermal cells of the challenge‐inoculated, leaf. Lignification ensued, and fungal growth was strongly inhibited. Protection was obtained provided the number of necrotic lesions was at least 12 per cotyledon, and was elicited even if the TNV‐infected leaf was removed 7 days after infection, before challenge inoculation. No protection was induced when the TNV‐infected leaf was removed 3 days after infection.
Reproduction of Symptoms of a Root Disease of Wheat by Toxic Metabolites Produced by Two Pythium Species and their Partial Characterization
Authors: Mojdehi H. , Singleton L. L. , Melouk H. A. , Waller G. R.
Published: May 2008

Abstract Three Pythium isolates [Pythium arrhenomanes isolates (320) & (323)], and Pythium irregulare produced in vitro metabolites that affect normal wheat seedling growth and development. P. arrhenomanes isolates (320 & 323) produced toxic metabolites that caused a general browning of root tissue of 2–3‐day‐old wheat seedlings, root stunting, inhibition of root hair formation, and reduced fresh and dry root weights. These symptoms were also seen in infected seedlings inthe field. Culture filtrates of P. irregulare only partly reproduced disease symptoms, as they inhibited root elongation, but did not cause any browning of root tissue or inhibition of root hair formation. P. irregulare filtrates also stunted shoot growth and stimulated root hair formation and elongation in a swollen area immediately behind the root tip. Autoclaving did not affect activity of P. irregulare culture filtrates, but did inactivate P. arrhenomanes culture filtrates, suggesting that they are different. Ultrafiltration separations of P. arrhenomanes (isolate 320) filtrates indicated that toxic metabolites were heterogeneous. One component was less than 1,000 mol.wt. and the other greater than 50,000 mol.wt., but less than 100,000 mol.wt.
Mycoplasma‐like Organisms in Narcissus sp.
Authors: Bellardi M. G. , Pisi A. , Vicchi V.
Published: May 2008

Abstract The use of electron and optical fluorescent microscope confirmed the presence of mycoplasma‐like organisms (MLO) in Narcissus sp. plants showing leaf chlorosis, phyllody and degenerated flowers. Unidentified multivesicular membrane bounded bodies were also found in some sieve tubes of the diseased plants.
Isolation and Cell Wall Regeneration of Protoplasts from Botrytis cinerea Pers.
Authors: Braun PeterJ. , Heisler Anneliese
Published: May 2008

Abstract A procedure for efficient isolation and cell wall regeneration of protoplasts from Botrytis cinerea is described. Protoplasts were obtained from mycelia using a lytic enzyme mixture containing β‐Glucuronidase, Cellulase R10 and Driselase with mannitol for osmotic support. The digestion of cell walls was checked by fluorescence microscopy. Protoplasts were purified from cell debris and lytic enzymes. Regeneration and reversion were performed by incubation on agar plates.
Volatile Production Induced by Penicillium digitatum in Orange Fruit and in Culture
Authors: Pesis Edna , Marinansky Rosa
Published: May 2008

Abstract Production of volatiles was stimulated by the infection of Penicillium digitatum in 'Shamouti oranges. During 7 days of disease development, there was a progressive increase in the emanations of the anaerobic metabolites acetaldehyde, ethanol and ethyl acetate. There was also an increase in other volatiles including methanol, acetone, and ethylene, accompanied by a high production of CO2. The production of acetaldehyde, ethanol and CO2 in cultures of P. digitatum was, highest on the first day after inoculation, and decreased as the fungus developed. Ethyl acetate and ethylene increased when sporulation had already begun. Neither acetone nor methanol was found in P. digitatum in vitro. The increase of the volatiles in the infected oranges was due to the host‐pathogen interaction and peel lesion.
Characterization of a Spanish Strain of Pepper Mild Mottle Virus (PMMV‐S) and its Relationship to Other Tobamoviruses
Authors: Garcia‐Luque I. , Serra M. T. , Alonso E. , Wicke B. , Ferrero M. L. , Diaz‐Ruiz J. R.
Published: May 2008

Abstract A Spanish strain of pepper mild mottle virus (PMMV‐S) (Alonsoet al. 1989) can be differentiated from the Italian PMMV (Wetteret al. 1984) by the responses of Capsicum spp. with resistance genes to tobamoviruses, by radioimmunoassay and by the electrophoretic mobility of their viral particles. Moreover, the analysis of the electrophoretic mobility of the viral particles in agarose gels and that of the viral coat proteins in polyacrylamide‐urea gels are reliable and rapid techniques for distinguishing PMMV isolates from other members of the tobamovirus group and thus can be used for diagnostic purposes. These results support the proposal of grouping these pepper viruses, including the “pepper strains” of TMV, as a new tobamovirus subgroup (PARES 1985, BETTI et al. 1987, WETTER et al. 1987, ALONSO et al. 1989).
Virus Infection of Forest Trees by Mechanical Transmission
Authors: Nienhaus F. , Büttner C. , Hamacher J.
Published: May 2008

Abstract Back transmission trials on young forest plants with isolates of purified viruses from the same tree species were performed using different inoculation techniques. Spruce seedlings and willow plants were successfully infected with tobacco necrosis virus (TNV) by the conventional method of mechanical inoculation of virus suspension mixed with celite as abrasive. Cherry leaf roll virus (CLRV) was transmitted to birches only after adding poly‐L‐orithine (PLO) to the inoculum. The same method was successful with brome mosaic virus (BMV) on beech seedlings. PLO also improved the rate of infection on TNV in willows. In only one case, was CLRV transmitted conventionally to a white ash seedling. The infection of white ash was increased when frozen powders, of infected ash leaves were directly rubbed onto leaves. BMV could not be transmitted to beech seedlings by carborundum pressure‐inoculation. Stem slashing‐inoculation of BMV and CLRV was successful with CLRV in one beech out of 60 seedlings.
Nematicidal Activity of Some Phenolics on Root Knot, Growth and Yield of Capsicum frutescens cv. California Wonder
Authors: Maheshwari D. K. , Anwar M.
Published: May 2008

Abstract Free living nematode Caenorhabditis elegans was used as a test system for screening anthelmintic phenolics. The most effective concentrations (100, 500 and 1000 μg ml−1) were used against root knot nematode Meloidogyne incognita. Effect of these phenolics was determined on growth and development of host plant Capsicum frutescens cv. California Wonder, Second stage juveniles of M. incognita were hatched from egg masses collected from roots of host plant and subjected to similar phenol concentrations for 48 h. Mortality of M. incognita was recorded on the basis of parameters used for test organism bioassay. Both healthy and inoculated plants of C. frutescens cv. California Wonder were treated withsolutions of salicylic acid (SA) and p‐betahydroxy benzoic acid (BA) so that each pot received 100, 500 and 1000 mg phenol. Control plants were supplied with distilled water, Plants were uprooted 21 days after inoculation and roots were gall indexed. Some plants were left in the pots for further growth and development. Surface sterilised seedlings of host plant were raised and inoculated with second stage Juveniles of M. incognita. Thereafter observations were recorded on the vegetative and reproductive parameters of the plants. Drench application of SA and BA were found quite effective with no apparent phytotoxic effect.
Effect of Ground Cover on Splash Dispersal of Phytophthora cactorum from Strawberry Fruits
Authors: Madden L. V. , Ellis M. A.
Published: May 2008

Abstract A rain simulator was used to investigate the influence of various ground covers (soil, straw, sand, and plastic) on splash dispersal of Phytophthora cactorum, the cause of leather rot of strawberry. Potted strawberry plants were held in a concentric circle by a wood frame, 30 cm from an inoculum source of 10 infected fruits with sporulating lesions. The canopy was exposed to 15 and 30 min of generated rain at intensities of 15 and 30 mm/h. Plastic mulch had the highest resulting fruit disease, incidence (e.g., ca. 80% of fruit infected at 30 min duration and 15 mm/h rain), followed by soil and sand (36–47%), then straw (ca. 15%). Except for straw, there was lower incidence at 30 than at 15 mm/h. There was a general increase in disease incidence over time.
Serological Comparison of Isolates of Cherry Leaf Roll Virus from Diseased Beech and Birch Trees in a Forest Decline Area in Germany with Other Isolates of the Virus
Authors: Jones A. T. , Koenig Renate , Lesemann D.‐E. , Hamacher J. , Nienhaus F. , Winter S.
Published: May 2008

Abstract Two isolates of cherry leaf roll virus (CLRV), one from diseased beech and one from diseased birch trees in an area with forest decline near Bonn in West Germany, were found to be serologically closely related, but not indentical as assessed by spurformation of precipitin lines in agarose gel double diffusion tests. Such tests also distinguished these German CLRV isolates from ten other distinct CLRV isolates obtained from different natural hosts and from various countries. The German beech isolate was most similar serologically to isolates from walnut and from birch in England and the German birch isolate to an English cherry isolate and an isolate from Sambucus racemosa in Finland. These results provide further evidence of the antigenicdiversity of CLRV.
Production of Phytohormones by Pseudomonas amygdali and their Role in the Hyperplastic Bacterial Canker of Almond
Authors: Iacobellis N. S. , Evidente A. , Surico G. , Sisto A. , Gammaldi G.
Published: May 2008

Abstract The cytokinin and auxin production by Pseudomonas amygdali was studied in relation to bacterial virulence on almond plants. All isolates of Pseudomonas amygdali used in this study secreted indoles and cytokinins in culture medium although their relative amount varied among the strains. t‐zeatin (t‐Z) and indole‐3‐acetic acid (IAA), which proved to be the main componenets of cytokinin and indole mixtures, ranged respectively, as determined by HPLC, from 0.013 to 4.621 mgl,−1 and from 0.1 to 15.14 mg l−1.

The production of IAA and t‐Z appeared to be correlated to virulence of P. amygdali. The highly virulent strains, having the shortest incubation period and inducing the longest cankers produced high levels of IAA and t‐Z in vitro. On the other hand, the weakly virulent strains, having longer incubation periods and inducing shorter cankers, secreted low levels of IAA and t‐Z. Strain A142, producing high level of IAA and low level of t‐Z had the same incubation, period as the highly virulent strains but a canker similar to that of the other weakly virulent strains.

These results suggest that in the disease process by P. amygdali on almond the amount of IAA and cytokinins are correlated respectively to the length of the incubation period and to the final length of the cankers.
Crystalline Structures Associated with the Infection of the Potexvirus Argentine Plantago Virus (APla V)
Authors: Diaz‐Ruiz J. R. , Feldman J. M.
Published: May 2008

Abstract An electron microscopy study of Argentine plantago virus (APlaV)‐infected plants has revealed that the virus induces crystal‐like inclusions in both the cytoplasm and the nucleus of infected cells, in addition to the charcteristic aggregates of virus particles formed by most potexviruses. These crystals are produced in different plants and in tissue at different stage of development and they can be readily detected by leaf dip preparations. We conclude that the crystalline inclusions are virus‐specific, and therefore can be regarded as a characteristic feature of APlaV infections.
Capsicum Yellows – A Disease Induced by a Luteovirus in Glasshouse Peppers (Capsicum annuum) in Australia
Authors: Gunn L. V. , Pares R. D.
Published: May 2008

Abstract Glasshouse production of capsicums in the Sunraysia district of NSW and Victoria is severely limited by infection with a range of viruses. Aphid transmission tests, electron microscopy and serological assays have shown that one of the viruses involved is a luteovirus – the frst record of a naturally occurring luteovirus in glasshouse capsicum. The relationship of this virus to other luteoviruses known to infect solanaceous hosts is examined, and data presented to show that it is most probably a capsicum strain of potato leafroll virus.
Sclerotinia sclerotiorum: Epidemiological Factors Affecting Infection of Greenhouse Aubergine Crops
Authors: Torés J.A. , Moreno R.
Published: May 2008

A series of greenhouse cultivations of Aubergine plants were studied for a three‐year period which included the 1981—1982, 1984—1985 and 1985—1986 growing seasons to determine the number of infections produced by S. sclerotiorum and the plant organs infected. A time‐phase difference was detected between the discharge of air‐borne spores and the appearance of infections. The appearance of flowers, the plant organ most susceptible to infection, appeared to mark the end of the latent period and the beginning of infections. The distribution of the infections within the greenhouse was random for two of the three seasons studied and fitted a Poisson distribution (p < 0.01). Analysis of the tendencies of the number of infections and numbers of infected plants revealed a sigmoidal curve that was a function of the accumulated hours in which relative humidity was 80 % or more.
Populationsänderungen von Pseudocercosporella herpotrichoides mit und ohne Fungizidselektion
Authors: Waldner‐Zulauf M. , Gisi U.
Published: May 2008

Population changes in Pseudocercosporella herpotrichoides with and without fungicide selection

A conidium mixture of W (wheat‐type) and R (rye‐type) strains of Pseudocercosporella herpotrichoides (W:R = 1:1) was incubated on PD‐agar without fungicide or amended with the imidazole prochloraz or the triazole cyproconazole. The W:R ratio was assessed over four generations using the different benomyl sensitivity of the strains as marker. In untreated mixtures, the R strain completely dominated the population already after two generations. Similarly, in cyproconazole‐treated mixtures, the R strain increased to 100% after the second generation, whereas in prochloraz‐treated mixtures the R strain either followed the same pattern as in untreated mixtures or fluctuated around the initial proportion of 50% over four generations. The W and R strains displayed different fitness properties. The average hyphal growth rate was 8.5 mm/10 d and 4.5 mm/10 d for the W and the R strains, respectively; the sporulation capacity was 80 and 400 conidia/colony, respectively, for the two strains. The different fitness resulted in a strong dominance of the R strains both in vitro and in field populations towards the end of the vegetation period. This shift towards R‐dominance occurred about equally fast with or without fungicide selection.
Infection of Arabidopsis thaliana by Plasmodiophora brassicae
Authors: Koch E. , Cox R. , Williams P. H.
Published: May 2008

Three populations of Arabidopsis thaliana (L.) Heynh. were inoculated with three isolates of Plasmodiophora brassicae Woron. Inoculation of young Arabidopsis plants caused clubbing of roots and, in the late flowering population CrGC 9–4, infection of shoots. In this population, the number of inoculated plants reaching the flowering stage was reduced, and the majority of plants died prematurely. Symptoms of shoot infections were compressed rosettes with thickened and stunted leaves containing resting spores of P. brassicae. The results showed clearly that A. thaliana is susceptible to P. brassicae.
Mechanism of Cold‐induced Peach Stem Infection by Pseudomonas s. pv. persicae: Water Congestion in Tissues
Authors: Vigouroux A.
Published: May 2008

We have previously shown that water congestion in tissues, caused by thawing after a period of slightly negative temperatures, results in the absorption and diffusion of bacteria in the bark tissues of peach stems (Prunus persica). In the present study we demonstrate that in peach branches acclimated to cold and inoculated with the bacterium Pseudomonas syringae pv. persicae, this freezing‐thawing process is sufficient to induce, with no further treatment than incubation at + 10 °C, the development of cankers very similar to those observed in orchards in the winter. The first step of the process induces a particularly effective form of contamination and thus corresponds to an epidemiological phenomenon. The diffused bacterium, then, initiates pathogenic activity in locations favorable to its development. Moreover, an additional freezing‐thawing sequence can result in the extension of ongoing infection by causing diffusion of bacteria from infected tissue to healthy areas.
Ascospore Discharge and Survival in Pseudopezicula tracheiphila, Causal Agent of Rotbrenner of Grape
Authors: Pearson R. C. , Siegfried W. , Bodmer M. , Schüepp H.
Published: May 2008

A recording volumetric spore trap was operated continuously amidst overwintered grape leaves in a vineyard at Walenstadt, Switzerland from early May to mid‐July 1988. Ascospores of Pseudopezicula tracheiphila were captured in the air beginning 11 May and 96 % of the total seasonal release occurred between 16 May and 2 June. Rain always preceded ascospore release. However, trap catches were associated with the simulataneous cessation of rainfall, decreased relative humidity (RH), increased temperature, and drying of foliage. Maximum ascospore release occurred in the second hour, following commencement of drying. Ascospores discharged dry onto glass coverslips survived with greater than 60 % viability after 1, 3, and 6 days exposure to 10, 15, 20, and 25°C at 70 % RH. Only at 30°C was viability reduced to slightly less than 50 % after 6 days.
Virus Free Garlic (Allium Sativum L.) Plants Obtained by Thermotherapy and Meristem Tip Culture
Authors: Conci VilmaC. , Nome S. F.
Published: May 2008

Virus infection in garlic considerably reduces yield and quality in Argentina. The production of virus free “seed” was attempted by means of thermotherapy and meristem tip culture.

A hot water treatment was employed to determine the lethal temperature/time combination for clonal type (c.t.) Blanco cloves. It was established that 50°C × 20 min, 50°C × 15 min and 55°C × 5 min were the limit thermal/time combinations which garlic could withstand. Those treatments were employed followed by meristem tip culture, however, none of the successfully developed plants after culture (only 13 %) were virus‐free.

Hot air treatments in a growth chamber at 36°C lasting for 30, 40 and 60 days, and at 25°–32° for 30 days in a greenhouse were tested on c.t. Blanco. Cloves kept at room temperature throughout the experiment were employed as controls. In the 25°–32°C treatment, 73% of meristems produced plants and, of these, 33 % were virus free. After 30 and 40 days at 36 °C, 62 % and 67 % of the meristems developed into plantlets, of which respectively 51 % and 50 % were virus‐free. Very few meristems (10 %) developed into plants when cloves had been kept at 36°C for 60 days but the resulting plantlets were all virus free. Controls produced 78 % of plants, of which 14 % were virus free.

Results of hot air treatments of 36 °C for 40 days performed on c.t. Colorado, Rosado, Paraguayo, Espaol and Hilario Ascasubi were similar to those obtained with c.t. Blanco. In Espaol and Hilario Ascasubi, no virus‐free plants were detected among control specimens (no thermotherapy treatment).

The only virus (from up to 3 that infected the plants) that persisted in some plants after themotherapy and meristem tip culture was garlic yellow streak.
Interaction between the Ectomycorrhizal Fungus Paxillus involutus, Damping‐off Fungi and Pinus resinosa Seedlings
Authors: Chakravarty C. , Peterson R. L. , Ellis B. E.
Published: May 2008

Paxillus involutus, an ectomycorrhizal fungus, had an inhibitory effect on the root pathogenic fungus Fusarium moniliforme and two isolates of F. oxysporum when grown in paired cultures on modified Melin Norkrans’ medium. In contrast, one isolate of F. oxysporum was not inhibited and another damping‐off fungus, Cylindrocarpon destructans inhibited growth of Pax. involutus in similar paried cultures. Survival of Pinus resinosa (red pine) seedlings was increased significantly when they were grown in vitro concomitantly with either Pax. involutus and F. moniliforme or Pax. involutus and the three isolates of F. oxysporum, compared with seedlings inoculated with either F. moniliforme or F. oxysporum isolates alone. pax. involutus showed no protective effect against C. destructans. The number of colony forming units of Fusarium spp. was reduced significantly in the root extract and rhizosphere substrate of P. resinosa seedlings inoculated with Pax. involutus. Spore germination of Fusarium spp. was reduced significantly when treated with culture filtrate of Pax. involutus and root extract of P. resinosa seedlings inoculated with Pax. involutus. Neither colony forming units nor spore germination of C. destructans was affected either by culture filtrate of Pax. involutus or root extract of P. resinosa seedlings inoculated with Pax. involutus.
Teliospore Germination of Soybean Rust Fungus (Phakopsora pachyrhizi Syd.)
Authors: Saksirirat W. , Hoppe H.‐H.
Published: May 2008

Teliospores of the soybean rust fungus (Phakopsora pachyrhizi Syd.) germinated after treatment with 10—12 wetting and drying cycles at room temperature. Spores swelled, vacuolated and germinated with a slightly curved basidium bearing 1—4 sterigmata with basidiospores. High germination rates were observed when telia were stored at 5 °C for 5—6 months before breaking dormancy.
Early Changes in the Nucleotide Pools of Germinating Rust Uredospores
Authors: Grabo P. , Wagner K. G.
Published: May 2008

Puccinia graminis uredospores were induced to germinate on a water surface and the nucleotide/nucleoside pools were determined by high performance liquid chromatography. Distinct phases of germination could be discriminated by correlating the changes of individual nucleotide pools with characteristic morphological changes. During the first 15 min no visible changes of the cell wall were observed whereas the adenine nucleotide pools increased strongly indicating an activation of the energy metabolism. The stage preceding hyphal growth revealed large increases in the precursor pool for cell wall synthesis (UDP‐N‐acetylglucosamine). The early phases of germination are obviously controlled by distinct metabolic transitions. Furthermore, correlations of pool contents and changes during germination with the germination efficiency of the three uredospore batches investigated are discussed.
Relationship between Phytotoxicity of Metabolites Produced in vitro by Strains of Phoma tracheiphila (Petri) Kanc. et Ghik. and Their Virulence
Authors: Rosciglione B. , Burgio A. , Bottalico A. , Laviola C.
Published: May 2008

Three wild isolates and three mutants of Phoma tracheiphila (Petri) Kanc. et Ghilk. were tested for virulence on young Lemon trees. Their respective culture filtrates were tested for toxicity to Tomato cuttings and Sour orange and Lemon leaves. No relationship between phytotoxicity of metabolites produced in vitro and virulence resulted.
Bacterial Streak Disease of Maize (Zea mays L.) in South Africa
Authors: Coutingo T. A. , Wallis F. M.
Published: May 2008

Bacterial streak disease of maize is currently causing some concern among breeders in South Africa. The causal organism of this previously undescribed disease was successfully isolated and its pathogenicity established using KoCH's postulates. Standard physiological and biochemical tests used to identify phytopathogenic bacteria indicated that the bacterium is a Xanthomonas campestris pathovar. Comparisons between this organism and other recognized X. campestris pathovars of the Poaceae indicated that apart from some minor differences the maize streak pathogen is physiologically similar to X. campestris pv. holcicola. However, in repeated reciprocal inoculation experiments all attempts to induce disease symptoms in sorghum with the maize streak pathogen were unsuccessful. Conversely, X. campestris pv. holcicola did produce symptoms in maize leaves. In all the maize cultivars tested the symptoms produced by the maize streak pathogen were, however, always considerably more severe than those caused by X. campestris pv. holcicola. Notwithstanding its physiological similarity to X. campestris pv. holicola it would appear that on the grounds of host specificity the maize streak pathogen warrants new pathovar status. The name X. campestris pv. zeae is proposed.
Comparison of Different Inoculation Techniques to Screen Resistance of Pea Lines to Downy Mildew
Authors: Stegmark R.
Published: May 2008

Pea lines with partial resistance to downy mildew were tested with different inoculation techniques. Lines with superior resistance to leaf and pod infection in the field also show superior resistance to artificial inoculation of germinating seeds or seedlings at different ages in greenhouse experiments. Increased resistance of older seedlings was found for all genotypes including the susceptible control. Juvenile leaves at the top of the seedlings plants at time of inoculation, developed the strongest symptoms. Selection for partial resistance can probably be carried out in the greenhouse to improve resistance of adult plants in field.
Mitigation of Tomato Spotted Wilt Virus Infection and Symptom Expression by Water Stress
Authors: Córdoba A. R. , Taleisnik E. , Brunotto M. , Racca R.
Published: May 2008

The effects of water stress on the infection and systemic movement of tomato spotted wilt virus (TSWV) in vegetative tomato plants are examined. Two groups of plants: water stressed (water potential −1.31 MPa) and well‐watered ones (water potential −0.65 MPa), were mechanically inoculated on the third expanded leaf from the top. Each group was then divided into a well‐watered and a water stressed one.

TSWV inoculation was effective both on water‐stressed and well‐watered plants. In all groups, infection was first detected in roots, then in shoot apices and subsequently in the rest of the leaves. Systemic virus infection was somewhat slower in the water stressed plants. Post inoculation stress treatments had a significant effect in reducing infection as well as in attenuating TSWV symptoms.

Results from the present work suggest that water stress may be effective in controlling virus concentration and systemic infection symptoms in tomato plants and could thus be used as a tool to study the regulation of development of TSWV infection in this system.
Structure of Syncytia Induced by Heterodera avenae Woll. in Roots of Susceptible and Resistant Wheat (Triticum aestivum L.)
Authors: Grymaszewska Grazyna , Golinowski Wladyslaw
Published: May 2008

The structure of syncytia induced by Heterodera avenae in roots of susceptible Triticum aestivum cv. ‘Capa’ and resistant wheat AUS 10894 was investigated. In susceptible plants the first syncytia were observed 4 days after placing the seedlings into a substrate containing nematode cysts. They were located on different root levels. In resistant plants syncytia were first found after 14 days, exclusively in the root maturity zone. In both wheats syncytia consisted mostly of stelar parenchymatic cells. The syncytia induced in roots of Triticum aestivum AUS 10894 were characterized by less immediate contact with the host tracheary elements than the syncytia induced in roots of susceptible Triticum aestivum cv. ‘Capa’. In both wheats a stimulation of pericycle cell divisions, giving rise to lateral roots, was found in parts where the syncytia developed.
Incidence of Stenocarpella and Fusarium Cob Rots in Monoculture Maize under Different Tillage Systems
Authors: Flett B. C. , Wehner F. C.
Published: May 2008

The incidence of maize cob rot caused by Stenocarpella maydis, S. macrospora, Fusarium moniliforme, F. subglutinans and F. graminearum was determined over two seasons under different tillage systems at various localities. Tillage had no effect on Fusarium spp. cob rots. S. macrospora occurred only at one locality, viz. Cedara, and no tillage effect was observed. Ploughing reduced the incidence of S. maydis cob rot at localities which had high incidences of disease. The relationship between severity of S. maydis cob rot and surface stubble mass was linear.
Intra‐ and Interspecific Variation in Plant Response to Inoculation with Deleterious Rhizosphere Pseudomonads
Authors: ÅStröm Boel
Published: May 2008

Accessions of wheat, spinach, lettuce and differentBrassicaspecies were tested in greenhouse experiments for reaction to inoculation with two isolates of growth‐inhibitory rhizosphere bacteria. Seedlings grown in non‐sterile soil were inoculated with bacterial suspension and shoot dry weight was measured after five weeks. Large differences were found between the plant species tested in their average sensitivity to each bacterial isolate, and in the majority of plant species, significant differences were also found between accessions in the response to one or both isolates. These findings suggest that, in addition to the variation between plant species, intraspecific variation in the reaction to deleterious bacteria is a common feature in plants. This supports the hypothesis that plant reaction to rhizosphere bacteria is under genetic control. The results further indicate specificity in the interactions between plants and bacterial isolates, both at the plant species level and at the accession level.
Strains of Colletotrichum coffeanum Noack Causing Coffee Berry Disease in Angola and Malawi with Characteristics Different to the Kenya Strain
Authors: Rodrigues C. J. , Varzea V. M. P. , Hindorf H. , Medeiros Emilia F.
Published: May 2008

Strains of Colletotrichum isolated from berries of Coffea arabica from Angola and Malawi were identified as C. coffeanum causing coffee berry disease (CBD). The isolates were highly aggressive to berries of the cultivar ‘Catimor’ and produced high numbers of acervuli and extremely large masses of pink conidia when cultivated in the dark. These strains are apparently different in aggressiveness and morphology to those described in the past from Kenya.